Дисертації з теми "Boilers Evaluation"

This thesis compares ash collected from different boilers cleaned using infrasound cleaning. The samples were evaluated from their physical properties, in an attempt to find connections between the difficulty to remove ash and its physical appearance. To get a deeper understanding of the mechanisms behind adhesion and fouling, and possibly explain results from the study of the ash samples, a literature review was carried out. The ash was also evaluated to see if any connections could be drawn between the physical properties of the ash and its fouling capabilities. A strong connection was found between ash density and its fouling capabilities. It was found that no dry ash with a density higher than 0.4 g/ml were difficult to remove with infrasound cleaning, and no ash with lower density was easy to remove. The ash density was calculated from a measurement of the weight of a certain volume of ash on a scale. Optical microscopy was used to study the ash samples, and gave an estimation of particle size, shape, and porosity. However, no clear connection could be observed with this method between the different samples and which were difficult to remove. The particle size for a few of the samples were also measured by a wet laser sieving method, and while it does give a good picture of particle size, the size was not found to be a useful prediction of the ash fouling behaviour. The exact mechanism giving rise to the density dependence need to be further investigated.

In the hope to increase the detection rate of faults in combined heat and power plant boilers thus lowering unplanned maintenance three machine learning models are constructed and evaluated. The algorithms; k-Nearest Neighbor, One-Class Support Vector Machine, and Auto-encoder have a proven track record in research for anomaly detection, but are relatively unexplored for industrial applications such as this one due to the difficulty in collecting non-artificial labeled data in the field.The baseline versions of the k-Nearest Neighbor and Auto-encoder performed very similarly. Nevertheless, the Auto-encoder was slightly better and reached an area under the precision-recall curve (AUPRC) of 0.966 and 0.615 on the trainingand test period, respectively. However, no sufficiently good results were reached with the One-Class Support Vector Machine. The Auto-encoder was made more sophisticated to see how much performance could be increased. It was found that the AUPRC could be increased to 0.987 and 0.801 on the trainingand test period, respectively. Additionally, the model was able to detect and generate one alarm for each incident period that occurred under the test period.The conclusion is that ML can successfully be utilized to detect faults at an earlier stage and potentially circumvent otherwise costly unplanned maintenance. Nevertheless, there is still a lot of room for improvements in the model and the collection of the data.
I hopp om att öka identifieringsgraden av störningar i kraftvärmepannor och därigenom minska oplanerat underhåll konstrueras och evalueras tre maskininlärningsmodeller.Algoritmerna; k-Nearest Neighbor, One-Class Support Vector Machine, och Autoencoder har bevisad framgång inom forskning av anomalidetektion, men är relativt outforskade för industriella applikationer som denna på grund av svårigheten att samla in icke-artificiell uppmärkt data inom området.Grundversionerna av k-Nearest Neighbor och Auto-encoder presterade nästan likvärdigt. Dock var Auto-encoder-modellen lite bättre och nådde ett AUPRC-värde av 0.966 respektive 0.615 på träningsoch testperioden. Inget tillräckligt bra resultat nåddes med One-Class Support Vector Machine. Auto-encoder-modellen gjordes mer sofistikerad för att se hur mycket prestandan kunde ökas. Det visade sig att AUPRC-värdet kunde ökas till 0.987 respektive 0.801 under träningsoch testperioden. Dessutom lyckades modellen identifiera och generera ett larm vardera för alla incidenter under testperioden. Slutsatsen är att ML framgångsrikt kan användas för att identifiera störningar iett tidigare skede och därigenom potentiellt kringgå i annat fall dyra oplanerade underhåll. Emellertid finns det fortfarande mycket utrymme för förbättringar av modellen samt inom insamlingen av data.

The use of wood pellet boilers for residential space heating has significantly increased over the past decade. Wood pellets are a biomass-based renewable energy made by pelletizing debarked wood fiber. Compared to log wood and wood chips, wood pellets have higher energy density, relatively uniform fuel quality, easier to automate their use, and therefore, are being more widely used.

