Influence of stripper operating parameters on the performance of amine absorption systems for post-combustion carbon capture: Part II. Vacuum strippers

Abstract

The alkanolamine absorption process is viewed favorably for use in the separation of carbon dioxide (CO2) from point emission sources such as coal-fired power plants. At present, natural gas sweetening is the most important application for this technology. However, on a number of accounts such as the feed conditions of gas, its composition and process economics; natural gas sweetening and carbon capture are very different applications. Current technology is optimized toward providing a high performance for the former. As a part of this two-part study, we have used the process simulation software ProMax® to perform a detailed analysis on the effect of stripper operating pressure on factors like reboiler energy duty, absorber and stripper column sizing and parasitic power loss. We have examined the performance of monoethanolamine (MEA), diethanolamine (DEA) and diglycolamine (DGA) which are all commercial absorbents that can be reliably modeled in ProMax®. In part I of this study, we have analyzed the performance of strippers operated at pressures ranging from 150kPa to 300kPa. In this part of the study, we examine the performance of vacuum strippers operating under low vacuum at pressures of 30kPa, 50kPa and 75kPa. Since vacuum strippers operate at lower temperatures than conventional stripper configurations, it is possible to use waste heat in the reboiler. In this study, we explore this possibility and consider 5 scenarios in which varying fractions of the reboiler steam are provided from waste heat sources located outside the turbine system. As with the cases presented in Part I, our comparisons of different configurations are based on energy consumption and column dimensions required for 90% CO2 capture (separation+compression) from a 400MW coal-fired power plant. CO2 separated from the flue gas is compressed to a pressure of 16MPa, typically maintained in the pipelines. On the basis of our findings, we report that vacuum stripping is an attractive alternative to conventional stripping. It is particularly attractive if significant sources of waste heat outside the turbine system can be located. We also conclude from our work that DEA and DGA have a superior performance than MEA when vacuum strippers are used. Use of vacuum strippers will certainly result in increased capital costs due to the need for larger equipment. However, in the view of potential savings in operating costs mainly by reduction in parasitic power loss; the increased capital expenditure may be justifiable.