CA2015987C - Solution removal of h2s from gas streams - Google Patents
Solution removal of h2s from gas streams Download PDFInfo
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- CA2015987C CA2015987C CA 2015987 CA2015987A CA2015987C CA 2015987 C CA2015987 C CA 2015987C CA 2015987 CA2015987 CA 2015987 CA 2015987 A CA2015987 A CA 2015987A CA 2015987 C CA2015987 C CA 2015987C
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Abstract
A process for the removal of H2S from sour gaseous streams is disclosed in which the sour gaseous stream is contacted with a solution containing solubilized iron chelates of a specified organic acid or acids. The contacting is carried out in first and second contacting zones, the first being a gas-solution mixture formation zone and the second comprising a plurality of contacting sections adapted to provide reaction of the H2S in the sour gaseous stream with the iron in the contacting solution without plugging due to deposition of sulphur.
Description
2~~.~~~~1 1 _ The presence of significant quantities of H2S in various "sour" industrial gaseous streams poses a persistent problem.
Although various procedures have been developed to remove and recover this contaminant, most such processes are deficient, for a variety of reasons.
In one cyclic method currently attracting attention, the sour gas is contacted with an aqueous polyvalent metal chelate or complex reactant solution to produce solid sulphur which is recovered either prior to or subsequent to regeneration of the reactant. Preferred reactants are iron (III) complexes in which the iron (III) forms complexes with specified organic acids and derivatives thereof.
While sour gaseous streams that contain relatively low concen-trations of H2S may be treated sucessfully in a variety of ways if deep removal; e.g., greater than 9S percent removal of H2S, is not required,, removal of this level, or greatex, demands efficiencies of operation if excessive costs of operation and materials are not to be incurred.
One scheme for carrying out the gas treatment utilizes a 20 two°stage contacting procedure in which a venturi-shaped contacting zone is utilized as an initial or primary contacting stage to remove the bulk of the H2S, and a follow-up or "clean-up",stage, such as a packed-column or sparged tower, is provided for removing the remainder of the H2S in the gaseous stream.
These configurations have a number of drawbacks, such as susceptibility to plugging, high gas pressure drop, and high cost.
It has been determined that the H2S removal rate by iron cheiate or complex systems is not limited by the reaction rate of the iron with the H2S, but by the rate of absorption of t'he H2S into the 30 reactant solution:
2 _ The present invention provides a process with an efficient contacting technique to insure good absorption rates of the H2S
into the contacting solution, while avoiding or minimizing plugging and high pressure drop might have great utility. U.S.
patent 4,664,902, and U.S. patent 4,758,416, describe a multizone contact procedure in which a specified contact zone comprises a plurality of serial flow contact sections. In one embodiment, a first contact section of the specified contact Zone comprises a plurality of discrete channels which provide a diverted flow path for the gas-solution mixture in process, the channelled section being followed by a redistribution section which is adapted to allow radial mixing and redistribution of solution in the gas, while inhibiting plugging. The invention is an improvement on this technique.
To this and the process for the removal of H2S from a sour gaseous stream according to the present invention comprises a) feeding the sour gaseous stream to a first contacting zone, and intimately contacting the sour gaseous stream in said first contacting zone with an aqueous reactant solution containing solubilized Fe(III) chelate of an organic acid, or mixture of said acids, and solubilized Fe(II) chelate of said acid or acids, at a temperature below the melting point of sulphur, and at a sufficient solution to gas ratio and conditions effective to convert H2S to sulphur and inhibit sulphur deposition, and praducing a gas~solution mixture comprising sour gas and aqueous reactant solution;
b) passing gas-solution mixture from step a) through a plurality of enclosed contacting sections in serial flow communication in a second contacting zone; under conditions to convert HZS
~o sulphur and at a temperature below the melting point of sulphur, the first contacting section of said second contacting zone comprising a plurality of discrete sulphur deposition resistant channels; each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow of the gas-solution mixture entering the section; the second contacting section through which gas-solution mixture is passed comprising an enclosed mixing section operative to or adapted to allow radial mixing of gas-solution mixture and re-distribution of solution in gas, and to inhibit plugging due to sulphur formation, the third contacting section through which gas-solution mixture is passed comprising a plurality of discrete sulphur deposition resistant channels, each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow of the gas-solution mixture entering the section; and producing a gas-reactant solution mixture containing solid sulphur in said second contacting zone, the reactant solution of said gas-reactant solution mixture having a reduced content of solubilized Fe(III) chelate of said acid or acids and the gas of said mixture having a reduced H2S
content;
c) passing the gas-solution mixture from the third contacting section through an addition contact section of said second contact zone and contacting the gas-solution mixture with aqueous reactant solution containing solubilized Fe(III) chelate of said acid or acids and solubilized Fe(II) chelate of said acid or acids, and forming a gas-solution mixture having an increased solution to gas ratio; and d) separating the gas having reduced H2S content from gas-reactant solution mixture produced in step c).
The gas having reduced H2S content may be separated from the w solution in the second contacting zone, but is preferably separated in a separate vessel or step. If further purification is necessary or desired, the spray contacting procedure of steps a) and b) may be repeated, or other contacting techniques or schemes, such as use of a sparged tower or towers, may be used. In such cases, appropriate measures will be taken for separation of the further purified gas and regeneration of the aqueous reactant solutions) employed. For example, the solution produced by step c) and additional solution from further purification or contacting steps may be combined and regenerated in a single regeneration step, sulphur removal being accomplished prior to or after the regeneration. Preferably, however, the gas having reduced H2S
content from step d) will simply be separated from the reactant solution, and a spent reactant solution containing sulphur will be recovered. In this case, sulphur will be removed from the spent reaetant solution containing sulphur, and the spent reactant solution from which sulphur has been removed will be regenerated, producing a reactant solution having an increased concentration of Fe(III) chelate.
In a second embodiment, the invention relates to a process for ~ the removal of H2S from a sour gaseous stream comprising a) feeding the sour gaseous stream to a first contacting zone, and intimately contacting the sour gaseous stream in said .
first contacting zone with an aqueous reactant solution containing solubilized Fe(III) chelate of an organic acid or mixture of said acids, and solubilized Fe(Ii) chelate of said acid or acids, at a temperature below the melting point of sulphur, and at a sufficient solution to gas ratio and conditions effective to convert H2S to sulphur and inhibit sulphur deposition, and producing a gas-solution mixture comprising roux gas and aqueous reactant solution;
b) passing gas-solution mixture from step a) through a plurality of enclosed contacting sections in serial flow communication in a second contacting zone; under conditions to convert H2S
to sulphur and at a temperature below the melting point of , sulphur, the first contacting section of said second contacting zone comprising a plurality of discrete sulphur deposition resistant channels, each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow ~fl~.~~~
Although various procedures have been developed to remove and recover this contaminant, most such processes are deficient, for a variety of reasons.
In one cyclic method currently attracting attention, the sour gas is contacted with an aqueous polyvalent metal chelate or complex reactant solution to produce solid sulphur which is recovered either prior to or subsequent to regeneration of the reactant. Preferred reactants are iron (III) complexes in which the iron (III) forms complexes with specified organic acids and derivatives thereof.
While sour gaseous streams that contain relatively low concen-trations of H2S may be treated sucessfully in a variety of ways if deep removal; e.g., greater than 9S percent removal of H2S, is not required,, removal of this level, or greatex, demands efficiencies of operation if excessive costs of operation and materials are not to be incurred.
One scheme for carrying out the gas treatment utilizes a 20 two°stage contacting procedure in which a venturi-shaped contacting zone is utilized as an initial or primary contacting stage to remove the bulk of the H2S, and a follow-up or "clean-up",stage, such as a packed-column or sparged tower, is provided for removing the remainder of the H2S in the gaseous stream.
These configurations have a number of drawbacks, such as susceptibility to plugging, high gas pressure drop, and high cost.
It has been determined that the H2S removal rate by iron cheiate or complex systems is not limited by the reaction rate of the iron with the H2S, but by the rate of absorption of t'he H2S into the 30 reactant solution:
2 _ The present invention provides a process with an efficient contacting technique to insure good absorption rates of the H2S
into the contacting solution, while avoiding or minimizing plugging and high pressure drop might have great utility. U.S.
patent 4,664,902, and U.S. patent 4,758,416, describe a multizone contact procedure in which a specified contact zone comprises a plurality of serial flow contact sections. In one embodiment, a first contact section of the specified contact Zone comprises a plurality of discrete channels which provide a diverted flow path for the gas-solution mixture in process, the channelled section being followed by a redistribution section which is adapted to allow radial mixing and redistribution of solution in the gas, while inhibiting plugging. The invention is an improvement on this technique.
