Study of thermal power plant flexible operation via integration of thermal and compressed air energy storage

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Abstract

The utilisation of renewable energy sources for power generation has increased dramatically in the last decade. Due to the unpredictable feature of power generation from renewable energy sources, the high penetration of renewable energy greatly imposes the impact on power system reliability and stability as the balance of power generation and load demand becomes extremely challenging. Currently, the balance is mainly maintained by fossil-fuelled thermal power plants, especially, gas-fired power plants in the UK. In reality, almost all the thermal power plants are designed for base load but they are often required to operate as balance service plants, that is, they frequently change the generation and operation in order to follow the demand changes. This causes three main issues: low operation efficiency, low load factor and short lifetime.

The previous studies focused on the optimisation of control strategies to enhance the operational flexibility of power plants. This thesis explores the potential of integrating energy storage into power plants to achieve flexible operation. The key idea behind is to allow the power plant generation following the electrical load demand but having relatively stable thermal or mechanical energy generation. The main strategy is to integrate energy storage into the power plant energy conversion cycle to create an energy buffer before electricity generation. The thesis investigates the potential of integration of thermal energy storage (TES) with supercritical power plant water-steam cycle and the feasible thermal energy charging and discharging points; studies the strategies for integrating TES and adiabatic compressed air energy storage (A-CAES) with combined cycle gas turbine (CCGT) power plants; and examines the effects on flexible operation for both types of power plants while energy storage process is integrated.

The investigation of integration strategies for supercritical coal-fired power plant with TES is carried out by using a 600 MW power plant simulation platform named SimuEngine. Three TES charging strategies, and two TES discharging strategies are investigated. With the TES integration, the power plant could operate in the range of 520 MW to 644.4 MW under the condition of rated boiler heat generation. XIV

Moreover, supercritical coal-fired power plant shows faster dynamic responses to the load demand variations and performs better in grid frequency control.

A 420 MW CCGT power plant dynamic model is developed in the software platform of Aspen Plus. The integration strategies of the CCGT power plant with TES or A-CAES are studied and presented by using Aspen Plus with the incorporation of FORTRAN subroutines. The dynamic simulation results demonstrate that the proposed integration strategies of the CCGT power plant with TES during the plant start-up, load-following and standby operations is technically feasible. With the TES integration, the steam turbine section could operate in the range of 66 MW to 143 MW, meanwhile, the gas turbine section is still running at the rated load condition. The operation flexibility of the CCGT power plant is significantly enhanced via A-CAES integration. The operation range of the CCGT power plant studied in this thesis is extended to 83-600 MW from 200-430 MW. A case study is carried out to illustrate how the CCGT power plant with A-CAES integration operates flexibly to smooth the gap between wind power generation and load demand.

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