Method of concentrating an aqueous caustic alkali using a catholyte heat recovery evaporator

1. 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.

2. The method of concentrating an aqueous caustic alkali of claim 1 further comprising:

splitting the sixth stream into a ninth stream and a tenth stream;

flowing the ninth stream through a second heat exchanger;

flowing the second vapor stream through the second heat exchanger after flowing through the second effect evaporator; and

joining the ninth stream and the tenth stream together to reconstitute the sixth stream.

3. The method of concentrating an aqueous caustic alkali of claim 1 further comprising:

splitting the sixth stream into a ninth stream and a tenth stream;

flowing the ninth stream through a second heat exchanger;

flowing the steam stream through the second heat exchanger after flowing through the first effect evaporator; and

joining the ninth stream and the tenth stream together to reconstitute the sixth stream.

4. The method of concentrating an aqueous caustic alkali of claim 1 further comprising:

splitting the sixth stream into a ninth stream and a tenth stream;

flowing the tenth stream through a second heat exchanger;

flowing the eighth stream through the second heat exchanger; and

joining the ninth stream and the tenth stream together to reconstitute the sixth stream.

5. The method of concentrating an aqueous caustic alkali of claim 1 further comprising:

splitting the seventh stream into a ninth stream and a tenth stream;

flowing the ninth stream through a second heat exchanger;

flowing the eighth stream through the second heat exchanger; and

joining the ninth stream and the tenth stream together to reconstitute the seventh stream.

6. The method of concentrating an aqueous caustic alkali of claim 1 further comprising:

splitting the seventh stream into a ninth stream and a tenth stream;

flowing the tenth stream through a second heat exchanger;

flowing the steam stream through the second heat exchanger after flowing through the first effect evaporator; and

joining the ninth and tenth stream together to reconstitute the seventh stream.

7. The method of concentrating an aqueous caustic alkali of claim 1 further comprising:

flowing the eighth stream through a second heat exchanger; and

flowing a cooling water stream through the second heat exchanger.

8. The method of concentrating an aqueous caustic alkali of claim 1 further comprising:

splitting the sixth stream into a ninth stream and a tenth stream;

flowing the ninth stream through a second heat exchanger;

flowing the ninth stream through a third heat exchanger;

flowing the tenth stream through a fourth heat exchanger;

joining the ninth stream and the tenth stream together to reconstitute the sixth stream;

flowing the second vapor stream, after flowing through the second effect evaporator, through the second heat exchanger;

splitting the seventh stream into an eleventh stream and a twelfth stream;

flowing the eleventh stream through a fifth heat exchanger;

flowing the twelfth stream through a sixth heat exchanger;

joining the eleventh stream and the twelfth stream together to reconstitute the seventh stream;

flowing the steam stream, after flowing through the first effect evaporator, through the fifth heat exchanger;

flowing the steam stream, after flowing through the fifth heat exchanger, through the third heat exchanger;

flowing the eighth stream through the sixth heat exchanger;

flowing the eighth stream through the fourth heat exchanger;

flowing the eighth stream through a seventh heat exchanger; and

flowing a cooling water stream through the seventh heat exchanger.

9. The method of concentrating an aqueous caustic alkali of claim 1 further comprising:

providing the aqueous caustic alkali is aqueous caustic soda;

providing the first alkali concentration is about 32% caustic soda by weight;

providing the second alkali concentration is about 35.7% caustic soda by weight;

providing the third alkali concentration is about 40.6% caustic soda by weight;

providing the fourth alkali concentration is about 44.9% caustic soda by weight; and

providing the final alkali concentration is about 50% caustic soda by weight.

10. The method of concentrating an aqueous caustic alkali of claim 1 further comprising:

providing the aqueous caustic alkali is aqueous caustic soda;

providing the first alkali concentration is between about 31.0% and about 33.0% caustic soda by weight;

providing the second alkali concentration is between about 34.6% and about 36.8% caustic soda by weight;

providing the third alkali concentration is between about 39.4% and about 41.8% caustic soda by weight;

providing the fourth alkali concentration is between about 43.5% and about 46.3% caustic soda by weight; and

providing the final alkali concentration is between about 48.5% and about 51.5% caustic soda by weight.

11. The method of concentrating an aqueous caustic alkali of claim 1 further comprising:

providing the aqueous caustic alkali is aqueous caustic soda;

providing the first alkali concentration is between about 31.0% and about 33.0% caustic soda by weight; and

providing the final alkali concentration is between about 48.5% and about 51.5% caustic soda by weight.

12. The method of concentrating an aqueous caustic alkali of claim 1 further comprising:

providing a first flow rate in the first stream and a second flow rate in the second stream, whereby the first flow rate is less than eight times the second flow rate.

