CA2078959A1 - Method of and apparatus for treating malodorous gases - Google Patents
Method of and apparatus for treating malodorous gasesInfo
- Publication number
- CA2078959A1 CA2078959A1 CA002078959A CA2078959A CA2078959A1 CA 2078959 A1 CA2078959 A1 CA 2078959A1 CA 002078959 A CA002078959 A CA 002078959A CA 2078959 A CA2078959 A CA 2078959A CA 2078959 A1 CA2078959 A1 CA 2078959A1
- Authority
- CA
- Canada
- Prior art keywords
- melt
- black liquor
- recited
- dissolving
- gases
- 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
- 239000007789 gas Substances 0.000 title claims abstract description 44
- 238000000034 method Methods 0.000 title claims description 37
- 238000002485 combustion reaction Methods 0.000 claims abstract description 40
- 239000000155 melt Substances 0.000 claims abstract description 38
- 239000000344 soap Substances 0.000 claims abstract description 37
- 239000003546 flue gas Substances 0.000 claims abstract description 31
- CDBYLPFSWZWCQE-UHFFFAOYSA-L sodium carbonate Substances [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims abstract description 28
- 238000011084 recovery Methods 0.000 claims abstract description 23
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims abstract description 15
- 239000007788 liquid Substances 0.000 claims abstract description 15
- 239000000126 substance Substances 0.000 claims abstract description 14
- 239000005864 Sulphur Substances 0.000 claims abstract description 13
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims abstract description 10
- 239000012530 fluid Substances 0.000 claims abstract description 9
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims abstract description 8
- 238000006243 chemical reaction Methods 0.000 claims abstract description 8
- 239000010802 sludge Substances 0.000 claims abstract description 8
- 229910021653 sulphate ion Inorganic materials 0.000 claims abstract description 8
- 239000002918 waste heat Substances 0.000 claims abstract description 7
- 239000001913 cellulose Substances 0.000 claims abstract description 6
- 229920002678 cellulose Polymers 0.000 claims abstract description 6
- 229910000029 sodium carbonate Inorganic materials 0.000 claims abstract description 6
- 229910052938 sodium sulfate Inorganic materials 0.000 claims abstract description 6
- 235000011152 sodium sulphate Nutrition 0.000 claims abstract description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 5
- 238000007599 discharging Methods 0.000 claims description 8
- 238000005201 scrubbing Methods 0.000 claims description 8
- 239000000463 material Substances 0.000 claims description 4
- 230000001590 oxidative effect Effects 0.000 claims description 4
- 239000002699 waste material Substances 0.000 claims description 4
- 238000001704 evaporation Methods 0.000 claims description 2
- 230000008020 evaporation Effects 0.000 claims description 2
- 238000001816 cooling Methods 0.000 claims 2
- 230000000694 effects Effects 0.000 claims 1
- 239000011734 sodium Substances 0.000 abstract description 13
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 abstract description 8
- 229910052708 sodium Inorganic materials 0.000 abstract description 8
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 12
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 description 9
- 239000003784 tall oil Substances 0.000 description 6
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 5
- 235000011941 Tilia x europaea Nutrition 0.000 description 5
- 239000004571 lime Substances 0.000 description 5
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
- 239000001117 sulphuric acid Substances 0.000 description 4
- 235000011149 sulphuric acid Nutrition 0.000 description 4
- 239000000203 mixture Substances 0.000 description 3
- 235000017550 sodium carbonate Nutrition 0.000 description 3
- 235000010269 sulphur dioxide Nutrition 0.000 description 3
- 239000004291 sulphur dioxide Substances 0.000 description 3
- 239000007832 Na2SO4 Substances 0.000 description 2
- 230000002411 adverse Effects 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
- 238000004880 explosion Methods 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 239000004155 Chlorine dioxide Substances 0.000 description 1
- 229930182558 Sterol Natural products 0.000 description 1
- BNOODXBBXFZASF-UHFFFAOYSA-N [Na].[S] Chemical compound [Na].[S] BNOODXBBXFZASF-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 238000004061 bleaching Methods 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 235000019398 chlorine dioxide Nutrition 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 235000014113 dietary fatty acids Nutrition 0.000 description 1
- 239000000194 fatty acid Substances 0.000 description 1
- 229930195729 fatty acid Natural products 0.000 description 1
- 150000004665 fatty acids Chemical class 0.000 description 1
- 239000013505 freshwater Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 239000011369 resultant mixture Substances 0.000 description 1
- 150000003432 sterols Chemical class 0.000 description 1
- 235000003702 sterols Nutrition 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
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
- D21C11/04—Regeneration of pulp liquors or effluent waste waters of alkali lye
-
- 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
- D21C11/00—Regeneration of pulp liquors or effluent waste waters
- D21C11/12—Combustion of pulp liquors
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working
Landscapes
- Treating Waste Gases (AREA)
- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The sulphur-containing gas emissions from a sulphate cellulose pulp mill are minimized by combusting malodorous gases produced by the pulp mill, and by minimizing the use of chemicals which can disrupt the sulphur/sodium balance of the pulp mill. Sulphurous malodorous gases are combined with soap and/or black liquor to produce a fluid, which is burned in a cylindrical water cooled reaction vessel to produce a melt containing sodium sulphate and sodium carbonate. Chemicals are recovered from the melt by dissolving it in liquid in a dissolving tank to produce a melt solution, combining the melt solution with weak black liquor, and burning the combination in a soda recovery boiler. The flue gases produced during combustion of the sulphurous gases and soap may be cooled and scrubbed, or may be fed to a waste heat recovery boiler and is burned with bark or sludge.
