Добірка наукової літератури з теми "Lime solar calcination"

We designed and tested a scaleable solar multitube rotary kiln to effect the endothermic calcination reaction CaCO3→CaO+CO2 at above 1300K. The indirect heating 10-kW reactor prototype processes 1-5mm limestone particles, producing high purity lime of any desired reactivity and with a degree of calcination exceeding 98%. The reactor’s efficiency, defined as the enthalpy of the calcination reaction at ambient temperature (3184kJkg−1) divided by the solar energy input, reached 30%–35% for solar flux inputs of about 2000kWm−2 and for quicklime production rates up to 4kgh−1. The use of concentrated solar energy in place of fossil fuels as the source of process heat has the potential of reducing by 20% CO2 emissions in a state-of-the-art lime plant and by 40% in a conventional cement plant.

We report the upper and lower bounds for the levelized cost of high-temperature industrial process heat, supplied from electricity generated with solar-photovoltaic (PV) and wind turbines in combination with either thermal or electric battery storage using hourly typical meteorological year (TMY) data, in systems sized to supply between 80% and 100% of continuous thermal demand at a site in the northern part of Western Australia. The system is chosen to supply high-temperature air as the heat transfer media at temperatures of 1000 °C, which is a typical temperature for an alumina or a lime calcination plant. A simplified model of the electrical energy plant has been developed using performance characteristics of real PV and wind systems and TMY data of renewable energy resources. This was used to simulate a large sample of possible system configurations and find the optimal combination of the renewable resources and storage systems, sized to provide renewable shares (RES) of between 80% and 100% of the yearly demand. This allowed the upper and lower bounds to be determined for the cost of heat based on two scenarios in which the excess energy is either dumped (upper bound) or exported to the electricity grid (lower bound) at the average generating cost. The lower bound of the levelized cost of energy (LCOEL), which occurs for the system employing thermal storage, was estimated to range from USD 10/GJ to USD 24/GJ for RES from 80 to 100%. The corresponding upper bound (LCOEU), also estimated for the system using thermal storage, are between USD 16/GJ and USD 31/GJ, for RES between 80% and 100%. The utilization of electric battery storage instead of thermal storage was found to increase the LCOE values by a factor of two to four depending on the share of renewable energy. Compared with current Australian natural gas cost, none of the systems assessed configurations is economical without either a cost for CO2 emissions or a premium for low-carbon products. The estimated cost for CO2 emission that is needed to reach parity with current natural gas prices in Australia is also presented.

Sm2O3/ZnO nanoparticles were prepared via microwave-assisted hydrothermal and sol-gel combustion synthesis. Characteristics of obtained samples were compared in dependence of Sm2O3 content and calcination temperature. Prepared nanostructures were characterized with scanning electron microscopy and X-ray diffraction. Nanoparticles prepared via microwave-assisted hydrothermal and sol-gel method have flower-like and spherical shape respectively. The photocatalytic activity of samples under solar light simulated illumination was found to be affected by content of Sm2O3, calcination temperature and preparation method. The first-order rate constant of MB solution degradation of samples prepared via microwave-assisted hydrothermal method approximately three times exceeds that of sol-gel samples.

A successful series of CuxZn1-xO (variable x = 0.05, 0.1, 0.15 and 0.2) were characterized by thermogravimetric (TG-DTA), Fourier Transform Infra-Red (FTIR) spectroscopy, and X-ray Diffraction (XRD) techniques. The photocatalytic activity of prepared samples was accurately assessed by the photocatalytic decomposition of LASER dye in an aqueous solution under irradiation of solar light and was compared favourably to non-dope commercially available ZnO photo-catalyst. The effect of various parameters like the amount of a catalyst, the calcination temperature on photocatalytic activity is also studied. The direct effect of various photosensitizing salts like NaCl, Na2CO3, and Na2S2O3 on photocatalytic activity of ZnO and Cu0.05Zn0.95O was carefully studied.

Flower like Bi2WO6 powders were synthesized via a mild hydrothermal method. Analysis of X-ray diffraction (XRD) revealed that optimal calcination temperature was believed to be 400 °C at which the photocatalyst displayed high surface area and small crystallite size. Scanning electron microscope (SEM) showed that obtained Bi2WO6 with a flower like shape, which greatly enhance the surface area of catalyst and increase the contact area with dyes. The photocatalytic activity of as-prepared catalyst was investigated using Rhodamine B as a model compound under solar light irradiation. Results showed that the prepared photocatalyst was an effective photocatalyst and exhibited high photocatalytic performance. In the presence of 1 g/L Bi2WO6, 80.76% decolorization efficiency of RhB could be achived after 150 min irradiation

Novel two-dimensional ZnO/Ti3C2Tx hybrid photocatalysts with modified surface areas were prepared using a simple calcination technique. The microstructures, crystalline features, and bonding states of the ZnO structure-covered Ti3C2Tx MXenes were closely characterized using various tools. The photoluminescence intensity of the hybrid photocatalyst was greatly reduced compared to the pristine ZnO, while its Brunauer-Emmett-Teller (BET) surface area increased by more than 100 times. Under solar light illumination, the photocatalytic degradation efficiency of the hybrid photocatalyst for organic pollutants (MO, RhB) appeared to be three-fold larger as compared to pristine ZnO. The superb photocatalytic performance of the photocatalyst was attributed to several factors, such as ideal band alignment, Schottky barrier formation, and large surface area. Moreover, the ZnO/Ti3C2Tx hybrid photocatalyst showed excellent cycling stability. These results suggest that the novel hybrid structure may be a potential candidate for removing organic pollutants in wastewater.

