Cyclone fired boiler uses cyclone furnace. Cyclone furnace is one of the most modern forms of the furnace. Cyclone furnace is a variety of wet bottom furnace where ash gets removed from the furnace in molten form. The furnace in the cyclone-fired boiler is in the form of a horizontal cylinder. The furnace requires the coal having low ash fusion temperature. The pulverised coal is fed to the furnace along the periphery of the cylindrical furnace. The hot gases enter the water tube section axially. The water tube section has a tight helix path for hot gas circulation. The ash particles mixed with flue gas deposited on the outer surface of the water tubes and create a thick layer of ash particles there.
The thicker layer of flue ash then goes down due to gravity and gets collected at the bottom. The heavier ash particles get deposited along the periphery, and smaller ash particles get deposited along the water tube surface. The exhausting gas will only have very fine particles of ash. Cyclone furnace has high pressure of flue gases inside, so it usually does not require induced draught fans to extract flue gases from the furnace, but if the draught fans are used there will be a less burden on them. The cyclone-fired boiler may have more than one cyclone installation which makes the boiler more responsive to the changing electrical load of the power system. This arrangement can make the boiler responsive to the load from 40% to 110% of its rated full load capacity.
One exciting feature of the cyclone furnace is that the boiler can be fired with dry pulverized fuel ash from adjacent dry bottom installation. This technique is called “Melting in Cyclones”.
The first cyclone-fired boiler was installed at the Calumet Station of Edison Electric Power Company USA.
There are many advantages of a cyclone-fired boiler.
- In cyclone-fired boiler, 85% of ash in the coal is burnt in the form of liquid slag.
- The fly ash problem is reduced too much lower limits in cyclone-fired boiler.
- It reduces the burden on the electrostatic precipitator used for dust collection.
- The collected ash can be utilized as a building material.
- The need for draught fans is minimised hence the initial and maintenance cost of the boiler is reduced.
- The quick load variation of power system can easily be handled by cyclone-fired boiler.
- Here, the pulverized fuel ash from the adjacent dry bottom can be used.
- There is a reduction in space and metal requirement.