Rozprawy doktorskie na temat „Biogas as a fuel”

This thesis concerns biogas-operated fuel cells. Fuel cell technology may contribute to more efficient energy use, reduce emissions and also perhaps revolutionize current energy systems. The technology is, however, still immature and has not yet been implemented as dominant in any application or niche market. Research and development is currently being carried out to investigate whether fuel cells can live up to their full potential and to further advance the technology. The research of thesis contributes by exploring the potential of using fuel cells as energy converters of biogas to electricity. The work includes results from four different experimental test facilities and concerns experiments performed at cell, stack and fuel cell system levels. The studies on cell and stack level have focused on the influence of CO, CO2 and air bleed on the current distribution during transient operation. The dynamic response has been evaluated on a single cell, a segmented cell and at stack level. Two fuel cell systems, a 4 kW PEFC system and a 5 kW SOFC system have been operated on upgraded biogas. A significant outcome is that the possibility of operating both PEFCs and SOFCs on biogas has been established. No interruptions or rapid performance loss could be associated with the upgraded biogas during operation. From the studies at cell and stack level, it is clear that CO causes significant changes in the current distribution in a PEFC; air bleed may recover the uneven current distribution and also the drop in cell voltage due to CO and CO2 poisoning. The recovery of cell performance during air bleed occurs evenly over the electrode surface even when the O2 partial pressure is far too low to fully recover the CO poisoning. The O2 supplied to the anode reacts on the anode catalyst and no O2 was measured at the cell outlet for air bleed levels up to 5 %. Reformed biogas and other gases with high CO2 content are thus, from dilution and CO-poisoning perspectives, suitable for PEFC systems. The present work has enhanced our understanding of biogas-operated fuel cells and will serve as basis for future studies.
QC20100708

From an environmental- and health perspective, biogas and other biomass-based fuels have several advantages; nevertheless the majority of motorists fill their cars with petroleum-based fuels. This thesis is designed to explore the profile of biogas in relation to its perceptions. It is a study concerning the communication between the biogas producing company Svensk Biogas and their biogas users and non biogas users. To obtain a thorough understanding of the profile and perceptions of biogas a qualitative approach was considered appropriate. Biogas users and non-users were interviewed at gasoline stations, while Svensk Biogas was interviewed as a group.

The three interview segments were analyzed and compared in order to identify patterns, similarities and differences. Based on research data the thesis concludes that the profiling arguments of biogas correlates to that biogas is the most environmentally friendly fuel, the least expensive fuel, and locally produced. Furthermore, the company profile of Svensk Biogas is equal to sustainable alternative, locally produced, trustworthy, environmentally friendly and climate smart [klimatsmart]. Given the arguments of the company profile, environmental values seem to be the core communicating value. Profiling Svensk Biogas happens through events and by using communication material such as company logotype.

Motorists have an overall positive perception of biogas. Biogas users states environmental benefits as the key argument behind their commitment. Non-users are positive toward biogas although expressing a lack of knowledge confusing biogas with ethanol and bio-fuels in general. According to motorists the negative perceptions, in addition to the prerequisites of biogas, are connected to insufficient infrastructure of biogas filling stations, a short range of the biogas tank, a high investment cost of a biogas car, a biogas price increase, scarcity of cars, and information (lack of information and misleading information).

The overall perception of Svensk Biogas among biogas users is positive. Biogas users express a negative perception concerning the Svensk Biogas filling stations and also wish for a lower biogas price. Non-users express modest perceptions of the company. This research also concludes that perceptions of the biogas producer are correlated to the perceptions of biogas. Furthermore, biogas producer, users and non-users wish to be directed by political decisions, guiding them toward environmentally friendly fuel alternatives.

A more sustainable and secure energy supply is required for the forthcoming generations; where the actual dependence on the fossil fuel reserves should be replaced by self-sufficiency and use of renewable energy resources. Conventional sewage treatment is an energy consuming process, or more specifically, an electricity consuming process. Notwithstanding, energy on Waste Water Treatment Plants is not only considered in terms of consumption reduction, but also in terms of production of renewable energy in form of biogas. Today, achieving energy self-sufficiency is limited by the low electrical efficiencies of conventional biogas-powered Combined Heat and Power systems; but fuel cell technology is appearing on the scene in the recent years offering both a higher electrical efficiency and a further reduced environmental impact. Biogas energy valorization in fuel cells combines a high-efficient technology for electrical generation, i.e.: fuel cell, with the use of a renewable fuel, i.e.: biogas. Raw biogas contains a wide range of contaminants, mainly sulfur and organic silicon compounds (siloxanes), which pose a risk to Solid Oxide Fuel Cell operation; hence biogas requires a thorough conditioning and cleaning process upstream the fuel cell unit. Moreover, monitoring of siloxanes levels remained somewhat controversial with discrepancies on optimal sampling procedure as well as quantification technique; hindering the design and operation of siloxanes removal technologies. This work is devoted to studying and validating the whole biogas energy valorization line, including the biogas treatment system and the fuel cell operation. The integration of low-cost biological desulphurization and deep polishing physico-chemical adsorption processes with a Solid Oxide Fuel Cell has been studied in an industrial 2.8 kWe pilot plant installed in a Waste Water Treatment Plant in Spain, showing that the stringent gas quality requirements of 0.5 ppmv S and 1 mg Si/Nm3 can be satisfied with over the long-term. The technical and economic comparison of Solid Oxide and Molten Carbonate Fuel Cell performance with conventional Internal Combustion Engines and Micro-Turbines has been also conducted for different plant sizes and raw biogas compositions, confirming the relevant role that fuel cells can play on carbon neutral sewage treatment; particularly in small- and medium-size plants. Today the final justification for biogas valorization in fuel cell systems needs to be found in environmental issues as some improvements both in the performance and costs are still required. Nonetheless, this thesis demonstrates that the economics for this next-generation technology are expected for the short-term. Further collaborative research between biogas producers, suppliers of biogas treatment systems and manufacturers of fuel cells is required in the near future for Solid Oxide Fuel Cell technology deployment in the sewage sector.
El subministrament d'energia sostenible i segur és un dels reptes més rellevants per a les properes generacions, on la dependència actual en les fonts d'energia basades en combustibles fòssils haurà de ser substituïda per l'autosuficiència i l'ús dels recursos energètics renovables. El tractament convencional d'aigües residuals urbanes és un procés que consumeix grans quantitats d'energia, o més específicament, grans quantitats d'electricitat. En aquest sentit, l'energia a les Estacions Depuradores d'Aigües Residuals s'ha de tractar no només en termes de reducció del consum, sinó també en termes de producció d'energia renovable a partir del biogàs. Avui en dia, no és possible assolir l'autosuficiència energètica a causa de les baixes eficiències elèctriques dels sistemes de cogeneració convencionals alimentats per biogàs. Tot i això, en els darrers anys, la tecnologia de les piles de combustible està apareixent en escena, oferint una millor eficiència elèctrica i una reducció en l'impacte ambiental. La valorització energètica de biogàs en piles de combustible combina una tecnologia d'elevada eficiència per a la generació d'energia (la pila de combustible), amb l'ús d'un combustible renovable (el biogàs). S'ha de tenir en compte que el biogàs brut conté una àmplia gamma de contaminants, especialment compostos de sofre i de silici orgànic (siloxans), que comporten un risc operatiu per al correcte funcionament de les piles de combustible d'òxid sòlid. Per tant, s'ha d'instal·lar una etapa d'acondicionament i neteja exhaustiu del biogàs abans que es pugui introduïr a la pila de combustible. D'altra banda, la monitorització de les concentracions de siloxans presenta discrepàncies en relació al procediment òptim per al seu mostreig i en la tècnica analítica de quantificació; dificultant d'aquesta manera el disseny i la operació de les tecnologies d'eliminació d'aquests compostos. Aquest treball es centra en l'estudi i validació de tota la línia de valorització energètica, incloent el sistema de tractament de biogàs i la operació de la pila de combustible. S'ha estudiat la integració de tecnologies de dessulfuració biològica de baix cost i de processos d'adsorció fisicoquímica amb una pila de combustible d'òxid sòlid en una planta pilot industrial de 2.8 kWe instal·lada en una Estació Depuradora d'Aigües Residuals a Catalunya (Mataró). Els resultats experimentals han demostrat que les tecnologies de tractament de biogàs són capaces d'assolir els exigents nivells de qualitat de 0.5 ppmv S i 1 mg Si/Nm3 tant en el curt com en el llarg plaç. Per altra part, s'ha realitzat una estudi tècnic-econòmic comparatiu entre les piles de combustible (d'òxid sòlid i de carbonat fos) amb els motors de combustió interna i les microturbines per a diferents tamanys de planta i composicions del biogàs. D'aquesta manera, s'ha confirmat el paper important que poden jugar les piles de combustible en l'assoliment d'un tractament d'aigües residuals autosuficient; particularment en plantes de tamany petit i mitjà. Avui en dia, els projectes de valorització energètica de biogàs a través de piles de combustible encara s'han de justificar per raons ambientals ja que es requereixen millores tant en el rendiment tècnic com en els costos d'inversió. No obstant, aquesta tesi demostra que aquesta tecnologia de pròxima generació serà econòmicament viable en el curt termini i podrà competir amb les tecnologies convencionals. La investigació col·laborativa entre productors de biogàs, proveïdors de tecnologies de tractament i fabricants de piles de combustible serà imprescindible durant els propers anys per tal que la tecnologia pugui convertir-se en una realitat en el sector del tractament d'aigües residuals urbanes.

För att minska dagens klimatpåverkan krävs fullgoda energialternativ till de fossila bränslena. Utsläpp från fossila bränslen är idag en av de största orsakerna till de negativa klimatförändringar som sker på jorden. Genom en ökad användning av alternativa fossilfria drivmedel kan en tydlig minskning av koldioxidutsläpp till atmosfären ske. Biogas är ett sådant fossilfritt drivmedel som idag klassas som ett av de renaste. Biogasen framställs från olika typer av restprodukter från samhället. Då fossila drivmedel ersätts med biogas sker en total reduktion av växthusgaser.

Kalmar Län har som mål att till år 2030 vara en helt fossilbränslefri region. Genom en ökad användning av gasen inom transportsektorn kan sådana typer av nationella mål uppfyllas. Västervik kommun i Kalmar Län har sedan 2008 producerat biogas lokalt, vilket bidrog till att en tankstation kunde öppnas under år 2009. Genom dessa åtgärder har kommunen genomfört ett stort steg för biogasens utveckling och framfart i samhället. Då tillgängligheten är säkrad är det upp till individer och företag att avgöra om de sedan väljer att nyttja gasen som fordonsbränsle. Detta val kräver en förändring av ett tidigare beteende. En attitydförändring är därför viktig om en förändring ska kunna ske. Det finns många olika faktorer och argument som påverkar övergången från en miljövänlig attityd till ett miljövänligt beteende.

Syftet med detta arbete var utifrån denna bakgrund att undersöka vilka faktorer som påverkar valet av fordonsbränsle hos privatpersoner och företag. Detta möjliggjordes genom en enkätundersökning för privatpersoner och ett frågeformulär för företag. Genom att privatpersoner och företag som både använder biogas och fossila bränslen ingick i undersökningen kunde dessa senare jämföras för att den aktuella frågeställningen skulle kunna besvaras. Undersökningen var av intresse för Västervik kommun, varav privatpersoner deltog både från kommunen och runt om i landet. 612 personer svarade på enkäten, 336 gasanvändare och 276 fossilanvändare. Sammanlagt ingick fem lokala företag i undersökningen samt tre lokala bilfirmor.

