EP0791101A1 - Geruchsbehandlung von übelriechenden kondensaten mit ozon-enthaltenden restgasen - Google Patents

Geruchsbehandlung von übelriechenden kondensaten mit ozon-enthaltenden restgasen

Info

Publication number
EP0791101A1
EP0791101A1 EP95938081A EP95938081A EP0791101A1 EP 0791101 A1 EP0791101 A1 EP 0791101A1 EP 95938081 A EP95938081 A EP 95938081A EP 95938081 A EP95938081 A EP 95938081A EP 0791101 A1 EP0791101 A1 EP 0791101A1
Authority
EP
European Patent Office
Prior art keywords
ozone
condensate
residual gas
pulp
gas
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP95938081A
Other languages
English (en)
French (fr)
Other versions
EP0791101B1 (de
Inventor
Anders Wernqvist
Hakan DAHLLÖF
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Metso Fiber Karlstad AB
Original Assignee
Kvaerner Pulping AB
Kvaerner Pulping Technologies AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kvaerner Pulping AB, Kvaerner Pulping Technologies AB filed Critical Kvaerner Pulping AB
Publication of EP0791101A1 publication Critical patent/EP0791101A1/de
Application granted granted Critical
Publication of EP0791101B1 publication Critical patent/EP0791101B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D21C11/06—Treatment of pulp gases; Recovery of the heat content of the gases; Treatment of gases arising from various sources in pulp and paper mills; Regeneration of gaseous SO2, e.g. arising from liquors containing sulfur compounds
    • D21C11/08—Deodorisation ; Elimination of malodorous compounds, e.g. sulfur compounds such as hydrogen sulfide or mercaptans, from gas streams
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
    • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone

Definitions

  • the present invention relates to the ozone bleaching of chemical paper pulp, especially paper pulp which is produced by the kraft pulp process.
  • the inven ⁇ tion concerns a method for utilizing the remaining ozone content in the residual gas after the bleaching by using the residual gas for the purifying treatment of condensate from a process for producing paper or paper pulp.
  • a goal for pulp producers is to create "the closed mill", in which discharges are minimized and return of liquid flows to the fibre line, and chemical recovery, are maximized.
  • it is advantageous for the bleaching process not to con ⁇ tain elemental chlorine or chlorine dioxide since, among other reasons, chlorine has a corrosive effect on the equipment and can form toxic compounds if it is combusted in the recovery boiler.
  • returning washing liquid in countercurrent to the fibre stream also places great demands on the purity of the liquid.
  • Some washing stages are more sensitive than others to impurities. For this reason, there is often the need for some form of purification of the different condensates which can be utilized as washing liquid. In this context, a dis ⁇ tinction is made between different types of condensate since they have different contents of impurities.
  • live steam is supplied to the first effect and the steam which has been obtained from liquor evporation in preceding stages is used as a heat source in the subsequent stages. This is possible owing to the gradual decline in pressure.
  • the heat content which remains in the steam from the final effect is condensed in one or more surface condensers.
  • a steam stripper usually separates off methanol, ethanol, terpenes and malodorous sulphur compounds
  • pure conden ⁇ sates The evaporation condensates which are not so heavily contaminated are often termed "pure conden ⁇ sates".
  • the problem is that they, nevertheless, contain some malodorous impurities.
  • malo ⁇ dorous substances for example dimethyl trisulphide, 2,3-dimethylphenol, and a variety of trithiolanes and trisulphides have been discovered in these condensates in addition to those which were previously known. It is therefore desirable to purify these condensates as well in order to avoid problems, inter alia with the working environment, when closing the kraft mill.
  • the dif ⁇ ferent methods which exist can be classified into the following groups: phase change (e.g. stripping and adsorption with active charcoal), biological treatment, thermal or catalytic oxidation and chemical oxidation.
  • phase change e.g. stripping and adsorption with active charcoal
  • biological treatment e.g. thermal or catalytic oxidation
  • chemical oxidation group which, inter alia, encompasses the oxidizing agents oxygen, chlorine, potassium permanganate, peroxides and ozone.
  • a method for purifying condensates from the kraft process has been patented by means of SE-C-462 169.
  • the condensates are treated concurrently, in a column, with an oxygen- containing gas in the presence of active charcoal as catalyst. Any oils and solid substances which are present have first to be separated off, and the catalyst has to be regenerated at regular intervals.
  • the patent GB 1 405 317 describes an ozone treatment method for a desulphurization process.
  • the ozone oxidizes sulphur compounds to sulphate and decreases the content of COD in the waste water.
  • Ultrox International has several patents (US
  • Ozone is a very reactive chemical which reacts rapidly with the lignin in the pulp.
  • the economically most advantageous method is to supply a quantity of ozone which is slightly greater than that which is stoichiometrically required for the bleaching.
  • a small quan ⁇ tity of unreacted ozone is often left in the gas, which ozone has to be conveyed away and destroyed in a so- called ozone destroyer.
  • this residual ozone can be used very expediently in a method for treating malodorous condensates, especially those condensates which are relatively pure with regard to their contents of methanol and COD. While ozone has a limited effect on methanol and COD content, its effect on odour is relatively large.
  • the method will be described below with reference to Figure 1, which shows a preferred embodiment of the invention, and Figure 2, which shows a device for separating off the residual gas from ozone bleaching. After cooking and washing, the pulp is treated with ozone which has been generated within the mill from air or oxygen.
  • This treatment with ozone takes place at a pH of approximately 3, a pulp concentration of between 8 and 12%, a pressure of 8 bar and a tem- perature of 50°C.
  • the ozone gas is mixed in with the pulp in a first mixer (1) ( Figure 1) and the mixing effect is subsequently amplified by the pulp having to pass through one or more additional mixers (2), preferably without any further admixture of gas.
  • the pulp is con ⁇ veyed, via a pipeline, to a blow tank (3) . Conse- quently, there is no requirement for a special reactor because of the dwell time.
  • the residual gas which principally consists of oxygen with an ozone content of approximately 0.5%, is separated off from the pulp in conjunction with the latter being conveyed to the blow tank, for example by means of a cyclone (4) ( Figure 2) in accordance with SE-A-9200183. Fibre is preferably removed from the separated residual gas, for example by means of the gas having to pass through liquid in a liquid seal device (5) of the type which is described in SE-A-9200183.
  • the residual gas (6) is conveyed to a device for condensate treatment, preferably a coun- tercurrent absorption tower (7) containing packing material, intermediate partitions or the like for creating the maximum area of contact between gas and liquid.
  • Condensate (8) preferably one of the purer liquor steam condensates from the black liquor evapora ⁇ tion, is introduced at the same time into the upper part of the absorption tower.
  • the condensate which is arriving is heated, for example by exchanging heat (13) with the departing condensate (9) and, where appropriate, by making use of heat from the ozone destroyer (12) .
  • Vola ⁇ tile substances are then given off more readily and can be attacked by the ozone or oxygen. It is also advanta ⁇ geous if, in association with entering the absorption tower, the condensate is subjected to a decline in pressure so that a stripper effect is achieved.
  • the condensate first meets a gas which principally consists of oxygen since the major part of the ozone has been consumed previously in the absorption tower.
  • the oxyger. is a positive oxidizing effect on impurities in the condensate, even if the oxidizing effect of the oxygen is not as great as that of the ozone.
  • the oxygen is able not only to decompose some COD and malodorous substances in the condensate but also, at the same time, like an air stripper, to drive off readily vola ⁇ tile substances which are then broken down either in the absorption tower or in the ozone destroyer.
  • the condensate flows down through the tower (7) and, in doing so, meets gas of gradually increasing ozone content. Impurities and malodorous organic sub ⁇ stances are oxidized by the ozone, resulting in the departing condensate (9) having a substantially less offensive smell, a lower COD content, a lighter colour and greater clarity.
  • additional ozone (10) can be supplied to the absorption tower, preferably at the same end of the tower as the condensate outlet.
  • the purified condensate (9) can, for example, be utilized in washing stages which place relatively high demands on purity and free ⁇ dom from odour, for example lime sludge dilution, lime sludge washing or peroxide-containing bleaching stages.
  • Gas (11) which leaves the tower (7) is conveyed to an _ozone destroyer so that any accompanying volatile sub ⁇ stances, or any remaining unused ozone, can be destroyed.
  • An advantage of treating the condensate in addition to that of providing the opportunity of reusing condensate in the process, which represents a simplification when increasing the closure of the mill, is that it improves both the working environment and the environment surrounding the mill.
  • the surrounding population can sometimes be very annoyed by malodorous gases emanating from a pulp mill.
  • the ozone stage is carried out at a pH of less than 7, preferably of approximately 2-4.
  • the pressure on the pulp should be at least 8 bar, the tem ⁇ perature at most 60°C preferably 20-40°C, and the concentration of the pulp should be 6-14%, preferably 8-12%.
  • the carrier gas preferably consists of oxygen
  • air can also be used.
  • the residual gas should preferably contain at least 0.3% by weight, preferably at least 0.5% by weight, and even more preferably at least 1% by weight, of ozone.
  • the condensate treatment can also be carried out, for example, in a tank having a stirrer, to which the gas is supplied while stirring.
  • the condensate can also be mixed with the gas in a mixer of the static type and subsequently conveyed into a contact tower having some form of mechanism for mixing the condensate and the gas and for maintaining a turbulent flow.
  • a mixer of the static type and subsequently conveyed into a contact tower having some form of mechanism for mixing the condensate and the gas and for maintaining a turbulent flow.
  • the condensate (8) is preferably supplied continuously to the water seal.
  • the condensate is preferably supplied to the pulp suspension before, or at the same time as, the latter is bleached with ozone so that the condensate treatment takes place at the same time as the actual ozone bleaching.
  • the invention can be applied to any other process water whatever and also, for example, to effluent from a bleaching stage before it is conveyed onwards in the process. While the invention has been described here on the basis of a hypothetical kraft pulp mill, the same positive effects will be achieved, for example, in the case of a sulphite pulp mill or an integrated paper and pulp mill.
  • a plant for condensate treatment in analogy with the invention can also be advantageous in which the ozone is replaced by other oxidizing agents which are used in bleaching, for example peracetic acid, persulphuric acid (Caro's acid) or hydrogen peroxide.
  • oxidizing agents which are used in bleaching
  • peracetic acid for example peracetic acid, persulphuric acid (Caro's acid) or hydrogen peroxide.
  • Caro's acid persulphuric acid
  • hydrogen peroxide hydrogen peroxide
  • such an oxidizing agent can be used to complement an ozone plant according to the invention.

