Reaction characteristics investigation of CeO_(2)-enhanced CaSO_(4) oxygen carrier with lignite

Calcium sulfate(CaSO_(4))has been verified as a promising oxygen carrier(OC)in the chemical looping combustion(CLC)for its high oxygen capacity,abundant reserve and low cost,but its low reactivity and deleterious sulfur species emission from the side reactions of CaSO_(4) should be well considered for its wide application in CLC.In order to promote the reactivity of CaSO_(4) and increase its potential to inhibit the gaseous sulfur emission,a CeO_(2)-enhanced CaSO_(4) OC mixed OC of core–shell structure was prepared using the combined template synthesis method.Reaction characteristics of the prepared CaSO_(4)-CeO_(2) mixed OC with a typical lignite was first conducted and systematically investigated,and an improved reactivity of the prepared CaSO_(4)-CeO_(2) mixed OC was demonstrated than its single component CaSO_(4) or CeO_(2) due to the fast transfer and exchange of oxygen from the CaSO_(4) substrate to coal via the doped CeO_(2).Furthermore,the solid products formed from the mixed CaSO_(4)-CeO_(2) OC with the selected coal were collected and analyzed.Especially,evolution and redistribution of the sulfur species of different forms were focused.At the latter reaction stage of YN reaction with the CaSO_(4)-CeO_(2) mixed OC,the SO_(2) emitted from the side reactions of CaSO_(4) was greatly diminished and the doped CeO_(2) was proven effective to directionally fix the SO_(2) released to turn into different solid sulfur compounds,which were determined as Ce_(2)O_(2)S,Ce_(2)S_(3) and Ce_(2)(SO_(4))_(3)·5H_(2)O and formed through the different pathways.In addition,good regeneration of the reduced CaSO_(4)-CeO_(2) mixed OC could be reached in spite of the unavoidable interaction between the included minerals in coal and the reduced mixed OC.Overall,the combined template method-made CaSO_(4)-CeO_(2) mixed OC reported herein was not only endowed with enhanced reactivity for coal conversion,but also owned the potential to directionally fix the gaseous sulfur emission,which is quite applicable as OC for simultaneous decarbonatization and desulfurization in the real CLC process.

Thermodynamics on Sulfur Migration in CaSO4 Oxygen Carrier Reduction by CO

CaSO4 is an attractive oxygen carrier for chemical looping combustion（CLC） because of its high oxygen capacity and low price. The utilization of a CaSO4 oxygen cartier suffers the problems of sulfur release, and deacti- vation caused by sulfur loss. With respect to the fact that partial sulfur release could be recaptured and then recycled to CaSO4 by CaO sorbent, the mixture of CaSO4-CaO can be treated as an oxygen carrier. Thermodynamics of CaSO4 and CaSO4-CaO reduction by CO have been investigated in this study. The sulfur migrations, including the sulfur migration from CaSO4 to gas phase, mutual transformation of sulfur-derived gases and sulfur migration from gas phase to solid phase, were focused and elucidated. The results show that the releases of S2, S8, COS and CS2 from CaSO4 oxygen carrier are spontaneous, while SO2 can be released at high reaction temperatures above 884 ℃. SO2 is the major emission source of sulfur at low CO/CaSO4 molar ratios, and COS is the major part of the byproducts as soon as the ratio exceeds 4 at 900℃. Under CO atmosphere, all the sulfur-derived gases, SO2, S2, S8 and CS2, involved are thermodynamically favored to be converted into COS substance, and are spontaneously absorbed and solidified by CaO additive just into CaS species, which may be recycled to CaSO4 as oxygen carrier in the air reactor. But high reaction temperatures and high CO2 concentrations are adverse to sulfur capture.

冶金尘泥制备钙铁双氧载体材料

化学链燃烧技术是实现CO2高效低能分离和捕捉的新型燃烧技术。以含铁冶金固废尘泥为研究对象,采用共沉淀法制备了钙铁双氧载体（CaSO4-Fe2O3）,并采用TG-DTA、XRD、SEM以及能谱扫描的分析手段,对CaSO4-Fe2O3双氧载体的材料特性及化学链燃烧反应特性进行了表征和分析。结果表明,由含铁冶金尘泥制备的CaSO4-Fe2O3双氧载体质量分数为93.58%,比表面积为10.37cm-2/g,与煤粉反应后的转化率为67.47%,具有较好的反应活性。结合SEM和EDS分析,造成载体活性降低的主要原因是循环燃烧过程中煤灰分的累积,致使载体成分复杂多元化,并发生化学反应和团聚效应,导致载体活性降低。