THE CORROSION CHEMISTRY OF BENFIELD CO_2 REMOVAL PLANT

摘要

The Benfield Process involves absorption of CO_2 in potassium carbonate solutions usually contained in carbon steel pressure vessels. The Eickmeyer Process is an adaptation of the Benfield Process, claimed to be effective for removing CO_2 from gas streams containing H_2S. Corrosion prevention requires the use of vanadate as an anodic corrosion inhibitor. The reliability of Benfield CO_2 removal plant depends on maintenance of an effective protective film in the face of the well-established "dangerous" characteristics of the anodic inhibitor whereby if the inhibitor concentration falls below a threshold value then corrosion is promoted. An additional level of complexity exists where the gas stream has a significant H_2S content, which will function as a reducing agent. A thermodynamic analysis involving an adaptation of the Pourbaix diagram for iron has been used to establish the protection mechanism as a function of H_2S concentration in a Benfield Train absorber and regenerator. Modeling of the redox chemistry of vanadate and its interaction with hydrogen sulphide has been part of this analysis.