NL8202061A - PROCESS FOR REMOVING CO2 AND ANY H2S PRESENT FROM A GAS MIX. - Google Patents

Description

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WEEKLY FOR THE REMOVAL VM COg AND ANY PRESENT HgS FROM EM GAS MMGSEL

The invention relates to a method for removing COg and any HgS present from a gas mixture.

In many cases, COg, and any HgS, 5 present, and other sulfur-containing contaminants, such as COS, are removed from gas mixtures. Removal of HgS and / or other sulfur-containing impurities from gas mixtures may be necessary to render these gas mixtures suitable for catalytic conversion using sulfur-sensitive catalysts, or to combat environmental pollution when said gas mixtures or the combustion gases resulting therefrom in the atmosphere.

Examples of COg-containing gas mixtures, from which HgS 15 and / or other sulfur-containing compounds generally have to be removed, are gases obtained by partial combustion or full or partial gasification of oil and coal, refinery gases, town gas, natural gas, coke oven gas , water gas, propane and propylene.

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Removal of COg from gas mixtures, as such from a gas mixture, which contains little or no HgS (for example natural gas), or COg mixed with HgS, is often necessary to give the gas mixtures a calorific value and / or to avoid corrosion in the transport pipelines and / or to avoid freezing in cryogenic devices and / or the transport of COg that has no value for the gas mixture that is ultimately used for a specific purpose.

The COg and any HgS present is in many cases removed from said gas mixtures by means of liquid solvents, which are often basic. At least a part of the COg which is fibrous in the gas mixtures will be absorbed with at least a part of the optionally fibrous HgS in the liquid solvent. The HgS and COg (which are also referred to as acidic gases in this specification) will be removed from said gas mixtures at the pressure of the respective gas mixture, i.e. in many cases at bend pressure.

The loaded solvent obtained after absorption of COg and any HgS present from the gas mixture must be partially or completely regenerated, releasing any HgS and COg present.

When HgS is present in a significant amount in the gas obtained after regeneration of the charged solvent, this gas cannot be vented into the atmosphere until at least most of the HgS has been removed. The HgS is highly scavenged from this gas by converting it to elemental sulfur which is separated off. The conversion of HgS to elemental sulfur is generally carried out according to a Claus method, oxidizing a quantity of the HgS to SOg, and sulfur and water are generated by the reaction between HgS and SOg, optionally using a suitable catalyst . To use a Claus method, the molar percentage of 35 HgS in a mixture with COg should be at least about 15. If 8202061 Λ ·· ** 3 this percentage is between unyear 15 and unyear, lean the The Claus method was carried out by separating a third of the gas, burning the H 2 S to SO 2 contained therein, and then mixing the resulting SO 2 -buring gum with the heat of the H 2 S S-containing gas, after which the Claus reaction can be carried out further at an elevated temperature and preferably with a catalyst present in hexd. When the gas beyat about kO mol% HgS or more, the Claus method can be carried out by burn gas with a volume of air 10 sufficient to convert a third of the H 2 S to SO 2 and then react the HgS with the S 2 to prepare sulfur and water.

In many cases, the gas released during the regeneration of the loaded solvent is unsuitable for use in a Claus-15 method, since its H 2 S content is too low and this gas is subject to further treatments to increase the HgS content must be subjected.

However, if the gas released during regeneration has such a high HgS content that it can be used in a Claiis method, it may be important to increase its H 2 S content, because in the last year the total amount of gas, which is to be used in the Claus method, is lower and therefore the devices may be smaller.

The H2S content of the gas released during the regeneration of the loaded solvent can of course be increased by selectively absorbing the HgS from this gas in a suitable solvent and regenerating the used solvent. However, such a second absorption treatment is not attractive in view of the additional equipment required and the additional amount of energy required for the regeneration of the charged solvent.

The invention relates to a process for the removal of CO2 and possibly present HgS from a gas mixture, in which process for the regeneration of the solvent loaded with CO2 and possibly present HgS, a very small amount of energy. is required, and in which process high HgS-gases suitable for a Claus method are obtained with a single absorption treatment by using nit HgS-containing gas mixtures.

