DE10352878A1 - Removing acid gases from a fluid stream comprises contacting the fluid stream with a liquid absorbent and regenerating the absorbent by heating to produce a compressed acid gas stream - Google Patents

Abstract

Removing acid gases comprising at least 50 mole% hydrogen sulfide from a fluid stream comprises contacting the fluid stream with a liquid absorbent, separating the loaded absorbent into an acid gas stream at 3-30 bar and a regenerated absorbent stream by heating and optionally expansion or stripping, cooling the regenerated absorbent by heat exchange with the loaded absorbent, and recycling the regenerated absorbent to the absorption step.

Description

The The present invention relates to a process for obtaining a under high pressure sour gas flow by removing the Sour gas from a fluid stream.

In numerous processes in the chemical industry, fluid flows occur which contain acid gases such as CO ₂ , H ₂ S, SO ₂ , CS ₂ , HCN, COS or mercaptans as impurities. These fluid streams may be, for example, gas streams such as natural gas, refinery gas or reaction gases resulting from the oxidation of organic materials such as organic wastes, coal or petroleum or composting organic matter-containing wastes.

The Removal of the acid gases is due to different reasons special meaning. For example, the content of sulfur compounds of natural gas by appropriate treatment measures directly at the Natural gas source can be reduced, because the sulfur compounds make in that of natural gas often entrained Water acids, which have a corrosive effect. For Therefore, the transport of natural gas in a pipeline must have predetermined limits the sulphurous impurities are maintained. The at the oxidation of organic materials, such as organic waste Coal or petroleum, or in the composting of organic substances containing waste materials must arise reaction gases be removed to prevent the emission of gases that damage nature or can affect the climate too prevent.

The washing solutions used in gas scrubbing processes also have extensive patent literature. Basically, one can distinguish two different types of absorption or solvents for gas scrubbing:
On the one hand, so-called physical solvents are used in which, after absorption, the dissolved acid gases are present in molecular form. Typical physical solvents are cyclotetramethylenesulfone (sulfolane) and its derivatives, aliphatic acid amides (acetylmorpholine, N-formyl morpholine), NMP (N-methylpyrrolidone), propylene carbonate, N-alkylated pyrrolidones and the corresponding piperidones, methanol, and mixtures of dialkylethers of polyethylene glycols (Selexol ^®, Union Carbide, Danbury, Conn., USA).

To the others become chemical solvents whose mode of action is based on chemical reactions, in which, after absorption, the dissolved sow ergase in the form of chemical Compounds are present. For example, in the industrial scale most frequently as chemical solvents used aqueous solutions from inorganic bases (e.g., potash solution in the Benfield process) or organic bases (e.g., alkanolamines) are formed upon dissolving sour gas ions.

The solvent can through membrane process, heating, relaxing at a lower Pressure or stripping are regenerated, with the ionic species back to sour gases react and / or stripped by steam. After the regeneration process can the solvent be reused.

occasionally it is not desirable The distant sour gases are simply channeled into the atmosphere, but they become otherwise used or disposed of. This is e.g. the case, though it is the sour gas is CO2 and the CO2 in subsequently for the production is used by urea. Even if the sour gas is not as a value product it can be used for reasons of climate protection make sense, the sour gas in underground deposits too or in deep water layers in open waters to solve.

For this Type of reuse or disposal requires that the acid gases have a pressure level that above the normal pressure lies.

The However, the above-described methods provide only sour gas streams on the Pressure level of normal pressure. The sour gas streams thus obtained had to therefore in a subsequent Step on the one you want Pressure to be compressed, which is ernegetisch consuming and additional Investment in compression equipment required.

The object of the present invention was thus to provide an economical process with it is possible to liberate fluid streams from the acid gases contained therein as impurities and to provide the sour gas streams at a high pressure level.

