CA2107764A1 - Combined ozone destruction and fiber scrubbing in paper pulp mills - Google Patents
Combined ozone destruction and fiber scrubbing in paper pulp millsInfo
- Publication number
- CA2107764A1 CA2107764A1 CA002107764A CA2107764A CA2107764A1 CA 2107764 A1 CA2107764 A1 CA 2107764A1 CA 002107764 A CA002107764 A CA 002107764A CA 2107764 A CA2107764 A CA 2107764A CA 2107764 A1 CA2107764 A1 CA 2107764A1
- Authority
- CA
- Canada
- Prior art keywords
- ozone
- recited
- stream
- stage
- 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.)
- Abandoned
Links
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 title claims abstract description 88
- 239000000835 fiber Substances 0.000 title claims abstract description 24
- 238000005201 scrubbing Methods 0.000 title claims abstract description 18
- 229920001131 Pulp (paper) Polymers 0.000 title claims abstract description 16
- 230000006378 damage Effects 0.000 title claims description 12
- 239000007788 liquid Substances 0.000 claims abstract description 36
- 239000007789 gas Substances 0.000 claims abstract description 35
- 238000004061 bleaching Methods 0.000 claims abstract description 28
- 239000002699 waste material Substances 0.000 claims abstract description 13
- 239000011368 organic material Substances 0.000 claims abstract description 9
- LSNNMFCWUKXFEE-UHFFFAOYSA-N Sulfurous acid Chemical compound OS(O)=O LSNNMFCWUKXFEE-UHFFFAOYSA-N 0.000 claims abstract description 5
- 238000000034 method Methods 0.000 claims description 28
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 14
- 239000001301 oxygen Substances 0.000 claims description 14
- 229910052760 oxygen Inorganic materials 0.000 claims description 14
- 238000011084 recovery Methods 0.000 claims description 9
- 239000000706 filtrate Substances 0.000 claims description 7
- 235000010267 sodium hydrogen sulphite Nutrition 0.000 claims description 7
- DWAQJAXMDSEUJJ-UHFFFAOYSA-M Sodium bisulfite Chemical compound [Na+].OS([O-])=O DWAQJAXMDSEUJJ-UHFFFAOYSA-M 0.000 claims description 6
- 238000000605 extraction Methods 0.000 claims description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 5
- 239000012530 fluid Substances 0.000 claims description 2
- 230000008569 process Effects 0.000 claims description 2
- 239000002002 slurry Substances 0.000 claims description 2
- 238000005406 washing Methods 0.000 claims description 2
- 238000004076 pulp bleaching Methods 0.000 claims 2
- LSNNMFCWUKXFEE-UHFFFAOYSA-M Bisulfite Chemical compound OS([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-M 0.000 abstract description 5
- 239000007844 bleaching agent Substances 0.000 description 4
- 239000012159 carrier gas Substances 0.000 description 4
- 230000003197 catalytic effect Effects 0.000 description 4
- 239000010808 liquid waste Substances 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 3
- 239000002912 waste gas Substances 0.000 description 3
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 2
- 239000000460 chlorine Substances 0.000 description 2
- 229910052801 chlorine Inorganic materials 0.000 description 2
- OSVXSBDYLRYLIG-UHFFFAOYSA-N dioxidochlorine(.) Chemical compound O=Cl=O OSVXSBDYLRYLIG-UHFFFAOYSA-N 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- BSYNRYMUTXBXSQ-UHFFFAOYSA-N Aspirin Chemical compound CC(=O)OC1=CC=CC=C1C(O)=O BSYNRYMUTXBXSQ-UHFFFAOYSA-N 0.000 description 1
- 239000004155 Chlorine dioxide Substances 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 235000019398 chlorine dioxide Nutrition 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000007872 degassing Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 239000002655 kraft paper Substances 0.000 description 1
- 238000002386 leaching Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- MYWUZJCMWCOHBA-VIFPVBQESA-N methamphetamine Chemical compound CN[C@@H](C)CC1=CC=CC=C1 MYWUZJCMWCOHBA-VIFPVBQESA-N 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- PVGBHEUCHKGFQP-UHFFFAOYSA-N sodium;n-[5-amino-2-(4-aminophenyl)sulfonylphenyl]sulfonylacetamide Chemical compound [Na+].CC(=O)NS(=O)(=O)C1=CC(N)=CC=C1S(=O)(=O)C1=CC=C(N)C=C1 PVGBHEUCHKGFQP-UHFFFAOYSA-N 0.000 description 1
- 239000002351 wastewater Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/66—Ozone
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D50/00—Combinations of methods or devices for separating particles from gases or vapours
- B01D50/40—Combinations of devices covered by groups B01D45/00 and B01D47/00
-
- 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
-
- 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
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Analytical Chemistry (AREA)
- Biomedical Technology (AREA)
- Environmental & Geological Engineering (AREA)
- Health & Medical Sciences (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Life Sciences & Earth Sciences (AREA)
- Wood Science & Technology (AREA)
- Paper (AREA)
- Treating Waste Gases (AREA)
Abstract
The off gases from an ozone bleaching stage of a paper pulp mill are treated so as to simultaneously destroy ozone in the off gases, and remove fibers (32) entrained in the off gases without the need for an ozone thermal destruct system. The gases are passed into a catenary grid (20) or venturi type scrubber using an alkaline liquid (28) containing dissolved organic material as the scrubbing liquid. The scrubbing liquid preferably is a waste liquid stream from another bleaching stage, such as from an Eo stage (29) having a pH of 9.0 or higher, or a bisulfite liquid stream from a sulfite mill (29).
