Phosphate reaction and gas washing

Phosphate rocks come from fossil deposits, which are the residues of prehistoric seas, and they are rich in calcium phosphate.
The rocks actually found in nature are in fact inert and in order to transform the phosphate into a form suitable for the plants,
we have to dissociate it from the calcium. To do this, it is necessary to reduce the rocks into very fine powders
and treat them with sulphuric or phosphoric acid, in order to produce two basic fertilizers:
SSP (Single Super Phosphate) or TSP (Triple Super Phosphate).

We design and manufacture the complete system of reaction for phosphate rocks, based on the Kuhlmann den principle.
We introduce the powders, the acid and the reaction water Into a dynamic mixer;
the slurry generated in the mixer falls onto a belt conveyor to complete the reaction.
A hood disposed over the entire length of the belt keeps the belt conveyor in depression by means of a suction system,
and prevents the gases and steams, which develop during the reaction of the acid attack, from spreading into the environment.
The gases and steams sucked from the Kuhlmann den are cleaned with a multi-stage depollution system.
In the early stages, by using a Venturi tube and a cyclone, we wash the solid particles, dragged by the stream and part of the reaction gases.
The final stages, constituted by a Venturi tube with a cyclone and by one or more scrubbers, complete the cleaning of the gases and control the pH of the purified air stream before outputting it into the atmosphere.

Dynamic mixer and reactants dosing

Inside a vertical cylinder coated with acid resistant material, a shaft fitted with blades of special steel rotates at a high speed.
The shaft and blades are acid resistant and wear resistant, in order to resist the abrasion of mineral powders.
This is the dynamic mixer.
The reactants, fine phosphate rock, acid and water are introduced from above while the slurry that falls into the Khulmann den exits from a side hole in the lower part. A belt feeder, electronically controlled by load cells and an encoder, continuously doses the phosphate rock.
The fluids, acid and water are continuously dosed by mass flow meters.

Kuhlmann den

A conveyor belt, moving at a very low speed, completes the reaction between acid, water,
and the phosphate rocks in order to transform insoluble phosphate into soluble phosphoric anhydride (P₂O₅).
A drive unit, positioned in the discharge part of the Kuhlmann Den, drives the conveyor belt,
and a counterweight, attached to the return drum, gives it tension.
The first part of the conveyor belt is shaped like a trough and the final part is flat.
The slurry coming from the dynamic mixer falls into the trough zone of the belt, while the gases and the steams,
that are produced from the chemical reactions, dry the slurry, which is thus transformed into a semi-solid mass.
After a few minutes the reactants and the reaction products assume a solid consistency, so that they can be transported by the flat belt.
Above the entire length of the conveyor belt is a hood, which is made of an anti-acid material
and ensures the suction of gases and steams produced by the chemical reaction.
At the opposite end of the mixer, the drive pulley is placed in a large hood together with the lump crusher that breaks up the solid phosphate,
which is now at the end of the reaction. The final product, that has the consistency of a slightly wet powder,
is convoyed to the warehouse where all the chemical reactions involved are completed.

Gas depollution system

A fan sucks the gases produced during the chemical reactions and is positioned further down the cleaning system.
This latter consists in a multiple stage washing.
The first stage consists in a Venturi pipe and a cyclone linked together.
The Venturi pipe has the function of facilitating the intimate contact between the gas and the washing water, before they go into the cyclone, in which, thanks to a centrifugal force, the solid particles present in the sucked gas stream are separated.
The scrubbers in the final stages complete the washing process and thus the stripping of pollutants in the gas.

The entire system of gas washing and purification is therefore made up of two or three stages with a Venturi tube and a cyclone,
one or two finishing scrubbers, a suction fan and an expulsion chimney.