Patent ID: 8317994

Claim:
A method of concentrating an aqueous caustic alkali comprising: providing an electrolytic cell with a cell membrane, a cathode, and an anode, wherein the cell membrane is located between the cathode and the anode and creates a cathode chamber and an anode chamber; inserting a feed material and water into the electrolytic cell; electrifying the cathode and the anode; removing a catholyte stream comprising aqueous caustic alkali with a first alkali concentration from the cathode chamber; splitting the catholyte stream into a first stream and a second stream wherein the first stream and the second stream have the first alkali concentration; flowing the first stream through a first heat exchanger; returning the first stream to the cathode chamber; flowing the second stream into a third effect evaporator wherein a first heat source to the third effect evaporator is a first vapor stream from a second effect evaporator; flowing a third stream from the third effect evaporator wherein the third stream has a second alkali concentration and whereby the second alkali concentration is greater than the first alkali concentration; flowing the third stream into a flash evaporation chamber; flowing a fourth stream from the flash evaporation chamber; splitting the fourth stream into a fifth stream and a sixth stream wherein the sixth stream has a third alkali concentration and whereby the third alkali concentration is greater than the second alkali concentration; flowing the fifth stream through the first heat exchanger; flowing the fifth stream into the flash evaporation chamber; flowing the sixth stream into the second effect evaporator wherein a second heat source for the second effect evaporator is a second vapor stream from a first effect evaporator; flowing a seventh stream from the second effect evaporator wherein the seventh stream has a fourth alkali concentration and whereby the fourth alkali concentration is greater than the third alkali concentration; flowing the first vapor stream from the second effect evaporator; flowing the first vapor stream through the third effect evaporator; flowing the seventh stream into the first effect evaporator wherein a third heat source for the first effect evaporator is a steam stream; flowing the steam stream through the first effect evaporator; flowing the second vapor stream from the first effect evaporator; flowing the second vapor stream through the second effect evaporator; and flowing an eighth stream from the first effect evaporator wherein the eighth stream has a final alkali concentration and whereby the final alkali concentration is greater than the fourth alkali concentration.