PROCESS AND PLANT FOR PRODUCING METHANOL AND AMMONIA

Abstract

What is proposed is a process and a plant for parallel production of methanol and ammonia by heterogeneously catalyzed reaction of hydrogen and carbon oxides on the one hand and hydrogen and nitrogen on the other hand. This includes producing a raw synthesis gas stream and dividing it into two portions. A first raw synthesis gas substream is used as input for a methanol synthesis to obtain raw methanol and a methanol synthesis purge stream. A second raw synthesis gas substream is subjected to a CO conversion, a carbon dioxide separation and a liquid nitrogen scrubbing and then sent to an ammonia synthesis. According to the invention at least a portion of the methanol synthesis purge stream is sent to the ammonia synthesis and at least one substream obtained from the second raw synthesis gas substream is passed to the methanol synthesis.

Claims

1. A process for producing methanol and ammonia from an input stream comprising hydrocarbons, comprising: (a) providing an input stream containing hydrocarbons, (b) supplying the input stream containing hydrocarbons to a synthesis gas production plant comprising, (b1) a steam reforming stage heated using burners and/or hot gases or (b2) an autothermal reforming stage or (b3) a partial oxidation stage or (b4) a combination of at least two of the stages (b1) to (b3), (c) at least partially converting the input stream containing hydrocarbons in the synthesis gas production plant under synthesis gas production conditions thereby producing a raw synthesis gas stream containing hydrogen, carbon monoxide and inert components such as methane, (d) discharging the raw synthesis gas stream from the synthesis gas production plant and dividing the raw synthesis gas stream into a first raw synthesis gas substream and into a second raw synthesis gas substream, (e) introducing at least a portion of the first raw synthesis gas substream into a methanol synthesis reactor, at least partially converting the first raw synthesis gas substream in the methanol synthesis reactor under methanol synthesis conditions, thereby producing a methanol-containing first reactor product stream, (f) discharging the methanol-containing first reactor product stream from the methanol synthesis reactor, cooling the first reactor product stream to below its dew point and separating the cooled first reactor product stream in a phase separation apparatus into a first liquid product stream and a first residual gas stream containing unconverted synthesis gas constituents and inert components, discharging the first liquid product stream from the process as a raw methanol product stream, (g) dividing the first residual gas stream into a methanol synthesis purge stream and into a recycle stream which is recycled to the methanol synthesis reactor, (h) introducing at least a portion of the second raw synthesis gas substream into a carbon monoxide conversion plant comprising at least one carbon monoxide conversion stage, converting the portion of the second raw synthesis gas substream introduced into the carbon monoxide conversion plant under carbon monoxide conversion conditions to afford a converted synthesis gas stream, discharging the converted synthesis gas stream, (i) introducing the converted synthesis gas stream into a sorption apparatus for removal of acidic gas constituents by means of a physical or chemical sorption process, discharging a deacidified synthesis gas stream and an acid gas stream containing acidic gas constituents from the sorption apparatus, discharging the acid gas stream from the process, (j) introducing at least a portion of the deacidified synthesis gas stream into a liquid nitrogen scrubbing stage, separating the deacidified synthesis gas stream in the liquid nitrogen scrubbing stage into the following substreams: (j1) an ammonia synthesis feed stream containing hydrogen and nitrogen as main constituents and carbon monoxide and inert components as trace constituents, (j2) a second residual gas stream containing hydrogen and carbon monoxide as main constituents and inert components as trace constituents, (j3) an inert gas stream which contains inert components as the main constituent and is discharged from the process, (k) introducing the ammonia synthesis feed stream into an ammonia synthesis reactor, at least partially converting the ammonia synthesis feed stream in the ammonia synthesis reactor under ammonia synthesis conditions, discharging an ammonia product stream from the ammonia synthesis reactor, (l) introducing at least a portion of the methanol synthesis purge stream into the sorption apparatus, (m) introducing into the methanol synthesis reactor one or more gas streams selected from the following group of: (m1) a portion of the converted synthesis gas stream from process step (h) (m2) a portion of the deacidified synthesis gas stream from process step (i) (m3) at least a portion of the second residual gas stream from process step (j2).