• a) man in wenigstens einem Absorptionsschritt den Fluidstrom mit einem flüssigen Absorptionsmittel in innigen Kontakt bringt und so einen von Sauergasen weitgehend gereinigten Fluidstrom und eine mit Sauergasen beladenes flüssiges Absorptionsmittel erzeugt (Schritt a),
• b) den von Sauergasen weitgehend gereinigten Fluidstrom und das mit Sauergasen beladene flüssige Absorptionsmittel voneinander trennt (Schritt b),
• c) das mit Sauergasen beladene flüssige Absorptionsmittel durch Aufheizen und ggf. Entspannen oder Strippen in einen Sauergasstrom mit einem Druck von 3 bis 30 bar und ein regeneriertes flüssiges Absorptionsmittel auftrennt (Schritt c)
• d) das regenerierte flüssige Absorptionsmittel in einen Wärmetauscher führt und dort abkühlt, indem man mit einem Teil seiner Wärmeenergie das mit Sauergasen beladene flüssige Absorptionsmittel in Schritt (c) aufheizt (Schritt d)
• e) das regenerierte flüssige Absorptionsmittel in Schritt a) zurückführt (Schritt e).

Accordingly, a process has been found for obtaining an acid gas stream under a pressure of from 3 to 30 bar by removing the acid gases from a fluid stream containing acid gases as impurities, the molar fraction of H ₂ S, based on the total amount of acid gases, being 50 mol. % is by

• a) bringing the fluid stream into intimate contact with a liquid absorbent in at least one absorption step, thereby producing a fluid stream largely purified of acid gases and a liquid absorbent laden with acid gases (step a),
• b) separating from each other the acid stream largely purified fluid stream and the acid gas-laden liquid absorbent (step b),
• c) separates the loaded with acid gases liquid absorbent by heating and optionally relaxing or stripping in an acid gas stream at a pressure of 3 to 30 bar and a regenerated liquid absorbent separates (step c)
• d) the regenerated liquid absorbent leads into a heat exchanger and cools there, by heating with part of its heat energy the acidic gas-laden liquid absorbent in step (c) (step d)
• e) the regenerated liquid absorbent in step a) returns (step e).

The absorbent according to the invention or the process according to the invention is suitable for removing acid gases from fluid streams which contain at least 50, preferably at least 75, mol% of H ₂ S. The other acid gases are, in particular, CO ₂ , COS, mercaptans, SO ₃ , SO ₂ , CS ₂ and HCN. Particularly advantageous is the proportion of CO ₂ in the acid gases is at least 50 mol%.

Fluids containing the acid gases include on the one hand gases such as natural gas, synthesis gas, coke oven gas, coal gasification gas, cycle gas and combustion gases and on the other hand with the absorbent substantially immiscible liquids such as LPG (Liquefied Petroleum Gas) or NGL (Natural Gas Liquids). The gas streams, in addition to one or more of said acidic gases (hereinafter also referred to as acidic gas constituents) further inert gas constituents, which are not absorbed by the absorbent to any appreciable extent included. Examples are volatile hydrocarbons, preferably C ₁ -C ₄ -hydrocarbons, such as methane, and also nitrogen and hydrogen. The process according to the invention is particularly suitable for removing CO ₂ and H ₂ S.

When Absorbents are practically all conventional absorbents.

• – Lösungen bestehend hauptsächlich aus aliphatischen oder cycloaliphatischen Aminen mit 4 bis 12 Kohlenstoffatomen, Alkanolaminen mit 4 bis 12 Kohlenstoffatomen, cyclischen Amine bei denen 1 oder 2 Stickstoffatome zusammen mit 1 oder 2 Alkandiylgruppen 5-, 6- oder 7-gliedrige Ringe bilden, Mischungen der vorstehenden Lösungen, wässrige Lösungen der vorstehenden Mischungen und Lösungen,
• – wässrige Lösungen enthaltend Salze von Aminosäuren
• – wässrige Pottaschelösungen, die ggf. Piperazin oder Methylethanolamin enthalten
• – wässrige NaOH-Lauge oder Kalkmilch.