The sulphur-containing gas emissions from a sulphate cellulose pulp mill are minimized by combusting malodorous gases produced by the pulp mill, and by minimizing the use of chemicals which can disrupt the sulphur/sodium balance of the pulp mill. Sulphurous malodorous gases are combined with soap and/or black liquor to produce a fluid, which is burned in a cylindrical water cooled reaction vessel to produce a melt containing sodium sulphate and sodium carbonate. Chemicals are recovered from the melt by dissolving it in liquid in a dissolving tank to produce a melt solution, combining the melt solution with weak black liquor, and burning the combination in a soda recovery boiler. The flue gases produced during combustion of the sulphurous gases and soap may be cooled and scrubbed, or may be fed to a waste heat recovery boiler and is burned with bark or sludge.
Description
2~78~9 METHOD OF AND APPARATUS FOR TREATING MALODOROUS GASES
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a method an apparatus for treating malodorous gases and sulphate soap from a cellulose pulp mill. The gases and soap (and like fractions thereof) are treated in a pulp mill in such a way that the recovery of chemicals entrained therein is improved without any disturbance to other subprocesses of the mill.
Throughout the world, there is an increasing need to minimize the sulphur emissions from sulphate pulp mills.
This requires maintaining a substantially constant balance between sulphur and sodium ("S/Na ratio"), that is maintaining the sulphidity constant. Maintaining an appropriate balance can be difficult, however, since sulphur is added to the process system in the form of sulphuric acid, and waste acid as a result of the utilization of chlorine dioxide bleaching chemicals.
A significant source of the sulphuric acid added to a sulphate mill is that added during the conversion of soap (formed as a by-product of the manufacture of the pulp) to tall oil, a malodorous resonance admixture of rosins, fatty acids, sterols, and other materials. The commercial significance of tall oil is decreasing, therefore if the tall oil subprocess can be eliminated there is no significant adverse commercial impact on the pulp mill, however the sulphur imbalance contributed by sulphuric acid normally used in the process of converting soap to tall oil can be eliminated. However the soap must still be used or disposed of.
In the past it has been suggested that it is possible to avoid the tall oil subprocess by combusting soap in a soda recovery boiler. However such combustion is not advantageous. Combustion of soap in the soda recovery ,, - .:: , . .
.': . : : :
.. .. .. . . : ~, ~
boiler carries with it the risk of a melt solution explosion. Also, combustion of the soap occupies a part of capacity of the boiler (for example about 3 to 5% of the capacity). Also combustion of soap might need to be stopped if the dry substance content of the black liquor being burned in the soda recovery boiler increases. These same concerns applicable to a soda recovery boiler are also typically applicable to combustion of soap in a lime kiln, and in addition combustion in the lime kiln is technically complicated.
The method in accordance with the present invention brings about several advantages compared with previous methods.
The method according to the present invention facilitates balancing the S/Na ratio of the mill. Further, the inventive method does not require the addition of sulphurous compounds that are added to the previous processes. The sodium in the soap in the present invention is recovered without disturbing the rest of the mill process, e.g. the combustion of black liquor in the soda recovery boiler. Further, it is possible to readily decrease the environmental loading of a pulp mill because the sulphur in the malodorous gases may be bound by means of the sodium in the soap without a significant use of other chemicals, e.g. sodium hydroxide, that are acquired elsewhere. The method according to the present invention is also energy efficient since the burner requires only minimal energy, e.g. oil or natural gas, acquired elsewhere during the start-up of the combustion process and/or during possible breakdowns.
Malodorous gases mainly containing organic sulphur compounds are generated in the manufacture of sulphate cellulose pulp. r~hese gases are mainly generated in the digester and in the black liquor evaporators. Preferably the odorous organic sulphur compounds in the gases are removed by combusting them to produce sulphur dioxide in a ..
