W火焰机组SCR催化剂低负荷下脱硝性能研究

On denitradation performance of SCR catalyst of W-flame unit under low load

为了探明W火焰机组SCR催化剂对低负荷烟气条件的适应性,以国内某W火焰机组为研究对象,进行了实际机组烟气条件下的SCR催化剂低负荷脱硝性能测试,探究催化剂活性衰减与恢复规律,并讨论在不同烟气SO_(3)体积比条件下的催化剂失活特性。采用N_(2)吸附-脱附、扫描电子显微镜(SEM)、X射线荧光光谱分析仪(XRF)等仪器表征手段对试验样品进行分析,推断催化剂低负荷失活的可能机理。结果表明:SCR催化剂在325℃条件下,活性均不随反应时间的延长而明显下降,可长时间稳定运行;SCR催化剂在304℃条件下出现了活性衰减现象,但其活性可随机组负荷升高而恢复;SCR催化剂在291℃条件下失活较快,随机组负荷升高催化剂脱硝活性无法完全恢复;烟气中SO_(3)体积比越低,催化剂低负荷失活显现就越轻微。SCR催化剂在低温失活后,出现了BET比表面积大幅下降、表面S含量增加等现象。结合测试仪器表征和性能测试结果,SCR催化剂低负荷条件下脱硝性能衰减主要是由于硫酸氢铵等物质的沉积造成。由于W火焰机组烟气具有高NO_(x)、高SO_(x)体积比的特性,其SCR催化剂在低负荷条件下运行具有更高的最低喷氨温度,更容易发生低温失活现象。因此,W火焰机组在低负荷运行时应密切关注SCR脱硝系统运行安全和NO_(x)达标排放。

The paper has taken the W-flame unit at home in China as the research target so as to make clear the adaptability of SCR catalyst in the somewhat W-flame unit at the lower load flue gas condition.The above said denitridation performance of the SCR catalyst at the lower load under the actual flue gas condition has been tested to explore the decay and recovery regularity of the catalyst activities.At the same time,the paper is also intended to discuss the problem of the deactivation features of the catalyst at the different SO_(3)concentrations.What is more,the experimental samples have also been made characterized by using the N_(2)adsorption-desorption through the electronic microscope scanning(EMS)and the X-ray fluorescence spectrometer(XRF),so as to deduce the probability mechanism of the catalyst deactivation at the lower load.And,then,since the activity of SCR catalyst wouldn’t be made decrease with the reaction time at 325℃,rather,it could run stable for longer period.The activity of the SCR catalyst,though it may get to decrease at 304℃,PPP it is also likely to get restored with the increase of the unit load.Therefore,as a matter of fact,the deactivation of the SCR catalyst may get more severe at 291℃,and,what is more,if the activity of the catalyst may not tend to get totally restored with the increase of the unit load,the lower the SO_(3)concentration turns to be in flue gas,the less deactivated the catalyst would appear under the lower load,the SCR catalyst may get to more and more deactivated at the lower temperature,so that the BET surface area may turn to get decreased significantly with the increase of the S content.According to the characteristic features and the results of the performance test we have done,the degradation of the de-NO_(x)performance SCR catalyst at the lower temperature load tends to be mainly caused by the deposition of the ammonium bisulfate and some other substances.At the same time,since the flue gas of the W-flame unit is characteristically featured with high NO_(x)and SO_(x)concentration,the SCR catalyst may have a higher minimum ammonia injection temperature under the condition of lower load,so that it may become more prone to being deactivated at lower temperatures.And,so,close attention has to be paid to the operation safety of the SCR denitrification system and the NO_(x)emission level on the condition when the W-flame unit has to be operating at lower loads.