CA2060819A1 - Treatment of organic sulfur gases especially in kraft pulping systems and processes - Google Patents

Treatment of organic sulfur gases especially in kraft pulping systems and processes

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Publication number
CA2060819A1
CA2060819A1 CA002060819A CA2060819A CA2060819A1 CA 2060819 A1 CA2060819 A1 CA 2060819A1 CA 002060819 A CA002060819 A CA 002060819A CA 2060819 A CA2060819 A CA 2060819A CA 2060819 A1 CA2060819 A1 CA 2060819A1
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Prior art keywords
gas
gas stream
hydrogen
recited
methane
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
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CA002060819A
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French (fr)
Inventor
Wayne Chamblee
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Kamyr Inc
Original Assignee
Kamyr Inc
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Classifications

    • DTEXTILES; PAPER
    • D21PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21CPRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C3/00Pulping cellulose-containing materials
    • D21C3/22Other features of pulping processes
    • D21C3/26Multistage processes
    • DTEXTILES; PAPER
    • D21PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21CPRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C11/00Regeneration of pulp liquors or effluent waste waters
    • D21C11/0064Aspects concerning the production and the treatment of green and white liquors, e.g. causticizing green liquor
    • DTEXTILES; PAPER
    • D21PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21CPRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C3/00Pulping cellulose-containing materials
    • D21C3/02Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
    • D21C3/022Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes in presence of S-containing compounds

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Gas Separation By Absorption (AREA)
  • Paper (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)
  • Industrial Gases (AREA)
  • Treating Waste Gases (AREA)

Abstract

ABSTRACT

Gases containing water vapor and over 10% (e.g.
about 15-80%) by weight organic sulfur compounds, such as off gases from a kraft or sulfite digester, black liquor evaporator, or apparatus for heating black liquor to reduce its viscosity, are converted into a gas stream comprising primarily hydrogen sulfide and methane. Hydrogen can be added to the gas, and the gas in the presence of the added hydrogen may be passed past a hydrogen desulfurization catalyst (nickel or cobalt molybdenum). Preferably the vast majority of the water vapor is removed before it is passed past the catalyst. The hydrogen source may be provided by the gas itself, by passing a portion through a methane/steam reformer and separating hydrogen from the stream, to produce a gas containing primarily methane and carbon dioxide which is used for a combustion gas. Hydrogen sulfide may be removed from the gas stream by passing it into contact with white or green liquor from kraft paper pulping processes.
Alternatively, substochiometric combustion of at least some of the gas may be effected, and after soot removal the gas may be passed into contact with a dirty shift catalyst (an alumina catalyst containing oxides of cobalt and molybdenum) to produce a gas stream comprising primarily hydrogen sulfide and methane with some carbon dioxide.

Description

~r~ 'a'~ 9 _ ATM~NT OE ORGANIC SULFUR G~SES ESPECIALJY IN
KRAFT PULPING SYSTEMS AND P~OCESSES

BACKGROUND AND SUMMARY OF THE INVENTION

In the production of kraft paper pulp, and like processes, it has been recognized for many years that off gases are produced which contain a high volume of organic sulfur compounds. Heretofore, no significant use has been made of such off gases, which typically occur from the digester, and from black liquor evaporators. Recently, in the commercialization of a method for decreasing black liquor viscosity disclosed in U.S. patent 4,929,307 it was found that very high volumes of off gases containing organic sulfur compounds including DMS, methyl mercaptan, and hydrogen sulfide are produced. Such high volumes of gas are produced that some technique must be utilized to act on the gases, otherwise the black liquor heating apparatus may become a significant source of air pollution, and a substantial volume of sulfur will be lost from the pulping system.
From all of the various sources of off gases containing organic sulfur compounds in kraft (and ~ulfite) pulping the concentrations o organic sulfur compounds are much higher than are found in other industries that have dealt with handling such gases on a commercial basis (for example the oil indu try). Typically in the oil industry, the concentration of organic sulfur ~ompounds is less than three percent, and there is virtually no water vapor present. However in the kraft pulping . . .~ .
, ~
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2 ~ , .9 industry, off gases from the digester, black liquor evaporators, and black liquor heaters, typically are in the range of a~out 10-80% (usually over 15%), and water vapor (in the form of steam) is virtually universally present.
According to the present invention, a method is provided for treatment of the off gases associated with kraft or æulfite pulping so as to change them from a source of pollution to a source of useful chemicals.
According to one aspect of the present invention a method of acting on a first gas stream consisting essentially of of gases from a kraft or sulfite digester, off gases from a black liquor evaporator, and mixtures thereo, i6 provided which comprises the steps of (a) treating the gases in the first gas stream to produce a second ga~ stream containing primarily hydrogen sulfide and methane, and then (b) separating the hydrogen sulfide from the methane. Step (a) may be practiced by adding hydrogen to the gas in the first gas stream, and passing the first gas stream -- in the presence of the added hydrogen -- past a hydrogen desulfurization catalyst (e.g. one selected from the group consisting essentially of nickel molybdenum and cobalt molybdenum) to produce a second gas stream. Alternatively step (a) may be practiced by effecting substochiometrlc combustion of at least some of the gas in the first gas stream to produce a third gas stream, removing particulates from the gas in the third gas stream, and passing the gas in the third gas stream into contact with a dirty shift catalyst (e.g. one containing oxides of cobalt and . 1 .

