Introduction to the 5 most commonly used compound fertilizer production method.

Slurry fertilizer production method for npk production:

• The production of compound fertilizer by slurry granulation method can be understood as: all or most of the materials entering the granulation system in the production of compound fertilizer are in the form of slurry.
• The slurry is the product of the reaction of phosphoric acid, nitric acid, sulfuric acid or some mixed acid with ammonia, and sometimes the reaction product of acid and phosphate rock powder.
• In this type of production process, solid nitrogen and potassium salts can be added evenly into the slurry, or directly added to the granulator together with the returned materials to prepare nitrogen, phosphorus, and potassium ternary compound fertilizers.
• Taking into account the maturity of the process, the actual situation of the equipment, and the economic rationality of production, the phosphorus-containing raw material of the slurry method high-concentration compound fertilizer is wet phosphoric acid. In most cases, the phosphoric acid is ammoniated into a slurry and mixed with Urea, ammonium chloride and potash are granulated into NP and NPK compound fertilizers.

Blending method for npk compound fertilizer production:

• The blending method of compound fertilizer is a mixture of two or more basic fertilizer ingredients with similar particle sizes. The resulting mixture can be applied in bulk or packaged form. In countries that lack high-concentration granular basic fertilizers, the production and application of blended fertilizers are difficult to develop.
• The key to this method is that all the basic fertilizers mixed are required to be granular, and the particle sizes should be approximately the same to prevent fertilizer segregation during transportation and application. The blending method of compound fertilizer may seem uneven in appearance, but from a macro-agrichemical perspective, its effect is equivalent to that of granular compound fertilizer with the same nutrients and the same form.
• The blending method of compound fertilizer requires that the particle size distribution of the raw material base fertilizer is relatively consistent. For example, the particle size distribution of ammonium nitrate or urea particles produced by tower melt granulation is inconsistent with the particle size distribution of diammonium phosphate, and they are generally not suitable for blending. For this reason, the production of ammonium nitrate or urea requires the use of drum or disc granulation so that the particle size distribution of its particles matches that of diammonium phosphate particles.

What are the disadvantages of compound fertilizer blending method?

• The biggest disadvantage of blended fertilizer is its unevenness. Obvious unevenness will bring difficulties to agricultural fertilization, causing certain nutrients to be locally over-applied and certain nutrients to be locally under-applied. The main reason why the compound fertilizer is uneven in this method is that when raw material base fertilizers with inconsistent particle sizes are mixed, particles with similar particle sizes will tend to aggregate and cause separation.
• When loading and unloading fertilizer, particle separation occurs due to the flow of the material itself, which is the so-called “cone pile effect”. Tossing can also cause particles to separate due to differences in particle size. Therefore, this method is most suitable for on-site mixing of fertilizers and immediate application on the spot.
• Another shortcoming of the blending method of compound fertilizer is that due to limitations in the variety and grade of raw material basic fertilizers, it is difficult to blend targeted compound fertilizers based on the fertilizer supply capacity of the soil and the fertilizer demand characteristics of the crops.

Compatibility of raw materials for the production of granular blended fertilizers.

• Whether chemical reactions occur between ingredients. For example, when granular superphosphate is mixed with granular urea, the main components of superphosphate, water and monocalcium phosphate, react with urea to form an adduct, and the crystallization water of monocalcium phosphate is turned into free water of the mixed material. If the material is wet, it is called incompatibility or poor compatibility. Its chemical reaction formula is as follows:
  Ca(H2PO4)2H2O+4(NH2)2CO=Ca(H2PO4)2·4(NH2)2CO+H2O
• However, if the superphosphate is ammoniated and granulated, the compatibility of urea and superphosphate can be improved. Its chemical reaction formula is as follows:
  Ca(H2PO4)2·H2O+NH3+H2O=NH4H2PO4+CaHPO4·2H2O
  Ca(H2PO4)2·H2O+NH4HCO3=NH4H2PO4+CaHPO4·2H2O+CO2
• The reaction reduces monocalcium phosphate in superphosphate, reduces water content, and reduces water-soluble P2O5, which alleviates the corresponding deliquescence.

Compatibility of raw materials for the production of granular blended fertilizers.

Generally speaking, the critical relative humidity of a mixture composed of two or more inorganic salt fertilizers is lower than the critical relative humidity of a single inorganic salt, and it is easier to absorb water. When selecting ingredients, the critical relative humidity should be as high as possible and avoid mixing fertilizers with particularly low critical relative humidity.

