DE1494803B2 - Process for drying and purifying supply gases - Google Patents

Description

The invention relates to a method for drying and cleaning, in particular for desulphurising Supply gases such as town gas, long-distance gas, natural gas, and the like.

The raw supply gases are required before they are distributed into the pipeline network and before they are used a cleaning that preferably focuses on the deposition of sulfur compounds, in particular of hydrogen sulfide. The mostly only low concentration in these gases, Malodorous organic sulfur compounds are often left in the gas to serve as an odor warning in the event of leaking pipes or taps can.

The carbon dioxide contained in these gases is often only partially washed out by means of the in the gas To be able to influence the calorific value of the gas by leaving the residual concentration of carbon dioxide.

Depending on the state conditions given by the extraction or generation, the aforementioned raw supply gases have a considerable moisture content, which in the course of the gas cleaning or is eliminated in a special preliminary stage. Such drying is necessary . to corrosion and the formation of hydrates of hydrogen sulfide and of hydrocarbons to avoid blockages in pipes and fittings.

It is known that the acidic components, H ₂ S and CO _{2 can} be washed out of such supply gases by means of aqueous alkaline solutions of alkali salts of weak inorganic or organic acids or strong organic bases and the solution loaded with the acidic components by relaxing, boiling and blowing out with a regenerate inert gas (stripping).

Since the acidic gas components are chemically bound in such solutions, this gas cleaning process is known as chemical washing. They are selective for acidic gas components such as CO ₂ , H ₂ S, SO ₂ over neutral gas components such as CO, H ₂ , CH ₁ and basic gas components such as NH ₃ and are still effective at normal and moderate gas pressures, i.e. independent of pressure. The mostly neutral organic sulfur compounds are only affected to a small extent by chemical washing.
If the supply gases occur under increased pressures of about 10 to 100 atü, as is the case with the product gases of the pressurized gasification of coal or the pressure splitting of liquid hydrocarbons and also with natural gases, the under

ίο summarized under the term "physical washing" Cleaning method preferred.

Organic solvents are mostly used as absorption liquids, which are to be washed out . Dissolve gas components according to Henry Dalton's law. Accordingly, the Solubility of the individual gas components in the solvent, except for a specific absorption coefficient and the temperature, its partial pressure and the total pressure.

The absorbent is so under increased pressure and at a low temperature with the The gas components to be washed are loaded and restored by relaxing and, if necessary, heating regenerated.

The simplest physical gas cleaning process is the well-known pressurized water scrubbing for removal of carbon dioxide from gases.

For the purification of raw supply gases containing hydrogen sulphide, organic liquid substances are used as absorbents, which ^{boil at around 200 c} C and above and which have a high selectivity for hydrogen sulphide over carbon dioxide in order to facilitate the utilization and further processing of the hydrogen sulphide produced during regeneration. The organic sulfur compounds are included in full because they are usually more soluble in organic solvents than hydrogen sulfide. Such solvents are, for example, dimethylformamide, tetraalkylureas, N-methylpyrrolidone, carbonic acid alkylene esters and the like. These absorbents are neutral. That is why the systems for absorption and regeneration can be built from steel.

In some individual cases, corrosion and deposits of iron sulfide have now been observed in such systems, which have caused considerable operational disruptions. Such disturbances occur in particular when very moist raw gases are dried by a treatment with an organic liquid desiccant such as glycol or glycol derivatives before the hydrogen sulfide is washed out. In these corrosives, however, decomposition products of the solvent for H ₂ S absorption, which are formed during regeneration due to excessive heating, also seem to have an effect.

The advantage of the comparatively low system costs, which results from the usability of simple steel, is thus lost. It has been found that the disturbances described can be avoided by prewashing the dried crude gas before entering the H ₂ S absorption with a small partial stream of the absorbent branched off from it and then cleaning and cleaning this partial stream by distillation under reduced pressure is added back to the main wash cycle. In the bottom of this vacuum distillation, iron compounds and the higher-boiling decomposition products of the absorbent and also the

3 4

from the pre-drying in vapor form entrained line 11 enters the washing tower 3 and out of this

Portions of the desiccant, which runs off again quite considerable through the line 12. The main crowd

Quantities can be and from the bottom product of the absorbent is through line 12 to

Vacuum distillation can be recovered. Regeneration passed into the regeneration column 4.

As an inhibitor for the hydrogen sulfide 5 The H ₂ S-GaS expelled therein flows through the line 13 and the cooler 14 for further use of the absorbent and the desiccant, z. B. in a Claus plant, for processing on caused corrosion and by-product formation sulfur. In the regenerated absorbent wild, an addition of triethanolamine through line 11 to the head of the main wash was found to be about 0.1% by weight. This io column was returned. The regeneration in the reginhibiting additive is able, in particular, to prevent the regeneration column 4 by expansion and separation of iron sulfide 14 is used for washing and vacuum distillation to reduce partial backwashing of absorbent vapor from the stiomes, and on the other hand is an effective 15 H ₂ S-containing exhaust gas from the regeneration column 4 and the same safeguard against operational malfunctions or under-is in the line 11 breaks back to the top of the column in this prewash. guided.