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molybdenum, or iron and chromium) to subject it to the water gas shift reaction namely:
H o + C0 -> H2 ~ C2 to ther~by produce the second gas stream. Step (b) may be practiced by passing the gas in the second gas stream into contact with white liquor from kraft paper pulp being processed to remove the hydrogen sulfide therefrom, and increase the sulfidity of the white liquor.
According to another aspect of the present invention, a method of converting a first gas stream in~luding water vapor and over 10% (e.g. about 15-80%) by weight organic sulfur compounds, into a second gas stream comprising primarily H2S and methane is provided. The first gas stream is preferably composed of off gases from kraft or sulfite pulping processes containing methyl mercaptan, DMS, and hydrogen sulfide, but other sources may also be treated according to the invention. The method comprises the steps of: ~a) Adding hydrogen to the gas in the first gas stream.
And, (b) passing the first gas stream, in the presence of the added hydrogen, past a hydrogen desulfurization catalyst to produce the second gas stream. There is also preferably the further step (c), prior to step (a), of removing the vast majority of the water vapor from the first gas stream. The method may consist of only these steps (a)-(c). Step (a) may be practiced by: (al~
Removing hydrogen sulfide from the gas in the second gas stream to produce a third gas stream containing primarily methane and hydrogen. (a2) Reacting the gas in the third gas stream with steam, and then 4 ~ S3 ~r3 ~

subjecting it to the water gas shift reaction in the presence of a catalyst to produce a fourth gas stream containing primarily hydrogen, methane, and carbon dioxide. And, (a3) separating the hydrogen from the fourth gas stream, to be added to the gas in the first gas stream, while producing a fifth gas stream containing primarily methane and carbon dioxide. There may also be the further step of combusting the gas in the fifth gas stream to provide heat to produce the steam utilized in step (a2).
According to yet another aspect of the present invention a method of converting a first gas stream including water vapor, and over 10% (e.g. about 15-80%) by weight organic sulfur compounds, into a third gas stream comprising primarily H2S and methane is provided. This method comprises the steps of: (a) Effecting substochiometric combustion of at least some the gas in the first gas stream to produce a second gas stream. (b) Removing particulates from the gas in the second gas stream.
And, (c) passing the gas in the second gas stream into contact with a dirty shift catalyst to subject it to the water gas shift reaction and thereby produce a third gas stream comprising primarily hydrogen sulfide and methane, with some carbon dioxide. Step (a) may be practiced to effect substochiometric combustion of only a first part of the gas in the first gas stream, and then there is a further step (d) of passing a second part of the gas in the first gas stream into the second gas stream before the practice of step (c). Alternatively, step (a) may be practiced to effect substochiometric - , :
.

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3~ ~ 9 combustion of essentially all of the gas in the first gas stream.
It is the primary object of the present invention to provide for the effective utilization of gases containing high amounts of organic sulfur compounds, particularly for producing the gas containing hydrogen sulfide and methane from such an off gas. 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 OE T~E DRA~I~GS

FIGURES lA and lB are a schematic of one exemplary embodiment of apparatus for treating gases containing organic sulphur compounds in accordance with the present invention;

EIGURE 2 is a schematic of an alternative method of treating gases containing organic sulphur compounds; and FIGURE 3 is a schematic like that of FIGURE 2 indicating a few process changes.