Preferred absorbents are, for example, chemical solvents selected from the group consisting of

• Solutions consisting mainly of aliphatic or cycloaliphatic amines having 4 to 12 carbon atoms, alkanolamines having 4 to 12 carbon atoms, cyclic amines in which 1 or 2 nitrogen atoms together with 1 or 2 alkanediyl groups form 5-, 6- or 7-membered rings, mixtures of above solutions, aqueous solutions of the above mixtures and solutions,
• - aqueous solutions containing salts of amino acids
• - Aqueous potash solutions containing possibly piperazine or methylethanolamine
• - aqueous NaOH lye or milk of lime.

Especially solutions are preferred as the chemical solvent consisting mainly monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), Diethylethanolamine (DEEA), diisopropylamine (DIPA), aminoethoxyethanol (AEE) and methyldiethanolamine (MDEA) mixtures of the above solutions and aqueous solutions the above mixtures and solutions used.

Especially proven in the US patent US 4,336,233 described absorbent. This is an aqueous solution of methyldiethanolamine (MDEA) and piperazine as an absorption accelerator or activator (aMDEA ^®, BASF AG, Ludwigshafen). The scrubbing liquid described therein contains 1.5 to 4.5 mol / l methyldiethanolamine (MDEA) and 0.05 to 0.8 mol / l, preferably up to 0.4 mol / l piperazine.

Regarding further preferred chemical solvent Reference is made to DE-A-10306254, DE-A-10210729, DE-A-10139453, and EP-A-1303345.

When Absorbents continue to have physical solvents selected from the group consisting of cyclotetramethylenesulfone (sulfolane) and its derivatives, aliphatic acid amides (acetylmorpholine, N-formylmorpholine), NMP (N-methylpyrrolidone), propylene carbonate, N-alkylated pyrrolidones and corresponding piperidones, methanol and mixtures of dialkyl ethers of polyethylene glycols proven.

The on sour gas components rich starting gas (raw gas) is in a Absorption step in an absorber in contact with the absorbent according to the invention brought, whereby the acid gas components at least partially be washed out.

When Absorber preferably acts in a conventional gas scrubbing process used washing device. Suitable washing devices are For example, packing, packing and tray columns, radial flow scrubbers, Jet scrubbers, Venturi scrubbers and rotary spray washer, preferred Packing, packing and Tray columns, more preferably packed and packed columns. The treatment of the fluid flow with the absorbent takes place preferably in a column in countercurrent. The fluid is here generally in the lower area and the absorbent fed to the top of the column.

The inventive method may be one or more, in particular two, successive absorption steps include. The absorption can be done in several successive steps carried out be, wherein the raw gas containing the acidic gas components in each of the substeps, each with a partial flow of the absorbent is brought into contact.

According to one preferred embodiment becomes the method according to the invention so performed that the fluid containing the acidic gases in an absorption step with the liquid Absorbent at a temperature of 30 to 100 ° C, preferably 40 to 90 ° C and in particular 50 to 80 ° C is treated. The total pressure is preferred in the absorption step 3 to 150 bar, more preferably 10 to 100, in general 1 up to 200 bar.

Out the absorbent laden with the acid gas components can the acid gas components in usual Manner (analogous to the publications cited below) in one Regeneration step to be released, with a regenerated Absorbent is obtained. In the regeneration step, the loading becomes of the absorbent is reduced and the resulting regenerated Absorbent is preferably subsequently in the absorption step recycled.

Preferably, the regeneration step step (c) before the heating includes an upstream pressure release of the loaded absorbent from a high pressure, as it prevails in the implementation of the absorption step, to a lower pressure. The pressure release can be done for example by means of a throttle valve and / or an expansion turbine. The regeneration with a relaxation stage is described for example in the publications US 4,537,753 and US 4,553,984 ,

If at this pressure release, the liquid absorbent a pressure is released which is below the desired one Pressure of the step (c) is separated sour gas, the pressure of the liquid absorbent subsequently, i.e. even before heating, preferably by means of a pump accordingly elevated.

The increase the pressure of the loaded liquid Absorbent at least the pressure that the sour gas in Step (c) should, of course, then also required if no upstream pressure release is made and the pressure at which the absorption (step (a)) is made lower is considered the pressure to which the sour gas is brought in step (c) becomes.