A typical wood pellet heating system has three components: the boiler (energy generation unit), the thermal energy storage (TES) tank (energy storage unit), and the building (energy consumption unit). The three components form into two loops: the boiler to TES tank loop and the TES tank to building loop.

Three modern wood pellet boilers were installed and monitored in this research. Two 25 kW boilers (PB and WPB) were installed in the end of 2014 and a 50 kW boiler (LGB) was installed in March of 2016. PB is used only for radiant floor heating and WPB is used for traditional baseboard/cast iron radiators space heating as well as providing domestic hot water (DHW) supply. LGB boiler is used for concrete slab heating. The three boiler installations provide different methods of heating and different levels of building heat demand.

This research first evaluated the performance of residential scale wood pellet boilers (25 – 50 kW) in terms of boiler operation characteristics, thermal efficiency, boiler emissions, TES tank stratification and discharge efficiency, etc. Comparisons were also made among different boilers and suggestions for improvements were made. A process dynamic simulation using VMGSim was built up based on the field monitoring data. Good agreement between the simulation and field data was found. The model was then used to size the TES tank with respect to different boiler capacities and heating demands. A system sizing algorithm was provided in the end. The results will be used to compose a guidance document for wood pellet boiler heating systems.

Thesis (MScAgric (Animal Sciences))--University of Stellenbosch, 2011.
Includes bibliography.
ENGLISH ABSTRACT: The objective of this study was to evaluate the use of Musca domestica (common house fly) larvae meal, as protein source, for broiler production. This was done by investigating the nutritive value of house fly larvae meal together with its total tract digestibility, potential toxicity and carcass characteristics of the broilers supplemented with house fly larvae meal. The proximate analysis of house fly larvae meal show that it contained, on a dry matter basis, a gross energy value of 20.10 MJ/kg, 60.38% crude protein, 14.08% crude fat and 10.68% ash and that the house fly pupae contained a gross energy of 20.42 MJ/kg, 76.23% crude protein, 14.39% crude fat and 7.73% ash. House fly pupae meal had the closest match of amino acid profile when compared with the ideal amino acid profile required by broilers and it has arginine relative to the lysine content closer to the ideal amino acid profile than the house fly larvae meal. The essential fatty acid, linoleic acid, was found at levels of 26.25 and 36.27% of the total fats for the house fly larvae and pupae meal respectively. House fly larvae meal supplementation did not induce gizzard erosion or showed toxicity (regarding the gastro intestinal tract, immune system and organ stress) in broilers. Results revealed that house fly pupae meal had higher total tract digestibilities for most nutrients than of the house fly larvae meal. House fly larvae meal had a crude protein total tract digestibility of 69% and that of pupae meal was 79%. Both larvae and pupae meal had high amino acid total tract digestibilities of all the amino acids analysed. The house fly larvae and pupae meal had an apparent metabolizable energy (AME) value of 14.23MJ/kg and 15.15MJ/kg respectively. The larvae meal total tract crude fat and crude fibre digestibilities were 94% and 62% respectively. The pupae meal total tract crude fat and crude fibre digestibilities were 98% and 58% respectively. House fly larvae meal supplementation in a three phase feeding system significantly increased average broiler live weights at slaughter, total feed intake, cumulative feed intake as well as average daily gain (ADG) when compared to commercial maize: soya oil cake meal diet. In direct comparison of larvae inclusion levels with fishmeal in isonitrogenous and isoenergetic diet, no significant differences were observed between a 10% house fly larvae and a 10% fish meal diets regarding