350MW机组锅炉SCR脱硝系统优化

准东煤田是我国目前最大的整装煤田,但准东煤在锅炉燃烧过程中易发生结焦问题,一般掺烧高岭土缓解结焦。某燃用准东煤350 MW机组,锅炉燃煤掺烧高岭土后烟气携带灰尘颗粒及灰尘量增大,出现SCR脱硝系统烟道积灰严重和喷氨量明显偏大问题,同时在空气预热器形成硫酸氢氨堵塞,使机组不能长周期稳定运行。通过与国内同类型多台机组锅炉对比后发现,脱硝系统均存在易产生积灰的脱硝转向室、催化剂上方及空气预热器入口斜坡积灰状况等情况。针对存在的问题,通过建立改造前、后的模型计算分析,进行了导流板布置的优化设计、CFD流场分布、优化SCR系统导流板设计、声波与蒸汽吹灰器结合吹灰和氨注射栅格优化升级等工作,应用德图480风速仪实测风速试验,发现脱硝烟道原导流板设计不合理及施工安装偏差;原导流板水平段跨距大,支撑不足,造成导流板压塌变形,影响烟气流场分布;锅炉所烧煤质为高钠煤,为防止锅炉结焦掺烧高岭土后,增加了烟气飞灰颗粒及灰尘量,飞灰具有很大黏性,易沉积在烟道导流板及烟道壁面上。因此,提出对脱硝内部各处导流板进行优化改造,对脱硝系统烟道易产生积灰的部位增加声波吹灰器,对喷氨格栅喷嘴数量及氨空混合器升级,同时开展锅炉SCR脱硝喷氨热态优化调整试验工作。通过开展相关工作,SCR烟气系统的烟气流场相对标准偏差优化5%,相同负荷下液氨消耗量降低45%,彻底解决脱硝系统积灰和空气预热器堵塞问题,实现机组满负荷达标稳定运行。锅炉长期运行半年后停炉检查,发现前期脱硝系统烟道高达1 m的积灰部位彻底解决,催化剂表面干净无杂物,解决了脱硝系统积灰问题,同时配合提高空气预热器冷端综合温度的措施,彻底解决锅炉空气预热器堵塞问题。同时,经济效益显著,每年可以分别节约液氨费用70万元,节约风机电耗费用100万元,节约检修清理积灰及检修费用80万元,节约空气预热器冲洗治理费用20万元,综合节约费用270万元/a,达到预期效果实现机组长周期安全经济稳定运行。

Optimization of SCR denitrification system for 350 MW unit boiler

Zhundong Coal Field is located in Xinjiang Changji Hui Autonomous Prefecture,which is currently the largest packaged coal field in China. However,Zhundong Coal is prone to coking during the combustion process of boilers. Kaolin is usually mixed to ease coking. In a 350 MW unit burning Zhundong coal,after the coal was burned with kaolin in a boiler,the amount of dust particles and dust carried by the flue gas increased,which resulted in the serious ash accumulation in the SCR denitration system and a significant increase in ammonia injection. The air preheater was blocked by ammonia hydrogen sulphate,which made the unit unable to run stably for a long period. After compared with the domestic boilers of multiple units of the same type,it is found that the denitration system has ash deposits in the denitrification steering room,over the catalyst,and the air preheater inlet slope. Aiming at the existing problems,by the calculation and analysis of setting the correct model and incorrect installation model modeling,the optimal design of the deflector layout,the CFD flow field distribution,the optimization of the SCR system deflector design,and the combination of sonic and steam soot blowers and the optimization and upgrading of ammonia injection grid were performed. Using Testo 480 anemometer measured wind speed test,it was found that the original deflector of the denitration flue was unreasonable in design and construction and installation deviation;the horizontal section of the original deflector has a large span and insufficient support,resulting in the guide plate to collapse and deform and affecting the distribution of the flue gas field. The coal burned by the boiler is high-sodium coal. To prevent the boiler from coking and adding kaolin,the amount of fly ash particles and dust in the flue gas is increased,and the fly ash is quite sticky. It is easy to deposit on the flue deflector and the flue wall. Therefore,it is proposed to optimize the deflectors inside the denitrification system,add sonic sootblower to the ash-prone parts of the denitration system,upgrade the number of ammonia injection grid nozzles and ammonia air mixer,and carry out boiler SCR test work on thermal adjustment and optimization of denitrification and ammonia spraying. Through relevant work,the relative standard deviation of the flue gas field of the SCR flue gas system was optimized by 5%,and the consumption of liquid ammonia was reduced by 45% under the same load. The problems of ash accumulation in the denitration system and the blockage of the air preheater were completely solved to achieve the stable operation of the full load of the unit. After the boiler was shut down for half a year after long-term operation,it was found that the ash deposits of up to 1 m in the flue of the previous denitration system were completely resolved,and the catalyst surface was clean and free of debris,which solved the problem of ash accumulation in the denitration system. At the same time,the blockage problem of the air preheater of the boiler was completely solved by cooperating with the measures to improve the comprehensive temperature of the cold end of the air preheater.At the same time,the economic benefits are significant,which can save 700 000 yuan in liquid ammonia costs,1 million yuan in fan power consumption,800,000 yuan in maintenance and cleaning of dust and overhaul,and 200,000 yuan in air preheater cleaning and treatment costs. The comprehensive cost saving is 2.7 million yuan/year,and the expected effect is achieved to realize the safe and economic stable operation of the unit group leader cycle.