Apparatus for the treatment of the contaminated air from aluminum electrolysis

Claim 1

APPARATUS FOR THE TREATMENT OF GASES GIVEN OFF DURING PRODUCTION OF ALUMINUM BY ELECTROLYTIC CELLS OF THE SODERBERG TYPE TO RECOVER COMPONENTS AND PRODUCE CRYOLITE, THE COMBINATION OF AN EARTH CIRCUIT FOR THE RECOVERY OF FLUORINE AND COMPOUNDS OF FLUORINE PRESENT IN LARGE CONCENTRATIONS IN THE GASES GIVEN OFF AT THE CELLS AND A ROOF CIRCUIT FOR THE RECOVERY AS THE FLUORIDE OR FLUORINE AND COMPOUNDS OF FLUORINE WHICH EXIST IN THE ATMOSPHERE WITHIN THE ENCLOSURE IN WHICH THE CELLS ARE LOCATED, THE EARTH CIRCUIT FOR THE IN WHICH THE CELLS ARE LOCATED, THE EARTH CIRCUIT COMPRISING A HOOD ABOUT EACH CELL FOR COLLECTION OF THE GASES GIVEN OFF FROM THE BATH, A SEPARATOR FOR THE REMOVAL OF SOLIDS IN THE FORM OF DUSTS, SOOT AND TARS FROM THE GASES, MEANS FOR TRANSMISSION OF THE GASES ARE CIRCULATED FROM THE SEPARATOR, FOR THE REMOVAL OF SOLIDS FROM THE GASES, A WASHER THROUGH WHICH THE CLEANED GASES ARE CIRCULATED FROM THE SEPARATOR, A MEANS FOR MIXING AN AQUEOUS WASH SOLUTION FORMED OF AN AQUEOUS SOLUTION OF SOLUBLE FLUORIDE RECOVERED FROM THE ROOF CIRCUIT AND AN AQUEOUS SOLUTION OF AN ALUMINATE SELECTED FROM THE GROUP CONSISTING OF AN ALKALI METAL ALUMINATE AND AMMONIUM ALUMINATE WHICH REACTS WITH THE FLUORINE AND COMPOUNDS OF FLUORINE TO PRODUCE AN ACID CRYOLITE, MEANS FOR CONTACTING THE CLEANED GASES IN THE WASHER WITH THE AQUEOUS WASH SOLUTION, MEANS FOR RECIRCULATING AT LEAST A PART OF THE WASH SOLUTION THROUGH THE WASHER, MEANS FOR BLEEDING OFF A PART OF THE WASH SOLUTION CONTAINING ACID CRYOLITE, A SEPARATOR FOR SEPARATION OF ACID CRYOLITE FROM THE WASH SOLUTION AND MEANS FOR RETURN OF THE WASH SOLUTION TO THE WASHER AFTER THE CRYOLITE HAS BEEN REMOVED, THE ROOF CIRCUIT COMPRISING MEANS FOR THE REMOVAL OF ATMOSPHERIC GASES AT A HIGH FLOW RATE, A WASHER THROUGH WHICH THE ATMOSPHERIC GASES ARE CIRCULATED, MEANS FOR CON-