To this and the process for the removal of H2S from a sour gaseous stream according to the present invention comprises a) feeding the sour gaseous stream to a first contacting zone, and intimately contacting the sour gaseous stream in said first contacting zone with an aqueous reactant solution containing solubilized Fe(III) chelate of an organic acid, or mixture of said acids, and solubilized Fe(II) chelate of said acid or acids, at a temperature below the melting point of sulphur, and at a sufficient solution to gas ratio and conditions effective to convert H2S to sulphur and inhibit sulphur deposition, and praducing a gas~solution mixture comprising sour gas and aqueous reactant solution;
b) passing gas-solution mixture from step a) through a plurality of enclosed contacting sections in serial flow communication in a second contacting zone; under conditions to convert HZS
~o sulphur and at a temperature below the melting point of sulphur, the first contacting section of said second contacting zone comprising a plurality of discrete sulphur deposition resistant channels; each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow of the gas-solution mixture entering the section; the second contacting section through which gas-solution mixture is passed comprising an enclosed mixing section operative to or adapted to allow radial mixing of gas-solution mixture and re-distribution of solution in gas, and to inhibit plugging due to sulphur formation, the third contacting section through which gas-solution mixture is passed comprising a plurality of discrete sulphur deposition resistant channels, each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow of the gas-solution mixture entering the section; and producing a gas-reactant solution mixture containing solid sulphur in said second contacting zone, the reactant solution of said gas-reactant solution mixture having a reduced content of solubilized Fe(III) chelate of said acid or acids and the gas of said mixture having a reduced H2S
content;
c) passing the gas-solution mixture from the third contacting section through an addition contact section of said second contact zone and contacting the gas-solution mixture with aqueous reactant solution containing solubilized Fe(III) chelate of said acid or acids and solubilized Fe(II) chelate of said acid or acids, and forming a gas-solution mixture having an increased solution to gas ratio; and d) separating the gas having reduced H2S content from gas-reactant solution mixture produced in step c).
The gas having reduced H2S content may be separated from the w solution in the second contacting zone, but is preferably separated in a separate vessel or step. If further purification is necessary or desired, the spray contacting procedure of steps a) and b) may be repeated, or other contacting techniques or schemes, such as use of a sparged tower or towers, may be used. In such cases, appropriate measures will be taken for separation of the further purified gas and regeneration of the aqueous reactant solutions) employed. For example, the solution produced by step c) and additional solution from further purification or contacting steps may be combined and regenerated in a single regeneration step, sulphur removal being accomplished prior to or after the regeneration. Preferably, however, the gas having reduced H2S
content from step d) will simply be separated from the reactant solution, and a spent reactant solution containing sulphur will be recovered. In this case, sulphur will be removed from the spent reaetant solution containing sulphur, and the spent reactant solution from which sulphur has been removed will be regenerated, producing a reactant solution having an increased concentration of Fe(III) chelate.
In a second embodiment, the invention relates to a process for ~ the removal of H2S from a sour gaseous stream comprising a) feeding the sour gaseous stream to a first contacting zone, and intimately contacting the sour gaseous stream in said .
first contacting zone with an aqueous reactant solution containing solubilized Fe(III) chelate of an organic acid or mixture of said acids, and solubilized Fe(Ii) chelate of said acid or acids, at a temperature below the melting point of sulphur, and at a sufficient solution to gas ratio and conditions effective to convert H2S to sulphur and inhibit sulphur deposition, and producing a gas-solution mixture comprising roux gas and aqueous reactant solution;
b) passing gas-solution mixture from step a) through a plurality of enclosed contacting sections in serial flow communication in a second contacting zone; under conditions to convert H2S
to sulphur and at a temperature below the melting point of , sulphur, the first contacting section of said second contacting zone comprising a plurality of discrete sulphur deposition resistant channels, each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow ~fl~.~~~
of the gas-solution mixture entering the section; the second contacting section through which gassolution mixture is passed comprising an addition contact section in which the gas-solution mixture is contacted intimately with additional aqueous reactant solution containing solubilized Fe(III) chelate of said acid or acids and solubilized Fe(II) chelate of said acid or acids to produce a gas-solution mixture having an increased solution to gas ratio; the third contacting section through which gas-solution mixture is passed comprising a plurality of discrete sulphur deposition resistant channels, each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow of the gas-solution mixture entering the section; and producing a gas-reactant solution mixture containing solid sulphur in said second contacting zone, the reactant solution of said gas-reactant solution mixture having a reduced content of solubilized Fe(III) chelate of said acid or acids and the gas of said mixture having a reduced H2S content;
c) separating the gas having reduced H2S content from gas-reactant solution mixture produced in step b).
The gas having reduced H2S content may be separated from the solution in the second contacting zone, but is preferably separated in a separate vessel or step. If further purification s necessary or desired, the spray contacting procedure of steps a) and b) may be repeated, or other contacting techniques or schemes, such as use of a sparged tower or towers, may-b$ used. In such cafes;
appropriate measures will be taken for separation of the further purified gas and regeneration of the aqueous reactant solutions) employed. For example, the solution produced by step c) and additional solution from further purification or contacting steps may be combined and regenerated in a single regeneration step;
sulphur removal being accomplished prior to or after th~ xe-generation. Preferably, however, the gas having reduced ki2S content from step b) will simply be separated from the reactant solution, and a spent reactant solution containing sulphur will be recovered.
In this case, sulphur will be removed from the spent reactant solution containing sulphur, and the spent reactant solution from which sulphur has been removed will be regenerated, producing a reactant solution having an increased concentration of the Fe(III) chelate of the given acid or acids. The regenerated solution will then be passed to the first contacting zone for use as aqueous reactant solution therein.
In another embodiment, which may be preferred in some situa-tions, the sulphur is separated after regeneration. That is, the .
spent reactant solution containing sulphur is regenerated, producing a regenerated reactant solution containing sulphur, sulphur is then removed from said regenerated solution, and the regenerated reactant solution from which sulphur has been removed is passed to the first contacting zone for use as the aqueous reactant solution therein. Sulphur may also be removed during regeneration, although this is not preferred.
As used herein, the term '°direction of flow" merely refers to the direction the bulk of the gas-solution mixture is proceeding at the respective entrances of the sections at any given time, it being recognized that a minor portion or portions of the mixture may have, at least temporarily, directional movements different , from the movement of the bulk or mass of the gas-solution mixture.
5 The acute flow path angles of the channels of a contacting section may vary considerably, but preferably the angles to the'direction of flow will range from about 5° to about 60°, most preferably from about 15° to about 4~°. Angles approaching 90° are less desirable, since such angles will increase the possibility of 30 sulphur deposition and plugging. A limited amount of "abrupt"
change of the flow of the gas-solution'mixture may thus be tolerated in the invention, provided the radial mixing and redistribution section or sections of the invention are employed, as described more fully hereinafter. The channels may be oriented 3~ in different directions with respect to each other, while ~~~~~z~g~
_,_ maintaining acute angles to the direction of flow. If a channel has a wide acute angle, or if the channel is positioned near the wall or walls of the second contacting zone, the flow of the gas-solution mixture will be directed to and contact the wall or walls of the second contacting zone, and secondary channels, at an obtuse angle to the direction of flow, communicating with these channels, may provide flow of the gas-solution mixture into the radial mixing sections. Preferably, the ratio of the length of the first contacting section to the length of the second contacting zone (length referring to the distance through the zone and section in the direction of flow) is no greater than about 0.5, preferably no greater than about 0.3. As used herein, the term "sulphur deposition resistant" refers to the quality or character of the walls of the discrete channels in being free or at least sub-stantially free of sites where sulphur, present or produced in the gas-solution mixture, may deposit. Such a suxface may be produced by polishing, such as by electropolishi.ng, or it may be formed by coating the surface with a suitable material, such as teflon type materials.
The addition contact section or sections accomplish the important function of adding and redistributing solution in the gas and inhibiting sulphur deposition. The enclosed contact sections) contains or contain means for allowing addition of additional solution, such as sprayers, spargers, etc., and will be of 5 sufficient width and length in the direction of flow to allow good mixing and prevent plugging due to sulphur formation. Those skilled in the art may determine by experimentation the minimum effective width and length of the addition contact section or sections (length referring to the distance through the sections in the direction of flow) and the appropriate ratio of the length of the respective channeled sections to the addition or redistribution sections. In practice, the ratio will preferably range ~rom about 0.1 to about 10, preferably from about 0.3 to about 4. Normally, the ratio of the length of the contacting section to the widest dimension of the section will range from about 0.2 to about 5, _$_ preferably about 0.3 to about 2. The dimensions of the first contacting zone are not critical, other than that it must be of a size where good distribution of the reactant solution in the gaseous stream is achieved. In this regard, the first contacting zone is an important part of the invention, since good initial intimate mixing of the gas stream and the reactant solution is important for efficiency.
