Corrosion experiments for CO_2 solvents

摘要

The removal of carbon dioxide from industrial gas streams by amine treating units is a well known process, extensively used for many decades. One of the most severe operational difficulties encountered is the corrosion of the process equipment. In practice, corrosion mitigation might be achieved by using appropriate inhibitors, by adequate design and use of corrosion resistant alloys, or by applying process modifications when no other solution is acceptable. Although corrosion problems frequently encountered in amine treatment plants are rather well described in the literature, the corrosion mechanisms are still not well understood. Furthermore, many different forms of corrosion are found, like erosion-corrosion, stress corrosion cracking, or generalized corrosion. The causes of these different types of corrosion might be extremely wide, as well as their consequences. CO_2 removal being an issue of growing importance, much work is performed to improve the energetic efficiency of current amine treating processes. With that aim, lot of research is done to find new, more efficient solvents. The present study is part of the UE CASTOR project, which aims at developing new, more efficient, solvent. Unfortunately, corrosion risks are extremely dependent on the nature of the amine solution. Other important parameters that might influence the corrosion are the concentration of the amine solution, the charging conditions and the composition of the gas to be treated. It is also well known that amine solvent degradation often increase corrosivity. Degradation of the solvent might be caused by high temperature during regeneration, but also by chemical reactions with some compounds of the gas, like oxygen or sulfur. Appropriate corrosion experiments are therefore required to take into account all such parameters, and to predict the risks of corrosion with new solvents. In the framework of the CASTOR project, our goal is to define a reproducible and selective experimental procedure for corrosivity evaluation of CO_2 solvents, in the specific situation of post combustion, with large volumes of flue gases with low CO_2 content and low pressure. An experimental procedure is proposed for a rapid assessment of corrosion in amine solutions. The tests are performed in a pressure vessel under controlled loading conditions. Amine degradation occurring during the test leads to an acceleration of corrosion reactions, close to real situation in an amine unit. Corrosion tests were performed by weight loss measurements of specimens exposed in the pressure vessel. Additionally, corrosion monitoring in a CO_2 capture pilot plant built during the CASTOR program was performed. The first run of the pilot consisted of a 500 hours run with MEA. Corrosion in the pilot plant was compared to laboratory corrosion tests with the same solvent blend.