The grate (stoker) serves dual functions:
1. Transports the solid waste and residue through the furnace to the point of residue discharge. The grate should be covered with a uniform depth of MSW across its width.
2. Promotes combustion by providing proper waste agitation and by permitting the passage of underfire air through the fuel bed. However, the agitation should not be so violent that it contributes to excessive particulate emissions.
The design of the grate system in the furnace is a critical element in the operation of a RDF facility. Eberhardt (1966) proposes ten elements to consider in the choice of a grate system:
The adaptability of the combustion process to handle wide variations in radiation effects The adaptability of the refractory to handle wide variations in radiation effects Provisions for controlling air quantity and temperature Provisions for an adjustable retention time based on the material being burned An adjustable height of the waste layer to be burned A controllable, stabilizing heat supply (auxiliary fuel) A controlled cooling of residue (by quenching) A controlled flue gas temperature prior to impinging on the radiation heating surface The capability of observing the fire layer and the fire gases
Technical design including: —Prevention of reignition —Positive conveyance of the refuse mass —Serviceability and replaceability of worn-out parts —Proper measuring and control systems
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