Comparison of advantages and disadvantages of commonly used nanometer calcium carbonate powder drying equipment

There are many conventional drying methods, such as tray drying, rotary flash drying, air drying, spray drying, belt drying, and the like. In the production process of nano calcium carbonate, more drying methods are belt drying, spray drying, rotary flash drying and the like.

There are many conventional drying methods, such as tray drying, rotary flash drying, air drying, spray drying, belt drying, and the like. In the production process of nano calcium carbonate, more drying methods are belt drying, spray drying, rotary flash drying and the like.

1, belt dryer

A belt dryer consists of several independent unit sections. Each unit section includes a circulating fan, a heating device, a separate or common fresh air intake system, and an exhaust gas exhaust system. Therefore, the operating parameters such as the amount of drying medium, temperature, humidity and circulation of the exhaust gas can be independently controlled to ensure the reliability of the operation of the belt dryer and the optimization of operating conditions. The belt dryer is to place the filter cake on a stainless steel perforated track or stainless steel mesh belt through a squeezer. Slowly passing through the dryer under the action of the transmission device, the hot air indirectly heated by steam is forced through the material layer through the blower to perform a top-down cycle to make the material dry.

The machine is characterized by large contact area between hot air and material, short drying time, stable operation during drying, small dust and large production capacity. The disadvantage is that the equipment has a large area, a large number of circulating fans, and high power consumption.

2, spray dryer

Spray drying is the liquefaction of liquid material into a very fine mist in a hot drying medium, which is completed in an instant by drying and granulation. The technology can be made into uniform spherical particles, and its fluidity and bulk density are large. The particle size and moisture of the powder can be controlled by adjusting the operating parameters of the dryer. The method is easy to operate continuously in production, and the production capacity is large. An effective method for industrial production. Hu Qingfu et al. also introduced the spray drying process in the new “double spray” process for manufacturing nanometer calcium carbonate. Gas using coal as the heat source (or stove using coal as the heat source), the combustion gas in direct contact with the wet material, high thermal efficiency, dry strength, and eliminates the step of pulverization and sieving.

Since the material can be dried in an instant and its temperature is kept in a low range, the spray drying process is particularly suitable for the production of nano-active calcium carbonate, and the best modification effect and uniform modification of the product can be obtained to prevent the cause. Excessive local temperature causes modification failure. However, this method has certain requirements on the dried slurry. The concentration or the size of the precipitated particles is too large, which will affect the atomization process, and the operation control is also complicated and has certain limitations.

3, rotary flash dryer

Rotary flash drying is a drying method for solid fluidization. The drying host has the function of mechanical dispersion and particle size adjustment of dry materials. After the filter cake material enters the drying host, it is mixed with the heated hot air. The material forms a granular fluidization under the action of hot air and mechanical dispersing force, and the heat and mass exchange is completed instantaneously. The dried material enters the trap to obtain a powdery product.

Flash drying has the following characteristics: 1) Instant drying, drying time 1~5 s, product is not hot, uniform quality, good fluidity; 2) system closed without cross-contamination, yield >99%; 3) heat source using hot blast stove , using coal, gas or liquid as fuel, the combustion mode is direct or indirect, hot air temperature is 90-800 °C; 4) high thermal efficiency, strong evaporation capacity; 5) adapt to filter cake, paste-like high moisture content dry. Although the application of rotary flash drying in the production of nanometer calcium carbonate is common, the phenomenon of powder agglomeration after drying is still a problem to be solved. Rotary flash drying of nano-calcium carbonate is shown in Figure 1.

In addition to these drying methods, some combined drying methods have also been applied. If multi-layer belt drying string rotary flash drying is used, it can not only exert the dry elasticity of the multi-layer belt dryer, but also can adapt to the drying advantage of high moisture materials, and can also use the characteristics of flash drying and rapid drying to ensure drying. , can guarantee the quality of products.