1. Dry Granulation and Wet Granulation
In general, compound fertilizer granulation technologies can be classified into two types: wet granulation and dry granulation. The difference between dry granulation and wet granulation is whether they use liquid solution. Dry granulation method is without using a liquid solution such as water or binder, while wet granulation does.
Dry granulation traditionally means the extrusion granulation technology because of no water or binder needing to be added during the compound fertilizer manufacturing process. In extrusion granulation, raw materials are aggregated under high pressure as primary powder, which will be squeezed between rollers to produce fertilizer granules. All finished fertilizer granules are free of drying or cooling, and can be packaged directly, so dry granulation method is widely for small and middle fertilizer plants with low investment. The fertilizer granules produced by dry granulation method are always with flat shape.
shape of compound fertilizer granules produced by extrusion granulator
Extrusion Granulation Technology
Double roller extrusion granulator is the most popular equipment in extrusion granulation technology. It adopts special extrusion sheet design, and uses screw, piston, rollers and rotary knives to press wet powder and extrude granules from holes.
uses of specially designed extrusion sheet.
Advantages of extrusion granulation technology
1.This extrusion granulation do not need dry and cool process.
2.The fertilizer granulation rate is high and the final fertilizer granules are rough, but with a high solidity.
3.This granulation technology can be used to produce compound fertilizer with low concentration.
Compared with dry method, wet granulation produces granular fertilizer with a higher moisture so the finished products need to be dried, cooled and solidified. In wet granulation process, the first 3 most commonly-used fertilizer granulators are rotary drum granulator, disc pan granulation machine, spray granulation machine and tower spray granulation equipment.
Rotary drum granulation technology
Rotary drum granulator is a key equipment in fertilizer industries to produce both high and low-density compound fertilizer. The theory of rotary drum granulation process is that all raw materials roll and solidify in the drum so that the raw materials could be fully react with each other. By means of rotary movement, material particles are granulated into compound fertilizer balls under pressing force.
Features of rotary drum fertilizer granulation method
1. It is widely used in large-scale compound fertilizer production plant.
2. The high steam temperature in the drum dries fertilizer granules, and improves the solidity.
3. Rotary drum granulators can be used to produce many kinds of compound fertilizer such as DAP(Di-ammonium phosphate), MAP (mono-ammonium phosphate), Ammonium Sulfate, TSP(Triple super phosphate), SSP(single super phosphate) and Urea etc.
Disc pan granulation technology
The theory of disc pan granulation is that all mixed raw materials roll in a slope disc pan, with the addition of binder and water to make different sizes of fertilizer granules.
Advantages of disc pan granulation:
1.Cheaper then rotary drum granulator or other compound fertilizer equipment, cost 30% less, with production capacity from 1-4 t/h.
2.Wild application in many fields, such as fertilizer, pharmacy, feeds, coal, metallurgy etc.
3.High granulation rat
Spray Granulation Technology
Spray granulation technology is widely used to produce urea with high N content more than 20%. The liquid urea is sprayed by high pressure pump into designed compound fertilizer granulation equipment, and then under the high temperature and screening process to produce granular urea.
This fertilizer spray granulation technology requires less for fertilizer formula, and granulates good shape of urea, but it costs more in terms of producing low N content urea.
Tower Granulation Technology
Tower granulation technology is a typical wet granulation method. It’s raw materials are all liquid solution. The theory of this tower granulation is that all melting materials mixed in a certain ratio are sprayed from a high point and become granules during falling. It is mainly to produce high concentration of NPK fertilizer such as NPK 21-21-21 and NPK 20-20-20. Besides, tower granulation technology costs more once the fertilizer plants change their fertilizer formula because of it’s high production capacity and limitations for raw materials. The fertilizer granules are always smooth and round, with low water content, so it no need drying process.
2. Compound Fertilizers Granulation Process
Here we introduce the granulation processes of 4 basic compound fertilizers – NPK, SSP(single super phosphate), DAP(Di-ammonium phosphate), and SOP(single super phosphate).
NPK Fertilizer Granulation Process
Azeus Fertilizer Machinery manufactures customized NPK fertilizer production line. The capacity varies from 20,000 tons to 100,000 tons per year. The whole lines are equipped with quality compound fertilizer machines.
Taking 50,000 t/y NPK fertilizer production line for example, its granulation process is as follow:
Granulated SSP (single super phosphate) Making Process
Raw materials for SSP production are rock phosphate and sulphuric acid, where rock phosphate is a natural deposit of calcium phosphate containing fluorine and carbonate.
Phosphate Rock + Sulphuric Acid → Single Superphosphate
Critical steps in the SSP granulating process include:
★ Crushing the rock phosphate to the correct size
★ Accurately metering the Phosphate Rock, Sulphuric Acid, and water
★ Blending all the raw materials together thoroughly
★ Time for the reactions to occur
After fully reaction, all the materials should be transferred into the rotary drum granulator and then be screened by rotary drum screen (If the size of SSP granules are not uniform, they needs to be re-crushed and re-granulated again) to produce granulated SSP.
SSP fertilizer granulation process
chemical properties of SSP
Being used as a highly demanded fertilizer to prepare land, the single super phosphate contains 16% p2o5 in water-soluble form and has traditionally been very popular in agriculture. Being as one of the cheapest forms of phosphate, it can supply sulphate and calcium for many crops and pasture needs and helps keep soil in good shape by maintaining soil structure.
DAP (Di Ammonium Phosphate) Manufacturing Process
Just like single super phosphate, diammonium phosphate is also a type of fertilizer that is rich in phosphate. The main raw material for DAP production is the phosphate ore form phosphate rock. The N:P ration of 1:1 makes it an effective source of nitrogen and phosphate and thus dissolves quickly in soil to release plant-available phosphate and ammonium.
chemical properties of DAP
DAP granulation method:
The phosphoric acid is made from the reaction between the phosphate rock and sulfuric acid, which is then reacted with ammonia in tanks to form a slurry. This slurry is then processed into rotary drum granulator to produce granular DAP. All DAP granules need to dry in rotary drum dryer to rounds and polishes all granules.
SOP (Sulphate of potash) Granulation Process
SOP fertilizer can supply two essential nutrients k2O(50%) and S(18%). Its nutrient composition is approximately:
SOP are used in crops that are sensitive to chloride, such as tea, potato, orange, apple and vegetables, or fertilizer burn like tobacco, pineapple or avocado, or where sulfur is deficient. It lowers soil salt index.
The SOP granulation technology is not very difficult. In general, the materials for SOP production are sop powder and other adhesives in a certain ratio.
Process of SOP manufacturing technology