The invention therefore provides a method for removing COg and any HgS present from a gas mixture, which method is characterized in that: a) the gas mixture is contacted in countercurrent pressure at a bend pressure with a solvent containing a tertiary amine and contains a physical abaorbent; b) the resulting loaded solvent is evaporated at least once by lowering the pressure to a level greater than the total partial pressure of the COg 15 and HgS present in the loaded solvent, at the prevailing temperature; c) the loaded solvent obtained in step * b) is evaporated at least once by lowering the pressure to a gene level which is lower than the total partial pressure of 20 COg and HgS present in the loaded solvent, at the prevailing temperature ; and the semi-loaded solvent obtained in step c), optionally after this image has been fully or partially regenerated, is used as the solvent in step a).

The solvent contains a tertiary amine, a physical absorbent and preferably water,

Acid gases can react with tertiary amines. Highly suitable tertiary amines are aliphatic, especially those containing at least one hydroxyalkyl group per molecule. Examples are triethanolamine, tripropanolamine, triisopropanolamine, ethyl diethanolamine, dimethylethanol amine, diethyl ethanolamine. Preference is given to methyl diethylamine.

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A physical absorbent is a yer bond in which acidic gasses dissolve without reacting with the yer bond,

Very suitable physical absorbents are sulfolane and substituted sulfolanes, alcohols with 1 to 5 carbon atoms per molecule (eg methanol), tetraethylene glycol dimethyl ether, N-methyl pyrrolidone, alkylated carboxylic amides (eg dimethyl formamide). Preference is given to sulfolane. The word "sulfolane" designates the compound "tetrahydrothiophene 1,1-dioxide".

The content of tertiary amine and physical abaorbent (and any water present) in the solvent can vary within wide limits. The solvent very suitably contains 10-60% w / t tertiary amine, preferably methyl diethanolamine, 15-55% physical absorbent, preferably sulfolane and 5-35% water by weight.

The solvent used in the method of the invention must contain a tertiary amine and a physical absorbent. In modified processes, which differ only from the method according to the invention, in that the solvent contains a secondary and / or a primary amine in plants of a tertiary amine, or a tertiary amine, but which does not contain any physical absorbent, is evaporated in step c) less COg free, and, when HgS was present in the original gas mixture, the semi-loaded solvent obtained in the partial regeneration in step c) therefore contains H 2 S and CO2 in a lower molar ratio than in the case of method according to the invention was obtained. In addition, in the case of the above modified processes for total regeneration (generally carried out by steam stripping) of the said half-loaded solvent, more steam is required and the mixture of CO 2 and H 2 S is obtained in a molar ratio which is less favorable for a Claus method than in the case of the method according to the invention.

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In a modified process, however, which differs according to the invention in that the agent only contains one or more physical absorbents and no anjines, absorption of the same amount of acidic gases in many cases requires more solvent and more absorption dishes. in the absorption column used in step a) than in the process according to the invention. In addition, more non-acidic gases are absorbed in solvents containing only one or more physical absorbents than in the solvents used in the method according to the invention. which non-acidic gases are released during the evaporation in step b). When using a solvent containing only one or more physical absorbents, this quantity of non-acidic gases is so great that it is not attractive to fuel (which is the case with the non-acidic gases released in step b) in the process according to the invention), and this non-acidic gas Hence, it must be put back under pressure (using capital-intensive compressors) before being returned to step a).

The gas mixture is contacted with the solvent in step a) at an elevated pressure, ie a pressure of at least 5 *, in particular of at least 10 bar. A pressure in the range of 20 to 100 bar is very suitable.

The gas mixture is suitably contacted with the solvent in a contact zone, for example an absorption column containing 15 to 80 contact layers, such as valved trays, bubble cap trays, baffle plates and the like. Surprisingly, it has been found that by using the solvent in the process of the invention, the E 2 S can be substantially removed from the gas mixture used as feed, while controlling the amount of CO 2 remaining in the purified gas. This amount can be controlled by adjusting the solvent circulation, i.e., the ratio of the amount of solvent introduced into the extraction zone to the amount of the amount of gas mixture fed to the zone. When no or almost no H 2 S is present in the gas mixture, the amount of CO2 removed therefrom can also be controlled by means of the solvent circulation.