As specified, in the first embodiment, at least two contacting sections are required in the second contacting zone, but beyond this, the number of addition contact sections in the second contacting zone is not critical. In the second embodiment, the bulk of the redistribution sections may be omitted, with the addition contact sections spacing apart at least the majority of the contacting sections. The addition of additional ferric-ferrous chelate solution in the addition contact zone not only increases gas-solution contact but provides additional wetting liquid for the channel surfaces following the addition section so that plugging is inhibited. The total number of contacting and addition contact sections will be determined primarily by the amount of H2S to be removed and the desired degree of gaseous stream purity. Normally, from 2 to 20 or 30 contacting, or channeled sections will suffice, with from 1 to 20 or 30 addition contact sections being sufficient.
It is a requirement of the invention that the contacting sections and the addition contact sections alternate in the sequence of flow, so that sulphur deposition and plugging are inhibited. The shape of the enclosing walls of the contacting sections is riot critical, but a generally cylindrical shape is preferred. The invention is admirably suited for use in the type of structure commonly referred to as a pipeline contactor, and the addition contact sections are formed from spaces between the sections containing the structured, channeled internals.
It is a preferred aspect of the invention that, by suitable flow rates and design of the channeled sections and the means of addition, tb.e flow of the gas-solution mixture through the second contacting zone will reach or approximate plug flow. Suitable _ g _ structures for providing the channeled flow include, but are not limited to, chevron-type mixers, such as Koch static mixers or Glitsch Gempak mixers. The velocity of the gas treated may vary widely. Suitable gas velocities may range from about 0.3 m/s to about 15 m/s, with a range of from about 1.5 m/s to about 9 m/s being preferred. As noted, the aqueous reactant solution to gas ratio must be sufficient to provide effective removal of H2S while inhibiting or preventing sulphur deposition in the reaction zones.
Preferably, the solution to gas ratio will range from 0.2:100 to 30:100, most preferably from 0.5:100 to 5:100, all by volume. Such ratios will generally be sufficient to provide good wetting of the channel surfaces so that sulphur deposition is inhibited or prevented. The addition contact sections comprise means, such as spray cones or nozzles, for addition of the chelate liquid.
The iron chelates employed are coordination complexes in which irons forms chelates with an organic acid. The organic acid may have the formula Y Y
N-R-N
/
y Y wherein - from two to four of the groups Y are selected from acetic and propionic acid groups;
- from zero to two of the groups Y are selected from 2-hydroxy-ethyl, 2-hydroxypropyl, and X
/
X, wherein X is selected from acetic and propionic acid groups, and wherein R is ethylene, propylene or isopropylene or alternatively cyclohexane or benzene where the two hydrogen atoms replaced by 2j nitrogen are in the 1,2 position.
~~~ ~~a~
Exemplary chelating agents for the iron include aminoacetic acids derived from ethylenediamine, diethylenetriamine, 1,2-propylenediamine, and 1,3-propylenediamine, such as EDTA
(ethylenediamine tetraacetic acid), HEEDTA (N-2-hydroxyethyl ethylenediamine triacetic acid), DETPA (diethylenetriamine pentaacetic acid); amino acetic acid derivatives of cyclic, 1,2-diamines, such as 1,2-diamino cyclohexane-N,N-tetraacetic acid, and 1,2-phenylene-diamine-N,N-tetraacetic acid, and the amides of polyamino acetic acids disclosed in Bersworth U.S. patent No. 3,580,950. The Fe(III) chelates of nitrilotriacetic acid and N-(2-hydroxyethyl) ethylenediamine triacetic acid are suitable chelating agents.
A further suitable iron chelate is the coordination complex in which iron forms a chelate with nitrilotriacetic acid (NTA).
' The iron chelates are supplied in solution as solubilized species, such as the ammonium or alkali metal salts (or mixtures thereof) of the iron chelates. As used herein, the term "solubilized" refers to the dissolved iron chelate or chelates, whether as a salt or salts of the aforementioned cation or cations, or in some other form, in which the iron chelate or chelates exist in solution. Where solubility of the chelate is difficult, and higher concentrations of chelates are desired, the ammonium salt may be utilized, as described in a similar process in U.S.A. patent No. 4,871,520. However, the invention may also be employed with more dilute solutions of the iron chelates, wherein the steps taken to prevent iron chelate precipitation are not critical.
The regeneration of the reactant is preferably accomplished by the utilization of oxygen, preferably as air. As used herein, the term "oxygen" is not limited to "pure" oxygen, but includes air, air enriched with oxygen, or other oxygen-containing gases. The oxygen will accomplish two functions, the oxidation of Fe(II) iron of the reactant to the Fe(III) state, and the stripping of any ,..
~~J~j)~
- 1.1 -residual dissolved gas (if originally present) from the aqueous admixture. The oxygen (in whatever form supplied) is supplied in a stoichiometric equivalent or excess with respect to the amount of solubilized iron chelate to be oxidized to the fe(III) state.
Preferably, the oxygen is supplied in an amount of from about 20 per cent to about 500 per cent excess. Electrochemical regeneration may also be employed.
The particular type of sour gaseous stream treated is not critical, the only practical limitation being the reactivity of the stream itself with the solutions employed, as will be evident to those skilled in the art. Streams particularly suited to removal of H2S by the practice of the invention are, as indicated, naturally-occurring gases, recycled C02 used in enhanced oil recovery, synthesis gases, process gases, and fuel gases produced by gasification procedures, e.g., gases produced by the gasific-ation of coal, petroleum, shale, tar sands, etc. Particularly preferred are coal gasification streams, natural gas streams, produced and recycled C02 streams, and refinery feedstocks composed of gaseous hydrocarbon streams, especially those streams of this type having a low ratio of H2S to C02, and other gaseous hydro-carbon streams. The term "hydrocarbon streams)°', as employed herein, is intended to include streams containing significant quantities of hydrocarbon (both paraffinic and aromatic), it being recognized that such streams contain significant "impurities" nor technically defined as a hydrocarbon. Again, streams containing principally a single hydrocarbon, e.g., ethane, axe eminently suited to the practice of the invention. Streams derived from the gasification and/or partial oxidation of gaseous or liquid hydrocarbon may be treated by the invention. The H2S content of the type of streams contemplated will vary extensively, but, in general, will range from about 0.005 per cent to about 10 per cent by volume. C02 may or may not be present, but if present, may range in content from about 0.1 per cent to about 99.0 per cent (or more) by volume. In this context, the invention may 'be used to remove H2S
from various C02 strearas, e.g., supercritical C02 streams.
Obviously, the amounts of H2S and C02 present are not generally a limiting factor in the practice of the invention. The stream treated may also have been treated initially for H2S removal, by this or some other technique.
The temperatures employed in the contacting zones are not generally critical, except that the reaction is carried out below the melting point of sulphur. In many commercial applications, such as removal of H2S from natural gas to meet pipeline specifications, absorption at ambient temperatures is desired. In general, temperatures of from 10 °C to 80 °C are suitable, and temperatures of from 20 °C to 60 °C are preferred. Total contact times may be varied widely, but will preferably range from about 0.5 second to about 10 seconds, with total contact times of about 1 second to about 5 seconds being most preferred.
Similarly, in the regeneration or stripping zone or zones, temperatures may be varied widely. Preferably, the regeneration zone should be maintained at somewhat lower temperatures compared to the contacting zone. In general, temperatures of from about 10 °C to 80 °G, preferably 20 °C to 50 °C, may be employed.
2p Pressure conditions in the contacting zones may vary widely, depending on the pressure of the gas to be treated. For example, pressures in the contacting zones may vary from 0.1 MPa up to 15 MPa or even 20 MPa. Pressures of from 0.1 MPa to about 10 MPa are preferred. In the regeneration zone, pressures may be varied considerably, and will preferably range from about 0.1 MPa to about or 40 MPa. Residence times for given volumes of admixture and oxygen will also vary, but preferably will range from about 1 minute to about 60 minutes, most preferably from about 1 minute to about 40 minutes. The pressure, fluid flow, and temperature 30 relationships involved are well understood by those skilled in the art, and need not be detailed herein. Other conditions of operation for this type of reaction process are further described in U.S.
Patent ~Io. 3,068,065, and in the aforementioned patent specification. Preferably, pH in the regeneration zone will range from about 6.5 to about 8.5, and the molar ratio of the ~~:~z; 3r nitrilotriacetic acid to total solubilized iron is from about 1.0 to 1.5. The process is preferably conducted continuously.
