Study on the performance of the purified CaSO4 oxygen carrier derived from wet flue gas desulphurization slag in coal chemical looping combustion
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摘要: 基于电厂烟气脱硫渣，采用多步酸洗工艺加以提纯并制备获得CaSO4载氧体。在高温固定床反应器上研究了还原反应温度、载氧体过量系数Φ、多次还原氧化循环等因素对提纯脱硫渣载氧体与煤化学链燃烧特性和气相硫演化规律的影响。结果表明，提纯脱硫渣载氧体有较高的反应活性，能够促进煤的充分转化；综合考虑碳的转化以及气相硫释放的抑制，最优反应工况中还原反应温度确定为900℃、载氧体过量系数Φ=1.0为最佳。经过五次还原氧化循环实验发现，随着循环次数的增加，CaSO4副反应的进行及气相硫的不断释放，导致提纯脱硫渣载氧体循环反应活性略有降低，反应稳定性受到了一定的影响。Abstract: Flue gas desulphurized slag was collected as the raw material and purified using the multiple steps of sour purification procedures, which was further prepared as CaSO4 oxygen carrier (OC). Reaction characteristics of the purified desulphurized slag OC with the selected lignite as well as release of the different gaseous sulfur species from the CaSO4 side reactions were investigated on in a lab-scale fixed bed reactor. Several main influencing factors, including reaction temperature, OC excess number Φ and the cycle numbers, were focused. The experimental results indicated that the purified CaSO4 OC was of high reactivity and promising to be applied in the coal-fueled chemical looping combustion process as OC. Furthermore, according to the pros and cons of the three influencing factors on the carbon conversion versus the gaseous sulfur release, the optimized reaction conditions were determined as 900℃ and the OC excess number around 1.0. Finally, under this optimized reaction condition, the effect of the cycle numbers was evaluated and found that the continuous release of gaseous sulfur from the CaSO4 side reactions deteriorated the reactivity of the purified CaSO4 OC and its reaction stability was diminished with the five cycles.
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图 2 平顶山脱硫渣提纯前后外观形貌变化
Figure 2 Morphological characteristics of PDS CaSO4
(a): before purification; (b): after purification; (c): SEM morphological feature
图 4 不同来源CaSO4与煤反应特性
Figure 4 Reaction characteristics of YN coal with CaSO4 of different sources
(a): gas concentration; (b): carbon conversion; (c): carbon conversion rate
图 5 反应温度对YN煤与PDS脱硫渣载氧体反应特性的影响
Figure 5 Effect of temperature on YN reaction with PDS CaSO4 OC
(a): carbon conversion; (b): carbon conversion rate
图 6 反应温度对PDS CaSO4与煤副反应中含硫气体释放的影响
Figure 6 Effect of reaction temperature on the gaseous sulfur release from YN coal reaction with PDS CaSO4 OC
(a): H2S release; (b): COS release; (c): SO2 release
图 7 不同还原温度下PDS CaSO4和煤产物XRD谱图
Figure 7 XRD patterns of the solid products between YN coal and the PDS OC at the different reduction temperatures
图 8 载氧体过量系数对脱硫渣载氧体与煤反应特性影响
Figure 8 Effect of the PDS CaSO4 OC excess numbers on its reaction with YN
(a): carbon conversion; (b): carbon conversion rate
图 9 CaSO4载氧体过量系数对气相硫释放的影响
Figure 9 Effect of CaSO4 oxygen excess numbers on the gaseous sulfur release
(a): H2S release; (b): COS release; (c): SO2 release
图 10 不同载氧体过量系数下脱硫渣载氧体与煤固相产物的XRD谱图
Figure 10 XRD patterns of the solid products between the OC and YN coal at the different oxygen excess numbers
图 11 循环次数对脱硫渣载氧体与煤反应特性的影响
Figure 11 Effect of the cycle numbers on the reaction between OC and YN coal
(a): carbon conversion; (b): carbon conversion rate
图 12 循环次数对脱硫渣载氧体与煤反应时气相硫的影响
Figure 12 Effect of the cycle numbers on the gaseous sulfur release between PDS OC and YN coal
(a): H2S release; (b): COS release; (c): SO2 release
图 13 多次还原氧化循环中脱硫渣载氧体与煤反应产物的XRD谱图
Figure 13 XRD patterns of the solid products between PDS OC and YN coal at the different cycle numbers
表 1 平顶山脱硫渣提纯前后化学组分变化
Table 1 Chemical composition before and after purification of the PDS desulfurization slag
Components Content w/% Na2O MgO Al2O3 SiO2 P2O5 SO3 K2O CaO TiO2 Fe2O3 SrO Cl Before purification 0.748 2.122 1.202 1.686 0.045 42.57 0.311 47.99 0.14 1.68 0.06 1.4 After purification - - 0.72 0.49 - 54.83 - 43.78 - 0.18 - - 
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表 2 褐煤的元素分析和工业分析
Table 2 Properties of the YN coal sample
UItimate analysis wd/% Proximate analysis wd/% C H N St O* Mar V A FC 71.13 4.64 0.94 0.13 18.53 6.06 49.69 4.63 39.62 *: by difference
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