Single Pass Vs. Triple Pass Rotary Dryer – Understanding the Differences
Rotary dryers are a versatile option for reducing moisture in a product. They are used with a variety of materials across a wide range of industries. Some of the novel ways our customers use rotary dryers to help repurpose materials that used to go to waste, include:
- Turning poultry bedding into fertilizer
- Turning municipal sludge into fertilizer
- Drying and sterilizing dairy bedding for reuse
- Drying hemp to prolong storage life
Uzelac Industries produces two types of rotary drums for our rotary drying systems—single pass and triple pass. In this blog post, we will explain the differences between the two to help you decide which type will work better for your drying requirements.
Single Pass Drum for Rotary Dryer
Single pass drums consist of one cylinder internally flighted. The drum rotates at a constant speed and product moves in one direction along the drum from inlet end to outlet end while being showered through an air steam with a large cross-sectional area. This drum mechanism is better at handling larger volumes of product without choking out the airflow. If you need to dry dense material, the single pass rotary dyer is the right choice.
Single pass drums have greater flexibility in flight design, helping us optimize shower pattern to spread material more evenly across the air stream. Another option we have in flight configuration for single pass drums is adding spiral flights in different patterns throughout the drum. These flights act like a screw conveyor and, depending on the orientation, can be used to either increase or decrease retention time.
Triple Pass Drum for Rotary Dryer
Triple pass drums consist of three concentric flighted cylinders nested inside of each other. The drum rotates at a constant speed and product moves in a serpentine path through the three cylinders. Product enters the inside of the inner cylinder and travels from inlet end to outlet end. When it gets close to the outlet end, the product hits the headplate at the end of the intermediate cylinder and changes direction, passing between the inner cylinder and intermediate cylinder and travels back toward the inlet end. Once it gets to the inlet end, product hits the headplate at the end of the outer cylinder, changes direction, and travels back toward the outlet end, between the intermediate cylinder and outer cylinder.
Triple pass drums are ideal for handling light materials and products that are sensitive to higher temperatures. This dryer mechanism can run at a lower temperature and has a higher air velocity due to the reduced cross-sectional area between the cylinders. Triple pass drums are more expensive up front but are more efficient and tend to have a lower cost of operation. This is because these drums run at a lower temperature, leading to less fuel consumption, and typically have a smaller drum drive since product is evenly dispersed between the three cylinders.
Another benefit to triple pass drums is that they have a smaller footprint, usually around 20% shorter than the equivalent sized single pass drum. If space is very limited, we also offer a shorter, larger diameter version of most single and triple pass drums, called a big belly drum. Big belly drums allow for an increase in drum volume without an increase in length.
When you need a reliable drying solution, our rotary dryers get the job done. We serve customers in many industries. Talk to us about your requirements and we can guide you to choose between single pass and triple pass rotary dryers. Contact us online or send us an email.