Burning High Ash Content Coal: Problems and Remedies

Quality of Coal (ash content in the coal) is one of the important factors which directly affects the power generation in the thermal power plant. It is disadvantage that poor quality of coal or high ash content in coal will reduce the efficiency of the steam power plant which implies in the reduction in the amount of power generation in thermal power plant. 

Problems of burning coal containing high ash content:

Therefore use of low quality coal creates some burning problems as the ash interferes in the combustion process and affects the thermal efficiency of the steam plant. Some of the problems associated with low quality coal combustion in thermal power plant are listed below:

• High ash content in the will reduce the thermal efficiency of the coal. The ash content interfere with the combustion of coal and reduces the temperature of the combustion zone.
• High ash content in coal results in the increase in cost for coal cleaning
• Higher ash content coal burns slow compared with low ash content coal under identical conditions of feed rate and excess air supplied. This results in reduction in the steam output of the boiler. 

New upcoming Thermal Power Plants

Therefore in order to fire high ash coal, some of the solutions should be sort out. The solutions for the existing plants and the solutions for new plants should be identified. It is easier to  implement changes in upcoming projects compared to already exiting thermal power plants.

Some of the Solutions for upcoming thermal plants where high ash content coal to be fired are given below:

• The coal pipes should be lined with ceramic glass
• Higher ID fan should be used so that it can run at lower speed without affecting the output.
• Increase the capacity of the electrostatic precipitators (ESP) to improve the collection efficiency of the ash
• The velocity of the flue gases is reduced to avoid erosion
• Low speed ball mills should be used for pulverizing as it provides constant size output over a longer time
• Coal blending (mixing high grade quality of coal and low grade quality coal) can also improve the thermal efficiency
• Flame stabilization should be achieved by one of the methods:

1. Increase in the are/volume ratio of the furnace
2. Increase primary air temperature
3. Ensure longer retention time of the coal particle in the ignition area

 

Existing Old Thermal Power Plants:

The problems for existing steam power plants is more difficult as major modifications are not possible. Some of the problems associated with old plants are the difficulties of the erosion of ID fans, pulverizers and flue gas pipes and reduction in the thermal efficiency. 

To avoid the above problems the size of the ID fans and use of low speed mills should be incorporated. This modifications does not change the ash levels but reduce the abrasive material content from coal and reduces the erosion problem. Blending of coal is another option to improve the efficiency and reducing the ash content. Using the above methods the thermal efficiency of the steam power plant can be improved.