In-situ study of effect of migrating alkali metals on gasification reactivity of coal char
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摘要: 本研究通过热重与高温热台显微镜分析了神木煤焦颗粒的原位气化行为，探究了单颗粒NaAlO2催化剂的原位催化作用，并结合SEM-EDX探究了碱金属的分布。结果表明，在气化初期，面积法与热重法得到的碳转化率曲线较为一致；在气化后期，煤焦中灰分会形成颗粒的骨架，在气化过程中使煤焦颗粒面积不发生变化，灰分阻碍气化剂向煤焦扩散，使气化速率降低，通过面积法计算的碳转化率小于热重法。单独的NaAlO2颗粒也具有催化作用，距离催化剂颗粒越近，碱金属的迁移量越大，煤焦颗粒的气化反应性越好，NaAlO2颗粒在900 ℃下迁移距离大于840 μm。Abstract: The migrating and diffusion of alkali metals affect catalytic gasification of coal char. The paper investigated in-situ gasification behaviors of coal char by TG and hot stage microscope, and studied catalytic performance of single NaAlO2 particle and Na distribution by SEM-EDX. The results show that in the beginning stage, the curve of carbon conversion obtained by area method is consistent with that by TG method. In the ending stage, the ash in coal char acts as framework of the particles, as a result, area of the particles keeps unchanged. Meanwhile, the ash hinders diffusion of gasifying agent into coal char, and decreases the gasification rate, so carbon conversion rate calculated by area change is lower than that from TG. The single NaAlO2 particle has catalytic performance. The coal char particles, which are closer to NaAlO2, have higher gasification reactivity, because the amount of migrating alkali is higher. The migrating distance of NaAlO2 is higher than 840 μm at 900 ℃ .
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Key words:
- catalytic gasification /
- alkali metals /
- gasification /
- migrating of alkali metals
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图 1 900 ℃下SM煤焦颗粒不同气化时间的热台照片
Figure 1 Image of SM coal char at various gasification time under 900℃
图 2 900 ℃下碳转化率随时间的变化
Figure 2 Carbon conversion curve with time at 900℃
(a): the gasification reactivity of A1-A5 SMC particles; (b): the gasification reactivity of A6-A10 SMC particles; (c): the average carbon conversion by area method and carbon conversion by TG method
图 3 900 ℃下NaAlO2颗粒催化煤焦颗粒气化反应的热台照片
Figure 3 Image of coal char at various gasification time with NaAlO2 particle under 900℃
图 4 距离NaAlO2颗粒不同距离煤焦颗粒的气化行为
Figure 4 Gasification behaviors of char particles with different distance to catalyst particles
(a): the gasification behaviors of char particles in A area; (b): the gasification behaviors of char particles in B area; (c): the gasification behaviors of char particles in C area; (d): the comparison of the mean gasification behaviors between different area and uncatalytic gasification
图 5 800 ℃下NaAlO2负载量为5%不同停留时间下碳转化率随时间的变化
Figure 5 Carbon conversion curve for various holding time with 5% NaAlO2 loaded
图 6 机械混合法负载NaAlO2在不同温度下煤焦的SEM-EDX照片
Figure 6 SEM-EDX images of char with mechanical mixing NaAlO2 at different temperatures
(a): holding temperature at 200 ℃; (b): holding temperature at 500 ℃; (c): holding temperature at 800 ℃
表 1 神木烟煤与煤焦的工业分析和元素分析
Table 1 Proximate and ultimate analyses of SM coal and SMC
Sample Proximate analysis
wad/%Ultimate analysis
wdaf/%V FC A M C H N S O* SM coal 32.46 59.25 6.73 1.56 82.63 5.07 1.10 0.16 11.04 SMC 1.40 87.72 10.31 0.57 96.36 0.79 1.39 0.15 1.31 ad: air-dried basis; daf: dry ash-free basis; *: by difference 
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表 2 神木烟煤煤灰的矿物质组成
Table 2 Ash compositions of SM coal
Sample Content w/% Al2O3 SiO2 Fe2O3 CaO TiO2 MgO Na2O SO3 K2O P2O5 SM coal 16.85 48.07 5.79 19.42 0.68 1.04 0.6 3.65 0.81 0.22
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