GB688776A - Improvements in or relating to a process for recovering finely divided pigments suchas carbon black - Google Patents

Abstract

<PICT:0688776/III/1> Finely divided pigments such as carbon black, zinc oxide, calcium carbonate, chromium oxide, magnesium oxide and alumina are recovered from aerosols thereof by forming a slurry by scrubbing the aerosols with an aqueous liquid, agitating a quantity of the same pigment in a dry fluffy state and gradually adding the slurry to the dry pigment, with agitation whereby self-sustaining pellets are formed. A wetting agent such as an aromatic or aliphatic sulphonic acid may be added to the slurry which may contain 2 to 10 per cent solids by weight, before addition to the dry pigment. The moisture content of the mixture of slurry and dry pigment is preferably between 75 and 25 per cent. In the carbon black recovery unit shown in the Figure carbon black aerosol, as flue gases from a furnace black plant, enters a cooler 10 where it is sprayed with water at 14 and recycled slurry at 16. The cooled aerosol then passes to an electric or sonic precipitator 18, cyclone separators 20 and 22 and finally to a scrubber 24 where the residual carbon black is recovered as a slurry in the water injected at 26. The gases then pass through an electric precipitator 28 before being reheated above the dew point at 32 and exhaustion to the atmosphere. The slurry is withdrawn from scrubber 24 through pipe 40 to a clarifier 42 from which the upper and lower sludges are transferred to a mixer 48 through pipes 46 and 54 respectively. Excess water from clarifier 42 is recycled to the scrubber 24. A wetting agent is added to the mixer 48 through pipe 68 and the resulting slurry is recycled in part to the cooler 10 by pipes 76, 80 and 86 to a bifluid nozzle 16. The remainder passes through pipes supplied with dry carbon black from the cyclone, 20, 22 and storage tank 88 through line 90. The finished pellets are passed to a drier 92, and a portion of them, preferably under and oversized pellets, are pulverized at 94 and recycled to the pellitizer 84 to control the solids/water concentration to 3 parts of carbon black to 1 to 9 parts of water.