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Electrolysis cell electrolyte pumping system

Electrolysis cell electrolyte pumping system description/claims

The present application claims priority to U.S. Provisional patent application 60/522,737, filed Nov. 2, 2004 and 60/594,869, filed May 13, 2005.

The present invention relates to a system for pumping electrolyte through an electrolysis cell.

Electrolysis cells use electrical energy to generate reaction gases by splitting a compound of an electrolyte. Due to the chemical reaction of electrolysis, the concentration of the electrolyte constantly increases. Electrolysis cells work properly within a limited range of electrolyte concentration. If the concentration is too low, the electrical resistance of the electrolyte becomes too high and the efficiency of the electrolysis cell goes down. Alternately, if the electrolyte concentration is too high, the electrolyte becomes very corrosive and the electrolysis cell might be irreversibly damaged. For an alkaline electrolysis cell, a typical concentration range may, for example, be from 15 to 30% KOH.

The energy efficiency of an electrolysis cell depends on its internal resistance. Thus the distance between positive and negative electrode of the electrolysis cell is kept small in order to have a low ohmic resistance between the electrodes. In some electrolysis cells, a typical distance is 1 mm. In an electrolysis cell with an active area of 100 cm2 the electrolyte volume inside the cell is 10 ccm. At a current density of 200 mA/cm2 about 6 to 7 ccm of water are consumed by the electrolysis cell per hour. Therefore, the electrolyte in some cells may be pumped from a reservoir through the cell in order to keep the cell's electrolyte concentration in the proper range. The size of the reservoir determines the operating time of the electrolysis system. The electrolyte flow that has to be pumped through the cell depends on the concentration of the electrolyte in the reservoir. For example, assuming that the highest accepted concentration is 30%, one has to replace the electrolyte in the electrolysis cell 5 times per hour at a starting concentration of 15% and 68 times per hour at a starting concentration of 29%. This means that the electrolyte flow that has to be pumped through the cell is between 50 and 680 ccm per hour.

The gas diffusion electrodes that are used in some electrolysis cells for generating the reaction gases work best with a small differential pressure between the reaction gases and the electrolyte, with the electrolyte pressure being lower than the gas pressure. One has to take care about the differential pressure when pumping electrolyte through the cell. For the same reason the electrolyte pressure has to be quite constant all over the cell and the pressure drop caused by the flow resistance has to be small. For example, typical operation pressures of electrolysis cells may be 0.5 to 3 bars and the electrolyte pressure may also have to be that high for proper cell operation.

Usually, the electrolyte is pumped by conventional pumps such as, for example, rotary pumps, gear type pumps, piston pumps or membrane pumps. However, in an efficient electrolysis system these pumps may offer one or more limitations, including for example, problems with handling low flow rates and/or high pressure flows and problematic power consumption.

In accordance with one aspect of the present invention, there is provided a system for pumping electrolyte through an electrolysis cell characterized in that the pressure of at least a portion of the gas generated by the electrolysis cell is used as driving force for the pumping.

It is to be understood that other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein various embodiments of the invention are shown and described by way of illustration. As will be realized, the invention is capable for other and different embodiments and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present invention. Accordingly the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.

Referring to the drawings wherein like reference numerals indicate similar parts throughout the several views, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein:

FIG. 1 is a schematic block diagram of an electrolysis cell and electrolyte pumping system according to one aspect of the present invention;

FIG. 2 is a schematic block diagram of an electrolysis cell and electrolyte pumping system according to another aspect of the present invention;

FIG. 3 is a schematic block diagram of an electrolysis cell and electrolyte pumping system according to another aspect of the present invention;

FIG. 4 is a schematic block diagram of an electrolysis cell and electrolyte pumping system according to another aspect of the present invention; and

• Provisional Patent
• Utility Patent

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