Development of Superior Sorbents for Separation of CO2 from Flue Gas at a Wide Temperature Range During Coal Combustion PDF Download
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Author: Danny Man-Leung Wong
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Category : Carbon dioxide
Languages : en
Pages : 220
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Abstract: Greenhouse gas emissions into the atmosphere have become an issue of concern with the increase in global population and demand for energy. In response to the demand for carbon emissions control, The Ohio State University has developed a novel high temperature multi-pollutant capture process that simultaneously captures carbon dioxide (CO2) and sulfur dioxide (SO2) from fossil fuels combustion flue gas streams. The multi- cyclic Carbonation Calcination Reaction (CCR) process utilizes a calcium-based sorbent in a high temperature reaction (carbonation) to capture the CO2 from the flue gas stream and releases a pure stream of CO2 that can be sequestered in the subsequent calcination reaction. The overall success of the technology depends on the development and optimization of the carbonation and calcination processes to create an integrated, cost and energy efficient process for carbon capture. The development of the CCR technology was further advanced from bench-scale research to an integrated, continuous, sub-pilot scale demonstration. Single-pass carbonation studies demonstrated high CO2 and SO2 removals using commercial calcium hydroxide as the sorbent in an entrained bed reactor. The high inherent pore volume of the commercial calcium hydroxide sorbent resulted in its demonstration of over 4 times the CO2 removal than commercial pulverized lime under similar process conditions. Bench-scale studies of the calcium carbonate (CaCO3) calcination reaction were conducted in the presence of steam and CO2 to effectively regenerate the spent CaCO3 sorbent in a manner suited for a carbon capture system. CaCO3 calcination in the presence of steam in the reactor lowers the partial pressure of CO2 such that complete calcination can be achieved at temperatures of 7500C and greater with significantly reduced calcination residence times. The resultant product CaO surface morphology is comparable to those achieved in calcination conditions of 100% CO2 despite known sintering effects of water vapor on the ionic structure of CaO.
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Regenerable sorbents based on sodium carbonate (Na2CO3) can be used to separate carbon dioxide (CO2) from coal-fired power plant flue gas. Upon thermal regeneration and condensation of water vapor, CO2 is released in a concentrated form that is suitable for reuse or sequestration. During the research project described in this report, the technical feasibility and economic viability of a thermal-swing CO2 separation process based on dry, regenerable, carbonate sorbents was confirmed. This process was designated as RTI's Dry Carbonate Process. RTI tested the Dry Carbonate Process through various research phases including thermogravimetric analysis (TGA); bench-scale fixed-bed, bench-scale fluidized-bed, bench-scale co-current downflow reactor testing; pilot-scale entrained-bed testing; and bench-scale demonstration testing with actual coal-fired flue gas. All phases of testing showed the feasibility of the process to capture greater than 90% of the CO2 present in coal-fired flue gas. Attrition-resistant sorbents were developed, and these sorbents were found to retain their CO2 removal activity through multiple cycles of adsorption and regeneration. The sodium carbonate-based sorbents developed by RTI react with CO2 and water vapor at temperatures below 80 C to form sodium bicarbonate (NaHCO3) and/or Wegscheider's salt. This reaction is reversed at temperatures greater than 120 C to release an equimolar mixture of CO2 and water vapor. After condensation of the water, a pure CO2 stream can be obtained. TGA testing showed that the Na2CO3 sorbents react irreversibly with sulfur dioxide (SO2) and hydrogen chloride (HCl) (at the operating conditions for this process). Trace levels of these contaminants are expected to be present in desulfurized flue gas. The sorbents did not collect detectable quantities of mercury (Hg). A process was designed for the Na2CO3-based sorbent that includes a co-current downflow reactor system for adsorption of CO2 and a steam-heated, hollow-screw conveyor system for regeneration of the sorbent and release of a concentrated CO2 gas stream. An economic analysis of this process (based on the U.S. Department of Energy's National Energy Technology Laboratory's [DOE/NETL's] 'Carbon Capture and Sequestration Systems Analysis Guidelines') was carried out. RTI's economic analyses indicate that installation of the Dry Carbonate Process in a 500 MW{sub e} (nominal) power plant could achieve 90% CO2 removal with an incremental capital cost of about $69 million and an increase in the cost of electricity (COE) of about 1.95 cents per kWh. This represents an increase of roughly 35.4% in the estimated COE - which compares very favorable versus MEA's COE increase of 58%. Both the incremental capital cost and the incremental COE were projected to be less than the comparable costs for an equally efficient CO2 removal system based on monoethanolamine (MEA).
