DE843757T1 - METHOD FOR REPROCESSING OZONE-CONTAINING GAS IN A PLANT BLEACHING PLANT - Google Patents

Abstract

A method for reprocessing an ozone-containing gas present in a pulp bleaching plant comprising the steps of supplying the ozone-containing gas to a scrubber and reducing the ozone concentration of the gas as the gas flows through the scrubber. The step of reducing comprises the steps of supplying an alkaline medium to the scrubber and flowing the ozone-containing gas in countercurrent relationship with the alkaline medium within the scrubber so as to provide intimate contact between the ozone-containing gas and the alkaline medium, thereby converting the ozone-containing gas into a substantially ozone-free gas. The alkaline medium may comprise one of the following: a sodium hydroxide solution; white liquor; post oxygen stage filtrate; weak black liquor; or filtrate from an Eo stage of the pulp bleaching plant. The method further comprises the step of separately discharging the ozone-containing gas and the alkaline medium from the scrubber. The ozone-containing gas may comprise an off-gas, which has been partially reacted with a pulp within a pulp bleaching stage or alternatively may comprise fresh bleaching gas, having an ozone concentration ranging from about 6 % to about 14 % by weight within a carrier gas, with the fresh bleaching gas being supplied directly from an ozone generator to the scrubber.

Claims (13)

96 927 319.2 Patent claims 1. A method for recycling an ozone-containing gas in a pulp bleaching plant, the method comprising the steps: introducing the ozone-containing gas into a gas scrubber; reducing an ozone concentration of the ozone-containing gas as the gas flows through the gas scrubber, the reducing step comprising the steps of: introducing an alkaline medium into the gas scrubber; passing the ozone-containing gas countercurrently to the alkaline medium within the gas scrubber so as to provide intimate contact between the ozone-containing gas and the alkaline medium within the gas scrubber and thereby converting the ozone-containing gas into a substantially ozone-free gas; the method further comprising the step of separately discharging the substantially ozone-free gas and the alkaline medium from the gas scrubber. 2. The process of claim 1, wherein the alkaline medium comprises a sodium hydroxide solution. 3. The process of claim 1, wherein the alkaline medium comprises white liquor. 4. A process according to claim 1, wherein the alkaline medium comprises a filtrate obtained after the oxygen step. 5. The process of claim 1, wherein the alkaline medium comprises weak black liquor. 6. The process of claim 1, wherein the alkaline medium comprises a filtrate from an Eo stage of the pulp bleaching plant. 7. The method of claim 1, wherein the alkaline medium has an alkali concentration ranging from about 1 g alkali/liter of solution to about 100 g alkali/liter of solution. 8. The method of claim 1, wherein: the ozone-containing gas comprises an exhaust gas which has been partially reacted with a pulp within a pulp bleaching stage of the pulp bleaching plant; the step of introducing the ozone-containing gas includes the step: Introducing the exhaust gas from the pulp bleaching stage into the gas scrubber. 9. The method of claim 8, further comprising the step of: reducing a carbon dioxide concentration of the exhaust gas as the exhaust gas flows through the scrubber. 10. The method of claim 1, wherein: the ozone-containing gas comprises fresh bleaching gas and the ozone concentration of the fresh bleaching gas ranges from about 6 wt.% to about 14 wt.% within a carrier gas before the fresh bleaching gas enters the scrubber; the step of introducing the ozone-containing gas includes the step of Introducing the fresh bleaching gas from an ozone generator into the gas scrubber without prior reaction of the fresh bleaching gas with pulp. 11. The method of claim 1, wherein the step of separately dispensing includes the steps of: Discharge of the alkaline medium at a liquid outlet of the gas scrubber; Discharge of the essentially ozone-free gas at a gas outlet of the gas scrubber to an ozone generator. 12. The method of claim 1, wherein the step of separately dispensing includes the steps of: Dispensing the alkaline medium at a liquid outlet of the DE / EP O 84375V Tl gas scrubber; Discharge of the essentially ozone-free gas at a gas outlet of the gas scrubber to a pulp bleaching stage of the pulp bleaching plant. 13. The method of claim 1, wherein: the gas scrubber is substantially vertically oriented and has a generally cylindrical housing in which an inner chamber is formed, the inner chamber having an upper portion and a lower portion, and the gas scrubber further having a gas inlet and a liquid outlet in fluid communication with the lower portion of the inner chamber and a gas outlet and a liquid inlet in fluid communication with the upper portion of the inner chamber; the step of introducing the ozone-containing gas includes the step Introducing the ozone-containing gas into the gas inlet of the gas scrubber; the step of introducing the alkaline medium includes the step Introducing the alkaline medium into the liquid inlet of the gas scrubber; the step of separate submission includes the steps: Discharge of the substantially ozone-free gas at the gas outlet of the gas scrubber; and Discharge of the alkaline medium at the liquid outlet of the gas scrubber. B-1ho/Z92-22A