ES349843A1 - Method of operating mercury cathode electrolytic cell plant - Google Patents

Abstract

In operating plant comprising flowing mercury cathode cells through each of which an electrolyzable salt solution (brine) is continuously recycled, a concentrated solution being fed to the cell and a depleted solution being withdrawn from it, in order to increase the operating efficiency by increasing the electrolyte flowrate through the cell and reducing the temperature and concentration differences between the feed and return streams without increasing the load on ancillary resaturation and purification equipment, at least one third of the depleted solution is recycled back to the cell without chemical treatment while the remainder is recycled via a resaturating and purification plant. As described the mercury circuit including a denuder of each cell is independent, but the brine, typically sodium or potassium chloride solution, may be fed from a header common to all the cells. Typically up to nine-tenths of the depleted solution may be recycled without chemical treatment. Either the whole (see Figs.1, 2 not shown) or at least a part of the resaturated salt stream is combined with the untreated stream before recycling to the cells. The combined solution stream may be introduced at one or more points intermediate the cell ends in addition to the upstream end of the cell (see Fig. 2). As shown combined solution stream is introduced at the upstream end and saturated solution is introduced at an intermediate point along the cell such as by pipe 16 and sparger 19. The cell is of the kind described in Specification 894, 769 in which graphite anodes 6 are supported by graphic rods 7 secured to a metal spider 11 secured to a beam 24 which is attached to bars 5 adjustably secured to posts 4 seating on the top flange 3 of the electrolyte trough 1. The anodes are provided with longitudinally directed slots 21 which communicate with gas escape holes 22 and baffle plates 20 are supported across the cell between groups of anodes, especially at locations where electrolyte is introduced, to effect stirring of the bath and so assist in gas removal and renewal of electrolyte between the anodes and flowing mercury cathode. The top of the cell is closed by a flexible rubber or plastics sheet through which the connections to the anode rods 7 and the electrolyte supply pipe 16 pass. A gauge 17 which may include means for automatic flowrate control and a manual valve 18 are also provided. On start-up the heat exchanger J may be operated so as to warm the brine fed to the cell while on shut-down with the arrangement shown in Fig.3 the cell is preferably fed with pure brine through the inlet end by suitable operation of valves K, L, M.