1. What is a Continuous Vacuum Belt Dryer?
Definition and Industrial Purpose
A continuous vacuum belt dryer is an industrial drying system that continuously feeds, dries, cools, and discharges materials under vacuum. It converts conventional static batch drying into a continuous process and can handle liquids, pastes, powders, granules, and crystalline materials. Machines of this type are used in the pharmaceutical, food, biotechnology, and chemical industries, where it is important to operate in a stable manner and to be able to control the drying process.
Vacuum Belt Dryer vs. Traditional Drying Equipment
Compared to a vacuum drying oven, continuous vacuum belt drying alters the process from static batch drying to continuous vacuum drying. For liquid and paste-like materials, the drying process can be significantly faster than conventional methods, which typically require 10–20 hours and, in extreme cases, much longer drying times, allowing for end point control and thereby reducing risk of degradation through protracted exposure to heat. Typical drying times for suitable materials are in the region of 30-60 minutes.
The lower product temperature of vacuum belt drying makes it more suitable for heat-sensitive products than spray drying. The enclosed system also reduces the risk of external contamination. As long as the process is set up correctly, compatible organic solvents can also be recovered.
2. Belt Dryer Working Principle: How It Works
By lowering the boiling point of the material’s liquid under vacuum, moisture or solvents evaporate at lower temperatures under vacuum conditions. The subsequent steps of conveying, cooling, size-reduction, and discharge are material-type dependent; i.e., whether the material is a liquid or paste or a powder and/or aggregate particle type.
Step 1: Continuous Material Feeding System
The process starts by feeding the material into a closed system. For liquids and pastes, the material is pumped into the dryer by an infeed pump and distributed to the dryer belts by a distribution device.
For powders and solid particles, the material is fed and distributed to the conveyor belts by a feeding and distributing device, operating under vacuum.
Step 2: Heating Zones and Vacuum Drying Process
Liquid and paste-like products are spread evenly on the belts and then dried on the heating plates, which are heated by steam, hot water, or thermal oil. The required heating as well as the belt speed can be influenced by the viscosity of the product, its thermal sensitivity, the initial moisture or solvent content, and the required residual moisture.
For powder and particle materials, the wet solid is distributed between the different layers of the conveyor belt in the cylindrical shell. The movement of the belts continuously turns and redistributes the material, improving its exposure to the controlled heating and vacuum conditions and promoting more uniform evaporation.
Step 3: Cooling and Discharge Mechanism
Liquid and paste vacuum belt dryers are equipped with a cooling zone before the end of the dryer. In this zone, the dried product is cooled. At the end of the dryer, a special vacuum crusher can be installed in order to mill the product into the required powder or granule form. After milling, the product can be further processed.
For powder and particle vacuum belt dryers, the product is then continuously discharged by vacuum through a collection device. Enclosed vacuum comminution and discharge help to prevent dust, product loss, and external contamination.
3. Main Types of Vacuum Belt Dryers
Liquid and Paste Vacuum Belt Dryers
A liquid and paste vacuum belt dryer is primarily used to dry highly viscous, easily agglomerating, sensitive to heat, or thermoplastic materials. The material is dried at a temperature of between 30 and 300°C for a period of between 30 and 60 minutes. Such a unit is ideal for drying products such as botanical extracts, herbal extracts, plant extract, malt extract, and instant beverage, etc.
Various models are available for different production conditions. An MJY30-4 model has a heating area of 30 m² and processes 15 to 25 kg/h of water evaporation, whereas an MJY200-10 model has a heating area of 200 m² and processes 160 to 180 kg/h of water evaporation.
Powder and Granule Vacuum Belt Dryers
Powder and particle vacuum belt dryers consist of a cylindrical housing with 3 to 11 conveyor belts in layers. With an increasing number of layers, the capacity is enhanced. The drying temperature can be varied from 20 to 300 °C and the drying time from 20 to 120 minutes. It is mainly suitable for drying various solid, crystalline, particle, powder, pill, fruit raw materials in industries such as chemical, new energy, new materials, pharmaceuticals, food, etc; And the equipment is particularly suited for easily oxidizing, flammable, explosive, irritating, or toxic materials.
