IL33147A - Electrogravitational desalination of saline water - Google Patents

Description

Electrogravltational desalination of saline water.

G ERAL MARINE TECHNOLOGY OORPORATIOli 0:31412 The present Invention relates to desalination of water, and particularly to rendering sea water potable and useful for agricultural purposes.

Desalination processes heretofore utilised have been expensive, due to the amounts of heat energy or electric energy required. Because of such expense, desalination has been used commercially only to a limited extent.

Principal purposes of the present invention are to create a simple, low-coet water desalination process, which as a by-product creates some useful electrical current.

Briefly summarizing the present invention, salt water is caused to flow slowly through a galvanic cell, or a series of galvanic cells. Each cell contains two dissimilar metal electrodes, electrically connected externally of the water in the cell. The positive and negative ions of the dissolved salts are attracted to the electrodes, giving rise to a flow of current from one electrode to the other.

As the ions are so attracted to the electrodes, the water immediately adjacent to the electrodes becomes laden with the ions of the salts/ and thus develops a higher density, so that it settles to the bottom of the container, where at least some of the salts are precipitated. As it settles, the remainder of the water, having a substantially lessened concentration of salt, rises to the top of the cell, from which it flows out. In the preferred embodiment, the the upward-flowing water is further desalinated in a succession of similar cells; while the extracted salt is removed in a concentrated brine, from the bottomsof the cells.

Various types of galvanic cell equipment, simple or complex, may be Utilized to carry out the present process Thus, a single horizontally elongated galvanic cell may have a horizontally-extended flow path; as the water flows above it, salt will be progressively extracted. For a better understanding of the process, however, the four-cell require ment herein described is thought to be preferable.

Four hollow Cylindrical copper vessels, each with removable bottom plug, are connected together by piping. An inflow port into each is located at about its midheight, and each has an outflow port at the top. The outflow port of the first copper vessel is connected to the inflow port of the second; its outflow port is connected to the inflow port of the third; its outflow port is connected to the inflow port of the fourth.

The copper vessels serve as hollow cylindrical cathode elements. Suspended along the center axis of each and reaching to a point spacedly above the bottom, is a small diameter aluminum: tube which serves as an anode element. The upper projecting ends of all of the aluminum anodes are electrically connected together; likewise, the side walls of the copper vessels are connected. An electrical connection is then made between the anode elements and cathode elements.

In using such equipment to carry out the present inventive process, saline water i& introduced into the Inflow port of the first copper vessel and permitted to flow at a slow rate of speed and to exit from the outflow port of the fourth container. An electrical current is produced in the connection "between the anode elements and the cathode elements. Its voltage is measured at approximately 0.5 volts.

Typical sea water may contain approximately 36,000 parts of salt per million parts of water. If such water is flowed through the four-cell apparatus described, the water flowing from the flow outlet of the fourth cell will be substantially desalinated, containing only approximately 370 parts of salt per million parts of water. Periodically the bottom plugs are to be removed from the copper vessels, to draw off a dense brine containing precipitated salt.

In so doing, a fairly substantial quantity of water, somewhat less than 209¾, will be lost.

As a by-product of the desalination process, electrical current is produced, which though relatively small in quantity, is quite likely to be sufficient for operating certain auxiliary apparatus, such as brine removal pumps.

Laboratory testing has established that the successful separation and removal of salts in the method hereinabove described proceeds on the principle of electro-gravitational separation. 3?he laboratory apparatus consisted of a wide-mouth glass jar of three pint capacity, filled with potable fresh water. Approximately one-half gram of ordinary table salt was dissolved in the water. To serve as electrodes, two metal plates, 1/16 inch thick, one of aluminum and one of copper, were cut to approximately 2-inch by 3-inch size. Two 1/4 inch diameter holes were drilled in the top corners of both plates to permit supporting them vertically in the jar by 1/4 inch wood dowels. Their spacing was adjusted by sliding the plates on the dowels. Small connector clips were soldered to both ends of a five-inch long piece of insulated wire; but this was not at first connected between the plates.

