变换单元洗氨塔腐蚀与防护探讨

Discussion on corrosion and protection of converted-gas ammonia scrubber in conversion unit

为解决煤制氢装置变换单元变换气洗氨塔内壁及塔盘存在严重腐蚀的问题,在对部分生产企业腐蚀调研和文献调研的基础上,探讨腐蚀机理及其影响因素,确认变换气洗氨塔腐蚀属于CO_(2)与H_(2)S共同存在下的腐蚀,腐蚀的发生与H_(2)S浓度、CO_(2)分压、pH等因素相关。在变换气洗氨塔操作条件下,变换气中的氨被洗涤水吸附后,CO_(2)破坏了不锈钢钝化层,形成腐蚀产物保护膜,低H_(2)S含量可破坏腐蚀产物膜导致腐蚀加剧;随着H_(2)S含量增加,生成的FeS和FeS_(1-x)逐渐转化为FeS保护膜减缓腐蚀;当变换气中H_(2)S含量大于临界值,在不锈钢表面形成完整的硫化物钝化膜,从而保护金属。工业实际应用表明,变换气中硫化氢浓度为不低于5335μg/g,相应体积浓度不低于0.35%时,变换气洗氨塔腐蚀轻微。在此基础上,对变换气洗氨塔提出了材质升级、H_(2)S浓度调整等方面的防腐改进措施。

For the problem of serious corrosion on the inner wall and trays of the ammonia scrubber of the conversion unit of the coal hydrogen production unit,the corrosion mechanism and influencing factors were discussed based on corrosion investigation in some production enterprises and literature investigation.The corrosion of the converted-gas ammonia scrubber belongs to the corrosion in the presence of CO_(2)and H_(2)S,and the occurrence of corrosion is related to factors such as H_(2)S concentration,CO_(2)partial pressure,and pH value.Under the operating conditions of converted-gas ammonia scrubber,the ammonia in the converted gas is adsorbed by the washing water.CO_(2)destroys the passivation layer of the stainless steel and forms a protective film of corrosion products.Low H_(2)S content can damage the corrosion product film and intensifies corrosion;As the H_(2)S content increases,the generated FeS and FeS_(1-x)are gradually transformed into FeS protective films to slow down corrosion.When the H_(2)S content in the converted gas is greater than the critical value,a complete sulfide passivation film is formed on the surface of the stainless steel,thereby protecting the metal.Industrial actual application shows that when the H_(2)S content in the converted gas is not less than 5335μg/g or the corresponding volume concentration is not less than 0.35%(v/v),the corrosion of the converted-gas scrubber is slight.On this basis,anti-corrosion improvement measures were proposed for the converted gas ammonia scrubber,including material upgrading and H_(2)S concentration adjustment.