2. The process according to claim 1, wherein the synthesis gas production plant comprises: (b2) an autothermal reforming stage or (b3) a partial oxidation stage or (b4) a combination of the stages (b2) to (b3) with one another or with a steam reforming stage heated using burners and/or hot gases and in that the raw synthesis gas stream produced has a stoichiometry number of less than 2.

3. The process according to claim 2, wherein the raw synthesis gas stream produced has a pressure of 40 bara or more.

4. The process according to claim 3, wherein the sorption apparatus operates by means of a physical absorption process and in that the sorption apparatus is at the same pressure level as the synthesis gas production plant.

5. The process according to claim 4, wherein the sorption apparatus operates by means of gas scrubbing with cold methanol and in that a carbon dioxide-rich stream having a carbon dioxide content of at least 98% by volume, is discharged from the sorption apparatus.

6. The process according to claim 5, wherein the carbon dioxide-rich stream discharged from the sorption apparatus is sent to a carbon dioxide capture and storage process and/or to a process for material utilization of carbon dioxide.

7. The process according to claim 1, wherein the one or more gas stream(s) introduced into the methanol synthesis reactor are adjusted, based on their molar flow, such that the stoichiometry number of the sum of the feed streams entering the methanol synthesis reactor is at least 2 or more.

8. The process according to claim 1, wherein two or more gas streams are simultaneously introduced into the methanol synthesis reactor, wherein the two or more gas streams comprise: (m3) at least a portion of the second residual gas stream from process step (j2) and in addition one or more further gas streams selected from the following group of: (m1) a portion of the converted synthesis gas stream from process step (h) (m2) a portion of the deacidified synthesis gas stream from process step (i).

9. A plant for producing methanol and ammonia from an input stream containing hydrocarbons comprising the following components and constituents in fluid connection with one another: (a) a means for providing the input stream containing hydrocarbons, (b) a synthesis gas production plant, a means for supplying the input stream containing hydrocarbons to the synthesis gas production plant, wherein the synthesis gas production plant comprises: (b1) a steam reforming stage heated using burners and/or hot gases or (b2) an autothermal reforming stage or (b3) a partial oxidation stage or (b4) a combination of at least two of the stages (b1) to (b3), (c) means for discharging a raw synthesis gas stream containing hydrogen, carbon monoxide and inert components such as methane from the synthesis gas production plant and means for dividing the raw synthesis gas stream into a first raw synthesis gas substream and into a second raw synthesis gas substream, (d) a methanol synthesis reactor, a means for introducing at least a portion of the first raw synthesis gas substream into a methanol synthesis reactor, (e) a means for discharging a methanol-containing first reactor product stream from the methanol synthesis reactor, a means for cooling the first reactor product stream to below its dew point, a phase separation apparatus, a means for separating the cooled first reactor product stream in the phase separation apparatus into a first liquid product stream and a first residual gas stream containing unconverted synthesis gas constituents and inert components, a means for discharging the first liquid product stream from the process as a raw methanol product stream, (f) a means for dividing the first residual gas stream into a methanol synthesis purge stream and into a recycle stream which is recycled to the methanol synthesis reactor, (g) a carbon monoxide conversion plant comprising at least one carbon monoxide conversion stage, means for introducing at least a portion of the second raw synthesis gas substream into the carbon monoxide conversion plant, a means for discharging a converted synthesis gas stream from the carbon monoxide conversion plant, (h) a sorption apparatus for removal of acidic gas constituents by means of a physical or chemical sorption process, a means for introducing the converted synthesis gas stream into the sorption apparatus, a means for discharging a deacidified synthesis gas stream and an acid gas stream containing acidic gas constituents from the sorption apparatus, a means for discharging the acid gas stream from the process, (i) a liquid nitrogen scrubbing stage, a means for introducing at least a portion of the deacidified synthesis gas stream into the liquid nitrogen scrubbing stage, a means for separating the deacidified synthesis gas stream in the liquid nitrogen scrubbing stage into the following substreams: (i1) an ammonia synthesis feed stream containing hydrogen and nitrogen as main constituents and carbon monoxide and inert components as trace constituents, (i2) a second residual gas stream containing hydrogen and carbon monoxide as main constituents and inert components as trace constituents, (i3) an inert gas stream containing inert components as the main constituent, (j) an ammonia synthesis reactor, means for introducing the ammonia synthesis feed stream into the ammonia synthesis reactor, a means for discharging an ammonia product stream from the ammonia synthesis reactor, (k) a means for introducing into the methanol synthesis reactor one or more gas streams, wherein the gas streams are selected from the following group of: (m1) a portion of the converted synthesis gas stream from process step (h) (m2) a portion of the deacidified synthesis gas stream from process step (i) (m3) at least a portion of the second residual gas stream from process step (j2).

