Corrosion Behavior of Carbon Steel in the CO 2 Absorption Process Using Aqueous Amine Solutions Amornvadee Veawab, Paitoon Tontiwachwuthikul,* and Amit Chakma Process Systems Laboratory, Faculty of Engineering, University of Regina, Regina, Saskatchewan, Canada S4S 0A2 The present study provides comprehensive information on the effects of process parameter variations on the corrosion behavior of carbon steel in CO 2 absorption systems using aqueous amine solutions. The process parameters of interest are amine type, concentration of the amine solutions, solution temperature, CO 2 loading, and oxygen content. An electrochemical testing technique was used for determining the system corrosiveness in terms of polarization behavior and corrosion rate. The experimental results suggest that the corrosion behavior is considerably sensitive to the variations in the process parameters. Increases in amine concentration, solution temperature, CO 2 loading, and oxygen content accelerate the corrosion rate in the systems. In addition, different amine types yield different degrees of the system corrosiveness. Comparisons of the corrosiveness among single amine systems as well as between mixed amine systems and their precursors are also presented. Introduction The CO 2 absorption process using aqueous amine solutions has been extensively used for the removal of CO 2 from gas streams in many industries. Common industrial applications include natural gas processing, coal gasification, and manufacturing of hydrogen and ammonia. In these processes, purification of process gas streams is to meet the needed requirements of product quality and to minimize operational difficulties, which may occur when the gas streams are further used in downstream processes. Other applications involve the production of CO 2 for uses in food, beverage, and petroleum industries. Besides such industrial applica- tions, the CO 2 absorption process is considered to be a potential technique for reducing greenhouse gas emis- sion from flue gas streams. Historically, the CO 2 absorption process using aque- ous amine solutions has long encountered corrosion problems. On the basis of plant experiences, 1-6 corrosion seems to take place in several plant locations including the bottom portion of the absorber, the rich-lean heat exchanger, the regenerator, and the reboiler. Both uniform corrosion and localized attacks such as pitting, galvanic, erosion, stress cracking, and intergranular corrosion were commonly detected. In general, the ways in which the process equipment was designed, fabri- cated, installed, and operated are key factors in deter- mining the corrosion types and degrees of the system corrosiveness. According to Kohl and Nielsen, 7 corrosion is consid- ered to be one of the most severe operational problems in the CO 2 absorption process. Chronic corrosion can lead to a direct impact on the plant’s economy since it results in unplanned downtime, production losses, reduced equipment life, and even injury or death. 6 The unplanned downtime of a typical plant can cost between $10 000 and $30 000 per day in terms of production losses. 8 Besides, the downtime also leads to a large portion of expenditure necessary for restoring the cor- roded systems and for treatments initiated to mitigate the corrosion. As stated by Gerus, 9 millions of dollars are annually spent on this particular purpose. In addition to the above direct impacts, the corrosion problems also indirectly affect the plant’s economy by limiting the operating ranges of the process. Generally, flexibility in varying the operating conditions is reduced due to excessive corrosion. Operating the process beyond the typical conditions may also cause a tremendous increase in the system corrosiveness. 6,10 Because of such limitations, the capacity of existing plants may not be easily increased at reasonable expenses. In practice, corrosion could be controlled by several approaches: (i) use of proper equipment design, (ii) use of highly resistant materials, and (iii) use of chemical treatments. However, the effectiveness of the controlling approaches could be affected by variations in the operating conditions of the process. For instance, by reducing the flow rate of the absorption solution, the corrosion protection efficiency might be deteriorated due to increases in the degrees of process parameters such as CO 2 loading and solution temperature. This would result in excessive corrosion in the system. Therefore, understanding the corrosion behavior due to variations in the process parameters becomes necessary for pre- venting such excessive corrosion. In the present study, comprehensive information on the effect of process parameters on corrosion behavior is provided. The process parameters studied include the type of amine, amine concentration, solution temperature, CO 2 loading, and oxygen (O 2 ) content. Ranges of the testing condi- tions are provided in Table 1. Experiments Experimental Setup. The experiments were carried out in a corrosion cell using an electrochemical tech- nique for corrosion analysis. The experimental setup * To whom correspondence should be addressed. Phone: (306) 585-4726. Fax: (306) 585-4855. E-mail: paitoon@ uregina.ca. 3917 Ind. Eng. Chem. Res. 1999, 38, 3917-3924 10.1021/ie9901630 CCC: $18.00 © 1999 American Chemical Society Published on Web 09/08/1999