48 research outputs found
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Development of Superior Sorbents for Separation of CO2 from Flue Gas at a Wide Temperature Range During Coal Combustion
In chapter 1, the studies focused on the development of novel sorbents for reducing the carbon dioxide emissions at high temperatures. Our studies focused on cesium doped CaO sorbents with respect to other major flue gas compounds in a wide temperature range. The thermo-gravimetric analysis of sorbents with loadings of CaO doped on 20 wt% cesium demonstrated high CO{sub 2} sorption uptakes (up to 66 wt% CO{sub 2}/sorbent). It is remarkable to note that zero adsorption affinity for N{sub 2}, O{sub 2}, H{sub 2}O and NO at temperatures as high as 600 C was observed. For water vapor and nitrogen oxide we observed a positive effect for CO{sub 2} adsorption. In the presence of steam, the CO{sub 2} adsorption increased to the highest adsorption capacity of 77 wt% CO{sub 2}/sorbent. In the presence of nitrogen oxide, the final CO{sub 2} uptake remained same, but the rate of adsorption was higher at the initial stages (10%) than the case where no nitrogen oxide was fed. In chapter 2, Ca(NO{sub 3}){sub 2} {center_dot} 4H{sub 2}O, CaO, Ca(OH){sub 2}, CaCO{sub 3}, and Ca(CH{sub 3}COO){sub 2} {center_dot} H{sub 2}O were used as precursors for synthesis of CaO sorbents on this work. The sorbents prepared from calcium acetate (CaAc{sub 2}-CaO) resulted in the best uptake characteristics for CO{sub 2}. It possessed higher BET surface area and higher pore volume than the other sorbents. According to SEM images, this sorbent shows 'fluffy' structure, which probably contributes to its high surface area and pore volume. When temperatures were between 550 and 800 C, this sorbent could be carbonated almost completely. Moreover, the carbonation progressed dominantly at the initial short period. Under numerous adsorption-desorption cycles, the CaAc{sub 2}-CaO demonstrated the best reversibility, even under the existence of 10 vol % water vapor. In a 27 cyclic running, the sorbent sustained fairly high carbonation conversion of 62%. Pore size distributions indicate that their pore volume decreased when experimental cycles went on. Silica was doped on the CaAc{sub 2}-CaO in various weight percentages, but the resultant sorbent did not exhibit better performance under cyclic operation than those without dopant. In chapter 3, the Calcium-based carbon dioxide sorbents were made in the gas phase by flame spray pyrolysis (FSP) and compared to the ones made by standard high temperature calcination (HTC) of selected calcium precursors. The FSP-made sorbents were solid nanostructured particles having twice as large specific surface area (40-60 m{sup 2}/g) as the HTC-made sorbents (i.e. from calcium acetate monohydrate). All FSP-made sorbents showed high capacity for CO{sub 2} uptake at high temperatures (773-1073 K) while the HTC-made ones from calcium acetate monohydrate (CaAc{sub 2} {center_dot} H{sub 2}O) demonstrated the best performance for CO{sub 2} uptake among all HTC-made sorbents. At carbonation temperatures less than 773 K, FSP-made sorbents demonstrated better performance for CO{sub 2} uptake than all HTC-made sorbents. Above that, both FSP-made, and HTC-made sorbents from CaAc{sub 2} {center_dot} H{sub 2}O exhibited comparable carbonation rates and maximum conversion. In multiple carbonation/decarbonation cycles, FSP-made sorbents demonstrated stable, reversible and high CO{sub 2} uptake capacity sustaining maximum molar conversion at about 50% even after 60 such cycles indicating their potential for CO{sub 2} uptake. In chapter 4 we investigated the performance of CaO sorbents with dopant by flame spray pyrolysis at higher temperature. The results show that the sorbent with zirconia gave best performance among sorbents having different dopants. The one having Zr to Ca of 3:10 by molar gave stable performance. The calcium conversion around 64% conversion during 102-cycle operations at 973 K. When carbonation was performance at 823 K, the Zr/Ca sorbent (3:10) exhibited stable performance of 56% by calcium molar conversion, or 27% by sorbent weight, both of which are less than those at 973 K as expected. In chapter 5 we investigated the performance of CaO sorbents by flame spray pyrolysis at higher temperature with much shorter duration period. Stable high conversions were attained after 40 cycles The results show that the sorbent could reach high CO{sub 2} capture capacity, be completely regenerated in short time and be quite stable even at these severe conditions. Several studies were devoted to identify sorbents which could effectively capture CO{sub 2} while survive in SO{sub 2} atmosphere. From the group of sorbents we checked, a couple of sorbents showed very promising behavior, namely CO{sub 2} uptakes higher than 60% (wt/wt sorbent) while they acquired higher than 95% of their original activity/performance characteristics in a short period of time
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Simultaneous Removal of NOx and Mercury in Low Temperature Selective Catalytic and Adsorptive Reactor
