Boiler Safety Series| Common Malfunctions and Solutions inside the Boiler

August 20, 2021

When the boiler is in operation, trial operation or pressure test, the boiler body, combustion chamber, main flue or steel frame, furnace wall, etc. are damaged, which is called a boiler accident.

Common malfunctions in the boiler include: boiler overpressure accident, boiler heating surface deformation accident, boiler flue explosion accident, tail flue secondary combustion accident, etc.

Malfunctions inside the boiler will generally cause greater damage to the boiler, and even cause the boiler to explode. Therefore, clarifying the causes and solutions of common malfunctions in the boiler is essential for the boiler safe and stable operation.

Boiler Overpressure

During in the boiler operation, the phenomenon that the pressure in the boiler exceeds the maximum allowable working pressure and endangers the safe operation of the boiler is called overpressure. Boiler overpressure is the direct cause of boiler explosion accident.

Boiler Overpressure accidents

Boiler Overpressure Accidents

1. The vapor pressure rises sharply, exceeds the allowable working pressure, the pointer of the pressure gauge exceeds the "red line", and the pressure is still rising after the safety valve is actuated

2. An overpressure alarm signal is issued, and the overpressure interlock protection device operates to stop the blower, induced draft fan and coal feeder

3. The steam temperature increases and the steam flow decreases

Boiler Overpressure Causes

1. The steam consuming unit suddenly stopped using steam, causing the steam pressure to rise sharply

2. The boiler worker did not monitor the pressure gauge, and did not correspondingly weaken the combustion when the load dropped sharply

3. The safety valve is out of order, the valve core is stuck to the valve seat, cannot be opened, or the safe exhaust steam capacity is insufficient

4. The pressure gauge tube is blocked or damaged, and the pointer indicates incorrectly, which cannot reflect the true pressure

5. The overpressure alarm fails and the overpressure protection device fails

6. For boilers used for pressure reduction, if the diameter of the safety valve does not change accordingly, the exhaust steam capacity is insufficient and the steam pressure cannot be controlled.

Boiler Overpressure Solutions

1. Quickly weaken the combustion, manually open the safety valve or vent valve

2. Increase the water supply, strengthen the sewage, reduce the boiler water temperature, and reduce the boiler pressure

3. If the safety valve fails or all the pressure gauges are damaged, the furnace should be stopped urgently, and the pressure will be increased after the treatment is completed.

4. When the boiler has overpressure, appropriate pressure reduction measures should be taken, and the pressure reduction speed is strictly prohibited

5. After the severe overpressure of the boiler is eliminated, shut down the boiler for internal and external inspections, deformation and eliminated leakage caused by overpressure , and repaired unqualified safety accessories.

Boiler Heating Surface Deformation

The heating surface of the boiler refers to the water wall tube, anti-coking box, convection tube bundle, furnace bladder, pyrotechnic tube, boiler tube, etc.

Boiler Heating Surface Deformation Accidents

1. When the water wall tube is deformed, it can be seen from the fire door or furnace door. If there is water shortage, the red curved water wall can be seen

2. The internal combustion furnace can be seen bulging and deforming toward the fire side, and the drum is bulging and deformed toward the fire side.

3. If the furnace tube is severely deformed, the sound of steam spray can be heard when the tube bursts at the same time; when it is lighter, it can only be found after the furnace is shut down and checked

Boiler Heating Surface Deformation Causes

1. The boiler is seriously short of water, and the heating surface cannot be effectively cooled and overheated and deformed

2. Poor design structure, local water speed is too low, stagnation, over-temperature deformation

3. Unqualified water quality, thick scale, poor heat transfer, and deformation due to overheating

Boiler Heating Surface Deformation Solutions

1. When the deformation of the heating surface is not serious, the boiler can be shut down for maintenance after the standby boiler is started.

