Systems and methods for producing regenerant brine and desalinated water from high temperature produced water

Patent metadata

Field	Value
Publication number	US-9932257-B2
Application number	US-201615223938-A
Country	US
Kind code	B2
Filing date	Jul 29, 2016
Priority date	Jul 29, 2016
Publication date	Apr 3, 2018
Grant date	Apr 3, 2018

Abstract

A process treats high temperature produced water by passing a stream to an electrocoagulation unit and then to a membrane distillation (MD) unit where the stream contacts a hydrophobic membrane on a feed side and deionized water contacts the membrane on a product side. A distilled water stream is recovered and collected with the product side stream to form a volume-depleted exit produced water stream on the feed side of the hydrophobic membrane. The exit product side stream is passed through a heat exchanger to form a stream that is returned to a location upstream of the MD unit for an additional pass through the MD unit, thereby recovering additional water. The stream can be returned multiple times to achieve high recovery and to form a final stream leaving the MD unit having a temperature from 40-60 ° C., a total oil and grease content no greater than 500 mg/L, and a suspended solids content no greater than 200 mg/L. A portion of the distilled water stream from the membrane distillation unit can be used to form a brine solution used to regenerate used ion exchange resin in a water softening system.

First claim

What is claimed is:

1. A process for treating high temperature produced water derived from hydrocarbon production operations, the process comprising:
a. passing a produced water feed stream at a feed temperature from 70° C. to 95° C. and having a total dissolved solids concentration less than 15,000 mg/L and a hydrogen sulfide content of up to 1000 ppm to an electrocoagulation unit or an electroflotation unit;
b. passing the produced water feed stream from the electrocoagulation unit or the electroflotation unit to a first direct contact membrane distillation unit wherein:
i. the produced water feed stream contacts a hydrophobic membrane on a membrane feed side; and
ii. an inlet product side stream comprising deionized water contacts the hydrophobic membrane on a membrane product side at a temperature of from 15° C. to 35° C.; such that a first distilled water stream is recovered from the produced water feed stream and collected with the inlet product side stream on the membrane product side to form an exit product side stream; and a volume-depleted exit produced water stream is formed on the membrane feed side of the hydrophobic membrane;

c. passing the exit product side stream in a pass through a heat recovery heat exchanger wherein the exit product side stream transfers heat to the volume-depleted exit produced water stream to form a return inlet produced water stream;
d. returning the return inlet produced water stream from the heat recovery heat exchanger to a location upstream of the first direct contact membrane distillation unit for an additional pass through the first direct contact membrane distillation unit, thereby recovering additional water from the membrane feed side to the membrane product side;
e. repeating steps (c) and (d) as needed to achieve a recovery of from 15 to 45 vol % of the produced water feed stream and to form a final exit produced water stream leaving the first direct contact membrane distillation unit having a temperature of from 40 to 60° C., a total oil and grease content no greater than 500 mg/L, and a suspended solids content no greater than 200 mg/L;
f passing a first portion of the first distilled water stream from the first direct contact membrane distillation unit to a brine tank at a temperature of from 55 to 80° C. wherein the first portion of the first distilled water stream is combined with sodium chloride to form a concentrated brine solution comprising from 8 wt % to 18 wt % brine; and
g. utilizing the concentrated brine solution to regenerate used ion exchange resin in a water softening system wherein monovalent sodium ions in the brine solution displace multivalent ions on the ion exchange resin.

2. The process of claim 1 , wherein the recovery in step (e) is from 15 to 30 vol % of the produced water feed stream.

3. The process of claim 1 , further comprising:
h. passing the final exit produced water stream from the first direct contact membrane distillation unit to a filtration unit comprising an ultrafiltration membrane, a polymeric membrane or a ceramic membrane to form a clarified stream substantially free of suspended solids, oil and grease;
i. passing the clarified stream from the filtration unit to an ion exchange unit thereby forming a soft water stream having a hardness of less than 10 ppm as calcium carbonate; and
j. passing the soft water stream through a reverse osmosis membrane to form a product stream and a reject stream.

4. The process of claim 3 , wherein the final exit produced water stream leaving the first direct contact membrane distillation unit has a temperature of from 50 to 60° C.; the filtration unit comprises a high temperature polymeric ultrafiltration membrane or a ceramic membrane; and the soft water stream passes through the reverse osmosis membrane at a temperature of from 55 to 65° C.

5. The process of claim 3 , further comprising passing the reject stream to a second direct contact membrane distillation unit such that a stream of desalinated water is provided having a second direct contact membrane distillation unit recovery of from 60% to 90% and a reject stream of water is provided having a total dissolved solids concentration of less than 250,000 mg/L.

6. The process of claim 1 , wherein the electrocoagulation unit includes a head space under vacuum of from 5 to 50 psi to remove at least a portion of the hydrogen sulfide.

7. The process of claim 3 , wherein the electrocoagulation unit or the electroflotation unit includes a head space and wherein the head space and the filtration unit are under vacuum of from 5 to 50 psi to remove gases thereby resulting in an oxygen-free water product stream.

8. The process of claim 3 , wherein the ultrafiltration membrane has a feed side and a permeate side and wherein the permeate side is under vacuum of from 5 to 50 psi to remove gases thereby resulting in an oxygen-free water product stream.

9. The process of claim 5 , further comprising boiling the stream of desalinated water to form steam.

10. The process of claim 9 , further comprising injecting the steam into a hydrocarbon producing formation in a process to enhance hydrocarbon recovery from the hydrocarbon producing formation.

11. The process of claim 3 , wherein the ion exchange unit contains a strong acid cation resin and wherein the concentrated brine solution from the brine tank is used to regenerate the strong acid cation resin in the ion exchange unit.

12. The process of claim 3 , wherein the ion exchange unit contains a strong acid shallow shell ion exchange resin having a surface functional group.

13. The process of claim 3 , wherein the ion exchange unit contains a functionalized microfiltration membrane comprising ion exchanging functional groups.

14. The process of claim 1 , further comprising passing the produced water feed stream from the electrocoagulation unit or the electroflotation unit to a clarifying unit selected from an induced gas flotation unit or a dissolved air flotation unit.

Assignees

• Chevron Usa Inc

Inventors

• Prakash Prakhar
• Chauhan Gini
• Hatakeyama Evan Shigeto

Classifications

• B01D2311/10

  Temperature control · CPC title

• B01D2311/04

  Specific process operations in the feed stream; Feed pretreatment · CPC title

• B01D61/147

  Microfiltration · CPC title

• B01D2311/06

  Specific process operations in the permeate stream · CPC title

• B01D61/16

  Feed pretreatment · CPC title