The results of a 18-month investigation to advance the development of a novel Low Temperature Selective Catalytic and Adsorptive Reactor (LTSCAR), for the simultaneous removal of NO{sub x} and mercury (elemental and oxidized) from flue gases in a single unit operation located downstream of the particulate collectors, are reported. In the proposed LTSCAR, NO{sub x} removal is in a traditional SCR mode but at low temperature, and, uniquely, using carbon monoxide as a reductant. The concomitant capture of mercury in the unit is achieved through the incorporation of a novel chelating adsorbent. As conceptualized, the LTSCAR will be located downstream of the particulate collectors (flue gas temperature 140-160 C) and will be similar in structure to a conventional SCR. That is, it will have 3-4 beds that are loaded with catalyst and adsorbent allowing staged replacement of catalyst and adsorbent as required. Various Mn/TiO{sub 2} SCR catalysts were synthesized and evaluated for their ability to reduce NO at low temperature using CO as the reductant. It has been shown that with a suitably tailored catalyst more than 65% NO conversion with 100% N{sub 2} selectivity can be achieved, even at a high space velocity (SV) of 50,000 h-1 and in the presence of 2 v% H{sub 2}O. Three adsorbents for oxidized mercury were developed in this project with thermal stability in the required range. Based on detailed evaluations of their characteristics, the mercaptopropyltrimethoxysilane (MPTS) adsorbent was found to be most promising for the capture of oxidized mercury. This adsorbent has been shown to be thermally stable to 200 C. Fixed-bed evaluations in the targeted temperature range demonstrated effective removal of oxidized mercury from simulated flue gas at very high capacity ({approx}>58 mg Hg/g adsorbent). Extension of the capability of the adsorbent to elemental mercury capture was pursued with two independent approaches: incorporation of a novel nano-layer on the surface of the chelating mercury adsorbent to achieve in situ oxidation on the adsorbent, and the use of a separate titania-supported manganese oxide catalyst upstream of the oxidized mercury adsorbent. Both approaches met with some success. It was demonstrated that the concept of in situ oxidation on the adsorbent is viable, but the future challenge is to raise the operating capacity beyond the achieved limit of 2.7 mg Hg/g adsorbent. With regard to the manganese dioxide catalyst, elemental mercury was very efficiently oxidized in the absence of sulfur dioxide. Adequate resistance to sulfur dioxide must be incorporated for the approach to be feasible in flue gas. A preliminary benefits analysis of the technology suggests significant potential economic and environmental advantages
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DEVELOPMENT OF SUPERIOR SORBENTS FOR SEPARATION OF CO2 FROM FLUE GAS AT A WIDE TEMPERATURE RANGE DURING COAL COMBUSTION
For this part of the project the studies focused on the development of novel sorbents for reducing the carbon dioxide emissions at high temperatures. Our studies focused on cesium doped CaO sorbents with respect to other major flue gas compounds in a wide temperature range. The thermo-gravimetric analysis of sorbents with loadings of CaO doped on 20 wt% cesium demonstrated high CO{sub 2} sorption uptakes (up to 66 wt% CO{sub 2}/sorbent). It is remarkable to note that zero adsorption affinity for N{sub 2}, O{sub 2}, H{sub 2}O and NO at temperatures as high as 600 C was observed. For water vapor and nitrogen oxide we observed a positive effect for CO{sub 2} adsorption. In the presence of steam, the CO{sub 2} adsorption increased to the highest adsorption capacity of 77 wt% CO{sub 2}/sorbent. In the presence of nitrogen oxide, the final CO{sub 2} uptake remained same, but the rate of adsorption was higher at the initial stages (10%) than the case where no nitrogen oxide was fed
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Development of Superior Sorbents for Separation of CO2 From Flue Gas at a Wide Temperature Range During Coal Combustion Annual Report
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DEVELOPMENT OF MULTI-TASK CATALYSTS FOR REMOVAL OF NOx AND TOXIC ORGANIC COMPOUNDS DURING COAL COMBUSTION
The work performed during this project focused on the identification of materials capable of providing high activity and selectivity for the selective catalytic reduction of nitric oxide with ammonia. The material surface characteristics were correlated with the catalytic behavior of our catalysts to increase our understanding and to help improve the DeNO{sub x} efficiency. The catalysts employed in this study include mixed oxide composite powders (TiO{sub 2}-Cr{sub 2}O{sub 3}, TiO{sub 2}-ZrO{sub 2}, TiO{sub 2}-WO{sub 3}, TiO{sub 2}-SiO{sub 2}, and TiO{sub 2}-Al{sub 2}O{sub 3}) loaded with varying amounts of V{sub 2}O{sub 5}, along with 5 different commercial sources of TiO{sub 2}. V{sub 2}O{sub 5} was added to the commercial sources of TiO{sub 2} to achieve monolayer coverage. Since the valence state of vanadium in the precursor solution during the impregnation step significantly impacted catalytic performance, catalysts were synthesized from both V{sup +4} and V{sup +5} solutions explain this phenomenon. Specifically, the synthesis of catalysts from V{sup 5+} precursor solutions yields lower-performance catalysts compared to the case of V{sup 4+} under identical conditions. Aging the vanadium precursor solution, which is associated with the reduction of V{sup 5+} to V{sup 4+} (VO{sub 2}{sup +} {yields} VO{sup 2+}), prior to impregnation results in catalysts with excellent catalytic behavior under identical activation and operating conditions. This work also added vanadia to TiO{sub 2}-based supports with low crystallinity. These supports, which have traditionally performed poorly, are now able to function as effective SCR catalysts. Increasing the acidity of the support by incorporating oxides such as WO{sub 3} and Al{sub 2}O{sub 3} significantly improves the SCR activity and nitrogen selectivity. It was also found that the supports should be synthesized with the simultaneous precipitation of the corresponding precursors. The mixed oxide catalysts possess Broensted and Lewis acid sites of comparable strength over a wide range of temperatures. Catalysts prepared from aged vanadium precursor solutions also demonstrated a wider temperature window for optimum operation