DE102016013753A1 - Process and apparatus for synthesis gas separation by acid gas scrubbing and cryogenic separation process - Google Patents

Abstract

The invention relates to a method and a device for decomposing a syngas (4) from which carbon dioxide and sulfur components in an acid gas scrubbing (M) are separated in order to obtain a largely consisting of hydrogen and carbon monoxide, methane-containing synthesis gas (6), from then in a cryogenic separation process (T) a carbon monoxide product (9) is obtained, wherein in the sour gas scrubbing (M) a stripping gas (14) is used at a first pressure level of a nitrogen source (L) with a second, above the first lying pressure level is provided. It is characteristic here that gas (12) provided by the nitrogen source (L) is used as the refrigerant (13) in the cryogenic separation process (T) and is thereby expanded to the first pressure level in order subsequently to be supplied to the sour gas scrubbing as stripping gas (14) ,

Description

The invention relates to a process for the decomposition of a syngas, from which carbon dioxide and sulfur components are separated in an acid gas scrubbing to obtain a largely consisting of hydrogen and carbon monoxide, methane-containing synthesis gas from which subsequently in a cryogenic separation process, a carbon monoxide product is obtained in the sour gas scrubbing a stripping gas is used at a first pressure level provided by a nitrogen source at a second pressure level above the first level.

Furthermore, the invention relates to a device for carrying out the method according to the invention.

In the present application, the terms "pressure level" and "temperature level" are used to characterize pressures and temperatures, which is intended to express that parameters for carrying out the method according to the invention need not have an exact value. Rather, they move around an average. Corresponding levels are in disjoint areas.

Methods and devices of the generic type are used approximately in the production of monoethylene glycol from coal. Here, the coal is reacted with the supply of oxygen by partial oxidation in a synthesis gas, which contains not only the main components of hydrogen and carbon monoxide and acid gases, especially carbon dioxide and sulfur components, and water and methane. After cooling and drying, the synthesis gas is fed to an acid gas scrubber in which the acid gases are separated by means of a methanol detergent, wherein a largely consisting of hydrogen and carbon monoxide, methane-containing synthesis gas and a laden with the separated acid gases detergent are obtained. To be used again in the sour gas separation, the loaded detergent is regenerated, wherein acid gases are usually expelled at a pressure between 1.5 and 3bar (a) by nitrogen used as stripping gas.

In order to avoid freezing, traces of acid gases and detergent residues are removed from the synthesis gas in a temperature change adsorber before it is decomposed into a carbon monoxide product and hydrogen sulfide in a cryogenic condensation process. The raw hydrogen is normally used for regeneration of the temperature change adsorber before it is purified by pressure swing adsorption to a hydrogen product and then reacted together with the carbon monoxide product to monoethylene glycol.

The oxygen needed for coal gasification is supplied by a cryogenic air separator, which also provides nitrogen as a stripping gas for sour gas scrubbing. Typically, the nitrogen in the air fractionator gasses at a pressure of between 4 and 6 bar (a), and therefore must be depressurized prior to its use in sour gas scrubbing. To relax the nitrogen is passed through a throttle body, with pressure energy is lost largely without economic benefits.

Object of the present invention is therefore to provide methods and apparatus of the type described above, by which it is possible to overcome the disadvantages of the prior art.

According to the invention, the stated object is achieved in that the gas provided by the nitrogen source is used as the refrigerant in the cryogenic separation process and is thereby expanded to the first pressure level in order subsequently to be supplied to the sour gas scrubbing as stripping gas.

By means of the method according to the invention, it is possible to use the nitrogen provided as stripping gas as refrigerant in the cryogenic part and at least part of the energy required for the operation of the cryogenic separation process from the pressure energy of the nitrogen gas source provided as stripping gas which is not used in the prior art to be used and economically exploited in this way. When used as a refrigerant, the chemical composition of the gas supplied from the nitrogen source is not changed, so that it requires no further treatment in order to be used as a stripping gas in the sour gas scrubbing.

The pressure level of the carbon monoxide product determines the minimum level of the pressure level at which the gas supplied from the nitrogen source must be supplied to the cryogenic separation process as a refrigerant. In particular, when the second pressure level does not reach this minimum level, it is proposed to compress the gas supplied from the nitrogen source from the second to a third pressure level which is greater than or equal to the minimum level before it is introduced into the cryogenic separation process.

