A drum dryer is a rotating drum drying machine that reduces the moisture content of materials like wet sand, coal, fertilizer, minerals, and sludge. The drum rotates as hot air or gas flows through the system, evaporating moisture from the material inside.
There are two main types of drum dryers: a single drum dryer (single pass) and a three drum dryer (triple pass). This blog compares their designs, performance, and costs to help you choose the right industrial dryer for your drying plant.
1. Applicable materials
Single drum dryers can dry all materials and have large processing capacities:
- Common sand, rocks, raw ore, minerals, slag, tailings, and fertilizer.
- Wet coal, such as seed coal, fine coal, clean coal, anthracite, bituminous coal, coal gangue, coal slime, coke, petroleum coke, etc.
- Sticky materials, such as clay, sludge (river sludge, municipal sludge, chemical plant sludge, etc.), desulfurized gypsum, etc.
- Biomass materials, including sawdust and wood chips.
Triple drum dryers can handle materials that are non-sticky, with particle sizes limited to 30 mm. The drying cost is low and the effect is good. Common materials include sand (river sand, manufactured sand, silica sand, etc.), minerals (limestone, phosphate rock, iron ore, etc.), tailings, industrial salt, sawdust, etc.
In short, single drum dryers have a wider range of applications and can handle a variety of materials, especially sticky ones such as sludge and clay.
2. Dryer structure and design
Single drum dryer diagram:
This dryer consists of a large rotating drum. Its structure is simple and maintenance-friendly. Material flows in a straight line from the inlet to the outlet. Hot air flows either co-currently or counter-currently through the drum, drying the material as it tumbles.
Three drum dryer diagram:
The tripe pass system uses three nested drying drums, one within the other. The material enters the innermost drum and then passes through the other two drums in a spiral path, extending the drying time. While its structure is more complex than a single-drum dryer, it occupies a smaller footprint.
In short, the single pass dryer is simpler and easier to maintain, while the triple pass dryer saves much space and allows for longer material drying time.
3. Drying efficiency
The drum dryer's heat source is determined by the customer based on their fuel source, environmental impact assessment requirements, equipment investment costs, and production costs. Both dryers can use similar heat sources:
- Solid fuels: coal, biomass pellets, rice husks, wood
- Gaseous fuels: natural gas, biogas, coal gas, liquefied petroleum gas, waste heat flue gas, steam
- Liquid fuels: diesel, heavy oil, biomass oil
However, the two types differ in heat utilization efficiency and distribution:
- Single-drum dryers utilize a simple, linear airflow path, providing uniform and sufficient heat transfer and drying for materials with medium and high moisture contents. Drying times are more controllable and shorter. The material humidity can reach 0.5–1%.
- Three-pass dryers utilize a three-pass design, circulating heat between multiple drums for a longer residence time. Long, curved material paths can lead to uneven drying and overheating, causing hot air to stagnate and reduce drying efficiency.
In short, a single drum dryer dries the material in a shorter and more even manner. The heat from a three-drum dryer allows the material to remain in the dryer longer, but this can lead to overheating and uneven drying.
4. Operation and maintenance
Single drum dryer:
This single pass dryer offers a simple design with fewer components, making it easy to install and operate. Technical parameters like drying temperature, speed, and dwell time are easy to control, making this rotary dryer an ideal choice for workers who demand reliable and stable drying performance.
Three drum dryer:
In contrast, the three pass system is slightly more complex to operate, particularly about the regard to the calibration of the inner drum. It generally requires more technical expertise to manage correctly.
5. Investment costs
The purchase cost and installation cost of a single drum dryer are not high. The single pass has fewer points of failure and generally has a longer service life. Its simple design makes it easy to maintain, allowing for quick cleaning, easier parts replacement, and reduced downtime.
The three drum dryer is cheaper to purchase and more compact, taking up less space. However, in practice, it is more expensive to maintain:
- Multiple moving parts, multiple layers, and internal sealing systems are more susceptible to wear
- The internal drum can be difficult to inspect and clean
- Maintenance is more challenging
- There is a higher likelihood of material buildup and blockages
In short, single drum dryers offer better value in the long run. While three-drum dryers are cheaper and take up less space, they are more expensive to maintain.
Conclusion
Both single drum dryers and triple drum dryers have their own strengths and ideal use cases. Single drum dryers offer a wide range of applications, excellent drying results, and easy installation and maintenance. Three drum dryers have a small footprint and low initial cost.
Before investing in a drum dryer, consult a professional equipment manufacturer to assess your material characteristics, production goals, and site conditions. FTM Machinery, with its extensive experience in drying equipment, can help you customize an optimal drying solution.
