The process of suspending preheating and rotary kiln calcination of kaolin

Kaolin, as an important non-metallic mineral material, is widely used in multiple industrial fields such as papermaking, ceramics, plastics, rubber, and coatings. With the growth of market demand and technological progress, the traditional calcination process has become unable to meet the requirements of high-quality and large-scale production. The suspension preheating plus rotary kiln calcination process, with its advantages of high thermal efficiency, low energy consumption, and stable product quality, has become one of the mainstream technologies in modern kaolin deep processing.

Process Description

The core principle of this process is to effectively preheat kaolin through a suspension preheating system, and then complete the high-temperature calcination process in a rotary kiln, thereby achieving the modification of the physical and chemical properties of kaolin, improving its whiteness, chemical stability and functionality.

This process has the following remarkable features:

High thermal efficiency: Utilizing the residual heat of flue gas to preheat the raw materials, thereby improving energy utilization rate;

Low energy consumption: The overall energy consumption is reduced by 20%-30% compared to traditional processes;

Continuous production: Suitable for large-scale industrial operation;

Stable product performance: Precise control of calcination temperature and time, resulting in high product quality consistency;

Good environmental performance: Facilitates tail gas treatment and reduces pollutant emissions.

Detailed Explanation of the Process

1.Raw material pre-treatment

To ensure the smooth progress of subsequent processes, the raw ore needs to be subjected to crushing and grinding treatment first:

Crushing: Crush the large pieces of kaolin ore to a particle size of ≤ 5mm;

Grinding and screening: Use equipment such as Raymond mill to grind the materials to a size of 200 mesh or above, and remove impurities;

Material adjustment: Add additives (such as fluxing agents) according to product requirements to optimize the calcination process.

2.Suspension preheating system

The suspension preheater is usually composed of multiple stages of cyclone tubes, forming an effective heat exchange system. At this stage: the fine kaolin powder flows in the opposite direction to the high-temperature flue gas from the rotary kiln, and undergoes rapid heat exchange in a suspended state in the pipeline;

The flue gas temperature drops from approximately 1000°C to 300-400°C;

The kaolin temperature rises to 500-700°C, completing the initial dehydration and partial decomposition reactions (such as hydroxyl removal).

3.Rotary Kiln Calcination

　　Calcination is the core step of the entire process, which is mainly carried out in a rotating cylinder that is inclined and installed:

The calcination temperature is controlled between 900-1250℃, causing kaolinite to undergo crystal transformation (such as converting into mullite and quartz);

The calcination time is generally 30 minutes to several hours, depending on the length of the kiln body, rotation speed and temperature regime;

The fuel can be coal powder, natural gas, etc., and clean energy can be selected according to environmental protection requirements;

Through multi-point temperature measurement and automatic combustion control systems, the temperature field is ensured to be uniform and stable.

4.Cooling and Post-Treatment

　　The calcined kaolin needs to undergo cooling and fine processing:

Quick cooling: Cool down rapidly through a vertical cooler or a rapid cooling device to prevent excessive crystal growth;

Grinding and modification: Perform ultrafine grinding (such as D90 = 2-5 μm) or surface modification (such as coupling agent treatment) according to the application;

Packaging and storage: The finished products are sieved, qualified, and then packaged, ready for shipment.

　Suspended preheater design: Optimized structural design to avoid short circuits and material accumulation, and improve gas-solid contact efficiency;

Rotary kiln temperature control: Utilize multi-point temperature measurement and intelligent combustion control system to ensure uniform temperature;

Raw material particle size control: Strictly control the grinding fineness and particle size distribution, which affects the preheating and calcination efficiency;

Atmosphere regulation: Adjust the oxidation, reduction or neutral atmosphere inside the kiln according to product requirements to inhibit iron and titanium coloration;

Automation control: Introduce PLC + DCS system to achieve intelligent monitoring and optimization throughout the process.

Application fields and product features

Application fields

　　Paper industry: As a filler and coating material, it enhances the whiteness and printing performance of paper;

Ceramic industry: Used in ceramic raw materials and glazes, it improves the sintering performance;

Plastics and rubber: Enhances the mechanical properties, heat resistance and dimensional stability of products;

Coatings industry: As a pigment, it improves the covering power and weather resistance of coatings.

Product features

　　High whiteness: up to 85%-95% (in accordance with ISO standards);

Good dispersibility: easy to disperse in the medium;

Strong chemical stability: resistant to acids and alkalis, and high temperature resistance;

Unique crystal structure: the mullite phase endows excellent thermal and mechanical properties.

Trend of industrial technology development

　　Intelligence and Automation: Promote full-process digital management to enhance production efficiency and product quality;

Energy Saving and Low Carbon: Develop waste heat power generation technology for flue gas and explore alternative clean energy sources such as hydrogen;

Product Specialization: Develop high-purity and high-activity calcined kaolin products for the high-end market;

Environmental Upgrade: Adopt low-nitrogen combustion technology and effective dust removal and desulfurization devices to meet stricter environmental standards.

Project Photos

A large domestic kaolin enterprise adopted the "4-stage suspension preheater + φ4.5×72m rotary kiln" process, with an annual output of calcined kaolin reaching 300,000 tons. The product has a whiteness of ≥ 92%, and the energy consumption is reduced by 25% compared to the traditional process. It is widely used in high-end paper coating and plastic fillers, with significant economic benefits and good demonstration and promotion value.

The suspension preheating and rotary kiln calcination process not only enables large-scale and efficient production of kaolin, but also significantly enhances the added value and market competitiveness of the products. With the continuous advancement of intelligent manufacturing and green manufacturing concepts, this process will play an even more important role in the future high-quality processing of kaolin, promoting the industry towards higher quality and sustainable development.