Description
WO 93tl8226 PCr/US93/01 144 ~ 21~)776~
COMBINED OZONE DESTRUCTION AND EIBER
SCRUBBING IN PAPER PULP MIL~S
BACKGROUND AND SUMMARY OF THE INVENTION
In the treatment of chemical paper pulps, ozone bleaching is becoming commercially accepted. A number of different ozone bleaching systems and procedures have been developed for treating pulp with varying consistencies.
These systems hold promise for greatly reducing the reliance on chlorine that presently exists in commercial pulp mills, and thereby avoid the environmental consequ~nces associated with chlorine bleaching. In typical ozone bleaching sequences, the ozone with oxygen as a carrier gas is intimately mixed with the pulp and, after a relatively short reaction time, the carrier gas with any remaining ozone is separated from the pulp utilizing a wide variety of different mechanisms. After the separation, for safety and in order to comply with good environmental techni~ues, it is necessary to destroy the residual ozone in the off-gas from the ozone bleaching stage. This is typically done utilizing a separate thermal or catalytic destruct system.
According to the invention, it has been determined that there is some cellulosic fiber in the waste gas stream from an ozone (Z) bleach stage. In a commercial installation, it i8 highly deslrable to remove the organic fiber before exhausting or recovering oxygen from the o-gases, and it i8 undesirable to feed fiber to the thermal ozone destruct system.
According to the present invention, the problems of removing fiber and unreacted ozone from the off-gases from a Z stage are solved simultaneously in a relatively inexpensive and eicient manner. Also, at the same time, the chemical oxygen demand ~COD) of a liquid waste stream in the pulp mill may be simultaneously reduced, in the same reaction in which ozone is destroyed.
.
210776~ -2-It is known from the treatment of waste water with ozone, such as shown in U.S. patents 3,546,114 and 4,007,118, that ozone will react with dissolved organic material in a liquid stream and that at alkaline pH levels, the rate of reaction is highest. Utilizing this information, according to the present invention a method and apparatus are provided which scrub the fibers from the off-gas stream of an ozone bleaching stage with a liquid containing dissolved organic material, preferably at an alkaline pH, so that not only does the scrubbing liquid effectively remove the fibers from the gas stream, but also reacts with the ozo~e, causing destruction of the ozone and eliminating the need for a separate thermal ozone destruct device.
According to one aspec. of the present invention, there is provided a method of simultaneously removing organic fibers and destroying ozone in a primarily gaseous stream containing organic fibers and ozone. The method comprises, in its most basic, broadest form, the step of (a) scrubbing the gaseous ctream with an alkaline liquid containing dissolved organic material. Preferably, the ~crubbing liquid is a liquid waste stream from a bleaching ~tage of the pulp mill, such a~ filtrate Ll-om an alkaline extraction stage such as an Eo stage at a pH of above about 9.~, or bisulfite containing liquid from a sulite mill.
Step (a) i~ preferably practiced in a catellary grid type ~crubber although it may also be practiced ~n a venturi type scrubber or the like. Also there is preferably the furthor step of pas~ing the scrubbed gaseous stream to oxygon recovery or atmosphere exhaust without the necessity o~ pa~alng it through a reparate ozone destruction ctage ~-uch a~ a thermal or catalytic stage), or at lea~t minimizing the ~ize o~ the thermal or catalytic stage.
Whore a catenary grid type scrubber is utilized, there is WO 93/1 8226 PCr/US93/0 1 1 4 1 - ~lQ776 1 .
also the step of further scrubbing (washing) the stream with water between the scrubbing with the alkaline liquid and the discharge from the scrubber.
According to another aspect of the present invention there is provided a meth~d of treating fluids and slurries from a paper pulp producing process, in a mill containing a plurality of different bleaching stages, including at least one ozone stage. The method comprises the steps of:
(a) bleaching paper pulp with ozone to produce bleached pulp and a gaseous stream containing oxygen, residual ozone, and organic fibers; and (b) simultaneously effectively removing the organic fibers and ozone from the gaseous steam from step (a) by bringing the gaseous stream into scrubbing contact with a waste liquid stream form one of the bleaching stages besides an ozone stage, or bisulfite liquid from a sulfite mill.
The scrubbing liquid is preferably as described above, and in some circumstances (e.g. if bisulfite liquid is used as the scrubbing liquid), a scrubbed gaseous stream can be passed to oxygen recovery or atmosphere e~ha~lst without pa~ing it through another special ozone destruction stage.