FIGURES lA and lB schematically illustrate at 10 apparatus for practicing a method of converting a gas stream having a large amount of organic sulfur compounds therein into a second gas stream comprising primarily H2S and methane. Typically the ., ' , ' ' ' : ' ' ' .

' ;' :' ', -' ;~, ` 5; ~ ~' q 9 off gas streams treated according to the invention include water vapor and over 10% (e.g. about 15-80%) by weight organic sulfur compounds. The organic sulfur compounds typically present are methyl mercaptan, dimethyl sulfide (DMS), and hydrogen sulfide, the water vapor is in the form of steam, and additional organic and inorganic compounds are also present. While the apparatus 10 is useful for the treatment of any gas stream having a high level of organic sulfur compounds, it is preferably utilized with -- and will be described with respect to herein -- the treatment of off gases from kraft ~or sulfite) pulping processes in the production of paper pulp.
In a typical kraft pulping process, a digester 12 (FIGURE lB) -- which may be a continuous digester such as that sold by Kamyr, Inc. of Glens Falls, New York, or a batch digester -- has a stream of off gases 13, and black liquor is withdrawn at an intermediate position as indicated at 14 in FIGURE
lB, while the kraft pulp produced is discharged at 15. When the black liquor in line 14 is discharged, it may be passed directly to black liquor evaporators, but preferably it is first subjected to a heat treatment process at step 17 to produce off gases in line 18. The heat treatment of block 17 in FIGURE lA is preferably that described in U.S.
patent 4,929,307. After heat treatment at 17 the black liquor passes to evaporators 19 which also produce off gases in line 20, then to a conventional recovery ~oiler 22, with conventional white liquor manufacture at block 23, to produce white li~uor in line 24 having conventional sulfidity.

' According to the present invention the off gases in line 18 -- which may include only those from the heat treatment 17, only those from the digester line 13, only those from the black liquor evaporators in line 20, or a combination of two or all of them -- are preîerably first subjected to a drying or absorption stage (as indicated schematically at 27 in FIGURE 1) in order to remove a majority of the water vapor. The removal of the water vapor increases the concentration of organic sulfur gases. Step 27 is accomplished by drying the gas stream by any conventional means and/or by absorbing or adsorbing the organic portion of the gas onto a solid, or additionally by absorbing the off gas into one of any non-polar li~uids (e.g.
kerosene or mineral oil). Treatment may be provided of a liquid mixture, but preferably according to the invention further treatment is of the concentrated gas.
The next steps in the practice of the invention as illustrated in FIGURE 1 are to add hydrogen, and then pass the gas in the presence of the added hydrogen past a hydrogen desulfurization catalyst.
This is accomplished in the hydrogen desulfurization (HDS) unit 28, with the hydrogen gas from line 29 added to the unit 28 along with the gas in line 18.
The hydrogen gas in line 29 can come from any source (e.g. be purchased , from water electroylsis, etc.). It is preferred that the hydrogen desulfurization catalyst consist essentially of a transition metal molybdenum alloy, particularly a nickel molybdenum or cobalt molybdenum alloy. An ?~ 9 example of the decomposition reaction that takes place in unit 28 is as follows:

This process is effective despite the fact that the concentration of organic sulfur compounds is typically higher than 15%. The temperature conditions in the unit 28 must be at least 50F over the dew point of the gas, and are typically 390-750F, preferably about 410-700F, and the pressure conditions are typically 150-300 psig, but can run from atmospheric pressure to 1,000 psig.
If liquid phase processing is practiced, the hydrogen sulfide, methane, and other sulfur free gases may be stripped from the liguid phase.
Typically however in gaseous processing, the product gas stream in line 30 is further acted upon. The gas stream in line 30 contains primarily methane, and hydrogen sulfide, with hydrogen also present.
Preferably the hydrogen sulfide is then separated out from the gas in stream 30. While the hydrogen sulfide may be separated as a gas and then used in its gaseous form in conventional pulping techniques, preferably it is fed to a scrubber 32 in which it is brought into contact with a caustic solution. In the preferred embodiment illustrated in the drawings, white liquor (although green liquor may also be advantageously utilized) from line 24 is passed into inlet 33 of scrubber 32, the hydrogen sulfide being absorbed in the white liquor and thereby significantly enhancing its sulfidity. The significantly enhanced sulfidity white liquor then passes through the outlet 34 of the ~crubber into line 35, to ~e used in the pulping process. The gas , ~