We elaborate the synthesis and remarkable photocatalytic efficiency of a series of heterojunction nanocomposites with a cauliflower-like architecture composed of copper oxide (CuO) and single-walled carbon nanotubes (SWCNTs). The photocatalysts with such a peculiar design were constructed via facile recrystallization followed by calcination and were symbolized as CuO-SWCNT-1, CuO-SWCNT-2, and CuO-SWCNT-3, representing the components and calcination time in hours. The photocatalytic efficiency of the synthesized nanocomposite samples were investigated by evaluating the decomposition of methylene blue (MB) solution under natural sunlight exposure. All of the as-synthesized photocatalysts were substantially effectual for the photo-deterioration of MB solution. Moreover, CuO-SWCNT-3 revealed the top photocatalytic capability with 96% decomposition of MB solution in 2 h while being exposed to visible light. Pristine CuO nanocrystals and the SWCNTs were employed as controls, whereas the photocatalytic performance of the hetero-composites was significantly better than that of pure CuO as well as SWCNTs. The recyclability of the photocatalysts was also explored, and the results asserted that the samples could be reused for five cycles without being altered notably in photocatalytic performance or morphology.

Developing full-spectrum photocatalysts that harvests solar light from ultraviolet to near-infrared light has aroused great interest in photodegradation of organic pollutants, due to the imminent energy crisis and growing pollution issues. Herein, we report an excellent full-spectrum photocatalyst derived from calcination of an Mg/Zn/Al/Er-hydrotalcite-like compound. The photocatalyst is a stable multi-phase oxide consisting of various syntrophic Er3+-doped metal oxides with different particle sizes and morphology. Its ultraviolet (UV) photocatalytic activity is maximized by increasing the fraction of Zn2+ and sustaining the pure hydrotalcite-like phase with an appropriate fraction of Mg2+ in preparing the Mg/Zn/Al/Er-hydrotalcite-like precursor. The visible and NIR photocatalytic activities are triggered by an indirect excitation involving an up-conversion process. The major active species of the photocatalyst in the photodegradation of methyl orange are superoxide anions and photogenerated holes. Nevertheless, hydroxyl radicals also play a moderate role in the photodegradation process. This work finds a new way to prepare full-spectrum photocatalysts with tunable chemical compositions via an environmentally friendly hydrotalcite-like precursor.

This study presents a novel method for the development of TiO2/reduced graphene oxide (rGO) nanocomposites for photocatalytic degradation of dyes in an aqueous solution. The synergistic integration of rGO and TiO2, through the formation of Ti–O–C bonds, offers an interesting opportunity to design photocatalyst nanocomposite materials with the maximum absorption shift to the visible region of the spectra, where photodegradation can be activated not only with UV but also with the visible part of natural solar irradiation. TiO2@rGO nanocomposites with different content of rGO have been self-assembled by the hydrothermal method followed by calcination treatment. The morphological and structural analysis of the synthesized photocatalysts was performed by FTIR, XRD, XPS, UV-Vis DRS, SEM/EDX, and Raman spectroscopy. The effectiveness of the synthesized nanocomposites as photocatalysts was examined through the photodegradation of methylene blue (MB) and rhodamine B (RhB) dye under artificial solar-like radiation. The influence of rGO concentration (5 and 15 wt.%) on TiO2 performance for photodegradation of the different dyes was monitored by UV-Vis spectroscopy. The obtained results showed that the synthesized TiO2@rGO nanocomposites significantly increased the decomposition of RhB and MB compared to the synthesized TiO2 photocatalyst. Furthermore, TiO2@rGO nanocomposite with high contents of rGO (15 wt.%) presented an improved performance in photodegradation of MB (98.1%) and RhB (99.8%) after 120 min of exposition to solar-like radiation. These results could be mainly attributed to the decrease of the bandgap of synthesized TiO2@rGO nanocomposites with the increased contents of rGO. Energy gap (Eg) values of nanocomposites are 2.71 eV and 3.03 eV, when pure TiO2 particles have 3.15 eV. These results show the potential of graphene-based TiO2 nanocomposite to be explored as a highly efficient solar light-driven photocatalyst for water purification.

