Maintenance of cement rotary kiln skinDate: 2019-07-22 Views:
1. Function of kiln skin
Kiln skin is cement clinker attached to the high temperature refractory surface in the kiln, which plays an important role in protecting kiln lining and prolonging refractory life.
The flame temperature of large new dry cement kiln is over 1700℃.Without kiln skin protection, the refractory surface will work at very high temperatures.Refractory materials are quickly destroyed by high temperature and erosion.The thermal conductivity of kiln skin is 1.16w/(m·K) and that of basic brick is 2.70w/(m·K).If there is 150mm thick kiln skin, the hot surface temperature of alkaline brick decreases from 1500℃ to 600 ~ 700℃, and the hot end expansion decreases from 105% to 006% ~ 007%.The workload has eased considerably.Thus, the erosion of refractory can be slowed down and the lining life can be maintained.
2. Formation process of kiln skin
In a cement rotary kiln, the flame continually heats the lining and the surface of the kiln charge.With the operation of the kiln, the kiln material is constantly tumbling.When the kiln material buries the lining material, the heat absorbed by the lining material is transferred to the kiln material, the temperature of the kiln material increases, the temperature of the lining material decreases, and part of the kiln material sticks to the lining material.When the kiln material is raised to the highest position, the kiln material falls under the action of gravity, the kiln material is separated from the kiln lining, and part of the kiln material attached to the kiln lining is torn off.This process is shown below.
With the extension of time, the surface of refractory began to "sweat", that is, liquid phase.At this point, the kiln material is buried in the kiln lining. The kiln lining transfers heat to the kiln material, and the temperature decreases, so that part of the kiln material can be attached and some of the fine kiln material can be "frozen" on the kiln lining.If there is more "frozen" kiln material and less "torn" kiln material falling, the kiln skin will slowly thicken.As the thickness increases, the surface temperature of the kiln skin increases.
If the temperature in the kiln or the composition of the kiln material changes sharply, or the "freeze" -" tear "balance is destroyed, or the kiln body expands/contracts to produce great stress. Or the kiln skin becomes pulverized due to the conversion of beta-c2s into gamma C2S in the kiln material, the kiln skin will fall off in a large area.However, as long as the firing conditions remain stable, the kiln skin will slowly form, and the refractory will play a protective role.If the firing condition changes too fast, the kiln skin frequently falls off, the life of the refractory will be greatly affected.
3. Maintenance of kiln skin
3.1 Hang on kiln skin
In general, it takes a long time (1 ~ 3d) to hang the kiln skin.In the process of hanging the kiln skin, the kiln skin shall be gradually thickened, and the speed shall not be too fast, so as to avoid hanging the loose kiln skin.
When hanging the kiln skin, the kiln body should be orderly and intact, the ovality should be normal, the operation of the kiln should be stable, and the frequency of opening and stopping the kiln should be reduced as far as possible.
When hanging the kiln skin, the composition of raw material and pulverized coal should be stable and appropriate to the kiln temperature, and the flame position and temperature field should be stable, so as to form melt with proper quantity and viscosity.
When hanging the kiln skin, the kiln material and lining brick should be adapted to each other, which is helpful for the kiln material to adhere to the brick surface and to infiltrate into the brick moderately, so that the kiln skin can be stable on the brick body.
At the beginning of hanging the kiln skin, the feed is 65% ~ 70% of normal, and the kiln speed is slowed down appropriately.When the kiln material is close to the firing belt, increase the wind and coal appropriately to make the surface of the firebrick "sweat", but not "burn flow".After the kiln reaches the firing belt, to ensure that the fire cooked, but not the fire, but also to control the grain size and uniform.Large clinker like walnut, small like peanut, small particles accounted for more than 80%, rolling flexible.After gradually increasing the feeding, until the 9th shift completely volatile normal.
3.2 Maintain kiln skin
Hanging kiln skin well is only the first step of long-term safe operation. More importantly, protecting kiln skin well creates conditions for high-quality, high-yield and long-term safe operation.Measures to maintain kiln skin are:
(1) stabilize the thermal system, maintain the fast rate of 85%;
(2) control the shape of the flame, do not make it brush kiln skin;
(3) avoid burning fire, burning top fire, prohibit burning flow or run yellow material, ensure the clinker granulation small and uniform, 5 ~ 20mm of small particles accounted for more than 80%, rolling flexible, into the cooling machine slightly raised dust;
(4) found that kiln skin is not good, to timely replacement hanging.