.
'' . ' ' - .. ~ ' .. , :
- . : . : - : .
.
2~78~5~
separate reactor vessel, or in a lime sludge reburning kiln. It has been found that the separate combustion procedure is preferred because the combustion in a lime kiln disturbs the actual lime sludge reburning process.
Further, during combustion, disturbances in the process result in the release of malodorous gases to the environment.
The previous separate combustion systems have the disadvantage that the sulphur contained therein can only be recovered by scrubbing the flue gases. This has been achieved by, for example, scrubbing the flue gases with a solution containing sodium hydroxide. However, NaOH is expensive, and disturbs the S/Na balance of the mill.
According to the present invention, a process and apparatus are provided which eliminate the problem of malodorous sulphurous gases from a pulp mill, while at the same time eliminating the use of sulphuric acid for the conversion of soap to tall oil, thereby helping to maintain the sulphur sodium ratio in the pulp mill, and minimizing the adverse environmental impact of a sulphate pulp mill.
This desirable result is accomplished according to the method of the present invention by destroying sulphurous malodorous gases while producing recoverable chemicals.
The preferred method according to the present invention comprises the following steps: (a) Combining sulphurous malodorous gases with material selected from the group consisting essentially of soap and black liquor, to produce a fluid. (b) Combusting the fluid from step (a) under oxidizing conditions to produce a melt containing sodium sulphate and sodium carbonate. And, (c) Recovering chemicals from the melt produced in step (b). Step (c) may be practiced, for example, by dissolving the melt to produce a solution, combining the solution with black liquor, and then combusting the black liquor in a conventional soda recovery boiler. The gas utilized may .
. ~, .' ' . ~' .'';'. ' . . ~
- - : .: . . ...
.
- : ~ . ' '' ' :
, .
2~7~
be any sulphurous off gas from a pulp mill, such as from a digester or evaporator. The flue gases that are generated during step (b) may be cooled and then passed to a scrubber, or they may be fed to a waste heat boiler which burns bark, sludge, or the like.
Normally soap includes a small amount of sulphur compared with its sodium content, the average ratio being about 6 kg sodium to about 0.5 kg sulphur. This ratio varies depending upon the tree species and the site location of the trees used to produce the cellulose pulp. During the oxidizing part of the combustion process the sulphur in the odorous gases reacts with the sodium in the soap forming Na2SO4 and some Na2CO3. The resulting melt solution that is formed from this combustion process is then dissolved in water to an appropriate concentration (selected in accordance with the precipitation point of the solution~. The solution is then further mixed with weak black liquor, and burned in a soda recovery boiler.
This results in the sodium in the soap being recovered without disturbing the S/Na balance of the mill.
The sulphur-free flue gases that are generated in the combustion process may be scrubbed with water in a conventional scrubber. This is done to decrease the particle emissions from in the mill process. The washing liquid may be passed to the dissolving section of the melt solution. Due to the composition of the soap the particle emissions from the combustion process remain very low.
It has also been discovered according to the invention that it is possible to combust black liquor with the odorous gases. The black liquor may be substituted for the soap or as a mixture along with soap. The treatment of black liquor comes into question, for example, when there is not enough soap for the combustion process in accordance with the present invention. Further, the treatment of black liquor is useful if the capacity of 2~7~5~
the soda recovery boiler is not sufficient to treat all black liquor in the system. During the combustion of black liquor the sulphur in the odorous gases forms SO2.
The resulting SO2 is bound to the melt solution, as it is in the combustion process of the soap.
The sulphurous odorous gases treated according to the invention may be any sulphurous gas generated in a pulp mill and capable of combustion in accordance with the present invention.
According to another aspect of the present invention, an apparatus for destroying sulphurous malodorous gases is provided. The apparatus comprises a reactor vessel (preferably a cylindrical water-cooled reactor) for effecting combustion, having a top portion and a bottom portion. The apparatus further comprises the following elements: Means for feeding sulphurous malodorous gases, soap and/or black liquor, and combustion air into the reactor vessel. Means for discharging melt produced during the combustion of malodorous gases, and soap and/or black liquor, in the reactor vessel from the bottom of the reactor vessel. Means for discharging from the reactor vessel flue gases produced during the combustion in the reactor vessel. And, a dissolving vessel communicating with the melt discharging means, for dissolving the melt.
The dissolving vessel is typically disposed beneath the reactor vessel, and has a flue discharge for leading flue gases from the reactor vessel through a cooler and then to a scrubber, or passing the flue gases to a waste heat boiler burning bark, sludge, or the like. A melt solution conduit extends from the dissolving vessel and merges with a weak black liquor conduit, which is then connected to a soda recovery boiler.
