Study of corrosion behaviour of A106 carbon steel absorber for CO2 removal in amine promoted hot potassium carbonate solution (Benfield solution)

Abstract

The CO2 absorber is one of the largest pressure vessels in ammonia plants, which are suffering from severe corrosion problems worldwide. The aim of the present study is to examine the corrosion behaviour of A106 carbon steel absorber for CO2 removal in amine promoted hot potassium carbonate solution (Benfield solution). This study simulates CO2 removal unit in ammonia production process at Abu Qir Fertilizers and Chemical Industries Company (Alexandria, Egypt) and many other plants all over the world. A typical Benfield solution contains hot potassium carbonate K2CO3, potassium bicarbonate KHCO3, diethanol amine (DEA) as a promoter and potassium metavanadate KVO3 as corrosion inhibitor. The rate of galvanic corrosion of carbon steel absorber/stainless steel pall packings couple in Benfield solution was measured without adding the corrosion inhibitor KVO3 in order to measure the influence of corrosive solution. The corrosion rate was measured by weight loss technique in relation to different operating parameters such as solution velocity, solution temperature, %K2CO3, CO2 loading, %DEA and the effect of the presence of solution contaminants. In general, increasing solution velocity, solution temperature, %K2CO3, CO2 loading and the presence of solution contaminations increase the corrosion rate. However, the increase in %DEA in solution decreases the corrosion rate. The strong dependence of corrosion rate on both solution and gas velocities indicates the diffusion controlled nature of the corrosion process. In addition, estimation of activation energy revealed a value of 4·8 kcal mol−1. Surface morphology study depicted the presence of a porous solid film of corrosion products on carbon steel surface. It has been found that the liquid phase diffusion of bicarbonate to the steel solution interface is the rate determining step.