Sulfur Tolerant Highly Durable CO.sub. 2 Sorbents PDF Download
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Languages : en
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A sorbent for the capture of carbon dioxide from a gas stream is provided, the sorbent containing calcium oxide (CaO) and at least one refractory dopant having a Tammann temperature greater than about 530.degree. C., wherein the refractory dopant enhances resistance to sintering, thereby conserving performance of the sorbent at temperatures of at least about 530.degree. C. Also provided are doped CaO sorbents for the capture of carbon dioxide in the presence of SO.sub. 2.
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Languages : en
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A sorbent for the capture of carbon dioxide from a gas stream is provided, the sorbent containing calcium oxide (CaO) and at least one refractory dopant having a Tammann temperature greater than about 530.degree. C., wherein the refractory dopant enhances resistance to sintering, thereby conserving performance of the sorbent at temperatures of at least about 530.degree. C. Also provided are doped CaO sorbents for the capture of carbon dioxide in the presence of SO.sub. 2.
Author: Hong Lu
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Languages : en
Pages : 169
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Global warming is unequivocal due to greenhouse effect, majorly caused by increasing concentration of carbon dioxide in the atmosphere. Using metal oxide sorbents, such as calcium oxide, is one of the most potent ways to separate CO2 in contrast to existing or emerging technologies today. Unlike other technologies, calcium-based separation can be applied easily above 550 °C for capturing CO2. Calcium-based sorbents were prepared first using inorganic and organometallic precursors (OMP) by calcination or wet chemistry. Sorbent performance was tested using a thermogravimetric analyzer (TGA). Amongst all, the sorbents prepared from calcium propionate and calcium acetate exhibited the highest capacity to uptake CO2, converting from calcium oxide to calcium carbonate. These two sorbents possessed higher BET surface area and larger pore volume than the other sorbents. Thermal decomposition of these two OMPs resulted in the maximum evolution of heat, which could eventually lead to the generation of larger macropores, thus explaining the resultant CO2 uptake capacity demonstrated. The sorbents originated from OMPs and involved more heat during formation of calcium carbonate exhibited better performance. Therefore, flame technique, which involves with combustion of OMPs, was applied to synthesis sorbents. Scalable flame spray pyrolysis (FSP) is unique in making controllable sized nanoparticles. Such flame-made sorbents consisted of nanostructured calcium oxide and calcium carbonate with high specific surface area (40-90 m2/g), exhibiting faster and higher CO2 uptake capacity than non FSP-made sorbents. In multiple carbonation/decarbonation cycles, the nanostructured sorbents demonstrated relatively stable, reversible and high CO2 uptake capacity sustaining molar conversion at about 50% after 60 such cycles, . The high performance of flame-made sorbents is best attributed to their nanostructure (30-50 nm grain size) that allows operation in the reaction-controlled carbonation regime, rather than in the diffusion-controlled one when sorbents made with larger particles are employed. To further boost durability of the FSP-made sorbents, refractory dopants (Si, Ti, Cr, Co, Zr, and Ce) were applied, aiming at developing sorbents with better mechanical strength. Amongst all, FSP-made Zr-doped CaO sorbents exhibited the best CO2 capture performance. The effect of Zr-dopant concentration on sorbent characteristics and performance was investigated in detail. A Zr/Ca = 3:10 atomic ratio resulted in the most robust nanosorbent for dozens of multi-cyclic operation. This sorbent retained, unchanged, its ability to capture CO2 during extended cycles and also demonstrated excellent stability in water vapor (10 vol. %). To understand sorbent tolerance for capturing CO2 in the presence of sulfur dioxide, three sets of experiments were carried on M/Ca sorbents, namely carbonation and sulfation, both separately and simultaneously. The results show that the capacity of the sorbents for capturing CO2 is reduced in the presence of SO2, due to reaction competition between carbonation and sulfation. TGA and X-ray photoelectron spectroscopy results indicate that the carbonation was totally reversible, while this is not the case with the sulfation. The Ce/Ca sorbent gave the best for CO2 capture and is the most SO2 tolerant. On the other side, the Mn/Ca promoted one has the strongest affinity for SO2, resulting the most permanent weight gain after sulfation.
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Languages : en
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Successful development of regenerable mixed-metal oxide sorbents for removal of reduced sulfur species (such as H[sub 2]S and COS) from coal-derived fuel gas streams at high=temperature, high-pressure (HTHP) conditions is a key to commercialization of the integrated-gasification-combined-cycle (IGCC) power systems. Among the various available coal-to-electricity pathways, IGCC power plants have the most potential with high thermal efficiency, simple system configuration, low emissions of SO[sub 2], NO[sub x] and other contaminants, modular design, and low capital cost. Due to these advantages, the power plants of the 21st century are projected to utilize IGCC technology worldwide. Sorbents developed for sulfur removal are primarily zinc oxide-based inorganic materials, because of their ability to reduce fuel gas sulfur level to a few parts-per-million (ppm). This project extends the prior work on the development of fluidizable zinc titanate particles using a spray-drying technique to impart high reactivity and attrition resistance. Specific objectives are to develop highly reactive and attrition-resistant zinc titanate sorbents in 40- to 150-[mu]m particle size range for transport reactor applications using semicommercial- to full commercial-scale spray dryers, to transfer sorbent production technology to private sector, and to provide technical support for Sierra Pacific's Clean Coal Technology Demonstration plant and METC's hot-gas desulfurization process development unit (PDU), both employing a transport reactor system.