Genom undersökningen kunde intressanta typer av mönster urskiljas gällande de attityder och faktorer som låg till grund för de val som privatpersonerna har gjort. Fossilanvändare ansåg att ekonomi är den viktigaste faktorn vid valet av bränsle. En ökad ekonomi eller ett minskat pris på gasfordon skulle kunna medföra en övergång till biogas. Gasanvändare har utvecklat ett miljövänligt beteende genom användandet av gasen, där det starkaste argumentet var just ett rent miljösamvete som biogasanvändningen bidrar till. Det framkom även att biogassystemet måste fungera som helhet för att en ökad användning ska kunna möjliggöras, då en del gasanvändare påpekade brister i det nuvarande systemet. För företag var även ekonomi och miljösamvete viktiga faktorer vid val av fordonsbränsle. Att biogasfordon har ett reducerat förmånsvärde var en viktig faktor för företags investering. Detta var även något som bilfirmor påpekade och att det hos privatpersoner trots allt är den egna plånboken som styr valet. Biogas är i dagsläget ett miljömässigt bra drivmedel och tidigare forskning har dessutom visat att det finns god potential till betydande förbättringar i framtiden.

Fossil fuels are amongst the largest contributors to the climate changes currently happening. Through an increased use of alternative fossil-free fuel it is possible to achieve a significant reduction of carbon dioxide emissions to the atmosphere. One such fuel is biogas, which is considered as one of the cleanest fuels available today. Biogas is produced from various types of waste materials, and replacing fossil fuel with biogas results in an overall reduction of green-house gas emissions.

The Kalmar County has set a target to become a completely fossil fuel-free region by the year 2030. Through an increased use of biogas in the transport sector, such types of national targets can be achieved. The Municipality of Västervik, a part of the Kalmar County, has since 2008 been producing biogas locally, which meant that a fuelling station could be built in 2009 and through this, the Municipality has taken a major step towards an increased use of biogas. With supply secured, it is up to individuals and companies to use it for vehicle fuel. This choice requires a change in human habits. The motivations for making changes vary among individuals and theirs attitudes.

The aim of this study was to examine which factors affect the choice of vehicular fuel among individuals and companies. This was achieved through a survey for individuals and a questionnaire for companies. Individuals and companies could then be compared to. The study was made for the Municipality of Västervik, and the study subjects were both local and non-local residents. 612 people replied to the survey, 336 users of gas and 276 users of fossil fuels. Totally five local companies were included in the survey and three local Car Dealers.

In this study, a number of interesting patterns regarding attitudes and affecting factors have been observed. Users of fossil considered the economic aspect as the most important factor for their choice. Users of gas have adopted environmentally friendly habits through the use of gas, where the strongest argument was the environmentally friendly approach. It was also found that biogas must be part of a coherent system in order to increase use; some biogas users pointed on shortcomings in the current system. The economic aspects and the environmental conscience were also important for companies for theirs choice of vehicles. The reduced benefit value was an important factor for investment of biogas vehicles. This was also something that Car Dealers pointed out; it is after all the own wallet that govern elections. Biogas is an environmentally friendly fuel in the current situation and previous research has also shown that there is good potential for significant improvements in the future.

A multi fuel biogas plant is under planning at Fiborgtangen, Norway. The plant will utilize biogas from several different sources, including fish silage, animal manures, sludge from the paper factory and straw. In order to make good decisions on how to design the plant, characterization of the substrates in regards to biogas potential and nutrient value was done, and laboratory scale models of a possible plant design was established. The characterization showed that a minimum of 42% of the DM should come from manure in order to meet the micro-nutrient demand, it also showed that some nitrogen rich substrates in addition to the manure needed to be present to avoid nitrogen limitation to balance out the high carbon substrates. A biochemical methane potential study was carried out for all substrates and showed promising results, with the exception of the fiber sludge from the paper factory that had a very poor methane potential. The mixed substrate fed to the reactor models gave a methane yield of 300 mL CH4/gVS in the biochemical methane potential study. A mix of all the substrates was fed to 4 semi continuous reactors with a HRT of 25 days and OLR of 3 gVS/L. The reactors performance was unstable, and operating with high propionic acid concentrations. The specific methane yield ranged from 170-230 mL CH4/gVS, but because the reactors did not reach steady state during the experimental period and the propionic acid concentrations were so high, it is not possible to conclude on what yield this design would give. It is recommended that the semi continuous experiments are continued until they reach steady state or collapse because of the high propionic acid concentrations. After this it would be recommended to start experiments with higher proportions of animal manure and to leave the fiber sludge out of the reactor feed as it is has very low methane and nutrient value.

Sugarcane cultivation is a major source and sinks of greenhouse gas emissions (GHGs). In 2019, approximately 30.04 x 106 t of sugarcane was harvested from 364,428 ha of land. Of the total cane harvested, sugarcane bagasse (SB) and sugarcane trash (ST) accounted for 30.1% and 14.9%, respectively. Further, fossil fuel consumption in the transport of cane to mills was 29.15 ML and is equivalent to 221.5 Mt CO2-equivalent GHG emissions. Anaerobic digestion (AD) of sugar industry wastes for biomethane production and use as vehicle fuel (bioCNG) would reduce the fossil fuel consumption and the associated GHG emissions in cane transportation to mill. The study aims to optimize biogas production and upgrade the produced biogas to vehicle fuel. For that the study is divided into different objectives. To determine the substrate characteristic and suitable AD parameters viz biodegradability (Experiment I), particle size (Experiment II), acid/base thermal pretreatment (Experiment III), C:N ratio (Experiment IV), and trace nutrient supplementation (Experiment V), to generate the maximum methane yield from ST with respect to SB was designed as objective I. At first, chemical composition and methane yields of ST and SB were determined through bench-scale biochemical methane potential (BMP) tests (Experiment I). Buswell’s equation predicted a theoretical methane yield of 291.0 and 349.4 mL CH4 g-1VSadded for ST (C107.8H179.1O101.4N1S0.08) and SB (C86.7H134.3O64.9N1S0.07), respectively. The corresponding methane yields with Modified Dulong’s equation were 266.3 and 298.7 mL CH4 g-1VSadded, respectively. The calculated energy value was 14.1 MJ for ST and 12.6 MJ for SB. However, experimental methane yields obtained were 161.8 and 187.9 mL CH4 g-1VSadded for ST and SB, respectively. First-order kinetic model revealed that experimental data fitted well (R2 = 0.99) with the modelling data and the hydraulic rate constant (khyd) values of 0.04 and 0.06 day-1 were obtained for ST and SB, respectively. However, modified Gompertz model had a lag phase () of 2.1 and 1.7 day, for ST and SB, respectively indicating hydrolysis was the rate limiting step for the studied lignocellulosic feedstocks. Thus, the effect of mechanical (Experiment II)., thermal and chemical pretreatments (Experiment III) on chemical composition and methane yields of ST and SB were evaluated. The effect of particle size of <0.25, 0.25-0.50, 0.50-1 and 1-2 mm on chemical composition and methane yields were determined. Results showed that particle size reduction had a profound effect on methane yields, especially for SB than for ST. For ST, particle size of 1-2 mm showed an improvement in methane yields by 19.1% over control (161.8 mL CH4 g-1 VSadded). For SB, the increase in methane yields over control (189.7 mL CH4 g-1 VSadded) were by 23.6%, 20.3%, 18.1% and 6.4% respectively at particle sizes of 1-2, 0.5-1, 0.25-0.5, 0.13-0.25 mm, respectively. These results suggest that the optimal particle size for anaerobic digestion of ST and SB will be 1-2 mm for maximum methane yield. Further, mechanical pretreatment through milling did not solubilise hemi-cellulose and/or improve delignfication but improved the surface area of the holocellulose. Therefore, the effect of chemical catalysts (dilute NaOH, H2SO4, HNO3) with and without steam explosion on chemical composition and methane yields was evaluated (Experiment III). Pretreatment conditions used for the steam explosion were 130 °C for 5 minutes at acid/base concentration of 2.5% catalyst loading. Results showed that the studied pretreatments had a profound effect on chemical composition and methane yields of ST. On comparison to control, dilute H2SO4, followed by NaOH and HNO3 addition with steam explosion improved the methane yields of ST by 63.5%, 52.1% and 45.6%, respectively. Steam explosion alone also improved the methane yields of ST by 40% over control. Biomass composition analysis showed that dilute H2SO4, HNO3, NaOH and steam explosion alone had improved the glucan content by 13.7%, 11.7%, 9.3% and 3% respectively than control. Dilute H2SO4 pretreatment improved the glucan availability by 45.2% and hemicellulose (xylan and arabinan) solubilisation by 63.7%-66.9%. Lignin depolymerisation in pretreated ST was improved (16.7%) over untreated ST. In Experiment I, chemical composition of ST and SB showed that the studied substrates were deficit in trace elements and contained high carbon to nitrogen (C/N) ratio of 92.4and 146.5 respectively. Therefore, the effect of C/N ratios of 15:1, 20:1, 25:1, 30:1, 35:1 and 40:1 with urea addition on methane yields of ST and SB was investigated (Experiment IV). Results showed that methane yields improved by 13.6% and 11.3% for ST when the C/N ratio was at 20:1 and 25:1, respectively. The corresponding values for SB were 14.2% and 14.3% at 20:1 to 25:1 C/N ratio, respectively. Both these results indicate that the optimal C/N was 20-25:1 for AD of lignocellulosic residues such as ST and SB. On the other hand, the effect of trace nutrients nickel (Ni), cobalt (Co), molybdenum (Mo), manganese (Mn), copper (Cu) and zinc (Zn) on methane yields during AD of ST and SB (Experiment V) showed that trace elements supplementation influenced the methane yields and both substrates responded differently. With ST, methane yields of 68.1% and 68.7% increase over control were noticed with addition of Co and Mo, respectively. For SB, methane yields increased by 48.6%, 63.9% and 4.8% with Co, Mo and Mn dosing at 2, 3, 90 mg kg-1 respectively. All other TE addition resulted in lower methane yields than control or inhibited the biogas production at different stages of incubation. All the batch BMP tests were conducted in triplicates at inoculum to substrate (ISR) ratio of 2 in serum glass bottles with a working volume of 100 mL and incubated statically at 37 °C. All the results were analysed for variance using LSD and Dunnett-t test giving methane yield as dependent variable (p<0.05). Second objective was designed to study the effect of organic loading on process performance and methane yields in four lab-scale stainless reactors (10 L working volume) and operated at an initial organic loading rate (OLR) of 1.5 gVS L-1 d-1 with hydraulic retention times (HRT) of 35 days for 225 days. Reactors were fed with untreated ST (ST), untreated SB (SB), pretreated SB (TB) and pretreated ST (TT). Dilute H2SO4 followed by steam explosion (Experiment II) was used for pretreatment of ST and SB. OLR was increased in a stepwise manner from the initial rate of 1.5 to 2.5 and 3.5 gVS L-1 d-1. OLR was changed upon achieving steady-state condition and/or operating for 2 consecutive HRTs. Methane production rates and yields responded with increase in OLR from 1.5 to 2.5 gVS L-1 d-1. Mean methane yields of 138, 173, 248 and 252 ml g-1VSfed were obtained at an OLR 1.5 gVS L-1 d-1 in ST, SB, TT and TB reactors, respectively. Increase in OLR to 2.5 gVS L-1 d-1 showed decrease in methane yields. Mean methane yields obtained for TB, TT, SB and ST were 121, 148, 226, 236 ml g-1VSfed with a VS removal rate of 48.5, 51.4, 51.5 and 52.4%, respectively. Process parameters such as pH, total ammoniacal nitrogen (TAN) and total volatile fatty acids (TVFA) were shown to be stable and were 7.3-7.5, 0.36-0.54 g L-1 and 0.79-0.98 g L-1 respectively during operational OLR’s. Further increase in OLR from 2.5 to 3.5 gVS L-1 d-1 resulted in further decrease in methane yields and unstable AD process. At OLR 3.5 gVS L-1 d-1, methane yields were 119, 139, 189 and 199 ml g-1VSfed for substrates ST, SB, TT and TB respectively. TVFA accumulation was noticed (1.55-2.49 g L-1) , pH was 7.4-7.5 and lower methane concentration (50.5-51.9%). Residual methane production (RMP) test after each OLR indicated the process efficiency. At OLR 2.5 gVS L-1 d-1, TT and TB reactors had the lowest RMP (32.1% and 30.2% respectively) with relatively high VS removal compared with SB and ST reactors. These results indicate that steam explosion with dilute sulphuric acid improved the biodegradability and methane yields of ST and SB. The results obtained from the lab-scale reactors were used to design and optimise process performance and methane yields from pretreated sugarcane trash in pilot-scale reactors (date not presented). Third objective was designed to evaluate detailed biogas composition and to develop and optimise high pressure water scrubbing technology (HPWS). For that, the biogas composition, energy content, siloxanes and trace volatile organic compounds in biogas generated from lab-scale biogas reactors were determined and compared with the pilot-scale. Laboratory biogas samples were collected during the steady-state condition when the reactors were operated at an OLR of 2.5 gVS L-1 d-1. Results showed that biogas collected from ST, SB, TT and TB reactor had methane concentration of 52.3, 52.2, 52.7, 52.7 %, respectively. The corresponding lower calorific values (LCV) were 18.4, 18.1, 18.9 and 19.2 MJ m-3 respectively. The wobbe index values in the biogases were 18.3, 18.2, 18.7 and 19.0 MJ m-3, respectively. Volatile organic compounds were noticed in the biogas samples. Organic silicon compounds (siloxanes) were in the range of 0-0.4 mg m-3. The reduced sulphur compounds and benzene and toluene content in the biogases were in the range of 0.7-1.3 mg m-3 and 0.2-0.7 mg m-3, respectively. Among the studied siloxanes, the proportion of cyclic siloxane (D3:D4:D5) viz., hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) were noticed. The ratio of D3:D4:D5 in biogases produced from lab-reactors were 68.5:5.7: 22.4 for ST, 33.9:4.9: 60.1 for SB, 25:8.6:69.3 for TT and 14.8:3.7:81.8 for TB. Trimethylsilanol, linear siloxanes and decamethylcyclohexasiloxane (D6) content in the biogases were below the detection limits. Volatile organic compounds, reduced sulphur compounds and siloxanes cause environmental impact and affect biomethane quality for vehicle fuel use. Biogas composition from pilot-scale biogas reactors (1.2 m3 reactor with 0.8 m3 working volume) fed with steam exploded ST at an OLR of 1.5 kgVS m-3 d-1 and HRT of 35 d was analysed to optimise the process parameters to achieve the desired biomethane quality and evaluate the energy requirements of pilot-scale biogas upgrading unit (10 m3 h-1) for biogas upgrading and bottling. Results showed that the biogas had 54.1% CH4 and 39.7% CO2 and the produced biogas was upgraded to 96.7% biomethane purity by using high pressure water scrubbing process. Experimental data from the biogas upgrading process was used to optimise biogas upgrading by using Aspen Plus software. The influence of process parameters such as absorber column pressure, water to gas flow rate, temperature on biomethane purity and percentage of H2S and CO2 removal were evaluated. Experimental results showed that at liquid flow rate of 3 m3/hr, fluid temperature of 20°C, at absorption column pressure of 8 bar with 4 m random packing material with redistributor at 2 m with 25 mm plastic pall ring packing material; biogas can be upgraded to biomethane of 96.8% CH4, 2.9% CO2, < 1 ppm H2S. These model results were validated with software simulation.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
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Thesis (Master of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2018.
Renewable energy security for the future and better use of natural resources are key challenges that can be concurrently managed by a practical anaerobic co-digestion approach in the production of methane. For this study, co-digestion of cassava and winery waste was investigated for the production of biogas. Cassava biomass is a good substrate for biogas production due to its high carbohydrate yield per hectare (4.742 kg/carb) than most plants. Winery wastes constitute a lot of challenge in South Africa due to high amounts currently being dumped at landfills. Due to the chemical properties of the two substrates, it is envisaged that their co-digestion will produce more biogas than use of a single substrate. Biomethane potential (BMP) tests were carried out in a batch, mesophilic (37 °C±0.5) reactor using cassava and winery waste singly and in combination at a ratio of 1:1 and ran for 30 days. Biogas optimization was also evaluated. The optimal conditions for methane production from anaerobic co-digestion of cassava biomass and winery solid waste using response surface methodology (RSM). The effects of temperature, pH and co-substrate ratios on the methane yield were explored. A central composite design technique was used to set-up the anaerobic co-digestion experiment was determined. Once the optimized values were established, biogas production from co-digestion of cassava biomass with winery waste was investigated using a single-stage 5 L mesophilic batch digester and the microbial dynamics inside the digester during co-digestion of cassava and winery waste in the single-stage 5 L mesophilic batch digester. The samples were collected on days 1, 15 and 30 of the anaerobic digestion period and DNA extracted from them while 16sRNA bacterial sequencing was performed. The results for the BMP tests showed that cumulative methane yield for cassava, winery waste and in combination were 42, 21 and 38 mLCH4 respectively. It was concluded that biogas production from anaerobic digestion was dependent on many factors such as pH, substrate properties and the ratio of different feedstocks used during co-digestion. The results from the optimization study were pH 7, temperature of 35 °C±0.5 and co-digestion ratio of 70:30 cassava to winery waste. The maximum methane yield of 346.28 mLCH4/gVSadded was predicted by the quadratic model at the optimal temperature of 35 oC±0.5, pH of 7 and 70:30 ratio of cassava biomass to winery solid waste. Experimental results showed a close fit but higher methane yield (396 mLCH4/gVSadded) than predicted values as indicated by the coefficient of determination (R2) value of 0.9521. The response surface model proved successful in the optimization process of methane yield. The single-stage 5L mesophilic batch digester with a co-substrate ratio of 70:30 cassava to winery waste produced a total of 819.54 mL/gVS biogas with a 62 % methane content. The study of microbial community dynamics showed the presence of the bacteria that is responsible for each stage of anaerobic digestion. The study concluded that both winery waste and cassava substrates were favourable for biogas production and most underprivileged people in the rural areas with no access to electricity can produce & utilise it.

