Shutdown maintenance of hot water boiler and steam boiler

Shutdown maintenance of hot water boiler and steam boiler In the operation of steam boiler, hot water boiler, gas boiler, oil boiler, coal-fired boiler, and energy-saving and environmental protection boiler, the boiler often needs to be shut down due to accidents, failures, power outages and the end of boiler operation, which involves the operation process of boiler shutdown and the maintenance work after boiler shutdown The following is an introduction of boiler shutdown methods and maintenance Steam boiler, hot water boiler, gas boiler, oil boiler, coal boiler, energy saving and environmental protection boiler shutdown can be divided into three situations: pressure fire shutdown, normal shutdown and emergency shutdown The first two are planned shutdown The combustion shall be stopped slowly and the load shall be reduced until the load of hot water boiler is reduced to zero The latter is the boiler in operation accidents, emergency interruption of combustion, so that the boiler load sharply reduced to zero Pressure fire (hot standby) boiler shutdown: when the external load is reduced, the boiler can be used for pressure fire to suspend the operation of one or several boilers In this way, when the load is increased, the stopped boiler can resume normal operation at a fast speed of Zui, which can avoid the preparation of ignition and shorten the time of pressure rise Pressure fire operation method of steam boiler: Before the boiler is pressed to fire, the party actually reduces the boiler load, and then thickens the coal seam (generally no more than 200 mm) according to the length of the boiler shutdown time, and properly speeds up the grate When the thickened coal seam is about 1 mm away from the laomm Eagle Iron (slag stopper), stop the turning of the grate, stop the blower and induced draft fan, and turn down the regulating plate and flue damper of sectional air supply properly, depending on the self However, the ventilation maintains the weak combustion of coal, and then carries out the blowdown to raise the boiler water level to Zui high allowable water level If the coal ram is burnt out, the grate can be started again to move the coal backward for a certain distance When the boiler needs to be restored to operation, it can be restored to operation as long as the induced draft fan and blower are started, the opening of smoke, air baffles and sectional air chamber baffles are adjusted, the thickness of coal seam is adjusted when the combustion is normal, and the grate is started Hot water boiler fire suppression operation method: hot water boiler usually adopts intermittent operation mode For the combustion method of stratified equipment, wet coal can also be used to completely compress the coal on the grate to shut down the boiler After the fire is put out, the air duct baffle and ash door shall be closed and the furnace door shall be opened (if there is no re combustion during the fire suppression, the furnace door can also be closed) However, it should be noted that the operation of the circulating water pump should not be stopped immediately after the shutdown of the pressure fire The network circulating water should continue to circulate in the system for a period of time The operation of the circulating water pump can be stopped only when the water temperature at the outlet of the boiler drops below 50oc Because the temperature of the furnace is still very high at this time, if the pump is stopped, the water circulation of the system will be interrupted immediately For the forced circulation hot water boiler, because of the stop of the water circulation, the boiler water will vaporize and water hammer or the high temperature heating surface will overheat and burn out Precautions for boiler shutdown under pressure fire: there is still steam pressure in the boiler during shutdown under pressure fire, so it is still necessary to pay attention to monitoring and keep the boiler at Zui high allowable water level; if the shutdown under pressure fire lasts for more than 6h, close the main steam valve of the boiler and open the drain valve of the superheater outlet header to cool the superheater If the air pressure rises after the main steam valve is closed, the pressure can be reduced by feeding water into the boiler and discharging at the same time When the boiler is restored to operation, it needs to go through the steps of boosting pressure and protection; during the period of fire suppression and boiler shutdown, it is necessary to properly discharge the sewage and remove the sediment in the boiler; for the boiler equipped with cast iron economized gas, after the boiler stops feeding water, it is necessary to close the economized gas flue damper, open the side flue damper or use it in the circulation pipeline, and stop the water temperature in the economized gas exceeding the specified value Normal hot water boiler shutdown is called normal shutdown because of load reduction, end of heating period, maintenance and other original reasons Normal boiler shutdown is generally carried out in the following order: stop fuel supply; stop air blowing, and then stop induced air; stop water supply, reduce pressure, and close water supply valve; close steam valve, open drain valve; close flue damper Emergency shutdown: in case of an accident during the operation of the boiler, if the boiler is not shut down immediately, it is possible to expand the risk of accident to personal and equipment Therefore, the boiler must be shut down immediately, which is called emergency shutdown The operation method of emergency shutdown of steam boiler: firstly, stop the coal supply and air supply The chain boiler shall be hung with arc damper closed The coal spreader boiler shall stop the coal throwing, reduce the induced air and close the flue damper According to the nature of the accident, some need to release the coal in the furnace, some don't want to release the coal The way to release the coal is: the grate shall send the coal into the ash hopper at a high speed of Zui After the coal ash hopper, water or sand can be used to extinguish the fire, and wet ash can be pressed on the coal to extinguish the fire, but under no circumstances shall water the furnace to cool the boiler After the steam boiler goes out, the main steam valve shall be closed to isolate the main steam pipe from the main steam pipe, and the induced draft fan shall be closed at the same time If necessary, the air valve, safety valve and Superheater drain valve can be opened to quickly discharge steam and reduce pressure Open the bypass flue of the provincial gas, close the main flue, and open the large flue damper, ash door and furnace door to promote air dredging and improve the cooling speed When the boiler is shut down in an emergency, there is no water shortage or full water The way of water supply and blowdown can be used to accelerate the cooling and reduce the pressure of the boiler When the