The amount of gas supplied from the nitrogen source and used as a refrigerant in the cryogenic separation process is preferably the same required in the sour gas scrubbing Strippgasmenge and is completely fed to the relaxation after the first pressure level of sour gas scrubbing. However, it should not be ruled out to use gas from the nitrogen source in an amount in the cryogenic separation process as the refrigerant, which is larger or smaller than the required Strippgasmenge.

If nitrogen is compressed from the second to a third pressure level before it is used in the cryogenic separation process and the amount of nitrogen used as refrigerant exceeds the gas quantity continued as stripping gas at the first pressure level, it is proposed that the excess amount of gas in their use as cryogen in the cryogenic separation process only to relax to the second pressure level and return to the third pressure level after compression as refrigerant in the condensation process.

If, on the other hand, only a portion of the stripping gas requirement of the sour gas scrubbing can be covered from the cryogenic separation process, the missing part is expediently supplied directly from the nitrogen source, with the nitrogen being expanded from the second to the first pressure level via a throttle element.

If the cold that can be generated via the gas supplied from the nitrogen source as the refrigerant for the operation of the cryogenic separation process is insufficient, liquid nitrogen can additionally be used as the refrigerant.

With particular preference, the method according to the invention is used when the cryogenic separation process is a condensation process.

The condensation process has been state of the art and known to experts for many years. It is preferably used for the decomposition of synthesis gases obtained by partial oxidation and therefore having a high carbon monoxide and a low methane content. The synthesis gas is in this case partially condensed by cooling in order to obtain a largely consisting of carbon monoxide and methane, hydrogen-containing first liquid phase, from which in a H ₂ -Strippkolonne by the separation of hydrogen, a second liquid phase is generated from which in a CO / CH ₄ separation column a carbon monoxide-rich gas phase having a purity that allows their release as a carbon monoxide product, as well as a largely consisting of methane and carbon monoxide bottom product. Provided a sufficiently deep cooling of the synthesis gas to be separated, the condensation process makes it possible to produce a carbon monoxide product with a yield of more than 85%, which has a methane content of less than 100 vppm and therefore used without further purification step, for example for the production of monoethylene glycol can be.

In order to provide in particular the peak cooling required for the cryogenic separation process and to generate a reflux at the top of the CO / CH ₄ column, a refrigeration cycle driven by a cycle compressor is used in the prior art in which either externally supplied nitrogen or internally circulate generated carbon monoxide as a refrigerant.

Both refrigeration circuits are driven by multi-stage compressors. While a two-stage, relatively low-cost compressor can be used in a nitrogen cycle, a carbon monoxide compressor incurs significantly higher costs. The reason for this is, on the one hand, that a carbon monoxide compressor must be designed with at least three compressor stages in order to avoid thermal decomposition of carbon monoxide and resulting soot deposits. On the other hand, it must be explosion-proof and be operated in a particularly secure area in order to prevent escaping carbon monoxide from causing damage to people and equipment. The costs for the compressor of a carbon monoxide cycle are therefore up to 50% higher than those for a compressor which is suitable for driving a corresponding nitrogen cycle.

The inventive method allows to operate the refrigeration cycle of the condensation process with a simpler, cheaper compressor and lower operating costs than in the prior art, since the gas from the nitrogen source is already supplied with a higher pressure and therefore must be less highly compressed. In addition to the level of the pressure of the gas supplied from the nitrogen source, the design of the compressor is influenced by the level of the third pressure level, which is significantly dependent on the process management within the condensation process. As in this regard, a condensation process of the type indicated above has been identified, in which the CO / CH ₄ separation column is heated by nitrogen used as a refrigerant and at least a portion of the synthesis gas to be separated, the second liquid phase into a first, a second and a divided third partial stream, of which the first evaporated against the cooled in the heating of the CO / CH ₄ separation column, condensing nitrogen and the second against partially condensing synthesis gas and the vapor phases thereby formed the CO / CH ₄ separation column are fed as an intermediate heating, while the third sub-stream of CO / CH ₄ separation column is abandoned as an intermediate reflux.