Human activities affect the climate. If the utilization of fossil and other hazardous fuel methods is eliminated, it would reduce the impact on climate change. By investigating fuel usage patterns in three rural areas of Kenya, looking at social, economic and ecological factors, a foundation to facilitate future local actions towards sustainable fuel consumption can be made. With the help of local surveys performed in Siaya, Kwale and Embu, correlations could be found. The data was not extensive enough to generate general conclusions but can act as a beginning to a foundation for future sustainable actions. More data should be retrieved and investigated regarding methods and local conditions included in this project to work as a well-rounded foundation for future local actions regarding fuel methods and practices.
Klimathot och miljöpåverkan är till stor del konsekvenser av mänskliga aktiviteter och vanor. Fossila bränslen genererar utsläpp och bidrar till ökade globala temperaturer, vilket kan innebära förödande effekter. Klimatförändringar innebär att balansen i ekosystem hotas, arter utrotas och händelsekedjor utan kända slut sätts i rullning. Genom att använda alternativ till fossila bränslen kan påverkan på klimatet från bränslen minskas. Ökad användning av förnyelsebara bränslen och hållbara alternativ är en stor del av ett framtida hållbart samhälle. I delar av mindre utvecklade länder är användningen av träbaserade bränslen högt. Att införa hållbara, billiga och tillgängliga alternativ i dessa områden kan göra skillnad. Rapporten strävar efter att undersöka sociala, ekonomiska och ekologiska korrelationer relaterade till bränslekonsumtion, i tre olika områden i Kenyas landsbygd. Egenskaper i lokala material, sociala förutsättningar och tillgängliga bränslealternativ diskuteras. Eventuella mönster och förutsättningar kan vara till stor nytta när nya aktioner mot ett hållbart samhälle ska utföras. Genom att använda data bestående av lokalt besvarade enkäter i de tre områdena Siaya, Kwale och Embu, kunde samband hittas. Data var inte omfattande nog för att dra definitiva slutsatser men arbetet kan verka som början på en grund av kunskap, att använda vid kommande beslut för framtida bränslenyttjande i Kenya och dess landsbygd. Korrelationer mellan utbildningsnivå på ansvarig för hushållet och huvudsaklig arbetssyssla visar att lokalbor med lägre eller ingen utbildning huvudsakligen arbetar med jordbruk. En utförd variansanalys visar att det är en signifikant skillnad i markstorlek mellan de undersökta områdena. Kol och andra träbaserade bränslen används till hög grad och det är ofta äldre kvinnor som står för insamlandet av ved. Värdet av tid värderas inte lika högt som pengar. Nästan alla hushåll i studien var villiga att prova alternativa bränslen, med hälsoskäl som största anledning. Inget utav hushållen svarade att miljöpåverkningar var den största anledningen. Detta skulle kunna förklaras med att fokus ligger på direkta problem som påverkar vardagen och att det kan vara svårt att se bortom dessa. Lösningar fokuserade på hälsoproblem och andra faktorer kan ha positiv inverkan även på miljön. Då data från enkäterna inte inkluderar kvantiteter eller priser går det inte att dra definitiva slutsatser gällande de tre områden som undersöks. Studien visar att platserna har liknande situationer med små skillnader och potentiella åtgärder för nya bränslevanor skulle kunna vara lönsamma i alla tre områden, där det finns material lokalt som kan verka som substitut för bränslen som inte är bra för miljön. Etanol eller biogas kan verka som bra alternativ till kol och andra träbaserade bränslen. Fler alternativ bör undersökas och mer data gällande bland annat kvantitet och priser bör insamlas för att kunna dra bra slutsatser som kan ligga grund för hållbara beslut gällande Kenyas bränslekonsumtion.

The present work is related to the complete analysis of biogas-fed SOFC system. The first part of the work has been related to a review on the concept of polygeneration system and on the analysis of the current status of SOFC installations, especially when fed with biogas. The use of a renewable fuel, coupled with carbon capture, can lead to negative emissions plants, defined as key technologies for reaching the goals set in the Paris Agreement. Furthermore, biogas and SOFC show many affinities which have been discussed in the works: from the high efficiency at low sizes to the availability of already existing subsidy schemes for electricity production. An analysis of the potential biogas production in EU is proposed, with focus on wastewater treatment plants. In this particular area, the work tries to point out the numbers of potential installed power by using SOFCs. The experimental and modeling activities are then proposed. The PhD activity is linked to two European projects, SOFCOM and DEMOSOFC. The first project is related to the analysis of biogas fed SOFC system with carbon capture and re-use. In this context, a demonstration plant has been developed and tested in the SMAT Castiglione wastewater treatment plant. Results show an easy process for the CO2 capture from the SOFC exhaust, thus pointing SOFC as a key technology in the framework of negative carbon emissions plants. More criticalities have been found in the choice of CO2 utilization for production of algae in a photobioreactor: the unstable quality of the inlet wastewater coming from the plant, the fluctuating algae productivity as function of the weather conditions, and the algae attachment to the pipe, pointed out a need for improvements and research on this technology. The experimental activity has been coupled with a modeling activity on the same concept of biogas fed SOFC, with the possibility of a downstream carbon capture and use/ sequestration. Different plant layout and different system sizes have been analyzed from a technical and economical point of view. Finally, the analysis of a real industrial size SOFC system is proposed. This activity has been developed in the framework of the DEMOSOFC EU project, where the first industrial size biogas fed SOFC system will be installed. Being the first installation of its kind, many issued and improvements have been detected. The analysis is related to the system design and description, for what concerning plant integration (electrical and thermal), system operation, and biogas processing. Biogas processing has been especially pointed out as a key component in a biogas-fed SOFC system. Because of the low admissible contaminants levels for fuel cell, a new and dedicated cleaning unit is required, which is not currently available on the market. The processing unit design is proposed and ongoing experimental activity on the adsorption with activated carbons are proposed. The main harmful contaminants found in wastewater biogas are sulphur (in the form of H2S) and siloxanes (mainly D4 and D5).