According to a still further aspect of the present invention, there is provided a system for treating paper pulp and off-gases rom paper pulp processing. The system hao the ollowing elements: An ozone bleaching vessel h~ving a pulp outlet. A means or separating the vast ma~ority o the pulp flbers from of gases in the ozone ~leaching ves8-l to produce a gaseous stream. A scrubber havln~ a gas discharge. A flrst conduit connecting the aerubber diroctly to tho moan3 or ~eparating pulp ibers ~rom o~f ga~e8. A ~ocond bl-aching ve~sel diQtinct from ~he ozone bleaching vessel, and having a waste liquid ~tre~m di8charge; and a second conduit connecting the :
, W093/18226 PCT/US93/011~
.
` 2~7764 -4-second bleaching vessel waste liquid stream discharge to the scrubber. Also, al1 oxygen recovery or an atmosphere . -exhaust zpparatus is preferably directly connected to the gas discharge from the scrubber without intervention of ~eparate apparatus specifically for ozone destruction, although a reduced size (compared to conventional) separate ozone destruction apparatus may be necessary in many circumstances. The scrubber preferably comprises a catenary grid type scrubber, although a venturi type or the like may be used.
It is a primary object of the present invention to provide a simple yet effective method for eliminating an ozone thermal destruct system in a Z bleacll stage in a pulp mill, while simultaneously removing organic fibers and ozone from the gaseous stream associated with the ozone bleach stage. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.
BRIEF DESCRIPTION OF THE DR~WINGS
FIGURE l is a schematic representation of an exemplary prior art system for ozone bleaching and destruction; and FIGURE 2 is a 8chematic representation ~howing a oy8tem for treating paper pulp, and off gafie~ from paper pulp procec~lng, according to the invention whlch effect pr~ctice of the method according to the inventlon.
DETAILED DESCRIPTION OF THE DRAWINGS
An exemplary conventional system for ozone bleaching pulp ~nd then handllng the residual ozone in tlle off gases WO93/1~26 PCT/US93/011~
,- . 21~77~
is illustrated schematically in FIGURE 1. The ozone bleach stage/vessel is illustrated schematically by reference numeral 10 and may be of any co~lventional type for treating ozone of low, medium, or high consistency. For example, in a medium-consistency system, a mixer 11 may be utilized to which pulp and ozone in a carrier gas (primarily oxygen) are ~upplied. The ozone typically is about 2-14% by weight of the gas supplied to mixer 11. After ozone bleaching, the pulp with entrained gas passes into outlet conduit 12 and then proceeds to a device 13 for separating the gas from the pulp. The device 13 may comprise any suitable conventional device such as a cyclone, degassing pump, particularly shaped vessel, etc. The conduit 14 extending from the top of the separating device 13 contains a gas stream which is primarily a carrier gas b~t also includes a small amount of residual ozone, and also -- depending upon the ozone stage 10 and device 13 -- a small amount of organic fiber. Conduit 14 leads to an ozone destruction device 15 such as a thermal destruct system and ultimately the gas steam, with the ozone removed, passes on to apparatus 16 for oxygen recovery and/or atmosphere exhaust.
FIGURE 2 illustrates a system according to the invention having the components 10 through 14 the same as in tho prlor art of FIGURE 1. The conduit 14 -- containing a gas stream with some ozone and organic fiber -- is dlrectly connectod to a scrubber 20 inlet 21. The scrubber 20 illu~tratod ln FIGURE 2 is a catenary grid type ccrubber, whlch is a type often used to scrub the waste gas from chlorine dioxide htagos in conventional pulp bleach pl~nt~. It includos a vossel 22 mounting A plurality of ~rids 23 through which the gas stream passes (flowing upwardly), the grids 23 typically vertically spaced about 2 ~eot. Ultimately the gas passes to the vanes 24, and then W093/18226 PCT/US93/~1144 f~ .
.....
210776~ -6-through an outlet 25 in the top of the vessel 22. The vessel 22 may have a diameter of about 14 inches at the bottom and 18 inches at the top. The height of the vessel may be on the order of 15-1/2 feet.
The scrubbing liquid for the gas flowing upwardly in the vessel 22 is supplied by inlet 2~. The scrubbing liquid prefera~ly is a waste liquid stream from another bleaching stage (besides an ozone stage) in the pulp mill, preferably an alkaline stage (e. g. an alXaline extraction stage), such as an Eo stage, at a pH of about 9.0 or higher (e.g. about 9-11).
In a sulfitè pulp mill (as opposed to a kraft mill), it i5 po~sible to use a stream containing sodium bisulfite a~ the ~crubbing liquid, and thereby remove a very high fraction of the residual ozone from the gas stream.
FIGURE 2 illustrates a conduit 28 from an Eo stage 29 supplying filtrate from the wash part of the Eo stage 29 to the inlet 27. Such liquid is alkaline, typically having a pH o over about 9 (e.g. about 9-11). Source 29' is a conventional, already existing, source of bisulfite liquid ln a sulfite mill.
