Indigo drying is mainly divided into raw powder indigo drying and commercial indigo drying. In general, the indigo used for export is mostly raw flour.
The method for drying the raw powder is mainly the synthesis of indigo, which is pressed into the dryer after the press filter presses the filter cake. At present, most of the dryers used for the drying of the original powder indigo are rake dryers, paddle dryers, and rotary dryers. In these three models, the heat transfer modes of the first two dryers are mainly conduction and heat transfer, and the latter is convection heat transfer. According to the production method, the rake dryer is intermittent drying, and the paddle dryer and rotary rapid dryer are continuous drying.
The author believes that when the production scale is small, the rake dryer should be used for drying; when the production scale is large, a continuous drying machine such as a paddle dryer or a rotary quick dryer should be used for drying. This is because paddle dryers and rotary rapid dryers have a high one-time investment and are not economical when they do not reach a certain scale. When the output is large, using these two models, although the investment is high, but the production efficiency is high, the working environment is good, the labor intensity is small, the production process is easy to realize automation, and the product moisture content is even. In addition, one problem that cannot be ignored is that indigo is easily entrained by dry gas because of its relatively low relative density (around 200 kg/m3). In these three dryers, the order of the amount of entrainment is: rotary quick dryer, paddle dryer, rake dryer. Therefore, when these types of dryers are used, the scale of gas filtration equipment is different. In particular, in the case of rotary rapid dryers using convection heat transfer, the particles of indigo can reach about 0.2 microns, and the process of gas-solid separation is more important, requiring a larger filter area for filter materials. The efficiency requirement is higher.
The production of commercial indigo requires the use of a spray dryer. The production of indigo requires the pretreatment to achieve the same standard strength. Standardized process treatment refers to high-speed beating in the liquid state after adding a variety of additives, the raw material is a flowable liquid, the solid content is 25% to 30%, so it needs to be spray-dried to obtain powder or granular product. If a pressure spray dryer is used for drying, the product particle size can be maintained between 80 and 180 mesh. Indigo is a relatively heat-resistant dye. Dry hot air inlet temperature can be between 230 °C ~ 240 °C.
The method for drying the raw powder is mainly the synthesis of indigo, which is pressed into the dryer after the press filter presses the filter cake. At present, most of the dryers used for the drying of the original powder indigo are rake dryers, paddle dryers, and rotary dryers. In these three models, the heat transfer modes of the first two dryers are mainly conduction and heat transfer, and the latter is convection heat transfer. According to the production method, the rake dryer is intermittent drying, and the paddle dryer and rotary rapid dryer are continuous drying.
The author believes that when the production scale is small, the rake dryer should be used for drying; when the production scale is large, a continuous drying machine such as a paddle dryer or a rotary quick dryer should be used for drying. This is because paddle dryers and rotary rapid dryers have a high one-time investment and are not economical when they do not reach a certain scale. When the output is large, using these two models, although the investment is high, but the production efficiency is high, the working environment is good, the labor intensity is small, the production process is easy to realize automation, and the product moisture content is even. In addition, one problem that cannot be ignored is that indigo is easily entrained by dry gas because of its relatively low relative density (around 200 kg/m3). In these three dryers, the order of the amount of entrainment is: rotary quick dryer, paddle dryer, rake dryer. Therefore, when these types of dryers are used, the scale of gas filtration equipment is different. In particular, in the case of rotary rapid dryers using convection heat transfer, the particles of indigo can reach about 0.2 microns, and the process of gas-solid separation is more important, requiring a larger filter area for filter materials. The efficiency requirement is higher.
The production of commercial indigo requires the use of a spray dryer. The production of indigo requires the pretreatment to achieve the same standard strength. Standardized process treatment refers to high-speed beating in the liquid state after adding a variety of additives, the raw material is a flowable liquid, the solid content is 25% to 30%, so it needs to be spray-dried to obtain powder or granular product. If a pressure spray dryer is used for drying, the product particle size can be maintained between 80 and 180 mesh. Indigo is a relatively heat-resistant dye. Dry hot air inlet temperature can be between 230 °C ~ 240 °C.
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