Introduction to eight types of drying equipment in the pharmaceutical industry

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Drying equipment is widely used in industry, and it is needed in many different fields. Similarly, it plays an important role in the pharmaceutical industry as well. Today, the author will introduce the applications of eight types of drying equipment in the chemical and pharmaceutical industries. A brief analysis of the application of eight types of drying equipment in the chemical and pharmaceutical industries.   (1) Belt dryer   The belt dryer is composed of several independent unit sections. Each unit section includes a recirculation fan, a heating device, a separate or common fresh air intake system, and an exhaust gas discharge system. The operating parameters such as the quantity of drying medium, temperature, humidity, and exhaust gas recirculation rate can be controlled independently, thereby ensuring the reliability of the belt dryer’s operation and the optimization of operating conditions. The dryer with a dryer unit offers flexible operation; wet materials are fed in, and the drying process takes place within a completely sealed chamber, resulting in favorable working conditions and preventing dust from escaping. It is used for drying sheet-like, strip-like, or granular materials with good air permeability, and is particularly suitable for dehydrated vegetables, traditional Chinese medicine slices, and other materials with high water content for which the material temperature cannot be too high.   (2) Drum scraper dryer   A drum scraper dryer is a continuous-operating device that uses a rotating cylinder to dry liquid or strip-shaped materials attached to the outer wall of the cylinder through heat conduction. The liquid material that requires drying flows from the high-level tank into the receiving tank of the drum dryer. Driven by the transmission, the drying drum rotates at a specified speed. The material is used by a film-forming device to create a film on the surface of the drum wall. A heating medium is continuously fed into the cylinder to heat it; heat transfer through the cylinder wall causes the moisture in the material film to vaporize. Subsequently, a scraper removes the material that has reached the desired dryness level, which is then conveyed via a screw conveyor into a storage tank for packaging. The moisture removed by evaporation can, depending on its nature, be introduced into appropriate treatment devices through a sealed enclosure; it is usually water vapor, which can be released directly into the atmosphere via an exhaust pipe at the top of the enclosure. This machine is mainly used for processing liquid materials; it can be supplied with steam, hot water, or hot oil for heating and drying, as well as cold water for cooling and flaking. Depending on the properties of the materials and the process requirements, feeding methods such as immersion, spraying, and rolling can be employed.   (3) Hollow paddle dryer (blade dryer)   The hollow paddle dryer, also known as the blade dryer, is mainly composed of a W-shaped shell with a jacket, two hollow paddle shafts, and a transmission mechanism. Hollow blades are arranged along the shaft, and a rotary joint for introducing the heat medium is installed at the end of the shaft. The heat required to remove moisture is transferred to the material via the inner wall of the jacketed W-shaped groove and the walls of the hollow blades. During the drying process, the hollow shaft with hollow blades heats the material while simultaneously stirring it, thereby updating the heating surface. It is a continuous conduction heating dryer. The heating medium is steam, hot water, or heat transfer oil. The heating medium is introduced into the shell jacket and the two hollow impeller shafts, and the material is heated and dried through conductive heating; the structure of the hollow impeller shafts varies depending on the type of material.      This machine is suitable for processing various pasty, granular, powdered, and other materials with good thermal stability. Under special conditions, it can also dry heat-sensitive materials and recover solvents during the drying process. It is commonly used for the drying or cooling of materials such as carbon black, light calcium carbonate, titanium dioxide, barium carbonate, cyanuric acid, gypsum, clay, manganese dioxide, nylon and polyester chips, polyethylene, and polypropylene (as a recovery solvent).   (4) Vacuum rake dryer   The material to be dried is fed from the exact center at the top of the vacuum rake dryer’s housing. As the rotating rake teeth stir the material, its surface is continuously renewed as it comes into contact with the walls of the housing. The material is heated indirectly by steam (or hot water, heat transfer oil), which causes the moisture in the material to vaporize; the vaporized moisture is then removed promptly by a vacuum pump. The material to be dried is indirectly heated by a heat carrier, causing the moisture in the material to vaporize. The vaporized moisture is promptly removed by a vacuum pump.   