EP2598618B1 - Method for producing substitute natural gas - Google Patents

Description

Field of the invention

The invention relates to a process for the production of synthetic natural gas. In particular, the invention relates to a process for producing and providing synthetic natural gas at pressures suitable for direct feed into natural gas pipelines.

State of the art

As a result of doubts about the availability and supply of natural gas in the 1970s, considerable efforts have been made to substitute natural gas (SNG) from the large known coal stocks. This was discussed in particular where there was a large local demand for natural gas as an important primary energy source, and at the same time considerable local coal deposits were available. The main component of the SNG is - as with natural gas - the methane. However, since comparatively high investment is required for coal-fired SNG production facilities, and subsequently large new natural gas deposits were discovered which gave reason to hope for a long-term supply of cheap natural gas, interest in SNG's industrial production subsequently declined initially ,

As the situation has changed so that the end of the previously known natural gas reserves can be foreseen, interest in methanation as an alternative source of natural gas replacement gas has recently increased again. In addition, the technology provides a way to more efficiently use large and remote coal deposits. Geopolitical considerations also call for greater independence from the comparatively small, large natural gas reserves. The production of SNG on an industrial scale is therefore attracting renewed interest. It is particularly advantageous that the infrastructure built for the supply of natural gas, such as existing pipelines, can be used virtually unchanged.

As stated in Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, 1998 Electronic Release, keyword gas production, the catalytic catalytic methane synthesis by hydrogenation of carbon monoxide (CO) with hydrogen (H ₂ ) is based on work by Sabatier and Senderens the year 1902. The reaction can be described by the following reaction equation:

CO + 3H ₂ = CH ₄ + H ₂ O

Carbon dioxide can also be converted to methane according to the equation

CO ₂ + 4H ₂ = CH ₄ + 2H ₂ O

Both reactions are linked by the CO conversion reaction (CO shift), which always proceeds simultaneously in the presence of active catalysts:

CO + H ₂ O = CO ₂ + H ₂

Both reactions for methane formation are highly exothermic and decrease in volume. The formation of methane in high yield after the above reactions is therefore favored at low temperatures and high pressures. To achieve acceptable reaction rates then the use of suitable catalysts required. There are therefore used catalysts based on nickel as the active metal component. The presence of catalyst poisons, as they are, for example, sulfur-containing components must be carefully avoided, since the deactivation of the catalysts used depends primarily on the presence of such catalyst poisons. Typical nickel-based methanation catalysts operate at temperatures of 300 to 700 ° C; For example, catalysts with a high nickel content are used on special alumina support materials which have been stabilized by doping with zirconium oxide.

Industrial processes for producing SNG on an industrial scale, starting from carbon monoxide and hydrogen-containing synthesis gas, have been known to the art for a long time. This is what the US patent teaches US 4005996 A a method for increasing the energy content of a syngas gas stream obtained by gasification of coal. The process involves the catalytic methanation of carbon oxides with hydrogen by means of highly active nickel catalysts, wherein a gas mixture containing methane and steam is produced in several reaction stages. The synthesis gas product of the coal gasification is first freed by gas scrubbing with suitable absorbents, for example methanol or amine-containing absorbents, catalyst poisons and other impurities and a portion of the carbon dioxide contained. Depending on the composition of the primary gas from the coal gasification further conditioning stages, such as adsorption to remove sulfur-containing components of zinc oxide-containing adsorbents, and additional conversion stages such as shift reactors to adjust the hydrogen and CO content of the synthesis gas. The purified and conditioned synthesis gas is then heated to the inlet temperature in the first methanation of about 260 ° C by heat exchange against recirculated product gas of the first methanation. The reactor pressure is about 25 bar (a). By adding the recycle gas to the fresh feed gas of the methanation, the gas composition is also advantageously changed in such a way that there is no longer any precipitation of solid carbon in the catalyst bed and at the reactor outlet of the methanation. In addition, the product gas recirculation serves to control the Congestion due to the high exothermicity of the above reactions. The first reaction stage of the methanization is followed by another methanation stage, which is operated without product gas recirculation. The enriched in its methane content and thus energy content product gas of the methanation is cooled and dried and thus has a quality that is suitable for introduction or admixture in conventional natural gas pipelines. For the introduction into a natural gas pipeline, the gas pressure of the SNG has to be increased to the pipeline operating pressure by means of compression in a pipeline head-end station Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, 1998 Electronic Release, keyword "Natural Gas" , Chapter 4.1.1 "Pipeline Transmission" can be up to 80 bar (a).

