Optimization of heat source side technical scheme of combined heat and water system based on a coal-fired power plant

Recovering the waste heat (WH) of a power plant can conserve energy and reduce emissions. Scholars have proposed utilizing the WH of power plants in a combined heat and water (CHW) system, which is considered an economical, energy-saving, and environment-friendly way to integrate water and heat supply into long-distance transportation in urban areas of northern China. However, to date, a detailed design of the case on the heat source side of the CHW has not been developed. Therefore, in this study, the heat source side of a CHW system was divided into two cases: a single-generator set and a double-generator set, and both cases were optimized. The parameters of a multi-effect desalination (MED) process were examined; the optimal number of evaporation stages during the MED process was 12, and the optimal heat source temperature during the first stage was 70 °C. Then, by matching the extraction and exhaust steam flows, the WH of the exhaust steam in the heating season was finally utilized. Further, under each case optimal conditions, energy, exergy, and cost were analyzed. The results showed that the exergy efficiency in the heating season for each case was approximately 50%, whereas that in the non-heating season was approximately 3.5%. The economy and water quality of the single-generator case were better than those of the double-generator case. However, the absorption heat pump required in the single-generator case is difficult to realize because it operates under two working conditions.