2. If the deformation is serious, the furnace bladder has bulged and deformed toward the fire side, and the tube wall has been obviously over-burned and deformed, so the furnace should be stopped immediately to prevent the situation from expanding

Furnace and Flue Explosion

Furnace and flue explosions mainly occur in suspended combustion boilers such as fuel oil, gas and coal-fired pulverized coal, and may occur during boiler ignition and operation.

Furnace and Flue Explosion Accident

1. When the furnace and flue explode, accompanied by dull noises, thick smoke and fireballs are rushed out from the explosion-proof door, furnace door, fire hole, etc., in severe cases, the furnace wall collapses and the furnace roof opens, etc.

2. When it is lighter, the explosion-proof door and furnace door are opened, smoke rushes out, and the chimney emits thick smoke

Furnace and Flue Explosion Causes

1. Before the boiler is ignited, the residual combustible gas in the furnace is not cleaned, and there is no ignition control program.

2. When the boiler is running under low load, the furnace temperature is too low to cause a fire, and the boiler worker does not strictly follow the procedure to re-ignite

3. The boiler flue gate is not fixed reliably. Once closed during operation, the flue gas in the furnace cannot be discharged, causing an explosion

4. The induced draft fan trips suddenly, but the fuel is not cut off in time, and the flue gas cannot be discharged in time

5. Excessively coarse pulverized coal, poor fuel atomization, insufficient air distribution, etc. cause a large amount of unburned fuel to enter the flue. After a certain amount, once the temperature is high, the flue will explode.

Furnace and Flue Explosion Solutions

1. Whether it is the first ignition or re-ignition after the fire is extinguished, the ignition procedure must be strictly followed. Ventilate for a few minutes, then ignite and feed fuel

2. After an explosion accident occurs, cut off the power, gas, and oil sources, stop the furnace in an emergency, and report to the relevant departments to prevent the situation from expanding

Secondary Combustion in the Tail Flue

Secondary combustion generally occurs in the tail flue of pulverized coal combustion and oil-fired boilers. In severe cases, the air preheater will be burned.

Secondary Combustion in the Tail Flue Accidents

1. When the tail flue is burning, the exhaust gas temperature rises sharply, the chimney emits thick smoke, and even flames appear.

2. There is positive pressure in the furnace, and the fire is sprayed out

3. When there is an air preheater, the hot air temperature rises sharply and the wind pressure is unstable

4. The induced draft fan vibrates, the noise increases, and the current increases

Secondary Combustion in the Tail Flue Causes

1. The pulverized coal is too coarse, the fuel atomization is poor, and the unburned combustibles enter the tail flue. After a certain amount is accumulated, combustion will occur when the temperature is high.

2. When the furnace is extinguished, a large amount of pulverized coal or oil mist accumulates on the heating surface of the tail, and it burns in case of high temperature flue gas or open flame

3. Clean the tail flue without stopping the furnace for a long time, and the accumulated coal powder or oil will burn to a certain amount when it encounters high temperature flue gas or open flame.

Secondary Combustion in the Tail Flue Accident Solutions

1. Open the economizer recirculation pipe valve to prevent water hammer from vaporization in the economizer

2 Close the air supply system, furnace door, inspection hole, etc., so that sufficient air cannot be obtained for combustion

3. Use steam or CO2, or other fire extinguishing methods to extinguish the fire, never use water to extinguish the fire

4. When the exhaust gas temperature drops below 150℃, the inspection hole can be opened for inspection

5. After checking that there is no fire source, the induced draft fan can be turned on to exhaust the gas in the flue. When the temperature drops below 50 ℃, the flue fouling, unburned grease and coal powder should be completely removed.

6. Check the heating surface of the tail, if it is not burned out, you can re-ignite and start, otherwise the burned out parts should be replaced before it can be put into operation

Conclusion

Through the above content, you can have a comprehensive understanding of the internal failure of the boiler, understand the malfunctions of the boiler and take corresponding measures to actively prevent it, so that your boiler can be used more safely and lastingly.