Parallel flow regenerative (PFR) double-bore lime kiln is an advanced kiln with high quality and high thermal efficiency. The kiln body consists of two vertical kiln chambers and a central connecting channel. The two kiln chambers work alternately. While one chamber calcines the material, the other chamber preheats the stone. The high-temperature gas is calcined in the combustion kiln chamber by the way of co-flow with the stone material, and then reaches the non-combustion chamber through the connecting channel, that is, the preheated kiln chamber. In the upper area of the preheated kiln chamber, the stone is countercurrent to preheat the limestone. At this time, the preheated kiln chamber becomes an efficient accumulator with tolerance for physical properties and dust, and the heat of the flue gas in the kiln is utilized to the maximum. The functions of the two kiln chambers will be exchanged after an interval of time, and the flow direction of the gas will also be reversed at a certain interval of time, so as to rotate the operation to maximize the use of the heat contained in the kiln smoke. The principle of parallel flow calcination is the most ideal way to produce high activity quicklime. Malz parallel flow regenerative lime kilns are characterized by a stable and reliable production capacity, a wide range of flexible fuels, and can calcination up to 1000 tons of calcined lime per day, suitable for gas, liquid or powdered solid fuels, and different combinations of these fuels. Depending on the required yield and the size of the calcined limestone, Maerz designs square, round parallel flow regenerative lime kilns or kilns dedicated to calcination of fine-grained limestone.