Shaft kiln, just as its name implies, is a kiln with erected shape. Shaft kiln with modern new technology has environmental protection function, energy-saving function, high mechanization, and high automaticity. It also has the ability to turn waste into wealth.
Shaft kiln is a cylindrical kiln. Materials are put into the kiln from kiln crown and are ejected from the bottom of the kiln. According to the different ranges of temperature, the kiln can be divided into three parts: preheating zone, calcining zone, and cooling zone. In the preheating zone, materials are preheated by smoke; In the calcining zone, materials are calcimined by fuel; In cooling zone, calcimined materials and blowed-in cold air process heating exchange to cool materials then heated air becomes combustion air in calcimining zone. To guarantee that materials process intact calcimining in every zone, the three zones should be maintained at a certain height and be stable. The motion of materials in kiln occurs under two circumstances: first, materials volume shrinkage makes upper materials move; second, lower materials ejectment leads to the whole materials motion.
Shaft kiln, during the descent, materials process complicated heat exchange with hot coal gas while limestone is decomposing and the grains of quicklime is growing and developing. After the whole process, materials are cooled down by combustion air to 60-degree centigrade higher than environmental temperature. Then lime is dumped on belt conveyor outside the kiln without disc ash machine and sealing valve leaking combustion wind. Then the size of limes less than or equal to 5mm and the size more than 5mm are respectively discharged into different silos after hoisting and sieving.
Shaft kilns combustion air is blown into the furnace from the lower part of the furnace by a Roots blower then overcomes the resistance of the pellet while lifting from the lower part to the top of the furnace. Under the drawing of the dust extraction fan, the flue gas is transported to the dust collector through the pipeline for dust removal. Due to the effect of induced draft fan, a micro-negative pressure zone is formed above the material surface in the kiln (about -10 Pa). This micro-negative pressure ensures smooth airflow in the furnace, which is very beneficial for the decomposition of limestone in the calcimining zone. The induced draft fan introduces all the flue gas into the dust collector for purification and then discharges it from the chimney to the atmosphere.
Ordinary shaft kiln relies on the mode of artificial feed and unloading or the mode of automatic feed and artificial unloading; while mechanical shaft kiln uses automatic feed and unloading. The mechanical shaft kiln is continuously operated, so it is higher than ordinary shaft kiln in the aspect of production, quality and labor productivity. According to the requirements of building materials technology and policy, small cement plants should use a mechanized vertical kiln to gradually replace ordinary shaft kiln.