Rotary Drum Granulator

Equipment Introduction

The rotary drum granulator (also known as a roller granulator or rotary pelletizer) is a wet granulation device with a tilted rotating cylindrical body as its core working chamber. It belongs to the wet agglomeration granulation equipment category. By adding an appropriate amount of liquid binder (or steam, water), powdery or fine-grained materials undergo agglomeration, compaction, and rounding processes under the tumbling motion generated by the rotation of the drum. Through the wetting effect of the liquid binder and surface tension, the materials form spherical or near-spherical particles with a certain strength and particle size.

This equipment is a key piece of equipment for large-scale continuous production in industries such as compound fertilizer, organic fertilizer, metallurgy, and chemicals. It is suitable for cold granulation, hot granulation, and the industrial production of high, medium, and low concentration compound fertilizers. Compared with disc granulators, rotary drum granulators have significant advantages such as higher capacity, better continuity, and the ability to introduce steam or reaction media for chemical granulation. However, the investment cost and material return rate are higher. In modern industry, rotary granulators are not only simple molding equipment, but also chemical/physical reaction platforms that integrate mixing, humidification, and reactions (such as ammoniation processes).

Equipment Structure Components

Drum Shell: Welded from high-quality carbon steel plates, typically lined internally with high-molecular-weight polyethylene (UHMW-PE) or stainless steel to prevent corrosion and adhesion by acidic materials.

Large Gear and Transmission Device: A large gear is mounted on the outside of the drum shell, driving a small gear via a reducer and motor to rotate the drum.

Riding Rings & Support Rollers: The drum shell sits on two sets of support rollers, supported by rolling belts to accommodate its weight.

Internal Lifting/Spraying System: Used to regulate the movement of materials within the drum and to spray steam, water, or phosphoric acid/ammonia solution to provide adhesion.

Equipment Application Scope

1. Compound Fertilizer and Chemical Industry (Core Main Scenarios): Professionally used for the large-scale granulation of NPK compound fertilizer, diammonium phosphate, monoammonium phosphate, trace element compound fertilizer, and functional slow-release fertilizer. It is a standard core equipment for chemical fertilizer plants, producing rounded granules with stable fertilizer effects and high market acceptance.

2. High-End Organic Fertilizer Industry: Used for the production of spherical bio-organic fertilizer, humic acid organic fertilizer, and soil-improving granular fertilizer. It solves the pain points of traditional organic fertilizer granules, such as loose texture, poor appearance, easy dust generation, and low selling price, significantly increasing the added value of organic fertilizer products.

3. Mineral Powder Molding Industry: Suitable for granulation of industrial mineral powders such as bentonite, kaolin, fly ash, and desulfurization gypsum, used for the production of environmental protection fillers, industrial auxiliaries, and desulfurization and denitrification granules.

4. Agricultural Environmental Protection and Resource Utilization Industry: Enables the resource-based recycling and granulation of livestock and poultry manure, agricultural and forestry waste, and industrial solid waste, complying with environmental protection policies and solid waste utilization standards, and suitable for the implementation of environmental protection projects.

5. Fine Chemicals and Auxiliary Materials Industry: Used in the production of fine powders such as feed additives, horticultural nutrient granules, chemical filler granules, and desiccant granules.

Equipment Applicable Raw Materials

Raw material moisture content is a key control parameter. For cold granulation, the moisture content is typically 10–25%; for hot granulation, due to the introduction of steam, the initial moisture content can be slightly lower. The ratio of recycled material (return material) to fresh feed in the granulation bed is usually 1:3 to 1:6.

Equipment Working Principle

Agglomeration

Its principle is based on "sphericity dynamics." Material rises within the rotating drum and rolls down under gravity. A liquid component (water or chemical slurry) is introduced through a spray system. Utilizing the surface tension between materials and the capillary force generated by the liquid phase, the powder continuously coats and deposits around the core, ultimately forming rounded granules.

