Double Roller Press Granulator

Description of Double Roller Granulator: 
As an important granulation equipment, the double roller granulator utilizes a non-drying, room-temperature process, which offers significant advantages in energy conservation and improved production efficiency. Its core operating principle is to force a properly proportioned mixture through a feed mechanism into the gap between a pair of equal-sized, rotating extrusion rollers.
Under the powerful extrusion pressure, air inside the material is expelled, the distance between particles is reduced, and the intermolecular forces are strengthened, resulting in the material being squeezed into dense sheets or strips. As the rollers continue to rotate, the pressure on the material exhibits a specific pattern: reaching its maximum value when the line connecting the two roller radii is horizontal, typically reaching several MPa or even higher, and then rapidly decreasing. At this point, the formed material recovers due to its own elasticity, breaking free from the contact with the roller surface under the action of the rebound force, and smoothly falls to the next process.
This granulation method fundamentally avoids the energy-intensive drying process required in traditional wet granulation. Calculated energy consumption is only 30%-50% of that of traditional wet granulation, significantly reducing energy consumption and production costs. Furthermore, the entire production process produces no wastewater, exhaust gas, or waste residue, fully complying with national environmental protection standards. This is a truly energy-saving and environmentally friendly granulation process.

Where are double roller granulators commonly used?

The double roller granulator has a unique working principle and structural design, and its adaptability to raw materials is extremely wide. It has outstanding performance in many fields. The specific application scenarios are as follows:

Fertilizer field
It is capable of producing various types of compound fertilizers with various concentrations (from low concentration of 20% to high concentration of more than 60%), such as the granulation of single fertilizers such as ammonium chloride and ammonium sulfate, as well as the production of compound fertilizers such as organic fertilizers, inorganic fertilizers, biological fertilizers, and magnetic fertilizers.
The technology has significant advantages in granulating rare earth, potash, and ammonium bicarbonate compound fertilizers. For example, it effectively addresses the moisture absorption and caking issues associated with traditional potash granulation methods, resulting in granular potash fertilizers with excellent fluidity and low hygroscopicity. This technology fills a gap in related fields in China and is at the forefront domestically.
It can also use ammonium carbon, urea, ammonium chloride, ammonium phosphate, potassium chloride, etc. as base materials to produce multi-element fertilizers with different proportions of nitrogen, phosphorus and potassium according to different soil fertility and crop needs, to meet the diverse nutrient needs of different crops such as rice, wheat, corn, vegetables and fruits.

Other industrial fields
Pharmaceutical industry: Suitable for granulation of various medicinal granules, such as Chinese medicine granules, raw material granules of Western medicine tablets, etc. The granulation process can effectively ensure the stability and uniformity of drug ingredients.
Chemical industry: It can be used for granulation of capsule filling particles, pigments (such as titanium dioxide particles), detergents (such as washing powder particles), catalysts (such as automobile exhaust catalyst particles), strontium carbonate, inorganic salts (such as sodium chloride particles), chloroisocyanuric acid, bleaching powder, pesticides (such as insecticide particles), oxides and other materials.
Feed industry: It can mix various feed raw materials, such as corn, soybean meal, fish meal, etc., and then extrude and granulate them to produce nutritionally balanced pellet feed that is easy to store and transport, reducing feed waste during transportation and feeding.
Industrial dust recovery: It also plays an important role in industrial dust recovery. For example, the dust from iron foundries contains a large amount of iron. These dust materials can be compressed and formed by mechanical pressure through the roller extrusion granulator without adding any wetting agent, thus ensuring the purity of the product. The formed particles can be reused in ironmaking production. Lead, zinc, aluminum dust, converter dust, filter dust, grinding dust and other dust can also be effectively recycled, which not only reduces environmental pollution but also improves resource utilization.