The liquid which has scrubbed the gas, and has thus removed the organic fiberc from it, is discharged from the outlot 31 at the bottom of the vessel 22. Fibers in the undorflow from outlet 31 may be recovered by filtering in a ~uitable fiber recovery device 32, such as a drum filter, flat w reon, pressure scroen, etc.
Utlllzing the catenary grid type scrubber 20, it is aloo d-sirable to ocrub or wash the gas with water at the vano asoembly 24. Vane wash water ~typically about l/lB
tho volumo of the alkallne liquid ~upplied in conduit 28) lo ~prayod upwardly -- utilizing spr~y head 33 -- to the vane assembly 24, being oupplied with water source 34.
W093/18226 PCT/US93/011~
( 2~077~
Ultimately, the gas discharged from the outlet 25 at the top of the vessel 22 passes through conduit 36 directly to an ozone destruct unit (not shown, but like the unit 15 in FIGURE 1 only typically having a smaller size), and then to the oxygen recovery and/or atmosphere exhaust 16. In some circumstances, depending upon the efficiency of the ozone reactions in the scrubber 20, the original content of ozone in the waste gas, etc., the ozone destruct unit can be eliminated completely.
Because the waste liquid stream in conduit 28 which is used to scrub the gas stream in scrubber 20 has diss~lved organic material, at least a significant portion, and often the majority, of residual ozone is destroyed during the scrubbing action, reacting with the dissolved organic material in the waste liquor stream. Also since the stream is preferably alkaline, decomposition is enhanced since ozone is unstable in aqueous solutions at high pH levels.
The residual ozone which does react with the dissolved ~olid material in the filtrate will partially oxidize the dlssolved material, and reduce the COD if the filtrate is sub~equently released to the environment.
While a catenary grid type scrubber 20 is illustrated in the drawings, other types of scrubbers also could be utllized, ~uch as a venturi type scrubber.
It will thus be ~een that the system of FIGURE 2 minimi~es ~or even eliminates) the need for the thermal or catalytic ozono destruct system and performs the functions o w rubbing ibers from an exhaust gas stream of an ozone ble~chlng ~tago 10, and dostroys the residual ozone th~roin, ~imultanoously, utilizing a liquid waste stream ulroady exl~tlng in tho mill. Thus, the ozone and fibers aro romoved in an officient and offective manner, and ~imultaneou~ly the COD of a liquid waste stream is reduced WO93/18226 PCTtUS93/011~
l_ 210776'~ -8-The following table illustrates the effectiveness of a waste stream having dissolved organic material in destroying ozone. The tests reported in the Table were done using an ozone generator connected to a mixer in which pulp was optionally mixed with the ozone for twenty four seconds in each test, and then to another station in which a destructor liquid was optionally mixed with the ozone and, if present, pulp, and finally to an ozone residual meter. For tests 3 and 4, sodium bisulfite tNaHS03), equivalent of 6% S02, was used as the destructor (scrubbi~g liquid); for tests 5 and 6 alkaline extraction waste liquor having a p~ greater than 9.0 (Alk. Ext.) was used; and for ~amples 1 and 2 no destructor was used. The original ozone charge was 0.24 g in each case, the oxygen flow rate 15.0 SCFM, the ozone concentration 6.0%, and the temperature 25.0 degrees C. The indication ''I'' means that pulp was mixed with the ozone (and, if present, the destructor), and "-" indicates no pulp was mixed with the ozonc (and, if preeent, the destructor). The Refiidual 03 tRes. 03) after treatment is in grams. Efficiency (Eff.), in percent, is determined by dividing the amount of ozone removed by the maximum amount that could be removed tO.078 in the tests reported).
TABLE
~eet #Pul~ De~tructor Res. 03 Eff.
1 - - 0.2~0 2 ~ - 0.078 3 ~ NaHS03 0.0 100 4 - NaHS03 0.005 9~
S ~ Akl. Ext. 0.040 49 6 - Akl. Ext. 0.200 17 W093/18226 PCT/US93/011~
21~77~
g , : `
It will thus be seen that most effective at removing ozone is a sodium bisulfite stream with pulp (dissolved organic material), however an alkaline extraction stream with pulp, and a sodium bisulfite stream without pulp, are al~o very effective.
While the invention has been herein shown and described and was presently conceived to be most practical and preferred embodiment thereof, it will be apparent to those of ordinary skill in the art that many modifications may be made thereo~ within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent methods and systems.
COMBINED OZONE DESTRUCTION AND EIBER
SCRUBBING IN PAPER PULP MIL~S
BACKGROUND AND SUMMARY OF THE INVENTION
In the treatment of chemical paper pulps, ozone bleaching is becoming commercially accepted. A number of different ozone bleaching systems and procedures have been developed for treating pulp with varying consistencies.
These systems hold promise for greatly reducing the reliance on chlorine that presently exists in commercial pulp mills, and thereby avoid the environmental consequ~nces associated with chlorine bleaching. In typical ozone bleaching sequences, the ozone with oxygen as a carrier gas is intimately mixed with the pulp and, after a relatively short reaction time, the carrier gas with any remaining ozone is separated from the pulp utilizing a wide variety of different mechanisms. After the separation, for safety and in order to comply with good environmental techni~ues, it is necessary to destroy the residual ozone in the off-gas from the ozone bleaching stage. This is typically done utilizing a separate thermal or catalytic destruct system.
