FERTILIZER INDUSTRY LECTURE 1

INTRODUCTION• Fertilizers are composed of nitrogen, phosphorus, and potassium compounds.

They also contain trace elements that improve the growth of plants.

• Plants use nitrogen in the synthesis of proteins, nucleic acids, and hormones.

• Plants also need phosphorus, a component of nucleic acids, phospholipids, and

several proteins.

• Potassium is another major substance that plants get from the soil. It is used in

protein synthesis and other key plant processes.

• Early scientists such as Francis Bacon and Johann Glauber describe the

beneficial effects of the addition of saltpeter to soil.

• Glauber developed the first complete mineral fertilizer, which was a mixture of

saltpeter, lime, phosphoric acid, nitrogen, and potash.

• A patent issued to Sir John Lawes, first outlined a method for producing a form of

phosphate that was an effective fertilizer.

The Manufacturing Process

Nitrogen fertilizers

1) Ammonia can be synthesized from in-expensive raw materials.

Natural gas and steam are pumped into a large vessel.

Next, air is pumped into the system, and oxygen is removed by the burning of natural gas and steam.

This leaves primarily nitrogen, hydrogen, and carbon dioxide.

The carbon dioxide is removed and ammonia is produced by introducing an electric current into the system.

Catalysts such as magnetite (Fe3O4 ) have been used to improve the speed and efficiency of ammonia synthesis.

The NPK Manufacturing Process

Nitrogen fertilizers (contd.)

2) Nitric acid:

Produced by first mixing ammonia and air in a tank.

In the presence of a catalyst, a reaction occurs which converts the ammonia

to nitric oxide.

The nitric oxide is further reacted in the presence of water to produce nitric

acid.

3) Ammonium nitrate:

Nitric acid and ammonia are used to make ammonium nitrate.

It is a good fertilizer component because it has a high concentration of nitrogen.

The two materials are mixed together in a tank and a neutralization reaction

occurs, producing ammonium nitrate.

This can be granulated and blended with the other fertilizer components.

The NPK Manufacturing ProcessPhosphatic fertilizer:

To isolate phosphorus from phosphate rock, it is treated with sulfuric acid,

producing phosphoric acid.

Some of this material is reacted further with sulfuric acid and nitric acid to

produce a triple superphosphate, an excellent source of phosphorous in solid

form.

2) Ammonium phosphate:

Some of the phosphoric acid is also reacted with ammonia in a separate tank.

This reaction results in ammonium phosphate, another good primary fertilizer.

1) Superphosphate:

The NPK Manufacturing Process

Granulating and Blending:

To produce fertilizer in the most usable form, each of the different compounds,

ammonium nitrate, potassium chloride, ammonium phosphate, and triple

superphosphate are granulated and blended together.

The solid materials are placed into a rotating drum which has an inclined axis. As

the drum rotates, pieces of the solid fertilizer take on small spherical shapes.

They are passed through a screen that separates out adequately sized particles.

A coating of inert dust is then applied to the particles, keeping each one discrete

and inhibiting moisture retention.

Finally, the particles are dried, completing the granulation process.

The blending is done in a large mixing drum that rotates a specific number of turns

to produce the best mixture possible.

After mixing, the fertilizer is emptied onto a conveyor belt, which transports it to

the bagging machine.

Composite fertilizer manufacture:

The NPK Manufacturing ProcessBagging:

Fertilizers are typically supplied to farmers in large bags. To fill these bags the fertilizer is first delivered into a large hopper. An appropriate amount is released from the hopper into a bag that is held open by a clamping device. The bag is on a vibrating surface, which allows better packing. When filling is complete, the bag is transported upright to a machine that seals it closed. The bag is then conveyored to a palletizer, which stacks multiple bags, readying them for shipment to distributors and eventually to farmers.

AMMONIA

Uses:

85% of ammonia production is used for nitrogen fertilizers

40% of ammonia produced is used in urea production

Other solid nitrogen fertilizers are ammonium nitrate, ammonium sulfate and

ammonium phosphates.

Synthesis:

Difficult to synthesize using Nitrogen from air due to the high BDE, IE&EA of

Nitrogen molecule is very high.

N2 +3H2 ↔ 2NH3 ∆H = -91.444 kJ/mol

Temperature is crucial parameter

Ammonia (mol%) in equilibrium synthesis gas; H2/N2 =3mol/mol

AMMONIA SYNTHESIS REACTORS

Reactor design in ammonia synthesis is critical since temperature control is

crucial. Methods applied to achieve this are:

1)Quench reactors- Cold feed gas is added at different heights in the

reactor.

2)The heat produced is removed between the catalyst beds by heat

exchangers. Hence, heat is removed at the highest possible temperature.

ICI quench reactor Temperature-Concentration profile

Kellogg a) Vertical (left fig.) b) Horizontal (right fig.) quench reactors

Haldor Topsoe radial flow reactors

Multi-bed converter with indirect cooling; (a) catalyst, (b) feed-effluent heat exchanger, (c) cold bypass, (f) product.

Integrated Ammonia Plant

Specific energy requirements of various ammonia processes

Process GJ (LHV)*/t ammonia

Classical Haber-Bosch (coke) 80-90

Reformer pressure 5-10 bar (1953-1955)

47-53

Reformer pressure 30-35 bar(1965-1975)

33-42

Low-energy concepts (1975-1984)

27-33

State of the art (since 1991) 24-26

*Lower heating value