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.
Therefore, it can make full use of cheap energy, especially the pollution-carry gas such as converter gas, blast furnace gas, calcium carbide furnace tail gas, etc.
Shaft Kiln Working Principle
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 kiln’s 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.
Kiln Operation Parameters
Mixed calcined lime shaft kiln’s performance parameter table
|Yield(t/d)||Effective Volume (m*3)||Effective Height (m)||Effective Section Diameter(m)||Limestone Size (mm)||Product Heat Loss(kJ/kg)||CaO(%)||Activity Degree(ml)|
Gas-fired lime shaft kiln’s performance parameter table
|Yield(t/d)||Effective Volume (m*3)||Effective Height (m)||Effective Section Diameter(m)||Limestone Size (mm||Product Heat Loss(kJ/kg)||CaO(%)||Activity Degree(ml)|
Shaft Kiln Classification
Shaft kiln can be divided into two kinds: ordinary shaft kiln and mechanical shaft kiln.
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.
Shaft Kiln Outstanding Advantages
- Shaft kiln’s energy conservation. The inner shaft kiln is divided into reheating zone, calcimining zone and cooling zone from the top to bottom. The cooling air is blown into the kiln from the bottom of the cooling zone. After heat exchange, the product is cooled while the cooling air is preheated. The cooling air carrying heat enters the calcining zone to participate in combustion to reduce energy consumption.
- Shaft kiln’s heat preservation. The kiln skin is built of four layers of refractory material, so the kiln skin temperature can be controlled at about 60 °C above the ambient temperature, and the energy-saving is remarkable.
- Shaft kiln’s refractory material’s long service life. The material does not directly collide with the refractory material’s working surface but relies on gravity settlement and friction of the working surface. This greatly reduces the wear rate of the refractory material, so normally the refractory material can be used for 6 to 10 years.
- Shaft kiln’s good sealing. The concentration of CO2 in the flue gas can reach more than 35%, and the recovery cost of CO2 is low, which is more suitable for the nanometer calcium carbonate industry.
- Shaft kiln’s fuel adaptability’s extensive. The mixed kiln can use block coal such as lump coal, coke, and petroleum coke; the gas kiln can use high calorific value fuel such as natural gas, coke oven gas, petroleum gas, etc or low calorific value fuels such converter gas, blast furnace gas, calcium carbide, furnace tail gas, blue carbon gas, and producer gas; oil kiln can use liquid fuel such as heavy oil and diesel oil.
- Shaft kiln’s small floor space. The vertical kiln is arranged upright. The single-hopper hoist is arranged at a large angle, and the functional areas are compactly arranged to greatly reduce the floor space.
- Shaft kiln’s less investment. The kiln steel structure has fewer machining parts and lower processing costs. The installation difficulty is not high, and the refractory masonry is not difficult.