Complex Fertilizer Manufacturing Description

Complex fertilizer process plants around the world use the raw materials with approximate purity of Phosphoric acid of conc. 46% and 26%, Sulphuric acid of 93%, Ammonia 99.5% maximum, Urea prills, Muriate of Potash, Fillers. Mostly as per the standard design the minimum plant capacity decided according to the grade as well as per 22 working hrs/ day, with allowance of 2 hrs/ day for cleaning and adjustments. An example of the ideal plant capacity suitable for the grade on basis effect of Water, Steam, Fuel, Electric Power, etc.. factors

Product      Capacity
20-20-0      750 mt/day
16-20-0      800 mt/day
14-35-14    850 mt/day

The final complex fertilizer product obtained in the solid granular form, its quality depends on the dissolution of chemicals and binding strength also. Primary variables tested are,

Granulometry:

  • Bigger than 4mm : 5% maximum
  • From 4-1mm : 90% minimum
  • Lower than 1mm : 5% maximum

Product water content:

  • Less than 1% of free moisture.

Chemical quality:

  • +/- 0.6 maximum deviation for individual nutrients subject to maximum of 1 for combined nutrients.

Complex Fertilizer Manufacturing Description of NP & NPK:

In this process the main reaction can be takes place in pipe reactor. P2O5, H2SO4 and Ammonia are fed to the pipe reactor. In this ammonium phosphate and ammonium sulphates are formed as slurry and this is sent to Granulator, the reactions takes place are
NH3 (gas) + H2SO4 —> (NH4)2SO4 +1800 kcal/kg of NH3 (gas)

NH3 (gas) + H3PO4 —> NH4H2PO4 +1500 kcal/kg of NH3 (gas)

NH3 (gas) + NH4H2PO4 —> (NH4)2H2PO4 +1300 kcal/kg of NH3 (gas)

Granulator:

  • Granulator is a rotary drum type and is inclined at an angle 20 with the horizontal. Ammonium phosphate or sulphate acid slurries coming from the pipe reactor are distributed inside the granulator drum over the solids bed, composed mainly of recycled fines and the solid raw materials fed. Those slurries are ammoniated with the ammonia is sprayed into the solid bed of granulator. The reactions takes places in this ammonization are
    NH3 (liq) + H2SO4 —>(NH4)2SO4 +1500 kcal/kg of NH3 (liq)

NH3 (liq) + NH4H2PO4—> (NH4)2H2PO4+1000 kcal/kg of NH3 (liq)

Drying:

  • The product from granulator has a free humidity between 1.6 % and 2.5%. Which should be reduced to 1% for the production specifications. So the drying takes place in a rotating drum into which the product from granulator enters by gravity. The drum has an internal diameter of 350mm and a length of 2700mm and 800mm long grizzly equipped with a combustion chamber which operates between 1.5 and 3 mm Kcal/hr. using heavy fuel oil. The drying temperature is between 100oC – 150oC.

Screening:

  • The screening section is composed of two decks type screens. Both are driven by electric mechanical vibrators. The over sizes on the first screen deck is sent to chain mills where they will be crushed. The undersize product particles of first screen retain on second screen are sent to cooler. And the fines are sent to recycle belt conveyor.

Cooling:

  • The solids coming from the screening are cooled using ambient air in co-current flow. The solids are cooled up to 40o – 45o C. and the solids coming from cooler is sent to polishing screens, and the gas is sent to cyclone separators.

Polishing Screens:

  • The product leaving rotary cooler are sent to polishing screens where if any fines present will be removed. This is a single deck type with a polishing screen vibrating feeders and divided by unbalanced motor. This is also provided with cloth cleaning systems. The cooled and screened product is now sent for bagging through final product belt conveyor and the rejected fines are sent to the recycle belt conveyor.

Cyclone Separators:

  • The gas coming from Dryer and Cooler are fed to a two different batteries of cyclone separators. In this dust present in the gas are removed, and is sent to recycle belt conveyor. The gas coming from cyclone separators for dryer or cooler are sent to dryer or cooler scrubber respectively.

Scrubbing Section:

There are 3 scrubbing units (that include the 3 scrubbing steps)

  • The first unit is composed of Granulator fumes pre-scrubber for the gases coming from the granulator mainly containing ammonia & dust. It is a vertical section/ cyclonic type scrubber. The washing liquid is normally constituted by phosphoric acid(20-40% P2O5) and some sulphuric acid. In this high pressure sprays are used for gaseous fluoride and ammonia absorption.
  • The second unit (second scrubbing step) is composed of granulator scrubber, Dryer scrubber, Cooler & Dedusting scrubber. The first one for the gases coming from the granulator pre-scrubber, the second one for gases coming from the dryer-cyclones.
  • The third one of gases coming from the cooler cyclones and dedusting cyclones, mainly containing dust. All the three scrubbers are of similar towers, venture/cyclonic type, but logically with different dimensions, and in this more diluted acids are used.
    The third unit is composed of the tail-gas scrubber in which all gases will be washed in two sub-steps. Tail-gas scrubber is composed by a horizontal duct washer equipped with several successive washing sections as a first sub-step scrubbing and by a cylindrical vertical tower cyclonic inlet, and the reactions are takes place are

NH3 (gas) + H2SO4 —> (NH4)2SO4 +1800 kcal/kg of NH3 (gas)

NH3 (gas) + H3PO4 —> NH4H2PO4 +1500 kcal/kg of NH3 (gas)

Process flow diagram of complex fertilizer manufacturing:

NPK compex fertilizer process flow sheet

Complex fertilizer production

Equipments in flow chart:

1. Pipe Reactor
2. Granulator
3. Dryer
4. Vibrating Screens
5. Cooler
6. Chain Mills
7. Polishing Screens
8. Bagging and Storage section
9, 10. Hopper Bins for Fillers, Urea, Potash
11. Cyclone Separator for Dryer
12. Cyclone Separator for Cooler
13. Dryer Scrubber
14. Cooler Scrubber
15. Granulator Scrubber
16. Granulator Pre – Scrubber
17. Pre – Sump
18. Main Sump
19. Recycle Conveyor
20. Final or Tail Gas Scrubber
21. Furnace