Problems with fuel boilers

Sliding parameter shutdown essentially means the simultaneous shutdown of both the boiler and the turbine. Under rated parameters and load conditions, the unit reduces the load on the turbine by gradually lowering the boiler’s steam pressure and temperature. Once the steam pressure and temperature reach certain values (specific values are specified by each plant), the boiler can be shut down. After the boiler is shut down, the turbine can continue to generate electricity using the low-temperature, low-pressure steam produced by the residual heat of the boiler. Generally, the generator is disconnected only when the steam pressure approaches zero. Throughout the process of reducing pressure and load in the entire unit, it is achieved by the boiler adjusting the combustion, in accordance with the requirements regarding steam temperature and pressure when the turbine reduces its load. Of course, the speed of pressure and temperature reduction also needs to take into account the cooling requirements of the boiler itself. For high-parameter, large-capacity units, the rate of decrease in superheated steam temperature should be controlled at 1–1.5°C/min ； The rate of decline in the reheat steam temperature is controlled at 2°C/min. Sliding parameter shutdown has the following advantages: (1) it reduces the overall cooling time of the plant. (2) Improved security. During the load reduction process, although the steam parameters gradually decrease, there is still a high volumetric flow rate, which provides good cooling effects for the components. Therefore, sliding-parameter shutdown is beneficial for protecting the heating surfaces of the boiler, for reducing the temperature difference between the upper and lower walls of the steam drum, for reducing the temperature difference between the upper and lower parts of the turbine cylinder, and for reducing the thermal expansion difference between the moving and stationary parts of the turbine. (3) The improved economic efficiency of shutting down the furnace is mainly achieved by utilizing the time when steam is discharged and the time required for cooling equipment to generate electricity, as well as by reducing losses of working fluid and heat.