Familiarity with different types of lime kilns
In ancient times, lime was originally cured in special kilns with arches of lime stone and it was placed (a place) under the kiln. Lime kiln was filled with limestone and fuel was placed in it as well, then limestone was heated to be cure for 4 days. The resulting lime is quick lime which chemically (this type of) calcareous (stone is a) calcium carbonate (that) is converted to calcium oxide by heating. Application (The use) of lime mortar in stone and brick buildings used as mortar and wall covering, was common since Parthians and this function (this type of use of) lime continued during the Sassanid Period.
The ancient people were well acquainted with the chemical and mechanical properties of lime and its mixing with other materials. Then they found out how to make resistant and impermeable materials by mixing clay with lime and other materials.
Furnace: it is the oldest type of lime kiln in Iran. In this (type of) lime kiln type, the location of lime stone and fire is fixed and temperature is not the same in different parts of kiln, the type of lime cured in this kiln is not homogeneous, and upon cooling, the heat of cured lime is decreased, consequently their application in curing lime is so limited.
Circular kiln: this type of kiln has been frequently used in lime curing and it would also have been operated like brick burning kilns. In this kiln, (lime carcasses or rubble) covers 30% of empty space, so that the flame of fire covers all stones.
Vertical kiln: it is used to supply lime to large industries such as metal industries, petrochemical industries, and sugar industry and refineries, etc. In this type of kiln, grinned lime stone is loaded under certain size from upper part of the kiln and then heated from the bottom or the sides with fuels such as coal, coke, liquid or gaseous fuel. (Advanced kilns have three zones: curing, preheating and pre-cooling zones). (in advanced kilns with three curing, pre-coolers and pre-heater) by fuel such as coal coke, liquid and gas fuels. This type of kilns can have a high quality production capacity of 150 tons per day. has production capacity of 150 tons in a day with high quality.
( rotary kiln): it is used to produce lime with high capacity and it would have been operated like cement kiln, however its heat is not so intense. In this type of kiln, lime stone is poured into kiln and quicklime is produced from kiln.
Fixed and intermittent kilns
In these kilns, which work in the traditional way, lime stone chips in size of 13cm are stacked and covered with thatch. Then they heat it up to 1333’c from the bottom with the help of fuel (shrub, wood, coal or black oil). After a certain time, they stop heating and when the kiln has been cooled down, they remove quick lime (since during extraction of lime, kiln doesn’t work, the kiln is called fixed and intermittent.
Mechanical and continuous kilns
There are different types of these kilns:
First type is Alberg kiln with a thick metal mesh at the bottom, on which a mixture of coal (as fuel) and lime stone is placed. The heat of burning coal raises the temperature of kiln, decomposes the lime stone and turns it into lime. Lime obtained from the bottom of the metal mesh and carbon dioxide gas comes out of the top of kiln. The main disadvantage of this type of kiln is that some coal ash enters the lime. The efficiency of this method is between 10 to 18 tons of lime per day.
Schomatola kiln
This kiln is similar to (Alberg) kiln, except that the ignition part (?) is located outside the kiln chamber, and therefore does not have the defect of mixing lime with coal ash. hence lime is not mixed with coal ash.
Rotary kilns
These kilns are similar to cement kilns. The efficiency of this type is higher than other types.