CN1062846C - Technology for production of modified calcium superphosphate compounded fertilizer - Google Patents

Abstract

The invention belongs to a method for manufacturing granular compound fertilizers.

The method is to use urea or ammonium nitrate granular soluble fertilizer as the core, and calcium superphosphate treated with powdery materials containing magnesium oxide as the covering layer, and spray inorganic acid or its composite binder in the granulator for mixing to produce Potassium fertilizer, trace element fertilizer and its chelating agent, plant growth regulator or pesticide can be added to the coating layer, and then calcium magnesium phosphate fertilizer, ammonium phosphate, phosphate rock powder and phosphorus-containing powdery dry material can be used as dusting agent to dust the particle surface Or additional coloring agent coloring. The process simplifies the traditional process, reduces the production cost, improves the appearance of the product, and slightly increases the fertilizer efficiency of the product.

Description

A kind of manufacturing method of wrapped type compound fertilizer

The invention belongs to a method for manufacturing granular compound fertilizers.

The present invention proposes a new method in order to overcome the deficiency of the traditional compound fertilizer production method (hereinafter referred to as the traditional method) using urea-superphosphate as the main raw material.

Superphosphate is one of the main phosphate fertilizer varieties in China at present, accounting for about 70% of the total phosphate fertilizer output. Due to the simple production process, low investment and low production cost of superphosphate, superphosphate will remain an important phosphate fertilizer for a long time to come.

At present, the vast majority of calcium superphosphate products leave the factory in the form of powder. According to the national chemical industry standard HG2740-95: its appearance should be loose powder. However, in actual production, this requirement is not strictly controlled, so that products containing a large number of agglomerates leave the factory, which brings many difficulties to use, packaging and transportation. Powdered products are not suitable for mechanized fertilization, and when powdered products are applied to soil, the available phosphorus is more likely to be fixed by iron and aluminum in the soil than granular products. Therefore, the fertilizer effect of granular superphosphate is better than powder superphosphate.

Superphosphate contains about 15% free water and 3.5-5.5% P ₂ O ₅ free phosphoric acid, and its main active ingredients are calcium dihydrogen phosphate monohydrate and free phosphoric acid. If urea is mixed with untreated superphosphate, these two active ingredients will easily form calcium dihydrogen phosphate-urea adduct and urea phosphate with urea and release crystal water in calcium dihydrogen phosphate, resulting in The water content increases, and these two products have high solubility, can dissolve in the liquid phase of superphosphate, increase the liquid phase of the mixture, and finally become viscous wet mud, which cannot be granulated. Therefore, superphosphate must be pretreated before it can be mixed with urea.

The main disadvantages of the traditional method are:

①Complicated raw material pretreatment

It is necessary to set up a separate workshop to dry superphosphate (reduce free water), crush, sieve and ammonify (neutralize free phosphoric acid).

The drying of superphosphate requires the free water to be reduced to less than 5%, and drying equipment needs to be installed, and the temperature control is strict. If the temperature is too high, the effective phosphorus will be degraded; if the temperature is too low, the material will not be easy to "dry".

Urea is a granular fertilizer containing 46% nitrogen and a diameter of 0.3-2.5 mm, which is the source of nitrogen in compound fertilizers. In the traditional method, urea should be crushed into a fine powder form below 0.8 mm during raw material pretreatment.

② High return rate

The traditional method needs to mix the crushed urea with other powdery materials (superphosphate, potassium chloride, etc.) and send it to granulation. Since there is no core before granulation, the particles grow gradually after the core is formed through agglomeration. In this way, on the one hand, the granulation efficiency is low, and on the other hand, the pelleting rate of the mixed material is also low, only 40-60%, and the unqualified particles exceeding 4 mm must be crushed and returned to the system with the powder that has not been granulated. Granulate. Granular urea crushing, re-granulation and a large number of returned materials circulate in the system, which not only consumes a lot of energy, increases production costs, but also deteriorates the operating environment.

