单塔抽氨酸性水汽提装置结垢原因分析及措施

Analysis of causes of fouling in single-tower sour water

某炼油厂配有两套酸性水汽提装置,2015年11月检修后开工后相继出现管线、换热器、塔盘结垢,严重影响装置正常运行。通过对酸性水组成、结垢成分分析认定结垢的原因是酸性水中含有钙、镁离子,1号装置侧线抽氨系统排出的分凝液含有高浓度的氨组分,碱性较高,与酸性水混合后使溶液pH值升高,是碳酸钙、碳酸镁等不溶性盐类析出的诱因;2号装置原料酸性水硫化氢含量较高,高碱性分凝液对混合液的pH值影响不大,但酸性水在汽提塔上部脱除硫化氢后,在塔中部形成的氨聚集区中,液相的pH值环境促使了不溶性盐类析出形成垢物。在合适条件下液相中可溶性重碳酸盐[Ca(HCO_3)_2,Mg(HCO_3)_2]分解生成不溶性的碳酸钙、碳酸镁形成结垢物,与溶于酸性水中的环烷酸铵盐、酚铵盐加热分解为不溶于水的环烷酸、酚,沉积在塔盘上的结垢有本质不同,为解决装置堵塞问题提供了新思路。

There are two sour water stripping units in a refinery. After the start-up following the shutdown for maintenance in November 2015,the pipelines,heat exchangers and trays suffered from fouling,which seriously affected the normal operation of the units. The analysis of the compositions of the sour water and the ingredients of the fouling confirm that the culprits of fouling are the calcium and magnesium ions in the sour water. The condensate from ammonia extraction side-draw of No. 1 sour water stripping unit has a higher ammonia and alkalinity. When it is mixed with the sour water,the p H value of the solution will rise,which is the incentive of separating out of calcium carbonate and magnesium carbonate. The hydrogen sulfide in the sour water of No. 2 unit is high. The condensate of higher alkalinity has little impact on the p H value of mixed liquid. Whereas,after the sour water is removed from hydrogen sulfide in the stripper and in the concentrated area of ammonia in the tower,the p H value of liquid-phase environment promotes the coming out of insoluble salts which form the fouling. At the proper conditions,the soluble heavy carbons such as Ca（ HCO3）2 and Mg（ HCO3）2 in the liquid decompose into calcium carbonate and magnesium carbonate which form the insoluble fouls. This discovery is essentially different from the study which presents that the naphthenic acid ammonium salt and the phenol ammonium salt that are dissolved into naphthenic acid and phenolic acid,and deposited in the tray causing the fouling. This new discovery provides another way of thinking to solve the plugging problem of the unit.