基于流场不均匀度对SCR效率影响的探究

The effect of Uneven Flow Field on the Efficiency of SCR

利用Fluent数值模拟软件对某600 MW燃煤电站锅炉的SCR(选择性催化还原法)脱硝系统进行数值模拟,研究了不同工况下SCR管道内部的流场和浓度场变化情况。引入相对标准偏差系数来衡量第一层催化剂入口处烟气浓度、速度以及温度的不均匀度,并重点分析了不均匀度随工况的变化趋势。研究表明:低负荷下烟气中的NO、NH_3浓度的不均匀度以及烟气温度的不均匀度高于其他工况,在50THA、75THA、THA、BRL、BMCR负荷下NO浓度、NH_3浓度和烟气温度的不均匀度逐渐降低。在50THA和BMCR负荷下,NO浓度不均匀度分别为0.399 131 436%、0.271 308 784%;NH_3浓度的不均匀度分别为11.431 272 594%、11.294 855 634%;烟气温度的不均匀度分别为0.081 935 553%、0.079 103 890%,NO和NH_3浓度变化趋势的吻合程度会下降。其原因是:低负荷下流场不均匀度升高导致SCR脱硝效率降低,可以通过有针对性地优化锅炉运行、SCR脱硝系统的设计等来减缓催化剂的失活速率。

The flow field in a selective catalytic reduction selective catalytic reduction( SCR) denitration reactor of a 600 MW coal-fired power plant was numerically simulated. Based on the relative standard deviation,the unevenness of NO and NH_3 concentration,the velocity,flue gas temperature as well as coincide trend of NO and NH_3 concentration at the entrance of the first layer of the catalyst were investigated. The results show that the unevenness of concentration and flue gas temperature are higher than other conditions,the unevenness of NO concentration、NH_3 concentration and flue gas temperature all reduced as the conditions become 50THA、75THA、THA、BRL、BMCR conditions. the unevenness of NO concentration was 0. 399 131 436% 、0. 271 308 784%; the unevenness of NH_3 concentration was 11. 431 272 594% 、11. 294 855 634%; the unevenness of flue gas temperature was 0. 081 935 553% 、0. 079 103 890% under 50THA、BMCR conditions,while the coinciding trend of NO and NH_3 concentration decrease at low load. The above indicate that the increasing unevenness of flow field at low load makes a great difference in reducing SCR denitration efficiency,which causes boiler operation,the design of SCR de NO_x system and so on are optimized to decrease the catalyst deactivation rate