This work presents a novel method of Sn-infiltration on SOFC anodes for SOFC operation in biogas dry reforming. Using commercially available NiYSZ-based anode supported half cells with hand-painted LSM/YSZ cathode layers, Sn-infiltrated NiYSZ SOFCs containing different amounts of Sn were manufactured. These SOFCs were tested for their electrochemical performance and quantity of deposited carbon during operation on simulated biogas of 1:2 volume ratio of CO2:CH4 without humidification but with 25% Helium added to the feed stream to enable measurements of the fuel cell outlet gas composition using a quadrupole mass spectrometer. Most of the SOFCs were tested in biogas for 1 day (22 hours), but several cells were tested for 6 days (150 hours) to evaluate performance degradation. The electrochemical performance tests at 750 oC showed that with H2 as fuel the non-infiltrated NiYSZ SOFCs were able to reliably generate a moderate level of current of 350 mA cm-2 at 0.7 V; however when simulated biogas was introduced, current dropped significantly to 90-200 mA cm-2. Contrary to non-infiltrated cells, a series of Sn-infiltrated cells under the same operating conditions performed equally well both on H2 and biogas producing 310 to 420 mA cm-2 at 0.7 V. Several cells showed stable electrochemical performance over 150 hours of operation both on H2 and biogas. Using Temperature Programmed Oxidation (TPO), both Sn-infiltrated and non-infiltrated SOFCs showed low quantities of carbon formed during 22 hours operation on biogas. Visual observation and SEM images of the anode surface after 150 hours operation on biogas showed no sign of deposited carbon. The conclusion is that Sn-infiltrated NiYSZ-based SOFC can be operated on simulated biogas with significantly higher electrochemical performance and low carbon deposition, given the anode is adequately modified.

With over one hundred years of commercial cultivation, sugar cane is one of the most valuable agricultural botanical resources in the World. This position is not only based on production of sugar from sugar cane but also it is, to a great extent, as a result of the increasing importance of sugar cane by-products and side industries. Furthermore, with the advancement of science; awareness of inharmonious growth of materials and energy consumption, and the desire to minimize the negative impacts of industrial pollutants and materials, the scope for using sugar cane is still developing rapidly. Bagasse, molasses and filtered mud are the most important by-products in the process of production of sugar from sugar cane. Among these by-products, bagasse is both a biomass resource for producing energy and is one of the most important agricultural wastes, which can be used in different side industries. Therefore, it was chosen for study in this research as it offers considerable potential as a source of energy. Bagasse is often used as a primary fuel source for sugar mills; when burned in quantity, it produces sufficient heat energy to supply all the needs of a typical sugar mill, with energy to spare. To this end, today a secondary use for this waste product is in combined heat and power plants where its use as a fuel source provides both heat and power. With a suitable energy production technology, bagasse can be used as a fuel in CHP for high efficiency energy generation. Today, with regard to the low efficiency of traditional methods, the high cost of disposal of waste materials and environmental pollution, the use of modern methods such as anaerobic digestion for the production of biogas has increased. The collected biogas from the process of anaerobic digestion provides a renewable energy source similar to natural gas, but with less methane and lower heating value, that is suitable for use in CHP plants. In this research, a comparison with different bagasse energy production technologies leads to the selection of anaerobic digestion as the most suitable for use in Iran. Then a typical biogas CHP is assumed, and the biogas system is designed. Finally, the potential for the development of biogas CHP plants with bagasse in Iran is addressed through a study of the economic and environmental aspects.

There is a growing interest in alternative transport fuels. There are two underlying reasons for this interest; the desire to decrease the environmental impact of transports and the need to compensate for the declining availability of petroleum. In the light of both these factors the Diesel Dual Fuel, DDF, engine is an attractive concept. The primary fuel of the DDF engine is methane, which can be derived both from renewables and from fossil sources. Methane from organic waste; commonly referred to as biomethane, can provide a reduction in greenhouse gases unmatched by any other fuel. The DDF engine is from a combustion point of view a hybrid between the diesel and the otto engine and it shares characteristics with both. This work identifies the main challenges of DDF operation and suggests methods to overcome them. Injector tip temperature and pre-ignitions have been found to limit performance in addition to the restrictions known from literature such as knock and emissions of NOx and HC. HC emissions are especially challenging at light load where throttling is required to promote flame propagation. For this reason it is desired to increase the lean limit in the light load range in order to reduce pumping losses and increase efficiency. It is shown that the best results in this area are achieved by using early diesel injection to achieve HCCI/RCCI combustion where combustion phasing is controlled by the ratio between diesel and methane. However, even without committing to HCCI/RCCI combustion and the difficult control issues associated with it, substantial gains are accomplished by splitting the diesel injection into two and allocating most of the diesel fuel to the early injection. HCCI/RCCI and PPCI combustion can be used with great effect to reduce the emissions of unburned hydrocarbons at light load. At high load, the challenges that need to be overcome are mostly related to heat. Injector tip temperatures need to be observed since the cooling effect of diesel flow through the nozzle is largely removed. Through investigation and modeling it is shown that the cooling effect of the diesel fuel occurs as the fuel resides injector between injections and not during the actual injection event. For this reason; fuel residing close to the tip absorbs more heat and as a result the dependence of tip temperature on diesel substitution rate is highly non-linear. The problem can be reduced greatly by improved cooling around the diesel injector. Knock and preignitions are limiting the performance of the engine and the behavior of each and how they are affected by gas quality needs to be determined. Based on experiences from this project where pure methane has been used as fuel; preignitions impose a stricter limit on engine operation than knock.
QC 20120626
Diesel Dual Fuel

In a context in which climate changes due to the continuous and out of control use of fossil fuels are becoming always more significant, it is very important to try to foster energy conversion systems with a lower environmental impact such as FC-based cogenerative systems. With the necessary precautions, this kind of systems can be feed with a wide range of fuels, from the most conventional, such as hydrogen and natural gas, to those produced from renewable sources, such as biogas or gasification gas. Unfortunately, most of these fuels contains traces of elements that result to be detrimental for FC-based systems operation. Among the different damaging substances, in the present work, the focus has been addressed to sulfur and sulfur-based compounds. Referring to this type of contaminant, usually a distinction can be made between the “natural” sulfur that is usually intrinsically present in the fuel adopted, according to its origins and processing procedures, and the “artificial” sulfur that can be added to the fuel depending on the specific use to which it is addressed, such the odorisation of the Natural Gas (NG). In the prosecution, some scenarios of management of the issues correlated to the presence of sulfur and sulfur-based components (especially H2S) will be presented as examples. For each of them, the current methods adopted in order to guarantee the correct and safe operation of these devices are described. In addition, where existing, some possible alternative solutions are supplied.

Sustainable waste management remains a great challenge for many cities throughout the world. Landfilling is worldwide the most common way of treating municipal solid waste (MSW) and landfilling of organic matter releases the high potent gas methane, which contributes to global warming. If the biogas instead is collected, either from landfills or produced in a more optimal and controlled environment, it can be used as a fuel to substitute fossil fuels. In this thesis, these sorts of systems are referred to as biogas solutions. In Brazil, the eight largest economy in the world and by far the largest economy in Latin America, landfilling of MSW is essentially the only way MSW is disposed of. Rio de Janeiro, the second largest city of Brazil, have had long issues with waste management, with up until 2012 deposing waste to one of the largest open landfills in the world. This study was done in collaboration with Biogas Research Center (BRC): a national biogas competence center with interests in the Brazilian biogas sector as well as contacts with the Federal University of Rio de Janeiro. Furthermore, as Swedish organic waste management practices are globally in the front edge, the Swedish perspective of waste management combined with local knowledge, could be valuable to find more efficient means of managing residues. Before initiating an actual biogas project, it is reasonable to perform an early assessment. This thesis aimed to perform an early assessment of the biogas sector in Rio, which was carried out by utilizing a multi-criteria framework. The framework consists of four categories (potential, feasibility, economic- and environmental performance), 14 key areas and 59 sub-questions, which helped gather, structure and assess information. An eight-week field study in Rio de Janeiro was part of the study. The results show that no full separation of organic content is performed as source in Rio, which is why the study included the waste streams of mixed MSW (disposed in landfills) and partly sorted organic waste (approximately 85 % organic content; referred to as Waste with High Organic Content, WHOC). Sewage sludge from wastewater treatment plants was excluded from the study to enable a focus on MSW. Potential and feasibility are significantly higher for MSW compared to WHOC, although the authors argue WHOC (or even fully sorted organic waste) have substantial growth opportunities. The landfill receives approximately 1.2 million tonnes of organic wet waste per year and provides a biogas yield of 140 million Nm3 / year (50 – 55 % CH4); whereas 26 – 42 thousand tonnes of dry matter (DM) per year can be collected from WHOC, with a biogas yield potential of 6.6 – 19.5 million Nm3 / year (55 – 63 % CH4). The feasibility analysis showed that all key areas – competing applications, legislation and infrastructure – except economic instruments, are better rated for biogas production from MSW compared to WHOC. The most feasible area of use for the biogas in Rio de Janeiro was deemed to inject the gas in into the grid. The indicated environmental performance shows that injection of biogas to the gas grid reduces GHG emissions with 68 %; and for every tonne of DM digestate, approximately 8 kg phosphorous and 36 kg nitrogen can be replaced. The economic performance shows that biogas production from the landfill is more cost-efficient than from a bioreactor, however none of the biogas productions in Rio de Janeiro is profitable, which usually is expected of a waste management system. The study concludes with identifying several challenges the biogas sector in Rio will be facing: a lack of supply of biogas and no plan in action for increasing demand; economic challenges indicating need for investment support; and a lack of value chain for biofertilizers. The results of the study can hopefully provide stakeholders with a better understanding of opportunities and challenges with biogas solutions in Rio de Janeiro municipality, that ultimately can increase the chance for successful implementation in the region.
Hållbar avfallshantering är fortsatt en stor utmaning för många städer runtom i världen. Deponering är globalt sett det vanligaste sättet att göra sig av med fast kommunalt avfall och deponering av organiskt avfall avger den potenta gasen metan, som bidrar till global uppvärmning. Om biogasen istället samlas upp, antingen från deponin eller produceras i en mer optimal miljö, kan gasen istället användas som bränsle för att substituera fossila bränslen. I denna rapport kallas denna typen av system för biogaslösningar. I Brasilien, världens åttonde största ekonomin och den avsevärt största ekonomin i Latinamerika, hanteras fast kommunalt avfall i princip endast genom deponering. Rio de Janeiro, Brasiliens nästa största stad, har länge haft problem med avfallshantering, som fram tills 2012 slängde allt sitt avfall i en av världens största öppna deponier. Denna studie genomfördes i samarbete med Biogas Research Center (BRC): ett nationellt kompetenscenter inom biogas med intresse av den Brasilianska biogassektorn, samt med kontakter till det federala universitetet i Rio. Eftersom Sverige ur ett globalt perspektiv ligger i framkant vad gäller hantering av organiskt avfall, kan den svenska synvinkeln av avfallshantering kombinerat med lokal kunskap vara värdefull för att hitta effektivare avfallshanteringssystem. Innan man genomför ett skarp biogasprojekt är det klokt att göra en förstudie. Denna uppsats syftar till att genomföra en förstudie av biogassektorn i Rio de Janeiro, som uträttades med hjälp av ett multi-kriterieramverk. Ramverket består av fyra kategorier (potential, genomförbarhet, samt ekonomisk- och miljömässig prestanda), 14 nyckelområden samt 59 underfrågor. Ramverket användes för att assistera i insamlandet, strukturerandet och utvärderandet av information. En fältstudie på åtta veckor i Rio de Janeiro var en del av studien. Resultatet visar att ingen fullständig separering av organiskt avfall sker i Rio, vilket är orsaken till att studien inkluderar avfallsströmmarna blandat kommunalt avfall (som deponeras; benämns MSW) och delvis sorterat organiskt avfall (innehåller 85 % organiskt innehåll; benämns WHOC). Avloppsslam exkluderades från studien för att fokusera på fast kommunalt avfall. Potentialen och genomförbarheten är markant högre för MSW jämfört med WHOC, dock skall det understrykas att tillväxtpotentialen för WHOC är stor vilket ej framgår av siffrorna. Deponin mottager årligen nära 1.2 miljoner ton organiskt avfall (inkl. vatten) som ger en biogasutdelning på 140 miljoner Nm3 / år (50 – 55 % CH4); medan WHOC har en potential på 26 – 42 tusen ton (torrvikt) per år med en biogasutdelning på 6.6 – 19.5 miljoner Nm3 / år (55 – 63 % CH4). Genomförbarhetsanalysen för avfallsströmmarna visade att alla nyckelområden förutom ekonomiska instrument var värderade högre för MSW jämfört med WHOC. Studien visar vidare att det mest genomförbara användningsområdet för biogasen är injektion till gasnätet. Miljömässiga prestandan visar att substituering av naturgas med biogas kan sänka växthusgasutsläpp med 68 %, och för varje ton (torrvikt) av rötrester kan ca 8 kg fosfor och 36 kg kväve ersättas. Ekonomiska prestandan visar att biogasproduktion från deponi är mer kosteffektivt än i en bioreaktor, samt att ingen av biogaslösningarna är lönsamma, vilket kan väntas av en avfallshanteringslösning. Studien avslutas med att identifiera en rad utmaningar som biogassektorn i Rio ställs inför: en avsaknad på tillgång av biogas och ingen aktiv plan för att öka produktionen; ekonomiska utmaningar som indikerar ett behov av investeringsstöd; en brist på värdekedja för biogödsel. Resultatet av studien kan förhoppningsvis ge intressenter en bättre förståelse för vilka möjligheter och utmaningar som biogaslösningar ställs inför i Rio de Janeiro kommun – som i förlängningen kan öka möjligheterna för framgångsrika implementeringar av biogasprojekt i regionen.