13. 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 creating 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 flash evaporation chamber;

flowing a third stream from the flash evaporation chamber;

splitting the third stream into a fourth stream and a fifth stream wherein the fifth stream has a second alkali concentration and whereby the second alkali concentration is greater than the first alkali concentration;

flowing the fourth stream through the first heat exchanger;

flowing the fourth stream into the flash evaporation chamber;

flowing the fifth 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 sixth stream from the third effect evaporator wherein the sixth stream has a third alkali concentration and whereby the third alkali concentration is greater than the second alkali concentration;

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 second vapor stream from the first effect evaporator;

flowing the second vapor stream through the second effect evaporator;

flowing the steam stream through the first effect evaporator; and

flowing an eighth stream from the third effect evaporator wherein the eighth stream has a final alkali concentration and whereby the final alkali concentration is greater than the fourth alkali concentration.

14. The method of concentrating an aqueous caustic alkali of claim 13 further comprising:

splitting the sixth stream into a ninth stream and a tenth stream;

flowing the ninth stream through a second heat exchanger;

flowing the second vapor stream through the second heat exchanger after flowing through the second effect evaporator; and

joining the ninth stream and the tenth stream together to reconstitute the sixth stream.

15. The method of concentrating an aqueous caustic alkali of claim 13 further comprising:

splitting the sixth stream into a ninth stream and a tenth stream;

flowing the ninth stream through a second heat exchanger;

flowing the steam stream through the second heat exchanger after flowing through the first effect evaporator; and

joining the ninth stream and the tenth stream together to reconstitute the sixth stream.

16. The method of concentrating an aqueous caustic alkali of claim 13 further comprising:

splitting the sixth stream into a ninth stream and a tenth stream;

flowing the tenth stream through a second heat exchanger;

flowing the eighth stream through the second heat exchanger; and

joining the ninth stream and the tenth stream together to reconstitute the sixth stream.

17. The method of concentrating an aqueous caustic alkali of claim 13 further comprising:

splitting the seventh stream into a ninth stream and a tenth stream;

flowing the tenth stream through a second heat exchanger;

flowing the eighth stream through the second heat exchanger; and

joining the ninth stream and the tenth stream together to reconstitute the seventh stream.

18. The method of concentrating an aqueous caustic alkali of claim 13 further comprising:

splitting the seventh stream into a ninth stream and a tenth stream;

flowing the ninth stream through a second heat exchanger;

flowing the steam stream through the second heat exchanger after flowing through the first effect evaporator; and

joining the ninth stream and the tenth stream together to reconstitute the seventh stream.

19. The method of concentrating an aqueous caustic alkali of claim 13 further comprising:

flowing the eighth stream through a second heat exchanger; and

flowing a cooling water stream through the second heat exchanger.

20. The method of concentrating an aqueous caustic alkali of claim 13 further comprising:

splitting the sixth stream into a ninth stream and a tenth stream;

flowing the ninth stream through a second heat exchanger;

flowing the ninth stream through a third heat exchanger;

flowing the tenth stream through a fourth heat exchanger;

joining the ninth stream and the tenth stream together to reconstitute the sixth stream;

flowing the second vapor stream, after flowing through the second effect evaporator, through the second heat exchanger;

splitting the seventh stream into an eleventh stream and a twelfth stream;

flowing the eleventh stream through a fifth heat exchanger;

flowing the twelfth stream through a sixth heat exchanger;

joining the eleventh stream and the twelfth stream together to reconstitute the seventh stream;

flowing the steam stream, after flowing through the first effect evaporator, through the fifth heat exchanger;

flowing the steam stream, after flowing through the fifth heat exchanger, through the third heat exchanger;

flowing the eighth stream through the sixth heat exchanger;

flowing the eighth stream through the fourth heat exchanger;

flowing the eighth stream through a seventh heat exchanger; and

flowing a cooling water stream through the seventh heat exchanger.

21. The method of concentrating an aqueous caustic alkali of claim 13 further comprising:

providing the aqueous caustic alkali is aqueous caustic soda;

providing the first alkali concentration is about 32% caustic soda by weight;

providing the second alkali concentration is about 37.1% caustic soda by weight;

providing the third alkali concentration is about 40.0% caustic soda by weight;

providing the fourth alkali concentration is about 44.2% caustic soda by weight; and

providing the final alkali concentration is about 50% caustic soda by weight.

22. The method of concentrating an aqueous caustic alkali of claim 13 further comprising:

providing the aqueous caustic alkali is aqueous caustic soda;

providing the first alkali concentration is between about 31.0% and about 33.0% caustic soda by weight;

providing the second alkali concentration is between about 36.0% and about 38.2% caustic soda by weight;

providing the third alkali concentration is between about 38.8% and about 41.2% caustic soda by weight;

providing the fourth alkali concentration is between about 42.9% and about 45.5% caustic soda by weight; and

providing the final alkali concentration is between about 48.5% and about 51.5% caustic soda by weight.

23. The method of concentrating an aqueous caustic alkali of claim 13 further comprising:

providing the aqueous caustic alkali is aqueous caustic soda;

providing the first alkali concentration is between about 31.0% and about 33.0% caustic soda by weight;

providing the final alkali concentration is between about 48.5% and about 51.5% caustic soda by weight.

24. The method of concentrating an aqueous caustic alkali of claim 13 further comprising:

providing a first flow rate in the first stream and a second flow rate in the second stream, whereby the first flow rate is less than eight times the second flow rate.