10. The plant according to claim 9, wherein the synthesis gas production plant comprises: (b2) an autothermal reforming stage or (b3) a partial oxidation stage or (b4) a combination of the stages (b2) to (b3) with one another or with a steam reforming stage heated using burners and/or hot gases.

11. The plant according to claim 10, further comprising at least one compression stage which allows the raw synthesis gas stream produced to have a pressure of 40 bara or more.

12. The plant according to claim 11, wherein the sorption apparatus operates by means of a physical absorption process and is configured such that the sorption apparatus is at the same pressure level as the synthesis gas production plant.

13. The plant according to claim 12, wherein the sorption apparatus operates by means of gas scrubbing with cold methanol and is configured such that a carbon dioxide-rich stream having a carbon dioxide content of at least 98% by volume is discharged from the sorption apparatus.

14. The plant according to claim 13, further comprising a means which allow the carbon dioxide-rich stream discharged from the sorption apparatus to be sent to a carbon dioxide capture and storage process and/or to a process for material utilization of carbon dioxide.

15. The plant according to claim 9, further comprising a means which allow one or more gas streams introduced into the methanol synthesis reactor to be adjusted, based on their molar flow, such that the stoichiometry number of the sum of the feed streams entering the methanol synthesis reactor is at least 2 or more.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Developments, advantages and possible applications of the invention are also apparent from the following description of working and numerical examples and the drawings. All features described and/or depicted, either in themselves or in any combination, form the invention, regardless of the way they are combined in the claims or the back-references therein.

[0070] FIG. 1 shows a schematic representation of the process/the plant according to one embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0071] In the configuration of a process/a plant according to the invention shown in FIG. 1 conduit 12 supplies an input stream containing hydrocarbons, for example natural gas, in a preferred example natural gas having a methane content of at least 80% by volume, to a synthesis gas plant 10 which in this embodiment comprises an autothermal reformer (ATR) and in one example is operated at a pressure of 60 bara.

[0072] The synthesis gas production plant 10 carries out an at least partial conversion of the input stream containing hydrocarbons under synthesis gas production conditions to afford a raw synthesis gas stream which contains hydrogen (H.sub.2), carbon monoxide (CO) and inert components such as methane (CH.sub.4) and is divided into a first raw synthesis gas substream and into a second raw synthesis gas substream.

[0073] Via conduit 14 the first raw synthesis gas substream is discharged from the synthesis gas production plant and supplied to a methanol synthesis reactor 20, in which there follows an at least partial conversion of the first raw synthesis gas substream under methanol synthesis conditions. Via conduit 22 a methanol-containing first reactor product stream is discharged from the methanol synthesis reactor 20, cooled to below its dew point and, in a phase separation apparatus not shown separately, separated into a first liquid product stream and a first residual gas stream. The first liquid product stream is sent via conduit 22 as a raw methanol product stream to a methanol workup apparatus 30, which in one example is configured as a distillation, preferably a multistage distillation. A pure methanol stream is discharged from the methanol workup apparatus 30 via conduit 32 and sent for further processing or use.