Biogas is a renewable gaseous fuel with low calorific value and a low burning velocity. This burning characteristic makes stabilizing biogas flame difficult especially in high flow velocity applications, and hence presenting a real challenge for power generation systems. This thesis presents an experimental investigation of the effect of burner geometry (i.e., fuel nozzle geometry and swirl strength of the co-airflow) on the stability limits of a turbulent non-premixed biogas surrogate flame. Three different co-airflow swirl strengths (S = 0, 0.31, 0.79) were implemented using swirl generators with vane angle of 0º, 25º and 50º, respectively. Six different fuel nozzle geometries were used in order to study the effect of fuel jet centerline velocity on the stability limits of a low swirling (i.e., 25º) non-premixed biogas flame. Moreover, the biogas surrogate fuel composition was kept constant (60% CH4 and 40% CO2 by volume) using a mixture of pure methane and carbon dioxide gases. The results of the effect of co-airflow swirl strength on the stability limits of biogas flame revealed that the swirl plays an important role on both the flame mode and its stability limits for both attached and lifted flames. The experimental results revealed that at low swirl strength the attached flame lifts off and stabilizes at a distance above the burner, while at high swirl strength the flame remains attached but shortens and burns blue. Overall, the high swirl attached flame was found to stabilize over a wider range of flow conditions in comparison to the attached and lifted flame produced by low swirl. Importantly, the central fuel jet characteristics (induced by varying the fuel nozzle geometry) were found to drastically influence the upper and lower blowout limits of the low swirl biogas lifted flame, while multi-hole fuel nozzle geometry was found to significantly enhance the stability ranges. 2D PIV data was used to explain the stability limits and the experimental flame results were used to propose semi-empirical correlations capable of describing the turbulent biogas blowout stability limits.
October 2016

Upgradering av biogas med tekniken vattenabsorption är vanligt i Sverige. Elva biogasanläggningar med tillsammans fjorton uppgraderingsanläggningar använder sig av tekniken. Problem med igensättning av fyllkroppar i absorptionskolonnen, samt i ett fall i desorptionskolonnen är vanligt förekommande och har en negativ effekt på uppgraderingen av rågas till fordonsgas. Fem av de nio anläggningarna i denna studie har problem med mikrobiell tillväxt på fyllkropparna. Syftet med denna rapport var att identifiera den mikrobiella tillväxten och avgöra vilka faktorer som reglerar den för att kunna rådge driftsansvariga hur man motverkar tillväxt.

En enkät skickades ut och studiebesök gjordes för att samla information om anläggningarna. Fosfolipidfettsyra (PLFA)-analyser utfördes för att bestämma mikrobiell biomassa och de organismer, som kan indikeras av de PLFA som är s.k. biomarkörer.

Prover samlades in från fyra uppgraderingsanläggningar: Jönköping, Kristianstad, Linköping och Uppsala. Proverna som samlades in var till utseendet olika, allt från gult slem från Linköping till röd-brun gegga som liknade kaffe-sump från Uppsala. I proverna från Linköping och Uppsala detekterades biomarkörer för metanoxiderande bakterier (metanotrofer) av typ I. Metanotrofer finns i jord, vatten och luft i miljöer med tillgång till metan och syre. I Jönköpingsproverna detekterades biomarkörer actinomyceter som är en vanligt förekommande bakterie i avloppsreningsverkens luftningsbassänger. Den mikrobiella tillväxten som samlades in från Kristianstad räckte enbart till ett prov och därför är det resultatet ej tillförlitligt.

I samtliga prover detekterades svamp (fungi) som förmodligen etablerats efter andra organismer.

Faktorer som kan anses påverka den mikrobiella tillväxten är processvattnets kvalitet, pH och temperatur. Rent vatten (dricksvatten) innehåller mindre mängd organiskt material, samtliga anläggningar som använder sig av avloppsvatten upplever problem. Lågt pH är gynnsamt för att minska den mikrobiella tillväxten eftersom de flesta organismer trivs bäst vid neutralt pH. Låg temperatur är gynnsam eftersom lösligheten för koldioxid och divätesulfid är större vid lägre temperaturer, vilket gynnar uppgraderingen av biogas.

Upgrading of biogas performed using the technique absorption with water wash is common in Sweden where eleven biogas plants, comprising a total of fourteen upgrading plants use this technique. However problems with microbial growth on the pall-rings in the absorption column, and in one case in the desorption column, have negative impact on upgrading the raw gas to vehicle gas. Five of the nine biogas plants studied here have experienced problems with microbial growth. The objective of this report was to identify the microbial growth and determine possible factors regulating microbial growth in order to give advice to process management.

A questionnaire was sent out and visits were made to the upgrading plants to collect information about the plants. A phospholipid fatty acid (PLFA) analysis was performed to determine microbial biomass and community structure, for which PLFA biomarkers are one type of indicator.

Samples were analysed from four upgrading plants: Jönköping, Kristinstad, Linköping and Uppsala. The cultures collected were visually different, varying from yellow and slimy to reddish brown with the consistency of coffee grounds. In the Linköping and Uppsala samples, biomarkers for methane-oxidising bacteria (type I methanotrophs) were detected. Methanotrophs live in environments with access to methane and oxygen and are inhibited by e.g. acetylene. In the Jönköping samples biomarkers indicating the bacteria actinomycetes common in the water of aeration tanks in sewage treatment plants, were detected. In Kristianstad there was only enough culture for one sample, so no reliable result was obtained. Fungi were detected in all samples and probably established after other organisms.

Factors affecting development of microbial growth were found to be water quality, pH and temperature of the process water. Clean water (drinking water) contains less organic material than cleaned water from sewage treatment plants. All plants using water from sewage treatment plants have experienced microbial growth. Low pH is beneficial for reducing microbial growth since most organisms prefer a neutral environment.

Low temperature is beneficial for minimising microbial growth since the solubility of carbon dioxide and hydrogen sulphide increases with decreasing temperature.

Energimyndigheten har från Regeringen blivit tilldelad 100 miljoner kronor att fördela som investeringsstöd för att främja en effektiv och utökad produktion, distribution samt användning av förnybara gaser såsom biogas. Myndigheten har samtidigt fått i uppdrag att utveckla en sektorsövergripande biogasstrategi och föreslå åtgärder som på kort och lång sikt kan bidra till ökad användning av biogas. Denna strategi ska också tjäna som ett underlag för fördelning av olika former av stöd inom sektorn.

Syftet med detta examensarbete är att sammanställa information som kan bidra som underlag vid upprättandet av den sektorsövergripande biogasstrategin. Ett annat syfte är att bidra med underlag för Energimyndighetens bedömning av var ett investeringsstöd kan ge störst effekt för den fortsatta utvecklingen inom biogasområdet. Detta stöd avser den senaste, ovan nämnda, utlysning som Energimyndigheten gjort inom området. Examensrapporten innehåller bland annat en sammanställning av gjorda insatser inom forskningsområdet biogas de senaste åren, finansierat av framför allt Energimyndigheten, men även en inblick i vilka biogassatsningar som är gjorda av andra nationella aktörer. Ett antal personer från bland annat branschorganisationer har intervjuats för att ta del av deras syn på den framtida biogasmarknaden, vilka satsningar som bör göras och vilka hinder som har störst inverkan. Organisationerna är valda utifrån kriteriet att de ska representera olika delar av biogasbranschen och att olika synvinklar därigenom ska framkomma. Rapporten innehåller slutsatser som dragits av tidigare biogassatsningar hos Energimyndigheten och identifiering av biogasområden där det föreligger stort behov av framtida satsningar för utökad produktion, distribution och användning. 

Ett område som i detta examensarbete har identifierats ha stort behov av framtida biogassatsningar är bland annat framtagande av alternativa rötningssubstrat, eftersom mängden tillgängligt substrat nuläget inte är tillräcklig. Detta utgör idag en begränsning för biogasproduktionen. Det bör även satsas mer på förbehandling av substrat innan rötning, vilket ökar gasproduktionen och förbättrar substratutnyttjandet i större utsträckning. Mer satsningar behövs också kring hur biogasprocessens slutprodukt, rötresten, kan bli en mer attraktiv produkt så att återcirkulering av växtnäring kan ske i större grad genom rötrestspridning på åkermark. Detta är av stor vikt eftersom en ökad volym rötningssubstrat ger upphov till större mängd rötrester som ska hanteras. Andra områden som är i behov av framtida stöd är utveckling av befintliga anläggningar för att öka och effektivisera produktionen. För att optimera processerna bör framför allt mer medel satsas på kunskapsuppbyggnad och spridning av den vetenskap som finns tillgänglig. Att länka samman universitet, högskolor och naturbruksgymnasium med anläggningar i drift kan vara det mest effektiva sättet att nå ut med relevant information och kunskap. Ur ett samhällsekonomiskt perspektiv bör mer medel läggas på att öka gödselrötning då detta minskar metanläckage.

Swedish Energy Agency has been allocated SEK 100 million from the government to distribute as investment grant to promote efficient and expanded production, distribution and use of renewable gases such as biogas. The Agency has also been given the task to develop a multidisciplinary strategy for biogas and propose measures which can contribute to increased use of biogas in the short and long term. This strategy will also serve as a basis for the allocation of various forms of support in the biogas sector. 

The purpose of this study is to compile information which can be used as input for the establishment of the multidisciplinary strategy for biogas. Another purpose is to provide information to support the Swedish Energy Agency in the assessment of which areas an investment grant will have the greatest impact for the future development of biogas. This grant refers to the latest call of Swedish Energy Agency in the sector. This report includes a summary of what areas grants have been given for research of biogas in recent years, mainly financed by the Swedish Energy Agency, but also an insight into efforts made by other national operators. A number of people from professional biogas organizations have been interviewed to share their views on the future biogas market. Which efforts should be made and the main obstacles to be overcome are other questions discussed. The report contains conclusions from the experience of previous support from the Swedish Energy Agency as well as identification of areas in which there is great need for future efforts in order to expand the production, distribution and use of biogas.

Some areas which have been identified in this thesis for need of future efforts in the biogas sector is for example the development of alternative substrates for anaerobic digestion, because the amount of available substrate is at present not sufficient. This is currently a limitation for the biogas production. There is also a need to further develop the pre-treatment of the substrate before digestion, in order to increase the gas production and improve substrate utilization to a greater extent. More focus are also needed on how the end product from the biogas process, the digestion residues, can become a more attractive product to the recycling of plant nutrients by use as a bio fertilizer on farmland. This is of great importance because larger volume of digestion will result in greater volume of digestion residues to be managed. Other areas in need of future investments are the development of existing facilities to increase and optimize the production. In order to optimize the production processes, more resources should be devoted to capacity building and dissemination of the available knowledge. Linking universities and colleges together with operating biogas plants could be the most effective way to reach out with relevant information and knowledge. From a socioeconomic perspective more resources should be spent on increasing the volume of manure digestion then it is today, which also will result in reduced methane leaks.