As indicated, the H2S, when contacted, is rapidly converted in the process of the invention by the solubilized Fe(III) chelate of the organic acid or acids to solid elemental sulphur. Since the iron chelates per se have limited solubility in water, the iron chelate compound or compounds are preferably supplied, as indicated previously. The amount of solubilized Fe(III) chelate of the organic acid or acids supplied or employed in solution is an amount sufficient to reduce the H2S concentration or content of the stream to the desired level. If total or substantially total removal is desired, the total amount supplied will generally be on the order of at least about two mots per cool of H2S. Ratios of from about 2 cools to about i5 cools of solubilized Fe(III) chelate of the organic acid or acids per cool of H2S may be used, with ratios of from about 2 cools per cool to about 5 mots of solubilized Fe(III) chelate per cool of H2S being preferred. The molar ratio of the Fe(III) chelate of the acid or acids to the Fe(II) chelate of the acid or acids present in the contacting solution will normally be less than about 6, and will preferably range from about G.2 to about 6, most preferably about 0.5 to about 6. The chelate solution will generally be supplied as an aqueous solution having a concentration of from about 0.1 molar to about 3 molar; a concentration of from about 0.5 to about 1.5 molar is preferred. The total iron concentration, as the chelates, will range from about 0.01 per cent, preferably about 0.5 per cent, to about 7 per cent by weight, based on the weight of the solution and the iron. As indicated, the solubilized iron chelates of the acid or acids may be formed in aqueous solution by the reaction of elemental iron or of an appropriate salt, oxide, or hydroxide of iron and the specified acid, in the presence of alkali metal or ammonium ions, or with the ammonium or alkali metal salt.
In order to describe the invention in greater detail, reference is made to the accompanying schematic drawing. Figure 1 illustrates an embodiment of the invention wherein at least one ~~ ~~~"1 redistribution section is utilized and the sour gas contacting zones are vertically disposed, sulphur removal is accomplished in a separate step before regeneration, and regenerated solution is returned to the contacting zone for use as the contacting solution.
Figure 2 illustrates an embodiment wherein additional chelate solution is supplied. All values axe calculated or merely exemplary, and all flows, unless stated otherwise, are continuous.
As shown, sour gas, e.g., a natural gas stream containing about 0.5 per cent H2S, in line 1 flows into generally cylindrical column 2 wherein it is intimately contacted in zone 3 thereof with a spray of an aqueous mixture from line 4 which comprises aqueous 0.35 M solution of ammonium Fe(III) NTA chelate, which mixture also contains 0.15 moles per liter of ammonium Fe(II) NTA chelate and about 0.25 mole per liter of ammonium thiosulfate, pH of the solution being adjusted to 7.5 to 8 by the addition of ammonium hydroxide. The solution is produced by utilization of the reducing effect of the H2S in the gaseous stream. That is, the initial solution employed in the contacting zone illustrated is a 0.35 M
aqueous solution of Fe(III) NTA also containing about 1.0 M
ammonium ion. After startup, and reaction with H2S in the gaseous stream, regeneration, described hereinafter, is controlled, so that regeneration of the ammonium Fe(III) NTA acid complex is not complete, in the ratios mentioned.
In zone 3, the gas stream containing H2S and the aqueous reactant mixture are intimately mixed to form a gas-reactant liquid mixture, sulphur almost immediately forming, and the gas-reactant liquid mixture is passed downwardly in cocurrent relationship to the first section S of contacting zone 6.
Although a spray device is illustrated, other suitable devices or techniques which provide intimate mixing or contacting of the gas and aqueous reactant mixture may be employed. For example, sparging units, cone sprayers, as well as venturis, may be utilized to produce a well mixed gas-solution or liquid mixture.
In any event, contacting section 5 comprises a chevron type flow directing element which provides a plurality of discrete channels for the passage and direction of the gas-reactant liquid mixture at a 30° angle to the direction of flow to the side of the cylindrical column. In this illustration, the element used is a Koch SMV. mixing element. To insure that the surfaces of the channels are resistant to sulphur deposition, the mixing element (and all those described hereinafter for zone 6) and the walls of zone 6 are electropolished before use. At least substantial plug flow overall through zone 6 is obtained. The superficial velocity of the gas is 6 m/s, and the liquid to gas volumetric flow ratio is 2:100. The width of the channels of the element is about 2.5 cm, and the diameter of the column is about 30.5 cm. The length of element 5 in the direction of flow is about 30.5 cm. As indicated, other types of elements may be employed. At the outlets of the channels of element 5, gas-reactant liquid mixture from the channels enters an open section 7 (also about 30.5 cm in length in the direction of flow) of contacting zone 6 where gas-liquid reactant mixture may mix radially and where redistribution of the solution and gas occurs. The open section also inhibits plugging, due to sulphur formation, which might occur if multiple chevron elements were placed end to end. The gas-reactant liquid mixture, with increasing solid sulphur content, passes through chevron element 8, which is identical to element 5. Element 8 may or may not be misoriented with respect to element 5.
The gas-reactant liquid mixture, upon leaving the channels of element $, passes through addition contact section 9, where the dimensions and operation are similar to that occurring in section 7. In section 9, the gas-liquid reactant mixture is contacted with additional reactant solution from sprayer 10, which is supplied via header 11 connected to line 12. As shown in the drawing, additional sprayers are provided in zone 6, following the next two contacting sections. The gas-liquid reactant mixture may be fresh mixture or regenerated mixture, as described hereinafter, or it may be supplied from some other source. The flaw of the gas-reactant liquid mixture through the remaining corresponding sections of zone 6 and the addition of additional chelate solution is similar to J 7J ~J
~~.'~f~%~'~
that described with respect to the first four sections, and need not be described, except to note that the H2S in the gas stream is continually being reduced, with concomitant sulphur formation and reduction of the Fe(III) chelate concentration.
The volume of solution supplied in the addition contact sections is not critical, sufficient solution being added simply to increase H2S removal and insure wetting of the upper portions of the respective channel sections. Preferably, the ratio of chelate solution supplied in the addition contact sections to that supplied in contact zone (3) will range from 0.1-1.0 to 2.0, but this is not critical.
The operation of the embodiment shown in.Fig~ is similar to that of Figure 1 the only difference being the addition of chelate liqu or solution in the first section (section 7) , following the first contact section.
At the lower end of column 2, the gas-reactant liquid mixture, now containing solid sulphur, passes from vessel 2, and is sent via line 13 to a separating unit or vessel 14 where the natural gas is separated from the liquid and sulphur. Purified natural gas is removed overhead via line 15, and "spent'° reactant liquid and sulphur are removed via line 16.
As those skilled in the art will recognize, solution concen-trations, sulphur content, and ferric-ferrous ligand concentrations and ratios must be regulated to achieve appropriate HzS removal.
To maintain appropriate Fe(III) concentrations and provide sulphur removal, stream 16 is sent for regeneration and sulphur removal.
More particularly, the aqueous admixture in line 16 is sent to a depressurization and degassing unit 17, which also serves as a sulphur concentration or thickening zone. A minor portion, e.g., 2 to 5 per cent by volume of the admixture in settler or thickener 17, and containing an increased sulphur concentration, is continuously withdrawn from the lower portion of settler or concentrator 17 and sent via line 18 to sulphur recovery in unit 19.
_ 17 Sulphur recovery may be accomplished in any suitable fashion, such as by filtration. For example, sulphur may also be recovered by that method described in U.S. patent No. 4,705,676. As those skilled in the art will recognize, sulphur may be removed after regeneration, if desired. In any event, solution recovered during sulphur recovery may be returned to any suitable point in the process, if proper adjustment is made. Preferably, however, the solution recovered is sent to the regeneration zone, as shown, via lines 20 and 21.
The major portion of the aqueous admixture in vessel 17 is removed via line 21 fox regeneration of the Fe(III) chelate of nitrilotriacetic acid. In regeneration zone or column 22, which may be a sparged tower, the admixture is contacted cocurrently with excess air in line 23 to convert Fe(II) chelate of NTA to Fe(III) chelate of NTA. Air velocity in the regenerator is in the range of 0.03 to 0.9 m/s, the temperature of the liquid is about 45 °C, and overall pressure is about 0.2 MPa. Spent air is removed via line 24, and regenerated admixture, having a ratio of Fe(III) chelate of NTA to Fe(II) chelate of NTA of about 2.5, is returned via line 25 to line 4, which connects, as mentioned, to column 2 and line 12.
Again, as will be understood by those skilled in the art, the solutions or mixtures employed may contain other materials or additives for given purposes. Fox example, U.S. Patent No. 3,933,993 discloses the use of buffering agents, such as phosphate and carbonate buffers. Similarly, U.S. Patent No. 4,009,251 describes various additives, such as sodium oxalate, sodium formate, sodium thiosulfate, and sodium acetate, which are beneficial, and other additives, such as additives to improve sulphur separation, or antifoaming and/or wetting agents, may be employed.
c) separating the gas having reduced H2S content from gas-reactant solution mixture produced in step b).