It is the primary object of the present invention to destroy malodorous gases from a sulphate pulp mill while at the same time preserving the S/Na ratio of the pulp - -.. . . . . - -- . : . -: . - .... ..
,: - . ~ . : . ' :'- ' :
. .
2~7~
mill. 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 DRAWING
The drawing figure is a longitudinal cross-sectional view of schematically illustrated exemplary apparatus according to the invention, and for practicing the method according to the invention.
DETAILED DESCRIPTION OF THE DRAWING
The drawing illustrates a cylindrical water-cooled combustion reactor 1 connected to a dissolving vessel 8.
The combustion reactor 1 has a conical upper end 2, a lower end 3, and vertical wall 7. Soap and/or black liquor 4, odorous gases 5, combustion air, and possibly fuel, are introduced homogeneously at several places (e.g.
three to five different places) into the upper end 2 of the combustion reactor 1. The temperature in the reactor is preferably 900-1000C during combustion.
When burning soap and/or black liquor and odorous gases react, a melt layer 6 is continuously generated on the inside of the reactor wall 7. The continuously generated melt layer 6 protects the reactor wall 7 from overheating, and flows downwardly under the force of gravity. The melt layer 6 is discharged from the lower end 3 of the reactor 1 into the dissolving vessel 8 that is located below the reactor 1.
The concentration of melt solution 10 produced in vessel 8 is controlled by an incoming fresh water flow 13 that enters the dissolving vessel 8, and is mixed with the melt 6 by mixer 8'. The liquid introduced at 13 may be wash liquid from a flue gas scrubber.
207~9 Flue gases that are generated in the reactor 1 also circulate through the dissolving vessel 8. These flue gases are then transported through a discharge opening 9 and are cooled by a conventional cooler 12. The flue gases are discharged from cooler 12 to a conventional scrubber 18 to be treated with water. The scrubber must also have the capability of treating gases with an alkaline composition, e.g. NaOH solution, since the generation of sulphur dioxide may occur in some circumstances. However, the generation of sulphur dioxide under most conditions is unlikely. The liquid used for scrubbing may -- after scrubbing -- be utilized to provide all or part of the dissolving liquid in line 13, as indicated by return line 19.
Melt solution 10 containing Na2SO4 and some Na2CO3 is mixed with weak black liquor in conduit 11. The resultant mixture of the melt solution 10 and the weak black solution in line 11 is directed via an evaporation plant (not shown) to a conventional recovery boiler 14 by the conduit 15 or other appropriate means. Thus, the chemicals that are present in the soap and/or black liquor and odorous gases are recovered for future chemical circulation within the mill.
The combustion system of the present invention also operates well at a low dry substance content of soap.
Further, there is no risk of a melt explosion.
The operatir,g capacity efficiency of the combustion system described above is about 9-25 megawatts (MW). When using black liquor in the combustion process, higher efficiencies are possible. Further, it is possible to combine a waste heat boiler with a system for the recovery of energy from flue gases in order to obtain high fuel efficiency. That is, under suitable conditions flue gases from discharge 9 may be passed (e.g. via conduit 16) to a vessel 17 ~e.g.
a boiler) for reaction with bark, sludge or the like, so ': '' : ~.
' -, ~
2~7~
that a separate treatment of flue ~ases in a scrubber is avoided.
The method in accordance with the present invention is especially suitable for the type of pulp mill which treats odorous gases in a separate system.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a method an apparatus for treating malodorous gases and sulphate soap from a cellulose pulp mill. The gases and soap (and like fractions thereof) are treated in a pulp mill in such a way that the recovery of chemicals entrained therein is improved without any disturbance to other subprocesses of the mill.
Throughout the world, there is an increasing need to minimize the sulphur emissions from sulphate pulp mills.
This requires maintaining a substantially constant balance between sulphur and sodium ("S/Na ratio"), that is maintaining the sulphidity constant. Maintaining an appropriate balance can be difficult, however, since sulphur is added to the process system in the form of sulphuric acid, and waste acid as a result of the utilization of chlorine dioxide bleaching chemicals.
A significant source of the sulphuric acid added to a sulphate mill is that added during the conversion of soap (formed as a by-product of the manufacture of the pulp) to tall oil, a malodorous resonance admixture of rosins, fatty acids, sterols, and other materials. The commercial significance of tall oil is decreasing, therefore if the tall oil subprocess can be eliminated there is no significant adverse commercial impact on the pulp mill, however the sulphur imbalance contributed by sulphuric acid normally used in the process of converting soap to tall oil can be eliminated. However the soap must still be used or disposed of.