The carbon monoxide yield of the condensation process depends essentially on the achievable temperature level of the peak cooling, which is determined by the first pressure level. Since nitrogen is used as the refrigerant, even between 2 and 3 bar (a) lying first pressure level is sufficient to achieve a comparable yield as with a much more expensive carbon monoxide cooling circuit.

In such a condensation process, the nitrogen used as the refrigerant is preferably depressurized by less than 13 bar, and more preferably by less than 10 bar, to reach the first pressure level.

Furthermore, the invention relates to a device for decomposing a syngas, with an acid gas scrubbing to obtain a largely consisting of hydrogen and carbon monoxide, methane-containing synthesis gas by separating carbon dioxide and sulfur components from the synthesis gas and using a stripping gas at a first pressure level, a cryogenic gas separator, in which a carbon monoxide product can be obtained from the synthesis gas, and a nitrogen source from which stripping gas can be removed at a second, above the first lying pressure level.

On the device side, this object is achieved according to the invention in that the cryogenic gas separator is connected to the sour gas scrubber and the nitrogen source in such a way that it can be supplied with gas from the nitrogen source in order to use it as refrigerant and subsequently to the first pressure level in the sour gas scrubber to be able to deliver as stripping gas.

In a preferred embodiment, the device according to the invention comprises a compressor connected to the nitrogen source and the cryogenic gas separator, via which gas taken from the nitrogen source as refrigerant is compressed to a third pressure level before being introduced into the cryogenic gas separator.

The cryogenic gas separator is particularly preferably designed for carrying out a condensation process, for which purpose it comprises at least one heat exchanger for cooling and partial condensation of the synthesis gas, a separator in which a first liquid phase can be separated from the partially condensed synthesis gas, an H ₂ -stripping column in which from the first liquid phase by separation of hydrogen, a second liquid phase can be generated, and a CO / CH ₄ separating column, which is connected to a reboiler, which is part of a cooling circuit and via the guided in the cooling circuit nitrogen and a part of heat dissipated synthesis gas and the CO / CH ₄ separation column can be supplied to the heating thereof, from the second liquid phase a carbon monoxide-rich gas phase with a purity that allows their release as carbon monoxide product, as well as a substantially consisting of methane and carbon monoxide bottom product erha wherein the second liquid phase can be divided into a first, a second and a third partial stream, of which the first evaporates against the condensed nitrogen cooled in the heating of the CO / CH ₄ separation column and the second against partially condensing synthesis gas and the thereby formed vapor phases of the CO / CH ₄ separation column can be fed as an intermediate heating, while the third partial stream of the CO / CH ₄ separation column can be abandoned as an intermediate reflux.

To supply the particularly preferred cryogenic Gaszerlegers needs to be compressed from the nitrogen source and used as a refrigerant gas only to a comparatively low, not more than 13bar above the first lying third pressure level, so that the compression already achieved by the use of a single-stage compressor can be, if the second pressure level is at least 2bar above the first pressure level.

Preferably, the nitrogen source is a cryogenic air fractionator which can provide nitrogen in gaseous form at a pressure between 4 and 6 bar (a).

Furthermore, the acid gas scrubbing is preferably carried out as methanol scrubbing, in which nitrogen can be used at a pressure level between 1.5 and 3 bar (a) as stripping gas in the detergent regeneration.

• Die 1 zeigt die Erzeugung von Monoethylenglykol, bei dem ein Syntheserohgas auf erfindungsgemäße Art zerlegt wird.
• Die 2 zeigt eine kryogene, nach dem Kondensationsprozess betriebene Trenneinrichtung, die vorteilhaft bei der Durchführung des erfindungsgemäßen Verfahrens eingesetzt werden kann.

In the following, the invention with reference to two in the 1 and 2 schematically illustrated embodiments will be explained in more detail.

• The 1 shows the production of monoethylene glycol, in which a synthesis gas is decomposed in the manner according to the invention.
• The 2 shows a cryogenic, operated after the condensation process separator, which can be advantageously used in carrying out the method according to the invention.

