GB707813A - Improved method and apparatus for the treatment of weak black liquor from a sulphatepaper pulp process - Google Patents

Abstract

<PICT:0707813/IV(a)/1> <PICT:0707813/IV(a)/2> Weak black liquor resulting from the digestion of cellulosic material in a sulphate paper pulp process is concentrated sufficiently to permit its combustion and burnt to produce water-soluble ash in the form of dust in suspension in the flue gases, from which the dust is electrostatically precipitated and delivered in the dry state directly into a pool of black liquor. As shown in Figs. 2 and 3, the flue gases enter the electrostatic precipitator 46 through the inlet pipes 66, 69 and 75 and flow downwardly through the inlet passages 65, 70 and 74 as shown by the arrows in Fig. 2, reverse direction around the bottom edges 64 of the baffles 63, 68, 72 and 73, flow upwardly through the precipitation chambers A and B and pass out of the top of the precipitator through the outlet pipes 67 and 71. The gases passing upwards through the precipitating chambers A and B travel between the parallel earthed plate electrodes 50 and the fine wire discharge electrodes 52 suspended from an insulated framework 53 supported on insulators 54. High-tension current is supplied in a known manner by the wires 52. Precipitated material is removed from the plates 50 by vibrating the plates with vibrators 76 and from the discharge electrodes 52 by vibrators 80 and 81, and falls into a pool of weak black liquor maintained in a sump 57 provided with an agitator 84, Fig. 5 (not shown). The agitator has a vertical shaft 85 extending from below the bottom of the precipitator. The shaft 85 carries a cross arm from which depend a number of agitator blades 91 dipping into the pool of liquor and mounted at such an angle on the arm that they force the liquid outwardly and into the corners of the sump when the agitator is rotated. The agitator is electrically driven through a reducing gear 96. Weak black liquor flows into the sump 57 from the valved pipe 55. Fortified black liquor leaves the sump by way of outlet pipe 54, pump 102 and control valve 103 operated by a controller 104 responsive to the level of liquor in valve control tank 105.