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Combustion chamber design for Coal firing

Combustion chamber design for Coal firing

Combustion chamber design for Coal firing

We are looking for help and guidance to re-design a coal fired combustion chamber.  Are there books / sites which can guide about grate design, coal bed thickness, insulation, etc.

We have made an indirect fired air preheater which uses coal as fuel.  

Coal CV-5000 KCal/Kg, Size- 50% below 1 inch + 50% of 1-5 inch.  Approx 65Kg/hr of this coal is to be burnt. Temperature of products of combustion (flue gas) is ~1000 Deg C, which is mixed after the combustion chamer with recirculated flue gasses, at 200-300 Deg C, for reduced mixed flue gas temperature of 600 - 700 Deg C., before it is taken to a gas to air heat exchanger.  The heat exchanger preheats approx 11,500 NmCu./Hr pure air from 25 to 175 Deg C.

The pilot plant has been in operation alomost continuously for 4 months now.  Combustion chamber is manually fed with a static grate made of mild steel flats of 40mm x 10 mm kept with a gap of 25mm between two grates.  Combution chamber is rectangular- 1500 mm lg x 950 mm wd x 800 mm ht with arch roof.  Insulation is with 51% alumina castable refractory of 250 mm thk fixed with SS 304 anchors.

The insulalation has started to fall off and grate is getting buckled. With this coal is falling through the grate literally as soon as it catches fire, and the grate bars have also started to melt.

We have been advised following -

1. Change grate bars to cast iron.
2. change insulation to standard refractory bricks.
3. increase bet thickness of coal on grate from about 75 mm now to about 200 mm.
4. Blow flue gases below grate which would keep bed cooler and also keep combustion chamber cooler.

We would be most thankfull for any help.

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