The Release of the acid gas constituents in the regeneration step carried out by means of heating is generally in a column, for example in a stress-relieving column, e.g. a vertically or horizontally installed flash container or a countercurrent column with internals, done. There can be several Relaxation columns are connected in series, in which different pressures is regenerated. For example, in a pre-relaxation column at high pressure, typically about 1.5 bar above the partial pressure the acid gas components is in the absorption step, and in a Hauptentspannungskolonne at a pressure of 3 to 30 bar, regenerated become. The lower limit of the preferred pressure range is included 5 bar. The upper limit of the preferred pressure range is preferably included 20, more preferably at 10 bar.

in the Regeneration step becomes the loaded liquid absorbent heated up in two ways. On the one hand, it becomes heat energy from outside fed. On the other hand, the heating takes place by heat exchange with the in the regeneration step generated regenerated liquid Absorbent.

The feed the heat from external can e.g. done so that in the column in which the Heating and possibly additional the relaxation or the stripping is done in the Column sump collecting regenerated liquid absorbent boiled up becomes. This is preferably done by one from the bottom of the column Stream of regenerated liquid Withdraws absorbent, leads to a reboiler and from there to the bottom of the column feeds back.

The Regeneration can be additionally supported by relaxation or stripping.

The inventive method is described below with reference to 1 explained.

In 1 schematically a device is shown, in which the absorption stage is carried out in one stage and the relaxation stage in two stages. The starting gas (hereinafter also referred to as feed gas) is via line 1 in the lower area of the absorber 2 fed. At the absorber 2 it is a column packed with packing to effect mass and heat exchange. Alternatively, the column can also be designed as a bell, valve or sieve bottom column. The absorbent, which is a regenerated absorbent having a low residual content of acidic gases, is passed over the line 3 on the head of the absorber 2 abandoned in countercurrent to the feed gas. The depleted in acid gases gas leaves the absorber 2 over head (pipe 4 ). The absorbent enriched with acidic gases leaves the absorber 2 on the ground via pipe 5 and enters the top of the high pressure flash column 6 which is generally operated at a pressure which is above the partial pressure of the acid gases of the feed gas fed to the absorber. The relaxation of the loaded liquid absorbent is generally carried out by means of conventional devices, for example a stationary control valve, a hydraulic turbine or a reverse pump. Relaxation releases most of the dissolved non-acidic gases and a small portion of the acidic gases. These gases are via line 7 from the high-pressure expansion column 6 discharged over head.

The absorbent, which is still loaded with most of the acidic gases, leaves the high pressure flash column via line 8th and will be with the pump as needed 18 compressed to a higher pressure and then in the heat exchanger 9 heated. Due to the heat input, a large part of the acidic gases can be released. The heated absorbent is placed in the upper part of a flash column 10 equipped with a packed body in order to achieve a large surface area and thus to effect the release of the sour gas and the adjustment of the equilibrium. Alternatively, the column can also be designed as a bell, valve or sieve bottom column. The relaxation column 10 is operated at pressures between 3 and 30 bar. Already on entering the Enspannungskolonne 10 a large part of the dissolved sour gas is released. Further sour gas is almost completely released by stripping in the column. The absorbent is regenerated in this way. At the head of the relaxation column 10 is a reflux cooler 11 with a collection container 12 provided to cool the liberated acid gases and to condense a portion of the vapor. The bulk of the sour gas leaves the reflux condenser 11 via wire 13 , The condensate is pumped 14 on the head of the relaxation column 10 pumped back. The regenerated absorbent containing only a small portion of the sour gas leaves the flash column 10 on the ground via pipe 15 and is for heat recovery in the heat exchanger 9 given and then by pump 16 via wire 3 on the head of the absorber 2 given up. To the heat input in expansion column 10 to cause part of the regenerated absorbent before heat exchanger 9 out of line 15 withdrawn and passed to a reboiler. The heated there regenerated absorbent is then in the internal part of the expansion column 10 recycled.

