The exploration of the essential need for decarbonization and the achievement of zero energy consumption in the CHP + carbon capture system

Sodium-based CO2 capture technology has considerable potential due to its low investment and simple operation, but it still faces challenges such as high energy consumption for regeneration and high operating costs. This paper presents a comprehensive thermodynamic analysis of the cogeneration and carbon capture system, highlighting that the fundamental requirement for carbon capture is exergy rather than heat. Moreover, this paper proposes a new concept of carbon capture “taking exergy instead of heat”, and optimizes the exergy-heat transfer network of the cogeneration + carbon capture system according to the proposed concept. This innovation realizes carbon capture with zero energy consumption. This research utilizes Aspen Plus to simulate a 300 MW cogeneration and sodium-based CO2 capture system. The findings reveal that the system can utilize a maximum of 18.45 % of the heat generated from decarbonization reactions before optimization. However, with optimization, the system can achieve 100 % heat utilization during carbon capture, enabling zero-energy carbon capture. Additionally, the thermal efficiency of the optimized system is increased by 43.6 % at maximum, and the maximum thermal efficiency reaches 117.45 %. The results of the exergy analysis show that the ordinary exergy efficiency of the system is only increased by a maximum of 4.55 % after the optimization, and this ordinary exergy analysis may not be sufficient to evaluate the combined exergy and heat use efficiency of the system. Therefore, in this paper, the objective exergy efficiency is introduced to evaluate the system from the point of view of the exergy conversion objective. This study offers significant application prospects and technical guidance for cogeneration plants and sodium-based CO2 capture technology.