A more modern process variant for the synthesis of SNG from synthesis gas is disclosed in the US patent application US 2009/0247653 A1 disclosed. This is how the local shows Fig. 2 a process in which the synthesis gas first passes through one or more methanation reactors to produce a primary methanation product gas which is subsequently cooled to separate water by condensation from the primary methanation product gas. A portion of the thus-dried primary methanation product is subsequently recycled as recycle gas before the entrance of the methanation reactors. The remaining portion of the primary methanization product gas is fed as feed to another adiabatic methanization reactor ("trim reactor"). Preferably, the process is carried out such that there are at least two series-connected methanation primary reactors, wherein the first reactor is supplied with fresh synthesis gas feed gas and the recycle stream and the second reactor is supplied with both the product gas of the first reactor and fresh synthesis gas feed gas , In this process as well, a cooled and dried methanization product gas is finally obtained, the pressure of which must be increased before it is discharged into a pipeline network.

The EP-A-0 120 590 discloses a multi-stage methanation process for converting synthesis gas and a sulfur-containing gas into a methane-rich, pipeline-grade product gas. In this process, it is considered advantageous to carry out the methanation at high pressure to provide the pipelined final product gas without additional compression.

From the US-A-3 928 000 For example, there is known a method of producing a methane-rich gas by partially oxidizing a sulfur-containing hydrocarbon fuel in a synthesis gas generator, wherein the methanation of the synthesis gas on a sulfur-resistant methanation catalyst occurs at the pressure provided by the syngas generator, thereby saving costly compressors.

The US-A-4 124 628 discloses a six-stage methanation process in which densification occurs after the fifth stage.

The SNG produced by methanation is often to be fed into an existing pipeline system for transport to consumers. Due to the pressure loss that the synthesis gas suffers when passing through the methanation plant and the lower pressure level in the methanation plant compared to the pipeline pressure it is necessary to compress the methane-rich product gas after the methanation plant to pipeline pressure. The brochure "From solid fuels to substitute natural gas (SNG) using TREMP ™", available on the Internet at www.topsoe.com, points out that it is often necessary to generate the generated SNG before it is fed into a pipeline system to increase in pressure. It is further stated that the pressure increase takes place after production and drying of the generated SNG, ie just before it is fed into the pipeline.

Description of the invention

The present invention has for its object to provide for the production of SNG from synthesis gas on an industrial scale and the subsequent feeding of the generated SNG in a pipeline system, a method that is characterized by particular energy efficiency.

The solution of the object according to the invention results essentially from the characterizing features of claim 1 in conjunction with the features of the preamble. Further advantageous embodiments of the invention will become apparent from the dependent claims.

In the known in the prior art method for the production of SNG and its introduction into a pipeline system, the adaptation of the target pressure of the product gas of methanation, ie usually the pipeline pressure, after the last reaction stage, and after cooling and drying of the product gas.

Surprisingly, it has now been found that considerable energy savings can be achieved if the setting of the target pressure also takes place before the main reaction zone and / or before or in the post-reaction zone by means of compression by an additional compressor. This is not obvious insofar as the pressure to be set there results as the sum of the target pressure and the pressure loss over the entire or the remaining methanization plant. The latter is not known a priori; the skilled person therefore avoids to set a target pressure upstream, if still generating pressure loss Plant components are interposed, but preferably the setting of the target pressure as close to the transfer point (here at the entrance to the pipeline).

In a methanation process according to the prior art, the methane-rich product gas after the methanization plant must be compressed by a lower pressure on the pipeline pressure due to the relaxation over the plant parts. Due to the higher pressure ratio, defined as the ratio of outlet pressure to inlet pressure of the compressor, more energy must be expended for the product compressor and for the cycle compressor together than in the inventive method.

