1, the characteristics of production methods and description

Extrusion granulation is a relatively new process of dry granulation to produce compound fertilizers. Extrusion granulation in the field of fertilizer used in the earliest granulation of potassium chloride, due to the special nature of potassium chloride physical and chemical properties used abroad for mixing fertilizer (BB fertilizer) required granular (1-4mm) chloride Potassium are basically produced by extrusion. In recent years, extrusion granulation for the production of compound fertilizer in foreign countries has been rapid development.
The same time as
Extruded granulation can be in the form of roller and roller type, the roller extrusion is first pressed into large pieces, and then broken into particles, so that the device capacity, high particle strength, low energy consumption, Roller extrusion is widely used abroad. And the rolling type is the material in the compression die plate directly into the column bar, and then cut into cylindrical particles, the current domestic extrusion granulation method is mostly rolling granulation method, because of its small production scale , A single machine can only reach a maximum of 3-5 tons / hour, and the granulation strength is limited, mold damage, the production of cylindrical particles, poor mobility, domestic development is slow. Abroad has been eliminated in the rolling granulation process. The extrusion granulation discussed in this report refers to roll extrusion granulation.

The principle of the roll extrusion granulation process is: dry material in the role of pressure under the reunion into a dense hard block (cake), known as the extrusion process; cake and then broken into a granular material called Granule process. The effect of squeezing is to squeeze the air between the particles, the other is to make the particle spacing close enough to produce such as van der Waals force, adsorption force, crystal bridge and embedded connections and other attractive. The granules of the extruded granules are mainly the strength of the particles formed by the force between the molecules.

Extrusion granulation production Compound fertilizer mainly has the following process characteristics:

Low energy consumption
Extrusion granulation is the material at room temperature for granulation, compared with other methods, do not need fuel, gas and other drying measures. Production consumes only a small amount of cooling water (for roller cooling), consumes only about 30kwh per ton of product.

No additional adhesive is required

Domestic commonly used compound fertilizer production method is steam granulation. Water vapor in the material between the molecules of condensation, crystallization, in the granulation process from the role of adhesive. But in the drying process and must be inside the particles and the surface of the water out, or fertilizer in the storage process easy to stick, agglomeration. And dry granulation without additional additives, just use the material itself, the intermolecular force, simplifying the process, reducing energy consumption.

Low investment
As a result of the drying process, while the return of material than low (accounting for the total amount of extruded about 35%), the process is simple, low investment. According to the IFDC (International Fertilizer Development Center) in 1987, a detailed study has been carried out to prove that in developing countries, for a new fertilizer plant, extrusion granulation in the economy is better than steam granulation and chemical Granulation or granulation. For an annual output of 120,000 tons of NPK compound fertilizer plant, the steam granulation investment is 19.5% higher than the extrusion granulation, while the chemical granulation or slurry granulation investment is 88.8% higher than the production cost ( On the 15-15-15) formula, steam granulation higher than 3%, while the chemical or slurry granulation is 12% higher.

Raw materials are flexible
Extrusion granulation production of compound fertilizer raw material route is more extensive, has been successfully used for extrusion granulation of the material there are more than 20 kinds: nitrogen fertilizer in the ammonium nitrate, urea, ammonium chloride, calcium nitrate, etc. Ammonium phosphate, calcium, phosphate powder, potash fertilizer potassium, potassium sulfate, etc., and can add trace elements such as boron, iron, copper, zinc, manganese and so on.

In addition, the use of extrusion granulation process can be very flexible in a very short period of time to achieve the replacement of product formulations, a set of foreign devices can produce more than 30 kinds of formula products.

Applicable raw material particle size range
Extrusion granulation on the raw material size is no special requirements, 1-4mm granular materials and fine powder materials are available, particle size of substandard powder and powder products better use, with powder material can reduce costs.

Wide range of capabilities
For the extrusion granulation device, the effect of economies of scale is not obvious, the capacity of the device from 12 tons / hour. Taiwan to 35 tons / hour. Taiwan can be more economical design, so the scope of application of a wide range.

