EP0791101B1 - Traitement des odeurs de condensats malodorants a l'aide de gaz residuel contenant de l'ozone - Google Patents

Traitement des odeurs de condensats malodorants a l'aide de gaz residuel contenant de l'ozone Download PDF

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Publication number
EP0791101B1
EP0791101B1 EP95938081A EP95938081A EP0791101B1 EP 0791101 B1 EP0791101 B1 EP 0791101B1 EP 95938081 A EP95938081 A EP 95938081A EP 95938081 A EP95938081 A EP 95938081A EP 0791101 B1 EP0791101 B1 EP 0791101B1
Authority
EP
European Patent Office
Prior art keywords
condensate
ozone
gas
residual gas
pulp
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.)
Expired - Lifetime
Application number
EP95938081A
Other languages
German (de)
English (en)
Other versions
EP0791101A1 (fr
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/fr
Application granted granted Critical
Publication of EP0791101B1 publication Critical patent/EP0791101B1/fr
Anticipated expiration legal-status Critical
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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 bleaching of chemical paper pulp with gas containing an oxidizing agent, especially paper pulp which is produced by the kraft pulp process.
  • the inven-tion concerns a method for utilizing the remaining content of oxidizing agent, preferably ozone, in the residual gas after the bleaching by using the residual gas for the purifying treatment of malodorous condensate from a process for producing paper or paper pulp, wherein the malodourous condensate is used as a liquid seal being able to separate out residual fibres in the residual gas.
  • 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.
  • a distinction is made between different types of condensate since they have different contents of impurities.
  • the black liquor is normally concentrated by evaporation in several stages.
  • the units, which are termed effects, are numbered in accordance with the route of steam supply within the plant.
  • 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.
  • Cooking department condensate and heavily contaminated condensate from the black liquor evaporation is normally conveyed to a steam stripper for purification.
  • a steam stripper usually separates off methanol, ethanol, terpenes and malodorous sulphur compounds (hydrogen sulphide, methylmercaptan, dimethyl sulphide and dimethyl disulphide, etc.) very efficiently.
  • the contaminants which have been separated off are obtained in a concentrated stream which has to be dealt with. It is usually conveyed away and combusted.
  • Condensate which has been treated in a steam stripper often has a very low content of COD.
  • Malodorous compounds which remain in the stripped condensate are, apart from traces of hydrogen sulphide, a number of terpenes such as ocimene, alfapinene, delta-3-carene and decanal. These substances do not smell as badly as the sulphur compounds which are otherwise common in malodorous condensates.
  • the evaporation condensates which are not so heavily contaminated are often termed "pure condensates".
  • the problem is that they, nevertheless, contain some malodorous impurities.
  • malodorous 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.
  • phase change e.g. stripping and adsorption with active charcoal
  • biological treatment 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 4,780,287, US 4,792,407, US 4,849,114 and US 4,941,957) for the treatment of gas or water which relate to a purification method which combines ozone, hydrogen peroxide and UV light.
  • the method makes use of the fact that the UV light breaks ozone and hydrogen peroxide down into very reactive OH radicals which, in turn, break organic matter in the water down into carbon dioxide, water and inorganic salts.
  • a method for making use of the residual gas from bleaching with gas containing an oxidizing agent, preferably ozone, and utilizing its remaining content of oxidizing agent , preferably ozone, for treating contaminated and malodorous condensate so that this condensate can be reused in the pulp manufacturing process.
  • an oxidizing agent preferably ozone
  • 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.
  • ozone destroyer a small quantity 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 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 temperature 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 conveyed, via a pipeline, to a blow tank (3). Consequently, 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 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 countercurrent 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 evaporation, 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). Volatile substances are then given off more readily and can be attacked by the ozone or oxygen. It is also advantageous 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 oxygen has 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 volatile 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 substances 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. If a higher concentration of ozone is required in the gas, 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 freedom 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 substances, or any remaining unused ozone, can be destroyed.
  • the condensate which is to be treated constitutes liquid in the liquid seal (5) for separating out fibres from the residual gas from the ozone bleaching.
  • the condensate (8) is preferably supplied continuously to the water seal.
  • the major advantage of the method according to the invention is that the remainder of a chemical which is utilized internally for bleaching, i.e. ozone, can be used in another process stage. As a result, use of the ozone is optimized at the same time as condensate is purified.
  • 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 temperature 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.
  • the condensate to be 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 incoming condensate (8) is heated to at least boiling temperature before it is conveyed into the cyclone (4), wherein the pressure in the cyclone (4) is at least 0.3 bar (absolute), perferably at least 1 bar, and wherein the average temperature in the cyclone is at least 65°C, preferably least 95°C.
  • 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.
  • such an oxidizing agent can be used to complement an ozone plant according to the invention.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
  • Treating Waste Gases (AREA)