③ The neutralization process is complicated

The traditional method often uses methods such as ammoniation for neutralization, which requires a large investment in equipment, and the control of ammoniation operation is also relatively strict. This is because the traditional method regards the neutralization operation as a single process, but does not combine it with the granulation process, so when selecting the neutralizer, the requirements of granulation are not fully taken into account.

The object of the present invention is to provide a kind of powdery material containing magnesia as calcium superphosphate pretreatment neutralizer, urea or ammonium nitrate granular soluble fertilizer is used as wrapped granulation core, processed calcium superphosphate or other The water-soluble phosphate fertilizer is the coating layer, and potash fertilizer, micro-fertilizer and its chelating agent, plant growth regulator or pesticide can be selectively added to the coating layer, sprayed into inorganic acid or its composite binder, and processed in the granulator. Granulation, adjusting the composition and dosage of the coating layer can be made into a special calcium superphosphate-coated compound fertilizer suitable for different crops, and the phosphorus-containing powdery dry material (such as calcium magnesium phosphate fertilizer, ammonium phosphate or rock phosphate powder) is used as the puffing agent. The process of powdering the surface of the powder or adding coloring agent to overcome the limitations of the traditional method, reduce production costs, protect the environment, and improve the appearance of compound fertilizers.

The solution is as follows: mix powdered raw materials containing magnesium oxide (such as magnesite, serpentine or dolomite) with powdered superphosphate, and then add granular soluble fertilizers (such as urea or ammonium nitrate) , treated powdered superphosphate or other water-soluble phosphate fertilizers, selectively add potassium fertilizers, micro-fertilizers and their chelating agents, plant growth regulators or pesticides, spray into inorganic acids or their composite binders, and Granulate in the granulator, and finally use phosphorus-containing powdery materials (such as calcium magnesium phosphate fertilizer, ammonium phosphate or phosphate rock powder) as the powdering agent to powder the surface of the granules or add coloring agents for coloring, and leave the factory after drying, screening and packaging.

Theoretical basis of the present invention is as follows:

Due to the high free water and free phosphoric acid in superphosphate, after adding magnesium oxide, free phosphoric acid and magnesium oxide react exothermicly, which not only neutralizes free phosphoric acid, but also evaporates the water in superphosphate. The magnesium hydrogen phosphate produced by the reaction is not only a slow-acting fertilizer, but also has three molecules of crystal water, which can convert part of the free water in superphosphate into crystal water, which objectively plays a role of drying, making the superphosphate Calcium phosphate is loose for subsequent granulation.

Another advantage of adding magnesium oxide is that no matter how much it is added, it will not "degrade" the available phosphorus in superphosphate. This property is different from adding ammonium bicarbonate, ammonia water and other substances to superphosphate in the traditional method.

During the granulation process, part of the magnesium oxide reacts with the inorganic acid or its composite binder, on the one hand, the temperature of the granulation material is increased, and on the other hand, the formed magnesium sulfate or magnesium phosphate salt is colloidal, with A certain degree of cohesiveness is conducive to agglomeration and granulation. Due to the exothermic reaction, the temperature rises, causing the water of crystallization in the magnesium hydrogen phosphate to change into free water again. Therefore, as long as the water content in the binder is adjusted, this part of the free water in the superphosphate plays the role of wetting the material during granulation.

Urea granules do not need to be crushed, and urea can be directly used as the granulation core during granulation. On the one hand, the granulation rate of a granulation is improved. On the other hand, because the process of forming the granulation core is omitted, it also shortens the granulation time.

Phosphorus-containing powdery dry materials are used as dusting agents based on two considerations. One is that wet superphosphate is difficult to grind after the superphosphate drying pretreatment is omitted, so the surface of the pelletized fertilizer particles is both wet and rough. This situation can be improved after powdering agent is added. Second, the content of available phosphorus and total phosphorus in superphosphate decreases after adding non-phosphorus neutralizer. Adding phosphorus powdering agent can act as a nutrient regulator. .

