At present, domestic enterprises producing nanometer calcium carbonate usually adopt first-grade drying equipment such as drying room, conveyor belt drying, disc drying, rotary cylinder drying, spray drying, vacuum rake drying, rotating rapid drying and so on. However, almost every drying equipment encounters the problem of secondary agglomeration of product particles, which makes some nanometer calcium carbonate particles unable to exist as primary particles or close to this state, and ultimately affects the function and application of its products. Here, in the first stage of drying after the general re-grinding grading and sieving process.
Although drying is economical and simple, it is an intermittent operation with low production capacity, large energy consumption, harsh operating environment and high labor intensity. It is easy to introduce impurities, and the drying is not uniform. After drying, there is still a need for crushing and grading operation process. Therefore, this drying equipment has been gradually replaced by new drying technology.
Conveyor belt drying is actually an improved drying room, which makes the drying process continuous. However, the equipment covers a large area and has low thermal efficiency.
Although disc drying equipment solves the problem of large floor space and low thermal efficiency of conveyor belt drying equipment, the equipment is complicated in structure and difficult in maintenance. In order to reduce the adhesion of materials on the disc, the added copy plate has serious wear on the disc, and the resulting impurities have a great impact on the product quality.
Rotary cylinder drying equipment is widely used in the production of ordinary light calcium carbonate, and its production capacity is relatively high. The annual output of a rotary cylinder dryer with a diameter of 1.8m and a length of 21m can reach 15,000-20,000 tons. However, its drying temperature is generally 600-700℃, unable to adapt to the wet activated nano calcium carbonate production, because at this high temperature, almost no surface modifier without coking can be found. Here, the rotary cylinder drying is only suitable for the drying of nanometer calcium carbonate with a water content of 30-40%.
Spray drying can quickly dry wet calcium carbonate with water content of more than 60% to products with water content of less than 0.5%, and the products are in good dispersion state, and do not need to be ground and crushed again. However, it has poor adaptability to active nano calcium carbonate, because the high temperature required by nano calcium carbonate spray drying (generally above 400℃) makes it easy to burn off the surface modifier.
Vacuum rake drying is not widely used in the production of nano calcium carbonate. Its advantages are low drying temperature and high thermal efficiency. However, it has many auxiliary equipment, mostly intermittent operation, and its production capacity is restricted.
At present, rotary rapid drying equipment (also known as rotary flash drying) is widely used in the production of nano calcium carbonate. This technology has made some progress in solving the problem of particle agglomeration, but there are still some problems such as sticking wall and grinding after drying.
On 2018-08-08 11:45:46
