Calcination Processes and Equipment for Common Synthetic Refractory Raw Materials
To compensate for the shortage of natural refractory raw materials and to meet the requirements of high-quality refractory production, Chinese researchers in the refractory materials field have developed a variety of synthetic refractory raw materials with excellent performance. These materials have been successfully put into industrial production and application, achieving favorable results.
At present, the main synthetic refractory raw materials produced and used in China include synthetic magnesia–alumina spinel, synthetic magnesia–chrome sand, and synthetic magnesia–calcium–iron sand.
To provide a better understanding of the calcination processes of these synthetic refractory raw materials, this article introduces the current calcination processes and equipment used for synthetic refractory raw materials in China.
01 Calcination Process and Equipment for Synthetic Magnesia-Alumina Spinel
At present, synthetic magnesia-alumina spinel produced by various enterprises in China can be classified into two types based on the raw materials used. One type is alumina-based magnesia-alumina spinel synthesized from industrial alumina and high-purity light-burned magnesia, while the other is bauxite-based magnesia-alumina spinel synthesized from high-quality bauxite and light-burned magnesia. The former belongs to high-purity products.
The calcination processes for synthetic magnesia-alumina spinel mainly include the dry briquetting high-temperature rotary kiln calcination process and the semi-dry pressing tunnel kiln calcination process.
1. Dry Briquetting & High-Temperature Rotary Kiln Calcination Process
High-purity light-burned magnesia is proportionally mixed with industrial alumina or high-quality high-alumina bauxite, followed by stirring, blending, and co-grinding. The mixture is then dry-pressed into briquettes using a high-pressure briquetting machine and subsequently fed into a high-temperature rotary kiln for calcination.
Enterprises adopting this process for producing synthetic magnesia-alumina spinel in China are mainly located in Liaoning and Henan Provinces. For example, a group company in Liaoning utilizes an ultra-high-temperature rotary kiln (φ2.0 m × 60 m) to calcine synthetic magnesia-alumina spinel. Heavy oil is used as the fuel, and the calcination temperature can exceed 1800 ℃. The rotary kiln has a production capacity of 3 t/h, with a fuel consumption of 250–300 kg per ton of product.
Magnesia-alumina spinel tends to adhere during the calcination process, and its adhesiveness increases with higher Al₂O₃ content. Therefore, careful operation is required when calcining synthetic magnesia-alumina spinel in rotary kilns-especially bauxite-based products-to prevent material adhesion to the kiln lining and the formation of clinker inside the kiln.
2. Semi-Dry Pressing & Tunnel Kiln Calcination Process
Light-burned magnesia is proportionally mixed with industrial alumina or high-quality bauxite, then blended and ground into a fine powder. A liquid binder is added to the powder in a roller mill to form a semi-dry mixture, which is then pressed into green briquettes using a friction press. After drying, the green briquettes are loaded onto tunnel kiln cars and pushed into the tunnel kiln for calcination.
An enterprise in Henan Province uses an ultra-high-temperature tunnel kiln to calcine both alumina-based and bauxite-based synthetic magnesia-alumina spinel. The tunnel kiln is 96 m long, uses heavy oil as fuel, and can reach a maximum temperature of 1800 ℃.
An enterprise in Shandong Province employs a 104 m gas-fired tunnel kiln to calcine bauxite-based synthetic magnesia-alumina spinel, with the calcination temperature ranging from 1620 ℃ to 1650 ℃.
During the calcination of bauxite-based magnesia-alumina spinel in tunnel kilns, the green briquettes are prone to adhesion and plastic deformation. This may lead to the collapse of briquette stacks, causing damage to equipment and kiln structures. Therefore, attention should be paid to the stacking method when loading green briquettes onto kiln cars, and various operational controls should be strengthened during calcination to prevent stack collapse.
At present, some enterprises in China also use high-temperature shuttle kilns to calcine synthetic magnesia-alumina spinel. This calcination process is suitable for applications involving multiple product varieties and relatively small production volumes.
02 Calcination Process and Equipment for Synthetic Magnesia-Chrome Ore
Synthetic magnesia-chrome ore is one of the earliest developed and most widely used synthetic refractory raw materials in China. The main raw materials used for its production include light-burned magnesia, chromite concentrate, industrial alumina, bauxite, and iron oxide powder.
The calcination processes for synthetic magnesia-chrome ore mainly include the semi-dry pressing tunnel kiln calcination process, the dry briquetting rotary kiln calcination process, and the dry briquetting shaft kiln calcination process.
1. Semi-Dry Pressing & Tunnel Kiln Calcination Process
The raw materials are proportionally batched, mixed, and ground into a fine powder. A liquid binder is then added in a roller mill to produce a semi-dry mixture, which is pressed into green briquettes using a friction press. After drying, the green briquettes are loaded onto tunnel kiln cars and pushed into the tunnel kiln for calcination.
