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Phosphoric acid production

Reactor design

Prayon reactors are uniquely designed and are renowned for their superior durability and reliability. Their multi-compartment design makes checking the sulfate in the attack section easy and flexible. This reduces calcium sulfate losses (*) thereby boosting yield and making the plant more profitable.

(*)Two types of insoluble losses occur during the production of phosphoric acid. These are co-crystallized losses and unattacked losses. The content of each of these losses in the gypsum depends on different parameters including the sulfate content. Where there is a high sulfate content in the attack tank slurry, co-crystallized losses are low. Where the sulfate content is low, unattacked losses are low. In the attack reactor, the phosphate is fed into the first compartment. Since the sulfuric acid is not added at this stage, the sulfate content is reduced. As a result, the rock dissolves in an environment where unattacked losses are low. In compartments two and three, the sulfate content becomes progressively higher in order to reduce co-crystallized losses. The attack tank is therefore designed to minimize insoluble losses. The increase in sulfates between one compartment and the next will vary depending on the process parameters and the origin of the phosphate.schema réacteur

Digestion

When leaving the attack tank, the reaction slurry is channeled to the digestion section where it will be de-saturated before being fed by the filter. As a result, the gypsum crystals will be larger and the resulting de-saturation of the pulp significantly reduces scaling on the filter. This means that the equipment can be kept running for longer in between washing. This increases stability, which in turn boosts the plant's yield, work rate and, consequently, the profitability of the investment.

Low-level flash cooler (LLFC)

The reaction of the phosphate with the sulfuric acid and the dilution of the sulfuric acid are exothermic reactions. To prevent the slurry from boiling in the reactor, and to obtain the desired form of calcium sulfate (gypsum or hemihydrate), the attack slurry must be cooled. Prayon processes have always used vacuum evaporation (*).This technique enables more accurate checks than air cooling, especially when the equipment is operating at above-normal capacity.

(*) The low level flash cooler (LLFC) is a vacuum chamber into which the slurry is pumped. The water in the slurry begins to boil due to energy from the slurry itself, and as a result, the slurry cools. To reduce scaling, there is little temperature difference (± 2°C) between the input and output of the flash cooler. This means that for cooling to be efficient, the slurry must flow through the LLFC quickly. This is achieved by using a high capacity axial flow pump with low manometric height and low power consumption.

Agitators

Agitation is a key stage in chemical processes because it improves the mass transfer of reagents and the crystallization conditions in the reaction environment.

During the reaction, agitation should :

  1. hold solids in suspension;
  2. renew the layer of liquid (reagent) on the phosphate granules;
  3. break up the foam present on the surface of the liquid.

To keep the cycle economically efficient, the process should consume as little energy as possible. Prayon Technologies has developed a special type of agitator for precisely this purpose. The bottom impeller blade is helical to maintain a high pump rate. This holds the solids in suspension and keeps the compartments clean. The middle impeller blade is a pitched pump blade. It also produces shear which boosts mass transfer and incorporation of reagents. The top impeller blade is a vertical turbine that breaks up any foam generated by splashing liquid onto the surface of the reactor, and helps to incorporate the reagents fed in on the reactor's surface. In the digestion section, major agitation is not always necessary. Only energy-efficient helical impeller blades are used.

Filters

Depending on our customers' requirements, we offer both tilting filters and belt filters

Prayon's tilting filter is the best known filter in the phosphoric acid industry. It offers the highest washing efficiency of all filters available on the market.

Recent technological developments in this kind of filtration (such as fast drain filtration cells, central cells, and tilting tracks) have improved its work rate and production capacity, reduced maintenance costs, and increased the ratio of filtering surface to ground surface.

Gaudfrin-Phosfil belt filters also offer major advantages: excellent washing efficiency, low power consumption, easily washable vacuum box and more.


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Sales contact

Prayon Technologies (PRT)
144, rue J. Wauters
4480 Engis
Belgium
Tel: +32 4 273 93 41
Fax: + 32 4 275 09 09
E-mail : prt@prayon.com

 

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Prayon technologies process with initial dihydrate reaction

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Operator training simulator for phosphoric acid plant

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Operator training simulator for phosphoric acid plant