The invention relates to a method for through the line 17 is a small partial flow of the Leaching of the hydrogen sulfide from absorbent loaded with di- from the scrubbing tower 3 and / or triethylene glycol or its derivatives are introduced into the prewash 2. This is where they get easy dried gases by means of high-boiling, physically condensable vapors of the desiccant releasing agent Absorbent, the gas being washed in and released from the absorbent. That represents In the main wash with absorbent from contaminated absorbent flows through the line the main wash is prewashed. 18 and the steam-heated heater 19

The method according to the invention is thereby a relief valve 33 in the pre-degasser 5, where indicates that with one from the main wash it by stripping gas from line 20 of the sulfur water circuit branched off partial flow of the absorbent is freed. Through additional indirect assessment is pre-washed, whereupon this partial flow is heated by means of the steam coil 21, other, fully or partially regenerated and expelled under reduced gases to the vacuum pump tem pressure of a maximum of 300 Torr redistilled and the 30 of the distillation 6 to relieve. The sulfur water distillate is added to the main wash circuit. Substance-containing gas is passed through line 22 into the rain

The vacuum distillation is expediently removed at ration column 4. This occurs through line 23

Pressures from 10 to 50 torr, no more than 300 torr. The degassed absorbent of the pre-washer into the

for the pre-washing of the dried raw gas - vacuum-operated vacuum distillation device

branched partial flow is a maximum of 5 percent by volume 35 device 6 with the heater 24 a. Here it becomes

of the absorption-absorbent circulated in the main wash evaporates and distilled over, while

medium current, expediently about 2%. The branch stream rend the higher-boiling impurities such as dry

volume can be 1 to 1.5 percent by volume of the main detergent and products of thermal decomposition

Circulation are measured if the total remain in the residue and through the line 25 out

circulating absorbent for H ₂ S about 0.1 V-40 can be drained from the sump. The fumes draw in

lum percent triethanolamine are added. These pass through the line 26 and are in the cooler 27

Concentration is condensed by a continuous addition. The so redistilled pure absorption

to be maintained, because from the sump of the invention is through the line 28, the vacuum seal

The vacuum 29, the pump 30 and the line 31 in the regenerator 4 belonging to the prewash stage according to the present invention

distillation, a small proportion of the triethanolamine 45 is always fed back into the main wash cycle. The Pum-

is also discharged and the bottom product pe 32 is used to generate a vacuum,

can be recovered. It is expedient to add the absorbent in

In the drawing, the flow diagram of a plant main wash circuit is still a small amount of one

to carry out the process according to the invention, ethanolamine, preferably triethanolamine. These

for example shown. 50 alkylolamines have the property of being iron complex

In this flow diagram, heat exchangers are to be linked to pumps. It was found that in the presence of pen and the like, insofar as they are not required for understanding triethanolamine, the precipitation of iron sulfide is subject, not shown. The system persists, even with changes in the water content of the essential from the drying system 1, the pre-sorbent as well as the pH value and the temperature washer 2, the main washing column 3, the regeneration 55. So there are no blockages by the abortion column 4, the pre-degasser 5 and the vacuum bearings.

distillation 6. Through line 7 the flows under This measure is particularly useful if

Crude gas containing hydrogen sulfide under pressure passed into the prewash 2 for some reason.

the drying system 1. This is where the drying process fails. The required additional amount is

kenmittel, z. B. with triethylene glycol, treated to 60 depending on the iron content of the detergent. At a

to remove the moisture. During the drying iron content of 0.2 g Fe / 1 is already an addition of

the gas takes small amounts of steam of 0.1% triethanolamine sufficient, but can

Desiccant. The dried gas can be safely increased to 1 to 2% by adding,

the line 9 in the H ₂ S main wash 3 and enters _R. ...

finally as desulphurized gas through line 10 65 eispie

the end. The main scrubbing 3 is carried out with one of the above From the probes of a natural gas field should 50,000 Nm ³

mentioned absorbent, z. B. with N-methyl natural gas per hour of industrial use as

pyrrolidone, operated as a detergent, which is supplied by the heating gas. The gas consists of

