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Usage of Induced Draft Fans in Thermal Plants

In a typical power plant, heat energy is generated by boilers. Generally, boilers use industrial fans for the following reasons:

  • To supply air required for combustion
  • Remove products of combustion
  • Deliver fuel to the burners
  • Circulate gases for better heat transfer.

These four functions are handled by various types of industrial fans. The fans are custom designed for operational and energy efficiencies. Draft fans are generally used to maintain the flow of gases through the boiler. The fans could be induced draft fans or forced draft fans. While forced draft fans are placed at the inlet of the boiler system, the induced draft fan is placed at the outlet of the boiler system.

How Do Induced Draft Fans Work?

The Induced draft fan (ID fan) is used to create a vacuum or negative pressure in a system like steam boiler. When mechanical ventilation is supplied to these boilers, the heat transfer rate increases. The induced draft fan is located between dust collector and chimney. It takes the hot flue gases from furnace via dust collector (dust separation system or fume extraction system) and delivers to the chimney. Induced draft fan produce the pressure lower than the atmospheric pressure in the system or we may say that they produce the negative pressure in the furnace to remove the flue gases from the furnace and to push through the chimney.

Advantages Of Induced Fans

  • Facilitate better distribution of air.
  • Reduced possibility of hot effluent air recirculating into the intake.
  • Better process control and stability as plenum cover 60 % of the bundle face area reducing the effects of sun and rain on the process.
  • Increased capacity in event of fan off or fan failure condition since natural draft stack effect is much greater.

Limitations

  • High horsepower required if effluent air is very hot.
  • Induced draft fans are suitable only when the process inlet temperature is less than 350-degree Fahrenheit.
  • Fans are less accessible for maintenance.

Induced draft plans play a key role in supporting the thermal power plant’s processes. 72% of the coal produced in India is consumed by its electricity sector. The Indian coal reserve is mostly having lower calorific value and high ash content. On average, power plants in India using local coal supply consume about 0.7 Kg to generate one KWH, this number is 0.45Kg in the USA. So the thermal plants in India need to have good induced draft fans to support the energy production using coal.