Efficiency improvements for the coal-fired power plant retrofit with CO2 capture plant using chilled ammonia process

• NH3 has been proposed as a viable solvent to reduce the efficiency penalty.
• Retrofit of a coal-fired power plant with a chilled ammonia process was analysed.
• A base case scenario showed that efficiency penalty fell between 10.4% and 10.9%.
• Alternative process configurations for the efficiency improvement were investigated.
• The efficiency penalty was reduced to 8.7%.

Development of clean coal technologies for power generation is crucial in meeting the European Union 2050 target to reduce greenhouse gas emissions. CO2 capture technology using chemical solvents currently has the highest potential to decarbonise coal-based power generation. Substitution of amine solvent with NH3 has been proposed as a viable option to reduce the efficiency penalty. In this study, the scenario of a supercritical coal-fired power plant retrofitted with a chilled ammonia process capture plant and CO2 compression unit was modelled in a common simulation environment. To fully assess the integration impact on power plant performance, the pressure loss due to steam extraction has been taken into account by using the Stodola ellipse law. Analysis of a basic integration scenario revealed that the efficiency penalty fell between 10.4% and 10.9% points depending on the stripper pressure. The quality of extracted steam became insufficient to meet the reboiler heat requirement above a stripper pressure of 21.8 bar, and the lowest efficiency penalty was obtained when reboiler condensate was returned to the deaerator in the power plant. In evaluating measures to improve integration, the efficiency penalty was reduced to 8.7–8.8% points through the integration of a single-stage or two-stage auxiliary steam turbine, respectively, and a back-pressure turbine. Nevertheless, the analysis has indicated that the net impact on power plant performance is similar to that of an amine-based post-combustion CO2 capture plant.

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