The working principle of the rotary drum granulator is based on wet agglomeration technology. The entire process can be divided into the following stages:

Stage 1: Feeding and Humidification

The powdered material, after crushing and mixing pretreatment, is continuously fed into the drum from the feed end. Simultaneously, the spray system injects steam, water, or chemical solutions (such as phosphoric acid, nitrogen solution, phosphorus ammonium slurry, etc.) into the drum to humidify the material within the drum. The addition of steam increases the material temperature, resulting in lower moisture content after sphericification, which is beneficial for improving subsequent drying efficiency.

Stage Two: Rolling Agglomeration

The main motor drives the belt and pulley, transmitting power to the drive shaft via a reducer. This power then engages with a large gear ring fixed to the machine body via a split gear, driving the cylinder to rotate. The material inside the cylinder rolls and tumbles as it rotates. Under specific humidity and temperature conditions, the moist powder particles collide and compress with each other during rolling, agglomerating into small spheres due to liquid bridging forces and intermolecular forces.

Stage Three: Growing into Spherical Formations

The formed spheres continue to roll, continuously absorbing surrounding powder and gradually growing larger, like a snowball. The cylinder's rotation speed and tilt angle control the residence time and rolling intensity of the material within the cylinder, thus affecting the particle size and sphericity.

Stage Four: Discharge

Spherical particles reaching the specified diameter continuously flow out from the discharge end of the cylinder. Due to the continuous inflow of material and the continuous rotation of the granulator, large-scale continuous production can be achieved.

Application of the Equipment in Production Lines

The rotary drum granulator cannot be used for simple standalone production; it must be integrated with a standardized assembly line. It is the core unit of a complete production line, with two main supporting solutions as follows:

1. Small to Medium-Sized Standardized Organic Fertilizer Production Line: Batching machine → Mixer → Ultrafine pulverizer → Rotary drum granulator → Rotary drum dryer → Cooler → Screening machine → Automatic packaging machine + fine powder recovery system. Fully automated continuous production without manual intervention.

2. Large-Scale Compound Fertilizer Industrial Production Line: Automatic batching system → Mixing and conditioning system → Steam atomization system → Large rotary drum granulator → Multi-layer drying and cooling system → Precision screening system → Polishing system → Automated packaging and storage system. Suitable for annual production of tens of thousands of tons.

The equipment has extremely high compatibility, capable of connecting to steam heating, automatic batching, and intelligent control systems. It is currently the most cost-effective and stable core unit in large-scale granulation production lines.

Granulation Processes of Equipment

The granulation processes of rotary drum granulators can be divided into the following modes:

1. Cold Granulation Process

2. Thermal granulation process (steam granulation)

The core advantage of hot granulation lies in the fact that steam heating increases the material temperature, reduces granulation moisture, significantly reduces the load on subsequent dryers, and improves overall efficiency. The pelleting rate can reach over 70%.

3. TVA Ammoniation Granulation Process

The TVA ammoniation granulator is a significant improvement on the rotary drum granulator. Its length and diameter are approximately equal, with annular dams at both ends but no lifting blades. Ammonia reacts with phosphoric acid and sulfuric acid below the surface of the tumbling bed; the heat of reaction simultaneously evaporates moisture and causes granulation. Heat is removed by injecting air. Ammonia and acid are supplied to the bed through perforated distribution pipes installed axially on the drum. In modern processes, the mixture of phosphoric acid and sulfuric acid with ammonia is neutralized in a pipe-cross reactor, and then the slurry, along with recovered materials, is fed into the drum while more phosphoric acid is sprayed onto the tumbling bed, and ammonia is fed into the bed. This process can produce NPK compound fertilizer.

Common Equipment Problems and Solutions

1. Low Particle Formation Rate, Excessive Fine Powder, and Inability to Form Balls

Core Causes: Insufficient material fineness, insufficient/uneven atomization spray volume, excessive cylinder speed, low material moisture content, and improper binder ratio; Solutions: Refine the material powder, unclog or replace atomizing nozzles, fine-tune and reduce cylinder speed, increase spray volume, and optimize binder ratio to ensure sufficient powder wetting and agglomeration.