Membrane technology can help alleviate problems of matching supply and demand associated with upgrading on a small-scale level through its flexibility in operation. This paper provides a techno-economic assessment of the use of membrane technology via a quantitative and partial qualitative analysis at farm-based level. The purpose of the analysis is to investigate how the economic and environmental utility of the membranes can be maximised, along with outlining the possible reasons to its lack of diffusion. It combines an applied system research method by way of linear programming with interviews and the use of the innovation-decision process theory. A framework was set out to deliver hard and soft data that could also provide contextual in-depth analysis and discussion. It was found that membranes could provide good compatibility with farm based upgrading systems with desirable outcomes for both an economic and environmental viewpoint. More specifically, upgrading to 80 percent (which is below natural gas standards of 96 percent), was found to be more favourable than to upgrade to 96 percent. However, in addition to much further research and deliberation needed before 80 percent biogas can be used commercially in tractors, the study also outlined priority that needs to be given to the local market demand as well as for the need to introduce closer, more personal engagement with the farmers and make trialing and observing membrane technology better facilitated and funded so as to increase its adoption.

Mallee biomass is considered to be a second-generation renewable feedstock in Australia and will play an important role in bioenergy development in Australia. Its production is of large-scale, low cost, small carbon footprint and high energy efficiency. However, biomass as a direct fuel is widely dispersed, bulky, fibrous and of high moisture content and low energy density. High logistic cost, poor grindability and mismatch of fuel property with coal are some of the key issues that impede biomass utilisation for power generation. Therefore, innovations are in urgent need to improve biomass volumetric energy densification, grindability and good fuel matching if co-fired with coal. Biomass pyrolysis is a flexible and low-cost approach that can be deployed for this purpose. Via pyrolysis, the bulky biomass can be converted to biomass-derived high-energy-density fuels such as biochar and/or bio-oil. So far there has been a lack of fundamental understanding of mallee biomass pyrolysis and properties of the fuel products.The series of study in this PhD thesis aims to investigate the production of such high-energy- density fuels obtained from mallee pyrolysis and to obtain some new knowledge on properties of the resultant fuels and their implications to practical applications. Particularly, the research has been designed and carried out to use pyrolysis as a pretreatment technology for the production of biochar, bio-oil and bioslurry fuels. The main outcomes of this study are summarised as follows.Firstly, biochars were produced from the pyrolysis of centimetre-sized particles of mallee wood at 300-500°C using a fixed-bed reactor under slow-heating conditions. The data show that at pyrolysis temperatures > 320°C, biochar as a fuel has similar fuel H/C and O/C ratios compared to Collie coal which is the only coal being mined in WA. Converting biomass to biochar leads to a substantial increase in fuel mass energy density from ~10 GJ/tonne of green biomass to ~28 GJ/tonne of biochars prepared from pyrolysis at 320°C, in comparison to 26 GJ/tonne for Collie coal. However, there is little improvement in fuel volumetric energy density, which is still around 7-9 GJ/m[superscript]3 in comparison to 17 GJ/m[superscript]3 of Collie coal. Biochars are still bulky and grinding is required for volumetric energy densification. Biochar grindability experiments have shown that the fuel grindability increases drastically even at pyrolysis temperature as low as 300°C. Further increase in pyrolysis temperature to 500°C leads to only small increase in biochar grindability. Under the grinding conditions, a significant size reduction (34-66 % cumulative volumetric size <75 μm) of biochars can be achieved within 4 minutes grinding (in comparison to only 19% for biomass after 15 minutes grinding), leading to a significant increase in volumetric energy density (e.g. from ~8 to ~19 GJ/m[superscript]3 for biochar prepared from pyrolysis at 400°C). Whereas grinding raw biomass typically result in large and fibrous particles, grinding biochar produce short and round particles highly favourable for fuel applications.Secondly, it is found that the pyrolysis of different biomass components produced biochars with distinct characteristics, largely because of the differences in the biological structure of these components. Leaf biochars showed the poorest grindability due to the presence of abundant tough oil glands in leaf. Even for the biochar prepared from the pyrolysis of leaf at 800°C, the oil gland enclosures remained largely intact after grinding. Biochars produced from leaf, bark and wood components also have significant differences in ash properties. Even with low ash content, wood biochars have low Si/K and Ca/K ratios, suggesting these biochars may have a high slagging propensity in comparison to bark and leaf biochars.Thirdly, bio-oil and biochar were also produced from pyrolysis of micron-size wood particle using a fluidised-bed reactor system under fast-heating conditions. The excellent grindability of biochar had enabled desirable particle size reduction of biochar into fine particles which can be suspended into bio-oil for the preparation of bioslurry fuels. The data have demonstrated that bioslurry fuels have desired fuel and rheological characteristics that met the requirements for combustion and gasification applications. Depending on biochar loading, the volumetric energy density of bioslurry is up to 23.2 GJ/m[superscript]3, achieving a significant energy densification (by a factor > 4) in comparison to green wood chips. Bioslurry fuels with high biochar concentrations (11-20 wt%) showed non-Newtonian characteristics with pseudoplastic behaviour. The flow behaviour index, n decreases with the increasing of biochar concentration. Bioslurry with higher biochar concentrations has also demonstrated thixotropic behaviour. The bioslurry fuels also have low viscosity (<453 mPa.s) and are pumpable at both room and elevated temperatures. The concentrations of Ca, K, N and S in bioslurry are below the limits of slurry fuel guidelines.Fourthly, bio-oil is extracted using biodiesel to produce two fractions, a biodiesel-rich fraction (also referred as bio-oil/biodiesel blend) and a bio-oil rich fraction. The results has shown that the compounds (mainly phenolic) extracted from bio-oil into the biodiesel-rich fraction reduces the surface tension of the resulted biodiesel/bio-oil blends that are known as potential liquid transport fuels. The bio-oil rich fraction is mixed with ground biochar to produce a bioslurry fuel. It is found that bioslurry fuels with 10% and 20% biochar loading prepared from the bio-oil rich fraction of biodiesel extraction at a biodiesel to bio-oil blend ratio 0.67 have similar fuel properties (e.g. density, surface tension, volumetric energy density and stability) in comparison to those prepared using the original whole bio-oil. The slurry fuels have exhibited non-Newtonian with pseudoplastic characteristics and good pumpability desirable for fuel handling. The viscoelastic behaviour of the slurry fuels also has shown dominantly fluid-like behaviour in the linear viscoelastic region therefore favourable for atomization in practical applications. This study proposes a new bio-oil utilisation strategy via coproduction of a biodiesel/bio-oil blend and a bioslurry fuel. The biodiesel/bio-oil blend utilises a proportion of bio-oil compounds (relatively high value small volume) as a liquid transportation fuel. The bioslurry fuel is prepared by mixing the rest low-quality bio-oil rich fractions (relatively low value and high volume) with ground biochar, suitable for stationary applications such as combustion and gasification.Overall, the present research has generated valuable data, knowledge and fundamental understanding on advanced fuels from mallee biomass using pyrolysis as a pre-treatment step. The flexibility of pyrolysis process enables conversion of bulky, low fuel quality mallee biomass to biofuels of high volumetric energy density favourable to reduce logistic cost associated with direct use of biomass. The significance structural, fuel and ash properties differences among various mallee biomass components were also revealed. The production of bioslurry fuels as a mixture of bio-oil and biochar is not only to further enhance the transportability/handling of mallee biomass but most importantly the slurry quality highly matched requirements in stationary applications such as combustion and gasification. The co-production of bioslurry with bio-oil/biodiesel extraction was firstly reported in this field. Such a new strategy, which uses high-quality extractable bio-oil compounds into bio-oil/biodiesel blend as a liquid transportation fuel and utilises the low-quality bio-oil rich fraction left after extraction for bioslurry preparation, offers significant benefits for optimised use of bio-oil.

The Swedish government announced in 2015 that Sweden will work towards becoming "one of the first fossil-free welfare states of the world". The objective is to reduce the usage of fossil fuels by 70 percent by the year 2030 compared with the levels of 2010. Important factors to achieve this is to reduce the amount of transport, increase the use of biofuels and increase the fuel efficiency. The public transport sector plays an important part in reaching these objectives. There is a lot of potential in the biofuel market and in recent years there has been a development in the segment of electric buses in the city traffic. The purpose of the study is to develop a strategy proposal for the use of fossil-free fuels in Uppsala's public transport. The study is delimited to examine the use of fuels in city traffic with a focus on the introduction of electric buses. The report contains an environmental analysis of the advantages and risks associated with the fuels that the public transport administration UL decided to proceed with; biodiesel, biogas, and electricity. Based on the analysis, a strategy proposal was developed for how these fuels can be distributed in city traffic in Uppsala between 2019 - 2029. The study also examines how energy use, carbon dioxide emissions, and traffic pollution are affected if the strategy proposal is implemented. The environmental analysis suggests that biogas will continue to be used in Uppsala's city traffic, together with electric buses. Biodiesel is likely to come to better use in other areas of the transport sector in order for Sweden to reach the target of a fossil-independent fleet of vehicles in 2030. If the strategy proposal is followed the result shows that energy use and emissions of carbon dioxide and traffic pollution will decrease. Energy consumption will be reduced because of the energy efficiency of electric buses. The reduction of traffic pollution is due to the electric buses, but also because vehicles with the Euro V engine has been replaced with vehicles with Euro VI engine, which lowers traffic pollutions.

This study aims to undertake a comprehensive analysis of different waste management systems for the wastes produced in Östersund municipality of Sweden with an impact assessment limited to greenhouse gas emissions and their total environmental effects in terms of global warming potential, acidification potential, and eutrophication potential. A life cycle assessment methodology is used by integrating knowledge from waste collection, transportation, waste management processes and the product utilization. The analytical framework included the definition of functional unit, system boundaries, complimentary system design, waste management, and partial use of the energy. Three different municipal solid waste management scenarios, incineration, composting, and digestion were considered for the study. All wastes from Östersund municipality were classified into biodegradable and combustible and thereafter treated for energy and compost production. Greenhouse gas emissions and total environmental impacts were quantified and evaluated their corresponding benefits compared to three different types of marginal energy production system. The results showed that the major greenhouse gas carbon dioxide and nitrous oxide emissions are greater in composting scenario, whereas methane emission is greater in digestion scenario. Composting scenario that uses additional coal fuel has greater global warming potential and acidification potential compared to other scenarios. Composting scenario using wood fuel additional energy has greater eutrophication potential. The highest reduction in global warming potential is achieved when digestion scenario replace coal energy. The greater reduction in acidification and eutrophication potential achieved when digestion scenario replaced coal energy, and wood fuel respectively. Based on the assumptions made, digestion scenario appears to be the best option to manage solid waste of Östersund municipality if the municipality goal is to reduce total environmental impact. Although there may have plentiful of uncertainties, digestion and incineration scenario results are competitive in reducing environmental effects, and based on the assumptions and factors used for the analysis, the results and conclusions from this study appear to be strong. Key words: Solid waste, incineration, composting, digestion, total environmental effect, wood fuel, biogas.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2016.
The high cost of fossil fuels and the fact that the world has arguably reached its peak oil production, has driven the need to seek alternative fuel sources. The main objective of the current study is to determine the performance of a laboratory-mounted diesel engine when fuelled with varying laboratory prepared biofuel and biodiesel and whether the advancement of the injection timing parameters will improve the engine power output and improve the smoke effect of these different fuel blends. The laboratory prepared biofuels used in this project range from 100% bio-fuel (BF100) to 50%, 30% and 10% biodiesel blends (BF50, BF30 and BF10, respectively). It should be noted that these blends are not commercially available, since they were blended in the laboratory specifically for these tests. The overall results of the study show that there is a distinct opportunity for using certain bio-fuel blends in specific applications as the power outputs are no more than one quarter less than that of base diesel. Concomitantly, the smoke opacity in all of the blends is lower than that of base diesel, which is a significant benefit in terms of their overall air emissions.