Due to the high operating vacuum, typically in the range of 400–700 mmHg, the vapor pressure of water on the surface of the material to be dried is much higher than that in the evaporation chamber inside the dryer. This facilitates the removal of both the internal and surface moisture from the material to be dried, as well as the movement of water molecules within that material, thereby achieving the purpose of drying. The vacuum rake dryer is suitable for heat-sensitive materials that are prone to oxidation at high temperatures, materials that tend to cake during drying, as well as materials whose vapors emitted during drying need to be recovered. Typical dry materials include sodium acrylsulfonate, CMC, phthalocyanine blue, dye intermediates, carboxymethyl starch, maltodextrin, and anthraquinone sulfonic acid.   (5) Double-cone rotary vacuum dryer  The double-cone rotary vacuum dryer has a shape somewhat resembling an olive; it has lids at both ends, and two shafts in the middle to support the body of the dryer. The vessel body is equipped with a jacket for heating; during drying, the vessel body can rotate, allowing the material to be in constant contact with the vessel walls, thereby overcoming the low thermal efficiency of vacuum ovens, where heat is primarily transmitted through the heating cylinder. Rotary vacuum dryers are widely used in fields such as fine chemicals and pharmaceuticals, but they are not suitable for materials with high viscosity or strong adhesiveness during rotation. This equipment is primarily used in industries such as pharmaceuticals, chemicals, and food processing for the concentration, mixing, and drying of powdered, granular, and fibrous materials. It is also suitable for drying materials that require low-temperature drying, such as biochemical products. It is particularly appropriate for drying materials that are prone to oxidation, volatile, highly sensitive to heat, toxic, or those whose crystals must not be damaged.   (6) Spray dryer  Spray drying is the most widely used process in the industries involving the shaping and drying of liquid materials. It is most suitable for producing powdered or granular solid products from solutions, emulsions, suspensions, and pasty liquid raw materials. Therefore, when the particle size distribution, residual moisture content, bulk density, and particle shape of the final product must meet certain standards, spray drying is a highly desirable process.   (7) Vacuum oven After decompression, the evaporation temperature of volatiles contained in the material can be lowered; thus, it is suitable for drying various heat-sensitive and easily oxidizable materials. This device is usually a cylinder or some other enclosure capable of operating under vacuum, with heating provided by electric heat or hot water/heat transfer oil through heating plates or tubes; it is suitable for small-batch, batch production.   An oven is a general-purpose drying device with a wide range of applications; it belongs to the category of tray-type batch drying equipment and is used in the pharmaceutical, chemical, and food industries. Heating, curing, drying, and dehydrating of materials and products in industries such as light industry and heavy industry. Such as active pharmaceutical ingredients, crude drugs, processed Chinese herbal medicines, extracts, powders, granules, instant mixtures, water-soluble pills, packaging bottles, pigments and dyes, dehydrated vegetables, dried fruits and melons, sausages, plastic resins, electrical components, baked paints, etc.   (8) Rotary flash dryer: The material to be dried enters the drying chamber through a spiral feeder, where it is crushed by the agitator blades located at the bottom of the dryer. The crushed material comes into full contact with hot air; under the combined action of the agitator blades and the air flow distributor, it moves upward and dries. The material whose particle size and moisture content meet the required standards passes through a classifier and then returns downward to continue drying until it meets the specified criteria.   Product features: Fast drying speed. The dryer can be completed in 1–10 seconds; the material residence time is adjustable. It can be adjusted between 1 and 500 seconds, making it suitable for drying heat-sensitive materials. Various feeding devices are available, ensuring continuous and stable feeding without the formation of bridges. The circumferential air velocity in the drying chamber is high, resulting in a short residence time for the materials, which effectively prevents sticking to the walls and degradation of heat-sensitive materials. The drying chamber is equipped with grading rings and swirl vanes, allowing for adjustable control over the particle size and final moisture content of the materials. It offers high drying efficiency.