Coal-fired power plant is utilizing the heat energy into mechanical energy to generate power. The production process of coal-fired power plant is a process of energy conversion, it utilizes the chemical energy contained in fuels (coal, oil, or natural gas, etc.), to become heat energy by combustion and pass the heat energy to the water in the boiler to make the water become steam with a certain pressure and temperature, which is guided to the steam turbine; In a steam turbine, the steam expands and works to convert the heat  energy into mechanical energy, to promote the steam turbine rotor to rotate. The steam turbine rotor drives the generator rotor to rotate in high-speed, thus converting the mechanical energy into electrical energy to the grid. So, in the production process of coal-fired power plant, water plays a important role in energy transferring and plays a role of cooling the medium.