Classification of Pulverized Coal Burners

Classification of Pulverized Coal Burners

Various types of coal burners are :

1. Vertical long fame burners.
2. Turbulent or short flame burners.
3. Tangential burners.
4. Cyclone burners.

1. Vertical Long Flame Burner :

• Vertical long flame burners as shown in Figure A are also called as U- Name stream lined burners. Figure A shows the arrangement of supply of primary air with coal and the secondary air.
• Tertiary air is supplied around the burner to form an envelope around the primary air and coal to provide better mixing.
• In this burner, the flame is required to travel a considerable distance as shown due to which it allows sufficient time to complete the combustion of fuel.
• Furnaces for low volatile coal are equipped with these type of burners for a long flame path for slower burning of coal particles.

Figure A

2. Turbulent or Short Flame Burners :

• A turbulent burner is shown in Figure B. These are installed horizontally in the furnace walls as shown in Figure B.
• The primary air mixed with coal and the secondary air is so supplied that good mixing is carried out in the burner itself.

Figure B

• The mixture is supplied in the turbulent form to the furnace.
• Due to high turbulence created, the mixture burns intensely and it produces a short flame which is intensely hot It gives high rate of combustion compared to other type of burners.
• Turbulent All modern plants use this type of burners having high volatile matter in coal.

3. Tangential Burners :

• These burners are installed at the four corners of the furnace as shown in Figure B. such that the flame produced by the burners is tangential to the imaginary circle at the centre of the furnace.
• It produces high degree of turbulence at the centre due to which no turbulence is needed in the burner itself.

Figure C

• High rate of heat energy release is possible with this method of firing.

Advantages of Tangential Burners :

1. Operation is simple.
2. It has high rate of energy release.
3. Combustion is almost complete.
4. No additional turbulence is necessary.
5. These type of burners can be used with either of the liquid, gaseous and pulverized coal fuels.

4. Cyclone Burners :

• The use of pulverized coal involves the extra cost of pulverization of coal and the cost d collection of fly ash (dust) in the gas circuit.
• In order to avoid these problems, an attempt is made to develop burners for the use of crushed coal instead of pulverized coal as shown in Figure D.
• In these burners, very high turbulence is created and use preheated air (about 2000°C) for combustion which is supplied under pressure.
• The fuel is immediately burnt and the ash in the form of molten film travels down on an inclined surface.

Figure D

Cyclone burners can use even low grade fuels efficiently.

Advantages of Cyclone Burners :

1. Simple coal crushing equipment can be used instead of costly pulverized mills. Therefore, the cost of milling the coal is reduced.
2. High furnace temperatures are obtained.
3. It does not need much excess of air since air is supplied by force draught fan.
4. It reduces the cost of operation.
5. It can burn low grade fuels. System can also be used with liquid and gaseous fuels.
6. Rate of combustion can be controlled by adjusting the rate of fuel feed and the rate of air flow.
7. Furnace temperatures attained are high, it improves the boiler efficiency.