[0074] The first residual gas stream contains unconverted synthesis gas constituents, i.e. hydrogens and carbon oxides, in particular carbon monoxide and carbon dioxide, and inert components, for example methane and/or noble gases, for example argon, unconverted in the synthesis gas production plant. The first residual gas stream is divided into a methanol synthesis purge stream and into a recycle stream, wherein the recycle stream is recycled to the methanol synthesis reactor (not shown separately) and the methanol synthesis purge stream is discharged from the methanol synthesis reactor via conduit 24.

[0075] Via conduit 16 the second raw synthesis gas substream is discharged from the synthesis gas production plant and introduced into a CO conversion plant 40 which comprises at least one CO conversion stage. Carried out in the CO conversion stage by addition of steam (not shown separately) is a conversion of the carbon monoxide present in the second raw synthesis gas substream under CO conversion conditions into a converted synthesis gas stream having a content of hydrogen and carbon dioxide which has been elevated relative to the second raw synthesis gas substream. The converted synthesis gas stream is discharged from the CO conversion plant 40 via conduit 42.

[0076] The converted synthesis gas stream is introduced via conduit 42 into a sorption apparatus 50 for removal of acidic gas constituents, especially carbon dioxide, by means of a physical or chemical sorption process. In one example the sorption apparatus 50 is configured for performing a gas scrubbing with the physical absorbent methanol (Rectisol process). This affords a deacidified synthesis gas stream which is discharged from the sorption apparatus 50 via conduit 52. Also obtained is an acid gas stream containing acidic gas constituents which is discharged via conduit 54. In one example the sorption apparatus 50 is configured and operated such that conduit 54 discharges from the sorption apparatus a dry, carbon dioxide-rich stream having a CO.sub.2 content of at least 90% by volume, preferably at least 99% by volume, most preferably at least 99.5% by volume. This makes it possible for the carbon dioxide-rich stream discharged from the sorption apparatus to be supplied to a CO.sub.2 capture and storage process (CCS) and/or to a process for material utilization of carbon dioxide directly, i.e. without a further conditioning or purification step.

[0077] The deacidified synthesis gas stream is introduced into a liquid nitrogen scrubbing stage 60 via conduit 52. In one example the deacidified synthesis gas stream is, prior to sending to liquid nitrogen scrubbing stage 60, supplied to one or more drying and carbon dioxide fine removal apparatuses (not shown separately) to remove traces of water and/or carbon dioxide which would otherwise freeze out in the liquid nitrogen scrubbing stage and can lead to blockages therein. It is advantageous that a deacidified synthesis gas stream which is freed of carbon dioxide down to the ppm range in the sorption apparatus and additionally dried is obtained from the second raw synthesis gas substream. This has the result that drying and carbon dioxide fine removal apparatuses, which in this example are arranged upstream of the liquid nitrogen scrubbing, may be made smaller.

[0078] The liquid nitrogen scrubbing stage 60 effects separation, for example multistage separation, of the deacidified synthesis gas stream in the liquid nitrogen scrubbing stage 60 into the following substreams:

[0079] (60.1) an ammonia synthesis feed stream containing hydrogen and nitrogen as main constituents and carbon monoxide and inert components as trace constituents,

[0080] (60.2) a second residual gas stream containing hydrogen and carbon monoxide as main constituents and inert components as trace constituents,

[0081] (60.3) an inert gas stream which contains inert components as the main constituent and is discharged from the process.

[0082] The obtained material stream (60.1) is introduced via conduit 62 into an ammonia synthesis reactor 70 as the ammonia synthesis feed stream. Appropriate configuration of the liquid nitrogen scrubbing stage 60/the operation thereof ensures that the trace proportions of carbon monoxide and inert components present in the ammonia synthesis feed stream do not adversely affect the subsequent ammonia synthesis. It is further ensured that the ammonia synthesis feed stream contains a hydrogen/nitrogen mixture of desired composition, for example having a molar hydrogen/nitrogen ratio of 3 according to the stoichiometry of the ammonia synthesis reaction.