performance characteristic. The 25% house fly larvae meal diet yielded significantly better average broiler live weights at slaughter, total feed intake, cumulative feed intake (from the second week until slaughter) as well as average daily gain when compared to the 25% fish meal diet in the growth phases. Carcass characteristics of the 10% larvae, 10% fishmeal and commercial diets were compared. Chicks that received either the 10% house fly larvae meal or 10% fish meal supplementation produced significantly heavier carcasses and breast muscle portions than the chicks that received the commercial maize: soya oil cake meal. No treatment differences were found regarding breast and thigh muscle colour or pH. This study showed that house fly larvae meal can be regarded as a safe protein source that can be used to replace other protein sources and that has the ability to promote broiler performance without having any detrimental effects on carcass characteristics.
AFRIKAANSE OPSOMMING: Die doel van die studie was om die effek van Musca domestica (gewone huisvlieg) larwe meel, as ‘n protein bron, in braaikuikens te evalueer. Dit was gedoen deur die nutrient waarde van huisvlieg larwe meel saam met die totale spysvertering verteerbaarheid, moontlike toksiesiteit en karkas-eienskappe van braai kuikens te evalueer. Laboratoruim analiese toon dat huisvlieg larwe meel 20.10 MJ/kg bruto energie, 60.38% ru- protein, 14.08% ru- vet en 10.68% as bevat en huisvlieg papie meel 20.42 MJ/kg bruto energie, 76.23% ru- protein, 14.39% ru- vet en 7.73% as bevat. Huisvlieg papie meel stem die meeste ooreen met die idiale amino suur profiel soos wat benodig word deur braaikuikens en dit het ‘n arginien tot lisien verhouding wat die meeste ooreenstem met die idiale amino suur profiel in vergelyking met huis vlieg larwe meel. Die essensiele vet suur, linolien suur, was geanaliseer teen vlakke van 26.25- en 36.27% van die totale vette onderskeidelik vir huisvlieg larwe- en papie meel. Huisvlieg larwe meel vervanging het nie spiermaag erosie of enige ander toksiese effekte te veroorsaak nie. Resultate het getoon dat huisvlieg papie meel, in vergelyking met larwe meel, het ‘n hoër totale spysvertering verteerbaarheid vir meeste van die nutrient. Die huisvlieg larwe meel het ‘n totale ru- protein spysvertering verteerbaarheid van 69% en die van papie meel van 79%. Beide larwe en papie meel het hoë amino suur spysvertering verteerbaarheid. Larwe meel en papie meel het skynbare metaboliseerbare energie waardes van 14.23MJ/kg en 15.15%MJ/kg onderskeidelik. Die larwe meel het ‘n ru-vet en ru- vesel spysvertering verteerbaarheid van 94% en 62% onderskeidelik, waar die papies ‘n ru-vet en ru- vesel spysvertering verteerbaarheid van onderskeidelik 98% en 58% het. Huisvlieg larwe meel vervanging in ‘n drie fase voer stelsel het getoon om die gemiddelde braaikuiken lewende gewigte by slag, totale voer iname, sowel as die gemiddelde daaglikse toename te verhoog waneer dit vergelyk word met ‘n kommersiele mielie- soya olie koek dieet. Geen mekwaardige verskille was waargeneem toe die 10% larwe meel dieet direk met die 10% vismeel diet vergelyk was rakende enige produksie einskappe gemeet nie. Die 25% larwe meel dieet het merkwaardig beter gemiddelde braaikuiken lewende gewigte by slag, totale voer iname, sowel as die gemiddelde daaglikse toename getoon wanneer vergelyk word met die 25% vismeel dieet gedurende die verskeie groei fases. Karkas eienskappe van die 10% larwe meel, 10% vismeel en die kommersiele diete was gevergelyk. Kuikens wat 10% larwe meel en 10% vismeel in die diete ontvang het, het swaarder karkasse gelewer met swaarder borsie massas wanneer vergelyk word met die kommersiele mielie- soya olie koek dieet. Geen behandelings verskille was gevind rakende die borsie- en dy spier kleure of pH nie. Die studie toon dat huisvlieg larwe meel as ‘n veillige protein bron kan beskou word, wat gebruik kan word om ander protein bronne te vervang. Huisvlieg larwe meel het ook die vermoë om braaikuiken produksie te verhoog sonder om enige negitiewe effekte rakende die karkas eienskappe te toon nie.