The subject of the process according to the invention is that the densification of the synthesis gas to adjust the target pressure in addition to the product compression before the main reaction zone and / or before or in the post-reaction zone, instead - as in the prior art processes - only after the methanation. As a result, the temperature increase due to the compression is used for the heating of the synthesis gas, which explains the energetic advantages of the process. In addition, it is advantageous that in the inventive method in the additional compressor, a colder synthesis gas is compressed in comparison to the cycle compressor, and that results in a more favorable pressure ratio for both the cycle compressor and for the additional compressor. These advantages offset the apparent drawback that a larger mass flow rate is compressed. The result is that the sum of the compression energy for auxiliary, cycle and product compressors is lower with this circuit. If the additional compressor is arranged before or in the post-reaction zone, the utilization of the more favorable pressure ratio leads to the energetic advantages of the process according to the invention. An arrangement in the post-reaction zone can take place if it comprises a plurality of reactors. In this case, the arrangement of the additional compressor before the last reactor of the post-reaction zone has proven to be particularly favorable. Before being introduced into the pipeline system, the SNG product gas may need to be cooled and dried, as is also provided in the prior art.

Preferred embodiments of the invention

Particularly preferably, the setting of the target pressure is carried out by compression in front of the main reaction zone and before the synthesis gas fresh gas stream is combined with the recycle stream. For this purpose, an additional compressor is arranged in front of the point of fusion of the synthesis gas fresh gas stream with the recycle stream. This can be followed, for example, the usually existing Feinentschwefelungsstufe. Since the synthesis gas fresh gas stream leaving the fine desulfurization stage is comparatively cold, part of the supplied compression energy can be advantageously used to preheat the synthesis gas fresh gas stream. In addition, the cycle compressor is relieved. In this embodiment of the invention particularly large energy savings are achieved, as the following numerical examples show. The product compressor can be dimensioned considerably smaller in terms of its compressor performance than in a methanization system according to the prior art.

In a further preferred embodiment, adjusting the target pressure comprises compressing before or in the post-reaction zone, after withdrawing the recycle stream after the main reaction zone. The additional compressor can be connected upstream of the cooler before entering the post-reaction zone; In this case, a part of the supplied compression energy is advantageously used for steam generation. It is particularly preferred, however, downstream of the cooler, since then a cooler and dryer gas can be compressed. Alternatively, the additional compressor can also be switched directly in front of the first catalyst bed of the post-reaction zone, whereby, as in the above case, part of the supplied compression energy can be used to preheat the gas stream entering the post-reaction zone. An arrangement of the additional compressor in the post-reaction zone is possible if it comprises several reactors. In this case, the arrangement of the additional compressor before the last reactor of the post-reaction zone has proven to be particularly favorable.

A preferred embodiment of the invention provides that the heating of the main reaction zone supplied synthesis gas feed stream is carried out in indirect heat exchange against a hot process own or foreign process fluid flow. Particular preference is given to heating the synthesis gas feed stream fed to the main reaction zone in indirect heat exchange with the recycle stream. The heat integration obtained in this way contributes to the energy efficiency of the method according to the invention.

The addition of the recycle stream to the syngas fresh gas stream also serves to control the exotherm in the main reaction zone. The dilution of the syngas fresh gas stream and the consequent reduction in the concentration of carbon oxides in the syngas feed stream reduces the risk of carbon deposits forming in the main reaction zone catalyst beds as well as at the catalyst bed exit.

Preferred embodiments of the invention provide that the reaction of the synthesis gas feed stream to a methane-rich intermediate gas stream occurs in the main reaction zone at temperatures between 200 and 700 ° C and at pressures between 15 and 120 bar (a) such that further reaction of the intermediate Gas stream to a methane-rich product gas stream in the post-reaction zone at temperatures between 150 and 500 ° C and at pressures between 30 and 120 bar (a), and reacting the synthesis gas feed stream in the main reaction zone and / or the intermediate gas stream in the post-reaction zone by means of methanation catalysts on nickel, iron or precious metal base. The use in particular of nickel catalysts for the methanation of carbon oxides with hydrogen is known per se and is used industrially, so that a large number of suitable catalysts is commercially available.

According to a preferred embodiment of the invention, the molar ratio of hydrogen to carbon monoxide in the synthesis gas fresh gas stream is between 0.4 and 5.0 mol / mol. Considering the stoichiometry of the reactions discussed above For the formation of methane by hydrogenation of carbon oxides, these molar ratios have been found to be particularly suitable.

