• Twin Shaft Kiln

Twin-shaft kilns were invented and designed by the Swiss Maerz company in the 1960s with a capacity of about 150 tons/day and with a rectangular cross-section. Due to technical advances, today it is possible to construct and operate them up to a capacity of 800 tons/day. This kiln consists of two identical vertical shafts that are connected to each other in the lower part with a horizontal channel. The main advantage of this structure is the high thermal efficiency due to the alignment of the flow of materials and heat, as well as the re-use of the thermal energy of the combustion gas in the preheating of the incoming limestone, which is also called the Regenerative feature, and is such that in time Fuel combustion takes place in one shaft with thermal energy produced by preheated limestone in another shaft. This process is reversed in alternating Production cycles between furnace shafts, and for this reason, the name Reversal is used for these furnaces. Other names of this system include Parallel Flow Regenerative (PFR) or Twin Shaft Regenerative.

The advantages of these kilns can be mentioned as increasing the quality of the product and reducing the residual percentage of carbon dioxide in lime, as well as the ease of production control compared to other standing furnaces.

The cross-sectional area of ​​twin-shaft kilns can be rectangular, circular or D-shaped, which is determined depending on the production capacity, fuel type, optimal conditions for limestone crushing and sorting, and other conditions.