Underfeed Stoker Boilers

In stoker boilers, fuel is either dropped or rammed onto a grate. Stoker boilers are identified by the type of feed mechanism and the type of grate. Feed may be by spreader, overfeed, or underfeed. Grates may be travelling, reciprocating, chain, or dump type. 

Approximately 12 stoker boilers are burning TDF supplementally on a commercial basis, all in the pulp and paper industry (see Chapter 5). One industrial stoker boiler at a tractor factory is testing TDF use. Five of these 13 are underfeed stokers, and 8 are spreader stokers. Of the spreader stoked boilers, 2 are reciprocating grates,... 

Combustion tests were conducted at the Bay Front Unit No. 3 of Northern States Power Co. in Ashland, WI, The coal-fired underfeed stoker with boiler rated at 45,400 kg/h steam at 5.1 MPa drum pressure and 455 C was modified to receive 4.6 m long whole tree sections from a charge chamber by means of a ram feeder. A higher pressure over-fire air system was added. The tests successfully demonstrated the feasibility of replacing coal with logs on a grate without a loss in boiler performance. 

Solid fuels that have not been pulverized require a stoker to introduce the fuel into the boiler furnace at a controlled rate. There are two broad classes of stoker (overfeed and underfeed) and often several types within each class. 

Fort Howard Corporation Croon Hay, Ul Currant 2 2 and 1 xl" 30 tons tlre/IOOO tons coal par day No Nona required plant has 0 boilers totals 3 underfeed type that use 2 s2 TDF 2 spreader-stoker type that use 1> 1 TDF 1 cyclone fed with no IDF use now, but use planned. Produce recycled paper coal other base load fuel. References 3 and 4... 

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