In 1 will be over line 1 a carbonaceous feed such as coal or heavy oil fed to the reactor R and there with oxygen 2 from the cryogenic air separation L implemented by partial oxidation to a synthesis gas, which after removal of soot via line 3 enters the syngas cooler K. The synthesis gas is cooled and dried 4 the sour gas scrubbing M supplied, are separated in the carbon dioxide and other acid gases using a methanol detergent, wherein a largely consisting of hydrogen and carbon monoxide, methane-containing synthesis gas 5 and a detergent loaded with the separated acid gases. In order to avoid frostbite in the subsequent process step, remaining traces of acid gases and detergent residues from the synthesis gas 5 separated in the temperature swing adsorber A, before it via line 6 the cryogenic, preferably operated as a condensation process separator T is supplied. Hydrogen obtained in the cryogenic separator T 7 is first used as a regeneration gas in the thermal cycler A and then in the pressure swing adsorber D to a hydrogen product 8th cleaned, which together with the also obtained in the cryogenic separator T carbon monoxide product 9 in the synthesis G to monoethylene glycol 10 is implemented. In addition to the oxygen required for the partial oxidation 2 the cryogenic air separator L supplies liquid nitrogen 11 to cover the refrigeration demand of the cryogenic separator T and gaseous nitrogen 12 at a pressure level between 4 and 6 bar (a), which is needed as stripping gas in the regeneration of the loaded methanol detergent in the sour gas scrub M. Before being used as stripping gas, the pressure of the gaseous nitrogen 12 with the aid of the preferably single-stage compressor P raised to a value between 12 and 16bar (a) and as a refrigerant 13 introduced into the cooling circuit of the cryogenic separator T, where it is released cold-performing to provide much of the required cooling capacity. At the pressure level of the stripping gas, the expanded nitrogen leaves 14 the cryogenic separator T and is forwarded to the sour gas wash M. If less nitrogen can be used as a refrigerant in the cryogenic separator T than is needed in the sour gas scrubbing M as a stripping gas, becomes a part 15 of gaseous nitrogen 12 branched off from the cryogenic air separator L upstream of the compressor P and relaxed via the throttle body a, before he is also supplied as stripping the sour gas scrubbing M.

In the in 2 shown cryogenic separator T is the cleaned in the thermal cycler A synthesis gas 6 with a pressure between 30 and 60bar (a) in a first heat exchanger E1 cooled against process streams to be heated without condensing and anschießend in a first 22 and a second partial stream 23 split, of which the first 22 for heating the CO / CH ₄ separation column T2 in the reboiler R heat is removed, wherein a further cooled, completely gaseous first partial stream 24 created, with the second, in the bypass to Reboiler R guided partial flow 23 to the synthesis gas stream 25 is united. To control the temperature conditions in the CO / CH ₄ separation column T2, the quantitative ratio of the two partial streams 22 and 23 be varied.

In the second heat exchanger E2, the synthesis gas stream 25 cooled so far that the condensation of components a two-phase mixture 26 arises, which is separated in the separator B in a largely consisting of carbon monoxide and methane, hydrogen-containing liquid and a hydrogen-rich gas phase. The gas phase is via line 27 withdrawn from the separator B and after warming in the heat exchangers E2 and E1 as raw hydrogen 7 used for the regeneration of the temperature change adsorber A, before it is forwarded to the pressure swing adsorber D. The liquid phase 29 in contrast, the H ₂ separation column T1 is supplied. For this purpose, it is split into two partial streams, of which the first 30 is expanded as reflux to the top of the H ₂ separation column T1, while the second partial stream 31 after relaxation and subsequent partial evaporation in the heat exchanger E2 the middle part of the H ₂ separation column T1 is given as an intermediate heating.

The H ₂ separation column T1, which is operated at a pressure of between one fifth and one third of the pressure of the synthesis gas 6 is located, serves to remove the in the liquid phase 29 dissolved hydrogen. It is powered by a water heater 32 heated, which is integrated in the heat exchanger E2.