The environmental concerns of C02 emissions resulting from the increasing consumption of fossil fuels over the past decades has called for greater utilisation of renewable energy resources such as solar energy, wind power and biomass energy. Currently, biomass combustion is the dominant conversion technology that is used to extract energy from biomass feedstock at all scales. However, biomass combustion can lead to significant amounts of gaseous (e.g. NOx, CO) and particulate matter (PM) emissions, which is a particular concern for simple and small scale biomass combustion stoves and boilers. The present PhD work aims to achieve low emissions of NOx, CO and PM with a 50kW commercial boiler burning different woody and non-woody biomass pellets by the use of combustion modifications and a particulate removal unit. The combustion performance and emissions of NOx, CO and PM of the boiler were experimentally investigated with three different types of woody and non-woody biomass fuels. Different operating conditions for the minimisation of NOx and CO emissions, including the 'air staging' method and the novel 'reverse flame box' system, have been studied. An innovative particulate filter unit was installed in the flue path of the boiler as a means to reduce PM emissions. CFD modelling of the tested boiler has been carried out and the simulation results have been presented and discussed in this thesis. The experimental results showed that the modified biomass boiler could handle woody biomass pellets while maintaining low levels of CO and NOx emissions. It could also handle non-woody biomass pellets if appropriate additives are added. An approximate 40% NOx reduction was achieved when the boiler was incorporated with a novel low emissions strategy termed as a 'reverse flame box', compared to the original boiler design. With the use of the innovative particulate filter unit, the PM emissions were reduced to about 1 mg/m3, which shows the particulate filter unit reduces PM emissions by over 98%. For the CFD simulation, the modelling results showed the correct trends, although it did not predict adequately the degree to which the boiler configurations affect the emissions.

Wood consists not only of cellulose, lignin and hemicellulose but also of so called extractives which includes fats and acids and these components are separated in the mill from the black liquor. These extractives are in the mill denoted as tall oil soap. Tall oil has a large field of applications like chemicals and fuel and as it is produced to the atmosphere if it can replace oil and thus reduce the oil consumption. Tall oil soap is separated from the black liquor in a skimmer and the focus of this thesis was to examine the effect of air injection and the soap layer thickness on the soap separation efficiency in a skimmer. The work was focused on in analyzing the soap content of the inlet and outlet black liquor flow of the skimmer and to detect if an enhancement has been achieved with the two mentioned methods. The reason for the pulp mill to improve the soap separation efficiency was to decrease the risk of foaming and fouling in the evaporator but also to be able to increase the production of tall oil. The air injection gave a 41% improvement of the soap separation efficiency and further improvements are probably possible to achieve. The air injection flow was about 7 l air /m3 liquor in the black liquor feed. The airflow lowers the density of soap, creating a greater difference in density between soap and black liquor and this improves the separation efficiency. A thicker soap layer could increase the likelihood for soap drops to raise and reach the soap-liquor interface, because the soap drops have the tendency to bind with each other and will be separated from the liquor instead of following with the skimmed liquor outlet (fig. i.2). However, this study shows no indication of improvement with thicknesses that exceeds 0,75- 3,5 m which also endanger the skimmer due to overflow from the skimmer or create a short circuit between the in- and the outlet black liquor flow.

Diploma thesis deals with design and comparison of heating systems. In diploma thesis is designed system with gas condensing boiler, system with heat pump and system with gas condensing boiler for heating and solar collectors for heating of hot water. Content of this thesis is calculation of house heat loss, design of radiators, design of heat systems including a check of protective components, regulation with the help of thermostatic radiator valve, calculation of economical evaluation and creation of design documentation. Design is made for systems with unified temperature fall 55/45. For the variation with heat pump is computed a possibility of using the heat pump as an univalent or bivalent heat source. In the analysis of costs is considered a usage of natural gas for heating and warming of hot water with a condensing boiler, annual consumption of electric energy for operation of electrical appliances in household, consumption of electric energy for operation of heat pump for heating and warming of hot water and consumption of electric energy for warming of hot water in case of system with solar collectors. In the final evaluation a pay-off period is determined.

