Process and apparatus for the recovery of heat and chemicals from pulp liquor

摘要

PICT:0753070/III/1 In the plant shown for recovering sodium carbonate and sodium sulphide from the digestor residual liquor-black liquor-emanating from pulp mills utilizing the so-called "soda" and "kraft" processes the liquor, delivered into the water cooled chamber 10 by an oscillatably mounted nozzle 22 is subjected to the heat of the gases rising from the char bed on the inclined hearth 15. A fan 27 delivers air from a heater 28 in the gas flow path through damper-controlled ducts 54 and a horizontal duct 56 to a primary air conduit 57 encircling the chamber and connecting with damper-controlled primary air ports 29. A pair of secondary air damper-controlled conduits 58 connect the heater to damper-controlled secondary air ports 30 arranged in the rear and side walls of the chamber. The combustion gases from the chamber pass successively over a water tube screen 21, superheater 34, generating tube banks 35, 36, economizer 33 and air heater 28 before passing through a Venturi type gas and liquid scrubber 43 and a cyclone separator 45. Some of the cleaned gases are returned to the furnace chamber being withdrawn for this purpose from the gas flow path by a fan 70 through a pipe 71 and discharged through a duct 72 fitted with a control damper 73 to the supply duct 56 for the primary air ports. Automatic regulation of the damper 73 in response to changes in the indication of an optical pyrometer pointed at the char bed can be readily effected. The chemicals are discharged, in a molten state, from the hearth 15 into a dissolving tank 17 through a spout 16. Additional chemicals are recovered from the combustion gases in the scrubber 43 the black liquor separated in the separator 45 being used as the wash liquor in the scrubber.