In the past it has been suggested that it is possible to avoid the tall oil subprocess by combusting soap in a soda recovery boiler. However such combustion is not advantageous. Combustion of soap in the soda recovery ,, - .:: , . .
.': . : : :
.. .. .. . . : ~, ~
boiler carries with it the risk of a melt solution explosion. Also, combustion of the soap occupies a part of capacity of the boiler (for example about 3 to 5% of the capacity). Also combustion of soap might need to be stopped if the dry substance content of the black liquor being burned in the soda recovery boiler increases. These same concerns applicable to a soda recovery boiler are also typically applicable to combustion of soap in a lime kiln, and in addition combustion in the lime kiln is technically complicated.
The method in accordance with the present invention brings about several advantages compared with previous methods.
The method according to the present invention facilitates balancing the S/Na ratio of the mill. Further, the inventive method does not require the addition of sulphurous compounds that are added to the previous processes. The sodium in the soap in the present invention is recovered without disturbing the rest of the mill process, e.g. the combustion of black liquor in the soda recovery boiler. Further, it is possible to readily decrease the environmental loading of a pulp mill because the sulphur in the malodorous gases may be bound by means of the sodium in the soap without a significant use of other chemicals, e.g. sodium hydroxide, that are acquired elsewhere. The method according to the present invention is also energy efficient since the burner requires only minimal energy, e.g. oil or natural gas, acquired elsewhere during the start-up of the combustion process and/or during possible breakdowns.
Malodorous gases mainly containing organic sulphur compounds are generated in the manufacture of sulphate cellulose pulp. r~hese gases are mainly generated in the digester and in the black liquor evaporators. Preferably the odorous organic sulphur compounds in the gases are removed by combusting them to produce sulphur dioxide in a ..
.
'' . ' ' - .. ~ ' .. , :
- . : . : - : .
.
2~78~5~
separate reactor vessel, or in a lime sludge reburning kiln. It has been found that the separate combustion procedure is preferred because the combustion in a lime kiln disturbs the actual lime sludge reburning process.
Further, during combustion, disturbances in the process result in the release of malodorous gases to the environment.
The previous separate combustion systems have the disadvantage that the sulphur contained therein can only be recovered by scrubbing the flue gases. This has been achieved by, for example, scrubbing the flue gases with a solution containing sodium hydroxide. However, NaOH is expensive, and disturbs the S/Na balance of the mill.
According to the present invention, a process and apparatus are provided which eliminate the problem of malodorous sulphurous gases from a pulp mill, while at the same time eliminating the use of sulphuric acid for the conversion of soap to tall oil, thereby helping to maintain the sulphur sodium ratio in the pulp mill, and minimizing the adverse environmental impact of a sulphate pulp mill.
This desirable result is accomplished according to the method of the present invention by destroying sulphurous malodorous gases while producing recoverable chemicals.
The preferred method according to the present invention comprises the following steps: (a) Combining sulphurous malodorous gases with material selected from the group consisting essentially of soap and black liquor, to produce a fluid. (b) Combusting the fluid from step (a) under oxidizing conditions to produce a melt containing sodium sulphate and sodium carbonate. And, (c) Recovering chemicals from the melt produced in step (b). Step (c) may be practiced, for example, by dissolving the melt to produce a solution, combining the solution with black liquor, and then combusting the black liquor in a conventional soda recovery boiler. The gas utilized may .
. ~, .' ' . ~' .'';'. ' . . ~
- - : .: . . ...
.
- : ~ . ' '' ' :
, .
2~7~
be any sulphurous off gas from a pulp mill, such as from a digester or evaporator. The flue gases that are generated during step (b) may be cooled and then passed to a scrubber, or they may be fed to a waste heat boiler which burns bark, sludge, or the like.
Normally soap includes a small amount of sulphur compared with its sodium content, the average ratio being about 6 kg sodium to about 0.5 kg sulphur. This ratio varies depending upon the tree species and the site location of the trees used to produce the cellulose pulp. During the oxidizing part of the combustion process the sulphur in the odorous gases reacts with the sodium in the soap forming Na2SO4 and some Na2CO3. The resulting melt solution that is formed from this combustion process is then dissolved in water to an appropriate concentration (selected in accordance with the precipitation point of the solution~. The solution is then further mixed with weak black liquor, and burned in a soda recovery boiler.
This results in the sodium in the soap being recovered without disturbing the S/Na balance of the mill.
The sulphur-free flue gases that are generated in the combustion process may be scrubbed with water in a conventional scrubber. This is done to decrease the particle emissions from in the mill process. The washing liquid may be passed to the dissolving section of the melt solution. Due to the composition of the soap the particle emissions from the combustion process remain very low.