Extrusion method for npk compound fertilizer production:

• Extrusion compound fertilizer is a mixture of two or more basic fertilizers, additives, and fillers, which are extruded by a certain amount of liquid phase into a cylindrical or tablet form; it is not suitable for mechanized fertilization.
• Since the extrusion method of compound fertilizer has strict requirements on the total liquid phase amount of raw material base fertilizers, additives, fillers and other auxiliary materials, the operating adjustment range is very small (generally the total liquid phase amount is 5% to 8%). Choices are limited, making toppings a bit difficult.
• The template of the extrusion granulator is easy to wear, and replacement of worn parts often affects production. The combination of various factors limits the development of this method.
• The extrusion granulation plant has a simple process for producing compound fertilizer, consumes less energy, and has low construction investment. It is suitable for small-scale on-site processing and manual fertilization.

Dry powder granulation/pelletization method for npk compound fertilizer production:

• The dry powder pellet method compound fertilizer uses two or more powdery basic fertilizers, with the help of spraying water or steam or simple fertilizer slurry or binder, in the granulator (disc, drum, double Shaft can be) internally granulated, dried, screened, cooled, and oiled and powdered to make the product.
• The characteristics of the modern development of the world’s fertilizer industry are: centralized production of basic fertilizers and intermediate products, decentralized compounding and sales. Therefore, the secondary processing of dry powder pelletization into compound fertilizer has developed rapidly. This method can produce high, medium and low concentration compound fertilizers, as well as special compound fertilizers containing trace elements, pesticides or hormones.
• Powdered basic fertilizers of nitrogen, phosphorus, and potassium are continuously added to the drum granulator through metering and mixed with the returned materials to physically and chemically granulate the ammonium sulfate mother liquor with dissolved trace elements or pesticides or hormones. The granulated material enters the desiccant and the hot flue gas to dry in parallel. Then it is screened, and some of the qualified particles are used as return material, and some are cooled, oiled and powdered to make products.
• The large pieces under the screen are crushed, together with the fine powder under the screen and some qualified particles, are returned to the drum granulator for re-granulation. The dry and cooled exhaust gases are washed by cyclone separators and stinging towers respectively and then vented. The washing liquid and ammonium sulfate mother liquor are mixed to dissolve trace elements and auxiliary materials (pesticides, hormones, etc.).

Two granulation methods based on powdered raw materials:

• The process of producing compound fertilizer through the pellet method based on powdered raw materials includes two types: return material and non-return material. The difference between the two is that the large particles screened in the return process are crushed and returned to the granulation process together with the fine powder and some qualified particles through mechanical transmission for granulation;
• The non-return material process requires a high granulation rate in the granulation process, and only a small amount of fine powder and large particles under the screen are crushed and returned to the granulation process for granulation by manual transportation. The latter is only suitable for compound fertilizer production with rich labor force and small production scale.

What is the production process of pelletized compound fertilizer with returned material design?

• If it does not contain urea or add no more than 10% of the calcium content in the ingredients, urea and other nitrogen, phosphorus and potassium should be crushed, screened, measured and mixed evenly. Dissolve the measured trace elements, pesticides, or hormones that need to be added with the measured aqueous solution, or steam, or binder, or the circulating liquid that circulates water and acid to wash, dry and cool the tail gas.
• The granulated material is granulated in the granulator. The granulated material is dried in parallel flow during the drying period using the flue gas from burning coal or heavy oil as the heat source. Finally, after screening, the qualified particles are partially used as returned materials and are cooled by counter-current flow of cold air in the cooler, or are oiled, powdered, and colored, and then screened and classified according to particle size for packaging into products.
• After being crushed, the granulated powder and large particles are returned to the granulator together with some qualified particles for further granulation. The dry and cooled exhaust gas is recovered and washed by dry and wet methods and then vented. The circulating washing liquid dissolves the auxiliary materials and then enters the granulator for physical granulation.

What is the detailed production process of pelletized compound fertilizer with returned materials design?

• Raw material process: The crushing fineness of various raw materials and auxiliary materials is -20 mesh 100%, and the measurement accuracy is ≥98%.
• Granulation process: The granulation rate is 80% to 90% with the return process, and the granulation rate is ≥90% without the return process. The liquid content of the outlet material of the disc granulator is 10% to 15%. Relevant data show that in the drum granulator, when the volume ratio of the liquid phase to the solid phase exceeds 16%, the average diameter of the particles increases rapidly; when the volume ratio of the liquid phase to the solid phase is about 28%, the particles of 1.5 to 3.5 mm The ratio is the largest and has the highest granulation rate; if the volume ratio of the liquid phase and the solid phase is increased, the proportion of particles with a diameter of 1.5 to 3.5 mm will drop sharply. Therefore, to obtain the required maximum proportion of finished product particles, the amount of liquid phase must be strictly controlled. The return multiple is generally 3~6.
• Drying and cooling process: For production with urea or ammonium nitrate added, the drying kiln gas inlet temperature is ≤155℃, the drying kiln outlet material temperature is 75~85℃, and the moisture content is ≤1%; for production without adding urea or ammonium nitrate, the drying kiln gas The inlet temperature is 250~300℃, and the material temperature at the outlet of the drying kiln is 80~90℃. The material temperature at the outlet of the cooler is ≤40°C, and the other indicators should meet the GB15063-94 national quality standard for compound fertilizers.
• Recycling and packaging process: The dust content of the vented air is ≤400mg/m3 (standard). The concentration and amount of recycling liquid, the concentration and amount of dissolved liquid, and the weight of bagged finished products must be strictly controlled.

