GB2194855A

GB2194855A - Reverse electrodialysis

Info

Publication number: GB2194855A
Application number: GB08719206A
Authority: GB
Inventors: Bernard Ramsay Bligh
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-06-13
Filing date: 1987-08-13
Publication date: 1988-03-16
Anticipated expiration: 2006-06-13
Also published as: GB2195818B; GB8719206D0; GB8719204D0; GB2197116B; GB2197116A; GB8719205D0; GB2194855B; GB2195818A

Abstract

A system for the production of electric power by reverse electrodialysis includes one or more batteries of cells separated by ion exchange membranes, means for supplying alternate cells with water containing sea water as electrolyte and water containing little or no electrolyte ("fresh water") and suitable electrical connexion means, the plant being installed at or near a coast at a level intermediate between high tide level and low tide level and being supplied with sea water at lower tide periods via a feed reservoir 81 filled during periods of high tide, sea water waste being released to a sink reservoir 82 at a level suitable for drainage to sea at periods of low tide. By using water power from a river and tidal power from the sea, there is no need to pump the liquids into the cells, which would reduce the economic usefulness of the batteries. <IMAGE>

Description

SPECIFICATION Improvements in electric batteries I, Bernard Ramsay Bligh, a British subject, of 4, Saint James's Avenue, Hampton Hill, Middlesex, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates particularly but not exclusively to a device for obtaining electrical energy from a supply of salt water and a supply of water which contains little or no salt.

It is known that "Free Energy" of mixing is available from a system in which there is a supply of relatively concentrated salt solution and a supply of liquid containing no salt or very little salt. Such systems have been described by R. E. Pattle (Brit. Pat. 731729, and in Nature, Vol. 174, p. 660, 1954, and in Chemical Process Engineering, Vol. 36, p.

351, 1955), by J.N.Weinstein and F.B.Leitz (in 1976, Science, Vol. 191, p. 557), by A.T.Emren and S.B.Bergstrom (in 1977, Proceedings of the International Conf. on Alternative Energy Sources, Florida, p. 2909) and by J.Jagur-Grodzinski and R.Kramer (in 1986, Industrial and Engineering Chemistry, Process Design Development, Vol, 25, p. 443). None of these studies has led to the manufacture of a practical facility on an industrial scale. All of the devices described in the above papers have practical problems. These problems will be referred to again later in this specification.

The invention to be described in this specification overcomes these problems.

Certain of the improvements to be described are also applicable to the desalination of salt water by electrodialysis.

Definitions and Explanations.

The term, "Salt Water", in this specification means an aqueous solution of any electrolyte: typically the solution is sea water, which contains about 32 kg of salts per cubic metre.

In this specification "Fresh Water" refers to water with very little dissolved salts compared with sea water, e.g. fresh water contains less than 3 kg of salts per cubic metre.

A "Cell" is a compartment containing either salt water or fresh water; the compartment is bounded on at least one side by a semipermable membrane; the compartment has a duct for supplying the water and a duct for withdrawing the water; usually a cell has two membranes on opposite walls, one is an anion exchange membrane and the other is a cation exchange membrane.

A "Battery" is a device with a number of cells in series; typically the cells are assembled such that the membranes are alternately anion and cation exchange membranes, and the cells contain alternately salt water and fresh water; at the two ends of the series of cells there are placed electrodes which are in contact with the water in the respective end cell.

A battery as described above can be utilized to produce electric power; this process is termed "Reverse Electrodialysis".

PTFE is an abbreviation for poly-tetra-fluoroethylene, which is a solid plastic and which is an electrical insulator and which has the property of a low coefficient of friction; in the present specification "PTFE" is meant to include any plastic which has properties similar to poly-tetra-fluoro-ethylene.

According to one aspect of the invention there is provided a system for the production of electric power by reverse electrodialysis including plant comprising one or more batteries of cells separated by ion exchange membranes, means for supplying alternate cells with water containing sea water as electrolyte and water containing little or no electrolyte ("fresh water") and suitable electrical connexion means, the plant being installed at or near a coast at a level intermediate between high tide level and low tide level and being supplied with sea water at lower tide periods via a feed reservoir filled during periods of high tide, sea water waste being released to a sink reservoir at a level suitable for drainage to sea at periods of low tide.

