Professor Zheng Shuilin talks about the status quo and trend of heavy calcium carbonate production technology in China

The main development trend of heavy calcium carbonate industry technology is large-scale, functional and intelligent, which is the intensification, stabilization, structural optimization or specialization of heavy calcium carbonate production, as well as improving production efficiency, reducing energy consumption, abrasion and reduction. The inevitable requirement of production cost is also an inevitable requirement for the market demand to increase significantly and to save the amount of resin in the polymer-based composite material for the development of production technology. Large-scale production is mainly due to the continuous increase in production capacity of a single production line.

The status quo of 1 heavy calcium carbonate production technology

The production technology of heavy calcium carbonate mainly involves beneficiation , ore crushing, milling and ultrafine grinding or ultrafine grinding and surface modification. Due to the rich resources of calcite , the high quality calcite resources with CaCO3 mass fraction ≥97% are abundant. At present, only simple washing and manual sorting are generally carried out in the production of heavy calcium carbonate in China.

The ore crushing generally adopts two sections. The first section mainly adopts a vermiculite crusher, and the second section adopts a hammer type or a counter crusher. When the original ore size is small and the mill feed size is coarse, a hammer crusher or a counter crusher can also be used.

1.1 Fine grinding and ultrafine grinding

At present, heavy calcium carbonate with d97≥5 mm is mainly produced by dry process. The equipment includes improved Raymond mill (suspension roller mill or pendulum mill) and roller mill (including roller mill/vertical mill, ring roller). Grinding, etc.) and ball mills, etc.

The ultrafine heavy calcium carbonate with d97 ≤ 5 mm is generally produced by a dry process, and partially by a wet grinding + drying process. Dry production mainly uses barrel ball mill + classifier, roller mill (including ring roller mill with internal grading, vertical mill / press roller mill), dry agitator mill + classifier. Papermaking grade superfine heavy calcium carbonate slurry with d97≤5 mm, especially d90≤2 mm, is generally produced by wet method. The main equipment is agitating mill and sand mill.

The ball mill + classifier production line is mainly used to produce heavy calcium carbonate fine powder and ultrafine powder with d97=5~43mm. It is characterized by continuous closed circuit production, multi-stage classification, large cyclic load (300%~500%), and single machine production capacity. Big. The production line has been in use since the mid-to-late 1990s and is one of the major production technologies for the world's largest ultra-fine heavy calcium carbonate production line.

Ring roller mill is the most widely used fine grinding and ultra-fine grinding equipment in the field of heavy calcium carbonate in China in the past 10 years. It is characterized by large crushing ratio and low energy consumption per unit product. The internal or external fine classifier can produce ultra-fine products with d97≤10 mm. The fineness of the product can be adjusted between d97=5~40 mm; the most suitable product size range is d97=10~30 mm. Since its application in 2005, the equipment has been continuously improved and its stand-alone production capacity has been continuously improved. Taking the production of d97=10 mm as an example, the production capacity has increased from the initial 500 kg/h to the current 3 500 kg/h; The consumption has been declining, from the initial 200 kW·h/t to the current 100 kW·h/t.

Roller grinding (vertical roll grinding / roller grinding) is one of the main large-scale equipment for fine grinding and ultra-fine grinding of heavy calcium carbonate. It is characterized by large pulverization ratio. The most suitable product size range is d97=15~45 mm. After the external fine grader, it can produce ultra-fine products with d97≤10 mm. The product has good grain shape and low oil absorption value. It is suitable for the production of heavy calcium carbonate filler for unsaturated polyester-based composites (artificial stone), and the energy consumption and wear per unit product are low.

Wet superfine grinding technology is mainly used to produce paper coating (slurry) grade products with d90 ≤ 2 mm and d97 ≤ 2 mm and ultra-fine heavy calcium carbonate with d60 ≤ 2 mm (used as plastic filler after drying). Generally, one or two continuous ultrafine grinding processes are used. It consists mainly of a wet agitator or sander and a corresponding tank and pump.

Due to the continuous increase in the demand for ultra-fine heavy calcium carbonate slurry in the Chinese paper market, the industry scale of heavy calcium carbonate wet superfine grinding has grown rapidly since 2000, and the pace of equipment enlargement has been accelerating. Before 2000, the ultra-fine heavy calcium carbonate slurry mainly used 80-500 L stirring mill or grinding and stripping machine; the 1500 L stirring mill was used around 2002; the 3 000 L vertical mixing mill was used in 2003; A 5 000 L vertical mixing mill was used; in 2010, 8 000 L vertical mixing mills were developed; 12 000 L vertical mixing mills have been developed.

Stand-alone production capacity (d90 ≤ 2 mm, dry basis) increased from 300 kg/h in 1995, 500 kg/h in 2000, 1 000 kg/h in 2003, and 2 000 kg/h in 2005. More than 5,000 kg/h in 2013; energy consumption per unit of product is about 250~300 kW·h/t in 1995, 180~300 kW·h/t in 2000, 120~150 kW·h/t in 2003, 2009 The annual temperature is 90~110kW·h/t, which is reduced to 70~90 kW·h/t in 2012.