Models for powder drying: MJG15-3, a model with a 15 square meter heating area. Evaporating capacity 8 to 12 kg/h. MJG220-11, a model with a 220 square meter heating area. Evaporating capacity 120 to 150 kg/h.
4. Core Advantages of Using a Vacuum Belt Dryer
High Efficiency with Continuous Production
The vacuum belt dryer continuously feeds, dries, cools, and discharges product within a closed vacuum system. In contrast to batch-type dryers, which have to be filled and emptied again and again in a time- and labor-intensive manner, continuous conveying within a vacuum belt dryer runs without interruptions. A PLC automatically controls operating conditions such as belt speed, vacuum, heating-zone temperature, and feed rate are controlled automatically and in a continuously running mode, thus making it possible to operate in a largely automated manner.
Low-Temperature Drying for Heat-Sensitive Materials
Moisture or solvent is able to evaporate under vacuum at a lower temperature than it would under atmospheric pressure. This allows the drying conditions to be adjusted for heat-sensitive materials and can reduce the risk of thermal degradation during prolonged processing. When the process parameters are properly matched to the material, the dryer can help preserve characteristics such as color, and aroma..
Energy Savings and Reduced Operating Costs
The short residence time, continuous operation, and fully automatic process control in comparison with long drying batches result in lower labor and energy expenses per end product. The closed system also has the advantage of lower material losses. By equipping the system with a suitable condenser and recovery system, compatible solvents such as ethanol, acetone, or methanol can also be recovered. Solvent recovery can lower raw-material replacement and waste-treatment costs, although the actual savings depend on the solvent properties, recovery efficiency, and operating conditions.
5. Key Considerations When Choosing Manufacturers
Equipment Customization Capabilities
Selection of a dryer configuration will depend on several factors such as the feed form, the viscosity of the material, the initial moisture or solvent content, the thermal sensitivity of the material, the target moisture content, and the production rate. Due to large variations in evaporation capacity based on material properties and operating conditions, pilot testing by a supplier is critical in determining factors such as heater area, number of belts, belt speed, vacuum level, temperature profile, etc., and associated solvent recovery configuration. Minjie Machinery provides a low-temperature drying and concentration test platform for initial material test work prior to the final selection of equipment.
Comprehensive After-Sales Service and Technical Support
A manufacturer’s infrastructure and certifications are crucial for reliable technical support. Shanghai Minjie Machinery was founded in 1998 and covers an area of 58,000 square meters. More than 250 employees, including 15 senior engineers, work for the company. To guarantee the quality of our products, we have invested more than 10 million RMB in importing high-quality equipment such as automatic argon arc welders, automatic laser cutters, and CNC machine centers.
FAQ
Q: How does the belt dryer working principle ensure uniform product quality?
A: Uniform drying of powders, granules, flakes, and sheet-like products is achieved by feeding them in a controlled manner and spreading them evenly on the conveyor belt. It is necessary to keep a constant belt speed, vacuum, feed thickness, and drying temperature in all the heating zones. For powder and granule applications, controlled material movement can further improve exposure to heat and vacuum. The aim of uniform drying is to achieve a uniform residual moisture content.
Q: What can be dried with a Vacuum Belt Dryer?
A: A continuous vacuum belt dryer can be used for all kinds of liquid, paste, solid, crystalline, and powder-like materials. In the pharmaceutical industry, it is used for botanical extracts, herbal extracts, plant extract, and fermentation liquids. The food industry uses it for malt extract, for carbohydrates, for instant beverages, for tea powder, for cocoa powder, and for corn paste. The chemical industry uses the dryer for products such as lithium battery materials and emamectin benzoate. Because of the closed system, the vacuum dryer is very suitable for products that are easy to oxidize, flammable, or highly toxic.
Q: Which has a higher cost: a continuous vacuum belt dryer or a traditional dryer?
A: Continuous vacuum belt dryers typically require a higher initial investment as they are configured with items such as vacuum, conveyor, heating/cooling zones, and a control system. However, for high-volume products and/or products that are heat sensitive, the operation can result in lower lifetime operating cost by reducing time to process, manual handling, etc., and better product recovery. Also, where appropriate, recovery of solvents. A cost comparison would typically include capital, production capacity, labor, energy, cleaning, yield of product, and value of solvent recovered.
