Patent CA-1106137-A (CA)
Inventor: DAVISTER ARMAND L
IPC: C01B25/22
Filed: 1978-06-22
Granted: 1981-08-04
Abstract: ABSTRACT OF THE DISCLOSURE The present invention provides a "wet" phosphoric acid manufacturing process comprising the reactions of "attack" of a phosphate rock by sulfuric acid, the crystallization of the so obtained calcium sulfate, the separation of the latter by filtrat-ion with water wash, and the recycling, to said "attack", as auxiliary attacking reactant, of part of the filtrates of said filtration and wash, the remaining part of said filtrates being the phosphoric acid produced, process in which the reactions are performed within an aqueous reaction slurry containing phosphoric acid and calcium sulfate as produced by previous reactions and crystallizations, this said reaction slurry being enclosed within a succession of reaction zones, in each of which a local slurry circulation is maintained, the reactants, i.e.  phosphate rock, sulfuric acid and the recycled part of the abovesaid filtrates, being introduced into the slurry of one or several of said reaction zones, whereas part of said reaction slurry is extracted from one of the reaction zones located downstream in relation with the zones wherein the reactants are introduced, the extraction flow of said latter part of the reaction slurry being equal to the flow of the products of the reactions and the crystallization as produced from the reactants introduced in the reaction slurry during the same lapse of time, said extraction flow of slurry being submitted to the above said filtration with washing, and considered as "basic slurry flow", one at least of the reaction zones being kept in communication within its slurry phase with at least one zone called "vacuum cooling zone" wherein a reduced pressure. is maintained, lower than the pressure above the slurry of the reaction zones, this reduced pressure producing within the slurry of said vacuum cooling zone, a controlled partial evaporation of the water enclosed therein, together with a corresponding temperature drop, the slurry being maintained in circulation, in closed circuit, through the vacuum cooling zone, as well as through a part at least of the reaction zones, this circulation being, in the latter, superimposed with each of the local cir-culations therein, and also, from the reactant introduction downstream to the slurry extraction towards the above mentioned filtration and washing, with the corresponding stream of the "basic flow" said process being characterized by the fact that an optimal combination of flows for the slurry circulations is maintained, at variance depending upon the kinds of phosphate rocks used, within the following limits:  A  a "general circul-ation" through reactionz zones, the flow of which remains between about 300 and 4000 % of the above said "basic slurry flow", B. a circulation through the vacuum cooling zone, the flow of which remains between about 2000 and 4000 S of the above said "basic slurry flow, C  local circulations in the various reaction zones, the flows of which remain between about 500 and 2200 % of the above said "basic slurry flow", D  the sum of the general and local circulations is maintained at least at 2500 % of the above said "basic slurry flow", within each of the reaction zones where any reactant is introduced and also each of the thereupon follow-ing zones within the order of the stream of the general circulation