1.2 Surface modification

Surface modification is one of the most important deep processing technologies for heavy calcium carbonate and ultrafine heavy calcium carbonate. In the past 10 years, the demand for surface modified products has increased at a rate of more than 12% per year. The surface modification of heavy calcium carbonate mainly adopts organic coating and composite modification methods. The organic coating modification is an organic coating, such as stearic acid and its salt, an aluminate coupling agent, a titanate coupling agent, a water-soluble polymer, etc. as a surface coating/modifying agent, and a heavy calcium carbonate. A method in which a powder is coated to modify it. At present, dry modification is the mainstream process of heavy calcium carbonate, and wet modification is rarely used unless a wet superfine grinding process is employed.

The dry modification process is a process in which the powder is dispersed in a surface modification apparatus after being dried or dried, and a surface modification agent is added at the same time to perform surface modification at a certain temperature. Before 2000, due to the small market demand, the surface modification of heavy calcium carbonate mainly used intermittent high-speed mixer. This batch surface modification equipment is difficult to meet the requirements of large-scale stable production and energy saving and environmental protection. Therefore, with the rapid growth of the demand for surface modified products and the improvement of product quality uniformity and stability, the company has gradually used continuous powder surface modification equipment (such as SLG continuous powder surface modification machine). Replace the intermittent surface equipment.

Since 2005, SLG continuous powder surface modification machine has become the mainstream equipment for dry surface modification of heavy calcium carbonate.

Composite modification is a surface modification method that uses physical or chemical methods to uniformly mix in heavy calcium carbonate superfine heavy calcium carbonate powder or to coat another inorganic powder on the surface of the particles, such as compounding in heavy carbon calcium. magnesium hydroxide or aluminum hydroxide, calcium carbonate powder such modified filler for the cable, in addition to the original function, the function further flame retardant.

There are also some surface modification of heavy calcium carbonate in parallel with fine grinding or ultra-fine grinding, that is, adding surface modifier during fine grinding and ultra-fine grinding, and simultaneously finishing fine grinding of heavy calcium carbonate in the same equipment. Ultrafine grinding and surface modification. For example, the surface modification of heavy calcium carbonate fillers for unsaturated polyester-based composites (artificial stone) is accomplished during the fine grinding process of a vertical roller mill.

2 heavy calcium carbonate industry development trend

2.1 Industry development trend

Since 2000, the annual average demand for heavy calcium carbonate in China has increased by more than 10% per year. In 2010, its demand has reached about 10 million tons. It is expected that the market demand for heavy calcium carbonate at the end of the “Twelfth Five-Year Plan” (excluding heavy calcium carbonate for desulfurization and feed) will exceed 16 million t/a.

The production and operation of China's heavy calcium carbonate industry will gradually develop from decentralized to intensive. Regions or enterprises with resource advantages will form regional and inter-regional large enterprises or enterprise groups through government guidance, capital operation, restructuring and alliance. This is the inevitable use of resources efficiently. At present, the major production areas of heavy calcium carbonate such as Zhejiang Changxing, Zhejiang Jiande and Guangxi Hezhou have initially completed the enterprise restructuring optimization, the number of enterprises has been greatly reduced, and the per capita production efficiency has been significantly improved.

2.2 Technology development trend

The main development trend of heavy calcium carbonate industry technology is large-scale, functional and intelligent, which is the intensification, stabilization, structural optimization or specialization of heavy calcium carbonate production, as well as improving production efficiency, reducing energy consumption, abrasion and reduction. The inevitable requirement of production cost is also an inevitable requirement for the market demand to increase significantly and to save the amount of resin in the polymer-based composite material for the development of production technology. Large-scale production is mainly due to the continuous increase in production capacity of a single production line.

Large-scale production lines will drive the development of large-scale pulverizing equipment, large-scale grading equipment (especially dry fine grading equipment), surface modification equipment (especially continuous surface modification equipment), and corresponding drying and packaging equipment. From the end of the "Twelfth Five-Year Plan", China will build more and more single heavy calcium carbonate and ultra-fine heavy calcium carbonate production lines with an annual output of more than 200,000 tons and a single dry surface modification with an annual output of more than 50,000 tons. Sexually activated heavy calcium carbonate and ultra-fine heavy calcium carbonate production line.

Functionalization means that the application performance of the product will be continuously optimized to meet the needs of the market, and is a value-added technology that enhances the performance and value of heavy calcium carbonate applications. The main processing techniques for improving the functionality of heavy calcium carbonate products are surface modification and fine grading. Surface modification reduces the oil absorption value of the product, improves the compatibility of the heavy calcium carbonate with the organic resin and the dispersibility in the resin, can increase the filling amount of the heavy calcium carbonate and reduce or save the filling of the polymer material. The amount of resin has a huge market demand and is one of the main production technologies of special heavy calcium carbonate products. Fine grading technology can improve the application performance of heavy calcium carbonate in the fields of ink, paint, etc. It is one of the important production technologies of special heavy calcium carbonate products.

Intelligentization refers to the optimization of production management and control, and the intelligentization of production line control will be one of the main development trends of calcium carbonate production technology in the future. The increase in demand for large-scale production and reliable and stable product quality, the rising labor costs and the scarcity of skilled workers will drive the continued development of intelligent control of heavy calcium carbonate production lines.

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