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Technology and know-how in grates for biomass boilers

Published Wednesday, August 1, 2007

Detroit Stoker Company’s spreader fired grate technology has been used to fire biomass for more than 60 years and continues to serve today’s market. Currently three types of spreader fired grate are utilized in the Pulp and Paper Industry, by Independent Power Producers, as well as in Forest Product industries throughout the world. Those used in Europe have primarily been air-cooled traveling grates (RotoGrates). However, Detroit Stoker Company also offers air-cooled and water-cooled vibrating grate (VCG RotoStokers & Hydrogrates).

The air-cooled traveling grate has been used in more industries and has fired a wider variety of fuels than most other firing systems. It has fired high and low quality coal, bark, bagasse, chicken litter, RDF (Refuse Derived Fuel) and MBM (Meat & Bone Meal).

One of Detroit Stoker Company’s most recent European projects was for Econoler, a plant in Cabra, Cordoba, Spain, that burns olive waste to produce 37tph of steam. The combustion system incorporates a RotoGrate, which is an air-cooled traveling grate, spreader fired stoker that is ideal for a broad range of applications. The olive waste is fed into the boiler by Detroit Air Swept Fuel Distributors, with high pressure air that sweeps the bottom of the distributors and spreads the fuel onto the grate. This spreader fired technique allows the olive waste to be burned simultaneously on the grate and in suspension utilizing a staged Overfire (Secondary) Air System to complete the combustion above the grate. The ash from the grate surface is continuously and automatically discharged at the front of the stoker.

The air-cooled and water-cooled vibrating grate stokers are used primarily to fire biomass and are particularly popular for boiler conversions. These grates operate similarly to the traveling grate, but instead of a continuous ash discharge, they utilize an intermittent ash removal system where the grate surface vibrates at low amplitudes for approximately 2% of the time to move the bed forward to discharge the ash off the front. These grates use very few moving parts and the drive mechanism is external to the heat, which increase grate life and reduces maintenance costs, resulting in high equipment availability.

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