Liquid complex fertilizers (LCF)

Liquid complex fertilizers are highly effective, quick-release fertilizers. In addition to condensed phosphates (70÷80% of the total mass of Р2О5) and nitrogen, the LCF may contain sulphur and magnesium. All nutrients are in solution, so they are easily available to plants. LCF is produced by neutralizing superphosphoric acid with ammonia gas. NIUIF employees together with Voskresensky JSC NIUIF have been developing and improving the technology of LCF manufacture since the 70s of the last century.

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LCF is a water solution of ammonium ortho- and polyphosphates, containing 10÷11% of nitrogen and 34÷37% of phosphorus recalculated to Р2О5, depending on the grade. It is possible to manufacture LCF with micronutrients such as zinc, boron, manganese, copper, molybdenum, in dissolved form.

Ammonium orthophosphates, part of LCF composition, are represented by monoammonium phosphate NH4H2PO4 and diammonium phosphate (NH4)2HPO4. Ammonium pyrophosphates are represented by diammonium pyrophosphate (NH4)2HP2O7 and triammonium pyrophosphate (NH4)3HP2O7.

The stages of LCF manufacture process are presented using the following basic chemical equations:

H3PO4+NH3→NH4H2PO4

H3PO4+2NH3→(NH4)2HPO4

t 200 °С - 300 °С

                (2Н3РО4 Н4Р2О7 + Н2О)

H4P2O7+NH3→NH4H3P2O7

H4P2O7+2NH3→(NH4)2H2P2O7

H4P2O7+3NH3→(NH4)3HP2O7

Liquid complex fertilizer is a clear, green-blue liquid, which contains almost no insoluble residues, suspensions.

Main physical and chemical parameters:

Mass fraction of nitrogen (N), %, not less than

11

Mass fraction of total phosphates (Р2О5), %, not less than

37

Conversion rate *, %, not less than

57

Mass fraction of water insoluble residue, %, not more than

0,4

Exponent of hydrogen ions, рН units

6÷7

Density at 20 0С, g/cm3

1,44+/-0,03

Viscosity at 20 0С, cPs, not more than

80

Crystallization temperature, not higher than

minus 20 °С

LCF solution boiling point

101÷107 °С

* - conversion rate features the polyphosphates content in LCF in % of the total content of Р2О5.

JSC NIUIF together with Voskresensky branch offers grade 11:37 LCF technology according to two flowsheets, differing from each other by the method of excess heat removal of superphosphoric acid and gas ammonia neutralization.

The process in both plants, is based on ammoniation of superphosphoric acid with gas ammonia in a pipe reactor, dissolving the resulting salt cake, cooling and preammonization of the resulting solution. In the first type plant, the heat of ammoniation chemical reaction is removed by water in external heat exchanger from the forcibly circulating LCF solution. In the second type plant, the excess heat is removed due to the evaporation of a certain amount of water from LCF solution.

LCF manufacture plant flowsheet with external circulation and external heat exchanger

Figure 1 shows flowsheet for LCF manufacture, equipped with external heat exchanger and forced external circulation of the reaction solution.

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Figure 1. LCF manufacture flowsheet, equipped with external heat exchanger and forced external circulation of the reaction solution

1. Tank; 2. C-pump; 3. Ammonia evaporation unit; 4. Pipe reactor; 5. Cup; 6. PN tank; 7. SPA tank; 8. Ammonia gas heater; 9. Heat exchanger; 10. SPA feed pump; 11. Circulation pump; 12. LCF discharge pump to storage.

Parent superphosphoric acid (SPA) with 68÷72% P2O5 concentration, heated to a temperature of 70÷90°C, enters the SPA tank 7. From there, the acid is fed into pipe reactor 4, where gas ammonia with 80°C temperature in the amount of 60÷100% of the total is also fed. The remaining gas ammonia enters preneutralizer. Ammonia is fed to the evaporator 3 in liquid form, where it evaporates due to the heat of the final product, and after being heated in the heater 8, is fed to the pipe reactor 4, and to the preneutralizer tank. The reactor is installed in a special cup 5, into which the cooled circulating LCF solution is fed, after the heat exchanger 9. Next, LCF solution is fed into preneutralizer tank 6. The LCF solution from preneutralizer enters the ammonia evaporation unit, then the heat exchanger 9, and again returns to the preneutralizer 6. A part of LCF with 20÷35°C temperature as a final product is sent, after the heat exchanger, to the final product storage.

High-velocity circulation of LCF through an external heat exchanger (ratio 6÷10), helps to maintain the necessary temperature in PN. To maintain the required concentration of LCF solution, process water flows into preneutralizer from the pressure tank.

The plant is equipped with an automatic control and monitoring system that allows to stabilize the flow rate of ammonia, process water, phosphoric acid, circulating LCF and specific density of the liquid fertilizer solution. The I&C system allows you to record the necessary temperature conditions and the flow rate of the main components.

Vacuum Plant for LCF manufacture in the airlift apparatus

Flowsheet for LCF manufacture is shown in Figure 2. The main element of the flowsheet is an airlift apparatus with a pipe reactor. In pipe reactor SPA reacts with gas ammonia. The pipe reactor is equipped with a cooling water jacket. From the pipe reactor, the salt cake is fed to the airlift apparatus. Due to the energy of chemical reaction, high-velocity natural circulation occurs (ratio 60÷80) in the airlift apparatus. Excess heat of chemical reaction is removed due to evaporation of a certain amount of water from LCF. The remaining gas ammonia is fed into the circulation chamber.

Water is continuously fed into the airlift apparatus from the pressure tank. The resulting LCF enters the sump tank, from where they are pumped to the final product storage. This plant has no liquid effluent. The plant is equipped with an automatic control system.

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Figure 2. Flowsheet for LCF manufacture

1. SPA tank; 2. SPA feed pump; 3. Pipe reactor; 4. Airlift apparatus; 5. Pressure tank; 6. Shell and tube condenser; 7. LCF tank; 8. LCF discharge pump to storage; 9. Water inlet pump; 10. Process steam condensate tank; 11. Spray trap; 12. Vacuum-pump; 13. Ammonia evaporation unit; 14. Gas ammonia heater.

Due to the absence of external circulation, the flowsheet is simplified, hence the possibility to reduce material consumption for the process and also heat removal flow rate. In addition, there are no problems associated with cleaning heat exchanger equipment. All these factors determine the advantages of a vacuum plant for LCF manufacture in the airlift-type apparatus.

The proposed flowsheet has been tested on pilot industrial and industrial plants.

The production capacity of one plant is from 50 up to 250 thousand tons of LCF per year.