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Advantages and disadvantages of rotary kiln

Release time:2019-11-11 From: Zhengnai Industry in China

Rotary kiln structure

It is mainly composed of kiln body, kiln head, kiln tail, support wheel, rim, retaining wheel, transmission device, sealing device, fuel nozzle and exhaust system. The rotary kiln body is a cylinder welded by steel plates, and refractory bricks are built inside.

 

Advantages and disadvantages of rotary kiln

The advantages of rotary kiln are low construction investment, large production capacity and high mechanization of operation. The main disadvantage is that the charcoal burnout is relatively large during calcination.
 

Two operations that cause serious damage to the rotary kiln

If the refractory material is improperly used or the operation is inadvertent, the furnace lining is often damaged, and the kiln body maintenance work is relatively large.
 

Rotary kiln process operation

The process operation of the rotary kiln is mainly to control the temperature gradient in the kiln, the length of the calcination zone, the feed amount and the negative pressure in the kiln.

Three temperature zones are formed in the rotary kiln

The fuel injected into the kiln and the volatiles discharged from the raw materials are burned to generate high temperatures, and three temperature zones, a pre-tropic zone, a calcination zone and a cooling zone are formed in the kiln.
 

Pre-tropical description

The pre-tropical zone is a section of the kiln body that is close to the kiln tail in the longitudinal direction. The raw material enters the kiln from the feeding pipe above the kiln tail. The temperature of the kiln tail is generally 800-900 ° C. The raw material moves from the kiln tail to the kiln head and then passes through the pre-tropical heating. , discharge water and some volatiles.

Size of graphite electrode

Item Unit UHP
300-500mm 550-600mm 700-800mm
Electric resistivity Electrode μΩm 4.6-6.2 4.5-6.0 4.5-5.8
Nipple 3.5-5.0 3.4-4.5 3.3-4.3
Bending strength Electrode Mpa ≥10.5 ≥10.0 ≥10.0
Nipple ≥20.0 ≥22.0 ≥23.0
Elastic modulus Electrode Gpa ≤14.0 ≤14.0 ≤14.0
Nipple ≤20.0 ≤22.0 ≤22.0
Bulk density Electrode g/cm3 1.66-1.73 1.68-1.74
Nipple 1.75-1.82 1.78-1.85
CTE(100-600℃) Electrode 10-6/℃ 1.20-1.50 1.10-1.50
Nipple 1.10-1.40 1.00-1.30
Ash % ≤0.3

Description of calcined zone

The calcination zone is the highest temperature in the kiln, generally reaching about 1300 °C, and the high temperature calcination should reach about 1450 °C. The length of the calcined zone is affected by the length of the kiln and the negative pressure in the kiln, which is about half of the length of the kiln under normal conditions.
 

3 relevant conditions for calcination zone temperature

1. The temperature of the calcined zone is related to the amount of fuel injected and the calorific value. 2. It is related to whether the injected fuel and volatile matter are fully burnt. 3. A sufficient amount of air is needed. When calcining the delayed coke with a large volatile content, the combustion of fuel and volatile matter requires a large amount of air. If there is not enough air to support combustion, the temperature in the kiln will not rise, but the excessive amount of air will increase the oxidation of the raw materials in the kiln. Loss and increase the amount of exhaust gas.
 



Treatment method for insufficient air in the kiln

It is not enough to suck the air by the kiln head when calcining the delayed coke. It is necessary to add a secondary blast to the middle of the kiln to supplement the air.
 

Carbon oxide raw material oxidation loss is large

When the carbonaceous raw material is calcined in the rotary kiln, it is in direct contact with the high temperature flame, so the oxidation loss is relatively large.
 

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