Working principle
The direct-heating furnace, is mainly made of three parts, i.e. furnace hearth, setting pocket and mixing room. The temperature is very high in the space between the setting pocket and the mixing room, to make the volatile combustible air burn sufficiently. The fuel is filled in by the furnace door, which forms burning layers on the grate. The air needed for combustion enters from the ashpit, through the grate and burning layers to make fuel burn sufficiently. Ash slags drop into the ashbin and discharged out of the ashpit. The combustion products (flue gas) in the chamber, through burning room, devided into ash and fire sparks by the setting pocket, then enters the mixing room, and pressed into the hot air room of the dryer after have been mixed with cold air to reach the temperature required. Auxiliary air gets preheated and enters the chamber to make the unburnt volatile and small carbon granules burn further.

In order that the slags and sparks are not carried away by cold air, the cold air inlet is set behind the setting pocket and spark quenching device and higher than setting pocket.
When fire is made in the chamber, the coal smoke produced enters the chimney by the passage and exhaust into the space. At the same time, when the dryer closes down or goes wrong, the flue gas can also be led out from the chimney.
The temperature of the hot air can be adjusted by cold air door or hot air door.