The diploma thesis deals with stating the aspects of reliability in product compatibility evaluation, namely with stating result uncertainty in product parameters testing and diagnosis which are imperative for introduction of the product to the market. The practical part of the thesis focuses on stating selected uncertainty in warm-water boilers testing, especially in gas fueled boilers with rated thermal input of max. 70 kW.

This thesis theoretically in Part A deals with the solution in savings heating building and heating hot water. It examines the impact of austerity measures on the overall need for and consumption of heat energy and its economic impact and compared with each other in order to achieve maximum efficiency. Part B is their subsequent application to a given object - a residental building, various design alternatives and the resulting energy savings improvements. Experimental Part C deals with indirect measurement of the thermal conductivity of building materials.

South Africa will continue to have a reliance on coal-fired power for the foreseeable future, given that coal is abundant, inexpensive and available. As much of the country’s good quality coal becomes depleted, the qualities available for power generation is fast declining. Therefore, pilot scale tests will be crucial in the development of methodologies for predicting coal performance in specific power plants. The main objective of this research is to validate the coal combustion performance of the Pilot Scale Combustion Test Facility (PSCTF) against four utility boilers to determine it’s scale up capabilities. Coal samples obtained from the operating feeders during each utility boiler test were evaluated at the PSCTF under conditions of similitude and at variations in excess air levels. This dissertation details the comparison of pulverized fuel (pf) burnout and gaseous emissions between the pilot facility and four coal-fired boilers of different configurations. The pilot furnace was able to simulate the pf burnout for the three full-scale wall-fired and the tangentially fired boilers at elevated excess air levels and under conditions of similitude respectively. The pilot carbon monoxide (CO) and sulphur dioxide (SO2) emission results were simulated under conditions similitude for all four boilers. The quantitative determination of the pulverized fuel burnout, CO and SO2 was found to be dependant on the boiler configuration (boiler size, burner type and burner arrangement) of the full-scale boiler which indicated the setup conditions at the PSCTF. The pilot furnace produces higher flame temperatures than the utility boilers which results in thermal NOx and inevitably significantly higher NOx emissions. The results emanating from this research has shown that the PSCTF is an effective tool for the evaluating and characterising coal combustion performance on a quantitative basis. Validation of more boilers is required to increase the degree of confidence in the PSCTF results and understanding the impact of the full-scale boiler configurations. All future validation tests should incorporate other pf combustion aspects. A quantitative methodology for the NOx emission should be further investigated.

碩士
國立交通大學
工學院產業安全與防災學程
100
During the annual inspection in April 2007, one coal-fired power plant in Taiwan discovered that the thickness of the broiler’s tube wall was under the borderline. Because it was not the time yet for an overall inspection, this problem was handled by welding. Later on in July 2008, this welded waterwall tube ruptured. The section of the broken tube was examined by observing the cross-section of the broken tube, testing the rigidity, and performing a microscopic metallographic analysis. The results suggested that this matter may be stress and corrosion induced rupture, and the stress here may be the residual stress from wielding. It was suggested that some cracks were formed at the internal wall of the starting or stopping end of welding. Once these cracks received water pressure inside the tube, the residual stress from welding and corrosion factors acted together and grew bigger. At the end, cracks were formed throughout the tube wall, causing the high pressure water inside the tube to spout and create more rupture. The objective of this study is to clarify causes for tube rupture using relevant tests and analyses. High velocity oxy fuel will be used to coat the surface of the wall of broiler tubes with WC/Co. This treatment will be followed by onsite testing. Three years later, the thickness of the sprayed surface will be compared for assessing the feasibility of giving broiler tubes comprehensive welding in the future.

