湿法脱硫石膏含水率高原因分析及治理措施

Analysis and Treatment Measures of WFGD Gypsum High Moisture Content

某火电厂2台机组2021年下半年脱硫系统运行异常,产出石膏含水率达40%。通过石膏浆液取样分析,直接原因是浆液里有大量细微石膏晶体存在(小于20μm石膏晶体占比73.8%),堵塞了真空皮带脱水机滤布,导致石膏浆液无法正常脱水。浆液中石膏晶体没有正常长大,经过分析主要原因是机组上半年长期燃用低硫煤低负荷工况运行,而石灰石供浆量没有按比例减少,运行pH值长期偏高(pH值约5.6),且脱硫系统浆液池容积设计裕量偏大,在这种浆液环境中,过饱和的石膏浆液会产生出大量细微晶核,而生长成合适大小的石膏晶体比例小。采取的措施是在脱硫塔浆液池中分2次加入30 t正常石膏晶种,同时降低浆液运行pH值至4.5,以改善浆液环境品质。为避免类似案例发生,提供借鉴。

In the second half of 2021,the wet flue gas desulfurization(WFGD)system of two units operated abnormally in a power plant.The gypsum moisture content reached 40%.Through the sample analysis by the particle size analyzer,it was found that the direct reason was that there were a large number of fine gypsum crystals in the gypsum slurry(less than 20μm size gypsum crystal account for 73.8%),these fine gypsum crystals blocked the filter cloth of vacuum belt dehydrator,resulting in the failure dehydration of gypsum slurry.The gypsum crystals in the slurry did not grow up normally,after analysis,it was found that the main reason was that the unit operated under low load and with low sulfur coal for a long time,while the limestone slurry supply did not decrease proportionally,the slurry pH was too high for a long time(pH was about 5.6),and the volume margin of the slurry pool was too large,in this slurry environment,supersaturated gypsum in slurry would produce a large number of fine crystal nuclei,and the proportion of appropriate size gypsum crystals was less.The measures were to add 30 t normal gypsum crystal seeds into the slurry tank by twice,and reduce the slurry pH value to 4.5 in order to improve the slurry quality.In order to avoid the similar case,it provides the reference.