循环流化床床料与燃料粒径对脱硝反应的影响

Influence of particle sizes of bed material and fuel on denitration reaction in circulating fluidized bed

随着能源动力产业的大力发展,大气污染形势日趋严峻,控制NOx排放的相关环保标准也日益严格。选择性非催化还原技术(SNCR)能有效降低NOx排放,为了进一步降低循环流化床的NOx排放,需要从源头降低NOx生成量,有必要研究床料及燃料粒径对脱硝反应的影响规律。利用循环流化床热态试验系统探讨了反应温度、氨氮摩尔比、床料粒径配比、煤粉平均粒径对NOx排放的影响。结果表明:氨还原剂有效还原NOx的温度为860~950℃;不同反应温度下,氨的脱硝效率随氨氮摩尔比的增大均先增大后减小;增大细颗粒床料占比能有效减少NOx生成量、提高脱硝效率、降低SNCR活性反应温度;其中,细颗粒占比最大的床料脱硝效率随NSR的增加不断升高,当NSR=2.0时,脱硝效率达到了最高42%,NOx排放量降至215 mg/m^3。适当减小煤粉平均粒径,可降低NOx生成量并促使SNCR反应在较低温度下进行。各温度下,平均粒径330μm煤粉产生的NOx较425μm煤粉下降10~30 mg/m^3。高温下,氨还原剂的脱硝效率随燃料粒径的增大明显上升;较低温度时,氨的脱硝效率随燃料粒径的增大可能下降。910℃时,燃烧平均粒径600μm煤粉在不同NSR下,脱硝效率比燃烧425μm煤粉显著高出20%~30%;860℃时,平均粒径425μm煤粉脱硝效率明显低于330μm煤粉。造成这一现象的主要原因是,氨的还原反应与NOx初始浓度和反应温度有关。在不同初始浓度和温度下氨具有不同的反应选择性。确定燃料粒径后,需要匹配合适的工艺操作参数以满足NOx排放要求。

With the vigorous development of the energy power industry,the situation of air pollution becomes increasingly severe,and the relevant environmental protection standards for NOx emission control become increasingly strict.Selective non-catalytic reduction technology(SNCR)can effectively reduce NOx emission,but the production of NOx needs to be reduced from the source in order to further reduce NOx emission in circulating fluidized bed.Therefore,the influence law of bed material and fuel particle size on denitration reaction has great research value.The effects of reaction temperature,molar ratio of ammonia to NOx,particle size ratio of bed material and average particle size of pulverized coal on NOx emission were investigated by using the circulating fluidized bed thermal experiment system.The results show that the temperature range of NOx reduction with ammonia reducing agent is 860-950℃.The denitration efficiency of ammonia increases first and then decreases with the increase of NSR at different reaction temperatures.Increasing the proportion of fine particle bed material can effectively reduce the production of NOx,improve the denitration efficiency,and reduce the SNCR active reaction temperature.Among them,the denitrification efficiency of the bed material with the largest proportion of fine particles increases with the increase of NSR.When NSR=2.0,the denitrification efficiency reaches the highest 42%,and the NOx emission decreases to 215 mg/m^3.By appropriately reducing the average particle size of pulverized coal,the production of NOx can be reduced and the SNCR reaction can be carried out at a lower temperature.At each temperature,the NOx generated by pulverized coal with an average particle size of 330μm decreases by 10-30 mg/m^3 compared with that of pulverized coal with an average particle size of 425μm.At high temperature,the denitration efficiency of ammonia reducing agent increases obviously with the increase of fuel particle size.At lower temperature,the denitration efficiency of ammonia may decrease with the increase of fuel particle size.At 910℃,the denitration efficiency of pulverized coal with an average particle size of 600μm is significantly 20%-30%higher than that of pulverized coal with an average particle size of 425μm under different NSR.At 860℃,the denitration efficiency of pulverized coal with an average particle size of 425μm is significantly lower than that of pulverized coal with an average particle size of 330μm.The main reason for this phenomenon is that the reduction reaction of ammonia is related to the initial concentration of NOx and the reaction temperature.Ammonia has different reaction selectivity at different initial concentration and temperature.After determining the fuel particle size,the appropriate process operating parameters should be matched to meet the NOx emission requirements.