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Languages : en
Pages : 2
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Through a U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL) funded cooperative agreement DE-NT0005649, ADA Environmental Solutions (ADA) has begun evaluating the use of solid sorbents for CO2 capture. The project objective was to address the viability and accelerate development of a solid-based CO2 capture technology. To meet this objective, initial evaluations of sorbents and the process/equipment were completed. First the sorbents were evaluated using a temperature swing adsorption process at the laboratory scale in a fixed-bed apparatus. A slipstream reactor designed to treat flue gas produced by coal-fired generation of nominally 1 kWe was designed and constructed, which was used to evaluate the most promising materials on a more meaningful scale using actual flue gas. In a concurrent effort, commercial-scale processes and equipment options were also evaluated for their applicability to sorbent-based CO2 capture. A cost analysis was completed that can be used to direct future technology development efforts. ADA completed an extensive sorbent screening program funded primarily through this project, DOE NETL cooperative agreement DE-NT0005649, with support from the Electric Power Research Institute (EPRI) and other industry participants. Laboratory screening tests were completed on simulated and actual flue gas using simulated flue gas and an automated fixed bed system. The following types and quantities of sorbents were evaluated: 87 supported amines; 31 carbon based materials; 6 zeolites; 7 supported carbonates (evaluated under separate funding); and 10 hydrotalcites. Sorbent evaluations were conducted to characterize materials and down-select promising candidates for further testing at the slipstream scale. More than half of the materials evaluated during this program were supported amines. Based on the laboratory screening four supported amine sorbents were selected for evaluation at the 1 kW scale at two different field sites. ADA designed and fabricated a slipstream pilot to allow an evaluation of the kinetic behavior of sorbents and provide some flexibility for the physical characteristics of the materials. The design incorporated a transport reactor for the adsorber (co-current reactor) and a fluidized-bed in the regenerator. This combination achieved the sorbent characterization goals and provided an opportunity to evaluate whether the potential cost savings associated with a relatively simple process design could overcome the sacrifices inherent in a co-current separation process. The system was installed at two field sites during the project, Luminant's Martin Lake Steam Electric Station and Xcel Energy's Sherburne County Generating Station (Sherco). Although the system could not maintain continuous 90% CO2 removal with the sorbents evaluated under this program, it was useful to compare the CO2 removal properties of several different sorbents on actual flue gas. One of the supported amine materials, sorbent R, was evaluated at both Martin Lake and Sherco. The 1 kWe pilot was operated in continuous mode as well as batch mode. In continuous mode, the sorbent performance could not overcome the limitations of the cocurrent adsorbent design. In batch mode, sorbent R was able to remove up to 90% CO2 for several cycles. Approximately 50% of the total removal occurred in the first three feet of the adsorption reactor, which was a transport reactor. During continuous testing at Sherco, CO2 removal decreased to approximately 20% at steady state. The lack of continuous removal was due primarily to the combination of a co-current adsorption system with a fluidized bed for regeneration, a combination which did not provide an adequate driving force to maintain an acceptable working CO2 capacity. In addition, because sorbent R consisted of a polymeric amine coated on a silica substrate, it was believed that the 50% amine loaded resulted in mass diffusion limitations related to the CO2 uptake rate. Three additional supported amine materials, sorbents AX, F, and BN, were selected for evaluation using the 1 kW pilot at Sherco. Sorbent AX was operated in batch mode and performed similarly to sorbent R (i.e. could achieve up to 90% removal when given adequate regeneration time). Sorbent BN was not expected to be subject to the same mass diffusion limitations as experienced with sorbent R. When sorbent BN was used in continuous mode the steady state CO2 removal was approximately double that of sorbent R, which highlighted the importance of sorbents without kinetic limitations.