According to the invention, it has been determined that there is some cellulosic fiber in the waste gas stream from an ozone (Z) bleach stage. In a commercial installation, it i8 highly deslrable to remove the organic fiber before exhausting or recovering oxygen from the o-gases, and it i8 undesirable to feed fiber to the thermal ozone destruct system.
According to the present invention, the problems of removing fiber and unreacted ozone from the off-gases from a Z stage are solved simultaneously in a relatively inexpensive and eicient manner. Also, at the same time, the chemical oxygen demand ~COD) of a liquid waste stream in the pulp mill may be simultaneously reduced, in the same reaction in which ozone is destroyed.
.
210776~ -2-It is known from the treatment of waste water with ozone, such as shown in U.S. patents 3,546,114 and 4,007,118, that ozone will react with dissolved organic material in a liquid stream and that at alkaline pH levels, the rate of reaction is highest. Utilizing this information, according to the present invention a method and apparatus are provided which scrub the fibers from the off-gas stream of an ozone bleaching stage with a liquid containing dissolved organic material, preferably at an alkaline pH, so that not only does the scrubbing liquid effectively remove the fibers from the gas stream, but also reacts with the ozo~e, causing destruction of the ozone and eliminating the need for a separate thermal ozone destruct device.
According to one aspec. of the present invention, there is provided a method of simultaneously removing organic fibers and destroying ozone in a primarily gaseous stream containing organic fibers and ozone. The method comprises, in its most basic, broadest form, the step of (a) scrubbing the gaseous ctream with an alkaline liquid containing dissolved organic material. Preferably, the ~crubbing liquid is a liquid waste stream from a bleaching ~tage of the pulp mill, such a~ filtrate Ll-om an alkaline extraction stage such as an Eo stage at a pH of above about 9.~, or bisulfite containing liquid from a sulite mill.
Step (a) i~ preferably practiced in a catellary grid type ~crubber although it may also be practiced ~n a venturi type scrubber or the like. Also there is preferably the furthor step of pas~ing the scrubbed gaseous stream to oxygon recovery or atmosphere exhaust without the necessity o~ pa~alng it through a reparate ozone destruction ctage ~-uch a~ a thermal or catalytic stage), or at lea~t minimizing the ~ize o~ the thermal or catalytic stage.
Whore a catenary grid type scrubber is utilized, there is WO 93/1 8226 PCr/US93/0 1 1 4 1 - ~lQ776 1 .
also the step of further scrubbing (washing) the stream with water between the scrubbing with the alkaline liquid and the discharge from the scrubber.
According to another aspect of the present invention there is provided a meth~d of treating fluids and slurries from a paper pulp producing process, in a mill containing a plurality of different bleaching stages, including at least one ozone stage. The method comprises the steps of:
(a) bleaching paper pulp with ozone to produce bleached pulp and a gaseous stream containing oxygen, residual ozone, and organic fibers; and (b) simultaneously effectively removing the organic fibers and ozone from the gaseous steam from step (a) by bringing the gaseous stream into scrubbing contact with a waste liquid stream form one of the bleaching stages besides an ozone stage, or bisulfite liquid from a sulfite mill.
The scrubbing liquid is preferably as described above, and in some circumstances (e.g. if bisulfite liquid is used as the scrubbing liquid), a scrubbed gaseous stream can be passed to oxygen recovery or atmosphere e~ha~lst without pa~ing it through another special ozone destruction stage.
According to a still further aspect of the present invention, there is provided a system for treating paper pulp and off-gases rom paper pulp processing. The system hao the ollowing elements: An ozone bleaching vessel h~ving a pulp outlet. A means or separating the vast ma~ority o the pulp flbers from of gases in the ozone ~leaching ves8-l to produce a gaseous stream. A scrubber havln~ a gas discharge. A flrst conduit connecting the aerubber diroctly to tho moan3 or ~eparating pulp ibers ~rom o~f ga~e8. A ~ocond bl-aching ve~sel diQtinct from ~he ozone bleaching vessel, and having a waste liquid ~tre~m di8charge; and a second conduit connecting the :
, W093/18226 PCT/US93/011~
.
` 2~7764 -4-second bleaching vessel waste liquid stream discharge to the scrubber. Also, al1 oxygen recovery or an atmosphere . -exhaust zpparatus is preferably directly connected to the gas discharge from the scrubber without intervention of ~eparate apparatus specifically for ozone destruction, although a reduced size (compared to conventional) separate ozone destruction apparatus may be necessary in many circumstances. The scrubber preferably comprises a catenary grid type scrubber, although a venturi type or the like may be used.
It is a primary object of the present invention to provide a simple yet effective method for eliminating an ozone thermal destruct system in a Z bleacll stage in a pulp mill, while simultaneously removing organic fibers and ozone from the gaseous stream associated with the ozone bleach stage. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.