Claims (10)

  1. Procédé associé à la production de pâte à papier chimique, dans lequel un gaz contenant un agent oxydant, de préférence de l'ozone, est utilisé pour le traitement du condensat (8), qui est obtenu dans la production de papier ou de pâte à papier, caractérisé en ce qu'une suspension de pâte est amenée en contact avec le gaz contenant un agent oxydant, après quoi le gaz résiduel (6) ayant une teneur restante partielle d'agent oxydant, est séparé de la suspension de pâte, et que ledit gaz résiduel est utilisé pour le traitement de l'odeur de condensat malodorant (8), avec une teneur relativement faible de COD et que le condensat (8) est utilisé dans un joint liquide (5) pour séparer les fibres résiduelles du gaz résiduel (6).
  2. Procédé selon la revendication 1, caractérisé en ce que le gaz résiduel (6) qui est séparé de la suspension de pâte consiste en un gaz support qui est principalement composé d'oxygène ou d'air, gaz support qui en plus contient au moins 0,3% en poids, de préférence au moins 0,5% en poids, et même plus préférablement au moins 1% en poids, d'ozone.
  3. Procédé selon la revendication 1, caractérisé en ce que le condensat impur (8) est dérivé d'une ou plusieurs unités pour évaporer la liqueur noire.
  4. Procédé selon les revendications 1 ou 3, caractérisé en ce que le condensat purifié (9) est utilisé dans la récupération chimique ou comme liquide de lavage dans la ligne de la fibre.
  5. Procédé selon les revendications 1 ou 3, caractérisé en ce que le condensat purifié (9) est utilisé comme liquide de lavage dans le lavage des boues résiduaires de chaux ou dans une étape de blanchiment contenant du peroxyde.
  6. Procédé selon les revendications 1 ou 3, caractérisé en ce que le condensat est purifié à un degré tellement élevé qu'il peut être utilisé pour finalement laver la pâte.
  7. Procédé selon la revendication 1, caractérisé en ce que le condensat purifié (9) est transporté pour être déchargé, si approprié après purification biologique.
  8. Procédé selon la revendication 1, caractérisé en ce que le condensat impur est amené à un élément de joint aqueux (4) pour le traitement par le gaz résiduel si bien que les fibres résiduelles sont aussi séparées du gaz résiduel (6).
  9. Procédé selon la revendication 1, caractérisé en ce que le condensat (8) est purifié au moyen du contact intime avec le gaz résiduel contenant de l'ozone dans une tour de contact à contre-courant (7).
  10. Procédé selon la revendication 9, caractérisé en ce que le condensat entrant (8) est chauffé à au moins la température d'ébullition avant qu'il soit transporté dans la tour de contact (7), en ce que la pression dans la tour de contact est au moins de 0,3 bar (absolu), de préférence au moins 1 bar, et en ce que la température moyenne dans la tour de contact est d'au moins 65°C, de préférence d'au moins 95°C.
EP95938081A 1994-11-08 1995-10-17 Traitement des odeurs de condensats malodorants a l'aide de gaz residuel contenant de l'ozone Expired - Lifetime EP0791101B1 (fr)

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 (fr) 1994-11-08 1995-10-17 Traitement des odeurs de condensats malodorants a l'aide de gaz residuel contenant de l'ozone

Publications (2)

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

Family

ID=20395879

Family Applications (1)

Application Number Title Priority Date Filing Date
EP95938081A Expired - Lifetime EP0791101B1 (fr) 1994-11-08 1995-10-17 Traitement des odeurs de condensats malodorants a l'aide de gaz residuel contenant de l'ozone

Country Status (6)

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

Families Citing this family (2)

* 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
TW590789B (en) 2001-09-14 2004-06-11 Ind Tech Res Inst Method of treating an air stream containing VOCs

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
CA2107764A1 (fr) * 1992-03-02 1993-09-16 Lawrence A. Hinkey Methode combinee de destruction de l'ozone et de lavage de la fibre dans un moulin a papier

Also Published As

Publication number Publication date
EP0791101A1 (fr) 1997-08-27
ATE203292T1 (de) 2001-08-15
DE69521809T2 (de) 2002-04-04
AU3884295A (en) 1996-05-31
DE69521809D1 (de) 2001-08-23
WO1996014464A1 (fr) 1996-05-17
SE9403818D0 (sv) 1994-11-08
SE9403818L (sv) 1996-05-09

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