The gas having reduced H2S content may be separated from the solution in the second contacting zone, but is preferably separated in a separate vessel or step. If further purification s necessary or desired, the spray contacting procedure of steps a) and b) may be repeated, or other contacting techniques or schemes, such as use of a sparged tower or towers, may-b$ used. In such cafes;
appropriate measures will be taken for separation of the further purified gas and regeneration of the aqueous reactant solutions) employed. For example, the solution produced by step c) and additional solution from further purification or contacting steps may be combined and regenerated in a single regeneration step;
sulphur removal being accomplished prior to or after th~ xe-generation. Preferably, however, the gas having reduced ki2S content from step b) will simply be separated from the reactant solution, and a spent reactant solution containing sulphur will be recovered.
In this case, sulphur will be removed from the spent reactant solution containing sulphur, and the spent reactant solution from which sulphur has been removed will be regenerated, producing a reactant solution having an increased concentration of the Fe(III) chelate of the given acid or acids. The regenerated solution will then be passed to the first contacting zone for use as aqueous reactant solution therein.
In another embodiment, which may be preferred in some situa-tions, the sulphur is separated after regeneration. That is, the .
spent reactant solution containing sulphur is regenerated, producing a regenerated reactant solution containing sulphur, sulphur is then removed from said regenerated solution, and the regenerated reactant solution from which sulphur has been removed is passed to the first contacting zone for use as the aqueous reactant solution therein. Sulphur may also be removed during regeneration, although this is not preferred.
As used herein, the term '°direction of flow" merely refers to the direction the bulk of the gas-solution mixture is proceeding at the respective entrances of the sections at any given time, it being recognized that a minor portion or portions of the mixture may have, at least temporarily, directional movements different , from the movement of the bulk or mass of the gas-solution mixture.
5 The acute flow path angles of the channels of a contacting section may vary considerably, but preferably the angles to the'direction of flow will range from about 5° to about 60°, most preferably from about 15° to about 4~°. Angles approaching 90° are less desirable, since such angles will increase the possibility of 30 sulphur deposition and plugging. A limited amount of "abrupt"
change of the flow of the gas-solution'mixture may thus be tolerated in the invention, provided the radial mixing and redistribution section or sections of the invention are employed, as described more fully hereinafter. The channels may be oriented 3~ in different directions with respect to each other, while ~~~~~z~g~
_,_ maintaining acute angles to the direction of flow. If a channel has a wide acute angle, or if the channel is positioned near the wall or walls of the second contacting zone, the flow of the gas-solution mixture will be directed to and contact the wall or walls of the second contacting zone, and secondary channels, at an obtuse angle to the direction of flow, communicating with these channels, may provide flow of the gas-solution mixture into the radial mixing sections. Preferably, the ratio of the length of the first contacting section to the length of the second contacting zone (length referring to the distance through the zone and section in the direction of flow) is no greater than about 0.5, preferably no greater than about 0.3. As used herein, the term "sulphur deposition resistant" refers to the quality or character of the walls of the discrete channels in being free or at least sub-stantially free of sites where sulphur, present or produced in the gas-solution mixture, may deposit. Such a suxface may be produced by polishing, such as by electropolishi.ng, or it may be formed by coating the surface with a suitable material, such as teflon type materials.
The addition contact section or sections accomplish the important function of adding and redistributing solution in the gas and inhibiting sulphur deposition. The enclosed contact sections) contains or contain means for allowing addition of additional solution, such as sprayers, spargers, etc., and will be of 5 sufficient width and length in the direction of flow to allow good mixing and prevent plugging due to sulphur formation. Those skilled in the art may determine by experimentation the minimum effective width and length of the addition contact section or sections (length referring to the distance through the sections in the direction of flow) and the appropriate ratio of the length of the respective channeled sections to the addition or redistribution sections. In practice, the ratio will preferably range ~rom about 0.1 to about 10, preferably from about 0.3 to about 4. Normally, the ratio of the length of the contacting section to the widest dimension of the section will range from about 0.2 to about 5, _$_ preferably about 0.3 to about 2. The dimensions of the first contacting zone are not critical, other than that it must be of a size where good distribution of the reactant solution in the gaseous stream is achieved. In this regard, the first contacting zone is an important part of the invention, since good initial intimate mixing of the gas stream and the reactant solution is important for efficiency.
As specified, in the first embodiment, at least two contacting sections are required in the second contacting zone, but beyond this, the number of addition contact sections in the second contacting zone is not critical. In the second embodiment, the bulk of the redistribution sections may be omitted, with the addition contact sections spacing apart at least the majority of the contacting sections. The addition of additional ferric-ferrous chelate solution in the addition contact zone not only increases gas-solution contact but provides additional wetting liquid for the channel surfaces following the addition section so that plugging is inhibited. The total number of contacting and addition contact sections will be determined primarily by the amount of H2S to be removed and the desired degree of gaseous stream purity. Normally, from 2 to 20 or 30 contacting, or channeled sections will suffice, with from 1 to 20 or 30 addition contact sections being sufficient.
It is a requirement of the invention that the contacting sections and the addition contact sections alternate in the sequence of flow, so that sulphur deposition and plugging are inhibited. The shape of the enclosing walls of the contacting sections is riot critical, but a generally cylindrical shape is preferred. The invention is admirably suited for use in the type of structure commonly referred to as a pipeline contactor, and the addition contact sections are formed from spaces between the sections containing the structured, channeled internals.
It is a preferred aspect of the invention that, by suitable flow rates and design of the channeled sections and the means of addition, tb.e flow of the gas-solution mixture through the second contacting zone will reach or approximate plug flow. Suitable _ g _ structures for providing the channeled flow include, but are not limited to, chevron-type mixers, such as Koch static mixers or Glitsch Gempak mixers. The velocity of the gas treated may vary widely. Suitable gas velocities may range from about 0.3 m/s to about 15 m/s, with a range of from about 1.5 m/s to about 9 m/s being preferred. As noted, the aqueous reactant solution to gas ratio must be sufficient to provide effective removal of H2S while inhibiting or preventing sulphur deposition in the reaction zones.
Preferably, the solution to gas ratio will range from 0.2:100 to 30:100, most preferably from 0.5:100 to 5:100, all by volume. Such ratios will generally be sufficient to provide good wetting of the channel surfaces so that sulphur deposition is inhibited or prevented. The addition contact sections comprise means, such as spray cones or nozzles, for addition of the chelate liquid.
The iron chelates employed are coordination complexes in which irons forms chelates with an organic acid. The organic acid may have the formula Y Y
N-R-N
/
y Y wherein - from two to four of the groups Y are selected from acetic and propionic acid groups;
- from zero to two of the groups Y are selected from 2-hydroxy-ethyl, 2-hydroxypropyl, and X
/
X, wherein X is selected from acetic and propionic acid groups, and wherein R is ethylene, propylene or isopropylene or alternatively cyclohexane or benzene where the two hydrogen atoms replaced by 2j nitrogen are in the 1,2 position.
~~~ ~~a~
Exemplary chelating agents for the iron include aminoacetic acids derived from ethylenediamine, diethylenetriamine, 1,2-propylenediamine, and 1,3-propylenediamine, such as EDTA
(ethylenediamine tetraacetic acid), HEEDTA (N-2-hydroxyethyl ethylenediamine triacetic acid), DETPA (diethylenetriamine pentaacetic acid); amino acetic acid derivatives of cyclic, 1,2-diamines, such as 1,2-diamino cyclohexane-N,N-tetraacetic acid, and 1,2-phenylene-diamine-N,N-tetraacetic acid, and the amides of polyamino acetic acids disclosed in Bersworth U.S. patent No. 3,580,950. The Fe(III) chelates of nitrilotriacetic acid and N-(2-hydroxyethyl) ethylenediamine triacetic acid are suitable chelating agents.
A further suitable iron chelate is the coordination complex in which iron forms a chelate with nitrilotriacetic acid (NTA).
' The iron chelates are supplied in solution as solubilized species, such as the ammonium or alkali metal salts (or mixtures thereof) of the iron chelates. As used herein, the term "solubilized" refers to the dissolved iron chelate or chelates, whether as a salt or salts of the aforementioned cation or cations, or in some other form, in which the iron chelate or chelates exist in solution. Where solubility of the chelate is difficult, and higher concentrations of chelates are desired, the ammonium salt may be utilized, as described in a similar process in U.S.A. patent No. 4,871,520. However, the invention may also be employed with more dilute solutions of the iron chelates, wherein the steps taken to prevent iron chelate precipitation are not critical.
