Online Corrosion Monitoring in a Postcombustion CO2 Capture Pilot Plant and its Relation to Solvent Degradation and Ammonia Emissions

Abstract

Corrosion in amine treating plants is known to cause integrity failures, plant shutdown, costly repairs, and so forth. The use of an amine treatment system for postcombustion CO2 capture brings additional challenges in terms of the flue gas quality, flue gas composition, operating conditions, scale of operation, and so forth. These differences are expected to have a significant impact on the overall well-being of the plant and the maintenance strategy over its lifetime. The degradation of solvent, by oxidative and thermal degradation pathways, leads to the formation of various degradation products which are known to be corrosive. The oxidative degradation of amine leads to the formation of ammonia which can be emitted to the atmosphere in the treated flue gas stream. This study aims at verifying the interrelation between (1) solvent degradation, (2) corrosion, and (3) NH3 emissions, based on two test campaigns of over 1500 operating hours, in a CO2 capture pilot plant. An online tool for real-time corrosion monitoring, SmartCET, is presented and compared with offline corrosion coupon. The different process and operating conditions such as the change in the flue gas composition, start-up and shutdown, and solvent replacement were correlated with the variations in the corrosion parameters (general corrosion rate, pitting factor, and corrosion mechanism indicator (CMI)), for both campaigns. The three parameters showed only a small increase for most part of both the campaigns (>75 days), and followed a similar trend. However, during both the campaigns, a rapid increase of all the three parameters was observed. In one of the campaigns, the three parameters increased by about 2 orders of magnitude in a time period of only about 20 days, which points toward an autocatalytic out of control solvent chemistry. The common characteristic before the onset of autocatalytic solvent chemistry, is the re-start-up of the pilot plant after an extended period of shutdown. On the basis of these tests, the use of an online corrosion monitoring tool will enable long-term steady state operation of a full scale postcombustion CO2 capture plant.