Process calculation of pellet granulation method

How to determine the organic fertilizer dosage added to the compound fertilizer?

• Crop nutrition requires fertilization and soil supply. Chemical fertilizers cannot replace organic fertilizers because soil fertility does not only provide nutrients for crops, but the accumulation of organic matter creates a soil aggregate structure that coordinates the contradictions of water, fertilizer, air, and heat fertility factors in the soil and provides crops with Absorb nutrients and create favorable environmental conditions.
• The generation of soil fertility is a movement phenomenon of soil microbial activity. The activities of microorganisms must have energy, which relies on the application of fresh organic fertilizers to stimulate the potential fertility of the soil, increase the fertilizer intensity of soil phosphorus and potassium, and degrade residual pesticides and complex harmful heavy metals in the soil. Chemical fertilizers can only increase the concentration of soil nutrients, but have little effect on maintaining and improving soil fertility. Pure “organic agriculture” and “inorganic agriculture” are both unworkable. A minimum amount of organic fertilizer must be applied to crops every season, and then chemical fertilizers must be applied according to the formula.
• The minimum amount of organic fertilizer that is sufficient to maintain and gradually improve soil fertility is calculated based on how much soil organic matter is mineralized (consumed) by growing crops for one season. According to research reports: the annual mineralization amount of soil organic matter is about 3%. For example, for soil with an organic matter content of 2%, the annual soil organic matter consumption is: 150,000kg topsoil × 2% × 3% = 90kg/acre of organic matter. This number can be converted into a physical amount using the humification coefficient of organic fertilizer. For example, if the humification coefficient of pig manure is 30% and the water content is 80%, the amount of pig manure that should be applied is: 90÷(30%×20%)=1500kg/acre.

How to determine the compound fertilizer grade concentration or ratio?

The best method is to conduct field trials of fertilizers over many years, but this is very time-consuming and requires a lot of investment in manpower and material resources. Below are two more calculation methods for determining the concentration or ratio of compound fertilizer grades.

1. Nutrient balance method
   This method is that the nutrients needed by the crops are equal to the sum of the nutrients that the soil can provide and the nutrients that the organic and inorganic fertilizers applied can provide, to achieve a nutrient balance.
2. Simple algorithm
   Use the yield in nitrogen-free areas to determine the amount of nitrogen fertilizer used in dry crops; use the empirical equation provided by International Rice to determine the amount of nitrogen fertilizer used in rice. First, use a simple experiment to determine the phosphate fertilizer coefficient, that is, how much phosphate fertilizer (P2O5) needs to be applied to increase 1ug of available phosphorus per gram of soil. kg), and then use the graphic method or formula calculation method to determine the amount of phosphate fertilizer.

How to determine the basic raw material ingredients of compound fertilizer

1. Analytical method
   The analytical method does not consider the balance between the amount of moisture brought into the production system by the raw materials and the moisture content required by the compound fertilizer product. As a result, the effective nutrient content in the compound fertilizer product is either higher than the calculated value or lower than the calculated value. When using the analytical method, attention should be paid to adjusting the amount of raw materials added by testing the quality of the compound fertilizer product.
2. Calculation method for ingredients based on product standard moisture content. The so-called “product standard moisture content” refers to the moisture percentage that must be reached in the compound fertilizer products produced. The calculation method is a series of calculations based on this basis.

                   High concentration [total nutrient content (N+P2O5+K2O) ≥ 40%], moisture (free water) ≤ 2.0%.
                   Medium concentration [total nutrient content (N+P2O5+K2O) ≥ 30%], moisture (free water) ≤ 3.0%.
                   Low concentration [total nutrient content (N+P2O5+K2O) ≥ 25%], moisture (free water) ≤ 5.0%.
                   Low concentration [total nutrient content (binary fertilizer) ≥ 20%], moisture (free water) ≤ 5.0%.

 The original data of nutrient and moisture (free water) content in raw fertilizers used in the calculation must be based on the test results of each batch of raw materials entering the factory.