农业废弃物再燃脱硝特性试验

为了缓解化石能源的不足,开发生物质清洁高效燃烧的利用方式,采用农业废弃物(稻壳、秸秆)和R90煤粉作为再燃燃料在恒温沉降炉上进行再燃脱硝试验。针对燃料种类、化学计量比(stoichiometric ratio)、停留时间、燃料粒度、再燃比等因素对再燃脱硝效率的影响进行了研究。结果表明:农业废弃物(秸秆、稻壳)的再燃脱硝能力明显高于煤粉,其中秸秆再燃脱硝效率最高,稻壳再燃脱硝效率中等,煤粉最低,不同的挥发分含量是造成农业废弃物(秸秆、稻壳)与煤粉再燃脱硝率差别的最主要原因。再燃脱硝率随再燃区化学计量比(SR2)的提高逐渐降低。SR2增加,燃料热解析出的还原组分被氧竞争性地消耗,导致NO还原反应弱化,再燃脱硝率降低。SR2对农业废弃物秸秆和稻壳再燃脱硝率影响明显强于煤粉,再燃比20%工况,SR2从0.8增加到0.9,秸秆再燃脱硝率减少了20.12%,稻壳减少20.07%,煤粉减少了8.38%。燃料粒度的改变将影响颗粒的升温过程,在相同条件下,较细的燃料颗粒能更快速释放出更多的挥发分,可以提供再燃还原NO所需的更多的还原物质,对提高再燃脱硝率是有利的。再燃停留时间增加,在富燃料条件下再燃燃料与NO的反应时间延长,有利于NO消减。采用农业废弃物秸秆、稻壳作为作为再燃燃料,合理的再燃停留时间在600 ms以内,明显低于煤粉。通过调整再燃比可以获得适合的再燃脱硝率,农业废弃物秸秆、稻壳的合理再燃比在15%~20%之间。

Experiment on NO reduction performance from reburning of agricultural wastes

Abstract: In order to develop clean and efficient utilization technologies of biomass to supplement insufficient fossil energy, the reduction of NO was studied in a drop tube furnace (DTF) using rice husk, straw, and pulverized coal as reburning fuels. The impacts of fuel type, stoichiometric ratio (SR), reburning reaction temperature, residence time in the reburning-zone, the ratio of fuel particle size and reburning fuel on NO removal efficiency were analyzed in this study. The results indicated that NO reduction efficiency of biomass fuels such as rice husk, straw and sawdust of pine were higher than that of pulverized coal. The NO removal efficiency of straw and sawdust of pine was the highest, but the efficiency of the pulverized coal was the lowest among these three fuels. The composition of volatile components in different fuels had major impacts on the efficiency. NO removal efficiency was decreased with SR increasing in reburning zone. As SR was increased, reducing components released during the devolatilization were consumed by oxygen at the same time with NO reduction, which weakened the reduction reaction of NO. The SR had major impacts on the efficiency of NO reduction of agricultural wastes including rice husk and straw than that of the pulverized coal. For the test case of reburning ratio of 20 %, the reduction efficiency of NO using straw and rice husk were decreased by 20.12 % and 20.07 %, respectively if the SR was increased from 0.8 to 0.9. It was decreased by 8.38 % when using the pulverized coal. The sizes of fuel particles affect heating process. Under the same conditions, the fine fuel particles produced more volatile components and supplied more reducing matters of NO, which increased the reduction efficiency of NO. The increase of resistance time also increase the reaction time between reburning fuel and NO, which facilitated the NO reduction. By using straw and rice husk as reburning fuel, reasonable residence time was shorter than 600 ms, which is much lower than that of using the pulverized coal. Adjusting reburning ratio can attain appropriate reduction efficiency of NO. Reasonable reburning ratios of straw and rice husk were preferred to be between 15%-20%.