摘要
相对于金属氧载体,CaSO4作为氧载体用于化学链燃烧,具有成本低、来源广泛和氧传递容量大等诸多优点,但是气相SO2以及各种固相硫沉积物对CaSO4用于化学链燃烧过程造成很大的障碍。基于热力学模拟,对CaSO4氧载体与以合成气为燃料的化学链燃烧进行了模拟研究,结果表明就CaSO4与合成气的反应而言,在燃料反应器中,100℃~400℃的低温反应条件下,主要发生的是合成气中CO和H2的甲烷化反应以及硫酸盐热化学还原反应,反应产物主要是H2S和CaCO3;在400℃~915℃,主要发生的是CO和H2与CaSO4的还原反应,还原产物是CaS和CO2;当反应温度高于915℃时,诸多副反应开始发生,反应物相除了CaS和CO2外,CaO等副产物开始出现;而在空气反应器中,在CaS的整个氧化过程中,CaS再生形成CaSO4的反应都是主要的,但是当空气过量系数ФAR<0.8时,CaSO4与CaS的固相反应以及CaS氧化形成CaO的两个副反应也同时起作用。在燃料反应器中,最优的反应条件是反应温度915℃、常压并严格控制CaSO4的加入量并确保CaSO4氧载体过量系数ФFR^1;而在空气反应器中,提供充足的空气量对于CaS的氧化非常重要,空气过量系数ФAR≥1不仅能确保CaS的充分氧化,而且还能避免CaS氧化过程中SO2的排放和CaO的产生。
Compared to metal oxides,CaSO4 adopted as oxygen carrier（OC） in chemical looping combustion（CLC） presents several advantages such as low cost,easy availability and superior oxygen transfer capacity,whilst the SO2 emission and solid sulfur deposit in the process could be a big concern.In this study,thermodynamic simulations were conducted to investigate the sulfur distribution in a CLC system with CaSO4 as OC and syngas derived from coal as the fuel.Several findings were attained：（i） On the main products and reaction pathways in the fuel reactor（FR）,at the low temperature of 100℃~400℃,the main sulfur species and carbon deposit were H2S and CaCO3 via the methanation of CO with H2 coupled with the shift reaction of CO with H2O（g） and the ensuing thermochemical sulfate reduction（TSR）.Then at 400℃~915℃,CaS and CO2 were the main products through the reaction of CaSO4 with H2 or CO,and both products increased with increasing FR temperature.Furthermore,at the FR temperature higher than 915℃,due to the initiation of the solid side reaction between CaS and CaSO4,the percentage of CaS declined.In contrary,the percentages of CaO,H2 and CO increased possibly due to the consumption of part of CaSO4 in the side reaction and thus not enough lattice oxygen available.In the air reactor（AR）,the oxidization of CaS by air into CaSO4 was always dominant.Besides at ФAR below 0.8,both the solid side reaction of CaSO4 with CaS and the oxidization of CaS into CaO were simultaneously in effect.（ii） In the FR,the optimized condition was suggested as at around 915℃,atmospheric condition and carefully controlled ФFR around unity.（iii） In the AR,sufficient supply of air was important for the oxidization of CaS,and ФAR ≥1 would ensure the full oxidization of CaS into CaSO4 and prevent the emission of SO2 and formation of CaO as well.Overall,this study provided the most suitable conditions of using CaSO4 as OC in CLC of syngas with the minimal SO2 emissions and CaO formation.
出处
《燃料化学学报》
EI
CAS
CSCD
北大核心
2011年第4期251-257,共7页
Journal of Fuel Chemistry and Technology
基金
National Natural Science Foundation of China(50906030,50936001)
A Star SERC Grant of Singapore(SERC 0921380025-M47070019)
partial funding from National Basic Research Program(2010CB227003,2011CB707301).
关键词
化学链燃烧
煤基合成气
氧载体
CASO4
热力学模拟
chemical looping combustion（CLC）
coal-derived syngas
oxygen carriers
CaSO4
thermodynamic simulation