:: :; :
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stream that remains, in line 38, contains primarily methane, but also some hydrogen. This is accomplished by splitting of gas flow in line 38 into lines 39 and 40 (FIGURE lA), line 39 providing a reformer feed gas line for a methane/steam reformer 42, while the gas in line 40 is part of the feed gas for the pressure swing adsorption ~PSA~ :
unit 43.
A feed water line 45 is provided through heat exchanger 46 in the hot gas exhaust conduit 47 of reformer 42. The feed water is turned into steam in 46, which passes in line 48 to mix with the reformer eed gas in line 39, in the line 49. In the reformer 42, the following reaction occurs:
CnHm ~ n H20 -> n C0 ~ (n ~ m/2) ~2 The gas in line 50 thus is primarily hydrogen and carbon monoxide. From line 50 it passes to a shift converter 52. In the shift converter 52, the gas is reacted over an appropriate mixture of the oxides of iron and chromium which act as catalysts to promote the water gas shift reaction H 0 ~ C0 -> H2 + C2 The temperature conditions in the unit 52 are at least 50F above the dew point of the gas, and are typically 450-950F, and the pressure conditions are typically 150-300 psig, but can run from atmospheric to 1,000 psig.
The product gas mixture from the water gas shift reaction in line 54 contains primarily hydrogen and carbon dioxide, and this is added with the methane from line 40 to the PSA unit 43. In ths unit 43, conventional adsorption or absorption methods are practiced to yield the pure hydrogen , .

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stream ~9, and a second stream 56 which contains primarily methane and carbon dioxide. The methane and carbon dioxide in line 56 may be split into a line S7 which is used as the fuel gas for the combustion chamber 58 of the methane/steam reformer 42 -- and thus providing the energy source for the reformer 42. If there is any excess fuel gas, it may be passed into storage at 60, or used as the combustion source for the lime Xiln typically associated with a kraft pulping plant.
While not part of the claimed method according to the invention, it is to be understood that the white liguor in line 35 may be very advantageously used in pulp processing. The liquor in line 35 has enhanced sulfidity compared to the conventional white liguor in line 24, and may be used in apparatus 62 (FIGURE lB) which comprises a conventional chip feed system, and/or a conventional impregnation vessel. The pulp slurry, with the increased sulfidity white liquor, in line 64 passes to the top of the digester 12 (typically a continuous digester), while white li~uor of conventional sulfidity passes in line 66 to be added to a circulation loop in the digester 12. Typically the conventional sulfidity white liquor in line 66 can be used in the MCC~ process of Kamyr, Inc. of Glens Falls, New York.
It is noted that when white liquor with enhanced sulfidity is utilized in the pulping process, it can be expected that the off gases in line 13 from digester 12 will have an increased amount of organic sulfur compounds, thereby either .. , ", ~. -..

