Rotary kiln use

Abstract: This paper introduces the application of nano porous insulation board in rotary kiln. After comparing many kinds of insulation and refractory materials, pointed out that the microporous nano microporous insulation plate for rotary kiln kiln shell temperature decrease, reduce heat loss and prolong the service life of equipment and improve the yield is a very suitable material.
Background: The operation of the rotary kiln is part of the process of producing portland cement and lime. The rotary kiln cylinder is usually large horizontal, the feeding position is slightly higher, by gravity to promote products through the kiln, through the slow rotation of the roll material in the kiln, continuous work at very high temperatures. The inner lining of the rotary kiln is protected by a dense refractory brick in order to avoid the high heat in the kiln.

Problem:
When the material is continuously rolled through the furnace, in order to withstand the long-term harsh mechanical wear, the kiln lining lining, must have a high enough density. This high density of refractories, in the case of effective wear resistance, also has two negative effects.
First of all, the dense refractory material has high thermal conductivity, and the refractory will wear off gradually with the time, which leads to the increase of shell temperature. In the case of rising fuel prices, the problem of high energy consumption, greatly affected the cost. The rise of the kiln shell temperature has a negative effect on the mechanical driving device and the safety of the workers in the area.
Second, the problem with dense refractories is that it exhibits a tendency to thermal shock. High density refractory material in the temperature change or the hot and cold temperature of the brick and the larger temperature gradient, there will be peeling or serious cracking occurs. If the refractory material is subjected to severe temperature changes, such as the rapid decrease of the shell temperature during the summer rainstorm, it is possible to cause the damage of the refractory lining, which will lead to the change of the lining of the kiln. Even slight spalling of refractory materials will also lead to reduced lining life. The maintenance of the refractory lining is required for the replacement of labor and materials, and is also costly to produce.

Insulation between refractory and steel shell:

In order to reduce the negative effects of high temperature and high density refractory conductivity and thermal shock tendency, the solutions adopted, can be achieved by simply putting the heat insulation material between the refractory material and the steel shell to achieve. Although this may sound simple, it is necessary to consider the following key points for choosing suitable insulation materials for such applications.

Heat resistance of insulating materials: The insulation must be able to work effectively at its exposure temperature, usually after the high density refractory brick. This temperature is different in different regions of the kiln, and in each region the temperature will rise with the increase of the refractory lining with long time in rolling contact wear of materials.

Thermal conductivity of insulation layer: Simply put, the lower the thermal conductivity of thermal insulation material, the better the lower heat loss, the greater the benefits of the use of. Thermal conductivity is governed by three mechanisms: conduction, convection and radiation. The best insulation layer will reduce the impact of all three mechanisms in the application temperature range. In addition to reducing the heat loss through the refractory lining, the low thermal conductivity of the insulating material will reduce the thermal gradient of the refractory lining (thermal surface temperature difference of the cooling surface temperature), resulting in a more uniform temperature distribution. This, in turn, reduces the thermal shock resistance of refractories.

Mechanical properties of thermal insulation materials: It is necessary to withstand the weight and movement of the bricks and tiles from the weight of the refractory brick and the continuous rotation of the kiln. If the insulation material is too soft, it will be compressed to its full advantage. If it is not able to withstand the continuous motion of the brick, the displacement of the brick or the movement of the whole brick ring will occur. No matter how small, it will decompose over time into powder, and cracking in the back of the refractory material, will endanger the integrity of the entire lining.

Insulation thickness: In the rotary kiln is the most commonly used refractory is high density refractory brick. The insulation material behind any refractory material will increase the total lining thickness, resulting in the reduction of the inner diameter of the furnace, so it is best to minimize the thickness of the insulating material. Some of the operators of the rotary kiln used refractory bricks placed behind the insulating brick, to reduce the heat loss, but compared to other insulation materials these bricks are high thermal conductivity and thick, while the need for more labor to install.

The best choice of insulation products is relatively thin (1 to 3cm), high thermal efficiency, and easy to install. Some rotary kilns use castable refractory, in which case the thermal insulation material is fixed with an alloy anchor, and the wet castable is then poured. In the case of pouring refractory material, the thickness of the insulation board can be slightly thicker, and the thickness of the inner lining can be controlled with a little casting material. However, in this case, it is necessary to avoid the microporous insulation board (core material) direct contact with water, insulation board can be used POF or aluminum foil packaging, to prevent water failure.

Selection of insulation materials:

The standard of choosing the best insulating material for rotary kiln has been stated as follows. The following are the most commonly used types of thermal insulation products, we analyze their advantages and disadvantages:

Insulating brick: Need a lot of labor, installation must be close. Thickness of 2.5 inches (more than 6.5 cm). But still has relatively high thermal conductivity.

Ceramic fiber blanket: 6-12mm ceramic fiber blanket can provide lower thermal conductivity than the insulation brick, and does not contain organic adhesive that will

burn at high temperature. But it does not have enough density to withstand the weight of the refractory lining and the mechanical wear in the application.

Ceramic fiber paper: Ceramic paper is thin and has a low thermal conductivity, but contains organic binder after heating, leaving only no mechanical strength of the

part.

Microporous insulation: Obviously the best choice for this application. A blend consisting of silica powder and fiber, as well as a special sunscreen, with a microporous structure, wrapped in a waterproof package. These products provide very good thermal stability, high compressive strength and very low thermal conductivity, thus minimizing heat transfer in all three ways

The benefits of using microporous insulation in rotary kiln:

- Has the lowest thermal conductivity in all high temperature resistant insulating materials because of the minimum heat transfer (conduction, convection and radiation)

of all three modes. This will greatly reduce the heat loss through the lining and reduce energy consumption.

- Reduces the temperature of the kiln shell and the heat of the driving device by reducing the heat loss of the lining.

- Insulating refractory brick placed behind the insulation material will reduce the thermal gradient of refractory bricks and refractory materials not prone to thermal

shock, thus prolonging lining life.

- Is easy to install, and only need to be cured by air cured refractory mud or contact adhesive.

- Microporous plate is thin, the standard thickness of 3mm to 15mm

Application case:

When the hot surface temperature of 1260 degrees C, the ambient temperature of 25 degrees, the use of 6 inches (about 15 cm thick) of high alumina brick, with microporous insulation board for calculation, using ASTM C-680.

Cross section of nano porous materials used in rotary kiln

Thus, as long as the laying of more than and 10 mm nanoporous insulation board, you can reduce the kiln shell temperature of more than and 200 degrees.

Summary:

The utility model can greatly reduce the heat loss, provide the life of the kiln body and the mechanical driving device, improve the loading capacity of the kiln body and protect the safety of the operators. This kind of material has been widely used in foreign countries. It is of great significance to promote this kind of materials to reduce the energy consumption and operating costs, and comply with the requirements of energy saving and emission reduction.