water temperature drops below 70oC, drain the water In case of emergency shutdown due to water shortage of the boiler, it is forbidden to feed water to the boiler, or open air valve or lifting safety valve, etc to strengthen the adjustment of exhaust gas, so as to prevent the boiler from expanding the accident due to sudden temperature or pressure change In case of full water accident of the boiler, the water supply shall be stopped immediately, the ventilation and flue damper shall be turned down, the combustion shall be reduced, and the drain valve shall be opened to drain the water, so as to reduce the water level properly; meanwhile, the drain valves on the main steam pipe, superheater, main steam pipe and sub cylinder shall be opened to prevent large amount of water carried by the steam and water impact in the pipe Emergency shutdown of hot water boiler: in case of emergency shutdown, the fuel supply shall be stopped immediately, and if necessary, the coal in the boiler shall be removed or the fire shall be extinguished with ash If the circulating water pump is normal, the pump shall not be stopped immediately The operation of the circulating water pump can only be stopped when the water temperature at the boiler outlet drops below 50oc Shutdown maintenance After the boiler stops and discharges water, the humidity in the boiler is very high, and the ventilation is poor The metal surface of the boiler is in a humid state for a long time In this way, under the action of oxygen and carbon dioxide, the metal of the boiler is corroded and rusted After the boiler is put into operation, the corrosion in the high-temperature boiler water continues to produce strong electrochemical corrosion, which leads to the deepening of corrosion and the expansion of the area, and the thinning of the metal wall of the boiler However, the strength of the pressure parts of the boiler is reduced, which will threaten the safe operation of the boiler and shorten the service life of the boiler Therefore, in order to ensure the safe and economic operation of the boiler, it is necessary to do a good job of anti-corrosion maintenance after boiler shutdown According to the length of shutdown time, boiler anti-corrosion maintenance usually includes thermal maintenance, wet maintenance and dry maintenance Thermal maintenance is applicable to hot standby; wet maintenance is applicable to short-term (generally no more than one month) shutdown; long-term shutdown with shutdown time more than one month adopts dry maintenance Thermal maintenance: keep a certain pressure in the hot water boiler, about 0.05-0.1mpa, so that the boiler water temperature is higher than 100oC and there is no nourishing condition, and the pressure in the boiler can prevent the outside air from entering the drum In order to maintain the temperature of boiler water, steam from other boilers can be used to heat the boiler water When there is no steam source for a single boiler during maintenance, it can be set to live in the furnace This method is generally used for hot standby boiler or boiler with shutdown time less than one week Wet maintenance is to use a certain concentration of alkaline solution to contact the metal on the inner surface of the boiler to form an alkaline protective film on the metal surface to prevent metal corrosion After the boiler is shut down, drain the boiler water, clear the scale and soot, close all the access holes, hand holes, valves, etc., and completely isolate the boiler from other running boilers Then the softened water is made into the boiler and injected to the low water level of Zui, and then the configured alkaline anti-corrosion liquid is injected into the boiler with a special pump The composition of the antiseptic solution is: sodium hydroxide, add 5-6kg per ton of pot water Or add 5-10kg of sodium carbonate per ton of boiler water When all the corrosive liquid is injected, open the feed valve to fill the boiler with softened water (including superheater and boiler economizer), until the boiler water emerges from the air valve At this time, close the air valve and feed water valve, and then open the special pump for water circulation, so as to make the concentration of the alkaline anti-corrosion solution in all parts of the boiler mix evenly During the maintenance period, external inspection shall be carried out frequently, and the alkalinity of the boiler water shall be tested regularly If the liquid level or alkalinity is found to drop, the cause shall be found out and treated in time, and the alkali solution shall be added; the pump shall be opened regularly for water circulation, so that the concentration of alkali solution everywhere is the same; the boiler water shall be prevented from freezing in winter, and the open-air boiler cannot be maintained by wet method When the wet maintenance Boiler returns to operation, the boiler water shall be discharged completely and the softened water shall be added again Dry method maintenance: dry method maintenance is to use the dryer to absorb moisture to keep the metal inside the boiler dry, so as to prevent the corrosion of the boiler Generally, quicklime or anhydrous calcium chloride is used as the desiccant After the boiler is shut down, drain the boiler water, remove the scale and soot, close the steam pipe, valves on the water supply pipe and drain pipe, and completely isolate the boiler in operation Then open the inlet hole to make the drum dry naturally If the boiler room is wet, Zui can use low fire to dry the boiler body, furnace wall and flue Then put the tray (or wooden box) containing quicklime or anhydrous calcium chloride on the furnace plate, as well as the drum header and flue, and if necessary, lift it in the drum with a cloth bag to absorb the moisture The amount of desiccant is determined according to the boiler volume: block quicklime, 2-3kg per cubic meter of boiler volume; if anhydrous calcium chloride is used, 1-2kg After Zui, close all valves of the boiler, such as holes, hand holes, and smoke to the wind shield and damper, so as to isolate the boiler from the outside and prevent the invasion of outside moisture During the maintenance, check the desiccant condition every 1-2 months If the quicklime changes from block to powder, replace it with new quicklime Check frequently at the beginning of maintenance The invalid calcium chloride can be heated to 105-110oc and dried before reuse The practice shows that the effect of dry maintenance is satisfactory, the cost is very low, and the operation is simple Therefore, it is suitable for any type of boiler for long-term shutdown maintenance, especially for the heating hot water boiler in summer The above are several aspects in the process of shutdown and maintenance of hot water boiler In addition, attention should be paid to the maintenance of auxiliary equipment, accessories and furnace wall, and regular and planned maintenance is an important link to ensure the safe, reliable and economic operation of boiler.