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Category :
Languages : en
Pages : 12
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Chemical reactivity was determined at GECRD by measuring sorbent sulfur loading (defined as grams of sulfur absorbed per 100 g of fresh sorbent) in fresh and in cycled samples from a bench-scale reactor. Only formulations that exhibited a good balance of chemical and mechanical performance as fresh pellets were selected for further cyclic testing in the benchscale reactor system. Details of the bench-scale reactor and procedures have been given before (Ayala, 1991). The important aspect of the benchscale testing is that both absorption and regeneration were conducted in a packed-bed reactor simulating the time/temperature environment to which the sorbent would be exposed in a typical cycle of the full-scale moving-bed system. Absorption was carried out at 1000[degrees]F using any of three gas compositions, all having a deliberately high H[sub 2]S concentration (1 %) to accelerate testing. The oxidative regeneration was carried out between 1000 and 1250[degrees]F and 1--21% oxygen during the early phases of regeneration, and at 1400[degrees]F during the final phase simulating the temperature rise of the sorbent bed. Sixteen zinc titanate formulations were prepared as cylindrical extrudates. For all formulations, the calcination time was held constant at 2 hours. The following results were obtained: Formulations containing a 0.8 Zn:Ti ratio produced mixtures of several stoichiometric titanates: Zn[sub 2]Ti[sub 3]O[sub 8], ZnTiO[sub 3], and Zn[sub 2]TiO[sub 4], with the relative amount of each depending on temperature. Formulations containing a 2.0 Zn:Ti ratio exhibited exclusively the Zn[sub 2]TiO[sub 4] structure. The higher calcination temperature of 1800[degrees]F significantly reduced the porosity available for chemical reactivity, while the lower calcination temperature of 1400[degrees]F produced, in some cases, formulations with traces of residual unreacted zinc oxide and anatase titanium dioxide.
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Languages : en
Pages : 58
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The objective of this contract was to identify and test fabrication methods and sorbent chemical compositions that enhance the long-term chemical reactivity and mechanical strength of zinc ferrite and other novel sorbents for moving-bed, high-temperature desulfurization of coal-derived gases. Desired properties to be enhanced for moving-bed sorbent materials are: (1) high chemical reactivity (sulfur absorption rate and total sulfur capacity), (2) high mechanical strength (pellet crush strength and attrition resistance), and (3) suitable pellet morphology (e.g., pellet size, shape, surface area, and average specific pore volume). In addition, it is desired to maintain the sorbent properties over extended cyclic use in moving- bed systems.
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Languages : en
Pages : 5
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Primary issues for the fluidized-bed/transport reactor process are high attrition resistant sorbent, its high sorption capacity and regenerability, durability, and cost. The overall objective of this project is the development of a superior attrition resistant zinc oxide-based sorbent for hot gas cleanup in integrated coal gasification combined cycle (IGCC). Sorbents applicable to a fluidized-bed hot gas desulfurization process must have a high attrition resistance to withstand the fast solid circulation between a desulfurizer and a regenerator, fast kinetic reactions, and high sulfur sorption capacity. The oxidative regeneration of zinc-based sorbent usually initiated at greater than 600 C with highly exothermic nature causing deactivation of sorbent as well as complication of sulfidation process by side reaction. Focusing on solving the sorbent attrition and regenerability of zinc oxide-based sorbent, we have adapted multi-binder matrices and direct incorporation of regeneration promoter. The sorbent forming was done with a spray drying technique that is easily scalable to commercial quantity.
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Languages : en
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The disclosure is directed to sorbent compositions for removing reduced sulfur species (e.g., H.sub. 2 S, COS and CS.sub. 2) a feed stream. The sorbent is formed from a multi-phase composition including a zinc titanate phase and a zinc oxide-aluminate phase. The sorbent composition is substantially free of unreacted alumina.
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Languages : en
Pages : 101
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Advanced integrated gasification combined cycle (IGCC) power systems require the development of high-temperature desulfurization sorbents capable of removing hydrogen sulfide from coal gasifier down to very low levels. The objective of this investigation was to identify and demonstrate methods for enhancing the long-term chemical reactivity and mechanical strength of zinc ferrite, a leading regenerable sorbent, for fluidized-bed applications. Fluidized sorbent beds offer significant potential in IGCC systems because of their ability to control the highly exothermic regeneration involved. However, fluidized beds require a durable, attrition-resistant sorbent in the 100--300 [mu]m size range. A bench-scale high-temperature, high- pressure (HTHP) fluidized-bed reactor (7.6-cm I.D.) system capable of operating up to 24 atm and 800°C was designed, built and tested. A total of 175 sulfidation-regeneration cycles were carried out using KRW-type coal gas with various zinc ferrite formulations. A number of sorbent manufacturing techniques including spray drying, impregnation, crushing and screening, and granulation were investigated. While fluidizable sorbents prepared by crushing durable pellets and screening had acceptable sulfur capacity, they underwent excessive attrition during multicycle testing. The sorbent formulations prepared by a proprietary technique were found to have excellent attrition resistance and acceptable chemical reactivity during multicycle testing. However, zinc ferrite was found to be limited to 550°C, beyond which excessive sorbent weakening due to chemical transformations, e.g., iron oxide reduction, was observed.
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Category : Spokane (Wash.)
Languages : en
Pages : 20
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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.