BRIEF DESCRIPTION OF THE DR~WINGS
FIGURE l is a schematic representation of an exemplary prior art system for ozone bleaching and destruction; and FIGURE 2 is a 8chematic representation ~howing a oy8tem for treating paper pulp, and off gafie~ from paper pulp procec~lng, according to the invention whlch effect pr~ctice of the method according to the inventlon.
DETAILED DESCRIPTION OF THE DRAWINGS
An exemplary conventional system for ozone bleaching pulp ~nd then handllng the residual ozone in tlle off gases WO93/1~26 PCT/US93/011~
,- . 21~77~
is illustrated schematically in FIGURE 1. The ozone bleach stage/vessel is illustrated schematically by reference numeral 10 and may be of any co~lventional type for treating ozone of low, medium, or high consistency. For example, in a medium-consistency system, a mixer 11 may be utilized to which pulp and ozone in a carrier gas (primarily oxygen) are ~upplied. The ozone typically is about 2-14% by weight of the gas supplied to mixer 11. After ozone bleaching, the pulp with entrained gas passes into outlet conduit 12 and then proceeds to a device 13 for separating the gas from the pulp. The device 13 may comprise any suitable conventional device such as a cyclone, degassing pump, particularly shaped vessel, etc. The conduit 14 extending from the top of the separating device 13 contains a gas stream which is primarily a carrier gas b~t also includes a small amount of residual ozone, and also -- depending upon the ozone stage 10 and device 13 -- a small amount of organic fiber. Conduit 14 leads to an ozone destruction device 15 such as a thermal destruct system and ultimately the gas steam, with the ozone removed, passes on to apparatus 16 for oxygen recovery and/or atmosphere exhaust.
FIGURE 2 illustrates a system according to the invention having the components 10 through 14 the same as in tho prlor art of FIGURE 1. The conduit 14 -- containing a gas stream with some ozone and organic fiber -- is dlrectly connectod to a scrubber 20 inlet 21. The scrubber 20 illu~tratod ln FIGURE 2 is a catenary grid type ccrubber, whlch is a type often used to scrub the waste gas from chlorine dioxide htagos in conventional pulp bleach pl~nt~. It includos a vossel 22 mounting A plurality of ~rids 23 through which the gas stream passes (flowing upwardly), the grids 23 typically vertically spaced about 2 ~eot. Ultimately the gas passes to the vanes 24, and then W093/18226 PCT/US93/~1144 f~ .
.....
210776~ -6-through an outlet 25 in the top of the vessel 22. The vessel 22 may have a diameter of about 14 inches at the bottom and 18 inches at the top. The height of the vessel may be on the order of 15-1/2 feet.
The scrubbing liquid for the gas flowing upwardly in the vessel 22 is supplied by inlet 2~. The scrubbing liquid prefera~ly is a waste liquid stream from another bleaching stage (besides an ozone stage) in the pulp mill, preferably an alkaline stage (e. g. an alXaline extraction stage), such as an Eo stage, at a pH of about 9.0 or higher (e.g. about 9-11).
In a sulfitè pulp mill (as opposed to a kraft mill), it i5 po~sible to use a stream containing sodium bisulfite a~ the ~crubbing liquid, and thereby remove a very high fraction of the residual ozone from the gas stream.
FIGURE 2 illustrates a conduit 28 from an Eo stage 29 supplying filtrate from the wash part of the Eo stage 29 to the inlet 27. Such liquid is alkaline, typically having a pH o over about 9 (e.g. about 9-11). Source 29' is a conventional, already existing, source of bisulfite liquid ln a sulfite mill.
The liquid which has scrubbed the gas, and has thus removed the organic fiberc from it, is discharged from the outlot 31 at the bottom of the vessel 22. Fibers in the undorflow from outlet 31 may be recovered by filtering in a ~uitable fiber recovery device 32, such as a drum filter, flat w reon, pressure scroen, etc.
Utlllzing the catenary grid type scrubber 20, it is aloo d-sirable to ocrub or wash the gas with water at the vano asoembly 24. Vane wash water ~typically about l/lB
tho volumo of the alkallne liquid ~upplied in conduit 28) lo ~prayod upwardly -- utilizing spr~y head 33 -- to the vane assembly 24, being oupplied with water source 34.
W093/18226 PCT/US93/011~
( 2~077~
Ultimately, the gas discharged from the outlet 25 at the top of the vessel 22 passes through conduit 36 directly to an ozone destruct unit (not shown, but like the unit 15 in FIGURE 1 only typically having a smaller size), and then to the oxygen recovery and/or atmosphere exhaust 16. In some circumstances, depending upon the efficiency of the ozone reactions in the scrubber 20, the original content of ozone in the waste gas, etc., the ozone destruct unit can be eliminated completely.
Because the waste liquid stream in conduit 28 which is used to scrub the gas stream in scrubber 20 has diss~lved organic material, at least a significant portion, and often the majority, of residual ozone is destroyed during the scrubbing action, reacting with the dissolved organic material in the waste liquor stream. Also since the stream is preferably alkaline, decomposition is enhanced since ozone is unstable in aqueous solutions at high pH levels.