An advantageous embodiment of the method according to the invention provides that the main reaction zone comprises at least two catalyst beds, and that a portion of the synthesis gas fresh gas stream is passed before entering the second catalyst bed of the main reaction zone. This measure, which is known per se, contributes significantly to distributing the high exothermicity of the methanation reaction more uniformly over both catalyst beds, so that a thermal overload of the first catalyst bed, which leads to accelerated deactivation of the catalyst used there, is avoided.

The target pressure in the process according to the invention is preferably between 30 and 120 bar (a), more preferably between 30 and 90 bar (a). This corresponds to the usual working pressure in natural gas pipelines.

In a development of the invention, the process according to the invention can be used for the processing of synthesis gas produced by gasification of coal. The coal gasification is followed by the following, known to those skilled in the process steps for conditioning the synthesis gas: A partial conversion of the CO to hydrogen to adjust the required H ₂ / CO ratio (CO shift), and a removal of acidic gas components, eg. Example by washing with cold methanol by the Rectisol® process in which sulfur compounds are almost completely and carbon dioxide partially removed. However, the inventive method can also for the processing of synthesis gas from other sources, eg. B. from natural gas or by gasification of biomass or liquid, hydrocarbon-containing starting materials synthesis gas can be used.

Further developments, advantages and applications of the invention will become apparent from the following description of exemplary embodiments and the drawings. All described and / or illustrated features form for itself or in any combination of the invention, regardless of their combination in the claims or their dependency.

Fig. 1

eine Methanisierungsanlage nach dem Stand der Technik,

Fig. 2

eine erfindungsgemäße Methanisierungsanlage gemäß einer ersten Ausgestaltungsform,

Fig. 3

eine erfindungsgemäße Methanisierungsanlage gemäß einer weiteren Ausgestaltungsform.

Show it

Fig. 1

a methanization plant according to the prior art,

Fig. 2

a methanation plant according to the invention according to a first embodiment,

Fig. 3

a Methanisierungsanlage according to the invention according to another embodiment.

In the exemplary embodiments illustrated in the figures, the methanization plant in each case adjoins a coal gasification plant, not shown in the figure, in which the synthesis gas intended for the conversion to SNG is produced in a manner known per se from feed coal and conditioned for use in the methanation plant ,

Fig. 1 shows a methanation plant 100 according to the prior art. Via line 101, synthesis gas produced and subsequently conditioned in the coal gasification plant is first supplied to a fine desulfurization 102 in order to remove last traces of sulfur compounds from the synthesis gas fresh gas stream. After passing through the fine desulfurization 102, a portion of the synthesis gas fresh gas stream is withdrawn via line 107 and fed to the second catalyst bed of the main methanation reaction zone. Furthermore, the fine-desulfurized synthesis gas fresh gas stream is fed via line 118, a recycle stream containing already partially converted to methane synthesis gas. In this way, a synthesis gas feed stream is obtained, which is fed via line 103 to a heat exchanger 104, in which the syngas feed stream in indirect heat exchange against the brought via line 115, 116 and 118, hot recycle stream to temperatures between 220 and 350 ° C. is heated. The recycle stream is conveyed via the cycle compressor 117 and compressed to the methanation pressure of 20 to 50 bar (a).

The preheated synthesis gas feed stream is fed via line 105 to the main reaction zone, which consists of two methanation catalyst-containing reactors 106 and 111. These are adiabatic fixed bed reactors, which are characterized by their constructive simplicity. However, the use of reactors of a different design and with different temperature control would also be conceivable. In the reactor 106, a partial conversion of the carbon oxides with hydrogen takes place on a commercial methanation catalyst based on nickel at temperatures of 220 to 700 ° C and pressures between 20 and 50 bar (a). The space velocity is between 2000 and 40,000 h ^-1 , the H ₂ / CO ratio is between 2.5 and 4.0 mol / mol. The partially converted intermediate product gas stream leaving the reactor 106 is fed via line 108 to a heat exchanger 109 in which it is cooled to temperatures of 220 and 350 ° C. Via line 110, the cooled intermediate product gas stream is fed to the second reactor 111 of the main reaction zone, where further conversion of the carbon oxides with hydrogen to methane takes place. Beforehand, the intermediate gas stream in line 110 is admixed with the partial gas stream introduced via line 107, whereby additional cooling is effected and the concentration of carbon oxides and hydrogen is increased. In reactor 111, a further partial conversion of the carbon oxides takes place with hydrogen, the reaction conditions being comparable to those in reactor 106. Via line 112, the further partially converted intermediate product gas stream leaving the reactor 111 is fed to a cooler 113, in which it is cooled to temperatures of 180 ° and 350 ° C. The heat dissipated in the heat exchangers 109, 113 and 119 is used to generate steam in the steam generating plant 130.

