Though industrial rotary dryers are used mainly in the chemical and mining industries, they are also used in other sectors. The food industry utilizes rotary dryers for dehydrating waste materials like vegetable trimmings and citrus peels. They’re also employed to minimize moisture in animal feed without directly contacting the material with heated gas.
Rotary dryer designs consist of a long, inclined drum or cylinder-shaped shell, which features internal lifters or flights. Rotating slowly on bearings, drying materials go through a tumbling or cascading action. The shell’s inclination also affects the tumbling actions, and the nature of the material determines the gas flow through the cylinder. While there are numerous configurations for industrial rotary dryers, understanding the basics of rotary dryer design will help producers get the most out of these machines.
Industrial Rotary Dryer Designs
Rotary dryers fall into two basic categories. They heat material directly or indirectly, though certain rotary dryer designs offer direct and indirect heating capabilities. Rotary dryers that directly heat are the most economical and are used when direct contact with hot air or gas isn’t detrimental to the material. With indirectly heated rotary dryer designs, the drum is heated from an external source, drying the material through contact with the heated internal walls of the cylinder.
Direct vs. Indirect Rotary Dryer Designs
Made for high efficiency, rotary dryer designs usually employ direct heating techniques, which are more economical on fuel. When higher temperatures are needed during the drying process, directly heated industrial rotary dryers often utilize a combustion chamber. With material sensitive to heat, a steam coil is used that uses lower temperatures to dry material.
When it’s not possible to apply direct heat to a material, indirect rotary dryer designs are used that ensure heated gases don’t come in direct contact with the material being dried. Indirect industrial rotary dryers are typically designed for materials that are negatively affected by direct heat. Indirect rotary dryer designs are used for fine and ultrafine material, especially when entrainment is an issue.
Industrial rotary dryers are utilized to process both end products and prepare material for further processing. They offer numerous advantages during for bulk processing of material. While their basic makeup is standardized, rotary dryer designs can be customized to handle unique material characteristics, making it an efficient and reliable piece of machinery for a plethora of processing situations.
Customizing Industrial Rotary Dryers
There are several different ways to customize an industrial rotary dryer to make it more practical for specific applications, materials, and environments. This may include various configurations and types of flights, adding a combustion chamber, altering the size of the drum, incorporating a control system, and optimizing off-gas handling.
One of the most important aspects of rotary dryer design is the flight. Also called material lifters or shoveling plats, these implements affect performance significantly. Flights scoop material from the bottom of the drum, causing it to shower through the gas stream while it rotates. This helps maximize heat transfer efficiency by forcing the material to spread across the width of the drum.
Flights come in an array of designs that include:
- single bend
- double bend
- customized formations
Besides the design of rotary dryer flights, their pattern can be customized to optimize heat transfer. Customization may entail staggering or advancing flights, which are spiral-shaped and assist with moving material into the processing zone and away from the inlet to facilitate heat transfer better. Another way to customize industrial rotor dryers involves removing flights from a dryer section, a configuration known as a bald section.
Adding a Combustion Chamber
Adding a combustion chamber to an industrial rotary dryer offers numerous benefits for certain applications. While the primary purpose is simply to prevent material directly coming into contact with flames to protect its integrity, there are several other advantages.
- allows utilization of otherwise wasted heat from elsewhere
- enables better fuel combustion
- improves efficiency
- improves temperature control of gas entering the rotary dryer
- promotes uniform material heating
- reducing carbon dioxide emissions
Though most beneficial for heat-sensitive material, it reduces attrition regardless of the product.
Size of Rotary Drum
One of the most significant contributors to cost comes from the rotary dryer’s drum size. Though the size of drums can’t be altered with certain rotary dryer designs, certain designs offer flexibility. Simply increasing the velocity of airflow can compensate for a smaller drum. This can be achieved by incorporating a discharge hood to mitigate this higher air velocity.
Adding a control system to rotary dryer designs can help optimize performance. Well-designed controls offer operators tools to improve efficiency.
Depending on the control system, it provides advantages that may include:
- allowing automatic starts and stoppages
- analysis of potential inefficiencies
- better troubleshooting of processes
- enabling predictive maintenance
- finetuning and adjusting of parameters while operating
- reporting on key factors of operation
It’s also possible to incorporate controls into existing industrial rotary dryers.
Optimizing Off-Gas Handling
Maximizing airflow can impact how well an industrial rotary dryer performs. Utilizing an industrial fan and installing ducts will create a negative pressure environment within the drum by pulling more air through the system.
The customizability of industrial rotary dryers makes them an essential piece of equipment for many in the bulk solids industry. They’re central to many operations, from processing ore to making fertilizer. Tailoring rotary dryer designs for specific purposes optimizes their performance and can be done with both new and existing machines.
Potential buyers should consider a number of factors when considering a rotary dryer. Design testing offers a means to establish what configuration may best suit a specific application. Additionally, many equipment manufacturers have testing facilities that help their customers establish parameters for specific material-processing challenges. Testing helps determine the best equipment configurations to ensure product quality.
Lab testing helps manufacturers determine factors to production like:
- air volume
- drum speed and slope
- feed rate
- retention time
Other ways labs enhance the performance of industrial rotary dryers include looking at temperature profiles. Testing will help predict operational costs from fuel usage and expectations for emissions and off-gas handling.
No piece of equipment can be expected to perform well if not properly maintained, even robust machinery like an industrial rotary dryer. Skimping on maintenance won’t just affect efficiency but the quality of the end product. Missing or worn flights reduce efficiency, while degraded seals also increase fuel costs and may even cause irreparable damage to the drum. It’s important to address maintenance issues immediately as set out by the original equipment manufacturer, which will support operational efficiency while preserving product quality.
This iteration of industrial rotary dryer design is the Rotordryer by IPEC (International Process Equipment Company). It receives wet material into its main body, where the material is ground and dried. Here the grinding rotor separates this moist material into exceptionally fine particles. Within the grinding chamber, these particles become fluidized by hot air from the air heater that’s kept at a controlled temperature. This hot air disperses the material, causing it to break down and increasing its surface area, which causes liquid within the material to evaporate immediately.
Benefits of IPEC’s Rotordryer include:
- Doesn’t damage product during controlled operations
- Easily integrated into existing processing systems
- Offers capital and operation savings over the long term
- Quick and uniform drying of wet bulk material
- Screenless long gap design
- Single-step that grinds and flash dries material
Along with the Rotormill, IPEC can design and deliver complete grinding and drying systems, including equipment and implements for controlling, feeding, collecting, blending, and packaging bulk product.