The hydrogen-rich top fraction 33 from the H ₂ -Trennkolonne T1 is after warming in the heat exchangers E2 and E1 as a flash gas 28 discharged at the plant boundary, while the largely hydrogen-free, consisting of carbon monoxide and methane sump fraction 35 in three sub-streams 36 . 37 and 38 split and in which at a pressure between 5 and 10bar (a) operated CO / CH ₄ separation column T2 is expanded. The CO / CH ₄ separation column T2 is heated via the reboiler R, in which the reboiler 39 is at least partially evaporated.

The peak cooling required for the cryogenic separation process is obtained via a refrigeration cycle driven by the compressor P, in which the nitrogen supplied in gaseous form by the cryogenic gas separator L is available 12 circulated as a refrigerant. The nitrogen 13 leaves the preferred single-stage compressor P with a pressure which is not more than 13bar above the pressure of the stripping gas required in the acid gas M, is subsequently cooled in the heat exchanger E1 and in the reboiler R together with the first partial flow 22 of the synthesis gas 6 against the reboiler stream 39 from the CO / CH ₄ separation column T2 further cooled, without condense. In the heat exchanger E3, the cooled nitrogen in the reboiler R. 40 against the partial flow 36 that typically contains more than 45% of the amount of bottom fraction 35 the H ₂ separation column T1 makes up, condenses, which thereby evaporates and as a gas stream 42 is continued. The second partial flow 37 the bottom fraction 35 is in the heat exchanger E2 against the partially to be condensed synthesis gas stream 25 also evaporated and as a gas stream 43 with the gas stream 42 to the gas stream 44 united, which is then performed as an intermediate heating in the CO / CH ₄ separation column T2. The third partial flow 38 the bottom fraction 35 , which accounts for only about 5-10% of their total amount, is given up after a relaxation of the CO / CH ₄ separation column T2 as an intermediate reflux.

A part 45 of the condensed in the heat exchanger E3 nitrogen 41 is cooled to the top of the CO / CH ₄ separation column T2 relaxed, where a capacitor C is arranged, which, cooled by liquid nitrogen, a temperature difference for driving an internal column carbon monoxide reflux 46 supplies. The second part 47 of condensed nitrogen 41 as well as gaseous nitrogen 48 From the top of the CO / CH ₄ separation column T2 are each cooled to the pressure level of the pressure required in the sour gas scrubbing stripping and cold pressure to the two-phase nitrogen flow 49 merged, which provides the peak cold for the cold end of the heat exchanger E2. After evaporation and heating in the heat exchangers E2 and E1, the nitrogen is 49 as stripping gas 14 the sour gas scrub M supplied.

Below the condenser C is a product purity having carbon monoxide fraction 50 withdrawn from the CO / CH ₄ separation column T2 and after heating in the heat exchangers E2 and E1 without further compression as carbon monoxide product 9 forwarded to monoethylene glycol synthesis G. Additional cold is the separation process via the liquid nitrogen from the cryogenic air separator L 11 supplied after evaporation and heating in the heat exchangers E2 and E1 via line 51 is discharged into the atmosphere or a flare system in gaseous form.

In the bottom space S of the CO / CH ₄ separation column T2, a methane-rich, carbon monoxide-containing liquid phase collects 52 , which is also evaporated in the heat exchangers E2 and E1 and warmed up before being used as fuel gas 53 can be delivered.

Claims (10)

