Recirculating fans

Flue gas recirculation (FGR) is the rerouting of some of the flue gases back to the furnace. By using the flue gas from the economizer outlet, both the furnace air temperature and the furnace oxygen concentration can be reduced. However, in retrofits FGR can be very expensive. Flue gas recirculation is typically applied to oil- and gas-fired boilers and reduces NO, emissions by 20 to 50%. Modifications to the boiler in the form of ducting and an energy efficiency loss due to the power requirements of the recirculation fans can make the cost of this option higher. 

What about Preventive maintenance A preventive maintenance program should be established in consultation with those responsible for the upkeep of the chamber during normal use. This should be done after successful qualification and prior to releasing the chamber for use. Components that are prone to malfunction due to normal wear and tear include solenoid valves, humidifier floats, and recirculation-fan drive motors. These components should be checked or replaced on a regular basis to prevent or minimize chamber downtime. 

The hot water heating system (VYS) supplies heated water to selected air handling units and unit heaters in the plant during cold weather operation and to the containment recirculating fans coil units during cold weather plant outages. 

Another manual control switch is required for shutting down the recirculating fans (which supply air to the HEPA/ULPA filter ceiling of the cleanroom) and shall be installed at an approved location outside the fabrication area. We recommend that one switch be provided for the makeup air and exhaust fans, with a separate switch for the recirculating HEPA fans. 

With Flue Gas Recirculation (FGR), flue gas is introduced with the combustion air and acts as a thermal diluent to reduce the combustion temperature. Usually, the amount of flue gas recirculated corresponds to 10-20% of the combustion air. FGR reduces only thermal NO (. It is suitable only for oil- and gas-fired boilers. Results with coal have been generally disappointing. In coal-fired stoker units, FGR provides better grate cooling. FGR has been successfully applied on industrial solid fuel-flred units and is considered appropriate for waste-to-energy plants. Retrofit modifications include new ductwork, gas recirculation fan(s), flue gas/air mixing devices and controls (Makansi, 1988 Wood, 1994). Gas recirculation fans can be troublesome. 

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