~ r~ 9 necessitating, or making more desirable, their treatment in the apparatus heretofore described.
In the ollowing example, a source of DMS at a high concentration was treated over a hydrotreating catalyst to demonstrate the feasibility of the process heretofore described. Because conventional testing facilities that are capable of hydrotreating streams of DMS are not set up to act upon the exact gas streams that will be utilized in the practice of the invention, but in order to effectively simulate such reactions, the DMS was processed in a blend of 25 volu~e percent DMS and 75 volume percent kerosene. The test is reported as follows:
Example 1 The initial processing conditions selected were: 6.0 LHSV, 150 psig and 2500 SCFB reactor gas rate (based on total feed, not just DMS). These conditions were sufficient to convert the great majority of the DMS when the temperature was raised to an average of 640F. Reducing the throughput to 3.0 LHSV resulted in a slight apparent increase in conversion. Reducing the reactor gas rate to 1600 SCFB did not slow the conversation of DMS (in fact it may have increased it), but reducing it to about 1000 SCFB did.
A reactor in a bench scale isothermal hydrotreating pilot plant was loaded with 87 ccs. of Criterion C324 nickel molybdenum hydrotreating catalyst.
After pressure testing and gas meter calibration checks, the unit was started up and the catalyst sulfided using standard procedure.
Kerosene containing 4 wt% DMS was used as sulfiding - : :
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12 ~ ,f~ g feed. After sulfiding was completed, the temperature was lowered to 500F and the run feed was introduced.
The run feed was a 25/7~ volume percent blend of DMS and kerosene. Assuming complete conversion of the DMS with no reaction of the kerosene, then the expected yield of ~2S would be 14.2 wt% of the total feed and the yield of Cl would be 13.3 wt%.
If there is some reaction of the kerosene it should not contribute more than 0.01 to 0.02 wt% to the H2S
yield. The contribution of the kerosene to the methane yield is expected to be small.
The unit was lined out at the initial run conditions of S00F, 6.0 LHSV, 150 psig and 2500 SCFB reactor gas rate (based on the total feed).
The conversion of DMS ~as very low at these conditions, so the temperature was raised. Between 500F and 520F, the DMS began to convert in large quantities, which generated a large exotherm. Once the reactor temperatures were ~rought under control, the reactor inlet temperature was increased as much as possible (to about 560F) so that the average reactor temperature was maximized at about 660F
while the hottest points were held to 734F.
Exceeding approximately 750F was avoided so as to avoid extensive thermal cracking of the kerosene, which could possibly cause a much greater exotherm.
At these conditions, the weight percent yields of hydrogen sulfide and methane were approximately 13.3 and 12.5, respectiveLy.
The reactor gas rate was reduced to 1575 SCFB, which did not reduce conversion at all. H2S and C
yields were 14.1 and 12.6, which indicate ., , , .;
:. . :; : . :

conversation is no lower and possibly even higher (perhaps due to increased residence time in the reactor~. The reactor gas was then reduced to 1040 SCFB which did cause the H2S yield to drop to 13.4 although the Cl yield increased to about 13.5.
The example indicated that near-complete conversion of DMS over a hydrotreating catalyst is feasible. The temperature at which the reaction begins to proceed very quickly is between 510F and 520F (at the catalyst inlet). A minimum gas rate o 1600 SCFB (based on total feed, the te~t feed being at 75/25 volume percent blend of kerosene and DMS) is desirable to keep the reaction rom being limited by hydrogen availability, but additional hydrogen may be necessary for long catalyst life.

Another embodiment according to the invention is schematically illustrated in FIGURE 2. In this embodiment, the off gases in line lB are split into two streams, 71 and 72, with the stream 71 led to the partial oxidation block 73 in FIGURE 2. That is the gas in line 71 is reacted with a substochiometric amount of oxygen or air from line 74 (with or without steam) to produce a gas in line 75 rich in hydrogen and carbon monoxide, and also containing carbon dioxide, hydrogen sulfide, carbonyl sulfide, methane, sulfur dioxide, and other compounds including particulates (soot). Nitrogen will also be present if the gas from source 74 is air instead of essentially pure oxygen. The gas in line 75 is preferably cleaned of soot by conventional techni~ues as indicated at 76, and feed gas in line 72 is recombined with the gas in line ' ~ ' ~.
" ~

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14 ~ ?~-75, either before or after the soot removal block 76. Then the gas in line 75 is passed over a special shift catalyst which can tolerate sulfur compounds, as indicated at 77 in FIGURE 2. The dirty shift catalyst in 77 -- which preferably comprises an alumina catalyst containing oxides of an cobalt and molybdenum (commercially available from BASF under the trade name K8-11) -- promotes the water gas shift reaction H20 ~ C0 -> H2 ~ C2 even in the presence of sulfur. The temperature and pressure conditions in 77 are about 450-950F, and about 150-300 psig. A normal catalyst for the water gas shift reaction, such as oxides of iron and chromium as described with respect tv FIGURE lA, is poisoned by sulfur compounds, ~ut catalysts containing oxides of cobalt and molybdenum can effectively treat such gases. This catalyst also promotes the hydrolysis of carbonyl sulfide into hydrogen sulfide as follows:
COS + H2 -~ H2S ~ C2 .:
The primarily hydrogen and carbon dioxide gas stream 79 produced can then be used to treat the remaining sulfur containing off gases which are added in line 72. The gases in line 72 may be added either as illustrated in FIGURE 2, or directly to the line 79. The gases in line 79 may also be added to an HDS unit 28 to effect organic sulfur decomposition, as indicated at box 80 in FIGURE 2.
The latter reaction may also be accomplished by passing the hydrogen, carbon monoxide, and sulfur containing off gas mixtures through several sulfur tolerant carbon monoxide shift reactors in series.
The sulfur tolerant catalyst in the shift reactor : , ~
.
.. . . . . ..
-, ~