It has also been discovered according to the invention that it is possible to combust black liquor with the odorous gases. The black liquor may be substituted for the soap or as a mixture along with soap. The treatment of black liquor comes into question, for example, when there is not enough soap for the combustion process in accordance with the present invention. Further, the treatment of black liquor is useful if the capacity of 2~7~5~
the soda recovery boiler is not sufficient to treat all black liquor in the system. During the combustion of black liquor the sulphur in the odorous gases forms SO2.
The resulting SO2 is bound to the melt solution, as it is in the combustion process of the soap.
The sulphurous odorous gases treated according to the invention may be any sulphurous gas generated in a pulp mill and capable of combustion in accordance with the present invention.
According to another aspect of the present invention, an apparatus for destroying sulphurous malodorous gases is provided. The apparatus comprises a reactor vessel (preferably a cylindrical water-cooled reactor) for effecting combustion, having a top portion and a bottom portion. The apparatus further comprises the following elements: Means for feeding sulphurous malodorous gases, soap and/or black liquor, and combustion air into the reactor vessel. Means for discharging melt produced during the combustion of malodorous gases, and soap and/or black liquor, in the reactor vessel from the bottom of the reactor vessel. Means for discharging from the reactor vessel flue gases produced during the combustion in the reactor vessel. And, a dissolving vessel communicating with the melt discharging means, for dissolving the melt.
The dissolving vessel is typically disposed beneath the reactor vessel, and has a flue discharge for leading flue gases from the reactor vessel through a cooler and then to a scrubber, or passing the flue gases to a waste heat boiler burning bark, sludge, or the like. A melt solution conduit extends from the dissolving vessel and merges with a weak black liquor conduit, which is then connected to a soda recovery boiler.
It is the primary object of the present invention to destroy malodorous gases from a sulphate pulp mill while at the same time preserving the S/Na ratio of the pulp - -.. . . . . - -- . : . -: . - .... ..
,: - . ~ . : . ' :'- ' :
. .
2~7~
mill. 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 DRAWING
The drawing figure is a longitudinal cross-sectional view of schematically illustrated exemplary apparatus according to the invention, and for practicing the method according to the invention.
DETAILED DESCRIPTION OF THE DRAWING
The drawing illustrates a cylindrical water-cooled combustion reactor 1 connected to a dissolving vessel 8.
The combustion reactor 1 has a conical upper end 2, a lower end 3, and vertical wall 7. Soap and/or black liquor 4, odorous gases 5, combustion air, and possibly fuel, are introduced homogeneously at several places (e.g.
three to five different places) into the upper end 2 of the combustion reactor 1. The temperature in the reactor is preferably 900-1000C during combustion.
When burning soap and/or black liquor and odorous gases react, a melt layer 6 is continuously generated on the inside of the reactor wall 7. The continuously generated melt layer 6 protects the reactor wall 7 from overheating, and flows downwardly under the force of gravity. The melt layer 6 is discharged from the lower end 3 of the reactor 1 into the dissolving vessel 8 that is located below the reactor 1.
The concentration of melt solution 10 produced in vessel 8 is controlled by an incoming fresh water flow 13 that enters the dissolving vessel 8, and is mixed with the melt 6 by mixer 8'. The liquid introduced at 13 may be wash liquid from a flue gas scrubber.
207~9 Flue gases that are generated in the reactor 1 also circulate through the dissolving vessel 8. These flue gases are then transported through a discharge opening 9 and are cooled by a conventional cooler 12. The flue gases are discharged from cooler 12 to a conventional scrubber 18 to be treated with water. The scrubber must also have the capability of treating gases with an alkaline composition, e.g. NaOH solution, since the generation of sulphur dioxide may occur in some circumstances. However, the generation of sulphur dioxide under most conditions is unlikely. The liquid used for scrubbing may -- after scrubbing -- be utilized to provide all or part of the dissolving liquid in line 13, as indicated by return line 19.
Melt solution 10 containing Na2SO4 and some Na2CO3 is mixed with weak black liquor in conduit 11. The resultant mixture of the melt solution 10 and the weak black solution in line 11 is directed via an evaporation plant (not shown) to a conventional recovery boiler 14 by the conduit 15 or other appropriate means. Thus, the chemicals that are present in the soap and/or black liquor and odorous gases are recovered for future chemical circulation within the mill.
The combustion system of the present invention also operates well at a low dry substance content of soap.
Further, there is no risk of a melt explosion.
The operatir,g capacity efficiency of the combustion system described above is about 9-25 megawatts (MW). When using black liquor in the combustion process, higher efficiencies are possible. Further, it is possible to combine a waste heat boiler with a system for the recovery of energy from flue gases in order to obtain high fuel efficiency. That is, under suitable conditions flue gases from discharge 9 may be passed (e.g. via conduit 16) to a vessel 17 ~e.g.
a boiler) for reaction with bark, sludge or the like, so ': '' : ~.