For example, a refractory materials company in China adopts this process to calcine synthetic magnesia-chrome ore and other synthetic refractory raw materials.
2. Dry Briquetting & Rotary Kiln Calcination Process
High-purity light-burned magnesia and chromite concentrate are proportionally batched, mixed, and ground into a fine powder, then dry-pressed into briquettes using a high-pressure briquetting machine and fed into a high-temperature rotary kiln for calcination.
At present, the main specifications of rotary kilns used for calcining synthetic magnesia-chrome ore in China are 1.7 m × 40 m and φ2.0 m × 60 m.
For instance, a refractory materials company in Henan Province uses a 1.7 m × 40 m ultra-high-temperature rotary kiln to calcine synthetic magnesia-chrome ore. Heavy oil is used as the fuel, and the calcination temperature ranges from 1850 ℃ to 1900 ℃. The elliptical briquettes fed into the kiln have dimensions of 38 mm × 25 mm × 15 mm. The production capacity is 1.0 t/h, and the fuel consumption is 250 kg per ton of product.
3. Dry Briquetting & Fuel-Fired Shaft Kiln Calcination Process
An enterprise in Liaoning Province uses high-purity light-burned magnesia and chromite concentrate as raw materials. After batching, mixing, and grinding, the materials are dry-pressed into briquettes using a high-pressure briquetting machine and then calcined in a high-temperature fuel-fired shaft kiln to produce high-purity synthetic magnesia-chrome ore.
03 Calcination Process and Equipment for Synthetic Magnesia-Calcium-Iron Ore
Synthetic magnesia-calcium-iron ore is mainly used in the production of dry ramming mixes for the hearths of ultra-high-power electric arc furnaces. The raw materials used for manufacturing synthetic magnesia-calcium-iron ore include light-burned magnesia, light-burned dolomite, quicklime, and iron oxide powder.
The calcination processes for synthetic magnesia-calcium-iron ore mainly include the semi-dry briquetting coke-fired shaft kiln calcination process, the semi-dry pressing tunnel kiln calcination process, and the dry briquetting rotary kiln calcination process.
1. Semi-Dry Briquetting & Coke-Fired Shaft Kiln Calcination Process
Light-burned magnesia powder, light-burned dolomite powder, and iron oxide powder are weighed separately and then proportionally fed into a roller mill, where they are mixed with water to form a semi-dry mixture. The mixture is subsequently sent to a briquetting machine and pressed into briquettes. After drying, the briquettes are charged into a shaft kiln fueled by coke or anthracite for calcination.
This calcination process is characterized by simple operation and low production costs, making the products well received by users. Most enterprises engaged in the production of synthetic magnesia-calcium-iron ore in Liaoning Province, China, adopt this calcination process.
2. Semi-Dry Pressing & Tunnel Kiln Calcination Process
Light-burned magnesia, slaked lime, and iron oxide powder are proportionally batched, mixed, and ground into a fine powder. The powder is then transferred to a roller mill and blended with water, after which it is pressed into green briquettes using a friction press. After drying, the green briquettes are loaded onto tunnel kiln cars and pushed into the tunnel kiln for calcination.
A company in Shandong Province applies this process to calcine synthetic magnesia-calcium-iron ore.
3.Dry Briquetting & Rotary Kiln Calcination Process
High-purity light-burned magnesia, high-purity light-burned dolomite, and iron oxide powder are proportionally batched, mixed, and ground into a fine powder. The mixture is then dry-pressed into briquettes using a high-pressure briquetting machine and subsequently fed into a high-temperature rotary kiln for calcination.
A refractory materials company affiliated with a group in Liaoning Province adopts this process to calcine high-purity synthetic magnesia-calcium-iron ore.
In the production of synthetic refractory raw materials, the development and promotion of the dry briquetting high-temperature fuel-fired shaft kiln calcination process are essential. This calcination process is characterized by simple operation, and the high-temperature fuel-fired shaft kiln offers advantages such as a high calcination temperature (exceeding 1900 ℃), large production capacity, and low fuel consumption.
It is currently regarded as one of the most advanced calcination processes for refractory raw materials in China and has already been applied in the calcination of high-purity synthetic magnesia-calcium ore. In the future, its application should be extended to the production of other synthetic refractory raw materials, such as synthetic magnesia-alumina spinel, synthetic mullite, and synthetic magnesia-chrome ore.
The wider adoption of this calcination process will play an important role in improving the calcination quality of China's synthetic refractory raw materials, as well as in saving energy and reducing consumption.