Via line 114, the partially reacted intermediate gas stream is removed from the main reaction zone of the methanation plant 100. From it, a partial stream is withdrawn via line 115 as a recycle stream and fed to the first reactor 106. The partially reacted intermediate gas stream is cooled in the heat exchanger 119 to temperatures between 40 to 350 ° C and fed via line 120 to the reactor 121, which represents the only methanization of the post-reaction in the present embodiment. In the adiabatic or isothermal reactor 121, a further conversion of the carbon oxides with hydrogen to methane takes place on a commercial methanation catalyst nickel based at temperatures of 180 to 370 ° C and pressures between 20 and 50 bar (a). The space velocity is between 2000 and 40,000 h ^-1 . The reactor 121 via line 122 leaving, methane-rich product gas stream is cooled in cooler 123 to temperatures of 20 to 120 ° C and in an in Fig. 1 dried drying system not shown. Via line 124, the cooled and dried product gas stream is fed to the product compressor 125, in which the product gas stream is compressed to the pipeline inlet pressure of 30 to 120 bar (a). Via line 126, the compressed product gas stream is fed to the pipeline, not shown in the figure.

Fig. 2 shows a Methanisierungsanlage 200 according to the invention according to a first embodiment. In each case, the system parts marked with the reference symbols 20x or 2xx correspond to those in FIG Fig. 1 according to the prior art, which have been designated there by 10x or 1xx, in terms of their nature, design, function and operating conditions, unless otherwise stated. In contrast to the methanation plant according to the prior art, the synthesis gas fresh gas stream is compressed before entry into the fine desulfurization 202 to a pressure of 40 to 120 bar (a) by means of additional compressor 227. In the reactor 206 and 211, partial conversion of the carbon oxides with hydrogen takes place on a nickel-based methanation catalyst at temperatures of 200 to 700 ° C. and pressures between 40 and 120 bar (a). The H ₂ / CO ratio is between 0.4 and 5.0 mol / mol. In the reactor 221, further conversion of the carbon oxides with hydrogen to methane takes place on a nickel-based methanation catalyst at temperatures of 150 to 500 ° C. and pressures between 40 and 120 bar (a). The methane-rich product gas stream leaving the reactor 221 via line 222 is cooled in cooler 223 to temperatures of 20 to 120 ° C. and poured into an in Fig. 2 dried drying system not shown. Via line 224, the cooled and dried product gas stream is first supplied to the product compressor 225 and finally via line 226 of the pipeline not shown in the figure.

Fig. 3 shows a Methanisierungsanlage 300 according to the invention according to a further embodiment. Again, each correspond to the reference numerals 30x or 3xx marked system parts with those of Fig. 1 according to the prior art, which have been designated there by 10x or 1xx, in terms of their nature, design, function and operating conditions, unless otherwise stated. In contrast to the methanation plant according to the prior art, the compression of the partially reacted intermediate gas stream takes place before entering the post-reaction zone by means of additional compressor 327 to a pressure of 40 to 120 bar (a). In the reactor 306 and 311, partial conversion of the carbon oxides with hydrogen takes place on a nickel-based methanation catalyst at temperatures of 200 to 700 ° C. and pressures between 20 and 75 bar (a). The H ₂ / CO ratio is between 0.4 and 5.0 mol / mol. In the reactor 321, further conversion of the carbon oxides with hydrogen to methane takes place on a nickel-based methanation catalyst at temperatures of 150 to 500 ° C. and pressures between 40 and 120 bar (a). The methane-rich product gas stream leaving the reactor 321 via line 322 is cooled in cooler 323 to temperatures of 20 to 120 ° C. and placed in an in Fig. 3 dried drying system not shown. Via line 324, the cooled and dried product gas stream is first supplied to the product compressor 325 and finally via line 326 of the pipeline not shown in the figure.