;,~ ?~' q ~3 can also promote the organic sulfur decomposition reaction as follows: CH3SCH3 ~ 2 H2 ~~~ 2 CH4 ~
H2S. ThP gas mixture is then again separated into a stream containing hydrogen sulfide and a stream containing clean fuel gas. If this processing scheme is employed, the final gas mixture before separation will contain carbon dioxide, methane, hydrogen, and hydrogen sulfide. The gas stream will also contain nitrogen if air was used as the oxygen source for the partial oxidation reaction.
The reaction then proceeds to the H2S recovery stage 81. If carbon dioxide can be tolerated in the hydrogen sulfide stream, a simple acid gas scrubbing system may be used to separate the carbon dioxide and hydrogen sulfide from the gas mixture. If carbon dioxide cannot be tolerated in the hydrogen sulfide stream, selective removal of the hydrogen sulfide by adsorption, absorption, or membrane may be employed. Scrubbing with a selective solvent such as methyldiethanolamine can remove essentially all of the hydrogen sulfide from the gas stream while removing only a small fraction of the carbon dioxide. The hydrogen sulfide in line 82 may be used directly in pulping, or absorbed into white or green li~uor as described with respect to FIGURE 1.
The gas in line 83 is primarily fuel gas, but it may contain nitrogen if air was used as the gas in line 74. The nitrogen may optionally be removed -- as indicated by line box 84 -- by adsorption, membrane separation, or other viable techniques so as to increase the heat value of the product fuel gas. The remaining gas may then be used as a fuel or the carbon dioxide and remaining hydrogen may be .

16 ~ ` q ~3 passed, at 86, over a methanation reactor containing an appropriate nickel catalyst where the carbon dioxide and hydrogen are converted into methane and water vapor as follows:
C2 + 4 H2 ~~ C~4 + 2 H2 The resulting ~uel gas stream 88 can then be dehydrated at 87, and used as a clean fuel source.
Example 2 The following table provides the summary of gas analysis in reacting DMS with oxygen, in the presence of nitrogen (simulating air) to demonstrate the composition of gases from the partial oxidation stage 73:
TAsLEI
Tille 20:00 24:00 04:00 08:00 0~ygen Rate, llhr 16.0 21.3 10.7 16.0 ~ol eslhr0 . 68 0 . 900. 45 0 . 68 Nitrogen Rate l/hr 22.6 22.6 0.0 0.0 ~oleslhr0,96 0.96 0.0 0.0 DMS Rate, g~/hr31.1 31.1 31.1 31.1 ~oles/hr0.50 0.50 0.50 0.50 Sa~pling ~lethodBrine Heat Heat Brine Special GC Analysis N, C0, C 66.7 65.7 29.0 38.0 SU I 9.6 1~.4 10.0 4.0 D~ 4.9 5.7 13.4 14.4 R S 0.0 0.003 0.0 0.0 C~S 1.4 0.6 ~.5 0.7 Standard GC Analysis C 0.9 1.8 4.2 3.4 i3-C 0.2 0.2 H 4 9.2 16.0 35.6 44.3 o2 1.4 1.7 2.9 3.1 112 55.4 50.7 0.1 0.4 c2 12.6 8,0 22.8 9.2 C0 14.9 18.7 29.8 35.8 C0 1.6 2.0 1.8 2.4 C D 2 . 5 1 . 1 2 . 4 1 . I
C22 0.2 0.06 0.1 0.1 -, . .

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18 ~ 9 The following table indicates similar results when water vapor is part of the feed to the partial oxidation stage 73:

