0086-510-85187837 24/7 Helpline
author：fly boy 2019-12-17
An accident in which the fuel in a boiler or flue explodes suddenly and violently, causing a sudden increase or softening of the gas pressure.
Under normal circumstances, the fuel into the furnace is immediately ignited, the smoke generated after combustion is discharged at any time, there is no combustible mixture in the furnace and flue, so there will not be an explosion.But if the improper operation personnel operating sequence, equipment or control system design is unreasonable, or equipment and control system failure is likely to happen a lot of fuel, gathered in the chamber of a stove or furnace explosion happened when meet fuel ignition can (furnace temperature), the furnace fuel stored up suddenly was lit, the flame propagation speed quickly, the generated flue gas volume increases suddenly, not by the chamber of a stove or furnace, making furnace pressure increase, more than the furnace wall of furnace explosion when it maximum pressure.
There are two kinds of external explosion and implosion, the former is the combustion of combustible mixture gathered in the furnace or flue, resulting in a rapid uncontrolled explosive combustion, rapid expansion of the gas accumulation, so that the furnace wall or flue to the outside burst.The latter is the furnace extinguish the fire, the smoke volume decreases rapidly with the temperature decreases, at this point, if send, lead the fan to adjust improper draft fan pumping force instant is too big, make furnace wall or flue to bear very big negative pressure and burst to the inside (large capacity boiler easy to appear this problem).Burst damage is very big, especially the external explosion, not only will cause the furnace or flue rupture, the steel frame of the boiler bending or fracture, but also will make the relevant heated surface tube damage and cause human casualties, repair work is difficult, long time out of service, direct and indirect losses are very large.
The accumulation of combustible mixtures in a furnace
When the furnace is in normal operation, the fuel sent into the furnace is ignited immediately, and the flue gas generated after combustion is discharged immediately. No combustible mixture accumulates in the furnace and flue, so the furnace explosion will not occur.A small amount of combustible mixture stored in a large volume furnace, even if deflagration, is only "shooting", will not cause damage.
When putting out the fire in the furnace, it is necessary to cut off all the fuel in time. The more quickly the fire is cut off, the less fuel enters the furnace, the safer the boiler will be.If all the fuel cannot be cut off in time after firefighting in the furnace, the storage capacity of fuel will increase with time.At the same time, a few fuel is pumped to the tail of the boiler, accumulate a large amount of fuel in high temperature furnace temperature rise slowly, and oxidation accelerated, traditional operas air volume at this time if no oil ignition or close to the furnace pressure was positively "cannons", even can make a large amount of fuel such as coal burning rapidly in a short time, caused the explosion.This deflagration energy is very large, easy to cause injury or damage to boiler equipment.In fact, a certain amount of fuel has entered the furnace during the period from the discovery of fire extinguishing to the cutting off of fuel. In addition, the lag time of the coal feeder, the lag of the valve and baffle and the lax closing may make the fuel quantity into the furnace reach the concentration of deflagration.Misjudgment and misoperation (such as continued use of powder and oil) will further increase the accumulation of fuel and combustion air.The most likely dangerous working conditions for combustible mixture accumulation in the furnace are as follows:
(1) the whole furnace is shut off without detection, resulting in the accumulation of combustible mixture of fuel and air, which will cause deflagration once ignited again;
(2) in the normal operation of multiple burners, when one or more burners suddenly lose flame and cannot be continued to ignite in the furnace, thus accumulating combustible mixture;
(3) fuel leakage into the deactivated furnace.Therefore, it is very important to purge the furnace before ignition and after fire extinguishing, and to close the coal mill's gate, oil gunner moving door and gas door timely after boiler shutdown
Fire extinguishing or combustion deterioration in furnace
Practice has proved that fire extinguishing is the most common cause of furnace explosion.Furnace fire extinguishing refers to the sudden interruption of the combustion in the furnace, boiler combustion instability is often the omen of furnace fire extinguishing.The following reasons often cause the boiler combustion instability, and even fire suppression in the furnace:
(1) the boiler auxiliary machine fails, such as induced fan, blower, coal mill and so on suddenly stop operation;
(2) improper switch of burner and operation of coal mill;
(3) the water-cooled wall blowing dust is not timely, resulting in a large area of slag, extinguish the flame;
(4) the water-cooled wall bursts the tube, and a large amount of soda water is ejected to blow out the flame and lower the temperature of the furnace;
(5) the single-end operation of double-in and double-out coal mill makes the interval between the combustors put into operation too big;
(6) improper automatic treatment (burner management) in case of (turbine fault quick load drop) or (boiler fault quick load drop);
(7) the fuel properties change suddenly, the stoker is not adjusted in time, and the new fuel after the change cannot adapt to the wind distribution of the original fuel, especially when the volatile content of the fuel decreases;
(8) failure of coal due to various reasons (such as failure of coal mill and coal feeder in direct blowing system, blockage of raw coal pipe, separator, primary air pipe, burning empty of raw coal bunker, failure of powder feeder in middle storage system, burning empty of powder bunker, blockage of lower powder pipe, blockage of primary air pipe, failure of powder exhausting machine in desiccation powder feeding system, etc.);
(9) long time of low-load operation or leakage into the furnace of a large number of cold air, resulting in a very low temperature drop in the furnace, causing serious fire extinguishing;
(10) severe coking in the furnace destroys the normal power field in the furnace, resulting in poor mixing of wind powder in the furnace;
(11) improper operation of ash blowing and defocusing, improper operation of fan and nozzle, unstable adjustment of combustion, improper operation, etc.;
(12) during the boiler starting process, the first coal grinder is not fully warmed before running, or there is not enough temperature and ignition energy to ignite the coal powder in the furnace.
The main purpose is to prevent firefighting in the furnace and correct handling after firefighting, stop sending people fuel to the furnace, and then light the fire according to the regulations after purging.In addition, according to the size of the boiler capacity, the furnace safety monitoring system should be set up, such as furnace pressure protection and flame monitor.For large capacity boiler furnace should be equipped with t more perfect furnace safety monitoring system, it has the furnace flame monitoring, report to replace, automatic timing blowing and furnace pressure protection, fire protection, automatic removal of fuel (MFT) and other functions, is one of the most effective means to prevent the outside of the furnace.In terms of preventing implosion, in addition to the strength design of the furnace and flue, the maximum pumping force that the induced draft fan may produce under low flue gas flow should be considered. In the control system, the pressure signal of the furnace should be transmitted to the control system of the induced draft fan, so as to directly lock and reduce the load when the negative pressure is too large, so as to reduce the possibility of implosion.