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A busca por fontes alternativas de geração de energia, menos agressivas ao meio ambiente e a base de combustíveis renováveis tem despertado grande interesse na comunidade científica. A utilização de células a combustível têm então ganhado espaço. A célula a combustível de óxido sólido SOFC destaca-se principalmente para fins estacionários, pois apresenta uma alta eficiência elétrica, por possibilitar o aproveitamento do calor liberado durante seu funcionamento e também pela capacidade de utilizar uma vasta gama de combustíveis. A produção do biogás através de resíduos para a geração de energia está consolidada em muitos países do mundo e inúmeros são os ganhos ecológicos da utilização deste. Nesta dissertação foi analisada a associação de célula a combustível de óxido sólido com um reformador a vapor de biogás. Através da reforma um gás de síntese (rico em hidrogênio) é obtido e encaminhado para a célula a combustível; uma câmara de combustão permite queimar o hidrogênio que não reagiu na célula e um recuperador de ar recicla parte do ar que não foi consumido na célula. Trocadores de calor também são utilizados para reaproveitar a energia contida nos gases de exaustão no processo e para a produção simultânea de água quente. A fim de avaliar a atratividade deste sistema foram realizadas análises de desempenho segundo as Leis da Termodinâmica, seguida de estudo econômico, baseada nas correntes de energia do sistema de cogeração. Em etapa final foi realizada a quantificação das emissões de poluentes do sistema, buscando a determinação do dióxido de carbono equivalente, do indicador de poluição e da eficiência ecológica do processo. Conclui-se que o sistema de cogeração proposto é uma opção interessante para geração de energia, apresentando bom desempenho energético e ... (Resumo completo, clicar acesso eletrônico abaixo)
The search for alternative sources of power generation, less harmful to the environment using renewable fuels has aroused great interest in the scientific community. The use of fuel cells has gained ground then. The Solid Oxide Fuel Cell (SOFC) stands out especially for stationary purposes; it presents a high electrical efficiency by enabling use of the heat released during operation and also by the capacity to use a wide range of fuels. The production of biogas through waste to power generation is established in many countries of the world and there are many ecological gains in this use. This dissertation analyzed the association between a solid oxide fuel cell with a biogas steam reformer. By reforming a synthesis gas (hydrogen-rich) is obtained and sent to the fuel cell; a combustion chamber allows to burn hydrogen unreacted in the cell and an air recuperator recycles part of the air that has not been consumed in the cell. Heat exchangers are also used for recovering the energy contained in the exhaust gases in the process and the simultaneous production of hot water. In order to evaluate the attractiveness of this system performance analyzes were conducted according to the Laws of Thermodynamics, then a economic study was performed based on energy currents of the cogeneration system. In the final step, the quantification of system pollutant emissions is made, seeking the determination of carbon dioxide equivalent, pollution indicator and ecological efficiency. It is concluded that the proposed cogeneration system is an interesting option for energy production, with good energy and exergetic performance. Regarding economic aspects, the payback period was considered high, since it is a residential system; this scenario should change, the trend that the compact SOFC reach a lower value with the spread of its use, by increasing the production volume of these. ... (Complete abstract click electronic access below)

Orientador: José Luz Silveira.
Coorientador: Celso Eduardo Tuna
Banca: José Alexandre Matelli
Banca: Lúcia Bollini Braga Maciel
Resumo: A busca por fontes alternativas de geração de energia, menos agressivas ao meio ambiente e a base de combustíveis renováveis tem despertado grande interesse na comunidade científica. A utilização de células a combustível têm então ganhado espaço. A célula a combustível de óxido sólido SOFC destaca-se principalmente para fins estacionários, pois apresenta uma alta eficiência elétrica, por possibilitar o aproveitamento do calor liberado durante seu funcionamento e também pela capacidade de utilizar uma vasta gama de combustíveis. A produção do biogás através de resíduos para a geração de energia está consolidada em muitos países do mundo e inúmeros são os ganhos ecológicos da utilização deste. Nesta dissertação foi analisada a associação de célula a combustível de óxido sólido com um reformador a vapor de biogás. Através da reforma um gás de síntese (rico em hidrogênio) é obtido e encaminhado para a célula a combustível; uma câmara de combustão permite queimar o hidrogênio que não reagiu na célula e um recuperador de ar recicla parte do ar que não foi consumido na célula. Trocadores de calor também são utilizados para reaproveitar a energia contida nos gases de exaustão no processo e para a produção simultânea de água quente. A fim de avaliar a atratividade deste sistema foram realizadas análises de desempenho segundo as Leis da Termodinâmica, seguida de estudo econômico, baseada nas correntes de energia do sistema de cogeração. Em etapa final foi realizada a quantificação das emissões de poluentes do sistema, buscando a determinação do dióxido de carbono equivalente, do indicador de poluição e da eficiência ecológica do processo. Conclui-se que o sistema de cogeração proposto é uma opção interessante para geração de energia, apresentando bom desempenho energético e ... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The search for alternative sources of power generation, less harmful to the environment using renewable fuels has aroused great interest in the scientific community. The use of fuel cells has gained ground then. The Solid Oxide Fuel Cell (SOFC) stands out especially for stationary purposes; it presents a high electrical efficiency by enabling use of the heat released during operation and also by the capacity to use a wide range of fuels. The production of biogas through waste to power generation is established in many countries of the world and there are many ecological gains in this use. This dissertation analyzed the association between a solid oxide fuel cell with a biogas steam reformer. By reforming a synthesis gas (hydrogen-rich) is obtained and sent to the fuel cell; a combustion chamber allows to burn hydrogen unreacted in the cell and an air recuperator recycles part of the air that has not been consumed in the cell. Heat exchangers are also used for recovering the energy contained in the exhaust gases in the process and the simultaneous production of hot water. In order to evaluate the attractiveness of this system performance analyzes were conducted according to the Laws of Thermodynamics, then a economic study was performed based on energy currents of the cogeneration system. In the final step, the quantification of system pollutant emissions is made, seeking the determination of carbon dioxide equivalent, pollution indicator and ecological efficiency. It is concluded that the proposed cogeneration system is an interesting option for energy production, with good energy and exergetic performance. Regarding economic aspects, the payback period was considered high, since it is a residential system; this scenario should change, the trend that the compact SOFC reach a lower value with the spread of its use, by increasing the production volume of these. ... (Complete abstract click electronic access below)
Mestre

Despite the huge national energy resources, many Nigerians do not have access to high quality, modern energy services. For those with access, energy supply lacks reliability, especially in the case of liquefied petroleum gas (LPG). Hence this research considers the possibility of enhancing the household use of LPG. It analyzes the factors affecting the current demand and supply. Salient features of the LPG supply and distribution system were also discussed. On the basis of the existing situation, barriers of increasing LPG use, in particular, the problems regarding affordability, priCing, government poliCies, safety, transportation and distribution were analyzed and identified statistically using the chi-square statistical method as a tool. Finally, on the basis of the challenges identified, suggestions and recommendations were made regarding the policies through which the problems could be overcome. Furthermore, a model was developed and tested for an effective marketing strategy of LPG in Warri Nigeria. ii
Thesis (M.Ing. (Development and Management Engineering))--North-West University, Potchefstroom Campus, 2009.

La dégradation de l’environnement ainsi que l’épuisement progressif des énergies fossiles devient très inquiétant et incite les états à définir des limites d’émission polluantes plus strictes. Ceci a conduit les constructeurs automobiles à poursuivre leurs recherches dans le développement de conception propre et efficace des moteurs en utilisant des combustibles alternatifs dans les moteurs à combustion interne.Dans le présent travail, on s’intéresse à l’étude des moteurs fonctionnant en mode DF afin d’améliorer ses performances tout en minimisant les émissions polluantes, en particulier les HC et les CO. Pour ce faire des études expérimentales ont été menées. Une réduction de 77% des émissions de HC a été observée en passant d’une richesse de 0,35 à 0,7. Par ailleurs, Il a été noté aussi qu’une diminution de 20% à 50% des émissions de CO avec une amélioration de 30% du rendement peut être visualisée en variant l’avance à l’injection de 4,5 °V à 6 °V. Concernant la mise en place de la pré-injection, une baisse de 30% des émissions de NOx a été observée avec un gain de 12% à 30% de rendement par rapport à une seule injection. En dernier terme, un modèle thermodynamique à une zone a été développé afin de prédire la température et la pression dans le cylindre. Une bonne concordance a été notée entre les deux résultats avec une erreur moyenne relative inférieure à 5%
Currently, the environmental degradation due to pollutant emissions and the gradual depletion of fossil fuels, becoming very worrying, are prompting European directives to set pollutant emission limits. These have led manufacturers to continue research in the development of clean and efficient engine designs using alternative fuels in internal combustion engines.In this work, we focus on the study of engines operating in dual-fuel mode to improve its performance while minimizing pollutant emissions, particularly HC and CO. For this, experimental studies were conducted. A reduction of about 77% in the HC emissions was observed as the equivalence ratio was varied from 0.35 to 0.7. Regarding the effect of injection timing, it was noted that the CO emissions decreased about 20% to 50% with an improvement in the brake thermal efficiency by 30% upon varying the injection advance from 4,5 °CA to 6 °CA. On the other hand, the introduction of pre-injection strategy led to a decrease by 30% in NOx emissions with an amelioration of brake thermal efficiency of 12% to 30% compared to a single injection. Lastly, a single zone thermodynamic model was developed to predict the in-cylinder temperature and pressure. A good agreement was noted between the predicted and experimental results. The average relative error was less than 5%

Anaerobic digestion is the process by which organic carbon is converted into biogas in the form of carbon dioxide (CO2) and methane (CH4). Both of these products are greenhouse gases that contribute to global warming. Therefore if anaerobic reactors are improperly maintained and biogas is leaked or intentionally released into the atmosphere because biogas production exceeds household demand, these reactors may become generators of greenhouse gas emissions instead of sustainable energy producers. The objective of this research was to develop a framework to assess if the demand for biogas by a rural adopter of an anaerobic digester matched with the associated local gas production. A literature review of the energy required to prepare commonly consumed food of rice and beans was conducted to establish required household biogas volumes. This review determined that 0.06 m3 of methane was required to prepare a half a kg of rice (on a dry weight basis) and 0.06 m3 of methane was required to prepare a half a kg of beans (on a dry weight basis). Furthermore an analysis of occupants of a rural Panamanian town was performed along with a design model for rural anaerobic reactor gas production to determine if an overproduction of biogas would occur if anaerobic reactors were built for families who owned swine. It was determined using this approach that all of the fifteen household would experience an overproduction of biogas based on household demand of methane and therefore would risk the release of greenhouse gases. Household size ranged from one to seven occupants and swine ownership ranged from one to fifteen per household. The differences of biogas supply with respect to demand from these fifteen situations ranged from 0.09 to 0.35 m3 of a biogas with 40% methane and 0.27 to 6.17 m3 of excess biogas with a methane content of 70% per household per day. An average of 0.45 m3 of a biogas with 40% methane per household per day was calculated and 0.87m3 for 70% methane for all fifteen households, excluding one outlier. However, because this research uses a model based on plug flow reactor mechanics, results may produce varied results from other studies concerning small scale anaerobic digestion.

