Overview of Vacuum Disc Drying Machine Equipment
Disc dryer, also known as disc dryer or plate dryer, is a mechanical stirring type conduction drying equipment developed on the basis of fixed bed conduction dryer and rake stirring type conduction dryer. In the 1950s and 1960s, the former Soviet Union had already used it for drying large quantities of brown coal. However, due to the generally low level of industrialization at that time and the high price of this complex drying equipment, it was difficult to promote to other industries. In the coal industry, it was also replaced by tube dryers with lower operating costs, which limited its further development. In his 1975 edition of "Drying Equipment", Tong Rongliang only cited inorganic salts as an example for the application of disc dryers. By the late 1970s, with the continuous improvement of production methods in industrialized countries, processing costs were no longer the main problem that troubled people. In addition, with the use of new materials and energy shortages worldwide, disc dryers once again entered people's vision with their outstanding energy-saving advantages. Germany, Belgium, Japan, the United States, Russia and other countries have specialized companies conducting research and manufacturing of disc dryers. Among them, Krauss Maffei, a German company with a longer history and greater success, has developed and manufactured a series of TT/TK (atmospheric pressure type), GTT (closed type), VTI (vacuum type) disc dryers, and successfully promoted them to the chemical, food, and pharmaceutical industries, evolving from the leader in coal drying equipment to modern fine chemical equipment.
The vacuum disc dryer is suitable for drying thermosensitive materials with very low temperature requirements, such as pharmaceuticals, vitamins, biological products, enzymes, solvent containing materials, etc. Wet materials are added in batches to a quantitative feeder that can withstand negative pressure. After turning on the vacuum pump to put the disc dryer in a negative pressure state, the materials are evenly added to the dryer through a continuous lock for drying operations. The dried materials are discharged from the discharge port at the bottom of the dryer. The moisture escaping from the material is recovered through the condenser and solvent receiving tank, and the entire operation process is carried out under vacuum.

Working principle of vacuum disc dryer
The wet material is continuously added to the first layer of drying disc on the upper part of the dryer by the feeder, and the rake arm with rake blades rotates to continuously flip the material. The material flows along an exponential spiral over the surface of the drying disc, and the material on the small drying disc is transferred to the outer edge, where it falls onto the outer edge of the large drying disc below. The material moves inward on the large drying disc and falls into the next layer of small drying disc from the middle feeding port. The drying plates of different sizes are arranged alternately up and down, allowing the material to flow continuously through the entire dryer. A hollow drying tray is filled with heating medium, which includes saturated steam, hot water, and thermal oil. The heating medium enters from one end of the drying tray and exits from the other end. The dried material falls from the second layer of the drying tray to the bottom of the shell, and is then transferred by the rake blades to the discharge port for discharge. Moisture escapes from the material and is discharged through the moisture outlet located on the top cover. Dry material discharged from the bottom layer can be directly packaged.
A vacuum disc dryer reduces the boiling point of moisture and removes moisture from materials at a pressure lower than atmospheric pressure, achieving the purpose of low-temperature drying. By using a vacuum pump to extract air and moisture, a vacuum state is formed in the working chamber, which accelerates the drying speed. Vacuum dryers are divided into static dryers and dynamic dryers, with the vacuum disc continuous dryer belonging to the dynamic vacuum dryer. The sealing between the upper and lower shafts of a vacuum disc dryer requires precision machining of the concentricity between the shafts. Packing can be added first, followed by mechanical sealing, welding of the cylinder, testing and pressure testing of the weld seam, and control of the continuous vacuum ball valve for feeding. These are all leakage points. If each link is not in place, it will affect the vacuum degree. Therefore, every link must be finely crafted to ensure a high vacuum disc dryer.