[0083] The obtained material stream (60.3) which contains inert components, in particular methane, as the main constituent is used as fuel gas for example on account of its calorific value after discharging from the process. It may alternatively be recycled to the synthesis gas production plant 10 as part of the input stream containing hydrocarbons. If the stream (60.3) contains significant proportions of components such as for example argon, which cannot be converted in the synthesis gas production plant, it is advisable to recycle only a portion of the stream (60.3) to the synthesis gas production plant to avoid accumulation of these substances.

[0084] The ammonia synthesis reactor 70 carries out an at least partial conversion of the ammonia synthesis feed stream under ammonia synthesis conditions. An ammonia product stream is then discharged from the ammonia synthesis reactor 70 via conduit 72 and sent for further use or processing.

[0085] According to the invention at least a portion of the methanol synthesis purge stream is introduced into the sorption apparatus 50 via conduit 24. The introducing may be effected directly into the sorption apparatus and/or into the conduit 42 which opens into the sorption apparatus. The sorption apparatus also separates the carbon dioxide proportion from the methanol synthesis purge stream, thus making the remaining proportions of carbon monoxide and hydrogen more amenable for utilization in the subsequent process steps/plant parts.

[0086] Furthermore, according to the invention the second residual gas stream (60.2) containing hydrogen and carbon monoxide as main constituents is recycled to the methanol synthesis reactor 20 via conduit 64, thus allowing material utilization of these main constituents in the methanol synthesis. Alternatively or in addition [0087] a portion of the converted synthesis gas stream from the CO conversion stage or downstream thereof and/or [0088] portion of the deacidified synthesis gas stream from the sorption apparatus or downstream thereof
may be recycled to the methanol synthesis reactor 20 (not shown separately in both cases). Mixtures of these three potential recycle streams are also possible to provide even greater flexibility in terms of the establishment of recycling streams to the methanol synthesis reactor.

[0089] The recycling of one or more of the recited material streams allows material utilization of the proportions of hydrogen and carbon monoxide present therein in the methanol synthesis reactor for production of additional methanol. This also allows the desired stoichiometry number in the methanol synthesis reactor to be established without the need to import hydrogen from outside the process or to withdraw hydrogen from a pure hydrogen stream. Such a pure hydrogen stream is in any case not readily available within the process according to the invention since the stream (60.1) already contains a stoichiometric proportion of nitrogen. In the context of the methanol synthesis nitrogen is an inert component and therefore unwanted therein.

[0090] Increasing the pressure in the synthesis gas production plant to 60 bara has a positive effect on the overall economy of the process since it contributes to a reduction in the compression energy required for the methanol synthesis. Furthermore, the pressure increase also results in an improved absorption of carbon dioxide in the physical scrubbing medium methanol in relation to lower pressures in the sorption apparatus configured according to the Rectisol process.

[0091] The passing on of purge gas from the methanol synthesis reactor to the CO.sub.2 removal in the sorption apparatus and subsequently to the cryogenic removal of methane and the subsequent passing on of the purified raw hydrogen and the CO proportion remaining therein for the methanol synthesis improve the efficiency of the overall process without any need for additional purification apparatuses such as a pressure swing adsorption (PSA) or membrane plants.

[0092] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.

LIST OF REFERENCE SYMBOLS

[0093] 10 Synthesis gas production plant [0094] 12 Conduit [0095] 14 Conduit [0096] 16 Conduit [0097] 20 Methanol synthesis reactor [0098] 22 Conduit [0099] 24 Conduit [0100] 30 Methanol workup apparatus (methanol distillation) [0101] 40 CO conversion plant [0102] 42 Conduit [0103] 50 Sorption apparatus (Rectisol) [0104] 52 Conduit [0105] 54 Conduit [0106] 60 Liquid nitrogen scrubbing stage [0107] 62 Conduit [0108] 64 Conduit [0109] 70 Ammonia synthesis reactor [0110] 72 Conduit