Gypsum Calcination Kilns
1- Pit kilns
The oldest type of gypsum kilns in Iran are well kilns, which are still common in many cities in Iran. It is a type of kiln in which gypsum mineral is placed and baked by heating. The temperature of this type of kiln cannot be controlled. all types of gypsum from baked gypsum to construction gypsum, burnt gypsum, anhydrite and decomposed gypsum are obtained through it. It’s obvious that the product from this type of kiln is not of quality because of its non-uniformity. The work of this furnace type is not continuous and for fuel, we can use wood, coal etc.
2- Frying kilns
This type of kiln has a uniform product. it is made of a large tray in which milled gypsum is poured and then it is heated. These kilns consist of an apparatus that mixes the adhered pieces of gypsum. so that the all the lumps of gypsum are heated evenly. This mixing apparatus is a comb like apparatus that is in the middle axis of the pan. and rotates around its own axis, similar to how seeds are roasted.
3- Rotary kilns
This type of kiln which is most common type of gypsum calcinating kiln, rotates in dormant cylinder around its axis. which has a slope of about 4 degrees to horizontal plane, and as it rotates the gypsum lumps move forward.
After coming out of kiln they are cooled by blowing cool air and to soften them, they’re taken to mill. After coming out they have a temperature of 100 degree C which is good to heat the primary raw materials. and to evaporate the physical water that they have. The heat in this type of furnace is controllable and has a uniform and high quality product.
The work of these furnaces is continuous, meaning that it can always continue to work without stopping. As long as the product of furnace is driven forward by rotation, the furnace can be loaded in same proportion.
In construction workshops that are far from gypsum and brick kilns. In order to acquire the needed bricks. they have to build a brick kiln in the workshop by placing some gypsum on the brick kiln. due to the low heat of the gypsum to bake. It needs to be cooked, cooked for a short time. then crushed and shifted with basic tools such as local mills and are then utilized.
