Lime, Calcined Dolomite, Cement Rotary Kiln Castables, Prefabricated Parts

Casting materials and prefabricated parts for lime, calcined dolomite and cement rotary kiln bodies

The rotary kiln is a dynamic kiln and is widely used in building materials, metallurgy, nonferrous metals, chemicals and other industries. Compared with other industrial kilns, the biggest feature of the rotary kiln is that the refractory materials built in the kiln rotate with the kiln body at high temperatures. The refractory materials are not only subject to thermal shock, erosion and wear by kiln gas and materials, but also to vibration stress and extrusion stress generated when the kiln body rotates. Therefore, the bricks of the kiln body are required to have sufficient strength, and the construction personnel are required to carefully build and strictly control.

As lime, calcined dolomite and cement rotary kilns, the kiln lining is more seriously worn because the materials entering the kiln are in block form. In addition, the kiln is often opened and stopped due to market and production needs. Sometimes the kiln is opened and stopped several times to more than ten times a year, and the temperature changes frequently, which is bound to put high demands on the wear resistance and thermal shock resistance of the kiln lining refractory materials.

 

Advantages and effects of lime, calcined dolomite and cement rotary kiln design

1. Composite prefabricated bricks are fixed to the kiln body by anchors, and the space between two rows of bricks is filled with shaped low thermal conductivity insulation boards and wear-resistant castables, so that the refractory material and the rotary kiln cylinder can operate synchronously, ensuring the integrity, firmness and thermal insulation of the masonry.

2. It meets the use conditions of the masonry being in a state of shock for a long time, ensuring that the average temperature of the high temperature section of the kiln shell is not higher than 210℃, improving the on-site operating conditions and increasing the service life.

3. Since the problem of bricks falling off during small brick masonry is solved, the maintenance frequency of refractory materials is effectively reduced, and the equipment operation rate and equipment operation safety are greatly improved.

4. The weight of the kiln lining is reduced, which reduces the operating load of the equipment motor and saves electricity.

5. The reduction of the surface temperature of the kiln effectively improves the thermal efficiency and reduces fuel consumption. The 500t/d calcined white kiln adopts this solution, and the annual energy saving can reach 3,000~4,000 tons of standard coal.

1. Material selection for high temperature section (discharge end to the middle of the kiln body)

Adopt our company's composite prefabricated bricks and castables for composite masonry. The composite prefabricated bricks used are made of wear-resistant layer and insulation layer composite prefabricated and baked at low temperature. The wear-resistant layer is made of wear-resistant mullite material. The selected materials mainly consider the material's thermal shock resistance, wear resistance, erosion resistance, high temperature strength and other aspects. Various materials are scientifically and reasonably proportioned to meet the various use conditions of the kiln. The insulation layer uses a standardized low thermal conductivity insulation board, which not only reduces the heat loss in the kiln, but also protects the kiln body to prevent the kiln body from being deformed due to excessive kiln temperature or excessive weight of refractory materials. In addition, when producing this prefabricated brick, high-quality and high-grade materials are selected as admixtures or composite admixtures to enhance its anti-stripping and wear resistance during use, while taking into account the high temperature strength and resistance to material impurities and gas erosion of prefabricated bricks. The casting material and low thermal conductivity insulation board used for composite masonry of prefabricated bricks are the same as the wear-resistant layer and insulation layer of prefabricated bricks in terms of material selection to ensure their synchronous reaction and overall performance.

2. Material selection for low temperature section (from the middle of the kiln body to the kiln tail)

The composite prefabricated bricks and castables of our company are used for composite masonry. The composite prefabricated bricks used are prefabricated with a wear-resistant layer and a thermal insulation layer and baked at low temperature. The wear-resistant layer of this section mainly uses wear-resistant materials. Its wear resistance and thermal shock resistance can not only meet the use requirements of this temperature section, but also its price is cheaper than that of the high temperature section materials, which reduces the overall cost of the rotary kiln refractory materials.

3. Material selection for the kiln head and kiln tail

The corundum mullite steel fiber wear-resistant castable is used, and the anchoring method is reinforced, that is: at a height of 130mm for the anchor hook, two reinforcing steel bars are welded in the circumferential direction to strengthen the integrity of the castables at the kiln mouth and kiln tail.