The regeneration of the reactant is preferably accomplished by the utilization of oxygen, preferably as air. As used herein, the term "oxygen" is not limited to "pure" oxygen, but includes air, air enriched with oxygen, or other oxygen-containing gases. The oxygen will accomplish two functions, the oxidation of Fe(II) iron of the reactant to the Fe(III) state, and the stripping of any ,..
~~J~j)~
- 1.1 -residual dissolved gas (if originally present) from the aqueous admixture. The oxygen (in whatever form supplied) is supplied in a stoichiometric equivalent or excess with respect to the amount of solubilized iron chelate to be oxidized to the fe(III) state.
Preferably, the oxygen is supplied in an amount of from about 20 per cent to about 500 per cent excess. Electrochemical regeneration may also be employed.
The particular type of sour gaseous stream treated is not critical, the only practical limitation being the reactivity of the stream itself with the solutions employed, as will be evident to those skilled in the art. Streams particularly suited to removal of H2S by the practice of the invention are, as indicated, naturally-occurring gases, recycled C02 used in enhanced oil recovery, synthesis gases, process gases, and fuel gases produced by gasification procedures, e.g., gases produced by the gasific-ation of coal, petroleum, shale, tar sands, etc. Particularly preferred are coal gasification streams, natural gas streams, produced and recycled C02 streams, and refinery feedstocks composed of gaseous hydrocarbon streams, especially those streams of this type having a low ratio of H2S to C02, and other gaseous hydro-carbon streams. The term "hydrocarbon streams)°', as employed herein, is intended to include streams containing significant quantities of hydrocarbon (both paraffinic and aromatic), it being recognized that such streams contain significant "impurities" nor technically defined as a hydrocarbon. Again, streams containing principally a single hydrocarbon, e.g., ethane, axe eminently suited to the practice of the invention. Streams derived from the gasification and/or partial oxidation of gaseous or liquid hydrocarbon may be treated by the invention. The H2S content of the type of streams contemplated will vary extensively, but, in general, will range from about 0.005 per cent to about 10 per cent by volume. C02 may or may not be present, but if present, may range in content from about 0.1 per cent to about 99.0 per cent (or more) by volume. In this context, the invention may 'be used to remove H2S
from various C02 strearas, e.g., supercritical C02 streams.
Obviously, the amounts of H2S and C02 present are not generally a limiting factor in the practice of the invention. The stream treated may also have been treated initially for H2S removal, by this or some other technique.
The temperatures employed in the contacting zones are not generally critical, except that the reaction is carried out below the melting point of sulphur. In many commercial applications, such as removal of H2S from natural gas to meet pipeline specifications, absorption at ambient temperatures is desired. In general, temperatures of from 10 °C to 80 °C are suitable, and temperatures of from 20 °C to 60 °C are preferred. Total contact times may be varied widely, but will preferably range from about 0.5 second to about 10 seconds, with total contact times of about 1 second to about 5 seconds being most preferred.
Similarly, in the regeneration or stripping zone or zones, temperatures may be varied widely. Preferably, the regeneration zone should be maintained at somewhat lower temperatures compared to the contacting zone. In general, temperatures of from about 10 °C to 80 °G, preferably 20 °C to 50 °C, may be employed.
2p Pressure conditions in the contacting zones may vary widely, depending on the pressure of the gas to be treated. For example, pressures in the contacting zones may vary from 0.1 MPa up to 15 MPa or even 20 MPa. Pressures of from 0.1 MPa to about 10 MPa are preferred. In the regeneration zone, pressures may be varied considerably, and will preferably range from about 0.1 MPa to about or 40 MPa. Residence times for given volumes of admixture and oxygen will also vary, but preferably will range from about 1 minute to about 60 minutes, most preferably from about 1 minute to about 40 minutes. The pressure, fluid flow, and temperature 30 relationships involved are well understood by those skilled in the art, and need not be detailed herein. Other conditions of operation for this type of reaction process are further described in U.S.
Patent ~Io. 3,068,065, and in the aforementioned patent specification. Preferably, pH in the regeneration zone will range from about 6.5 to about 8.5, and the molar ratio of the ~~:~z; 3r nitrilotriacetic acid to total solubilized iron is from about 1.0 to 1.5. The process is preferably conducted continuously.
As indicated, the H2S, when contacted, is rapidly converted in the process of the invention by the solubilized Fe(III) chelate of the organic acid or acids to solid elemental sulphur. Since the iron chelates per se have limited solubility in water, the iron chelate compound or compounds are preferably supplied, as indicated previously. The amount of solubilized Fe(III) chelate of the organic acid or acids supplied or employed in solution is an amount sufficient to reduce the H2S concentration or content of the stream to the desired level. If total or substantially total removal is desired, the total amount supplied will generally be on the order of at least about two mots per cool of H2S. Ratios of from about 2 cools to about i5 cools of solubilized Fe(III) chelate of the organic acid or acids per cool of H2S may be used, with ratios of from about 2 cools per cool to about 5 mots of solubilized Fe(III) chelate per cool of H2S being preferred. The molar ratio of the Fe(III) chelate of the acid or acids to the Fe(II) chelate of the acid or acids present in the contacting solution will normally be less than about 6, and will preferably range from about G.2 to about 6, most preferably about 0.5 to about 6. The chelate solution will generally be supplied as an aqueous solution having a concentration of from about 0.1 molar to about 3 molar; a concentration of from about 0.5 to about 1.5 molar is preferred. The total iron concentration, as the chelates, will range from about 0.01 per cent, preferably about 0.5 per cent, to about 7 per cent by weight, based on the weight of the solution and the iron. As indicated, the solubilized iron chelates of the acid or acids may be formed in aqueous solution by the reaction of elemental iron or of an appropriate salt, oxide, or hydroxide of iron and the specified acid, in the presence of alkali metal or ammonium ions, or with the ammonium or alkali metal salt.
In order to describe the invention in greater detail, reference is made to the accompanying schematic drawing. Figure 1 illustrates an embodiment of the invention wherein at least one ~~ ~~~"1 redistribution section is utilized and the sour gas contacting zones are vertically disposed, sulphur removal is accomplished in a separate step before regeneration, and regenerated solution is returned to the contacting zone for use as the contacting solution.
Figure 2 illustrates an embodiment wherein additional chelate solution is supplied. All values axe calculated or merely exemplary, and all flows, unless stated otherwise, are continuous.
As shown, sour gas, e.g., a natural gas stream containing about 0.5 per cent H2S, in line 1 flows into generally cylindrical column 2 wherein it is intimately contacted in zone 3 thereof with a spray of an aqueous mixture from line 4 which comprises aqueous 0.35 M solution of ammonium Fe(III) NTA chelate, which mixture also contains 0.15 moles per liter of ammonium Fe(II) NTA chelate and about 0.25 mole per liter of ammonium thiosulfate, pH of the solution being adjusted to 7.5 to 8 by the addition of ammonium hydroxide. The solution is produced by utilization of the reducing effect of the H2S in the gaseous stream. That is, the initial solution employed in the contacting zone illustrated is a 0.35 M
aqueous solution of Fe(III) NTA also containing about 1.0 M
ammonium ion. After startup, and reaction with H2S in the gaseous stream, regeneration, described hereinafter, is controlled, so that regeneration of the ammonium Fe(III) NTA acid complex is not complete, in the ratios mentioned.
In zone 3, the gas stream containing H2S and the aqueous reactant mixture are intimately mixed to form a gas-reactant liquid mixture, sulphur almost immediately forming, and the gas-reactant liquid mixture is passed downwardly in cocurrent relationship to the first section S of contacting zone 6.
Although a spray device is illustrated, other suitable devices or techniques which provide intimate mixing or contacting of the gas and aqueous reactant mixture may be employed. For example, sparging units, cone sprayers, as well as venturis, may be utilized to produce a well mixed gas-solution or liquid mixture.
In any event, contacting section 5 comprises a chevron type flow directing element which provides a plurality of discrete channels for the passage and direction of the gas-reactant liquid mixture at a 30° angle to the direction of flow to the side of the cylindrical column. In this illustration, the element used is a Koch SMV. mixing element. To insure that the surfaces of the channels are resistant to sulphur deposition, the mixing element (and all those described hereinafter for zone 6) and the walls of zone 6 are electropolished before use. At least substantial plug flow overall through zone 6 is obtained. The superficial velocity of the gas is 6 m/s, and the liquid to gas volumetric flow ratio is 2:100. The width of the channels of the element is about 2.5 cm, and the diameter of the column is about 30.5 cm. The length of element 5 in the direction of flow is about 30.5 cm. As indicated, other types of elements may be employed. At the outlets of the channels of element 5, gas-reactant liquid mixture from the channels enters an open section 7 (also about 30.5 cm in length in the direction of flow) of contacting zone 6 where gas-liquid reactant mixture may mix radially and where redistribution of the solution and gas occurs. The open section also inhibits plugging, due to sulphur formation, which might occur if multiple chevron elements were placed end to end. The gas-reactant liquid mixture, with increasing solid sulphur content, passes through chevron element 8, which is identical to element 5. Element 8 may or may not be misoriented with respect to element 5.
