Hollow blade dryer is a horizontal stirring continuous drying equipment mainly based on heat conduction. Due to the shape of the stirring blades resembling ship paddles, it is called a paddle dryer, and also known as a trough dryer or stirring dryer in foreign countries.

As the heat required for drying the device relies on indirect heating through thermal conduction, the drying process does not require or only requires a small amount of gas to remove moisture. Greatly reducing the heat loss carried away by the airflow and improving the heat utilization efficiency, it is an energy-saving drying equipment. Paddle dryers are widely used in industries such as petrochemicals, chemicals, metallurgy, food, pharmaceuticals, pesticides, etc. for drying powdered, granular, filter cake, and slurry materials.

Changzhou Lima Drying Engineering Co., Ltd. has improved and optimized the wedge-shaped hollow blade dryer based on the absorption of advanced technologies at home and abroad. It can indirectly heat or cool paste, granular, powdered, and slurry materials, and can complete unit operations such as drying, cooling, heating, sterilization, reaction, and low-temperature calcination. The special wedge-shaped stirring heat transfer blade in the equipment has high heat transfer efficiency and self-cleaning function of the heat transfer surface.

  working principle

The heat transfer surface of the hollow blade dryer consists of several parts such as blades, stirring shafts, and walls, and the heat transfer area of the blades accounts for a large part. Therefore, the equipment has a compact structure and a large heat transfer area per unit volume. In addition, stirring and mixing cause the material to vigorously flip, thereby achieving a high heat transfer coefficient, resulting in a small footprint and space, saving on factory construction costs. The drying process requires less gas and has a low flow rate, resulting in less dust being carried away by the gas. Therefore, the recovery of gas and dust after drying is convenient, and the recovery equipment has a small volume, which can save equipment investment. For the drying process that requires solvent recovery, the solvent concentration can be greatly increased. Due to the unique structure of the blade, the material undergoes alternating compression and relaxation during the drying process, which enhances the drying process. The filling rate of materials in the drying room is very high, which can reach 80% -90%. The residence time of materials can be adjusted by adjusting parameters such as feeding speed, stirring shaft speed, and material filling degree, from a few minutes to several hours. In addition, the material in the dryer moves from the feeding port to the discharging port in a piston motion, with a narrow residence time distribution, resulting in a uniform moisture content of the product. The blade has a certain axial angle on the mixing shaft, so it can continuously dry materials.

  Equipment structure

Taking the double axis dryer as an example, introduce its structure (hollow blade dryer can be divided into single, double, and four). It consists of a W-shaped shell with a jacket end face, an upper cover, two hollow shafts with blades, end covers at both ends, a rotating joint with a medium, a metal hose, and a transmission mechanism including gears and sprockets.

The core of the equipment consists of two hollow shafts and hollow stirring blades welded to the shafts. The blade shape is a wedge-shaped hollow semicircle that can be fed with heating medium. In addition to its stirring function, it is also the heat transfer element of the equipment. The two main heat transfer sides of the blade are inclined, so when the material comes into contact with the inclined surface, as the blade rotates, the particles quickly slide away from the inclined surface, constantly updating the heat transfer surface and enhancing heat transfer. A scraper is installed at the bottom of the triangular blade to scrape the material deposited at the bottom of the shell and prevent blind spots.

The arrangement of propeller blades and the dimensions of each part have certain requirements, and in addition to the propeller blades, auxiliary mechanisms are also installed in the feeding area, drying area, and discharging area to ensure stable operation and uniform drying of the whole machine. In addition, the duration of stay can also be adjusted.

  Equipment features

The main features of the blade dryer are:

1. The equipment has a compact structure, a large effective heat transfer area, and a small footprint

2. Uniform mixing, high thermal efficiency, and good drying effect

3. The propeller shaft can mesh with each other and has a self-cleaning effect, which can prevent materials from sticking to the wall

4. Low energy consumption and low operating costs

5. Small dust entrainment and minimal material loss

6. Indirect heating, non polluting materials

7. The blade shaft has low rotational speed and does not damage the shape and properties of the product

8. The equipment has great flexibility in operation and runs smoothly and reliably

  application

The paddle dryer has been successfully used in fields such as food, chemical, petrochemical, dye, and industrial sludge. The characteristics of heat transfer, cooling, and stirring of the equipment enable it to perform the following unit operations: calcination (low temperature), cooling, drying (solvent recovery), heating (melting), reaction, and sterilization. The stirring blade is also a heat transfer surface, which increases the heat transfer area per unit effective volume and shortens the processing time. The wedge-shaped blade heat transfer surface also has self-cleaning function. The compression expansion mixing function ensures uniform mixing of materials. The material moves in a "piston flow" along the axial direction, and within the axial range, the temperature, humidity, and mixing gradient of the material are very small.

Using thermal oil as the heat medium, the blade dryer can complete low-temperature calcination work. For example, calcium sulfate dihydrate (CaSO4 · 2H2O) is calcined and converted into calcium sulfate hemihydrate (CaSO4 · 1/2H2O). Sodium bicarbonate (NaHCO3) is converted into pure alkali (Na2CO3) through calcination.

Cooling media such as water, cooling salt water, etc. can be used for cooling. For example, the blade type cooling alkali machine used in the soda ash industry replaces the old-fashioned air-cooled cooling alkali machine, saving energy and exhaust gas treatment equipment, reducing operating costs, and can also be used for cooling titanium dioxide, nickel iron alloy powder, and various granular materials. The material can be cooled from 1000 ℃ to less than 40 ℃ in a single machine.

Drying, the main function of the equipment, does not use hot air, making solvent recovery, energy consumption, and environmental control in an ideal state that is easy to handle. It is particularly suitable for solvents that need to be recycled, flammable and easily oxidizable heat sensitive materials. It has been widely used in the fine chemical, petrochemical, and dye industries.

The uniformity of temperature, humidity, and mixing degree within the axial range allows the equipment to be used for heating or melting, or for some solid material reactions. It has been successfully used in the compound fertilizer and modified starch industries. Paddle dryers can be used to sterilize food and flour. The large heating area within the effective volume of the unit quickly heats the material to the sterilization temperature, avoiding prolonged heating and changing the quality of the material.

  Adapt to materials

1. Petrochemical industry: polyolefin powder, polycarbonate resin, high and low density polyethylene, linear low density polyethylene, polyacetal particles, nylon 6, nylon 66, nylon 12, acetate fiber, polyphenylene sulfide, propylene based resin, engineering plastics, polyvinyl chloride, polyvinyl alcohol, styrene, polypropylene, polyester, formaldehyde, styrene acrylonitrile copolymer, ethylene propylene copolymer.

2. Environmental protection industry: PTA sludge, electroplating wastewater sludge, boiler ash, pharmaceutical factory waste, sugar factory waste, monosodium glutamate factory waste, coal ash.

3. Feed industry: soy sauce residue, bone based feed, distiller's grains, food scraps, apple pomace, orange peel, soybean meal, chicken bone feed, fish meal, feed additives, and biological sludge.

4. Food industry: starch, cocoa beans, corn kernels, salt, modified starch, pharmaceuticals.

5. Chemical industry: Soda ash, nitrogen phosphorus potassium compound fertilizer, kaolin, bentonite, white carbon black, carbon black, phosphogypsum, sodium fluoride oxide, nitric acid, calcium, magnesium carbonate, sodium cyanide, aluminum hydroxide, barium sulfate, calcium sulfate, calcium carbonate, dyes, molecular sieves, saponins.

  Characteristic parameter table