Numerical examples

In order to clarify the advantages of the method according to the invention, numerical examples are reproduced below in which important operating parameters of a methanation process according to the prior art are compared with the corresponding operating parameters of methanation processes according to the invention according to the two previously described embodiments. All three subsequent cases are based on the following composition of the synthesis gas fresh gas stream from an off-stream gasification of coal. component stream H ₂ 14027 kmol / h CO 4608 kmol / h CO ₂ 47 kmol / h CH ₄ 1 kmol / h N ₂ 156 km / h Ar 23 kmol / h

The methane-rich product gas has the following composition at an outlet pressure of 80.0 bara for the three operating cases: case Compaction of the SNG product stream (prior art, Fig. 1 , Appendix 100) Compression before the post-reaction zone (invention, Fig. 3 , Appendix 300) Compaction before the main reaction zone (invention, Fig. 2 , Appendix 200) H ₂ 117 kmol / h 82 kmol / h 33 kmol / h CO 0.5 kmol / h 0 kmol / h 0 kmol / h CO ₂ 25 kmol / h 17 kmol / h 5 kmol / h H ₂ O 40 kmol / h 16 kmol / h 16 kmol / h CH ₄ 4633 kmol / h 4641 kmol / h 4653 kmol / h N ₂ 156 km / h 156 km / h 156 km / h Ar 23 kmol / h 23 kmol / h 23 kmol / h

In the following table, important operating parameters for the three cases discussed, in particular the requirements for electrical energy, are compiled and compared. It becomes clear that in particular the in Fig. 2 illustrated embodiment of the invention, which provides a compaction on pipeline pressure before the main reaction zone, to considerable. Savings in electrical energy leads.

Industrial Applicability

The invention provides a process for the production of synthetic natural gas (SNG) and its provision at pipeline operating pressure which is distinguished by its high energy efficiency compared to the processes known in the prior art. This advantage is achieved essentially by the use of a Zusazuverdichters at a suitable point in the process, accompanied by an adjustment of the process parameters. The advantages of the methods known in the prior art with respect to their robustness and high availability of operation of the system according to the invention continue to exist. case Compaction of the SNG product stream (prior art, Fig. 1 , Appendix 100 Compression before the post-reaction zone (invention, Fig. 3 , Appendix 300 Compaction before the main reaction zone (invention, Fig. 2 , Appendix 200) auxiliary compressor Admission Flow 9702 m3 / h 18688 m3 / h Eintrittsmolstrom 5484 kmol / h 18866 kmol / h inlet pressure 15.5 bar (a) 25.8 bar (a) CDP 40.9 bar (a) 50.8 bar (a) inlet temperature 59.9 ° C 30.0 ° C pressure ratio 2.6 2.0 energy needs 6,60 MW 13.88 MW Cycle compressor Admission Flow 145558 m3 / h 145558 m3 / h 54752 m3 / h Eintrittsmolstrom 62029 kmol / h 62028 kmol / h 62216 kmol / h inlet pressure 15.5 bar (a) 15.5 bar (a) 40.9 bar (a) CDP 24.2 bar (a) 24.2 bar (a) 49.7 bar (a) pressure ratio 1.6 1.6 1.2 inlet temperature 174.9 ° C 174.9 ° C 174.8 ° C energy needs 39.75 MW 39.75 MW 16.55 MW product compressor Admission Flow 16133 m3 / h 3461 m3 / h 3461 m3 / h Eintrittsmolstrom 4994 kmol / h 4885 kmol / h 4885 kmol / h inlet pressure 8.0 bar (a) 35.5 bar (a) 35.5 bar (a) CDP 80.0 bar (a) 80.0 bar (a) 80.0 bar (a) inlet temperature 41.6 ° C 42.5 ° C 42.5 ° C number of steps 3 2 2 pressure ratio 10.0 2.3 2.3 energy needs 14.03 MW 4.41 MW 4.41 MW Total energy demand 53.78 MW 50.76 MW 34.84 MW