Author: Qiang Wang
Publisher: Royal Society of Chemistry
ISBN: 1788015452
Category : Technology & Engineering
Languages : en
Pages : 318
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Inorganic solid adsorbents/sorbents are attractive materials for capturing carbon dioxide (CO2) from flue gases after fossil fuel combustion. Post-combustion Carbon Dioxide Capture Materials introduces the key inorganic materials used as adsorbents/sorbents with specific emphasis on their design, synthesis, characterization, performance, and mechanism. Dedicated chapters cover carbon-based adsorbents, zeolite- and silica-based adsorbents, metal–organic framework (MOF)-based adsorbents, and alkali-metal-carbonate-based adsorbents. The final chapter discusses the practical application aspects of these adsorbents used in carbon dioxide capture from flue gases. Edited and written by world-renowned scientists in each class of the specific material, this book will provide a comprehensive introduction for advanced undergraduates, postgraduates and researchers from both academic and industrial fields wishing to learn about the topic.
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Author: Alan Yao Wang
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Languages : en
Pages : 154
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Future investigation of the hydration process may focus on its kinetic behavior with respect to pressure and temperature at isothermal conditions. For scaling up, the installment of a heat-exchanging device is highly recommended. The heat of reaction can be extracted to preheat the combustion air, thus contributing to the overall process heat integration.
Author: Javad Abbasian
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Languages : en
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The specific objective of this project was to develop physically durable and chemically regenerable MgO-based sorbents that can remove carbon dioxide from raw coal gas at operating condition prevailing in IGCC processes. A total of sixty two (62) different sorbents were prepared in this project. The sorbents were prepared either by various sol-gel techniques (22 formulations) or modification of dolomite (40 formulations). The sorbents were prepared in the form of pellets and in granular forms. The solgel based sorbents had very high physical strength, relatively high surface area, and very low average pore diameter. The magnesium content of the sorbents was estimated to be 4-6 % w/w. To improve the reactivity of the sorbents toward CO{sub 2}, The sorbents were impregnated with potassium salts. The potassium content of the sorbents was about 5%. The dolomite-based sorbents were prepared by calcination of dolomite at various temperature and calcination environment (CO{sub 2} partial pressure and moisture). Potassium carbonate was added to the half-calcined dolomite through wet impregnation method. The estimated potassium content of the impregnated sorbents was in the range of 1-6% w/w. In general, the modified dolomite sorbents have significantly higher magnesium content, larger pore diameter and lower surface area, resulting in significantly higher reactivity compared to the sol-gel sorbents. The reactivities of a number of sorbents toward CO{sub 2} were determined in a Thermogravimetric Analyzer (TGA) unit. The results indicated that at the low CO{sub 2} partial pressures (i.e., 1 atm), the reactivities of the sorbents toward CO{sub 2} are very low. At elevated pressures (i.e., CO{sub 2} partial pressure of 10 bar) the maximum conversion of MgO obtained with the sol-gel based sorbents was about 5%, which corresponds to a maximum CO{sub 2} absorption capacity of less than 1%. The overall capacity of modified dolomite sorbents were at least one order of magnitude higher than those of the sol-gel based sorbents. The results of the tests conducted with various dolomite-based sorbent indicate that the reactivity of the modified dolomite sorbent increases with increasing potassium concentration, while higher calcination temperature adversely affects the sorbent reactivity. Furthermore, the results indicate that as long as the absorption temperature is well below the equilibrium temperature, the reactivity of the sorbent improves with increasing temperature (350-425 C). As the temperature approaches the equilibrium temperature, because of the significant increase in the rate of reverse (i.e., regeneration) reaction, the rate of CO{sub 2} absorption decreases. The results of cyclic tests show that the reactivity of the sorbent gradually decreases in the cyclic process. To improve long-term durability (i.e., reactivity and capacity) of the sorbent, the sorbent was periodically re-impregnated with potassium additive and calcined. The results indicate that, in general, re-treatment improves the performance of the sorbent, and that, the extent of improvement gradually decreases in the cyclic process. The presence of steam significantly enhances the sorbent reactivity and significantly decreases the rate of decline in sorbent deactivation in the cyclic process.
