Process and plant for producing methanol from substoichiometric synthesis gas

A process for producing methanol from a carbon-containing input stream comprising:

• (a) producing a synthesis gas input stream containing hydrogen and carbon oxides using a synthesis gas production process under synthesis gas production conditions from the carbon-containing input stream,
• (b) combining and mixing the synthesis gas input stream with a recycle stream containing hydrogen and carbon oxides to afford a first reactor feed stream,
• (c) introducing the first reactor feed stream into a first methanol synthesis reactor containing at least one catalyst zone comprising a solid, granular catalyst active for methanol synthesis, at least partially converting the first reactor feed stream in the first methanol synthesis reactor under methanol synthesis conditions,
• (d) discharging a first reactor product stream containing methanol and water from the first methanol synthesis reactor, cooling the first reactor product stream below its dew point and supplying the cooled first reactor product stream to a first phase separation apparatus,
• (e) separating the cooled first reactor product stream in the first phase separation apparatus into a first liquid product stream and a first residual gas stream containing unconverted synthesis gas constituents,
• (f) dividing the first residual gas stream into a second reactor feed stream and into a first purge stream,
• (g) introducing the second reactor feed stream into a second methanol synthesis reactor containing at least one catalyst zone comprising a solid, granular catalyst active for methanol synthesis, at least partially converting the second reactor feed stream in the second methanol synthesis reactor under methanol synthesis conditions,
• (h) discharging a second reactor product stream containing methanol and water from the second methanol synthesis reactor, cooling the second reactor product stream below its dew point and supplying the cooled second reactor product stream to a second phase separation apparatus,
• (i) separating the cooled second reactor product stream in the second phase separation apparatus into a second liquid product stream and a second residual gas stream containing unconverted synthesis gas constituents,
• (j) dividing the second residual gas stream into the recycle stream recycled to step (b) and into a second purge stream,
• (k) discharging the first and the second liquid product stream from the process as a crude methanol product stream,
• (l) introducing at least a portion of the first purge stream and at least a portion of the second purge stream into a hydrogen recovery apparatus, separating the first purge stream and the second purge stream in the hydrogen recovery apparatus into a hydrogen-enriched supplementary stream and a hydrogen-depleted third purge stream, and
• (m) recycling at least a portion of the hydrogen-enriched supplementary stream to the first methanol synthesis reactor and discharging the hydrogen-depleted third purge stream from the process.