Electrodialysis device for the desalination of water for oil and gas applications
The invention relates to an electrodialysis device for the desalination of water for oil and gas applications comprising: a membrane stack comprising alternating cation- and anion-exchange membranes ( 2.1, 2.3 ) and a plurality of spacers ( 2.2, 2.4 ), each spacer being arranged between two successive membranes; wherein at least one of the spacers ( 2.2, 2.4 ) comprises a recessed area ( 3.2 ) and a non-recessed area ( 3.3 ), a central opening ( 3.1 ) within the recessed area ( 3.2 ); the spacer ( 2.2, 2.4 ) is provided with at least four orifices ( 3.4, 3.5 ) within the non-recessed area ( 3.3 ); and with respective channels ( 3.6 ) which connect at least two of the orifices ( 3.4 ) with the central opening ( 3.1 ); and one membrane ( 2.1, 2.3 ) is accommodated in the recessed area ( 3.2 ). The invention also relates to a water desalination process using the electrodialysis device mentioned above.
1. An electrodialysis device for desalination of water in an oil and gas environment, the electrodialysis device comprising:
a membrane stack comprising alternating cation- and anion-exchange membranes; and
a plurality of spacers, each spacer being arranged between two successive membranes and having a thickness;
wherein at least one of the spacers comprises a recessed area and a non-recessed area, the non-recessed area surrounding the recessed area,
and wherein:
the spacer comprises a central opening within the recessed area, wherein the central opening has a peripheral edge;
the spacer is provided with at least four orifices within the non-recessed area;
the spacer is provided with respective channels extending from at least two of the orifices to the peripheral edge of the central opening, each channel comprising (i) a first portion located in the recessed area and extending to the peripheral edge of the central opening and (ii) a second portion located in the non-recessed area; and
a cation-exchange or anion-exchange membrane is accommodated in the recessed area;
wherein the entire first portion of each channel runs through the entire thickness of the spacer, and the entire second portion of each channel runs through only part of the thickness of the spacer.
2. The device of claim 1 , wherein a spacer net is arranged in the central opening of the spacer and wherein the spacer net has an average thickness from 55 to 95% of the thickness of the recessed area of the spacer at a temperature of 20° C.
3. The device of claim 2 , wherein the average thickness of the spacer net is less than the average thickness of the recessed area of the spacer by 0.00 to 0.05 mm, at a temperature of 70° C.
4. The device of claim 1 , wherein the spacer is substantially rectangular- or square-shaped and has a width and a height, and wherein the spacer has a height-to-width ratio from 1:1 to 4:1.
5. The device of claim 1 , wherein the recessed area of the spacer has a width around the central opening which is less than 30 mm, and/or wherein the recessed area has a depth relative to the non-recessed area which is equal to or less than 50 μm lower than an average thickness of the membrane accommodated in the recessed area at a temperature of 20° C., and/or wherein the recessed area of the spacer has a width around the central opening and a distance between each orifice and the membrane is at least equal to the width of the recessed area.
6. The device of claim 1 , wherein the spacer comprises a single part or wherein the spacer comprises two or more stacked parts.
7. The device of claim 1 , wherein the spacer comprises a spacer core having a central opening, stacked with at least one membrane frame having a central opening larger than the central opening of the spacer core.
8. The device of claim 7 , wherein the spacer further comprises a cover sheet stacked between the spacer core and the membrane frame.
9. The device of claim 8 , wherein the spacer further comprises an additional cover sheet, the spacer core being stacked between the cover sheet and the additional cover sheet.
10. The device of claim 8 , wherein the cover sheet has a central opening which is smaller than the central opening of the membrane frame.
11. The device of claim 1 , wherein the membrane stack comprises two adjacent cation-exchange membranes at one end of the membrane stack, or wherein the membrane stack comprises two adjacent cation-exchange membranes at each end of the membrane stack.