PROCESS FOR TREATING PULP MILL CONDENSTATES USING A HOLLOW FIBER CONTACTOR

• US 20100122784A1
• Filed: 07/24/2008
• Published: 05/20/2010
• Est. Priority Date: 07/26/2007
• Status: Active Grant

• Current Assignee: FPInnovations
• Original Assignee: FPInnovations
• Inventors: O'connor, Brian, Jemaa, Naceur, Paleologou, Michael
• Granted Patent: US 8,349,130 B2
• Time in Patent Office: Days
• US Class Current: 162/14
• CPC Class Codes: B01D 2311/13 Use of sweep gas
• CPC Class Codes: B01D 61/246 Membrane extraction
• CPC Class Codes: B01D 63/02 Hollow fibre modules
• CPC Class Codes: C02F 1/20 by degassing, i.e. liberation of dissolved gases degasification of liquids in general B01D19/00; arrangement of degassing apparatus in boiler feed supply F22D
• CPC Class Codes: C02F 2103/28 from the paper or cellulose industry
• CPC Class Codes: C02F 2301/063 Underpressure, vacuum
• CPC Class Codes: D21C 11/00 Regeneration of pulp liquors or effluent waste waters

Abstract

A method and apparatus for the treatment of pulp mill condensates is described. A hollow fiber contactor, incorporating a hydrophobic membrane, was used to remove several undesirable compounds from pulp mill condensates. For example, TRS compounds and SO₂ were efficiently stripped from kraft and sulphite mill evaporator condensates, respectively. Methanol was also removed from kraft mill condensates but at a lower efficiency than TRS. Furthermore, other undesirable compounds found in condensates of pulp mills that contribute to the BOD and COD loading to effluent treatment systems were also removed. These contactors are cost effective since air, vacuum or a suitable solvent or scrubbing solution can be used as the stripping medium to drive off through the membrane several undesirable compounds from the feed solution. The undesirable compounds removed can thus be burned in the recovery boiler, lime kiln or a dedicated boiler.

Claims

1. A method for removing off gas contaminants from an aqueous evaporation condensate pulp mill effluent stream, which aqueous evaporation condensate contains methanol and off gas contaminants selected from the group consisting of sulphur dioxide and total reduced sulphur (TRS) compounds comprising:

providing a hollow fibre membrane contactor comprising a plurality of hollow fibres, each fibre having a hydrophobic membrane wall having first and second opposed sides;

flowing the aqueous evaporation condensate through said contactor, in contact with the first sides of the walls of the fibres; and

allowing said off gas contaminants in said aqueous evaporation condensate to migrate through the membrane walls to said second sides of the walls of the fibres, leaving an aqueous methanol stream at said first sides of said walls.

2. A method according to claim 1, further including flowing an acceptor fluid through the contactor, in contact with the second sides of the walls of the fibres, and said flowing acceptor fluid extracting the undesirable compounds migrating through the membrane walls.

3. A method according to claim 2, wherein said acceptor fluid is a stripping gas.

4. A method according to claim 3, wherein said gas is nitrogen, carbon dioxide or air.

5. A method according to claim 2, wherein said acceptor fluid is an aqueous alkaline solution.

6. A method according to claim 1, wherein a vacuum is formed at said second sides, said vacuum extracting the off gas contaminants migrating through the membrane walls.

7. A method according to claim 2, wherein said aqueous evaporation condensate and said acceptor fluid flow through a plurality of contactors in series, whereby said aqueous evaporation condensate is depleted in said off gas contaminants at each successive contactor and said acceptor fluid is enriched in off gas contaminants at each successive contactor.

8. A method according to claim 1, wherein said off gas contaminants are total reduced sulphur (TRS) compounds selected from the group consisting of hydrogen sulphide, methyl mercaptan, methyl disulphide and dimethyl disulphide.

9. A method according to claim 1, wherein said aqueous evaporation condensate is steam stripper off gas condensate.

10. In a process of pulp manufacture in a pulp mill in which an aqueous evaporation condensate pulp mill effluent stream, which aqueous evaporation condensate contains methanol and off gas contaminants selected from the group consisting of sulphur dioxide and total reduced sulphur (TRS) compounds is formed, the improvement wherein off gas contaminants are removed from the aqueous evaporation condensate by the method of any one of claims 1 to 8, and an aqueous methanol stream is recovered for use.

11. The process according to claim 10, wherein said aqueous methanol stream is recycled in the pulp mill for generation of chlorine dioxide.

12. The process according to claim 10, wherein said pulp mill is a kraft pulp mill and said off gas contaminants are total reduced sulphur (TRS) compounds selected from the group consisting of hydrogen sulphide, methyl mercaptan, methyl disulphide and dimethyl disulphide.

13. The process according to claim 10, wherein said aqueous evaporation condensate is steam stripper off gas condensate.