Process flowchart of vacuum disc dryer

Main features of vacuum disc dryer
(1) The disc dryer is a typical conduction heating dryer, which relies solely on heating the wall surface for material heating. The drying process does not require or only uses a small amount of dry gas to carry moisture. The heat lost due to exhaust is very small, and the thermal efficiency is high, theoretically reaching 100%. In practice, it can generally reach 60% to 80% or more. The energy consumption is low, with a unit steam consumption of 1.3-1.6kg steam/kg water.
(2) Due to the special stirring device, the material layer is thin, the stirring intensity is high, the heating surface renewal rate is high, and the exposed area of the material is almost larger than all conduction drying equipment. The heat and mass transfer resistance is small, the efficiency is high, and the total heat transfer coefficient can reach 250-670kj/(m2 · h. ℃) or more.
(3) Due to the thin material layer and good mixing effect, the dry and wet materials in the material layer, as well as the mixing of upper and lower materials, are well mixed. The drying time of the materials is much shorter than that of a general conduction dryer, usually within 5-60 minutes, and the discharge temperature is relatively low, which can be suitable for heat sensitive materials with less strict requirements.
(4) By changing the heating temperature, number of layers, number and speed of rake bars, structure and quantity of rake blades, and thickness of the material layer of the drying disc, the drying time can be controlled, and the material flow can be free from backmixing, thus obtaining uniform dried products. Materials with extremely low final moisture requirements can also be completed in one go.
(5) The low rotation speed of the agitator has little effect on material crushing, which can maintain the complete crystal form of the crystalline material. At the same time, the power consumption of the agitator is small, and the motor and reducer used are smaller than other rotary conductive drying equipment.
(6) Drying is mainly carried out by a heating plate, without introducing hot air or only introducing a small amount of hot air. The cross-sectional wind speed inside the dryer is low, and the dust entrainment is small. In some cases, the dust separation system can even be omitted, simplifying the process.
(7) Dryers can operate under normal pressure, as well as in a closed or vacuum, positive pressure environment, and can recover solvents. They are very suitable for drying heat sensitive, flammable, explosive, and toxic materials, and have a wide range of applications.
(8) Vertical structure, small footprint.
(9) No dust, low noise, no vibration, in compliance with environmental protection requirements.
(10) Compared with other types of drying equipment, the structure is more complex, the processing difficulty is greater, and the cost is higher.
(11) Due to the fact that materials cannot be highly dispersed during drying like convection drying, the material layer has a certain thickness, and the overall drying rate is generally lower than that of convection drying. A dryer with the same processing capacity usually has a larger volume than convection drying.

Scope of application of vacuum disc dryer
In recent years, vacuum disc dryers have been fully recognized by the engineering community at home and abroad for their excellent energy-saving characteristics. They are increasingly widely used in chemical, dye, plastic, pesticide, pharmaceutical, mineral products, food and agricultural products processing fields, such as activated carbon, activated calcium carbonate, ultrafine calcium carbonate, boric acid, dyes and dye intermediates, niacin, salt, caffeine, sodium cyanide, aluminum fluoride, acrylic acid salts, cellulose derivatives, melamine, plastic additives, foaming agents, accelerators, insurance powder, vulcanizing agents, sulfur, citric acid, fumaric acid, vitamin C and its intermediates, lanthanide compounds, mycelium, sterilizers, synthetic resins, bisphenol A, threonine, etc Meneb、 Pharmaceuticals, organic products, sucrose, sulfur concentrate, nickel concentrate, polyoxymethylene, ammonium nitrate, potassium sulfate, barium carbonate, aluminum hydroxide dry gel, potassium dihydrogen phosphate, graphite, etc. It can be widely used for continuous heating, drying, and cooling processing of materials in various industries that contain water or solvents, are easy to flow, non stick, loose powder particles, crystals, and amorphous materials.

With the increasing understanding of disc dryers in the industrial sector, new application areas are constantly being developed, such as dry acetylene for chemical reactions and calcination of various inorganic salts. In recent years, disc dryers have been rapidly applied to new energy lithium battery materials, and the projects involved are relatively large. The requirements for disc dryers used in lithium battery materials are higher, and the production materials for vacuum disc dryers are very high.

Photo of the production site of the vacuum disc dryer