The objectives of this research investigation are to answer fundamental questions regarding the effectiveness of using concentrated solar energy as the sole heating source for the thermo-chemical decomposition of limestone-marble, supplied by Penrice, Angaston. Specifically, scientific analyses are used to investigate the energy requirements for the efficient manufacture of quicklime using solar thermal energy. To achieve these aims, the energy requirements for an industrial scale solar lime manufacturing system were first evaluated. The main conclusion from this analysis is that the thermal efficiency of a solar energy supplied lime manufacture system compares favourably with the best fossil fuelled system. A good heat recovery system as well as a comprehensive preheating system is recommended to minimise the energy losses from the system. A zero dimensional model was then used to determine that the most energy efficient shape for a travelling grate solar furnace is a triangular cross section. This shape maximise the exposure of the limestone to the radiant energy while minimising structural heat losses. This analytical evaluation also identified that the open area of entrance and exit openings, which allow the process materials to flow through the kiln and for the exhaust gases to escape the kiln, should be minimised. Thirty three times more heat flux is lost through these openings than through the kiln structure. Minimising the openings area therefore improves kiln thermal efficiency. This investigation then evaluated the maximum bed thickness for the limestone when using a grate bed system within the proposed solar furnace. Due to the nature of radiation it is recommended that the limestone layer be no thicker than 2.5 times the nominal diameter of the limestone in use. This thickness optimises the exposure of the stone to the direct radiation and increases the heat transfer to the stones lower within the bed and allows for the unrestricted diffusion of CO2 away from these stones. The investigation then experimentally quantified the effects of radiant heat flux intensity on the calcination kinetics of the Penrice, Angaston marble as a function of stone size. This experimental investigation involved comparing results from an electric muffle furnace, an atmospherically open solar radiation furnace, and an enclosed triangular shaped solar radiation furnace. The muffle furnace provided a baseline values to which the solar calcination rates could be compared. The open system solar calcination experiments showed that the preheating time of the stone is directly proportional to the illuminated surface area of the stone and the intensity of the heat flux to which it is exposed. Additionally, the reaction rate is directly proportional to the radiant heat flux, and is independent of the stone size for heat fluxes greater than 430kW/m2. The enclosed solar furnace experiments identified a 45% improvement in decomposition time could be achieved by using the triangular shaped solar furnace compared to the open solar system calcination. This benefit to the calcination time is best for the more intense heat fluxes and for the larger stone sizes. The measured calcination times were similar to those found for a conventional rotary kiln. This demonstrates the practicalities of using solar radiation technology for interchange with, or as a supplementary heating source to, a combustion driven lime manufacturing industrial plant. A multi-zone two dimensional mathematical model was then used to evaluate the radiant heat exchange within the triangular solar furnace. The developed mathematical scheme provides a comprehensive package with a validated base model for future evaluations of solar furnace designs. A modified shrinking core calcination model was then developed, which uses an energy balance approach to calculate the preheating times and calcination rates for the Penrice marble exposed to various intensities of radiant heat flux. This version of the heat transfer based shrinking core model was used after considering the one sided heating of the stone from the point source radiation.
Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering and School of Chemical Engineering, 2010

Currently, increasing world population demands a higher cement production. Therefore atmospheric emissions and energy consumption become two of the most important environmental and economic issues. Fuel and electricity consumption for the production of cement represent 40% of the total production cost [1]. It is known that cement production is an energy-intensive process which contributes with approximately 5% of the worldwide carbon dioxide (CO2) emissions [2] [3]. By using Concentrated Solar Thermal (CST) at the calcination process in the cement production line, CO2 emissions can be reduced by 40% and savings of up to 60% through fuel substitution can be obtained if all the fuel used at the calcination step is substituted. The aim of the study is not to propose a detailed design of the solar process but to examine and quantify the various options in order to define the favorable economic conditions and the technical issues to face in a conventional cement plant aiming: substituting energy sources and achieving continuous operation of the cement plant employing a hybrid mode. Three options related with how to apply the CST technology were evaluated. The best solution is a Central Tower with Solar Reactor at the Top of the Tower since it allows energy substitution with high thermal energy efficiency. This implies, compared with the other options, the minimum changes in the process. Several energy substitution scenarios are investigated considering different energy losses and amount of energy to be replaced. It was found that the solar energy availability is not a constraint, meaning that from the technical point of view it is possible to replace up to 100% of the energy requirements for the calcination process. Economic results are promissory since the application of the proposed approach (Go Process) became attractive. The Payback Time (PBT) obtained (from 6 to 10 years) is lower when it is compared with the PBT for applications of CST for electricity production. Besides, the IRR values obtained (from 8% to 11%) are adequate in accordance with the typical values expected by most of the equity investors in renewable energy projects (between 8% and 12%) [4]. It is expected that CST technology will become more attractive and profitable due to economic aspects like increments in fossil fuels and alternative fuels cost and the current deployment of the CST technology to produce electricity. Other aspects such as more strict legislation related with CO2 emissions combined with encouraging legislation to use of renewable energy also play an important role in the economic attractiveness of the proposed application.