Boiler/water tank insulation With the development of China's power industry, in order to improve the economy of power plant operation and reduce pollution emissions in recent years, the state in the increasingly mature supercritical technology on the basis of the implementation of ultra-supercritical power generation technology research, Plant 1000MW Level project, relying on, research and development of China's independent property rights of ultra-supercritical generating units, and in ultra-supercritical boilers,Boiler/water tank insulation the start-up system is one of the key technologies to ensure that the unit safety, economic start and stop, low load operation and proper Accident handling of the important means to start the system to be selected to consider its technical characteristics, system investment and power plant operation mode and other factors.
Ultra-supercritical boilers are the direct current furnace, the DC furnace must be started before the start of a certain start-up flow and start-up pressure, forced fluid flow through the hot surface, to get cooling. However, the DC boilers do not have a drum as a whisker as a fixed point, and water is steamed directly in the boiler tube, steamed and overheated directly to the steam turbine, and may be provided during start-up and low-load operation Not qualified steam, is a soft drink mixture, or even water. Therefore,Boiler/water tank insulation the DC boilers must be equipped with a unique start-up system to ensure the safety and normal steam supply of the water wall during boiler start-up and low-load operation.
The start-up system of the direct current furnace is divided into a built-in splitter start-up system and an external splitter starting system, depending on whether the splitter is in the normal operation of the system or in the system.
1) External splitter start system
External start-up system refers to the start-up separator in the unit start and outage process put into operation, and run above the DC load solution out of the system outside the start system, the system is suitable for constant pressure operation.
Figure 1 is a composite cycle of the external splitter start system. The boiler is equipped with boiler throttle BT and throttle bypass valve BTB, its role is to control the water wall pressure within the specified range.
The start-up process is as follows: After the boiler is ignited, the BEB valve is opened with the temperature of the working temperature of the water wall. After opening the BE valve to control the water wall pressure, BT and BTB valves are closed. The steam separated by the separator is sent to the superheater to raise the temperature of the superheater and the main steam pipe, and the hydrophobes are sent to the condenser via the motor bypass valve SD. The steam of the separator can also be sent to the deaerator or AA valve as auxiliary steam source via DA valve. When the separator pressure of 6MPa, with SP valve control pressure unchanged,Boiler/water tank insulation WD valve control water level. Boiler throttle (BT, BTB) before the working temperature of 415 ℃ into the separator after all the working fluid into steam, WD valve closed; after the beginning of the removal of the separator, BT, BTB valve decompression, steam into the superheater The
Outside the start-up system is difficult to control the boiler steam temperature, water wall refrigerant in the start-up phase has been in a state of high pressure,Boiler/water tank insulation complex operation, not suitable for quick start and stop, only with the basic load. In addition, due to the large fluctuations in the system steam temperature, the operation of the turbine is not conducive, therefore, the current foreign super-critical unit start-up system has rarely used this start system.
) Built-in separator to start the system
Built-in start-up system refers to the start of the unit, the normal operation, outage process, start the separator are put into operation, the difference is in the boiler start and stop and low load operation, start the separator wet operation, (Usually 30% BMCR or 35% BMCR) during normal operation of the boiler (the load is above the minimum DC load). The microheated steam from the water wall passes through the separator and enters the superheater, where the separator is only connected Channel effect. The start-up splitter of the built-in start-up system is located between the evaporation zone and the overheated section. There is no valve between the start-up separator and the evaporator and the superheater. The system is simple and easy to operate and does not require an external boot system Separator disassembly or commissioning operation, fundamentally eliminates the separation of the separator or put into operation caused by the steam temperature fluctuations, but the separator to withstand the full pressure of the boiler,Boiler/water tank insulation its strength and thermal stress requirements are higher. The built-in splitter start-up system is suitable for pressure-operated boilers. At present, in the world super (super) critical boiler, built-in boot system is widely used.