Polygeneration is identified as an effective way to overcome the challenges of energy efficient utilization and CO₂ emission reduction. This paper analyzes the energy saving mechanism and carbon reduction laws of decarbonized polygeneration systems, and discusses the compatibility of CO₂ capture for different integral schemes. Based on the novel method of chemical exergy balance, two typical methanol-power polygeneration systems with CO₂ recovery are analyzed in detail, and integral factors that indicate the level of energy cascade utilization and the compatibility with CO₂ capture are proposed. Both polygeneration systems show large performance improvements compared to the single production systems, but the advantages of scheme (b), removing the composition adjustment and capturing CO₂ from unrecycled gas after synthesis, are more prominent. This scheme has an excellent compatibility with CO₂ recovery, and it shows a fairly optimal performance in the full working field. Further, according to the analysis of the integral factors, a higher CO₂ recovery ratio is recommended for scheme (b), while a lower one is recommended when scheme (a) is employed.

Fuel conversion is accompanied by the enrichment of CO_x, and a polygeneration system has the potential to capture CO₂ with a low energy penalty. This paper analyzes the energy saving performance of two typical methanol-power polygeneration systems with CO₂ recovery. It shows that Scheme (b), the integral scheme of removing the composition adjustment and capturing CO₂ from unrecycled gas after synthesis, has better performance and combines CO₂ capture in a more compatible way. Compared to the polygeneration system without CO₂ capture, not only does ESR not decrease apparently, but it yields a fairly optimal performance in the field. Further, by dividing exergy into physical exergy and chemical exergy, this paper proposes a novel exergy analysis method. This method provides the ability to omit the physical processes in a complex system and simplify the system into one with only chemical processes, which more easily reveals the mechanism of chemical energy cascade utilization. According to the chemical exergy balance analysis, integral factors that indicated the system integral level are proposed. The performance improvements of polygeneration systems are attributed to three aspects: profit from chemical energy cascade utilization, profit from energy penalty reduction of CO₂ capture and the effects of related physical processes. From this new perspective, this paper reveals the energy saving mechanism of polygeneration and proposes the integration principles of CO₂ recovery to provide guidance for actual production. First, for different integral schemes, the profits from chemical energy cascade utilization are very similar when chemical production is required, and the difference in integral level is mainly due to benefits from the penalty reduction of CO₂ recovery. As a result, those schemes with greater potential to obtain a higher CO₂ concentration should have a higher priority. Second, a higher demand of CRR (>90%) is recommended for Scheme (b), since the advantage of CO₂ separation in this scheme is prominent when a higher CRR is demanded. If a higher chemical production that exceeds the production capacity of Scheme (b) is required, Scheme (a) should be employed. Combined with the analysis of integral factors, the compatibility between chemical energy cascade utilization and CO₂ capture in Scheme (a) has been proven stronger at a lower CRR (<66%).