Active lime has the characteristics of large output, uniform calcination, high product activity, and few impurities, and it occupies a dominant position in the production of metallurgical lime. In the active lime rotary kiln, the refractory materials in the three main machines of the preheater, rotary kiln, and cooler play a vital role in the operation of the equipment. The inlet, kiln head, kiln tail and partition beam of the rotary kiln are complex in structure. They are repeatedly impacted and rubbed by block materials during the operation of the rotary kiln, and are prone to damage and peeling. They are the parts with the shortest service life in the rotary kiln system. The transfer chute is used to transfer materials into the rotary kiln. It is funnel-shaped and is easily damaged by the impact and wear of limestone, the scouring of high-temperature airflow and the erosion of alkaline materials. Due to the limitations of shape and position, the linings of these parts are mainly castables, and the performance requirements are relatively high. For example, the life of the wear-resistant castable of the active lime rotary kiln is lower than that of the refractory bricks of the kiln lining, which will cause abnormal maintenance and affect production.

There are many types of castables for lime rotary kilns, such as wear-resistant refractory castables, which are formed by integral casting and embedded with Y-shaped anchors to extend the service life of the kiln lining: Baosteel has developed a clay self-flowing castable for the top lining of the lime kiln preheater, which has good self-flowing properties, can be degassed, and has a dense and smooth castable body: Ma Steel has developed a castable based on the characteristics of the Fucas lime kiln, which is composed of fused magnesia and sintered magnesia as aggregates, micropowder as a binder, and steel fiber, etc., and has better physical and chemical properties than refractory bricks. A high-strength, low-cement refractory castable for large lime kilns has been developed, with mullite as the main raw material, fused white corundum powder as the matrix, and various micropowders added. The castable has high strength, good erosion resistance and thermal shock stability.

The kiln body speed of the active lime rotary kiln is 1.1-1.3r/min, the firing temperature is controlled at about 1300-1350℃, and the preheater temperature is generally 700-900℃. The castables used in the rotary kiln inlet and preheating chamber need to have high strength and wear resistance, and must withstand the erosion of high-temperature secondary air and materials entering the kiln. Therefore, they are also required to have good alkali resistance and thermal shock stability. Now, combined with the on-site investigation and the structure and working operation mode of the active lime rotary kiln, the physical and chemical performance requirements of the wear-resistant castables used are explained.

(1) Chemical composition. The composition setting of the wear-resistant castables used in the active lime rotary kiln system mainly considers the safety of refractory materials. AL2O3 is the main component of the wear-resistant castable, and its content directly affects the strength and high-temperature performance of the castable, so it is limited.

(2) Physical properties. The volume density of the wear-resistant castable after drying at 110℃X24h is close to the actual material demand per unit volume. The volume density index of the wear-resistant castable of the active lime rotary kiln is specified. The castable has a good density, which is conducive to resisting the wear of the raw materials in the kiln. Since the working condition of the active lime rotary kiln is the process of the raw materials rotating and rolling from one end to the other in the kiln, the lining is impacted and rubbed by the raw materials, and bears a high material load and heat load. The wear-resistant castable of the kiln lining has a certain compressive strength, thereby ensuring that the product has good anti-scouring and wear capabilities. Due to the large temperature difference between the kiln head and the kiln tail of the rotary kiln, about 300-400℃, and the castables at the kiln head and the feeding port are subjected to thermal stress caused by the alternating effects of cold and heat, it is easy to produce cracks inside and on the surface, reducing the strength and corrosion resistance of the castable, and easily leading to the peeling and falling of the lining castable, thus affecting the normal production of the rotary kiln. The thermal shock resistance of the wear-resistant castable of the active lime rotary kiln can be measured by the room temperature flexural strength index after 5 cycles of rapid cooling and heating at 1100℃ and room temperature water. The flexural strength of the castable after alternating hot and cold can also be measured. The castable's resistance to shear damage and spalling in the state of rotation at the working temperature of the rotary kiln can ensure that the furnace lining does not collapse or peel off under high temperature conditions, and is safe to use. The reburning line change rate and load softening temperature should be controlled within an appropriate range. The former determines the retention method of the expansion joint, and the construction body shrinks less after drying to avoid cracks in the joints with other materials that affect its use effect. The latter can show the quality of some raw materials. ​​​

Prefabricated parts for rotary kiln lining

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