Ti~e 17:00 18:00 O~ygen Rate, 1/hr 21.3 21.3 ~oles/hr 0 90 0.90 Nitrogen Rate, I/hr 17.8 17.8 ooles/hr0 75 0,75 DMS Rate, g~/hr31.1 31.1 noles/hr 0.50 0.50 Water Rate, g~/hr 9.0 9.0 roles/hr 0 50 0 50 Sa~pling MethodSaturated S04 Solution Special ~C Analysis N, C0, Cl 90.7 92.7 Su 0.0 0.0 DM~S 4.6 2.4 R S 0.8 0.8 C~S 4 0 4.1 Standard GC Analysis C 0.5 0.3 '12 6.4 1.5 0 0.8 0.9 N22 46.4 64.1 C 21.1 12.8 C~ ~.7 1.6 C2 10.3 16.0 C2~ 4.3 2.4 C2 0.5 0.4 . .... : , ~ ' ' ' '- . :
: ,- :. : : , - . : , .. :
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;, 9 FIGURE 3 illustrates a slightly modified form of the process of FIGURE 2. In FIGURE 3 components comparable to those in FIGURE 2 are shown by the same reference numeral. The major distinction of the method of FIGURE 3 is that the substochiometric combustion is for the entire gas stream in line 71.
Also, block 91 is provided indicating the heat value of the gas may be incxeased by passing it over a sulfur tolerant direct methanation catalyst (such as one available from Haldor Topsoe Company~ which promotes the following reaction:
2 C0 + 2 H2 ~~ CH4 + C02 The gas mixture may then be purified and the sulfur compounds isolated as described with respect to FIGURE 2.
It will thus be seen that according to the present invention it is possible to very effectively act upon the off gases from a kraft or sulfite digester, or black liquor evaporators, as well as off gases from the heating of black liquor to reduce its viscosity, which off gases contain high levels of orqanic sulfur compounds and water vapor, the gas typically containing over 10% ~e.g. about 15-80%) by weight organic sulur compounds. While the invention has been herein shown and described in what is presently conceived the most practical and preferred embodiment it will be apparent to those of ordinary skill in the art that many modifications may be made thereof 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 processes and procedures.

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,

Claims (24)