The product is flexible and the operation varies widely
Extrusion granulation A set of devices can produce up to dozens of products, small batch production is also feasible. According to the switch to clear the total amount of raw materials required and the original material on the new formula of the degree of impact, up to each class (8 hours) production of three batches of products. Therefore, the extrusion granulation production of compound fertilizer can be adapted to small batch, multi-species compound fertilizer needs.

The only drawback of extruded granulation to produce compound fertilizers is that the shape of the product is irregular particles, but the irregular particle shape has no effect on the application of the fertilizer. With the extrusion granulation production of fertilizer has sufficient strength, less dust, no caking, particle size distribution range is narrow, good mobility. Extrusion granulation production of fertilizers, especially grain potassium fertilizer, in foreign mechanical fertilization has been widely used to prove that the particle shape will not become a fertilizer application factors. Domestic extrusion pressure is low, so the product compressive strength is low, while the extrusion pressure of foreign advanced extrusion equipment 2-3 times higher than the domestic, so the product of high compressive strength, product performance than it is good.

2, the production flow chart and the process of narrative

Extrusion system consists of four parts, described as follows:

1. Storage, metering, mixing
Fertilizer raw materials such as urea, ammonium phosphate, potassium chloride, etc. by the bucket elevator and belt conveyor to the silo. The number of storage silos, the complexity of metering and mixing techniques, are related to the number of components in the product formulation.

Production of compound fertilizer, the general use of intermittent mixing operation, the ingredients of the ingredients in the weighing warehouse weighing, to meet the requirements of the formula, all joined the intermittent mixer in the system, installed in the system balance warehouse, After the other equipment is continuous operation.

In the mixer can also add trace elements. In order to ensure trace element distribution of trace elements, the choice of high-strength mixer.

After mixing the material and the return material by the bucket lift machine, in the biaxial paddle mixer mixed with the return material, the material is broken and sieved after the unqualified particles, recycled materials and new material ratio of about 35: 65 (when producing 1-4mm products).

2. extrusion

The mixed fertilizer mixture is extruded through a roll extruder by the principle that the material is formed by extrusion.

The mixed material is fed through a vertical screw feeder into the gap between the two rotating rollers in the opposite direction. During the extrusion process, the pressure of the material is gradually increased. When the gap between the two axes is the smallest, the material is pressed The largest, and then gradually reduced until 0. During the extrusion process, the apparent density of the mixture can be increased by 1.5-3 times due to the reduced volume of the material.

The extruded product is typically a plate with a thickness of 5-20 mm (chunks). The structure and size of the roll extruder are determined by a number of parameters, which are generally determined by the nature of the material and the experiment.

3. Broken, graded

The plates formed in the roll extruder are further broken and the desired particle size is obtained by classification. There is a specially designed plate crusher under the roller press, where the plate is pre-broken into several small pieces (flakes). The sheets are easier to transport and are easily broken by subsequent crushers.

The broken raw material is divided into super-large particles, product granules and fine granules on the multi-stage sieve. The fine particles on the lowest sieve are recycled to the mixer and then extruded. And in the multi-stage sieve too much of the super-large particles need to be further broken. Crushed and then returned to sieving.

In high-strength crushers, the softer portions of the sheet are broken into high-strength and wear-resistant particles that are not tarnished during transport and use.

Proper selection of crushing and screening equipment is essential for the economics of fertilizer extrusion / granulation systems. The size of the particles (usually cube), the size of the particles (1-5 mm or 2-4 mm) and the amount of circulation after crushing and sieving determine the yield and capacity of a set of devices.

3. Polished and trimmed

In the usual case, the final product is subjected to one or two steps of polishing. Irregularly shaped particles are rounded through polished rounds. The fine powder produced during the polishing process is circulated by sieving (a sieve). Dressing, the general also added anti-caking agent.

The final product of the unit is a granular fertilizer (1-4 mm) within a certain range of particle size.