The residual ozone which does react with the dissolved ~olid material in the filtrate will partially oxidize the dlssolved material, and reduce the COD if the filtrate is sub~equently released to the environment.
While a catenary grid type scrubber 20 is illustrated in the drawings, other types of scrubbers also could be utllized, ~uch as a venturi type scrubber.
It will thus be ~een that the system of FIGURE 2 minimi~es ~or even eliminates) the need for the thermal or catalytic ozono destruct system and performs the functions o w rubbing ibers from an exhaust gas stream of an ozone ble~chlng ~tago 10, and dostroys the residual ozone th~roin, ~imultanoously, utilizing a liquid waste stream ulroady exl~tlng in tho mill. Thus, the ozone and fibers aro romoved in an officient and offective manner, and ~imultaneou~ly the COD of a liquid waste stream is reduced WO93/18226 PCTtUS93/011~
l_ 210776'~ -8-The following table illustrates the effectiveness of a waste stream having dissolved organic material in destroying ozone. The tests reported in the Table were done using an ozone generator connected to a mixer in which pulp was optionally mixed with the ozone for twenty four seconds in each test, and then to another station in which a destructor liquid was optionally mixed with the ozone and, if present, pulp, and finally to an ozone residual meter. For tests 3 and 4, sodium bisulfite tNaHS03), equivalent of 6% S02, was used as the destructor (scrubbi~g liquid); for tests 5 and 6 alkaline extraction waste liquor having a p~ greater than 9.0 (Alk. Ext.) was used; and for ~amples 1 and 2 no destructor was used. The original ozone charge was 0.24 g in each case, the oxygen flow rate 15.0 SCFM, the ozone concentration 6.0%, and the temperature 25.0 degrees C. The indication ''I'' means that pulp was mixed with the ozone (and, if present, the destructor), and "-" indicates no pulp was mixed with the ozonc (and, if preeent, the destructor). The Refiidual 03 tRes. 03) after treatment is in grams. Efficiency (Eff.), in percent, is determined by dividing the amount of ozone removed by the maximum amount that could be removed tO.078 in the tests reported).
TABLE
~eet #Pul~ De~tructor Res. 03 Eff.
1 - - 0.2~0 2 ~ - 0.078 3 ~ NaHS03 0.0 100 4 - NaHS03 0.005 9~
S ~ Akl. Ext. 0.040 49 6 - Akl. Ext. 0.200 17 W093/18226 PCT/US93/011~
21~77~
g , : `
It will thus be seen that most effective at removing ozone is a sodium bisulfite stream with pulp (dissolved organic material), however an alkaline extraction stream with pulp, and a sodium bisulfite stream without pulp, are al~o very effective.
While the invention has been herein shown and described and was presently conceived to be most practical and preferred embodiment thereof, it will be apparent to those of ordinary skill in the art that many modifications may be made thereo~ within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent methods and systems.
Claims (21)
1. A method of simultaneously removing organic fibers and destroying ozone in a primarily gaseous stream containing organic fibers and ozone, comprising the step of: (a) scrubbing the gaseous stream with an alkaline liquid containing dissolved organic material.
2. A method as recited in claim 1 wherein step (a) is practiced using filtrate from an alkaline extraction stage of a paper pulp bleaching plant.
3. A method as recited in claim 2 wherein step (a) is practiced using filtrate from an Eo stage having a pH of about 9.0 or higher.
4. A method as recited in claim 3 wherein step (a) is practiced in a catenary grid type scrubber.
5. A method as recited in claim 1 wherein step (a) is practiced using a stream of sodium bisulfite.
6. A method as recited in claim 5 comprising the further step (b) of passing the scrubbed gaseous stream to oxygen recovery or atmosphere exhaust without passing it through a separate ozone destruction stage.
7. A method as recited in claim 4 comprising the further atop (c) of washing the scrubbed stream with water between steps (a) and (b).
8. A method as recited in claim 3 wherein step (a) is practiced in a venturi type scrubber.
9. A method as recited in claim 1 wherein step (a) is practiced in a catenary grid type scrubber.
10. A method as recited in claim 1 comprising the further step (b) of supplying the off gases from a paper pulp bleaching stage that uses ozone as the gaseous stream in step (a).
11. A method as recited in claim 10 wherein step (a) is practiced with sodium bisulfite liquid from a sulfite pulp mill.
12. A method of treating fluids and slurries from a paper pulp producing process, in a mill containing a plurality of different bleaching stages, including at least one ozone stage, comprising the steps of:
(a) bleaching paper pulp with ozone to produce bleached pulp and a gaseous stream containing oxygen, residual ozone, and organic fibers; and (b) simultaneously effectively removing the organic fibers and ozone from the gaseous stream from step (a) by bringing the gaseous stream into scrubbing contact with a liquid stream already existing in the pulp mill.