LIST OF REFERENCE NUMBERS

101, 201, 301

management

102, 202, 302

Feinentschwefelungsreaktor

103, 203, 303

management

104, 204, 304

heat exchangers

105, 205, 305

management

106, 206, 306

methanation

107, 207, 307

management

108, 208, 308

management

109, 209, 309

heat exchangers

110, 210, 310

management

111, 211, 311

methanation

112, 212, 312

management

113, 213, 313

heat exchangers

114, 214, 314

management

115, 215, 315

management

116, 216, 316

management

117, 217, 317

Cycle compressor

118, 218, 318

management

119, 219, 319

heat exchangers

120, 220, 320

management

121, 221, 321

methanation

122, 222, 322

management

123, 223, 323

heat exchangers

124, 224, 324

management

125, 225, 325

product compressor

126, 226, 326

management

227, 327

auxiliary compressor

228, 328

management

130, 230, 330

Steam generating plant

Claims (10)

1. Process for producing a methane-rich product gas stream at a defined target pressure from a synthesis gas fresh gas stream containing carbon oxides and hydrogen, wherein said process comprises the following process steps:

   (a) providing a synthesis gas fresh gas stream at an entry pressure,

   (b) combining the synthesis gas fresh gas stream with a recycle stream to afford a synthesis gas input stream,

   (c) heating the synthesis gas input stream and supplying to a main reaction zone,

   (d) reacting the heated synthesis gas input stream to afford a methane-enriched intermediate gas stream in a main reaction zone under methanization conditions, wherein the main reaction zone contains at least one catalyst bed containing methanization catalyst,

   (e) withdrawing a substream of the methane-rich intermediate gas stream downstream of the main reaction zone as a recycle stream, wherein the recycle stream is recycled upstream of the main reaction zone using a circuit compressor and combined with the synthesis gas fresh gas stream to afford the synthesis gas input stream,

   (f) supplying the proportion of the methane-rich intermediate gas stream remaining after step (d) to a postreaction zone,

   (g) converting the intermediate gas stream supplied to the postreaction zone into a methane-rich product gas stream under methanization conditions, wherein the postreaction zone contains at least one catalyst bed containing methanization catalyst,

   (h) withdrawing the methane-rich product gas stream from the postreaction zone and supplying said stream to a product compressor,
   characterized in that the main reaction zone and/or the postreaction zone has an auxiliary compressor arranged upstream of it and in that the establishment of the target pressure is effected using the product compressor and the auxiliary compressor.
2. Process according to Claim 1, characterized in that the compressing is effected using an auxiliary compressor upstream of the main reaction zone and upstream of the combining of the synthesis gas fresh gas stream with the recycle stream.
3. Process according to Claim 1 characterized in that the compressing is effected using an auxiliary compressor upstream of the last catalyst bed of the postreaction zone and downstream of the withdrawing of the recycle stream downstream of the main reaction zone.
4. Process according to any of the preceding claims, characterized in that the heating of the synthesis gas input stream supplied to the main reaction zone is effected in indirect heat exchange against a hot fluid stream internal or external to the process.
5. Process according to any of the preceding claims, characterized in that the converting of the synthesis gas input stream to afford a methane-rich intermediate gas stream in the main reaction zone is effected at temperatures between 200°C and 700°C and at pressures between 15 and 120 bar (a) in the presence of a methanization catalyst.
6. Process according to any of the preceding claims, characterized in that the converting of the intermediate gas stream to afford a methane-rich product gas stream in the postreaction zone is effected at temperatures between 150°C and 500°C and at pressures between 30 and 120 bar (a) in the presence of a methanization catalyst.
7. Process according to any of the preceding claims, characterized in that the amount of substance ratio of hydrogen to carbon monoxide in the synthesis gas fresh gas stream is between 0.4 and 5.0 mol/mol.
8. Process according to any of the preceding claims, characterized in that the main reaction zone comprises at least two catalyst beds.
9. Process according to Claim 9, characterized in that part of the synthesis gas fresh gas stream is conducted upstream of the entrance into the second catalyst bed of the main reaction zone.
10. Process according to claim 1, characterized in that the target pressure is between 30 and 120 bar(a), preferably between 30 and 90 bar(a).

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