Engineered Systems - February 2008 - (Page 32) Chipping Away At Emissions FREE INFO: 16 Multi-fuel, solid fuel-fired steam boilers were installed at both La Sarre and Macamic hospitals, along with back-up oil burners, in case there is ever a problem with the fuel handling. The fuel is kept in a storage area that is located 30 ft down in the ground, which keeps the wood from freezing. ESM02084Parker.indd 1 of 1/18/08 1:34:05 PM oil and gas is going up, too. The wood waste costs 35% to 40% of what it would to buy oil or gas, which is a big savings.” The fuel in the ground rests on a “walking” floor, which allows the bulk biomass to transition from the storage area into the fuel feed circuit as called for by the power system it is supplying. The walking floor moves the fuel to a conveyor belt and then to a feed/transfer conveyor supplying a metering bin. The metering bin maintains a minimal reserve of fuel, however, its primary function is to provide a positive head of fuel above the variable pitch metering screw to ensure a relatively constant delivery rate per revolution. The metering bin is fitted with a level indicating device, so as the load on the energy system is increased (i.e., steam pressure drops), the demand for fuel correspondingly increases, lowering the fuel level in the bin. A metering screw located immediately below the metering bin is used to transport the fuel, at a measured rate, to a rotary air lock device. The air lock device acts as a draft barrier, allowing fuel to pass from the metering screw to the stoker screw while limiting the intrusion of air through the fuel system. The stoker then brings the fuel into the boiler (the underfeed stoker system is used at the Quebec hospitals). To control particulate emissions, the boilers are equipped with two multi-cyclones, commonly called collectors, in series. The principle of operation of the cyclones is identical: Hot particle laden flue gases enter the unit and are directed down through the outer of two concentric tubes. Access to the outer cast iron tube is through spinner vanes that impart a centrifugal motion to the flue gases. The heavier entrained particles are forced to the outside of the larger outer tube and fall to the bottom of the cyclone hopper. The gases exit the larger tube through the smaller steel center tube. Approximately 95% of the particulate matter is removed at the primary collector. The ash/particulate drops to the bottom of the FREE INFO: 49 32 En gi neer ed S y stem s February 2008 http://www.parkerboiler.com http://www.parkerboiler.com
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