(a) bleaching paper pulp with ozone to produce bleached pulp and a gaseous stream containing oxygen, residual ozone, and organic fibers; and (b) simultaneously effectively removing the organic fibers and ozone from the gaseous stream from step (a) by bringing the gaseous stream into scrubbing contact with a liquid stream already existing in the pulp mill.
13. A method as recited in claim 12 wherein step (b) is practiced using a waste liquid stream from one of the bleaching stages besides an ozone stage.
14. A method as recited in claim 12 wherein the pulp mill is a sulfite mill, and wherein step (b) is practices using a stream of sodium bisulfite.
15. A method as recited in claim 14 comprising the further step (c) of passing the scrubbed gaseous stream from step (b) to oxygen recovery or exhaust without passing it through another special ozone destruction stage.
16. A method as recited in claim 12 wherein step (b) is practiced by bringing the gaseous stream into scrubbing contact with a waste stream from an alkaline bleaching stage.
17. A method as recited in claim 12 wherein step (b) is practiced by bringing the gaseous stream into scrubbing contact with filtrate from an Eo stage having a pH of about 9.0 or higher.
18. A method as recited in claim 12 wherein step (b) is practiced in a catenary grid type scrubber.
19. A system for treating paper pulp and off gases from paper pulp processing, comprising:
an ozone bleaching vessel having an outlet for pulp;
means for separating the vast majority of the pulp fibers from off gases in said ozone bleaching vessel to produce a gaseous stream;
a scrubber having a gas discharge;
a first conduit connecting said scrubber directly to said means for separating pulp fibers from off gases;
a second bleaching vessel distinct from said ozone bleaching vessel, and having a waste liquid stream discharge; and a second conduit connecting said second bleaching vessel waste liquid stream discharge to said scrubber.
an ozone bleaching vessel having an outlet for pulp;
means for separating the vast majority of the pulp fibers from off gases in said ozone bleaching vessel to produce a gaseous stream;
a scrubber having a gas discharge;
a first conduit connecting said scrubber directly to said means for separating pulp fibers from off gases;
a second bleaching vessel distinct from said ozone bleaching vessel, and having a waste liquid stream discharge; and a second conduit connecting said second bleaching vessel waste liquid stream discharge to said scrubber.
20. A system as recited in claim 19 further comprising an oxygen recovery or exhaust apparatus directly connected to said gas discharge from said scrubber, without intervention of separate apparatus specifically for ozone destruction.
21. A system as recited in claim 19 wherein said scrubber comprises a catenary grid type scrubber.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US84306692A | 1992-03-02 | 1992-03-02 | |
| US07/843,066 | 1992-03-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2107764A1 true CA2107764A1 (en) | 1993-09-16 |
Family
ID=25288998
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002107764A Abandoned CA2107764A1 (en) | 1992-03-02 | 1993-02-10 | Combined ozone destruction and fiber scrubbing in paper pulp mills |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA2107764A1 (en) |
| WO (1) | WO1993018226A1 (en) |
| ZA (1) | ZA931384B (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2078276C (en) * | 1992-09-15 | 2004-05-25 | Derek Hornsey | Recovery of oxygen-rich gas from ozone bleaching processes |
| SE9403818L (en) * | 1994-11-08 | 1996-05-09 | Kvaerner Pulping Tech | Method of ozone bleaching |
| PT843757E (en) * | 1995-08-07 | 2000-04-28 | Beloit Technologies Inc | METHOD FOR REPROCESSING A GAS CONTAINING OZONE PRESENT IN A PAPER PASTE BLEACHING INSTALLATION |
| US5695604A (en) * | 1996-08-05 | 1997-12-09 | Beloit Technologies, Inc. | Method for reprocessing an ozone-containing gas present in a pulp bleaching plant |
| US6348129B1 (en) | 2000-04-28 | 2002-02-19 | Praxair Technology Inc | Treatment of pulp mill condensate with ozone |
| SE0003391L (en) * | 2000-09-22 | 2002-03-23 | Metso Paper Inc | Bleaching process and systems therefore |
| ATE277681T1 (en) * | 2000-12-01 | 2004-10-15 | Linde Ag | METHOD FOR PURIFYING EXHAUST GAS FROM A PULP MILL |
| FI20080008L (en) * | 2008-01-08 | 2009-07-09 | Andritz Oy | Treatment of ozone-containing gas in connection with pulp bleaching |
| EP3970835A1 (en) | 2020-09-22 | 2022-03-23 | SUEZ Groupe | Ozone scrubber and ozone scrubbing method |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE343092B (en) * | 1970-06-22 | 1972-02-28 | Mo Och Domsjoe Ab | |
| US4279649A (en) * | 1978-06-16 | 1981-07-21 | Nippon Telegraph And Telephone Public Corporation | Electrical contact material |
-
1993
- 1993-02-10 WO PCT/US1993/001144 patent/WO1993018226A1/en active Application Filing
- 1993-02-10 CA CA002107764A patent/CA2107764A1/en not_active Abandoned
- 1993-02-26 ZA ZA931384A patent/ZA931384B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| ZA931384B (en) | 1993-09-22 |
| WO1993018226A1 (en) | 1993-09-16 |
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