Author: M. Mercedes Maroto-Valer
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Languages : en
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This research program focused on the development of fly ash derived sorbents to capture CO{sub 2} from power plant flue gas emissions. The fly ash derived sorbents developed represent an affordable alternative to existing methods using specialized activated carbons and molecular sieves, that tend to be very expensive and hinder the viability of the CO{sub 2} sorption process due to economic constraints. Under Task 1 'Procurement and characterization of a suite of fly ashes', 10 fly ash samples, named FAS-1 to -10, were collected from different combustors with different feedstocks, including bituminous coal, PRB coal and biomass. These samples presented a wide range of LOI value from 0.66-84.0%, and different burn-off profiles. The samples also spanned a wide range of total specific surface area and pore volume. These variations reflect the difference in the feedstock, types of combustors, collection hopper, and the beneficiation technologies the different fly ashes underwent. Under Task 2 'Preparation of fly ash derived sorbents', the fly ash samples were activated by steam. Nitrogen adsorption isotherms were used to characterize the resultant activated samples. The cost-saving one-step activation process applied was successfully used to increase the surface area and pore volume of all the fly ash samples. The activated samples present very different surface areas and pore volumes due to the range in physical and chemical properties of their precursors. Furthermore, one activated fly ash sample, FAS-4, was loaded with amine-containing chemicals (MEA, DEA, AMP, and MDEA). The impregnation significantly decreased the surface area and pore volume of the parent activated fly ash sample. Under Task 3 'Capture of CO{sub 2} by fly ash derived sorbents', sample FAS-10 and its deashed counterpart before and after impregnation of chemical PEI were used for the CO{sub 2} adsorption at different temperatures. The sample FAS-10 exhibited a CO{sub 2} adsorption capacity of 17.5mg/g at 30 C, and decreases to 10.25mg/g at 75 C, while those for de-ashed counterpart are 43.5mg/g and 22.0 mg/g at 30 C and 75 C, respectively. After loading PEI, the CO{sub 2} adsorption capacity increased to 93.6 mg/g at 75 C for de-ashed sample and 62.1 mg/g at 75 C for raw fly ash sample. The activated fly ash, FAS-4, and its chemical loaded counterparts were tested for CO{sub 2} capture capacity. The activated carbon exhibited a CO{sub 2} adsorption capacity of 40.3mg/g at 30 C that decreased to 18.5mg/g at 70 C and 7.7mg/g at 120 C. The CO{sub 2} adsorption capacity profiles changed significantly after impregnation. For the MEA loaded sample the capacity increased to 68.6mg/g at 30 C. The loading of MDEA and DEA initially decreased the CO{sub 2} adsorption capacity at 30 C compared to the parent sample but increased to 40.6 and 37.1mg/g, respectively, when the temperature increased to 70 C. The loading of AMP decrease the CO{sub 2} adsorption capacity compared to the parent sample under all the studied temperatures. Under Task 4 'Comparison of the CO{sub 2} capture by fly ash derived sorbents with commercial sorbents', the CO{sub 2} adsorption capacities of selected activated fly ash carbons were compared to commercial activated carbons. The CO{sub 2} adsorption capacity of fly ash derived activated carbon, FAS-4, and its chemical loaded counterpart presented CO{sub 2} capture capacities close to 7 wt%, which are comparable to, and even better than, the published values of 3-4%.
