Grate-type incinerator

This type of incinerator consists of the grate, the ventilation system and the flue gas treatment section, and waste completes drying, combustion and burnout in sequence on the grate. Grate movement keeps the waste turning and in contact with air, so the combustion process stays stable.

Structure and working process

Waste enters the incinerator through the feed inlet and falls onto the grate, and first goes through the drying stage, where the moisture in the waste is evaporated by the hot gas in the furnace. As the grate moves, the waste is pushed slowly forward into the combustion stage, where it burns fully with a sufficient air supply and produces high-temperature flue gas and heat. The residue after combustion is discharged at the end of the grate, while the high-temperature flue gas passes into the downstream flue gas treatment system.

Grate and air distribution

The grate usually consists of fixed grates and moving grates: the fixed grate supports the fuel, and the moving grate is driven by a mechanism to move sideways or back and forth. Grate bars come in many shapes and arrangements, and some overlap like fish scales, which stops waste falling through the grate gaps and also stirs the waste as they move. A ventilation system below the grate sends air evenly into the waste layer above and adjusts the air volume of different zones according to the combustion stage, with a smaller volume in the drying stage and a larger one in the combustion stage.

Operation and heat recovery

When combustion is stable, the temperature and flow of the high-temperature flue gas are also relatively stable, which helps heat recovery. A waste heat boiler can convert the flue gas heat into steam for power generation or heating; a large waste-to-energy plant can use the steam to drive a turbine for power generation. By adjusting grate speed and ventilation volume, combustion can be controlled flexibly according to the calorific value and quantity of the waste, so that the incinerator keeps running stably under different conditions.

Suitable waste and applications

A grate incinerator can handle waste of complex composition, varied shapes and changing moisture, including municipal solid waste and some industrial waste such as packaging materials and wood offcuts. Kitchen waste with high moisture can gradually reach a good combustion state through slow grate movement and prior drying; an incineration plant near a paper mill can also receive industrial waste such as waste paper scraps and discarded packaging and burn it together with municipal waste.

Municipal solid waste treatment plants use this kind of grate to reduce waste volume, converting organic matter into harmless carbon dioxide and water vapour while producing electricity or heat. An incineration plant in a medium-sized city can handle several hundred tonnes of municipal waste a day.