Capes; CNPq
A geração de energia renovável desafia as empresas a envolver um processo em cadeia, no qual, todos os elos são corresponsáveis pela geração de novos produtos, processos, e pelo consumo e produção responsável, protegendo o meio ambiente e melhorando a vida das pessoas com que mantém interações. A presente pesquisa objetivou propor uma abordagem teórica do processo de geração de biometano a partir de resíduos agroindustriais. Para a realização da abordagem teórica, foi construído um Portfólio Bibliográfico e adotadas técnicas de revisões sistemáticas de literatura, para assegurar que estudos recentes e relevantes sobre o tema da pesquisa fossem capturados. A abordagem teórica foi dividida em três principais fases, sendo que a primeira fase do processo de geração de biometano incluiu a escolha, o pré-tratamento e o transporte do material orgânico até o biodigestor. A segunda fase do processo incluiu decisões como, a escolha do modelo do biodigestor e a utilização final do biofertilizante e do biogás gerado. Por fim, a terceira fase do processo de geração de biometano incluiu decisões como, a escolha da tecnologia a ser utilizada para o processo de purificação, e o uso final do biometano. O processo de geração de biometano a partir de resíduos agroindustriais, é um tema de poucas publicações no Brasil. O uso do biometano em países como Alemanha, Reino Unido e Suécia, está em um estágio consideravelmente avançado em relação a legislação e tecnologias, comparado ao Brasil. Desta forma, a proposta formulada neste estudo, auxilia acadêmicos, pesquisadores e gestores na área, na compreensão do processo como um todo e na tomada de decisões sustentáveis.
Renewable energy generation challenges companies to engage in a chain process in which all links are co-responsible for the generation of new products, processes and responsible consumption and production, protecting the environment and improving the lives of people with whom Interactions. The present research aimed to propose a theoretical approach of the biomethane generation process from agroindustrial waste. For the accomplishment of the theoretical approach, a Bibliographic Portfolio was constructed and techniques of systematic literature reviews were adopted to ensure that recent and relevant studies on the research topic were captured. The theoretical approach was divided into three main phases, and the first phase of the biomethane generation process included the selection, pretreatment and transport of the organic material to the biodigester. The second phase of the process included decisions such as the choice of biodigester model and the final use of biofertilizer and biogas generated. Finally, the third phase of the biomethane generation process included decisions such as the choice of technology to be used for the purification process and the final use of biomethane. The process of generating biomethane from agro-industrial waste is a subject of few publications in Brazil. The use of biomethane in countries such as Germany, the United Kingdom and Sweden is at a considerably advanced stage compared to legislation and technologies compared to Brazil. Thus, the proposal of this study assists academics, researchers and managers, in understanding the process as a whole and in making sustainable decisions.

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

The emergence of biomass based energy warrants the evaluation of syngas from biomass gasification as a fuel for personal power systems. The objectives of this study were to determine the performance and exhaust emissions of a commercial 5.5 kW generator modified for operation with 100% syngas at different syngas flows and to compare the results with those obtained for gasoline operation at same electrical power. Maximum power output for gasoline operation was 2451 W and maximum power output for syngas operation was 1392 W. Overall efficiencies of the generator were same at maximum electrical power outputs for operation with both the fuels. At four different electrical power output categories, the exhaust concentrations of carbon monoxide and oxides of nitrogen were significantly lower while the carbon dioxide emissions were significantly higher for the syngas operation. The unit cost of electricity generation was $6.38/kWh for syngas operation and $0.56/kWh for gasoline operation.

In-Storage-Psychrophilic-Anaerobic-Digestion (ISPAD) is a technology which allows livestock producers to operate an anaerobic digester with minimum technological knowhow and for the cost of a conventional storage cover. Nevertheless, the system is exposed to ambient temperatures and biogas production is expected to vary with climatic conditions. The objective of the present project was therefore to design an automated biogas composition monitoring system for ISPAD and analyse the biogas composition produced during the time span of the project. The challenges in designing this monitoring system were: respecting the concentration range expected for CH4 and CO2, building air-tightness gas lines to prevent contamination and corrosion of the electronic devices inside the metallic box housing the monitoring system and; automating the gas line flushing operations. In the laboratory, the system was designed, calibrated and validated using gas samples of known CO2 and CH4 concentrations. Once connected to a field ISPAD system treating grower hog manure, the system was further validated by feeding CO2 and CH4 mixtures of known composition and by sampling the ISPAD biogas for gas chromatography analyses. Both in the laboratory and field, the automated system read CO2 and CH4 concentrations with a maximum error of 16 and 9%, respectively. Although a monthly calibration is recommended, the sensors demonstrated very little drift over a period of up to 55 days. Once validated, the automated monitoring system was able to measure biogas CO2 and CH4 concentrations and fluctuations respecting fully all ISPAD operations.
La Digestion-Anaérobie-Psychrophile-En-Stockage (DAPES) est un concept permettant aux éleveurs agricoles d'opérer un digesteur anaérobie nécessitant un minimum de connaissance techniques et pour un prix comparable à une couverture de fosse à lisier conventionnelle. Néanmoins, le system anaérobique est assujetti à la température ambiante et la production de biogaz peut varier au gré des conditions climatiques. L'objectif du présent projet était donc de concevoir un système automatique d'analyse de la composition de biogaz pour le concept DAPES et d'analyser les résultats obtenus durant la période du projet. Les défis rencontrés lors de la conception du système étaient : le respect de la plage de concentration prévue pour le CH4 et le CO2; la calibration précise des senseurs; l'étanchéité du système afin de prévenir la contamination et la corrosion des instruments électroniques à l'intérieur de la boîte métallique abritant le système d'analyse; et l'automatisation du système de purge de la ligne d'alimentation en biogaz. En laboratoire, le système fut conçu, calibré et testé en utilisant un gaz ayant une concentration de CH4 et de CO2 connue. Une fois connecté au système DAPES traitant du lisier porcin, le système était à nouveau testé afin de vérifier l'exactitude des données en utilisant un gaz ayant une concentration de CH4 et de CO2 connue et en échantillonnant du biogaz du système DAPES pour l'analyser à l'aide d'un chromatographe à phase gazeuse. Tant au laboratoire qu'au site de recherche, le système a permis d'obtenir des lectures de concentration de CO2 et de CH4 ayant une erreur maximale de 16 et 9%, respectivement. Bien qu'une calibration mensuelle soit recommandée, les senseurs n'ont démontré qu'une petite dérivation des lectures sur une période atteignant 55 jours. Une fois calibré, le système d'analyse automatique pouvait mesurer des fluctuations de la concentration de CO2 et de CH4 durant toutes les étapes d'opération d'un système DAPES.

This study involved two avenues of investigation: a new concept of Direct Carbon Fuel Cell (DCFC) and the production of carbon from biomass. The new concept of DCFC merges a solid oxide electrolyte and a molten carbonate electrolyte called the “hybrid direct carbon fuel cell” using tubular geometry. The tubular cell was chosen for several reasons, such as sealing process, reduction of stress during the sintering process and reduction of the final size of the stack. In addition, it makes the fuelling process easier than in planar geometry. The previous tests carried out on tubular hybrid direct carbon fuel cell at the University of St Andrews showed promising results. In fact, a power of 85 mW was achieved at 800ºC. However this temperature was too high and so the focus of the new project was on decreasing the operating temperature to 650ºC, replacing the YSZ electrolyte used in the previous configuration with an electrolyte such as GDC, which showed better performance at low temperature. YSZ was substituted for GDC in the anodes and cathode in order to prevent an increase in the interface resistance due to the possible reaction between electrolyte and electrodes at the interface. Anodes with different proportions of NiO and GDC were investigated in order to understand the electrochemical phenomena in the presence of GDC compared to YSZ. Three different electrical configurations were investigated by AC impedance studies because the electrochemistry of the cell changes as function of the position and the surface of the current collector, which is dipped into the anode chamber. Performance improved when the surface area of the current collector increased, which combined a silver wire with strip of nickel mesh. Two types of seals (552 ceramabond and ToKu adhesive) and the sealing process were also studied in order to prevent leakage, which affects the performance of the entire cell. The leakages were reduced using a composite seal composed of alumina paste and a combination of flexi disks of mica and alumina fibre disk. In the preliminary test using 70-30%wt NiO GDC and LSM-GDC with composite nickel mesh and silver wire current collector and the composite seal, a promising value of power of 191mW was achieved at 700ºC using GDC electrolyte. The value of power was improved by reducing the thickness of the electrolyte and the cathode manufacture. However, the best performance was achieved when LSM-GDC cathode was replaced with LSCF- GDC. LSCF was chosen for the promising results shown at low temperature, and a power of 240mW was achieved at 650ºC when it was used as the cathode in our cell. The carbon fuel used for these fuels was a medium density fibreboard pyrolysed at 500°C. The choice of this carbon fuel was based on the production and characterization of carbon fuels in this project. The investigations were focused on the production and characterization of carbon fuel from biomass such as MDF and pellet wood produced by pyrolysis. Secondary products resulting from the pyrolysis process were also investigated in order to use them as alternative fuels. All of the types of carbons produced and 3 commercial carbons were characterized by SEM, XRD, infrared spectroscopy, surface area and elemental analysis, while their electrochemical performances were investigated by hybrid direct carbon fuel cell with planar geometry. The investigations highlight that the structure of the carbon used does not affect the performance of the cell, which is in fact affected by the ability of the carbon to gasify in the presence of carbonate.

Disposal of large quantities of surplus straw, which lie in the fields after harvest, is a major annual problem to cereal farmers. The current preferred solution of burning the straw where it lies is environmentally unsatisfactory and appears to be a huge waste of a potentially valuable, renewable energy source. None of the currently available straw packaging systems provides an economically viable alternative. A process is proposed for producing industrial quality fuel briquettes using a tractor towed implement. The economic feasibility of such a system is investigated and comparisons are made with existing straw disposal methods. The projected cost of fuel, produced in this way, is compared with prevailing fossil fuel prices. A multistage continuous process machine concept is described and the various stages are proven workable both experimentally, in the laboratory, and analytically. Laboratory experiments determine the forces required to produce acceptable quality briquettes and comparisons are made between the power available from the tractor, the economical throughput rate and the energy consumed in the compaction process. The mechanism of bonding within the straw packages, under compression, is examined so that the parameters necessary to give the optimum machine design may be understood. The effect, on briquette quality, of variations in die shape within the constraints imposed by the machine concept is fully investigated. Experiments extend to compression at speeds representative of 'live' field operation and a die shape is developed which produces packages of consistently good durability. Many of the design ideas put forward in this thesis have now been incorporated in an original prototype machine, built and successfully field-tested by the company who has supported this project and now holds the relevant patents.

The ready availability of biomass in Brazil makes this type of fuel a major candidate to integrate the country's energy matrix. Although this fuel is used as a primary energy source, its use for electricity generation is still modest. On the other hand, high efficiency and power density achieved by modem gas turbine engines make them a promising option for the power generation market. Thus, this thesis has as main objective to analyse the marriage between the solid fuel, biomass in this case, and gas turbines. Two main types of power plants are studied; the biomass integrated gasification gas turbine cycle (BIGGT) and the externally fired cycle (EFGT), which for the first time is thoroughly studied for the use of biomass fuel, plus the intercooled and recuperated variants of these power plants. The results are compared with the ordinary natural gas fuelled cycle. The method involves on- and off-design point performance and exergy analysis. The economic performance and optimisation for each cycle is also explored in order to assess their feasibility. The optimisation technique adopted is the Genetic Algorithm (GA) connected to the conventional hill-climbing methodology. This merge uses the GA to identify the region of optimum values, which are then passed on to the hill-climbing algorithm. In this way the long time demanded by the GA to converge is shortened and the unreliability of the hill-climbing method in finding the global optimum is overcome. The codes developed for design-point performance analysis and optimisation, compared with a commercial package, proved reliable and robust. The tools developed for exergy analysis (on- and off-design) are also robust and flexible, with the capability of analysing and calculating the properties of mixtures made of 23 different gases. The emissions equations are sufficiently accurate for the purposes of this thesis. The relationship proposed for calculating the variable operating and maintenance costs proved to be consistent with the current knowledge. The results show that the optimised cycles are competitive with current technology in terms of cost of electricity, the EFGT being the more competitive biomass cycle, with costs of electricity (US$ 0.07/kWh) comparable with those of the natural gas fuelled power plants. The BIGGT in its turn shows a cost of electricity 29 percent higher than its natural gas and externally fired counterparts (US$0.09/kWh) counterparts. The method used to work out the best investment - the required revenue (RR) method - demonstrated that the EFGT is again comparable with the NGGT cycle, with its RR being only 7 percent higher. The BIGGT cycle shows a higher RR due to its costly gasification/cleaning system. The minimisation of the exergy destruction ratio indicates that little improvement would be achieved after the reduction of this parameter, and a penalty - an 85 percent increase in the cost of electricity - must be paid. The environmental advantage of the biomass-fuelled cycles over the natural gas cycle is clear, making these systems very promising as low emissions alternatives. Both BIGGT and EFGT cycles presented very low CQ2 emissions. Regarding NO., emissions, the EFGT cycle has the lowest rates, whereas the BIGGT has the highest.