Thermodynamic Performance of Molten Salt Heat Storage System Used for Regulating Load and Supplying High Temperature Steam in Coal-Fired Cogeneration Power Plants

Haihua Luo,Shien Sun,Qiang Shen,Houlei Zhang,Yunfei Chen,Junguang Lin,R Weerasinghe,J Wu,C.-H Weng

doi:10.1051/e3sconf/202019401034

Abstract

In order to accept more electricity from renewable energy, cogeneration power plants are considering to reduce electricity production, which affects the heat supply. Here we present a molten salt heat storage system for coal-fired cogeneration power plants, which can supply high temperature steam to users and decouple the heat and electricity production. The first and second law-based analytical models for the cycle and a real device are built. Two water input methods are taken into account. The results show that the high and low temperatures in the two molten salt tanks influence the design of the components and the entropy generation distribution significantly. The pinch temperature difference in the discharge duration limits the lowest molten salt temperature. The device with real heat exchangers produces higher entropy generation and lower second law efficiency. Environmental water input requires more heat and entropy generation for the same steam supply. Recommendations are provided for practical designs.

Highlights

Renewable energy is more and more widely utilized in power generation
The electricity production cannot be dropped too much for ensuring the safety of the equipment and high efficiency
On the other side, when the electricity load decreases, the corresponding heat output may not be enough to fulfill the requirement of the heat users

Summary

Introduction

Many coal-fired power plants in operation are considering (or required) to reduce their load output in order to accept more electricity from renewable energy [1, 2]. On the other side, when the electricity load decreases, the corresponding heat output may not be enough to fulfill the requirement of the heat users To address these problems, some new operation strategies and new techniques have been explored and studied. Li and Wang [5] studied a 600 MW supercritical coal-fired power plant with high temperature salt phase change heat storage. Their simulation results show that the design has faster dynamic response to the load demand changes and the grid frequency services. Based on the analytical results, we may determine the thermodynamic performance and identify the irreversibility distribution for the heat storage system which forms the basis of further design optimization

Configuration of the heat storage system

Thermodynamic cycle model

Steady device model

Thermodynamic cycle analysis

Conclusions