Rotary dryers are a cornerstone of modern industrial processing, offering efficient, high-capacity drying for a wide range of materials. From traditional techniques to novel processes, rotary dryers are a diverse and reliable option for any facility looking to dry bulk solids.

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The following covers the many benefits these industrial drying systems can offer as well as applications and limitations. The article also explains how these dryers work and discusses considerations in design. 

Why choose a rotary dryer?

While a number of industrial dryer types are available, rotary dryers have remained a preferred choice for decades thanks to several key advantages: 

Customization. Rotary dryers are extremely customizable, allowing producers to tailor a system to their precise material and process goals. 

Reliability and longevity. Thanks to a robust build and simple mechanical operation, rotary dryers are recognized for their reliability and longevity. When properly maintained, a rotary dryer can operate for decades without issue. 

Tolerance to feedstock variation. One key advantage particularly suited to many bulk solids processing operations is the rotary dryer&#;s tolerance to variation in feedstock and processing conditions. Unlike with some other dryer types, slight changes in particle size distribution, moisture content, and even throughput do not cause process upsets. 

Added polishing of granules. Producers looking to dry a granular product also favor the rotary dryer for the &#;polishing&#; it can offer. The dryer&#;s rolling action helps to break off particle edges and further round granules, creating a premium product. 

High throughput. Rotary dryers are also favored for their high-capacity processing, which ranges from 1 tph to over 200 tph. This makes them an ideal fit for working with bulk solids. 

Rotary dryer operation

Rotary dryers consist of a large rotating cylinder (called the &#;drum&#;) set horizontally but at a slight angle. Material passes through the drum and is heated by a heating medium according to a predetermined temperature profile and retention (or residence) time to achieve a target moisture content. 

A burner is mounted at one end of the drum, and exhaust gas handling equipment is mounted at the other end. Flexible seals connect the rotating drum to stationary inlet and outlet breechings. 

Riding rings, or tires, support the drum and facilitate smooth rotation of the unit on trunnion roller assemblies. A drive assembly, most commonly a gear and pinion type, provides the power to rotate the drum. 

Material is fed into the drum at one end and discharged at the other end, with gravity and the rotation of the drum shell helping to convey material along the slight downward slope through the unit.

Rotary Dryer

Rotary dryer or rotary drum dryer is widely used to dry humidity granularity materials in the industries of mineral dressing, building material, metallurgy and chemical, coal mining, etc. Wide supply scope and simple operation are its main features, materials should be dried to 3-10% water content to meet the demands for briquetting.

Application

Coal, coke
Clays, phosphates
Starch Pulp
Minerals, fertilizers
Beet pulp
Floatation concentrates
Animal feeds
Germ, stillage
Sludges
Etc.

Rotary drying line

1. Furnace
1-1. Gas Stove
2. Materials
3. Feeding Conveyor
4. Inlet

5. Feeding Cover
6. Roller Ring
7. Carrier Roller
8. Drum
9. Transmission

10. Gear Ring
11. Roller Ring
12. Carrier Roller
13. Discharge Cover
14. Dust Collector

15. Chimney
16. Induced Draft Fan
17. Motor
18. Outlet
19. Discharging Conveyor

How it works

The material is fed in the rotary drum dryer by the conveyor, and when it&#;s coming through the cylinder, the hot air will flow from it and makes it dried,. The dried material will be collected at the output.

In this drying process, the material will move as the cylinder rotation. With the gravity, the material will fall from high-end to low-end. There are also copy boards in the dryer to raise the material, so that the material and hot air&#;s contact surface area increases, which helps to increase the drying rate and let the material forward.

After drying, the fine particles are collected by the dust collector and the exhaust gas is discharged by the dust collector.

Details show

inside

inside

drum

drum

riding wheel

riding wheel

cover plate

cover plate

Heat Source

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gas, diesel, coal, wood, steam, etc.

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Drying way

• Parallel flow: The wettest material comes in contact with the hottest gas as they enter the dryer. This results in a rapid evaporation and rapid cooling of the hot process gas. This typically allows the dryer shell to operate slightly cooler than the counter-flow configuration, which extends the life cycle and decreases maintenance of the dryer.

Features for parallel flow:

1. At the input area, the hot air is much higher than the raw material which leads a rapid heat exchange between the hot air and the raw material, moisture becomes easy to evaporate. This heat way is suitable for high moisture materials.

2. For the viscous materials, when it feeds into the dryer, as the rapid water evaporates, the moisture down and helps to reduce the bonding rate, the easier-move material increase the drying efficiency.

3. The low negative pressure in the feeding place leads to low air leakage from the input, thus keeps the hot air in the dryer steadier with the temperature and the velocity.

• Counterflow: Wet material is introduced into the drum on the opposite end that the hot gas enters the dryer and dry material discharges on the opposite end of the dryer as the exhaust vapour.

Features for counter flow:

1. Suitable for material with low moisture and low heat sensitive.

2. The drying rate is evenly distributed. So counter flow is more suitable for material which is strict with the final moisture.

3. Low dust. As the heating air move from the dry end to the wet end, as the function of the wet air, there will be less dust in the exhaust.

cocurrent dryer (Parallel flow)

cocurrent dryer (

counter current dryer (Counter flow)

counter current dryer (

Note: The heating way depends on the requirement of the final product.

Features for rotary drum dryer

Compare to other drying machines, the rotary dryer has advantages as follow:

1. With high capacity, continuous production;

2. Simple structure, easy on operating;

3. Low failure rate, low cost of maintenance.

4. The wide range of adaptation, it can be used to dry varies of material even with high adhesion;

5. Flexible operation. The quality of final product won&#;t be much changed when the capacity changes.

6. Easy to clean.

Parameter

Model Gradient (%) Diameter (mm) Length (mm) Speed (rpm) Power (kw) Capacity (t/h) Weight (t) RD 3-5 600 3-8 3 0.5-1.5 2.9 RD 3-5 600 3-8 4 0.6-1.2 3.1 RD 3-5 800 3-8 4 0.8-2.0 3.5 RD 3-5 3-8 4 0.8-2.5 5.6 RD 3-5 3-8 5.5 1.0-3.5 6.7 RD 3-5 3-8 5.5 1.5-3.5 7.2 RD 3-5 3-8 7.5 2-4 8.8 RD 3-5 3-8 7.5 1.8-5 9.8 RD 3-5 3-8 11 2-6 10.5 RD 3-5 2-6 15 3.5-9 13.5 RD 3-5 2-6 15 4-11 15.4 RD 3-5 2-6 18.5 5-12 18.9 RD 3-5 2-6 18.5 5-15 23.2 RD 3-5 2-6 22 8-20 26.1 RD 3-5 2-6 30 8-23 36.5 RD 3-5 2-6 37 10-24 38.8 RD 3-5 1.5-6 37 10-25 42.3 RD 3-5 1.5-6 37 12-28 45.2 RD 3-5 1.5-5 45 18-30 50.7 RD 3-5 1.5-5 55 20-35 60.4 RD 3-5 1.5-5 75 25-35 70.4 RD 3-5 1.5-5 75 25-40 78.2 RD 3-5 1.5-5 75 30-45 104.9

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