If desired, the COg can be removed in a very large amount. If necessary, the circulation of the solvent can be further reduced by removing charged solvent at a point in the lowest part of the contact zone, cooling the separated charged solvent externally and feeding it back to the lowest part of the contact zone to re-enter it. contacting the gas mixture to be purified, for example, as described in British Patent 1,589,231.

The temperature during the contact between the gas mixture and the solvent in step a) can vary within wide limits. Temperatures from 15 to 110 ° C are very suitable, temperatures from 20 to 80 ° C are preferred.

In step a), the entire amount of optional COS, or most of it, is removed from the gas mixture.

The loaded solvent obtained in step a) contains COg, optionally HgS and, in general, amounts of dissolved non-acidic components originating from the gas mixture to be purified, for example hydrocarbons and / or hydrogen and / or carbon monoxide. These non-acidic gases must be removed at least in part from the charged solvent by evaporating the solvent in step b) to a pressure which is higher than the total partial pressure of the acid gases present in the charged solvent.

In this way, only very small amounts of acidic gases are released together with the non-acidic gases, for example hydrocarbons and / or hydrogen and / or carbon monoxide. The gas mixture 30 obtained after evaporation in step b) can, if desired, be recycled to step a), but in order to avoid this gas mixture being compressed again it is preferably used for another purpose, for example as fuel gas (if desired after removal part of the entire amount of HgS or 8202061 8 present, e.g. by contacting said gas mixture with a small amount of unloaded solvent). Acid gas must be removed from the charged solvent before the solvent is evaporated to a pressure lower than the total partial pressure of the acid gas, since otherwise the hydrocarbons and / or hydrogen and / or the carbon monoxide together with a significant amount of acidic gases would be removed. Since in many cases these acidic gases or the resulting combustion gases must be discharged into the atmosphere, the hydrocarbons and / or the hydrogen and / or the carbon monoxide would be discharged or burned simultaneously, which would be a loss of these valuable compounds.

Although the whole solvent can be evaporated several times in step b), always at a lower pressure, the greatest amount of dissolved non-acidic components will in most cases be removed in an evaporation treatment, and for this reason it is preferred indicated to evaporate the loaded solvent once in step b).

The loaded solvent obtained in step b) - which, in addition to acid gases, contains only small amounts of other dissolved compounds - is evaporated in step c) to a pressure which is lower than the total partial pressure of the acid gases in said charged solvent, at the prevailing temperature.

25 Has turned out. that in the method of the invention (in which a solvent containing a tertiary amine and a physical absorbent is used) the amount of COg released is much greater than in modified methods which differ from the method of the invention only in that the solvent contains a contains secondary and / or primary amine in place of a tertiary amine or contains a tertiary amine, but none physically. absorbent. When the loaded solvent also contains HgS, the released gas after the pressure drop in step c) has a much higher molar ratio of COg to HgS

8202061 then the molar ratio in which these gases were originally present in the charged solvent. It is advantageous to heat the loaded solvent vSSr.or during the evaporation in step c), for example to a temperature of 5 K5 to 100 ° C, because in this case the molar ratio of COg to HgS 'in the gases the pressure drops have been released, yet verier is increased. The above-mentioned modified - · £ ··.

cited method, whereby; use is made of a solvent containing a secondary or primary amine and a physical absorbent or a solvent containing a tertiary amine and no physical absorbent, giving a much lower molar ratio of COg to HgS in the post-pressure release gas. Since the gas released in step c) has a higher molar ratio of COg to HgS than that of the initially loaded solvent, the molar ratio of HgS to COg in the solvent is that after the pressure drop in step c) remaining, higher than original ratio, Since with each pressure drop in step c) the molar ratio of HgS to COg in the residual solvent 2Q is increased, it may be advantageous to evaporate the loaded solvent in step c) at least twice , each time to a lower pressure or a higher temperature when the original gas mixture contains HgS. The pressure of the charged solvent will generally be approximately atmospheric after the pressure drop in step c).

In step c) a large amount of COg is released and the loaded solvent is therefore in fact regenerated to a considerable extent, whereby a half-loaded solvent is obtained. When the original gas mixture is substantially free of HgS, the half-loaded solvent obtained in step c) COg as the only acidic gas and preferably preferably at least partly as: solvent used in step a), j in many cases the amount of COg present in the semi-loaded solvent obtained in step c} will be so small there are 8202061

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it is preferred to use this half-loaded solvent as the sole solvent in step a). The semi-loaded solvent obtained in step c) can be completely or partially regenerated if desired (for example by stripping with S steam). and in step a) ala solvent are used.

