Dynamic modelling and analysis of post-combustion CO2 chemical absorption process for coal-fired power plants

Abstract

Post-combustion capture by chemical absorption using MEA solvent remains one of the most popular technologies for CO 2 emission mitigation for coal-fired power plants. This paper presents a study of the dynamic responses of a post-combustion CO 2 capture plant by modelling and simulation. Such a plant consists mainly of the absorber (where CO 2 is chemically absorbed) and the regenerator (where the chemical solvent is regenerated). Model development and validation are described followed by dynamic analysis of the absorber and regenerator columns linked together with recycle. The gPROMS (Process Systems Enterprise Ltd.) advanced process modelling environment has been used to implement the proposed work. The study gives insights into the operation of the absorber-regenerator combination with possible disturbances arising from integrated operation with a power generation plant. It is shown that the performance of the absorber is more sensitive to the molar L/G ratio than the actual flow rates of the liquid solvent and flue gas. In addition, the importance of appropriate water balance in the absorber column is shown. A step change of the reboiler duty indicates a slow response. A case involving the combination of two fundamental CO 2 capture technologies (the partial oxyfuel mode in the furnace and the postcombustion solvent scrubbing) is studied. The flue gas composition was altered to mimic that observed with the combination. There was an initial sharp decrease in CO 2 absorption level which may not be observed in steady state simulations.

Dynamic simulation of MEA absorption process for CO2 capture from power plants

“…That is, the integration between absorber and stripper, which represent the complete MEA absorption process, was not considered in those studies. Lawal et al (2010) extended their previous models (Lawal et al, 2009a;Lawal et al, 2009b) to consider the complete MEA absorption process by integrating both absorber and stripper with the recycle stream. The analysis of the dynamic response with respect to changes in flue gas flow rate and compositions, and reboiler heat duty were discussed.…”

“…The constants used in this equation are given in Table 3.10. (Kvamsdal and Rochelle, 2008;Kvamsdal et al, 2009;Lawal et al 2010), the dynamic model developed in this work was also implemented in gPROMS. Also, gPROMS is also a suitable tool to conduct controllability studies.…”

“…The inlet conditions entering the heat exchanger for the tube and shell side are shown in Table 4.16. The length and number of tubes were determined such that the temperature of liquid stream entering the stripper was about 80 o C (Lawal et al, 2010). The shell diameter was calculated using the preferred tube length to shell diameter ratio which is in the range 5 to 10 (Edwards, 2008).…”

“…Also, the reboiler heat duty has also been proposed by previous control studies to control the reboiler temperature, e.g., Lawal et al (2010) and Lin et al (2011). The other input variable that can be considered as manipulated variable is the valve stem position that regulates the amount of lean liquid solvent flow rate that enters at the top absorber column.…”

“…Accordingly, the lean solvent flow rate directly affects the CO 2 absorbed in this process can be potentially used to control the percentage of CO 2 absorbed. The previous control studies of the MEA absorption process published in the literature also manipulate the lean solvent flow rate to control the percentage of CO 2 absorbed in the absorber column (Lawal et al, 2010;Lin et al, 2011).…”