Guide: When shutting down coal-fired boilers, the operation of auxiliary equipment such as water pumps, blowers, and induced draft fans should be stopped in strict accordance with operating requirements to achieve scientific shutdown and maintenance should be done to ensure safe and stable operation of the boiler. How to operate the shutdown of coal-fired boiler? How to reduce the coal consumption of coal-fired boilers?
When shutting down coal-fired boilers, the operation of auxiliary equipment such as water pumps, blowers, and induced draft fans should be stopped in strict accordance with operating requirements to achieve scientific shutdown and maintenance should be done to ensure safe and stable operation of the boiler. How to operate the shutdown of coal-fired boiler? How to reduce the coal consumption of coal-fired boilers?
1. Shutdown operation of coal-fired boilers
The shutdown of coal-fired boilers is divided into normal shutdown and emergency shutdown. The operating sequence for normal shutdown is:
1. Gradually reduce the heat supply, stop coal supply and air supply, and weaken the induced air;
2. When the original fuel in the furnace is basically burned out, stop the induced air, and close the flue baffle, pull out the unburned coal in the furnace, and remove the ash and slag. Then close the furnace door and ash door to prevent the boiler from cooling down sharply;
3. While stopping the operation of the combustion equipment, do not stop the operation of the circulating water pump. The pump can only be stopped when the boiler outlet water temperature drops below 50°C. When stopping the pump, in order to prevent water hammer, the outlet valve of the water pump should be closed gradually, and the pump should be stopped after the outlet valve is basically closed;
4. After shutting down the furnace for 6 hours, open the flue baffle for ventilation. At the same time, the backwater valve and outlet valve of the hot water boiler should be closed to isolate the boiler from the system, and then drain the boiler water;
5. After the boiler is shut down, partitions should be installed in the return water, outlet water, sewage and other pipelines. The thickness of the baffle should ensure that it will not be pushed up by the pressure in the outlet water and return water pipes and the blowdown pressure of other boilers, and ensure reliable isolation from other boilers in operation. Before that, no one should enter the boiler to work.
6. After stopping the furnace and draining the water, the scale and sludge should be removed in time to prevent the scale from becoming dry and hard after cooling (difficult to remove). After the furnace is shut down and cooled, the ash deposits on each heated surface should be removed in time;
There is another situation in the normal shutdown of the furnace, that is, the furnace is shut down by pressing the fire. Pressure fire shutdown is also called temporary shutdown. When the heat user does not need to supply heat temporarily (generally no more than 12h), the furnace can be pressured, and the fire can be started when the operation needs to be resumed. The boiler should minimize the number of times of pressing and shutting down the furnace, otherwise, due to frequent thermal expansion and contraction, additional stress will be generated, causing metal fatigue damage, and causing joints and expansion joints to leak.
There are two types of pressure fire partial pressure full furnace and half pressure furnace. When the furnace is full, use wet coal to completely compress the coal on the grate, then close the air duct baffle and ash door, and open the furnace door. If it can be guaranteed that it will not re-ignite during the pressure, the furnace door can also be closed. . When the furnace is half pressed, the coal is grilled to the front or rear of the grate to gather it, and then pressed tightly with wet coal, close the air duct baffle and the ash door, and open the furnace door, if it can be guaranteed during the pressure fire The furnace door can also be closed without re-ignition.
During the pressurization, the furnace operator shall not leave the operating position. The temperature and pressure of the medium in the boiler should be checked frequently; check whether the air duct baffle and ash door are closed tightly to prevent the pressurized coal from extinguishing or reigniting. In general, the operation of the circulating water pump should not be stopped during the compression fire to prevent boiler water vaporization and pipeline freezing. The operation of the circulating water pump can be stopped only when it is guaranteed that vaporization and freezing will not occur. During the compression fire, once the temperature of the boiler water is found to rise, the circulating water pump should be activated immediately to prevent the boiler water from over-temperature vaporization. When it is necessary to restore the heat supply to the system users and start the fire again, the circulating water pump should be turned on first to allow the water to circulate in the system before the fire can be started.
2. The general procedure for emergency shutdown is
Immediately stop adding fuel and air supply, weaken the induced air, try to extinguish the open flame in the furnace, the layer burning furnace can use sand or wet ash to extinguish the fire, the chain furnace can speed up the operation of the grate, send coal into the slag pit, and the oil and gas furnace stop The operation of the burner; after the fire is extinguished, open the furnace door, ash door and flue baffle to enhance ventilation and cooling; close the main steam valve, open the air valve, safety valve and superheater trap, exhaust steam and reduce pressure; Replace the pot water with the water, and the pot water is cooled to about 70°C and allowed to drain. However, when the boiler is shut down due to a water shortage accident, it is strictly forbidden to pour water on the boiler, and it is not allowed to open the air valve and safety.
3. How to reduce the coal consumption of coal-fired boilers
Improving the thermal efficiency of the boiler is to increase the effective use of heat and reduce the heat loss of the boiler. The key point is to reduce the heat loss of boiler exhaust and mechanical incomplete combustion loss, and reduce the cost of coal-fired boilers.
1. Reduce heat loss of boiler exhaust gas
Reduce the air leakage rate of the air preheater, especially the air leakage rate of the rotary air preheater.
Strictly control the water quality index of the boiler water. When the scale content in the water wall tube reaches 400mg/m, it should be pickled in time.
Try to burn high-quality coal with low sulfur content to reduce the air temperature at the inlet of the air preheater. Modern large-capacity power generation boilers are equipped with air preheaters to prevent condensation on the heated surface of the cold front end of the air preheater, which leads to air preheating. The device is corroded at low temperature. The method of increasing the inlet air temperature of the air preheater and increasing the boiler exhaust gas temperature (increased exhaust heat loss) is adopted to extend the service life of the air preheater.
2, reduce the heat loss of mechanical incomplete combustion
Adjust the combustion conditions according to the boiler load and time, reasonably distribute the air, and reduce the center of the furnace flame as much as possible, so that the coal can be fully burned in the furnace.
Adjust the amount of coal fed according to the volatile content of the raw coal and the time, so that the amount of coal is maintained at the best value.
Reduce the heat loss of the boiler, and mainly strengthen the maintenance and repair of the boiler pipe and the insulation layer of the body.
In order to protect the environment and protect the homes on which mankind depends, environmental protection requirements have become more stringent. Domestic coal-to-gas and low-nitrogen gas-fired boilers have been upgraded successively. Each region has local environmental protection standards. Users must implement local environmental protection requirements before purchasing boilers to ensure Procurement of boilers correctly. The above briefly introduced the method of shutting down the coal-fired boiler and the method of reducing the coal consumption of the coal-fired boiler. I hope it will be helpful to you.