When fully regenerated solvent and half loaded solvent both ala solvent are used in step a),. the former solvent is preferably introduced into the contact zone at a point which is earlier from the inlet of the gas-mixture is removed from the inlet of the semi-charged solvent.

When the original gas mixture beats not only CO 2 but also HgS, the acidic gases released during the evaporation in step c) will in some cases contain such small amounts of HgS that they can become in the atmosphere after combustion Tanned, If desired or required, the H 2 S present in the gases released during the evaporation in step c) can be removed by contacting these gases with a solvent under conditions favorable to Remove H ^ S selectively from CO2. For this selective removal, for example, suitable use can be made of a mixture containing an amine and optionally a physical absorbent, in particular the solvent to be used according to the present invention. In order to achieve a high selectivity for the removal of HgS, the contact takes place very suitably at a high gas velocity in a column with less than 20 contact trays, for example as described in British patent 1,362,38U.

When HgS is present in the original gas mixture, it contains in step c). obtained half-loaded solvent HgS and ΟΟ ^ in a high molar ratio. Due to the high HgS content, this half-loaded solvent is not suitable for use as a solvent in step a) and the 8202061 33 must be used.

The acidic gauze contained therein and emit are removed. The acidic gases are removed from said semi-solvent solvent by completely regenerating it into an solvent solvent. The regeneration is carried out very carefully by means of the solvent in a regeneration column. heating (for example up to a tender temperature of 80 to 160 ° C, which heating is preferably carried out by steam stripping.

The gas obtained during this regeneration has such a HgS content that it can be used in IQ a Claus method for sulfur grazing,

The uncharged solvent obtained after regeneration can very suitably be reused in step a) and, if desired, it can also be brought into contact with the evaporated gas from step h) or c).

In order to keep the amount of energy required in the method as low as possible, it is of course advantageous to subject the flows used in the method to heat exchange, if possible.

PREPARATION 1 2Q An amount of 10,000 kmol./h of a gas mixture (total 80 vol. # Methane, 5 vol. # Ethane, 3 vol, # propane, 1 vol. # Hutane, 1 vol, # HgS and 10 vol It is fed a temperature of <RTI ID = 0.0> 0 C </RTI> and a pressure of 50 har to the lower end of an adsorption column which contains 30 trays with 25 valves. This gas mixture is contacted in countercurrent 3 at 300 m / h of an uncharged solvent consisting of 50 wt% methyl diethanolamine, 25 wt sulfolane and 25 wt water. Purified gas exits the absorption end at the top of the head in an amount of 9-513 kmol / h; this gas 30 contained 6cc kmol / h 00 ^ and less than 4 parts by volume per million (vdpm) HS.

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The whole solvent (300 m / h) is removed from the absorption column at the bottom; it increased to 99 km / h HgS and 356 km / h CO 2. This whole solvent is evaporated to a pressure of 15 bar at a temperature of 69.2 ° C. The evaporated gas (U5 kmol * / h). contains 1 kmol / h HgS, 10.7 kmol./h COg, the rest is nitrocarbon. The solvent charged after this first evaporation contains 98.6 kmol / h HgS 5 and 3U5 kmol. / h COg. It is heated by heat exchange with an uncharged solvent and evaporated to a pressure of 1.3 bar at a temperature of 70 C. The gas released during this second evaporation (293 * 6 kmol./h) consists of 35 * 6 kmol. / b HpS and 258 kmol./h COg. It is contacted counter-current with 1 8 m / h on-10 solvent in a second absorption column with 13 trays with valves at a temperature of 10 ° C and a pressure of 1.1 bar, whereby 212 kmol ./h gas is obtained consisting of COg with 300 ppm HgS. The loaded solvent obtained in the latter absorption column is regenerated together with the semi-charged solvent obtained after the second evaporation. This semi-loaded solvent contains 63 kmol / h HgS and 87 kmol / h COg. The regeneration is carried out by s-stripping to obtain a gas consisting of 98.6 kmol./h HgS and 133 kmol./h COg, which gas is very suitable for becoming in a Claus method applied.

