Hoffman kiln is a continuous, moving fire kiln in which the fire is always burning and moving forward through the bricks stacked in the circular, elliptical or rectangular shaped closed circuit with arched roof. The fire movement is caused by the draught provided by a chimney or a fan.
Hoffman kiln is a kind of sustainable production of sintering equipment. By comparison, the Hoffman kiln has lower requirements for technology, easier operation. It is a sintering equipment with less investment and quick benefit returning.
Description and Working
- In a Homan kiln, there moves through the bricks stacked in an elliptical or rectangular shaped annular circuit (central perimeter 80 – 90 m) which is covered with an arched roof. The kiln structure is usually covered with a shade to protect it from rains.
- Their movement is caused by the draught provided by a chimney (25 – 35 m high) which is located on one side of the kiln. Sometimes a fan is also used to augment the draught. The chimney is connected to the central flue duct of the kiln through an underground duct.
- There are 3 distinct zones in an operating Homan kiln: Brick ring zone where the fuel is fed and combustion is happening, Brick preheating zone (in front of the ring zone) where green bricks are stacked and being pre-heated by the flue gases and Brick cooling zone (behind the ring zone) where red bricks are cooled by the cold air flowing into the kiln.
- Air Inlet: Air enters into the kiln from the back end of the cooling zone which is kept open to allow air entrance. Seal to guide flue gas: The front end of the preheating zone is sealed to guide the flue gas to the chimney through the flue gas duct system. The kiln is connected to the central flue duct through openings provided in the inner wall of the kiln. Openings just before the seal are kept open to allow the entrance of flue gases from the kiln to the central flue duct.
- Feed holes are provided in the kiln roof for the feeding of fuels. Solid fuels (mainly firewood or coal) are fed from the feed holes by a single fireman standing on the roof of the kiln. Fuel is fed at an interval of every 15-20 minutes and each fuel feeding lasts for 5-10 minutes.
- The fire travels a distance of around 10 m in 24 hours and fires 30,000 to 50,000 bricks. Daily, fired bricks are unloaded from the back end of the brick cooling zone and an equivalent batch of green bricks is loaded ahead of the brick preheating zone.