The heat recovery is of particular importance in this method, as set by the comparison with the prior art increased operating pressure in the stripper higher sump drain temperatures than is usually the case. Accordingly, the larger in the heat exchanger 9 recoverable energy. Via wire 17 Fresh water can be fed in to balance the water discharged with the gases.

experimental part

A model calculation was carried out for the treatment according to the invention of a gas stream in a plant according to FIG 1 , The most important process parameters and the composition of the feed gas can be found in Table 1. As the liquid absorbent, an aqueous solution containing methyldiethanolamine and piperazine was used. The result of the calculation is in 2 played. There is the required power of the reboiler 19 against the pressure at the head of the expansion column 10 is set, applied. The model calculation shows that for pressure ranges above 3 bar in the process no additional energy must be expended to provide acid gases with a high pressure level. Therein, the method differs in principle from the known methods, in which the relaxation is carried out to a low pressure level and the pressure increase is then carried out by compressors.

Table 1

Claims (9)

A method for obtaining an acid gas stream under a pressure of 3 to 30 bar by removing the acid gases from a fluid stream containing H ₂ S and possibly other acid gases as impurities, wherein the molar fraction of H ₂ S, based on the total amount of acid gases 50 mol%, by a) bringing the fluid stream into intimate contact with a liquid absorbent in at least one absorption step, thus producing a fluid stream substantially purified by acid gases and a liquid absorbent laden with acid gases (step a), b) that of acid gases c) separates the laden with acid gases liquid absorbent by heating and optionally relaxing or stripping in an acid gas stream with a pressure of 3 to 30 bar and a regenerated liquid absorbent separates (Step c) d) the regenerated liquid A Bsorptionsmittel leads into a heat exchanger and there cooled by heating with part of its heat energy loaded with acid gases liquid absorbent in step (c) (step d) e) the regenerated liquid absorbent in step a) returns (step e). Process according to claim 1, wherein the liquid absorbent is a chemical solvent selected from consisting of the group - consisting of solutions mainly from aliphatic or cycloaliphatic amines having 4 to 12 carbon atoms, Alkanolamines of 4 to 12 carbon atoms, cyclic amines, in which 1 or 2 nitrogen atoms together with 1 or 2 alkanediyl groups Form 5-, 6- or 7-membered rings, mixtures of the above Solutions, aqueous solutions the above mixtures and solutions, - Containing aqueous solutions Salts of amino acids - aqueous potash solutions, which optionally contain piperazine or monoethanolamine (MEA) - Aqueous NaOH solution or lime milk starts. Method according to one of the preceding claims, wherein as a sorbent, a physical solvent selected from the group consisting of cyclotetramethylenesulfone (sulfolane) and its derivatives, aliphatic acid amides (Acetylmorpholine, N-formylmorpholine), NMP (N-methylpyrrolidone), Propylene carbonate, N-alkylated pyrrolidones and corresponding piperidones, Methanol and mixtures of dialkyl ethers of polyethylene glycols, starts. Method according to one of the preceding claims, wherein as a washing solution an aqueous one Solution, containing methyldiethanolamine and piperazine. Method according to one of the preceding claims, wherein in step (a) a liquid Absorbent, which contains water and one carries out step (c) by the heated up with acid gases loaded liquid absorbent on heads the head of a column and there in the column in countercurrent to a steam stream leads to the bottom of the column, and the water vapor stream produced by the regenerated liquid absorbent formed there heated so much that in the liquid absorbent to be regenerated contained water partially evaporated. Method according to one of the preceding claims, wherein in step (d) in the heat exchanger the temperature difference between the exiting regenerated liquid Absorbent and the incoming laden liquid absorbent 5 to 30 ° K is. Method according to one of the preceding claims, wherein the temperature difference between that in step (a) in the heat exchanger entering regenerated liquid Absorbent and exiting the heat exchanger regenerated liquid Absorbent 50 to 200 ° K is. Method according to one of the preceding claims, wherein the acid gases contained in the fluid stream is a mixture which, besides H ₂ S, contains one or more acid gases selected from a group consisting of CO ₂ , H ₂ S, COS, mercaptans SO ₃ , SO ₂ , CS ₂ and HCN. The method of claim 8, wherein the proportion of CO ₂ to the other acid gases is at least 50 mol%.