Corrosion of Carbon Steel in Ethanolamine
F. Gui, N. Sridhar, R. Thodla, and C. S Brossia CC Technologies-A DNV Company 5777 Frantz Road Dublin, OH 43017
ABSTRACT Monoethanolamine (MEA) is traditionally used for gas treatment in natural gas and refinery operations to remove H2S. It is also used in the CO2 capture and sequestration process to separate CO2 from other post combustion gases. Thiswork investigates the corrosion of carbon steel in monoethanolamine. A set of parameters that could be encountered in the refinery operation and CO2 capture process were investigated to understand their impact on the corrosion of carbon steel in monoethanolamine. It was found that MEA solution is generally more corrosive at lower concentrations and elevated temperatures whereas the MEA solutionsare benign at room temperature independent of concentration. The presence of CO2 makes the MEA solutions more corrosive than without CO2; the combination of CO2 and elevated temperature also make the MEA solutions more corrosive but protective FeCO3 could form under certain conditions. The results established a baseline for further understanding the corrosion of carbon steel in amine environmentsin the future which should take into consideration gas impurities such as NO2 and SO2 as well as other process parameters. Key words: Amine, MEA, corrosion, CO2 capture, refinery
INTRODUCTION Monoethanolamine (MEA) is traditionally used to remove H2S or CO2 in the natural gas industries and refinery operations. In refinery operations, the gas treatment process by amine is often referred asamine treatment. Pure MEA and concentrated MEA/water solutions are alkaline in nature with pH in the range of 11 to 12 depending on the concentration of MEA. Therefore, carbon steels tend to be passive in the highly concentrated MEA solutions and could experience localized attack. Furthermore, in the practical operations, MEA could become generally corrosive to cause active dissolution of carbon steeldue to the pH change resulting from the absorption of H2S and/or CO2 (i.e. rich amine). Additionally, the impurities carried over from crude oil, such as chloride, also could change the corrosivity of the MEA considerably.
MEA has also found great use in the CO2 capture and sequestration process as an attempt to reduce the concentration of green house gas in the environment. In this process,the CO2 in the flue gases produced by the combustion of the primary fuel is removed to produce a concentrated stream of highly pressurized CO2 that can be used to enhance oil recovery or stored in depleted oil/gas/mine reservoirs 1. Typically, the amine concentrations used in the CO2 capture process are higher than that used in the refinery process. Although CO2 capture is a different process fromamine treatment in refinery operations, the corrosion problems that the materials used in these processes experience share many similarities. For instance, the pH of the amine could eventually drop to a near neutral or even acidic range and thus cause active dissolution of carbon steel; the organic acids or heat-stable salt could form during both processes that could impair the corrosionresistance of the materials significantly. Therefore, the objective of the present work is to investigate the corrosion behavior of carbon steel in MEA solutions. Particularly, the impact of a set of variables, which could be encountered in the operation of a refinery gas treatment process or a CO2 capture process, on the corrosion behavior of carbon steel were studied. The effort was focused onestablishing a baseline for further understanding the corrosion of carbon steel in amine environment in the future which should take into consideration gas impurities such as NO2 and SO2 as well as other process parameters.
EXPERIMENTAL APPROACH MEA (99.99%)* was mixed with deionized (DI) water to achieve desired concentration (wt%). The tests were conducted in solutions as it is after mixing (i.e....
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