碩士
國立中山大學
機械與機電工程學系研究所
93
This research aims to develop a method to evaluate the deterioration of the tube material within a boiler, in order to reduce the failure of it. In this thesis, natural frequency measurement method and ultrasonic attenuation method are mainly applied, and it has reached to a conclusion that the ultrasonic attenuation method is more reliable. Traditionally, the inspectors used the ultrasonic thickness measurement machine to evaluate the thickness and track the condition of a boiler. However, besides the thickness, the inspectors could not have clear understanding of the material and situation within a boiler. To improve the inspection effectiveness, the researcher measures the natural frequencies of the tube material in the new and old boilers by using natural frequency measurement. They found that the used tube material has been altered due to the difference between the natural frequencies. The ultrasonic attenuation conditions of the tubes are also evaluated in this thesis. The echoes of the ultrasound propagating through the thickness of the tube can be analyzed by relative comparison and absolute comparison, respectively. The relative comparison compares the echoes of the multiple back reflections of the ultrasound between the tubes of old and new boilers. In addition, the absolute comparison analyzes the amplitude of the echoes of the ultrasonic multiple back reflection to calculate the ultrasonic attenuation of the tube. Besides the two major techniques, the material analysis, metallurgical analysis, internally scale analysis and mechanical property evaluation are also applied in this thesis to help developing a method to evaluate the deterioration of the tube material within a boiler. This research demonstrates that the ultrasonic attenuation measuring methods can offer reliable results to evaluate the quality of the boiler.

碩士
國立中興大學
環境工程學系所
104
Recently, the Environmental Protection Administration of Taiwan has strengthened the regulation on air pollution emissions of stationary source, 100 mg/Nm3, to improve environmental quality. Under the current strengthened emission regulation, industries which employ heavy oil boiler will have biggest impact since most of these factories do not install any air pollution prevention and control equipment. In this study, four heavy oil boilers in different factories with installment of particulate pollutants collector including cyclone separator, scrubber and bag filter, and additional three heavy oil boilers being converted to natural gas boiler were selected for cost-benefit analysis, assessment of pollution reduction and difference on air pollution charges. Furthermore, in the case of Nantou county, the benefit of reduction as the heavy oil boilers being substituted for natural gas boilers was studied as well. Results indicate that the small-scale heavy oil boiler with cyclone separator, scrubber and bag filter or natural gas boiler are all possible control technology for particulate pollutant control. Among these, bag filter and natural gas boiler were confirmed to be the best available control technology. Without considering the fuel cost, heavy oil boiler installed with cyclone separator will produce highest operational cost and the lowest operational cost is from cyclone separator and bag filter installed in series. However, when fuel cost was considered, the natural gas boiler has the highest cost for dealing with particulate removal per kilogram. In the case of Nantou county, if all the heavy oil boilers are being substituted by natural gas boilers, particulate pollutant contributed by manufacturing industry could reduce about 4%, the emission of SOx could reduce about 57.8%, NOx could reduce about 35.7%, VOCs could reduce about 0.1%. Although the replacement of natural gas boilers could potentially increase the fuel cost, it (1) does not have secondary pollution, (2) could fit under BACT, (3) has noticeable pollutant reduction, (4) has less impact from strengthened regulation, also (5) could lower air pollution control fee. In conclusion, natural gas boiler should have the highest installment priority in related factory.

