A novel cascade heating system for waste heat recovery in the combined heat and power plant integrating with the steam jet pump

Abstract

Waste heat utilization is an essential approach for improving the energy utilization efficiency of the combined heat and power (CHP) plant and a significant low-carbon way to achieve clean urban heating. To recover the excess exhaust steam heat of the CHP plant with the high back-pressure turbine (CHP-HBP), this paper proposed a novel heating system integrated with the steam jet pump (SJP). The EBSILON software was applied for modeling the proposed thermal system and analyzing the thermal performance of the CHP-HBP heating system under different operating conditions. On this basis, the coupled component-system design solution was proposed by combining the 1-D mathematical design model of the SJP with the heating system performance. Compared with the conventional system, under the design condition, the exhaust steam recovery rate and the heating capacity of the novel system had a significant increment of 8.66% and 31.8 MW with the same power output. Meanwhile, the total exergy loss and standard coal consumption rate for electricity generation of the novel system reduced by 5.74 MW and 6.77 g/kWh, respectively, with about 2.32% improvement in electricity generation efficiency. The critical parametric influence analysis on the overall performance showed that the novel system has better adaptability with some fluctuations of turbine back-pressure, supply/return water temperatures, and heating load. Under off-designed conditions, the recovery rate of the exhaust steam of the novel system was 5–20% higher than that of the conventional system, and the coal consumption rate and electricity generation efficiency both performed better. In all, the proposed system provided a promising method for the effective utilization of waste heat in the field of clean heating and the energy system optimization and integration for the coal-fired CHP plants.