硫磺回收装置钠法烟气脱硫若干问题探析

Discussion on several issues of sodium flue gas desulfurizationin sulfur recovery unit

在硫磺回收装置基础上增设以氢氧化钠(NaOH)为吸收剂的烟气碱洗单元,可满足GB 31570—2015《石油炼制工业污染物排放标准》大气污染物特别排放限值或更加苛刻的地方标准要求。调节循环碱液pH值对装置运行至关重要,pH值低有利于防止结垢物质生成,pH值高有利于吸收尾气中二氧化硫(SO_(2)),同时会过量吸收二氧化碳(CO_(2))。综合考虑碱洗塔脱硫效果和含盐废水曝气氧化效果,整个系统的pH值建议控制在7左右。提高尾气焚烧炉温度至750℃以上,可有效避免CO对SO_(2)检测结果的干扰,避免未燃尽的有机物进入含盐废水导致COD超标。针对硫磺回收装置开(停)工过程尾气流量低(约为正常值的1/3),SO_(2)质量浓度高(15-20 g/m^(3))等特点,需制订开(停)工尾气脱硫的操作方案,避免腐蚀、结垢(结晶)与堵塞等情况发生。

On the basis of sulfur recovery unit,a flue gas alkaline washing unit with NaOH as absorbent is added,which can meet the special emission limit of air pollutants in GB 31570—2015“Emission standard of pollutants for petroleum refining industry”or more stringent local standards.Adjusting the pH value of circulating lye is crucial to the operation of the unit.Low pH value is conducive to prevent the formation of scaling substances.High pH value is conducive to absorb SO_(2) in the tail gas and excessive absorb CO_(2).Considering the desulfurization effect of caustic washing column and the aeration oxidation effect of salinity waste water,it is suggested that the pH value of the whole system should be controlled at about 7.Increasing the temperature of tail gas incinerator to above 750℃ can effectively avoid the interference of CO on SO_(2) detection results and the excessive of COD caused by unexhausted organic matter into salinity waste water.According to the characteristics of low tail gas flow(about 1/3 of the normal value)and high SO_(2) concentration(15-20 g/m^(3))in the start-up(shutdown)process of sulfur recovery unit,the operation scheme of start-up(shutdown)tail gas desulfurization should be formulated to avoid corrosion,scaling(crystallization)and blockage.