Landscapes

  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
  • Treating Waste Gases (AREA)
EP95938081A 1994-11-08 1995-10-17 Geruchsbehandlung von übelriechenden kondensaten mit ozon-enthaltenden restgasen Expired - Lifetime EP0791101B1 (de)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
SE9403818 1994-11-08
SE9403818A SE9403818L (sv) 1994-11-08 1994-11-08 Sätt vid ozonblekning
PCT/SE1995/001207 WO1996014464A1 (en) 1994-11-08 1995-10-17 Odour treatment of malodorous condensates with ozone-containing residual gas

Publications (2)

Publication Number Publication Date
EP0791101A1 true EP0791101A1 (de) 1997-08-27
EP0791101B1 EP0791101B1 (de) 2001-07-18

Family

ID=20395879

Family Applications (1)

Application Number Title Priority Date Filing Date
EP95938081A Expired - Lifetime EP0791101B1 (de) 1994-11-08 1995-10-17 Geruchsbehandlung von übelriechenden kondensaten mit ozon-enthaltenden restgasen

Country Status (6)

Country Link
EP (1) EP0791101B1 (de)
AT (1) ATE203292T1 (de)
AU (1) AU3884295A (de)
DE (1) DE69521809T2 (de)
SE (1) SE9403818L (de)
WO (1) WO1996014464A1 (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6780223B2 (en) 2001-09-14 2004-08-24 Industrial Technology Research Institute Method and apparatus for treating an exhaust gas containing volatile organic compounds

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6348129B1 (en) 2000-04-28 2002-02-19 Praxair Technology Inc Treatment of pulp mill condensate with ozone

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NO150971C (no) * 1981-04-10 1985-01-23 Papirind Forskningsinst Fremgangsmaate ved rensning av kondensater fra sulfatprosessen
SE9200183L (sv) * 1992-01-23 1993-07-24 Kamyr Ab Avskiljningsanordning samt foerfarande
WO1993018226A1 (en) * 1992-03-02 1993-09-16 Kamyr, Inc. Combined ozone destruction and fiber scrubbing in paper pulp mills

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9614464A1 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6780223B2 (en) 2001-09-14 2004-08-24 Industrial Technology Research Institute Method and apparatus for treating an exhaust gas containing volatile organic compounds

Also Published As

Publication number Publication date
AU3884295A (en) 1996-05-31
ATE203292T1 (de) 2001-08-15
SE9403818L (sv) 1996-05-09
SE9403818D0 (sv) 1994-11-08
DE69521809D1 (de) 2001-08-23
EP0791101B1 (de) 2001-07-18
WO1996014464A1 (en) 1996-05-17
DE69521809T2 (de) 2002-04-04

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