2. Excessively Wet Particles, Severe Adhesion and Clumping

Core Causes: Excessive spray volume, excessively high material moisture content, excessively slow cylinder speed, and excessively long material residence time in the cylinder; Solutions: Reduce atomization spray volume, dry pre-treated materials, appropriately increase cylinder speed, and shorten material residence time.

3. Drum misalignment, axial movement, and operational vibration

Core causes: Uneven force on the support rollers, worn and ineffective thrust rollers, cylinder tilt angle deviation, loose foundation anchors, and uneven material loading; Solutions: Calibrate the support rollers for levelness and coaxiality, replace worn thrust rollers, recalibrate the cylinder tilt angle, tighten foundation bolts, and ensure even feeding to avoid uneven loading.

4. Abnormal noise during equipment operation and excessive gear noise

Core causes: Improper gear meshing clearance, insufficient grease, worn gears, damaged support roller bearings due to lack of oil, and foreign objects stuck in the transmission parts; Solutions: Adjust gear meshing clearance, add high-quality grease, replace worn gears and bearings, and clean foreign objects from inside the equipment.

5. Nozzle clogging and poor atomization

Core causes: High levels of impurities in the adhesive liquid, material dust clogging the nozzles, and long-term lack of cleaning of accumulated scale; Solutions: Filter the adhesive liquid, unclog nozzles daily, clean the spray pipes regularly, and install a pipe filter.

6. Decreased production capacity and slow discharge speed

Core causes: Severe material adhesion to the cylinder liner, uneven feed rate, improper speed matching, and insufficient transmission torque; Solutions: Thoroughly clean the material adhering to the cylinder, stabilize quantitative feeding, optimize speed parameters, and check the operating condition of the reducer and motor.

7. Dust overflow and seal leakage

Core causes: Aging and wear of seals, excessive inlet and outlet gaps, and failure of negative pressure dust removal; Solutions: Replace flexible seals, adjust sealing gaps, and install negative pressure dust removal equipment.

Equipment demand groups

1. By industry

Compound fertilizer/compound fertilizer production enterprises: large-scale production of high, medium and low concentration compound fertilizers

Organic fertilizer production enterprises: pelleting of livestock and poultry manure, straw and other organic raw materials

Biofertilizer and controlled release fertilizer manufacturers

Chemical enterprises: granulation and processing of chemical raw materials

Environmental protection enterprises: resource utilization of sludge and other wastes

2. Divide by role

Corporate decision-makers/bosses: focus on equipment investment return, production scale, and long-term operating costs

Production director/workshop director: focus on equipment stability, production capacity, and ease of operation

Technical Engineer: Focus on granulation process, parameter control, and equipment principles

Purchasing staff: focus on model selection, price, and after-sales service

Front-line operators: Pay attention to whether the operation is simple and whether the maintenance is easy

3. Suitable customer characteristics

Large production scale (annual output from tens of thousands to hundreds of thousands of tons)

Requires large-scale, continuous production

Have high requirements on particle strength and roundness

Steam heating or chemical reaction granulation can be used

The production line is fully equipped with follow-up processes such as drying and cooling.

Rotary drum granulators, with their core advantages of high output, high pelletizing rate, flexible processing (both hot and cold processing), and high pellet strength, have become the preferred granulation equipment for large-scale production in the fertilizer industry, including compound fertilizers and organic fertilizers. Their core technology lies in utilizing a rotating drum and wet granulation process to agglomerate powdery materials into high-strength spherical pellets under liquid phase conditions. The equipment is robust and durable, easy to operate and maintain, and has a wide capacity range from 3 tons/hour to 35 tons/hour. Compared to disc granulators, rotary drum granulators offer higher output and are more suitable for large-scale continuous production; compared to extrusion granulators, rotary drum granulators use a wet process, resulting in higher pellet roundness and better appearance. With the large-scale and intensive development of the fertilizer industry, the market demand for rotary drum granulators will continue to grow due to their comprehensive advantages of high capacity, high quality, and low operating costs.

Whether you are building a new fertilizer production line and need a complete equipment solution, upgrading an existing production line and need equipment selection advice, or dealing with equipment malfunctions and needing technical support—we are always ready to provide you with professional and sincere service.