Overview of Vacuum Disc Drying Machine Equipment
Vacuum rake dryer is used for drying materials in industries such as medicine, food, and chemical engineering: suitable for slurry, paste, and paste. At present, the conventional rake dryer includes a frame, a drying cylinder set on the frame, a feeding port and a discharging port on the drying cylinder, a rotating shaft passing through the drying cylinder, and a driving mechanism located on one side of the drying cylinder to drive the rotating shaft to rotate around itself. The rotating shaft is equipped with a rake type flipping structure, and the material enters the drying cylinder from the feeding port. The rake type flipping structure is driven by the driving mechanism to flip the animal material. Some drying cylinders are also equipped with a jacket to pass through the drying heat source, which accelerates the drying efficiency of the material in the drying cylinder. However, this type of rake dryer still has unsatisfactory drying efficiency and drying effect, mainly due to the following defects:
1. The vacuum rake dryer cannot be evacuated during feeding and discharging. In general, the entire process from feeding to discharging takes 6-8 hours, and only one batch of materials can be dried at a time, which cannot be produced continuously.
2. Due to the solid rake shaft of the vacuum rake dryer, no heating medium can enter the interior, resulting in the heat transfer interface of the dryer being only the inner wall of the cylinder. Due to the large filling capacity of the material inside the dryer, which can only reach 70%, the heat transfer area of the dryer is small, the drying time is long, and the output is low.
In response to the national energy-saving trend and environmental protection needs, Baide Drying has developed and designed a single axis disc vacuum continuous dryer to solve the problems of existing vacuum rake dryers not being able to continuously vacuum and produce, with small heat transfer area and low output. The application and development prospects are broad.

Process flowchart of vacuum disc dryer

Working principle of vacuum disc dryer
The vacuum disc dryer integrates heat conduction drying and stirring conveying, and is a novel and efficient energy-saving continuous vacuum drying equipment. It was first used for low-temperature drying of fish meal and has been successfully applied in multiple industries. In addition to drying sludge generated by urban and industrial wastewater treatment plants, it is also widely used in fish processing, meat product processing, brewing, and drying of different types of industrial products.
Vacuum disc dryer is a typical indirect heating drying equipment. The heat medium enters the jacket of the dryer cylinder, the central shaft, and the inner cavity of the disc. The wet material enters the dryer through the feeding port, and is flipped and stirred under the action of the hollow disc, constantly updating the heating surface. It contacts the disc and the inner wall of the cylinder to transfer heat, and the moisture evaporates, causing the material to dry. The heat medium condenses in the hollow cavity of the disc, forming condensed water, which is discharged from the dryer through the condenser tube. The transportation of materials in the dryer is achieved by disc plates. In order to prevent materials from adhering to the turntable and causing material accumulation, scrapers are installed between the discs. The scraper is fixed on the cylindrical shell and extends into the gap between the disks, scraping off the material bonded to the heating disk to clean the heat transfer surface and enhance the drying effect.
Under the continuous stirring of various scrapers, the wet material in the dryer constantly updates its heating interface, and is fully and uniformly heated after coming into contact with the inner wall of the cylinder and the heating disk. The large amount of steam generated during drying is pumped by the vacuum pump through the induced draft duct to the tube condenser, where it exchanges heat with the cooling circulating water in the heat exchange tube of the tube condenser. A large amount of exhaust gas releases heat and is converted into exhaust gas condensate, which is pumped out of the machine by the condensate pump and enters the sewage tank for centralized treatment.

Design points of vacuum disc dryer
1. The main shaft of the vacuum disc dryer is a hollow seamless thick walled tube, with a steam inlet at one end and a condensate outlet at the other end. Several heating discs are arranged in parallel on the shaft;
2. The heating disc is a hollow heating circular blade, horizontally connected in series and welded to the hollow shaft. Each heating disc is equipped with a scraper on the outer surface, and steam inlet pipes are installed inside the disc. Each steam inlet pipe is connected to the hollow shaft. At the position where each disc is connected to the hollow shaft, there is a condensate outlet pipe, and each condensate outlet pipe is connected to the hollow shaft; The disc and scraper are perpendicular to each other. The end of the steam inlet pipe near the hollow shaft extends into the interior of the hollow shaft, while the end of the condensate outlet pipe near the disc does not extend into the interior of the blade;
3. The sealing structure set at both ends of the hollow shaft adopts a double sealing form of packing sealing and encrypted sealing chamber. In the sealing component, the packing is always in a compressed state, so that the interior of the cylinder is always in a vacuum state, which can eliminate the gap formed between the hollow shaft and the packing due to rotation and ensure reliable sealing.
4. The hollow shaft of the single axis vacuum disc dryer is uniformly arranged with concentric heating disc blades. Both the hollow shaft and the disc are hollow structures, and heating medium can be introduced into their interiors. Steam enters from the steam inlet end of the hollow shaft and then enters each disc through steam inlet pipes. The condensed water in the blades is collected in the hollow shaft and discharged from its condensed water outlet. The material is heated in the single axis vacuum disc dryer due to the heat transferred by the disc and the inner wall of the cylinder, and is stirred under the rotation of the scraper on the disc before being discharged from the discharge port. Due to the fact that steam can be introduced into both the hollow shaft and the disc, the single axis vacuum continuous disc dryer increases the heat transfer area per unit volume, shortens the drying time, increases output, and reduces production costs.
5. To solve the problem of continuous feeding and discharging of the disc dryer during continuous vacuum operation, a vacuum switching valve is installed at the outlet of the feed and discharge ports in the single axis vacuum disc dryer to ensure that the interior of the single axis vacuum disc dryer can only be fed in and out while maintaining a vacuum state.

Structural diagram of vacuum disc dryer equipment

Comparison of Application of Vacuum Disc Drying Machine
1. Comparison with conventional rake dryer
Compared with conventional rake dryers, the total energy consumption (converted to standard coal) of a vacuum disc dryer for producing 1000 tons of citric acid is 33.7% to 38.8% of that of a rake dryer, saving 70-92 tons of coal; Drying efficiency>61%, twice that of rake type; The drying strength is about three times that of the rake type; The drying time is 15-60 minutes, which is 1/4 to 1/20 of the rake type.
2. Comparison with box dryer
Similarly, based on the production of 1000 tons of active CaCO3, the total energy consumption of the plate dryer is 21% to 27% of that of the box type, the drying efficiency is 4 to 5 times that of the box type, the drying intensity is 7 to 8 times that of the box type, and the drying time is only 1/10 to 1/50 of that of the box type.

Practice has shown that the vacuum disc dryer, as a novel and efficient energy-saving continuous conduction drying equipment, has the characteristics of high operational flexibility, good performance, reliable operation, closed and continuous production, high drying efficiency, low energy consumption, and good environmental protection. It has become one of the ideal industrial equipment for continuous drying and/or cooling processing in various industries, and its application and development prospects are broad.