This specification may be considered in conjunction with my two co-pending patent applications.

The Figure is a diagram in side view demonstrating a cycle of operations.

It will be appreciated by engineers that power is required to pump salt water and fresh water through a battery or a group of batteries, and Jagur-grodzinski and Kramer have shown that the power for the pumps is in appreciable fraction of the power obtainable from the batteries. Therefore pumping the liquids detracts from the economic usefulness of the batteries. This invention overcomes this problem by using water power from a river supply and tidal power from the sea. In each case this power comes from the available hydrostatic height of water.

Batteries may be installed at a level between high tide level and low tide level at a coastal site; there may be two lagoons (or reservoirs) and means for passing salt water from a relatively high tide level through the batteries to a relatively low tide level, and means for passing fresh water from a relatively high level through the batteries to a relatively low tide level.

The invention is described with reference to the Figure, which is intended to show the cycle of operations as the sea water goes from high tide through to low tide and back to high tide. There are two lagoons (or reservoirs) 81 and 82, there is a conduit, 91, for filling la goon, 81, with salt water at high tide, and there is a conduit, 92, for emptying lagoon, 82, at low tide. The group of one or more batteries, 83, is positioned approximately midway between the high tide level and the low tide level. There is a conduit, 93, supplying salt water from lagoon, 81, to the battery group, and a conduit, 94, taking salt water from the battery group to lagoon, 82. There is a a conduit, 95, supplying fresh water to the battery group; typically the supply of fresh water comes from a ppint in a river upstream of the lagoons.There is a conduit, 96, discharging fresh water from the battery group to lagoon, 82. There is a conduit, 97, taking salt water from the sea to the battery group.

There are valves and other instruments (not shown) for controlling the flow of liquids; control valves and the like are well understood by engineers and require no further description herein.

The process runs in a continual cycle from high tide to low tide and back to high tide again.

(1) At high tide salt water flows from the sea along conduit, 97, to the battery group and thence along conduit, 94, to lagoon, 82, which has ben previously emptied at low tide.

Also at high tide, lagoon, 81, is filled to the highest possible level with salt water via conduit, 91.

(2) When the tide falls to about 70% of high tide, the supply of salt water by conduit, 97, is discontinued and salt water is supplied to the battery group from lagoon, 81, via conduit, 93.

(3) At low tide the supply of salt water continues from lagoon, 81, and effluent from the battery group continues to lagoon, 82, but lagoon, 82, is discharged to as low a level as possible to the sea via conduit, 92.

(4) As the tide rises the flow of salt water continues from lagoon, 81, through the battery group to lagoon, 82.

(5) Finally, when the tide rises to 70% of full tide, the salt water is supplied directly to the battery group via conduit, 97, and lagoon, 81, is refilled with salt water via conduit, 91.

(6) During all the operations (1) to (5) fresh water is supplied to the battery group via conduit, 95, and fresh water is discharged via conduit, 96, to lagoon, 82.

In Figure for those sections denoted by "mid-tide" and "low tide" some of the conduits are omitted; this omission is partly for simplicity and partly to show that those conduits are not used at those periods of the cycle.

My invention is most suitably applied near a river estuary where there is a plentiful supply of salt water and fresh water.

Claims

1. A system for the production of electric power by reverse electrodialysis including plant comprising one or more batteries of cells separated by ion exchange membranes, means for supplying alternate cells with water containing sea water as electrolyte and water containing little or no electrolyte ("fresh water") and suitable electrical connexion means, the plant being installed at or near a coast at a level intermediate between high tide level and low tide level and being supplied with sea water at lower tide periods via a feed reservoir filled during periods of high tide, sea water waste being released to a sink reservoir at a level suitable for drainage to sea at periods of low tide.

2. A system for the production of electricity by reverse electrodialysis substantially as described herein with reference to the accompanying drawing.