Study on Post Combustion CO₂ Capture in Power Plant Integrated With Double Absorption Heat Transformer

In this paper, a new CO₂ capture method is proposed. A double absorption heat transformer (DAHT) will be employed to upgrade the energy level of the low-temperature extraction steam from the last stage of the steam turbine and make the temperature of the steam more matched with the CO₂ regeneration process. At the same time, the exhaust heat in the flue gas of the boiler will be recovered to preheat the circulation water and thereby the energy penalty can be further reduced. The system is simulated with the aid of Aspen Plus software and the results are verified by the experimental data. The results show that the power efficiency enhancement in the proposed method has a trend of increase first and then decrease with CO₂ capture rate. For a 350 MW coal-fired power plant, the optimum CO₂ capture rate is 53.65% and the corresponding efficiency enhancement is 2.06 percentage points. With 90% CO₂ capture rate, 10.5% energy penalty can be reduced in the proposed method compared with the traditional mode, and the energy efficiency will be improved by 1.25 percentage points. In our study, the cascade utilization of the thermal energy is achieved and the irreversible destruction in the CO₂ regeneration process is reduced. The investigation in this paper provides a new way to reduce the energy penalty in CO₂ capture.