From Steam Plant Operation, Eighth Edition

5.10 Mechanical Draft: Fans

There are essentially three methods of applying fans to boiler units:

  1. Balanced draft. A forced-draft fan delivers air to the furnace and an induced-draft fan or a stack produces the draft to remove the gases from the unit. The furnace is maintained at 0.05 to 0.10 in of water (gauge) below atmospheric pressure.

  2. Induced draft. A fan or stack is used to produce sufficient draft to cause the air to flow into the furnace and the products of combustion to be discharged to the atmosphere. The furnace is maintained at a pressure sufficiently below that of the atmosphere to induce the flow of combustion air. This type of system is not used on modern designs.

  3. Pressurized furnaces. A forced-draft fan is used to deliver the air to the furnace and causes the products of combustion to flow through the unit and out the stack. The furnace is maintained at a pressure sufficiently above that of the atmosphere to discharge the products of combustion. The FD fan must be designed to handle both the air resistance and draft loss through the boiler.

Forced-draft (FD) fans handle cold (ambient temperature), clean air and provide the most economical source of energy to produce flow through boilers and their auxiliary systems. Induced-draft (ID) fans handle hot flue gas and thus a larger flue gas volume. Because of this higher temperature and greater volume of gases, they require higher electric power and are also subject to a...

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Products & Services
HVAC Fans and Blowers
HVAC fans and blowers are used to move air through heating, ventilating, and air conditioning (HVAC) systems. They are an integral part of the air handling systems that bring or draw fresh air into buildings.
Pressure Blowers and Fans
Pressure blowers and fans are used to create and sustain a positive pressure for inflatable structures, clean rooms, laboratories, and medical facilities. Pressurization blowers are fans that create a positive pressure in a sealed or restricted environment.
Burners are heating devices that use air supplied specifically for the combustion of a fuel gas.
Cooling Towers
Cooling towers are defined as any open water recirculation device that uses fans or natural draft to draw or force air to contact and cool water by evaporation.
Combustion Analyzers
Combustion analyzers and flue gas analyzers measure the gas content of emissions in order to monitor the combustion efficiency of fuel-burning equipment.

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