Annular Shaft Kiln

After the annular sleeve kiln was introduced into China, it was widely used due to its low heat consumption, high lime activity, strong fuel adaptability and high level of automation. The lime in the sleeve kiln is calcined in the annular space, the air flow distribution is more uniform, the sleeve kiln has a simple structure, low failure rate, and is easy to maintain. It is suitable for steel, calcium carbide, chemical and other industries

Principle of sleeve lime shaft kiln

Through the upper and lower two layers of combustion chamber and the inner sleeve, in the annular area between the inner and outer two cylinders, four parts of the pre-tropical, counter-current calcination zone (upper and middle), parallel flow calcination zone and lime cooling zone are formed, and the limestone is decomposed more fully under the action of the parallel flow calcination zone and circulating gas, and the internal quality of lime is further improved.

Introduction to the process of sleeve lime shaft kiln

Annular Shaft Kiln, also known as annular kiln, is an efficient thermal equipment, mainly composed of two concentric cylinders to form an annular furnace cavity, which is used for calcining lime in metallurgy, chemical and building materials sectors. This kiln type originated from the German Kenbach Wellman Steler Company, and was developed and promoted by the Wilmsteller Company of the Federal Republic of Germany in the 60s of the 20th century. At present, more than 300 sleeve shaft kilns have been put into use in the world, especially in Europe and Japan.

Technical features

The sleeve lime shaft kiln has the characteristics of small footprint, low heat consumption, uniform product quality and high activity. Not only can it be adapted to a wide range of limestone and fuel types, but it can also improve the calcination effect of lime through a combination of counter-current calcining and parallel flow calcination. In addition, the model adopts negative pressure operation, and further reduces energy consumption through technologies such as waste heat recovery, heat exchanger and secondary circulating air.

Calcination process of sleeve lime shaft kiln

The calcination process of sleeve lime shaft kiln mainly includes four areas: pre-tropical, counter-current firing zone, parallel flow calcination zone and cooling zone:

1. Pre-heating: The material enters from the top of the shaft kiln and is first preheated by convection through the pre-heating. The pre-heating uses calcined exhaust gases to preheat the stone, and about 70% of the exhaust gases pass through this area.

2. Counter-current calcination zone: the preheated material enters the upper calcination zone, and the incompletely burned hot flue gas rising from the middle calcination zone is completely burned in the zone, and the material is heated and decomposed. In countercurrent calcination, limestone needs to absorb a lot of heat in the early stage of decomposition, so it generally does not produce overburning.

3. Parallel flow calcination belt: The material then enters the middle calcination belt, and obtains the hot flue gas diverted from the lower calcination belt for further heating and decomposition. The material then enters the lower calcination zone and continues to be calcined in parallel flow heating until it is completely decomposed. Parallel flow calcination is the key to the entire calcination process in the sleeve kiln, where the lime is finally fired.

Cooling belt: The burned material moves down into the cooling belt, and because the kiln adopts negative pressure operation, the air of the cooled material is sucked in from the lower part of the kiln by the negative pressure in the kiln. The material after cooling 4 is discharged to the lime silo through the discharge table of hydraulic transmission at the lower part of the kiln.

Equipment composition

The sleeve lime shaft kiln is mainly composed of two concentric cylinders, a feeding device, a discharging device, a combustion system, a blower system, an air preheating device, a flue gas purification device and a hydraulic transmission device. Among them, the upper inner cylinder county is hung on the top of the kiln, and the lower inner cylinder is located in the middle and lower parts of the entire shaft kiln. The upper and lower inner cylinders are made of boiler steel plates, with two layers, and an annular gap is formed between the two layers, and the annular gap is forced to cool by air. The inner and outer sides of the inner cylinder are coated with refractory materials to ensure the high temperature resistance of the kiln body.

Operational points of sleeve lime shaft kiln

1. Raw material requirements: the ratio of limestone blockage into the kiln should be controlled to 2:1 or 3:1, and the minimum blockage should not be less than 30mm. At the same time, the MgO content of the raw material should be ≤ 1.0%, otherwise it is easy to cause blockage of the equipment (heat exchanger).

2. Fuel type: The kiln can use natural gas, coke oven gas, calcium carbide furnace exhaust gas, fuel oil, etc. as fuel. The choice of multiple fuels allows the sleeve lime shaft kiln to take full advantage of the cheap local energy source and reduce production costs.

3. Calcination temperature: The calcination temperature is about 1100~1150°C. In this temperature range, limestone can fully decompose, while avoiding the occurrence of over-burning phenomenon 4, product quality: the lime produced by the sleeve lime shaft kiln has a high degree of activity, up to more than 350ml (some high-quality products can reach more than 360ml). High-quality lime can meet the high requirements of active lime in steel, chemical and other industries.

Technical performance and main characteristics of annular sleeve kiln

1. Production capacity: Our company provides the design of 150t/d, 300t/d, 500t/d, 600t/d specification annular sleeve kiln, with corresponding manufacturing production capacity, the output can be adjusted within a certain range, and the production can be stabilized.

2. Limestone particle size: 40~ 80mm, particle size range ratio 1:2.

3. Fuel type: The kiln can use pulverized coal, coke oven gas, calcium carbide furnace gas, natural gas, high coke mixed gas, converter gas, etc. as fuel.

4. Lime quality: the residual amount of C02 can be no more than 2% (24-hour average), and the activity is greater than 360ml (4N, HCL 10min).

5. Heat consumption: Under normal conditions, the heat consumption of finished ash is less than 950kcal/kg. The power consumption is low, about 32kWh per ton of active lime, which is lower than that of double-shaft kiln.

6. High operation rate: 340 days of working ≥ a year.

7. Calcination method: the combination of countercurrent calcination and parallel flow calcination will not overburn, but also ensure the full decomposition of lime, so that the activity of lime is greatly improved.

8. The operation is very stable and belongs to the trouble-free kiln type, so the consumption of spare parts is very low.

9. Because it is negative pressure production, it is very conducive to environmental protection and safe production.

10. Because it is a single-barrelshaft kiln, the area is smaller than that of double-shaft kiln and rotary kiln.