Principle, Construction, Working, Uses, Merits and Demerits of Drum Dryer

Drum Dryer

Principle

During the drying process, the outside of the rotating drum is coated with a thin layer of the product to be dried. Steam is used to heat the interior of the drum, quickly evaporating any liquid contained within. A knife is then used to remove the dried film or powder from the drum after almost one full revolution.

Constructions

Drum dryers move along with the beds they dry. In addition to being clean and resistant to chemical attacks, the unit is constructed of cast iron and stainless steel. It is meticulously machined so that the drums achieve a maximum and repeatable heat transfer over their entire lifetime, both to ensure maximum heat transfer and to accommodate high steam temperatures and pressures. Horizontally mounted hollow drums with a diameter of 0.6 to 3.0 meters and a length of 0.6 to 4.0 meters have smooth polished surfaces. Heating coils or steam can be used to force heat into the drum. Using a thermostat, heat can be transferred to a material by conduction. The drum is rotated at 1-10 r.p.m. by an electric motor.

Double Drum Dryer

The use of a double drum dryer can provide extra capacity. Dual drum dryers are commonly used to dry products with low to medium viscosities, along with being called double drum dryers. By spinning in opposite directions, the two drums form a pool. The product is then fed into this pool. In order to achieve the desired layer of film, it is possible to accurately set the small space between the drums. It is possible to combine these combinations depending on the desired product.

Vacuum Drum Dryer

Applications and measurements of equilibrium moisture content and rate of drying curve. Under vacuum, these drum dryers offer a higher capacity with less product loss. A high vacuum is used to turn two drums heated by steam in an air-tight housing. After the liquid has been fed between the drums from the top, it is dried before it is scraped off. No product residues accumulate and the material is not recirculated. Inspections and maintenance of the drum dryer are easy. The application ranges from damage prevention to evaporation of solvents at low temperatures, as well as protection of heat-sensitive components. Condensed vapors are collected elsewhere. A reproducible product quality depends on pollution and climatic conditions being absent. Such care can be beneficial for feed materials. Within seconds, the water vapor evaporates without the risk of oxidation. Enzymes and proteins that are thermolabile are maintained and prevented from being blocked. A liquid can easily dissolve the finished product. The dryer can also be used to process chemical products using a vacuum process and undergoing a drying process. It can keep its environment inert by using gases such as nitrogen.

Working

Single Drum Dryer

Drum dryers are still in use today because of their robust construction, which has allowed them to be used efficiently for over 60 years. Steam is used to heat the inside of the drum dryer. The steam-heated drum surface provides a uniform temperature distribution in order to provide a high-quality product. In the drying drum, steam condenses. So that the drum's interior remains as bare as possible for condensation of the steam, condensate is continually removed from the drum. It is a closed system, so it is impossible for the product to come into contact with steam or condensate. Depending on the design of the drum dryer, the drying product is applied either on the underside or on the top of the main drum. A drum dryer rotates, heating the inside and drying the outside of the product. By exposing the product for a short time at a high temperature, the product is less likely to be damaged. Water or solvent evaporating from the drum reduces its risk of damage. The vapor may also be sucked out of a drum via suction if necessary. At last, the dried product layer is scraped off with a knife.

Double Drum Dryer

While the drums are rotating together, the liquid is pumped into the valley between them and applied to each drum as it is applied to it. Each drum is equipped with a knife for removing the dry product. The drum rotates slightly less than one full rotation from one side to the other to complete the drying of wet materials. By scraping with a knife, dried materials are collected in a product receiver. Only a few seconds of contact between the hot metal and the materials is necessary. It is therefore closely controlled and monitored what film thickness is used and what temperature the drum is at. The electronic inverter in the control panel controls the shaft-mounted main drive speed. As the drum rotates, a thin layer of liquid or paste material adheres to the external surface of the feed pan.

Product Removal

Using a rigidly clamped alloy steel doctor blade or knife mounted in a cast iron knife bar assembly, the product is removed from the drum dryer surface. Pneumatic cylinders at the ends of the dryer apply the knife to the drum's surface. With either disposable or conventional knives, an oscillating knife system improves knife life and reduces drum maintenance. After the product has been removed from the drum, it is collected by a transverse screw conveyor. This conveyor is specially designed to break up the product film or flakes into easily handled pieces. An air compressor is available for products after removal from the drum that requires cooling.

Uses

• Drum dryers are used for drying sticky and highly viscous liquids and pastes.
• Drying temperature-sensitive items is done under vacuum, including proteins, vitamins, yeast, pigments, malt extracts, hormones, and antibiotics.
• The process is conducted within an enclosed area, protecting the environment and/or the product.
• Solution, slurry, suspension, etc. are dried with drum dryers.
• Starch products, ferrous salts, suspensions of zinc oxide, suspensions of calcium, insecticides, barium carbonates, etc., can be dried using these dryers.
• Vacuum drum drying is used in a variety of industries including instant beverage production, chocolate manufacturing, chemicals and recovery of solvents, foods, and beauty soaps.

Merits

• Its mass transfer rate is higher than drum dryers, so it provides rapid drying (few seconds).
• Heat is applied continuously to the entire material. Short drying times and minimal product heating are characteristics of this process.
• We offer tailored models that are compact and 100% closed systems.
• Because of their simplicity, only a few people need to learn how to operate them, and they don't require specialized maintenance.
• Drum dryers have the advantages of cheap installation and continuous operation 24 hours a day.
• A vacuum facility can be installed to prevent dust emission and thus ensure optimal hygiene throughout the entire production process.
• With its minimal energy consumption, this dryer does not require multiple filters to collect dust.
• By transferring heat through steam to the (metal) wall, this heat is transferred to the product on the other side. By transferring all the heat through the wall, there is no waste heat, making this dryer a more efficient way to dry products.
• These dryers enable control of product supply. Furthermore, drums prevent lumps from forming because they create a kneading action.
• The system is ideal for processing doughy or pasty products due to its ideal distribution over the entire length of the drum.
• Through the use of steam pressure, the drum temperature can be controlled in accordance with the requirements of the drying task and is therefore ideal for processing heat-sensitive products.

Demerits

• The operating conditions must be monitored since they are critical.
• Controlling feed rate, film thickness, rotation speed, and temperature requires skilled operators.
• Low concentrations or suspensions with low viscosities are not suitable.

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