Selection of organic pigment drying equipment
The drying equipment mainly used in the production process of organic pigments includes: hot air circulation oven, belt dryer, rotary flash dryer, spray dryer, double cone rotary vacuum dryer and the like. Hot air circulation ovens are widely used in the pigment industry as a traditional drying equipment. The hot air circulation oven equipment is simple in operation and strong in applicability. Through continuous improvement in recent years, the thermal efficiency and production efficiency of the hot air circulation oven have been significantly improved, but due to the fatal shortcomings such as the difficulty in controlling the quality of the product, it is gradually being phased out.
Old-fashioned belt dryers have been widely used in other industries for a long time, but the pigment industry is rarely used. The main reason is that filter cake-like organic pigments cannot be dried directly using a belt dryer. To use a belt dryer, the pigment must be preformed. Therefore, choosing a suitable pigment forming system has a great influence on the performance of the belt dryer. It has a direct impact on drying uniformity, equipment production capacity, energy consumption, product appearance and tail gas treatment.
The through-flow belt dryer has only been used in the production process of organic pigments in recent years. It has high production efficiency, high degree of automation, stable product quality and high thermal efficiency. With the continuous improvement and improvement of belt dryers, The use of flow-through belt drying equipment is becoming more and more popular, and it has become the first choice for drying units in the production of organic pigments.
Selection of indigo pigment drying equipment
At present, the drying equipment used for drying the original powder indigo is mostly a drier dryer, a paddle dryer, a rotary quick dryer, and the like. Among the three models, the heat transfer modes of the first two dryers are mainly conduction heat transfer, and the latter one is convection heat transfer. According to the production method, the rake dryer is intermittent drying, and the paddle dryer and rotary quick dryer are continuous drying.
Indigo drying is mainly divided into raw powder indigo drying and commercial indigo drying. In general, the indigo used for export is mostly the original powder. When the production scale is small, dry drying equipment should be used for drying; when the production scale is large, it should be dried by a continuous dryer such as a paddle dryer or a rotary quick dryer. This is because the one-time investment of the paddle dryer and the rotary quick dryer is relatively high, and it is uneconomical when the scale is not reached. When the output is large, the two models are adopted. Although the investment is high, the production efficiency is high, the working environment is good, the labor intensity is small, the production process is easy to be automated, and the product moisture content is uniform. In addition, one problem that cannot be ignored is that indigo is easily entrained by dry gas because of its relatively low density (at around 200 kg/m3). In the three types of dryers, the order of the amount of entrainment is arranged as follows: a rotary quick dryer, a paddle dryer, and a rake dryer. Therefore, when these dryers are selected, the scale of the gas filtration equipment is different. Especially in the case of a rotary fast dryer based on convective 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 filtration area of ​​the dust collector and an efficiency requirement for the filter material. higher.
A spray dryer is required to produce the product indigo. Pretreatment is required for the production of commercial indigo to achieve the same standard strength. Standardized process treatment refers to high-speed beating in liquid state after adding various additives. The raw material is a flowable liquid with a solid content of 25% to 30%, so it needs to be spray-dried to obtain powder or granular. product. If the pressure spray dryer is used for drying, the product size can be maintained between 80 and 180 mesh. Indigo is a relatively heat-resistant dye, and the dry hot air inlet temperature can be between 230 ° C and 240 ° C.