The gas-reactant liquid mixture, upon leaving the channels of element $, passes through addition contact section 9, where the dimensions and operation are similar to that occurring in section 7. In section 9, the gas-liquid reactant mixture is contacted with additional reactant solution from sprayer 10, which is supplied via header 11 connected to line 12. As shown in the drawing, additional sprayers are provided in zone 6, following the next two contacting sections. The gas-liquid reactant mixture may be fresh mixture or regenerated mixture, as described hereinafter, or it may be supplied from some other source. The flaw of the gas-reactant liquid mixture through the remaining corresponding sections of zone 6 and the addition of additional chelate solution is similar to J 7J ~J
~~.'~f~%~'~
that described with respect to the first four sections, and need not be described, except to note that the H2S in the gas stream is continually being reduced, with concomitant sulphur formation and reduction of the Fe(III) chelate concentration.
The volume of solution supplied in the addition contact sections is not critical, sufficient solution being added simply to increase H2S removal and insure wetting of the upper portions of the respective channel sections. Preferably, the ratio of chelate solution supplied in the addition contact sections to that supplied in contact zone (3) will range from 0.1-1.0 to 2.0, but this is not critical.
The operation of the embodiment shown in.Fig~ is similar to that of Figure 1 the only difference being the addition of chelate liqu or solution in the first section (section 7) , following the first contact section.
At the lower end of column 2, the gas-reactant liquid mixture, now containing solid sulphur, passes from vessel 2, and is sent via line 13 to a separating unit or vessel 14 where the natural gas is separated from the liquid and sulphur. Purified natural gas is removed overhead via line 15, and "spent'° reactant liquid and sulphur are removed via line 16.
As those skilled in the art will recognize, solution concen-trations, sulphur content, and ferric-ferrous ligand concentrations and ratios must be regulated to achieve appropriate HzS removal.
To maintain appropriate Fe(III) concentrations and provide sulphur removal, stream 16 is sent for regeneration and sulphur removal.
More particularly, the aqueous admixture in line 16 is sent to a depressurization and degassing unit 17, which also serves as a sulphur concentration or thickening zone. A minor portion, e.g., 2 to 5 per cent by volume of the admixture in settler or thickener 17, and containing an increased sulphur concentration, is continuously withdrawn from the lower portion of settler or concentrator 17 and sent via line 18 to sulphur recovery in unit 19.
_ 17 Sulphur recovery may be accomplished in any suitable fashion, such as by filtration. For example, sulphur may also be recovered by that method described in U.S. patent No. 4,705,676. As those skilled in the art will recognize, sulphur may be removed after regeneration, if desired. In any event, solution recovered during sulphur recovery may be returned to any suitable point in the process, if proper adjustment is made. Preferably, however, the solution recovered is sent to the regeneration zone, as shown, via lines 20 and 21.
The major portion of the aqueous admixture in vessel 17 is removed via line 21 fox regeneration of the Fe(III) chelate of nitrilotriacetic acid. In regeneration zone or column 22, which may be a sparged tower, the admixture is contacted cocurrently with excess air in line 23 to convert Fe(II) chelate of NTA to Fe(III) chelate of NTA. Air velocity in the regenerator is in the range of 0.03 to 0.9 m/s, the temperature of the liquid is about 45 °C, and overall pressure is about 0.2 MPa. Spent air is removed via line 24, and regenerated admixture, having a ratio of Fe(III) chelate of NTA to Fe(II) chelate of NTA of about 2.5, is returned via line 25 to line 4, which connects, as mentioned, to column 2 and line 12.
Again, as will be understood by those skilled in the art, the solutions or mixtures employed may contain other materials or additives for given purposes. Fox example, U.S. Patent No. 3,933,993 discloses the use of buffering agents, such as phosphate and carbonate buffers. Similarly, U.S. Patent No. 4,009,251 describes various additives, such as sodium oxalate, sodium formate, sodium thiosulfate, and sodium acetate, which are beneficial, and other additives, such as additives to improve sulphur separation, or antifoaming and/or wetting agents, may be employed.
Claims (12)
1. A process for the removal of H2S from a sour gaseous stream comprising a) feeding the sour gaseous stream to a first contacting zone, and intimately contacting the sour gaseous stream in said first contacting zone with an aqueous reactant solution containing solubilized Fe(III) chelate of an organic acid, or mixture of said acids, and solubilized Fe(II) chelate of said acid or acids, at a temperature below the melting point of sulphur, and at a sufficient solution to gas ratio and conditions effective to convert H2S to sulphur and inhibit sulphur deposition, and producing a gas-solution mixture comprising sour gas and aqueous reactant solution;
b) passing gas-solution mixture from step a) through a plurality of enclosed contacting sections in serial flow communication in a second contacting zone, under conditions to convert H2S
to sulphur and at a temperature below the melting point of sulphur, the first contacting section of said second contacting zone comprising a plurality of discrete sulphur deposition resistant channels, each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow of the gas-solution mixture entering the section; the second contacting section through which gas-solution mixture is passed comprising an enclosed mixing section operative to or adapted to allow radial mixing of gas-solution mixture and re-distribution of solution in gas, and to inhibit plugging due to sulphur formation, the third contacting section through which gas-solution mixture is passed comprising a plurality of discrete sulphur deposition resistant channels, each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow of the gas-solution mixture entering the section; and producing a gas-reactant solution mixture containing solid sulphur in said second contacting zone, the reactant solution of said gas-reactant solution mixture having a reduced content of solubilized Fe(IIi) chelate of said acid or acids and the gas of said mixture having a reduced H2S
content;
c) passing the gas-solution mixture from the third contacting section through an addition contact section of said second contact zone and contacting the gas-solution mixture with aqueous reactant solution containing solubilized Fe(III) chelate of said acid or acids and solubilized Fe(II) chelate of said acid or acids, and forming a gas-solution mixture having an increased solution to gas ratio; and d) separating the gas having reduced H2S content from gas-reactant solution mixture produced in step c).
b) passing gas-solution mixture from step a) through a plurality of enclosed contacting sections in serial flow communication in a second contacting zone, under conditions to convert H2S
to sulphur and at a temperature below the melting point of sulphur, the first contacting section of said second contacting zone comprising a plurality of discrete sulphur deposition resistant channels, each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow of the gas-solution mixture entering the section; the second contacting section through which gas-solution mixture is passed comprising an enclosed mixing section operative to or adapted to allow radial mixing of gas-solution mixture and re-distribution of solution in gas, and to inhibit plugging due to sulphur formation, the third contacting section through which gas-solution mixture is passed comprising a plurality of discrete sulphur deposition resistant channels, each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow of the gas-solution mixture entering the section; and producing a gas-reactant solution mixture containing solid sulphur in said second contacting zone, the reactant solution of said gas-reactant solution mixture having a reduced content of solubilized Fe(IIi) chelate of said acid or acids and the gas of said mixture having a reduced H2S
content;
c) passing the gas-solution mixture from the third contacting section through an addition contact section of said second contact zone and contacting the gas-solution mixture with aqueous reactant solution containing solubilized Fe(III) chelate of said acid or acids and solubilized Fe(II) chelate of said acid or acids, and forming a gas-solution mixture having an increased solution to gas ratio; and d) separating the gas having reduced H2S content from gas-reactant solution mixture produced in step c).
2. The process of claim 1 wherein the gas having reduced H2S
content from step d) is contacted with additional aqueous reactant solution containing solubilized Fe(III) chelate of said acid or acids, at a temperature below the melting point of sulphur and under conditions effective to convert H2S to sulphur, in at least one additional contacting zone, and a gas having further reduced H2S content and a solution having a reduced content of the solubilized Fe(III) chelate of said acid or acids are produced.
content from step d) is contacted with additional aqueous reactant solution containing solubilized Fe(III) chelate of said acid or acids, at a temperature below the melting point of sulphur and under conditions effective to convert H2S to sulphur, in at least one additional contacting zone, and a gas having further reduced H2S content and a solution having a reduced content of the solubilized Fe(III) chelate of said acid or acids are produced.
3. The process of claim 2 wherein at least one of said additional contacting zone or zones comprises a spraying zone wherein the gas having reduced H2S content is passed cocurrently through a spray of said additional reactant solution.
4. The process of claim 3 wherein the solution having a reduced content of the Fe(III) chelate of said acid or acids and the solution having a reduced content of said acid or acids from said additional contacting zone or zones are regenerated in a regeneration zone.
