Production of phosphoric acid by a two-stage crystallization process

Abstract

A process and system for producing phosphoric acid. Phosphate rock is dissolved in phosphoric acid in a reaction vessel to form a slurry. The slurry is then reacted in a first stage of crystallization with sulfuric acid to produce calcium sulfate hemihydrate and phosphoric acid. The product acid is separated from the hemihydrates via filtration, and the filter cake is then reacted, in a second crystallization step, with additional sulfuric acid to produce dihydrate calcium sulfate (gypsum) and recovery solution. The gypsum is separated from the recovery solution via filtration and removed as a by-product. The recovery solution is recycled back to the transformation tank and to the hemihydrate filtration step. A feed acid tank combines wash solution, recovery solution and product acid. Once adjusted to a target P2O5 concentration, it is fed to the initial reactor vessel to dissolve the phosphate ore.

Description

[0001] Related applications [0002] This application claims US Provisional Application Serial No. 61 / 775049, filed March 8, 2013, the entire contents of which are incorporated herein by reference. technical field [0003] The present invention relates generally to the production of phosphoric acid, and more particularly to a process that employs a feed acid tank assembly and a recovery solution tank assembly to produce 2 o 5 A two-stage crystallization and filtration process for high-recovery high-strength phosphoric acid. Background technique [0004] Phosphoric acid (H 3 PO 4 ) has several commercial uses ranging from its use in the production of agricultural products such as fertilizers and animal feed to its incorporation into food products. Phosphoric acid concentration can be expressed in several ways, including percentage of phosphoric acid (%H 3 PO 4 ), the percentage of phosphorus pentoxide (%P 2 o 5 ) or percentage of phosphorus (%P), which can be convert...

AI Technical Summary

Problems solved by technology

For example, if there is variability in the measurement system such that the measurement of one or more of the recycle lines is inaccurate, this can shift the concentration of reactants in the crystallizer off target (e.g. low sulfate levels) , which causes the crystallizer not to function properly, resulting in e.g. small crystal sizes

In turn, this leads to poor filtration or filtration variability, which leads to P 2 o 5 losses and ultimately increased production costs

Likewise, if the incoming feed is poorly controlled, i.e. denaturation is too high, then unwanted co-crystallization can occur with similar downstream effects and lead to poor digestion in the acidification tank

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