There exist several chemical dye compounds known as chemical indicators, which have the characteristic of changing color when the solution containing the indicator reaches a certain acidity or alkalinity. The term pH is used to scale the acidity, with zero being the strong acid and 14 the strong alkali. The range of pH for typical natural waters is 5 to 9. A low pH (acid) is indicative of a high hydrogen ion concentration in the water.

A very small quantity of an indicator, thymol blue, was dissolved in the prepared water. Hypodermic syringes containing very dilute solutions of acetic acid and sodium hydroxide were used to add minute quantities to the water until its acidity was at the level at which the indicator would operate. At this point the water had an orange color; addition of a drop of acetic acid would increase the hydrogen ion concentration and cause the color to change to red; addition of a drop of sodium hydroxide would cause the color to change to a clear yellow.

The aluminum and copper plate electrodes, with no electrical connections between them, were suspended in the prepared water from the wood dowels, with a spacing of 1/2 inch between the plates. After thirty minutes there was no visible change in the orange color of the water.

Then the connector clips of the insulated wire wer attached to the top portion of the plates, above the water level.

This served to establish a galvanic cell. After several minutes, noticeable changes in the previously orange water became apparent. The copper plate was blanketed with a thin layer of red water, demonstrating an increase in hydrogen ion concentration; that is, the copper cathode had attracted positive ions, decreasing the pH at the copper and causing the indicator in this region to turn bright red. The aluminum plate was blanketed with clear yellow water, demonstrating that negative ions had been attracted to it.

After ten minutes, the colored zones were about 1/16 inch thick on each side of the metal plates. At this time streams of red and yellow water were noted coming off the bottoms of the metal plates and descending to the bottom of the Jar. Continued operation indicated no change in the appearance of the plates, but the size of the colored zones in the bottom of the Jar increased. After several hours' operation, small flecks of aluminum hydroxide were noticed on the aluminum plate. - 7 - This laboratory demonstration model discloses that the principle of operation of the invention is electro-gravitational separation. The concentration near the plates of ions of the dissolved salts increased the density of the fluid adjacent to the plates. This increase in density set up a gravitational convection flow, the denser fluid settling to bottom of the jar, while the water partly depleted of dissolved salts rose to the upper part of the jar.

Returning to a consideration of the 4-vessel. apparatus first mentioned, the progression of flow through the individual galvanic cells causes the water to be progressively desalinated. The same effect may be achieved in a single horizontally elongated cell wherein water flows slowly from one end of the cell to the other. In any such apparatus, where current may flow between dissimilar metal electrodes, portions of the dissolved salts are attracted to each electrode, increasing the density of the liquid adjacent the electrodes.

Gravity causes such denser water, containing the concentration of dissolved salts, to settle to the bottom, leaving the water thereabove relatively desalinated. As such relatively desalinated water is processed thereafter in a similar galvanic cell, or in a horizontal extension of the same cell, desalination progresses to the point of rendering the water suitable for agricultural use. Assuming no serious concentrations of other impurities exist, the water so desalinated will be potable.

Claims (2)

CLAIMS .

1. The process of desalination of salt water which comprises flowing such water "between spaced-apart substantially vertically arranged dissimilar metal electrodes in a cell-like means, the electrodes being connected by an electrical conductor outwardly of the water, whereby an electrical current flows between them, attracting, by such flow of current, portions of the salts to each electrode, whereby to cause an increaae in density in the water adjacent to each electrode, permitting settlement downward from adjacent the electrodes to the bottom of the cell-like means, and removing from the bottom a brine of greater concentration than that of the water thereabove.

2. The process as defined in Claim 1, together with the subsequent steps of flowing the upper portions of such water tru cJt between electrodes of further cell-like means, and repeating therein the remainder of the steps so set forth, whereby to effect progressive desalination.