The wet granular compound fertilizer produced by the present invention can adopt a drying process, and also can adopt a non-drying process, and without a drying process, a highly water-absorbing substance (such as sodium tripolyphosphate, etc.) needs to be added to the dusting agent.

In the present invention, the calcium superphosphate neutralizer and the granulation binder are unified, and the liquid phase in the material is adjusted by a chemical method, and the free water in the superphosphate is used to reduce the added water, avoiding the traditional method of drying first The disadvantage of post-humidification (using water as the binder) reduces the drying energy consumption, and at the same time improves the granulation ability and granule strength.

The main difference between the technical invention and the traditional method is as follows:

① The drying pretreatment of superphosphate is omitted;

② The crushing treatment of granular urea is omitted;

③Enhance the granulation efficiency, reduce or even avoid the returning material;

④ The drying load of the product is reduced, which reduces the production cost;

⑤Improve the appearance of the granules, and enhance the identification of real and fake compound fertilizers;

It can be treated in the same way when heavy superphosphate and rich superphosphate are used instead of superphosphate for production.

Embodiment one

Weigh raw materials according to the following proportions:

Urea (46% nitrogen) 21.7 parts

Calcium superphosphate (containing effective P ₂ O ₅ 14%) 60.0 parts

Calcium magnesium phosphate fertilizer (containing effective P ₂ O ₅ 18%) 8.8 parts

Calcined magnesite (containing MgO85%) 6.0 parts

Sulfuric acid (converted to pure H ₂ SO ₄ 100%) 1.5 parts

Superphosphate is crushed to a particle size of less than 0.5 mm, and calcined magnesite is crushed to a particle size of less than 0.2 mm, and mixed uniformly to form a mixture, and then the granular urea and the mixture are mixed in a rotating granulator, and sulfuric acid is sprayed , while granulating, after the granulation is completed, add calcium magnesium phosphate fertilizer for powdering, and then send the granular material into the drum dryer for drying. Millimeter granules are finished products. The finished product contains 10% nitrogen, 10% available phosphorus and 5.1% magnesium oxide.

Embodiment two

Weigh raw materials according to the following proportions:

Urea (46% nitrogen) 17.4 parts

Calcium superphosphate (containing effective P ₂ O ₅ 12%) 40.7 parts

Calcined magnesite (containing MgO85%) 10.1 parts

Potassium chloride (containing K ₂ O60%) 16.7 parts

Diammonium phosphate (containing N18%, P ₂ O ₅ 46%) 11.1 parts

Sulfuric acid (converted to pure H ₂ SO ₄ 100%) 2.0 parts

Superphosphate is crushed to a particle size of less than 0.5 mm, calcined magnesite, potassium chloride and diammonium phosphate are crushed to a particle size of less than 0.2 mm, and calcium superphosphate is uniformly mixed with calcined magnesite powder and potassium chloride to form Mix the materials, then put the granular urea and the mixed materials in the rotating granulator, spray sulfuric acid while granulating, after the granulation is completed, add diammonium phosphate for dusting, and then send the granular materials into the drum dryer Drying, the temperature of the gas entering the dryer is 100-140°C, and the 1-4 mm particles are sieved after discharge as the finished product, which contains 10% nitrogen, 10% available phosphorus, 10% potassium oxide, and 8.6% magnesium oxide.

Claims (2)

1, a kind of manufacture method of wrapping type compound fertilizer, it is characterized in that this method is with urea or ammonium nitrate granular soluble fertilizer as core, with the calcium superphosphate that contains magnesia powder material processing as wrapping layer, in making Spray inorganic acid or its composite binder in the granulator for mixing and granulation. Potassium fertilizer, trace element fertilizer and its chelating agent, plant growth regulator or pesticide can be added to the coating layer, and then calcium magnesium phosphate fertilizer, ammonium phosphate, Phosphorus rock powder Phosphorus-containing powdery dry material is used as dusting agent to dust the surface of the particles or add coloring agent for coloring. 2. The method according to claim 1, characterized in that said superphosphate can be replaced by rich superphosphate or double superphosphate.