Alternative fuels like biomass have become really popular in the last decades as a substitute to fossil fuels. One of the most used technologies in Sweden for the obtention of the energy from the biomass is its direct combustion in a boiler. Bomhus Energi is a company with the purpose of creating steam and district heating for Billerudkorsnäs pulp and paper mill in Gävle and district heating for the city by operating a biomass BFB boiler. Despite being a quite new boiler, there are many sources of errors, losses and unnecessary costs. Between huge number of different losses that can happen in this kind of industrial boilers, the concern about internal leakages is not usually popular among plant designers and operators. This often leads to forget about them or not giving the importance that they could have.This study consists on, firstly, an analysis of different boiler equipment that have potential possibilities of internal leakages by mass and energy balances and by the tracking of possible mass losses. The second point of this thesis is to evaluate the cost of internal leakages that could have happen before, in order to be aware of how important they are. Additionally, measures are proposed in order to avoid or reduce the duration of the internal leakages, where the most common problem is the ignorance of their existence. This study focuses partially on the valve condition and maintenance. It is highly important to carry out valve maintenance procedures at least once per year during the general stop of the plant. Checking and verifying valve perfect conditions, can avoid a waste of a huge quantity of money just by replacing some internal elements that are possibly damaged due to the extreme working conditions. This small damages in valve can lead to a non-proper water tightening, which will be increasing its leakage over time. In the present paper, possible internal leakages through the valves belonging to the feedwater, steam drum, preheater and pressure vessel in general have been the principal aim. The key of this study was to take into account that biggest part of the draining system and valves that are supposed to be closed end in the Bottom blowdown tank. By then a deep study was done regarding this tank. The results show that there is a clear relationship between mass that is getting loss from feedwater tank and pressure vessel and the necessary cooling flow in the bottom blowdown tank. This means that if the cooling flow increases at the same rate as a possible leakage in mass and energy balance, there is an internal leakage somewhere in the system. The author proposes add an alarm to the DCS system in order to alert the plant operations of possible internal leakages. On the other hand, this paper also recommends to carry out a general valve maintenance per year and check which of them could be leaking, a general stop is the perfect time for carrying it out.In conclusion, the study finds that internal leakages can be even automatically detected if the system is provided with the necessary tools for it. The study concludes that internal leakages are not impossible to detect and their cost is non-negligible: the latest two internal leakages in the boiler, happened in the last two years, were from the feedwater draining system and from the steam drum heating loop with a total cost of 200,000 SEK (4240 SEK/day during 47 days) and 263,000 SEK (2120 SEK/day during 124 days) respectively. Additionally, days after the study, the plant general stop was carried out, finding that 12 valves were leaking due to internal damage. The cost of repairing the broken or damaged elements were almost negligible compared with the expected savings estimated in 2 Million SEK per year.

碩士
嘉南藥理科技大學
產業安全衛生與防災研究所
98
The steam generated from steam boiler is the main source of power to support petrochemical plants operations. Even equipped with automated control system and set multiple safeties interlocks to the boiler, unfortunately, boiler accidents still occur frequently. The main reasons are that specified equipment maintenance schedules and procedures are not followed properly. In addition, the operator errors are also known to contribute to the accidents. There are three main area in the stream boiler plant: (1) boiler area (contains: heavy oil area, feeding water area, the reagent area), (2) denitrification and (3) desulfurization. The current technique of Hazard and Operability Study (HAZOP) uses the information that deviated from the designed process steps to analyze the causes of specific sections of the process (or nodes). However, if the factors such as probability, severity, and the risk level resulting from the process deviations are introduced and analyzed at the process design stage, then we can either prevent the occurrences of accident, minimize occurrences of accidents, better understand hazard scenario at the time of the accident, or implement some design strategies to handle accidents effectively when they happen. Hazard Tree Analysis (HTA) treats the whole process as a system, such as boiler, as a node, the analyzed results strongly reflect the hazards of the system and provide better recommendations for correction, preventive measures to prevent accidents from occurring. In this thesis, we selected a boiler plant of an unnamed company as our object. By using the techniques of HAZOP and HTA we intend to find the potential risks of the boiler and to compare the accuracy of these two techniques on the assessment of the risks. We also try to incorporate the effect of the severity to the HTA to demonstrate the root causes of the accidents and the corresponding degree of severity of the accidents. We first drew the hazard tree diagram and list all possible deviations from the designed process, the effects of these deviations to the occurrences of the accidents, the associating correction actions, the root causes and the corresponding prevention actions. We then systematically applied the HAZOP analysis technique to evaluate the nature of the process deviations of the boiler and the control strategies. From the results of the analysis, we find that both techniques give similar conclusions. By incorporating the severity of accidents into HTA, we found some characteristics as follow: (1) the entire process, instead of its individual sections of the process, is considered when the risk analysis is conducted, (2) the degree of the accident occurrence can be categorized by different colors representing the degree of severity, (3) we can clearly picture the severity and the actions to prevent the accidents to happen, such as to control the deviation of process to happen or to the occurrence to happen by improving the process at design stage or after process had been implemented.