0.5 volume percent H ₂ S
10.8 volume percent CO ₂
88.5 percent by volume CH ₁

0.2 percent by volume of other hydrocarbons

and is saturated with water vapor under a pressure of 60 atmospheres at 54 "C. It is dried in the drying system by washing with triethylene glycol and is then practically anhydrous, but contains 8 ppm (0.0008 percent by volume) of triethylene glycol. At 30 ^: C this gas is now _{passed through a pipeline into an H 2} S scrubbing system 10 km away and operated with N-methylpyrrolidone as the absorbent, where the gas is fed at 58 atmospheres with 24 m ^a / h of N-methylpyrrolidone with 0.2 percent by weight of water up to 2 mg H ₂ SZNm ^3. Simultaneously the detergent also absorbs some CO ₂ and CH ₁ as well as 2.8 kg triethylene glycol / h. This loaded detergent is removed by decompression, heating in heat exchangers and with indirect heating by steam and stripping with H ₂ S-free carbonic acid A downstream CO ₂ scrubber regenerates H ₂ S and methane practically completely, while a small amount of CO ₂ and all of the triethylene glycol taken up is in the N-methylpyr rolidon lag behind. The absorbent then returns to the H ₂ S wash via a heat exchanger and cooler. The triethylene glycol is continuously accumulating in the detergent, so that with a total content of 50 m ^{: j} N-methylpyrrolidone, the detergent already contains 2000 kg of triethylene glycol after one month, i.e. 4.0 "" was dissolved in the detergent to 0.4 g iron / l. Iron sulfide was found in the heat exchangers, which forced repeated shutdowns for cleaning purposes. In addition, the absorbent contained 3 g decomposition products per liter.

Example 2

In the same way, 50,000 Nm ³ / h of natural gas of the same composition are dried in the drying plant operated with triethylene glycol. The emerging dry gas with a content of 8 ppm triethylene glycol, however, is first washed in a tray column 2 as a pre-scrubber with 0.2 m ³ / h N-methylpyrrolidone, which was branched off from the main washing circuit, with the triethylene glycol and any other solid or contained high-boiling impurities are removed from the gas. In addition to H ₂ S and CO ₂ and some CH, the N-methylpyrrolidone now also contains 1.4 percent by weight of triethylene glycol. The 0.2 m ³ / h of the loaded absorbent are fed from the prewash 2 through the line 18 and a preheater 19 to the small stripping column 5 and stripped from line 20 at 110 ° C. while releasing the pressure ^{with 10 Nm 3} / h CO _{2 gas} . The stripping gas is fed together with the expelled hydrogen sulfide, carbon dioxide and methane in line 28 of the regeneration column 4 of the main washing circuit. This stripping of the hydrogen sulfide in the column 5 is necessary because the N-methylpyrrolidone then passes into the vacuum distillation device 6 operated at a pressure of 20 torr. However, hydrogen sulfide and the other dissolved gases would be very annoying in the vacuum section and unnecessarily load the vacuum pump. In the distillation device 6, the N-methylpyrrolidone is ^{distilled off at a temperature of 100 to HO 0} C, while triethylene glycol (boiling point 280 to 290 ° C at 760 Torr) and other high-boiling impurities and iron compounds remain in the residue and through line 25 from the Column bottom be drained. The evaporated N-methylpyrrolidone (is condensed in the condenser 23 and fed via a vacuum receiver 29 to the regeneration column 4 and thus to the main washing circuit. The N-methylpyrrolidone must be distilled off in vacuo at a pressure of at most 300 torr, preferably 10 to 50 torr, to avoid thermal decomposition.

In this way, triethylene glycol and other high-boiling impurities as well as iron compounds do not accumulate in the main wash circuit. There are no corrosion or malfunctions there by iron sulfide deposits. Collect the substances kept away from the main wash circuit are in the bottom of the vacuum distillation and are separated by working up the bottom product or regained. As a precaution, there is a concentration in the N-methylpyrrolidone of the main wash circuit maintained by 0.1% triethanolamine, around an accumulation of triethylene glycol in the detergent and a resulting iron content of 0.4 g Fe / 1 Malfunctions due to precipitation of iron sulfide and blockages in the heat exchangers to prevent. The complex-bound iron is also found in the bottom of the vacuum distillation again.

The quantities, pressures and temperatures listed are only examples. The inventive Process can also be used in the drying and desulphurisation of other gases.

1 sheet of drawings

Claims (2)

Patent claims: 1. Process for leaching hydrogen sulfide with di- and / or triethylene glycol or their derivatives dried gases using high-boiling, physically dissolving absorbents, wherein the gas before entering the main wash with absorbent from the main wash is pre-washed, characterized in that that is prewashed with a branched off from the main wash circuit substream of the absorbent, whereupon this substream is wholly or partially regenerated and under reduced pressure of a maximum of 300 torr redistilled and the distillate is added to the main wash circuit. 2. The method according to claim 1, characterized in that the partial flow amount is a maximum of 5%, is preferably 1% of the amount circulating in the main circuit.