Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-07-06
2001-09-04
Valentine, Donald R. (Department: 1741)
Metal working
Method of mechanical manufacture
Electrical device making
C204S257000, C204S279000
Reexamination Certificate
active
06282774
ABSTRACT:
This application is a 371 of PCT/CP97/04402, Aug. 13, 1997.
The invention pertains to an electrolyser for the production of halogen gases from aqueous alkali halogenide solution using several plate-like electrolysis cells arranged side by side in a stack and electrically connected. Each cell is encased in two semi-shells made from electroconductive material with contact strips on the outer side of at least one of the casing's rear walls, the said casings being fitted with feeders for the cell current and the electrolysis feedstock, with devices for discharging the cell current and the electrolysis products and consisting of an anode and a cathode which each have a fundamentally level surface and are separated from one another by a partition, arranged parallel to one another and electrically connected to the rear wall of the respective casing via metal reinforcements.
The invention also pertains to a preferred process for the manufacture of such an electrolyser in which the individual electrolysis cells are manufactured first by joining together the two semi-shells of each respective casing whilst incorporating all requisite devices including the cathode, anode and partition, the latter being fixed using metal reinforcements, and by electrically connecting the anode and the cathode to the casing. The plate-like electrolysis cells produced are electrically connected and arranged side by side in a stack and braced against each other within the stack to ensure sustained contact.
The cell current is fed to the cell stack via the outer cell of the stack from where it is distributed in an essentially vertical direction throughout the cell stack to the centre planes of the plate-like electrolysis cells before being discharged via the outer cell on the other side of the stack. When applied to the centre plane, the cell current achieves an average current density of at least 4 kA/m
2
.
The applicant knows of such an electrolyser which is mentioned in EP 0 189 535 B1. In this known electrolyser the anode and the cathode are both connected to the rear wall of the respective semi-shells via metal reinforcements arranged in a braced fashion. Each anode and cathode semi-shell is fitted with a contact strip at the rear which is used to ensure electrical contact with the adjacent electrolysis cell which is identical. The current flows along the contact strip through the rear wall into the metal reinforcements. From here it is distributed throughout the anode from the metallic contact points (reinforcement/anode). Once the current has passed through the membrane it is taken by the cathode to enable it to flow along the bracing-type reinforcements into the rear wall on the cathode side and then back into the contact strips before entering the next electrolysis cell. The electroconductive components are connected by spot-welding. The cell current collects at the weld points to create peak current density.
One drawback of the known electrolyser lies in the fact that the current does not flow across the entire surface of the contact strip. This is due to the fact that the current leaving the metallic connection between the bracing-type reinforcement and the rear wall of the cathode is passed into the contact strip at one single point As the current-carrying surface area decreases, the voltage required for the current flow, the so-called contact voltage, increases, and because the specific energy requirement necessary for the production of electrolysis products increases linear to the voltage, production costs also increase.
A further disadvantage of the known electrolyser lies in the fact that for reasons of flexibility, the bracing-type reinforcements connecting the rear wall and the electrodes are not arranged vertically between the rear wall and electrode. This leads to a prolongation of the current paths which also causes the cell voltage to increase. In addition, the current from the bracing-type reinforcement only enters the electrode at one single point leading on the one hand to uneven current distribution and on the other to a renewed increase in the cell voltage. The uneven current distribution on the electrodes also causes the electrolyte to be depleted which results in a decrease in current efficiency and shortens the service life of the membrane.
The purpose of the invention is to create an electrolyser in which the current-carrying surfaces are as large as possible, thereby preventing current from being fed into the electrodes and the contact strips at only one single point thus avoiding uneven current distribution.
In accordance with the invention, the type of electrolyser described in the introduction fulfils this purpose by having metal reinforcements designed in the form of solid plates which are flush with the contact strips and whose side edges run up the entire height of the rear wall and of the anode or cathode.
The electrolyser constructed in accordance with the invention practically prevents uneven current flow through the surfaces as the current is fed into the electrodes and the contact strips across the whole surface and not from one single point The current paths themselves are short as the reinforcing plates can be arranged vertically between the respective rear wall and electrode. The embodiment of the invention described herein ensures that the cell voltage required for the electrolyser is much smaller than that of the known electrolyser.
The cathodes can be made from iron, cobalt, nickel or chrome or from their alloys, and the anodes from titanium, niobium or tantalum, from an alloy of these metals or from a metal-ceramic or oxide-ceramic material. In addition these electrodes are covered with a catalytically active coating, whereby it is preferable for the electrodes to have openings (perforated plate, expanded metal, trellis work or thin sheet metal with louvre-type openings), which allow the gas formed during the electrolytic process to easily enter the space at the rear of the electrolysis cell. This degassing ensures that the electrolyte between the electrodes has as few gas bubbles as possible and is thus able to achieve maximum conductibility.
The partition, or so-called membrane, is an ion-exchanger membrane which is usually made from a copolymer produced from polytetrafluoroethylene or one of its derivatives and a perfluorovinylether sulphonic acid and/or perfluorovinyl carbonic acid. The membrane ensures that the electrolytic products do not mix and its selective permeability with regard to the alkali metal ions permits current flow. Diaphragms can also be used for the partition. A diaphragm is a fine-porous partition which prevents the gases from mixing and which produces an electrolytic connection between the cathode and anode thus permitting current flow.
The solid plates forming the metal reinforcements can be realised as solid surfaces or can be provided with openings or slits.
A further advantage of the electrolyser involves the inlet distributor through which the electrolytes can be fed into the semi-shells to permit optimal electrolyte supply. This inlet distributor is preferably constructed in such a way that each segment of a semi-shell can be provided with fresh electrolyte through at least one opening in the inlet distributor and that the sum of the areas of the openings in the inlet distributor is smaller or equal to the inlet distributors area of cross section.
Provision is also made for the anode and cathode to be integrally connected to the solid plates via an electroconductive twin connection. A preferred embodiment is to integrally link the plane-parallel contact strips to the rear wall and to the solid plate below using an electroconductive, metallic triple connection.
Alternatively, it can also be provided for each respective rear wall to be integrally linked to the solid plates via a metallically conductive twin connection, the contact strips being formed from build-up welds on the rear wall.
The integral linking of the twin or triple connections dispenses with the need for seams between the solid plate and the rear wall on the on
Borucinski Thomas
Dulle Karl-Heinz
Gegner Jürgen
Wollny Martin
Krupp Uhde GmbH
Rosenman & Colin LLP
Valentine Donald R.
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