Method for recovering chemicals from waste liquor obtained during the production of cellulose

Claim 1

A METHOD FOR RECOVERING CHEMICALS FROM WASTE LIQUOR OBTAINED BY COOKING CELLULOSE CONTAINING FIBER MATERIALS WITH A COOKING LIQUOR CONTAINING ALKALI METAL SALTS OF SULPHUROUS ACID AND ALKALI METAL SALTS OF CARBONIC ACID IN ONE COOKING STAGE WHICH COMPRISES THE STEPS OF (A) EVAPORATING AND BURNING THE WASTE LIQUOR FROM THE COOKING STAGE AND DISSOLVING THE SMELT SODA THEREBY PRODUCED IN WATER TO FORM A SMELT SODA SOLUTION WHICH CONTAINS ALKALI METAL SULFIDE AND ALKALI METAL CARBONATE, (B) REACTING SAID SMELT SODA SOLUTION WITH SUBSTANTIALLY PURE CARBON DIOXIDE GAS WHEREBY A SUBSTANTIALLY SULFIDE FREE ALKALI METAL BICARBONATE-CARBONATE SOLUTION AND A GAS MIXTURE OF CARBON DIOXIDE AND HYDROGEN SULFIDE ARE FORMED, (C) DRAWING OFF A PORTION OF SAID SOLUTION FOR USE IN THE PREPARATION OF A COOKING LIQUOR FOR THE COOKING STAGE, (D) DECARBONIZING THE REMAINING PORTION OF THE SAID SOLUTION WITH A SULFIDING AGENT OF THE GROUP CONSISTING OF ALKALI METAL BISULFITE SOLUTION AND SO2 THEREBY FORMING A SOLUTION OF ALKALI METAL SALTS OF SULPHUROUS ACID WHICH IS USED IN THE PREPARATION OF COOKING LIQUOR FOR THE COOKING STAGE, AND GASEOUS CARBON DIOXIDE WHICH IS USED IN STEP (B), (E) CONVERTING THE HYDROGEN SULFIDE RELIEVED WITH THE CARBON DIOXIDE IN STEP (B) BY CONVERTING IT IN A CONTACT FURNACE WITH SUBSTANTIALLY PURE SO2 TO ELEMENTARY SULPHUR WHICH IS SEPARATED AND USING THE CARBON DIOXIDE RELIEVED FROM THE HYDROGEN SULFIDE TOGETHER WITH THE CARBON DIOXIDE FORMED IN STEP (D) IN STEP (B), AND (F) COMPENSATING THE LOSS IN CARBON DIOXIDE IN THE RECOVERY SYSTEM CAUSED BY DRAWING OFF SAID PORTION OF THE SUBSTANTIALLY SULPHUR FREE ALKALI METAL BICARBONATE-CARBONATE SOLUTION IN STEP (C) BY ADDITION OF CO2 INTO THE SYSTEM.

Claim 2

A METHOD FOR RECOVERING CHEMICALS FROM WASTE LIQUOR OBTAINED BY COOKING CELLULOSE CONTAINING FIBER MATERIALS WITH A COOKING LIQUOR CONTAINING ALKALI METAL SALTS OF SULPHUROUS ACID AND ALKALI METAL SALTS OF CARBONIC ACID IN ONE COOKING STAGE WHICH COMPRISES THE STEPS OF (A) EVAPORATING AND BURNING THE WASTE LIQUOR FROM THE COOKING STAGE AND DISSOLVING THE SMELT SODA THEREBY PRODUCED IN WATER TO FORM A SMELT SODA SOLUTION WHICH CONTAINS ALKALI METAL SULFIDE AND ALKALI METAL CARBONATE, (B) REACTING SAID SMELT SODA SOLUTION WITH SUBSTANTIALLY PURE CARBON DIOXIDE GAS WHEREBY A SUBSTANTIALLY SULFIDE FREE ALKALI METAL BICARBONATE-CARBONATE SOLUTION AND A GAS MIXTURE OF CARBON DIOXIDE AND HYDROGEN SULFIDE ARE FORMED, (C) DRAWING OFF A PORTION OF SAID SOLUTION FOR USE IN THE PREPARATION OF A COOKING LIQUOR FOR THE COOKING STAGE, (D) DECARBONIZING THE REMAINING PORTION OF THE SAID SOLUTION WITH A SULFIDING AGENT OF THE GROUP CONSISTING OF ALKALI METAL BISULFITE SOLUTION AND SO2 THEREBY FORMING A SOLUTION OF ALKALI METAL SALTS OF SULPHUROUS ACID WHICH IS USED IN THE PREPARATION OF COOKING LIQUOR FOR THE COOKING STAGE, AND GASEOUS CARBON DIOXIDE WHICH IS USED IN STEP (B), (E) CONVERTING THE HYDROGEN SULFIDE RELIEVED WITH THE CARBON DIOXIDE IN STEP (B) BY CONVERTING IT IN A CONTACT FURNACE WITH SUBSTANTIALLY PURE SO2 TO ELEMENTARY SULPHUR WHICH IS SEPARATED AND USING THE CARBON DIOXIDE RELIEVED FROM THE HYDROGEN SULFIDE TOGETHER WITH THE CARBON DIOXIDE FORMED IN STEP (D) IN STEP (B), AND (F) COMPENSATING THE LOSS IN CARBON DIOXIDE IN THE RECOVERY SYSTEM CAUSED BY DRAWING OFF SAID PORTION OF THE SUBSTANTIALLY SULPHUR FREE ALKALI METAL BICARBONATE-CARBONATE SOLUTION IN STEP (C) BY ADDITION OF CO2 INTO THE SYSTEM.