Methods of preparing high-concentration phosphoric acid

Claim 1

A PROCESS FOR PRODUCING CONCENTRATED PHOSPHORIC ACID COMPRISING THE STEPS OF INTRODUCING PHOSPHORIC ACID CONTAINING ABOUT 50 WEIGHT PERCENT P2O5 INTO AN EVAPORATION ZONE MAINTAINED UNDER A VACUUM OF ABOUT 5-10 MM. HG, HEATING THE PHOSPHORIC ACID WITHIN THE EVAPORATION ZONE BY INDIRECT HEAT EXCHANGE WITH A HOT FLUID MEDIUM TO FORM A MIXTURE OF STEAM AND CONCENTRATED PHOSPHORIC ACID, SEPARATING THE STEAM FROM SAID CONCENTRATED PHOSPHORIC ACID, PASSING THE CONCENTRATED PHSOPHORIC ACID FROM THE SYSTEM, INTRODUCING THE SEPARATED STEAM INTO A LIQUIDGAS CONTACT ZONE MAINTAINED UNDER A VACUUM OF ABOUT 5-10 MM. HG, INTRODUCING BOTH CONCENTRATED SULPHURIC ACID AND DILUTE SULPHURIC ACID INTO SAID CONTACT ZONE TO ABSORB THE STEAM BY DIRECT CONTACT TO DILUTE AND HEAT THE SULPHURIC ACID WITHIN SAID CONTACT ZONE, SEPARATING THE SULPHURIC ACID DILUTED WITHIN SAID CONTACT ZONE INTO TWO STREAMS, COOLING A FIRST STREAM OF THE SEPARATED SULPHURIC ACID IN A ZONE REMOTE FROM SAID EVAPORATION ZONE, RECYCLING THE COOLED FIRST STREAM TO FORM THE DILUTE SULPHURIC ACID INTRODUCED INTO SAID CONTACT ZONE, AND REMOVING SAID SECOND STREAM OF SEPARATED SULPHURIC ACID FROM THE SYSTEM.