5. A process as claimed in claim 1, wherein the organic acid is selected from those having the formula - from two to four of the groups Y are selected from acetic and propionic acid groups;
- from zero to two of the groups Y are selected from 2-hydroxy-ethyl, 2-hydroxypropyl, and wherein X is selected from acetic acid and propionic acid groups;
and wherein R is ethylene, propylene or isopropylene or alternatively cyclohexane or benzene where the two hydrogen atoms replaced by nitrogen are in the 1,2 position.
- from zero to two of the groups Y are selected from 2-hydroxy-ethyl, 2-hydroxypropyl, and wherein X is selected from acetic acid and propionic acid groups;
and wherein R is ethylene, propylene or isopropylene or alternatively cyclohexane or benzene where the two hydrogen atoms replaced by nitrogen are in the 1,2 position.
6. A process as claimed in claim 1, wherein the organic acid is nitrilotriacetic acid.
7. A process for the removal of H2S from a sour gaseous stream comprising:
a) feeding the sour gaseous stream to a first contacting zone, and intimately contacting the sour gaseous stream in said first contacting zone with an aqueous reactant solution containing solubilized Fe(III) chelate of an organic acid or mixture of said acids, and solubilized Fe(II) chelate of said acid or acids, at a temperature below the melting point of sulphur, and at a sufficient solution to gas ratio and conditions effective to convert H2S to sulphur and inhibit sulphur deposition, and producing a gas-solution mixture comprising sour gas and aqueous reactant solution;
b) passing gas-solution mixture from step a) through a plurality of enclosed contacting sections in serial flow communication in a second contacting zone; under conditions to convert H2S
to sulphur and at a temperature below the melting point of sulphur, the first contacting section of said second contacting zone comprising a plurality of discrete sulphur deposition resistant channels, each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow of the gas-solution mixture entering the section; the second contacting section through which gas-solution mixture is passed comprising an addition contact section in which the gas-solution mixture is contacted intimately with additional aqueous reactant solution containing solubilized Fe(III) chelate of said acid or acids and solubilized Fe(II) chelate of said acid or acids to produce a gas-solution mixture having an increased solution to gas ratio; the third contacting section through which gas-solution mixture is passed comprising a plurality of discrete sulphur deposition resistant channels, each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow of the gas-solution mixture entering the section; and producing a gas-reactant solution mixture containing solid sulphur in said second contacting zone, the reactant solution of said gas-reactant solution mixture having a reduced content of solubilized Fe(III) chelate of said acid or acids and the gas of said mixture having a reduced H2S content;
c) separating the gas having reduced H2S content from gas-reactant solution mixture produced in step b).
a) feeding the sour gaseous stream to a first contacting zone, and intimately contacting the sour gaseous stream in said first contacting zone with an aqueous reactant solution containing solubilized Fe(III) chelate of an organic acid or mixture of said acids, and solubilized Fe(II) chelate of said acid or acids, at a temperature below the melting point of sulphur, and at a sufficient solution to gas ratio and conditions effective to convert H2S to sulphur and inhibit sulphur deposition, and producing a gas-solution mixture comprising sour gas and aqueous reactant solution;
b) passing gas-solution mixture from step a) through a plurality of enclosed contacting sections in serial flow communication in a second contacting zone; under conditions to convert H2S
to sulphur and at a temperature below the melting point of sulphur, the first contacting section of said second contacting zone comprising a plurality of discrete sulphur deposition resistant channels, each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow of the gas-solution mixture entering the section; the second contacting section through which gas-solution mixture is passed comprising an addition contact section in which the gas-solution mixture is contacted intimately with additional aqueous reactant solution containing solubilized Fe(III) chelate of said acid or acids and solubilized Fe(II) chelate of said acid or acids to produce a gas-solution mixture having an increased solution to gas ratio; the third contacting section through which gas-solution mixture is passed comprising a plurality of discrete sulphur deposition resistant channels, each discrete channel providing a diverted flow path for gas-solution mixture through the section, such that gas-solution mixture is directed at least initially at an angle acute to that of the direction of flow of the gas-solution mixture entering the section; and producing a gas-reactant solution mixture containing solid sulphur in said second contacting zone, the reactant solution of said gas-reactant solution mixture having a reduced content of solubilized Fe(III) chelate of said acid or acids and the gas of said mixture having a reduced H2S content;
c) separating the gas having reduced H2S content from gas-reactant solution mixture produced in step b).
8, The process of claim 7 wherein the gas having reduced H2S
content from step c) is contacted with additional aqueous reactant solution containing solubilized Fe(III) chelate of said acid or acids, at a temperature below the melting point of sulphur and under conditions effective to convert H2S to sulphur, in at least one additional contacting zone, and a gas having further reduced H2S content and a solution having a reduced content of the solubilized Fe(III) chelate of said acid or acids are produced.
content from step c) is contacted with additional aqueous reactant solution containing solubilized Fe(III) chelate of said acid or acids, at a temperature below the melting point of sulphur and under conditions effective to convert H2S to sulphur, in at least one additional contacting zone, and a gas having further reduced H2S content and a solution having a reduced content of the solubilized Fe(III) chelate of said acid or acids are produced.
9. The process of claim 8 wherein at least one of said additional contacting zone or zones comprises a spraying zone wherein the gas having reduced H2S content is passed cocurrently through a spray of said additional reactant solution.
10. The process of claim 9 wherein the solution having a reduced content of the Fe(III) chelate of said acid or acids and the solution having a reduced content of Fe(III) chelate of nitrilotri-acetic acid from said additional contacting zone or zones are regenerated in a regeneration zone.
11. A process as claimed in claim 7, wherein the organic acid is selected from those having the formula - from two to four of the groups Y are selected from acetic and propionic acid groups;
- from zero to two of the groups Y are selected from 2-hydroxy-ethyl, 2-hydroxypropyl, and wherein X is selected from acetic acid and propionic acid groups;
and wherein R is ethylene, propylene or isopropylene or alternatively cyclohexane or benzene where the two hydrogen atoms replaced by nitrogen are in the 1,2 position.
- from zero to two of the groups Y are selected from 2-hydroxy-ethyl, 2-hydroxypropyl, and wherein X is selected from acetic acid and propionic acid groups;
and wherein R is ethylene, propylene or isopropylene or alternatively cyclohexane or benzene where the two hydrogen atoms replaced by nitrogen are in the 1,2 position.
12. A process as claimed in claim 7, wherein the organic acid is nitrilotriacetic acid.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US34823489A | 1989-05-05 | 1989-05-05 | |
| US348,234 | 1989-05-05 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2015987A1 CA2015987A1 (en) | 1990-11-05 |
| CA2015987C true CA2015987C (en) | 2000-11-28 |
Family
ID=23367149
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2015987 Expired - Lifetime CA2015987C (en) | 1989-05-05 | 1990-05-03 | Solution removal of h2s from gas streams |
Country Status (3)
| Country | Link |
|---|---|
| CN (1) | CN1034556C (en) |
| CA (1) | CA2015987C (en) |
| RU (1) | RU2070824C1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8372365B2 (en) * | 2010-10-27 | 2013-02-12 | Merichem Company | High pressure reduction-oxidation desulfurization process |
| RU2447927C1 (en) * | 2010-11-22 | 2012-04-20 | Общество с ограниченной ответственностью "Пантекс" | Absorbent for cleaning gas from hydrogen sulphide |
| CN106512656B (en) * | 2016-12-12 | 2019-08-30 | 江苏君竹环保实业有限公司 | A kind of low pressure drop the methods of odour control and low pressure drop odor treatment system |
| CN110817809B (en) * | 2018-08-14 | 2023-09-15 | 中国石油化工股份有限公司 | Claus tail gas treatment method and treatment system |
| CN116410721B (en) * | 2021-12-29 | 2024-04-19 | 中国石油天然气股份有限公司 | Sulfur-dissolving agent, sulfur-dissolving amount measuring method, preparation method and application of sulfur-dissolving agent |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4871520A (en) * | 1985-08-23 | 1989-10-03 | Shell Oil Company | Process and composition for H2 S removal |
| DE3737386A1 (en) * | 1987-11-04 | 1989-05-18 | Skf Gmbh | SWIVELING EXECUTIVE ROLLER BEARING WITH DEVICE FOR SYNCHRONOUSLY ADJUSTING THE ROLLER BODY CAGE |
-
1990
- 1990-05-03 RU SU4743958 patent/RU2070824C1/en not_active IP Right Cessation
- 1990-05-03 CN CN90102586A patent/CN1034556C/en not_active Expired - Lifetime
- 1990-05-03 CA CA 2015987 patent/CA2015987C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| RU2070824C1 (en) | 1996-12-27 |
| CN1034556C (en) | 1997-04-16 |
| CN1047041A (en) | 1990-11-21 |
| CA2015987A1 (en) | 1990-11-05 |
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