' -, ~
2~7~
that a separate treatment of flue ~ases in a scrubber is avoided.
The method in accordance with the present invention is especially suitable for the type of pulp mill which treats odorous gases in a separate system.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Claims (22)
1. A method of destroying sulphurous malodorous gases from a cellulose pulp mill while producing recoverable chemicals, comprising the steps of:
(a) combining sulphurous malodorous gases with material selected from the group consisting essentially of soap and black liquor, to produce a fluid;
(b) combusting the fluid from step (a) under oxidizing conditions to produce a melt containing sodium sulphate and sodium carbonate; and (c) recovering chemicals from the melt produced in step (b).
(a) combining sulphurous malodorous gases with material selected from the group consisting essentially of soap and black liquor, to produce a fluid;
(b) combusting the fluid from step (a) under oxidizing conditions to produce a melt containing sodium sulphate and sodium carbonate; and (c) recovering chemicals from the melt produced in step (b).
2. A method as recited in claim 1 wherein step (c) is practiced by dissolving the melt in a liquid to form a melt solution, combining the melt solution with black liquor, and burning the black liquor in a soda recovery boiler.
3. A method as recited in claim 2 wherein step (c) is practiced utilizing weak black liquor, which is evaporated prior to burning.
4. A method as recited in claim 1 wherein step (a) is practiced by mixing the malodorous gases with material to produce a fluid prior to introduction into a reaction vessel, and introducing the fluid at a plurality of different locations near the top of the reaction vessel;
and wherein step (b) takes place in the reaction vessel.
and wherein step (b) takes place in the reaction vessel.
5. A method as recited in claim 4 wherein step (b) is practiced at a temperature of about 900-1000°C.
6. A method as recited in claim 1 wherein step (b) also produces flue gases, and wherein the method comprises the further steps of: separating the melt from the flue gases; cooling the flue gases; and scrubbing the flue gases with liquid.
7. A method as recited in claim 1 wherein step (b) also produces flue gases, and wherein the method comprises the additional steps of: separating the flue gases from the melt; feeding the flue gases to a waste heat boiler; and burning the flue gases in a waste heat boiler with bark, sludge, or the like.
8. A method as recited in claim 6 wherein step (c) is practiced by dissolving the melt in a liquid to form a melt solution, combining the melt solution with black liquor, and burning the black liquor in a soda recovery boiler.
9. A method as recited in claim 7 wherein step (c) is practiced by dissolving the melt in a liquid to form a melt solution, combining the melt solution with black liquor, and burning the black liquor in a soda recovery boiler.
10. A method as recited in claim 2 wherein step (b) also produces flue gases, and wherein the method comprises the further steps of: separating the melt from the flue gases; cooling the flue gases; and scrubbing the flue gases with liquid.
11. A method as recited in claim 10 comprising the further step of using the scrubbing liquid, after scrubbing, to dissolve the melt in the practice of step (c).
12. Apparatus for destroying sulphurous malodorous gases, comprising:
a reactor vessel for effecting combustion, and having a top portion and a bottom portion;
means for feeding sulphurous malodorous gases, soap and/or black liquor, and combustion air into said reactor vessel;
means for discharging melt produced during the combustion of malodorous gases, and soap and/or black liquor, in said reactor vessel from the bottom of said reactor vessel;
means for discharging from said reactor vessel flue gases produced during the combustion in said reactor vessel;
and a dissolving vessel communicating with said melt discharging means, for dissolving the melt.
a reactor vessel for effecting combustion, and having a top portion and a bottom portion;
means for feeding sulphurous malodorous gases, soap and/or black liquor, and combustion air into said reactor vessel;
means for discharging melt produced during the combustion of malodorous gases, and soap and/or black liquor, in said reactor vessel from the bottom of said reactor vessel;
means for discharging from said reactor vessel flue gases produced during the combustion in said reactor vessel;
and a dissolving vessel communicating with said melt discharging means, for dissolving the melt.
13. Apparatus as recited in claim 12 wherein said means for feeding sulphurous malodorous gases, soap and/or black liquor, and combustion air into said reactor vessel comprises means for introducing malodorous gases, soap and/or black liquor, and combustion air at a plurality of locations into the top portion of said reactor vessel.
14. Apparatus as recited in claim 13 wherein said dissolving vessel is located below said reactor vessel, adjacent said bottom portion thereof, and wherein said dissolving vessel includes means for introducing dissolving liquid therein, and a mixer.