How is the double roller granulator designed according to the granulation process?
The double roller granulator consists of several key parts working together. The structure and function of each part are as follows:

Feeding device
Usually consists of a hopper, screw conveyor or belt conveyor. The hopper is used to temporarily store mixed materials. Its capacity depends on the production scale and can generally hold 1-5 cubic meters of materials.
A screw conveyor or belt conveyor is responsible for smoothly and quantitatively transporting the material from the hopper to the extrusion rollers. Its conveying speed can be adjusted by a variable frequency motor to ensure a stable material supply and lay the foundation for the smooth progress of the subsequent extrusion process. During the conveying process, sensors installed on the feed device can also monitor the material flow in real time, enabling automatic adjustment.
As the core component of the equipment, the extrusion roller is usually made of high-strength alloy steel, such as 45 steel, chrome-molybdenum steel, etc. After tempering, quenching and other heat treatment processes, the surface hardness can reach HRC50-60, and it has good wear resistance and pressure resistance.
The surface is typically designed with regularly arranged grooves, holes, or protrusions of uniform shape and size. The grooves can be circular, square, or diamond-shaped, with a depth of 2-10 mm and a spacing of 5-20 mm. These special designs optimize the extrusion of the material, allowing it to be better shaped during the extrusion process, producing pellets that meet specific shapes and specifications.

Discharging device
It is generally composed of an inclined chute and a conveyor belt. The chute is usually made of stainless steel to prevent material adhesion and corrosion.
It is used to receive the formed materials falling from the extrusion rollers and convey them to subsequent processes such as crushing and screening. The design of the discharge device must ensure smooth material transportation. The inclination angle of the chute is usually 30°-45° to avoid material blockage or accumulation.

Transmission and control systems
The transmission system is driven by an electric motor (usually a three-phase asynchronous motor, with a power ranging from 5.5kW to 55kW depending on the equipment model) to drive the belt and pulley, which is transmitted to the driving shaft through a reducer (commonly used gear reducers, cycloid pinwheel reducers, etc.), and synchronized with the driven shaft through split gears, so that the two extrusion rollers work in opposite directions. The speed can generally be adjusted within the range of 10-50 rpm.
The control system, comprised of a PLC control cabinet, touch screen, and sensors, precisely regulates equipment operating parameters such as speed, extrusion pressure, and material flow. Operators set these parameters via the touch screen, and the system automatically adjusts based on sensor feedback to meet the needs of different materials and production processes, ensuring stable and efficient operation.

How does the roller extrusion granulator make fertilizer?

The granulation process of the double roller granulator is a systematic process. Each link has an important impact on the quality of the final product. The specific steps are as follows:

Storage, metering, mixing
First, various raw materials are stored in different storage silos. The storage silos usually adopt steel or concrete structures, which have good sealing and moisture-proof properties to prevent the raw materials from absorbing moisture and deteriorating.
According to the recipe requirements, various raw materials are accurately weighed and measured using electronic measuring scales, with a measurement accuracy of up to ±0.5%, ensuring that the proportions of each ingredient are accurate.
For complex formulas like compound fertilizers, intermittent mixing is often employed. Metered raw materials are placed in a mixer (such as a twin-shaft paddle mixer or conical mixer) for a typical mixing time of 5-15 minutes. Professional mixing equipment ensures thorough mixing to evenly distribute the components and ensure consistent product quality. The moisture content of the mixed material should be controlled between 5% and 15% to meet the requirements of subsequent extrusion granulation.
Extrusion molding: The uniformly mixed material is fed through a feeder into the space between the rollers of a double roller granulator. Under the powerful extrusion pressure (adjustable between 5-30 MPa depending on the material's characteristics), the material density increases significantly, transforming from a loose powder or granular form into a dense sheet or strip. The density can be increased from an initial 0.5-0.8 g/cm³ to 1.2-1.8 g/cm³, completing the initial molding process.
During the extrusion process, the speed and extrusion pressure of the extrusion roller need to be adjusted in real time according to the characteristics of the material to ensure the forming effect.
Crushing, screening and extrusion of flake or strip materials need to enter the crusher (such as cage crusher, hammer crusher, etc.) for crushing. The speed of the crusher is generally 800-1500 rpm, which breaks them into particles of relatively uniform size. The particle diameter is usually between 1-6 mm.
The fertilizer pellets are then filtered through screening equipment (such as a vibrating screen) according to preset particle size standards to select the granular fertilizers that meet the requirements. The mesh size of the screening equipment is determined by the desired particle size, generally ranging from 8 to 40 mesh. The fine powder produced during the screening process (typically accounting for 10%-20% of the total output) can be recycled back to the mixing process through a circulation system for reuse, improving raw material utilization and reducing production costs.
Finishing: The sieved particles are further trimmed, usually using equipment such as a polishing machine or a rounding machine to round the edges and corners of the particles to make them more round and regular.
This not only improves the appearance quality of the product, makes the particles more regular and beautiful, and enhances the competitiveness of the product in the market, but also reduces the wear of the particles during storage and transportation.