Working principle of rotary dryer

Types of rotary dryers

A rotary dryer is a kind of industrial dryer. It is called a rotary dryer because its drum rotates. The main function of the rotary dryer is to produce a dry product by removing moisture or liquid from wet material. In the 19th century, the rotary dryer was invented. The initial use of a rotary dryer was to dry flint clay. Since then, various types of rotary dryers have been developed. Different kinds of rotary dryers are used to meet various industrial and commercial needs today.

Rotary dryers typically consist of a cylindrical drum or shell that is inclined slightly from the horizontal and supported on two or more carrying idlers that rotate the drum. The wet material is fed into the rotary drum through the slope's higher end, while the heated air or gas flows through the lower end, which is also the exit end. The motion of the revolving drum along with the heated air or gas helps to dry the material effectively. This is how rotary drum dryers work in general. However, different types of rotary dryers may have different working principles.

• Direct-fired rotary dryer: A direct-heated rotary dryer first heats the material, then dries it. In this type of rotary dryer, a burner in the rotary dryer usually puts out hot gas. The combustion gas or hot air moves inside the rotating cylinder while touches and heats the wet material in it to dry it. This type of rotary dryer is usually more energy-efficient because it transfers heat effectively to the material. Moreover, direct-fired rotary dryers are usually less expensive to buy and operate than indirect rotary dryers.
• Direct/combined rotary dryer: A direct/combined rotary dryer mixes two different drying processes. It uses hot gas to dry the material partly and heating the shell of the rotary dryer to dry the material further. Direct/combined rotary dryers are suitable for drying materials that have stickiness or low thermal conductivity.
• Indirect-fired rotary dryer: The method of heating the shell of the rotary drum to dry the material inside it is called indirect drying. Indirect rotary dryers transfer heat from the outside of the cylinder to the wet material inside it. Indirect dryers have less material loss due to overheating because the material never comes into contact with the hot gas. Therefore, they are ideal for drying material that is chemically sensitive.
• Air-swept rotary dryer: An air-swept rotary dryer uses a fan or blower to create air movement in the rotary dryer. The fan or blower brings fresh air to the rotary dryer and pushes the moister air out of the dryer. An air-swept rotary dryer usually produces larger airflow and better drying performance.
• Multi-pass rotary dryer: A multi-pass rotary dryer has two or more drum shells placed concentrically. All the drums rotate together. Multi-pass rotary dryers use the same principle as direct rotary dryers, but they are more energy-efficient than single rotary drums. The multi-pass design can save installation areas.

Specifications and maintenance of rotary dryers

Specifications

• (Dryer) diameter: Often ranges from 1 m to 5 m.
• (Dryer) length: The length of the rotary dryer can usually be between 5 m and 30 m or longer.
• Production: Generally, 5 tons to 2000 tons per day.
• Power: Normally, from 20 kw to 2000 kw.
• Temperature: The working temperature of the rotary dryer can reach 150 °C to 500 °C, or even higher.
• Fuel: Gas; oil; coal; electricity; biomass; natural gas; nuclear energy, etc. are all available.
• Moisture removal: Normally, it is 1 ton/h to 1000 tons/h.

Maintenance

• Weekly: Check lubricating oil and replenish if required. Inspect chains and tighten them if necessary. Thoroughly clean up all debris and buildup around machines and in work areas.
• Monthly: Adjust belt tension, inspect, and clean all accessories to ensure proper operation and function. Check for loose fasteners and re-tighten as needed. Monthly, also inspect, remove, and replace damaged or worn parts.
• Quarterly: Service all equipment according to the indicated schedule and repair as needed. For equipment that is used in regular processes, lubricate parts quarterly.
• Yearly: Adjust clutches, check lining, and inspect all drive belts, chains, and sprockets. Re-lining clutches and brakes should be done every year.

Working principle of rotary dryer usage scenarios

The food industry has a high demand for rotary food dryers due to the increasing demand for dried food items. Such items include dried fruits, vegetables, meat, nuts, and food powder, like milk powder and protein powder.

Because of the rising population and the desire for preserved food items with an extended shelf life, the食品加工行业also heavily utilizes rotary dryers. The extensive utilizations in these two industries lead to high demands for food production dryer machines.

Organic recycling plants also employ rotary dryers to dry solid organic waste to create compost or other organic fertilizers. The dried waste can also be used as animal bedding or fuel.

Textile and paper industries have also utilized the machine due to its ability to reduce moisture content. This not only improves the quality of the final product but also enhances the machine's manufacturing efficiency.

Construction and cement industries also utilize a rotary dryer when producing construction materials, such as clay, which has a high moisture content. By removing the moisture, the material becomes more suitable for processing and can be used in the production of cement.

Due to its ability to produce output that has a high value and to increase a company's productivity, the rotary dryer remains an indispensable component in many industries. This has translated to high demands for the machine in the market.

How to Choose a Rotary Dryer

Before shopping for a rotary dryer for sale, it's essential to understand how its features and specifications impact its performance and capacity.

Here are some key things to consider:

• Material Adaptability: A suitable rotary dryer for sale should have material adaptability. Business buyers may need to process different materials. Adapting to various materials can reduce the investment in equipment and improve production efficiency.
• Heat Sources: Rotary dryers offer various heat sources, such as coal, gas, electricity, biomass, and waste heat. Each heat source has its advantages. For example, biomass provides a sustainable and eco-friendly option, while waste heat utilization improves energy efficiency.
• Feeding and Discharging Methods: Feeding and discharging methods influence production efficiency and labor costs. Consider the automation level and ease of operation. A rotary dryer with a closed-loop system will minimize dust emissions and environmental impact.
• Drying Temperature: The drying temperature affects the quality and yield of materials. Higher temperatures improve production efficiency but may affect material quality. Find a balance based on specific material processing requirements.
• Fan Power: Fan power determines the airflow and separation efficiency. A powerful fan supports optimal separation but consumes more energy. Assess separation needs and choose the suitable fan power to match it.
• Energy Recovery Systems: Systems for recovering energy, such as heat exchangers or insulation, can cut energy consumption and operating expenses. Consider the potential for integrating such systems to improve energy efficiency.
• Production Scale: Small and medium businesses typically need 1 to 5 tons of dryers, such as S4030A, while large-scale ones require more than 20 tons. Big firms may utilize models like S6010 with a 500mm cylinder diameter and a 10-ton daily capacity.

Q&A

Q: What are the recent developments of rotary dryers?

A: Recently, there has been a trend of developing energy-saving dryer machines for industries. Now there are many different types of dryers that save energy to a great extent by reusing heat or recycling it.

Q: How long does a rotary dryer take to dry?

A: Rotary dryers are designed to dry large volumes of material quickly. In general, there are around 1-6 hours’ processing time for materials in rotary dryers.

Q: Do rotary dryers have any special maintenance requirements?

A: Rotary dryers are often built to take all kinds of weather. They will not deteriorate, and they are relatively easy to maintain. Manufacturers suggest periodic inspections of rotary dryers to make sure they always run well.