15. Apparatus as recited in claim 14 wherein said dissolving vessel further comprises a mixer.
16. Apparatus as recited in claim 14 wherein said means for discharging flue gases comprises means defining a discharge opening in said dissolving vessel, gases from said reaction vessel discharging into said dissolving vessel.
17. Apparatus as recited in claim 12 wherein said reactor vessel comprises a cylindrical water cooled vessel.
18. Apparatus as recited in claim 12 further comprising:
a conduit for removing melt solution from said dissolving vessel; means for combining the removed melt solution with black liquor; a soda recovery boiler; and means for introducing the combined melt solution and black liquor into said soda recovery boiler to effect combustion thereof.
a conduit for removing melt solution from said dissolving vessel; means for combining the removed melt solution with black liquor; a soda recovery boiler; and means for introducing the combined melt solution and black liquor into said soda recovery boiler to effect combustion thereof.
19. Apparatus as recited in claim 12 further comprising a waste recovery boiler, and means for passing flue gases discharged from said reactor vessel to said waste recovery boiler.
20. Apparatus as recited in claim 12 wherein said dissolving vessel is located below said reactor vessel, adjacent said bottom portion thereof, and wherein said dissolving vessel includes means for introducing dissolving liquid therein.
21. A method of minimizing sulphur gas emissions from a sulphate cellulose pulp mill which produces soap, sulphurous malodorous gases, and black liquor as waste products, comprising the steps of:
(a) combining sulphurous malodorous gases with soap and/or black liquor to produce a fluid;
(b) burning the fluid from step (a) under oxidizing conditions to produce a melt containing sodium sulphate and sodium carbonate;
(c) dissolving the melt with liquid to produce a melt solution;
(d) combining the melt solution with weak black liquor;
and (e) burning the weak black liquor/melt solution combination after evaporation in a soda recovery boiler to recover chemicals therefrom.
(a) combining sulphurous malodorous gases with soap and/or black liquor to produce a fluid;
(b) burning the fluid from step (a) under oxidizing conditions to produce a melt containing sodium sulphate and sodium carbonate;
(c) dissolving the melt with liquid to produce a melt solution;
(d) combining the melt solution with weak black liquor;
and (e) burning the weak black liquor/melt solution combination after evaporation in a soda recovery boiler to recover chemicals therefrom.
22. A method as recited in claim 21 wherein step (b) produces flue gases, and comprising the further step of burning the flue gases with bark or sludge in a waste heat recovery boiler to recover the energy value thereof.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI914521A FI914521A (en) | 1991-09-26 | 1991-09-26 | OIL ANCHORING FOER BEHANDLING AV EN CELLULOSAFABRIKS STARKLUKTANDE GASER |
| FI914521 | 1991-09-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2078959A1 true CA2078959A1 (en) | 1993-03-27 |
Family
ID=8533185
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002078959A Abandoned CA2078959A1 (en) | 1991-09-26 | 1992-09-23 | Method of and apparatus for treating malodorous gases |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPH0694637B2 (en) |
| CA (1) | CA2078959A1 (en) |
| FI (1) | FI914521A (en) |
| SE (1) | SE9202781L (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5562804A (en) * | 1993-07-23 | 1996-10-08 | Tampella Power Oy | Method for adjusting the sulphur/sodium ratio in the flue gases of a soda recovery boiler |
| WO2009030805A3 (en) * | 2007-09-03 | 2009-05-07 | Andritz Oy | Method in the treatment of odorous gases of a chemical pulp mill |
-
1991
- 1991-09-26 FI FI914521A patent/FI914521A/en unknown
-
1992
- 1992-09-23 CA CA002078959A patent/CA2078959A1/en not_active Abandoned
- 1992-09-25 SE SE9202781A patent/SE9202781L/en not_active Application Discontinuation
- 1992-09-28 JP JP4258083A patent/JPH0694637B2/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5562804A (en) * | 1993-07-23 | 1996-10-08 | Tampella Power Oy | Method for adjusting the sulphur/sodium ratio in the flue gases of a soda recovery boiler |
| WO2009030805A3 (en) * | 2007-09-03 | 2009-05-07 | Andritz Oy | Method in the treatment of odorous gases of a chemical pulp mill |
| US9080286B2 (en) | 2007-09-03 | 2015-07-14 | Andritz Oy | Method in the treatment of odorous gases of a chemical pulp mill |
Also Published As
| Publication number | Publication date |
|---|---|
| FI914521A0 (en) | 1991-09-26 |
| JPH05295689A (en) | 1993-11-09 |
| JPH0694637B2 (en) | 1994-11-24 |
| FI914521A (en) | 1993-03-27 |
| SE9202781L (en) | 1993-03-27 |
| SE9202781D0 (en) | 1992-09-25 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |