Mass Burning in Waterwall Furnaces

In mass-burning in waterwall furnaces, most or part of the refractory in the furnace chamber is replaced by waterwalls made of closely spaced steel tubes welded together to form a continuous wall. Water is continuously circulated through these tubes. In newer waterwall designs, the steam production is around 3 lb of steam per pound of MSW. The increase in thermal efficiency is mostly due to a reduction in the excess air (from about 150% for refractory-walled furnaces to about 80% for waterwall furnaces).

Coating a substantial height of the primary combustion chamber, which is subject to higher temperatures and flame impingment, with a thin coat of silicon carbide refractory material and limiting the average gas velocities to under 15 ft/sec (4.5 m/sec) is recommended. Gas velocities entering the boiler convection bank should be less than 30 ft/sec (9.0 m/sec) (Velzy 1986). The efficiency of heat recovery in such units ranges from 65 to 70%.

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