Twin-shaft Parallel Flow Regenarative Vertical Lime Kiln

الوصف

Operation Principle
Twin-Shaft Lime Kiln is named as  Parallel Flow Regenerative (PFR) Twin-Shaft lime vertical kiln, it consists of two kiln shafts named Shaft A and Shaft B which are connected by channel at the bottom of calcining Zone, and the raw material moved down along with the two kiln shafts. When the calcination works in shaft A, the combustion air and fuel are parallel flow with the material in the kiln shaft A, by which the fire flame can contact with the materials of the lower temperature and max heat absorption, relatively speaking, the low temperature combustion gas contacts with the stepwise well-calcined material, in order to achieve uniform calcination conditions, and also obtain the high heat efficiency. The produced air and CO2 decomposed by the material flow into shaft B across the channel. At this point, the shaft B as regenerative kiln shaft, the limestone in the shaft B absorbs heat from the exhaust air, while the exhaust air is cooled to low temperature. The material accumulates heat, and reheats the combustion air before joining in the burning in the next cycle. In this case, the kiln shaft A is burning kiln shaft, embodying the characteristics of parallel flow; the kiln shaft B embodies the regenerative characteristics. In the next cycle, two shafts makes mutual rotation, namely the kiln shaft A is regenerative kiln shaft, the kiln shaft B become burning kiln shaft. So the process works in circles to continuously calcine limestone.
Burning and non burning kiln shafts operate by switch, which has the following two remarkable characteristics: A. combustion air and limestone are parallel flow in the calcining zone; B. all combustion gas is regenerative in the preheating process.
Twin-shaft lime kiln is the least heat loss type in all current lime kilns.
 
The following figure 1, figure 2 represent the temperature change curves of gas and material inside of the kiln for two kinds of calcining process, The green line represents the temperature curve of materials and products, the red represents the temperature curve of the combustion air and waste gas, the blue represents the temperature curve of cooling air.
 
2) Types of fuel: natural gas, generator gas, liquefied petroleum gas, converter gas, coke-oven gas, blast furnace gas (calorific value >**0 kcal/m3), the mixed coal gas or pulverized coal, the mixed fuel of pulverized coal and coal gas, heavy oil and light oil
 
3) low heat consumption, reasonable heat utilization. The PFR lime kiln is the lowest unit heat consumption, about **0Kcal/Kg of lime. The calcination and pre-heating operates alternately, which can maximize the heat recovery. The temperature of  exchanged exhaust air is lower than **0ºC
 
4) the calcining way is parallel flow, the heat exchanging is counter flow, which is consistent with the chemical reaction mechanism of calcium carbonate decomposition