Process for decomposing a crude synthesis gas (4) from which carbon dioxide and sulfur components are separated off in an acid gas scrubber (M) to obtain a methane-containing synthesis gas (6) consisting largely of hydrogen and carbon monoxide, which is subsequently isolated in a cryogenic separation process ( T) a carbon monoxide product (9) is obtained, wherein in the sour gas scrubbing (M) a stripping gas (14) is used at a first pressure level, which is provided by a nitrogen source (L) with a second, above the first lying pressure level, characterized in that the gas (12) provided by the nitrogen source (L) is used as refrigerant (13) in the cryogenic separation process (T) and is thereby expanded to the first pressure level in order subsequently to be supplied to the acid gas scrubbing as stripping gas (14). Method according to Claim 1 , characterized in that as refrigerant from the nitrogen source (L) withdrawn gas (12) is compressed prior to its introduction into the cryogenic separation process (T) to a third pressure level. Method according to Claim 2 , characterized in that not as stripping gas in the sour gas scrubber (M) required, as refrigerant (13) in the cryogenic separation process (T) used nitrogen only expanded to the second pressure level and recycled after compression to the third pressure level again as a refrigerant in the condensation process becomes. Method according to one of Claims 1 to 3 , characterized in that the synthesis gas (6) is partially condensed in the cryogenic separation process by cooling, in order to obtain a largely consisting of carbon monoxide and methane, hydrogen-containing first liquid phase (29) from which in an H ₂ -trip column (T1) by the separation of hydrogen is a second liquid phase (35) is generated, which in a carbon dioxide-rich by the nitrogen used as a refrigerant (13) and at least a portion (22) of the synthesis gas (6) heated CO / CH ₄ separation column (T2) Gas phase (50) having a purity allowing its release as carbon monoxide product (9) and a bottom product consisting largely of methane and carbon monoxide (52), the second liquid phase (35) being divided into a first (36), a second (35) 37) and a third partial flow (38) is divided, of which the first (36) against the cooled in the heating of the CO / CH ₄ separation column (T2), condensing nitrogen (40) and the second (37) evaporated against partially condensing synthesis gas (25) and the vapor phases (42, 43) of the CO / CH ₄ - Separating column (T2) are supplied as an intermediate heating, while the third part stream (38) of the CO / CH ₄ separation column (T2) is abandoned as an intermediate reflux. Method according to Claim 4 , characterized in that the nitrogen used as refrigerant (13) in the cryogenic separation process (T) by less than 13bar and preferably by less than 10 bar is relaxed to reach the first pressure level. Apparatus for decomposing a synthesis gas (4), with an acid gas scrubbing (M) to obtain a largely consisting of hydrogen and carbon monoxide, methane-containing synthesis gas (6) by separating carbon dioxide and sulfur components from the syngas and using a stripping gas (14) on a first pressure level, a cryogenic gas separator (T), in which from the synthesis gas (6) a carbon monoxide product (9) can be obtained, and a nitrogen source (L), from the stripping gas (12) on a second, above the first lying pressure level removable characterized in that the cryogenic gas separator (T) is connected to the sour gas scrubber (M) and the nitrogen source (L) such that gas (12) can be supplied to it from the nitrogen source (L) to be used as the refrigerant use and subsequently released to the first pressure level relaxed in the sour gas scrubbing (M) as stripping gas (14). Device after Claim 6 characterized in that it comprises a compressor (P) connected to the nitrogen source (L) and the cryogenic gas separator (T) via the gas (12) withdrawn as refrigerant from the nitrogen source prior to its introduction into the cryogenic gas separator (T) a third pressure level can be compressed. Device after Claim 7 , characterized in that the cryogenic gas separator (T) comprises at least one heat exchanger (E2) for cooling and partial condensation of the synthesis gas (25), a separator (B) in which a first liquid phase (29) from the partially condensed synthesis gas (26) can be separated, a H ₂ -Strippkolonne (T1), in which from the first liquid phase (29) by separation of hydrogen, a second liquid phase (35) can be generated, and a CO / CH ₄ separation column (T2) comprises with a reboiler (R) is in communication, which is part of a refrigeration cycle and over the guided in the cooling circuit nitrogen (13) and a part (22) of the synthesis gas to be separated (6) heat extracted and the CO / CH ₄ separation column (T2 ) can be supplied to the heating to from the second liquid phase (35) a carbon monoxide-rich gas phase (50) having a purity that allows their release as carbon monoxide product (9), and a largely of methane and carbon monoxide best The second liquid phase (35) can be divided into a first (36), a second (37) and a third partial flow (38), of which the first one (36) is opposite to that during heating the CO / CH ₄ separation column (T2) cooled, condensing nitrogen (40) and the second (37) vaporizable against partially condensing synthesis gas (25) and the resulting vapor phases (42, 43) of the CO / CH ₄ separation column (T2 ) can be fed as intermediate heating, while the third partial stream (38) of the CO / CH ₄ separation column (T2) can be abandoned as an intermediate reflux. Device after Claim 8 , characterized in that the compressor (P) is designed in one stage. Device according to one of Claims 6 to 8th , characterized in that the nitrogen source (L) is a cryogenic air separator.

Images