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The uncharged solvent obtained after regeneration {kk8 nr / h)

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part (1U8 nr / h) is recycled to the second absorption column and part (300 m / h) (after heat exchange with the loaded solvent from the first evaporation) is used as unloaded solvent in the absorption column.

Y00R FIGURE 2 10,000 kmol./h of a gas mixture (composition 90.65 vol,% methane and 9 * 35 vol, $ COg) was fed at a temperature of 35 ° C * and a pressure of 91 bar. 30 absorption column containing 20 valves dishes. This gas mixture was contacted in countercurrent with 8 Uh m / h of a solvent consisting of methyl diethanolamine (50 wt%), sulfolane (25 wt%) and water (25 wt%). This solvent was half loaded; it contained 137 ^ kmol./h COg and no methane. The 8202061 33 Λ 'ί * - «η gas.' that the absorption column oyer the top yerlite (90 ^ 9 kmolt / hj consisted for 98 vq1, $ of methane, the remainder being CQ,

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The loaded solvent (8 µm / h) was stirred at the bottom of the absorption column; it heated 2331 kmol / h 5 COg and 37¾ kmol / h methane and had a temperature of 53 ° C.

This loaded solvent was evaporated to a pressure of 2an bar and a temperature of 53 ° C. The evaporated gas. (20¾ kmol./h) consisted of 359 kmol./h. methane and ^ 5 kmol./h CO2. The loaded solvent obtained after this first evaporation (8¾¾ nr / hl 10% 2086 kmol./h COg and 35 kmol./h. Metrack. It was heated and evaporated to a pressure of 3.3 bar and a temperature yan. 0 ° C. The gas released during this second evaporation (727 bmol./h) consisted of 35 kmol./h methane and 732.kmol./h CCL. The semi-charged solvent obtained in the second evaporation. (8¾¾ m / h) contained 337¾ kmol / w O 2 ^ and no methane and was lyophilized at the top of the absorption column as a solvent for the gas mixture to be purified, as described above.

Comparative Example 2Q The procedure described in Example 2 was carried out for comparison with a solvent consisting of diisopropanolamine (50 wt%), sulfolane (25 wt%) and water (25 wt%) (not according to the invention), In order to remove the same amount of ^00 from the feed gas using un regenerated, half-loaded solvent at the absorbtion, the solvent had to be circulated in an amount 5 times as high as the process according to the invention, as described in Example 2, Boyendien was absorbed about 5 times soy metolean in the absorption column per hour and removed in the first evaporation; the quantity of metbaan released in the first evaporation was so high that this gas had to be compressed and recycled again for economic reasons, necessitating the installation of expensive compressors, 8202061

Claims (11)

2, Method according to claim 1, characterized in that the solvent contains water, A method according to claim 1 or 2, characterized in that the tertiary amine is aliphatic and contains at least one hydroxy-alkyl group per molecule. Process according to claim 3, characterized in that the tertiary amine is methyl diethanolamine. 5. Procedure. according to any one of the preceding claims, characterized in that the physical absorbent is tetrahydrothiophene 1,1-dioxide, 8202061 £ * 6. Process according to any one of the preceding claims, characterized in that the solvent contains methyl diethanolamine, tetrahydrothiophene 1,1-dioxide and water, 7. The yolgena process according to claim 6, characterized in that the solvent contains IQ-60 wt.% Methyl diethanolamine, 15-55 wt.% Tetrahydrothiophene], 1-dioxide and 5-35 wt.% Water. 8. Process according to any one of the preceding claims, characterized in that the gas mixture in step a) is cracked into contact with the solution in a contact zone containing 15-80 contact layers. Method according to any one of the preceding claims, characterized in. that step a) is carried out at a pressure of 20-100 bar. 10. A method according to any one of the preceding claims, characterized in that step a) is carried out at a contact temperature of 20-80 ° C. Process according to any one of the preceding claims, characterized in that the loaded solvent is evaporated to atmospheric pressure in step c). Process according to any one of the preceding claims, characterized in that the semi-loaded solvent obtained in step c) is regenerated by steam stripping the bet before it is used as a solvent in step a). 13. Process according to any one of claims 1-11, characterized in that the gas mixture is substantially free of H 2 S and the semi-charged solvent obtained in step c) is used if the sole solvent in step a) is used, 8202061