What Is a Steam Dryer?
A steam dryer is a drying machine that utilizes steam to heat and dry processed materials.
Numerous rotating hollow discs, tubes, drums, casings, etc., pass steam through them to heat and dry the processed materials articulately. It is characterized by efficient heat transfer and substantial heat capacity. Commonly used for drying industrial waste such as sludge, sake lees, and pressed residue, as well as raw materials like ores and wood, the dried products are recycled as new raw materials.
Uses of Steam Dryer
The applications of steam dryers are rapidly expanding.
1. Reduction and Fuelization of Industrial Waste Sludge
Sludge generated from various factory water treatment facilities contains 60-85% moisture even after dewatering, and the higher the moisture content, the higher the disposal cost. By drying the sludge to around 10-30% moisture with a steam dryer, the volume of waste sludge is reduced, leading to a reduction in processing costs.
For organic waste sludge, effective utilization as fuel is possible. Examples include wood chips, coffee grounds, tea leaves, soybean meal, livestock manure, food residues, residues from vegetables and fruits, and byproducts of aquatic processing.
2. Feed and Fertilizer Production
Breweries produce byproducts such as sake lees and whisky lees during the manufacturing process, which become industrial waste. These byproducts contain abundant nutrients and fertilizer components. By using a steam dryer to reduce their moisture content to 10-30%, they can be easily handled as a powdery substance, allowing for effective use as feed and fertilizer.
3. Food Drying
Steam dryers are used for drying food items such as seaweed and shiitake mushrooms.
4. Applications in Industrial Raw Materials
Steam dryers are used in various applications, including recycling, sterilization, drying of resins, drying of inorganic minerals and fertilizers, drying of coke oven-inserted charcoal in steel mills, and sludge drying. They are also used for drying copper ore, iron ore, iron oxide, gypsum, incineration ash, soda ash, and more.
Principle of Steam Dryer
Steam dryers perform indirect drying using steam as a heat source. When gaseous steam condenses into a liquid during heat exchange, it generates significant latent heat. This heat is used to heat and dry the processed materials. The evaporated liquid from the processed materials, along with a small amount of carrier gas, is then expelled externally.
The moisture content of the dried product can be adjusted in two ways. One method involves changing the steam pressure to alter the drying temperature, and the other involves changing the rotation speed of the dryer’s axis. Adjusting the residence time of the processed materials in the dryer allows for moisture content adjustment.
Steam dryers use saturated steam as a heat source and combine conductive and convective heat transfer for efficient drying. Due to their low-temperature drying, even high-moisture organic waste can be heated and dried without altering its composition.
After drying, the product can be used as fuel, fertilizer, soil conditioner, feed, etc. While a steam dryer is used for drying wood using hot air, controlling factors such as the airflow path, temperature, and velocity is crucial. This process can reduce the time required for natural drying from 3-4 months to approximately 7-10 days.
Other information on Steam Dryer
1. Characteristics of Steam Dryer
Steam dryers have several characteristics:
1. Low Exhaust Volume
Due to being an indirect heating type, the exhaust gas volume is extremely low, resulting in compact exhaust gas treatment and deodorizing equipment.
2. Energy Efficiency
High thermal efficiency allows for reduced running costs.
3. Easy Operation
Capable of handling significant changes in processing volume and moisture content, making operational management easy.
4. Others
The high stirring effect minimizes moisture deviation, ensuring a uniform drying product. The system is sealed from the external environment, preventing gas leaks from the interior and external air inflow, making liquid recovery easy, and minimizing the use of carrier gas.
2. Types of Steam Dryer
Dryers are classified into direct heating and indirect heating types based on the utilization of the heat source. They are further categorized into natural circulation, forced circulation, and vacuum drying based on the air circulation method.
Steam dryers, for the most part, adopt the forced circulation method as an indirect heating type. They are further divided into disc type, tube type, drum type, chamber type, etc., based on the type of heat exchange part.
1. Disc Type
A shaft with numerous discs is installed inside a cylindrical shell. The discs, shaft, and shell are hollow, and steam is passed through to heat the entire shell. The shell is rotated, and the processed material introduced into the shell is dried and discharged from the shell exit. There is a method to prevent the adhesion of sticky processed materials by changing the rotation speed of multiple disc shafts.
2. Tube Type
Numerous tubes are arranged inside the shell. Steam is passed through, and the entire shell is rotated to dry the processed material inside the shell. Continuous operation is possible.
3. Drum Type
Steam is passed through a rotating drum, and the processed material adhering to the outer surface of the drum is dried, and the dried material is scraped off.
4. Chamber Type
Processed materials are placed in a drying chamber, and steam-heated drying air is directed at the processed material for drying. This is used for batch processing, such as wood drying.