1. A method of converting a first gas stream including water vapor, and over 10% by weight organic sulphur compounds, into a second gas stream comprising primarily H2S and methane, comprising the steps of:
(a) adding hydrogen to the gas in the first gas stream; and (b) passing the first gas stream, in the presence of the added hydrogen, past a hydrogen desulfurization catalyst to produce the second gas stream.
2. A method as recited in claim 1 comprising the further step (c), prior to step (a), of removing the vast majority of the water vapor from the first gas stream.
3. A method as recited in claim 2 consisting essentially of steps (a)-(c).
4. A method as recited in claim 1 wherein step (b) is practiced by passing the first gas stream in the presence of hydrogen into contact with a catalyst selected from the group consisting essentially of transition metal-molybdenum alloys.
5. A method as recited in claim 1 wherein step (b) is practiced by passing the first gas stream in the presence of hydrogen into contact with a catalyst selected from the group consisting essentially of nickel molybdenum and cobalt molybdenum.
6. A method as recited in claim 1 wherein step (a) is practiced by: (a1) removing hydrogen sulfide from the gas in the second gas stream to produce a third gas stream containing primarily methane and hydrogen; (a2) reacting the gas in the third gas stream with steam, and then subjecting it to the water gas shift reaction in the presence of a catalyst to produce a fourth gas stream containing primarily hydrogen, methane, and carbon dioxide; and (a3) separating the hydrogen from the fourth gas stream, to be added to the gas in the first gas stream, while producing a fifth gas stream containing primarily methane and carbon dioxide.
7. A method as recited in claim 6 wherein step (a3) is practiced by adsorption or absorption.
8. A method as recited in claim 6 wherein step (a1) is practiced by passing the gas in the second gas stream into contact with white or green liquor from kraft paper pulping processes.
9. A method as recited in claim 1 comprising the further step of passing the gas in the second gas stream into contact with white or green liquor from kraft paper pulping processes to remove the hydrogen sulfide therefrom, so as to produce a third gas stream containing primarily methane and hydrogen.
10. A method as recited in claim 1 wherein the gas from the first gas stream has 15-80% organic sulfur compounds and is selected from the group consisting of off gases from a kraft or sulfite digester, off gases from a black liquor evaporator, off gases from the heat treatment of black liquor above digestion temperature, and mixtures thereof.
11. A method as recited in claim 6 comprising the further step of combusting the gas in the fifth gas stream to provide heat to produce the steam utilized in step (a2).
12. A method of converting a first gas stream including water vapor, and over 10% by weight organic sulphur compounds, into a third gas stream comprising primarily H2S and methane, comprising the steps of:
(a) effecting substochiometric combustion of at least some the gas in the first gas stream to produce a second gas stream;
(b) removing particulates from the gas in the second gas stream; and (c) passing the gas in the second gas stream into contact with a dirty shift catalyst to subject it to the water gas shift reaction and thereby produce a third gas stream comprising primarily hydrogen sulfide and methane, with some carbon dioxide.
13. A method as recited in claim 12 wherein step (c) is practiced by passing the gas in the second gas stream into contact with a catalyst containing oxides of cobalt and molybdenum.
14. A method as recited in claim 12 wherein the gas from the first gas stream has about 15-80%
organic sulfur compounds and is selected from the group consisting of off gases from a kraft or sulfite digester, off gases from a black liquor evaporator, off gases from the heat treatment of black liquor above digestion temperature, and mixtures thereof.
15. A method as recited in claim 12 wherein step (a) is practiced to effect substochiometric combustion of only a first part of the gas in the first gas stream, and comprising the further step (d) of passing a second part of the gas in the first gas stream into the second gas stream before the practice of step (c).
16. A method as recited in claim 12 wherein step (a) is practiced to effect substochiometric combustion of essentially all of the gas in the first gas stream.
17. A method as recited in claim 12 comprising the further step of separating the hydrogen sulfide from the third gas stream by scrubbing it with a solvent, absorption, adsorption, or by utilizing a diffusion membrane.
18. A method as recited in claim 12 comprising the further step of passing the gas in the third gas stream into contact with white or green liquor from kraft paper pulping processes to remove the hydrogen sulfide therefrom, so as to produce a fuel gas stream containing primarily methane.
19. A method as recited in claim 12 comprising the further steps of separating the hydrogen sulfide from the third gas stream to produce a fuel gas stream, and then removing nitrogen water vapor from the fuel gas stream.
20. A method of acting on a first gas stream consisting essentially of off gases from a kraft or sulfite digester, off gases from a black liquor evaporator, and mixtures thereof, comprising the steps of (a) treating the gases in the first gas stream to produce a second gas stream containing primarily hydrogen sulfide and methane, and then (b) separating the hydrogen sulfide from the methane.
21. A method as recited in claim 20 wherein step (a) is practiced by adding hydrogen to the gas in the first gas stream; and passing the first gas stream, in the presence of the added hydrogen, past a hydrogen desulfurization catalyst to produce the second gas stream.
22. A method as recited in claim 20 wherein step (a) is practiced by: effecting substochiometric combustion of at least some the gas in the first gas stream to produce a third gas stream; removing particulates from the gas in the third gas stream;
and passing the gas in the third gas stream into contact with a dirty shift catalyst to subject it to the water gas shift reaction and thereby produce the second gas stream.
23. A method as recited in claim 20 wherein step (b) is practiced by passing the gas in the second gas stream into contact with white or green liquor from kraft paper pulping processes to remove the hydrogen sulfide therefrom.
24. A method as recited in claim 22 wherein step (a) is practiced by passing the gas in the third gas stream into contcat with a catalyst containing oxides of cobalt and molybdenum.
CA002060819A 1991-09-10 1992-02-07 Treatment of organic sulfur gases especially in kraft pulping systems and processes Abandoned CA2060819A1 (en)

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US5234546A (en) * 1991-09-10 1993-08-10 Kamyr, Inc. Polysulfide production in white liquor
US8940129B2 (en) 2010-12-30 2015-01-27 Uop Llc Process for reducing one or more insoluble solids in a black liquor
CN103608109A (en) * 2011-06-14 2014-02-26 国际壳牌研究有限公司 Aqueous catalyst sulfiding process
US10870810B2 (en) 2017-07-20 2020-12-22 Proteum Energy, Llc Method and system for converting associated gas

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US4067767A (en) * 1972-10-05 1978-01-10 Texaco Inc. Liquid phase coking of spent kraft pulping liquors
US4254094A (en) * 1979-03-19 1981-03-03 Air Products And Chemicals, Inc. Process for producing hydrogen from synthesis gas containing COS
US4839326A (en) * 1985-04-22 1989-06-13 Exxon Research And Engineering Company Promoted molybdenum and tungsten sulfide catalysts, their preparation and use
GB8803767D0 (en) * 1988-02-18 1988-03-16 Ici Plc Desulphurisation
CA2103664C (en) * 1991-02-06 1997-08-19 Rolf Ryham Method of recovering energy and chemicals from black liquor

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