Comparative designs and optimizations of the steam ejector for a CHP system

Abstract

High-efficiency heating in the combined heat and power (CHP) system is considered a promising strategy for energy conservation and emission reduction with the explosion of the heating demands. To recover the excessive waste heat from the exhaust steam and reduce the exergy destruction of the heating supply, we proposed a novel CHP cascade heating system integrated with a steam ejector and carried out research about ejector comparative designs and optimizations. Three methods were applied for the ejector designs in a CHP system and the software Fluent was used for numerical simulation to analyze and compare the performance and internal flow characteristics of the ejector. The ejector designed with the optimized thermodynamic method yielded the largest heating capacity and the highest system heating exergy efficiency of 212 MW and 71.0%, thus offering greater strengths for designing ejectors in the CHP cascade heating systems. On this basis, the thermodynamic performance of the designed ejector was further optimized by adjusting the structure of the mixing chamber based on the exergy analysis. The ejector entrainment ratio maximally increased by 11.4% and 6.4% through optimizing the inlet angle and the length of the contraction section of the mixing chamber. Compared with the existing ejector in the CHP heating system, the entrainment ratio of the designed ejector had a significant increment of 24.9% with a higher pressure lift ratio. Meanwhile, the heating capacity of the designed ejector and system heating exergy efficiency improved by 19 MW and 6.1%, respectively. This work provided an applicable method for the ejector designs and optimizations in a CHP system.