| 摘要 |
<PICT:0936726/III/1> HF is recovered from the furnace gases from electrolytic aluminium furnaces, without absorption of sulphur oxides, by washing the gases with fresh water in a column of vertically-spaced perforated plates on each of which a film of solvent is maintained, the gases passing upwardly through the perforations in contact with the films, wherein used solvent is not reintroduced into the column at a level above that of the lowered plate, and the relative speeds of fresh water and gas flow are so adjusted that the F content of the used washing liquid is at least 5 grms./l. The gas as bubbles is contacted with the washing liquid by passing the gas at 8 up column 1 equipped with spaced perforated plates 2 on which a film of liquid rests flowing from plate to plate through pipes 6. Several columns may be arranged in series and the gas may be cooled before washing. Contact of gas and liquid may be improved by stirring. At least the first column may be provided with a pre-cleaning chamber below the plates in which the gas is dry or wet cleaned either by passing the gas tangentially at 8 into column 1 or by spraying in used washing liquid at 13 from tank 10, or using a liquid in which tar constituents are soluble. The lower sides of the perforated plates of the column are rinsed with water injected through nozzles 4 from pipes 3 to move upwardly with the gas. The gas is delivered to each perforated plate through funnels 5, the lower end of smaller cross-section than the column being to increase the speed of gas flow, and the upper end covering the whole of the under-side of each plate. Drop-catcher plates 7 may be disposed above each plate, and the wash water may contain a surface active ingredient to reduce deposition of dust and/or tar on the plates. Specification 838,703 is referred to.
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