Recovery of co2 in a process for synthesis of methanol

Abstract

A process for producing methanol, where a hydrocarbon feedstock ( 1 ) is reformed and a make-up syngas is reacted in a synthesis loop, obtaining crude methanol which is further treated to obtain high-grade methanol, and where the carbon dioxide dissolved in the crude methanol is recycled to the reforming section in order to adjust the stoichiometric number of the make-up syngas. In a preferred embodiment, a flash gas ( 9 ) separated from the crude methanol ( 8 ) and light ends ( 10 ) coming from distillation are recycled to a compressor ( 106 ) and fed to a primary reformer ( 100 ); further carbon dioxide can be recycled from the flue gas ( 11 ).

1 . A process for producing methanol, comprising the steps of:
 a. reforming a hydrocarbon feedstock in a reforming process step, obtaining a make-up syngas comprising carbon oxides and hydrogen;   b. reacting said make-up syngas in a methanol synthesis loop, obtaining crude methanol;   c. processing said crude methanol to obtain methanol of a required purity;   d. recovering at least one CO 2 -containing stream from the processing of said crude methanol, and   e. recycling said at least one CO 2 -containing stream as an input stream for said reforming process step.   
     
     
         2 . A process according to  claim 1 , where said step d) of recovering a CO 2 -containing stream from the crude methanol comprises the recovering of a flash gas stream released by de-pressurization of the crude methanol. 
     
     
         3 . A process according to  claim 1 , where said step d) of recovering a CO 2 -containing stream from the crude methanol comprises the recovering of a gas stream containing carbon dioxide released by the crude methanol in a distillation process. 
     
     
         4 . A process according to  claim 1 , where
 where said step d) of recovering a CO 2 -containing stream from the crude methanol comprises the recovering of a flash gas stream released by de-pressurization of the crude methanol and comprises the recovering of a light-ends gas stream containing carbon dioxide released by the crude methanol in a distillation process,   wherein said flash gas stream and said light-ends stream are mixed together in a single CO 2 -containing flow, forming said input stream recycled to reforming.   
     
     
         5 . A process according to  claim 1 , where said CO 2  containing stream is compressed in a suitable CO 2  compressor and mixed with a hydrocarbon feed at the inlet of a reformer of said reforming section. 
     
     
         6 . A process according to  claim 1 , where:
 a first carbon-dioxide containing stream is recovered from flue gas of reforming;   said first stream is recycled to a reforming section via a CO 2  compressor; and   said at least one CO 2 -containing stream recovered from said crude methanol is fed to the suction side of said compressor, and recycled to the reforming section together with said first stream.   
     
     
         7 . A process according to  claim 1 , further comprising the steps of:
 recovering a purge gas from the methanol synthesis loop;   obtaining a hydrogen-rich stream and a fuel stream from processing of said purge gas;   recycling said hydrogen-rich stream to the synthesis loop; and   recycling said fuel stream to the reforming section.   
     
     
         8 . A plant for producing methanol comprising:
 a reforming section receiving a hydrocarbon feedstock, and producing a reformed make-up syngas comprising carbon oxides and hydrogen;   a methanol synthesis loop, fed with the make-up syngas and producing crude methanol;   a section where said crude methanol is processed to obtain methanol of a required purity;   means for recovering at least one CO 2 -containing stream separated from processing of said crude methanol, and   means feeding said at least one CO 2 -containing stream to said reforming section.   
     
     
         9 . A plant according to  claim 8 , comprising a flash gas separator obtaining a flash gas containing CO 2  from crude methanol, and a piping feeding said flash gas to a compressor, said compressor delivering a CO 2 -containing stream at the inlet of the reforming section. 
     
     
         10 . A plant according to  claim 9 , further comprising a piping adapted to feed a further CO 2 -containing stream recovered from distillation of crude methanol to the inlet of said compressor. 
     
     
         11 . A plant according to  claim 9 , further comprising a CO 2  recovering section, adapted to recover a CO 2  rich stream from flue gas of the reforming process, and feeding said CO 2  rich stream to said compressor. 
     
     
         12 . A plant according to  claim 8 , said reforming section comprising a stand-alone primary reformer, or a primary reformer followed by a secondary reformer, or an autothermal reformer. 
     
     
         13 . A method for revamping of an existing plant for producing methanol, said existing plant comprising at least:
 a reforming section receiving a hydrocarbon feedstock, and producing a reformed make-up syngas comprising carbon oxides and hydrogen;   a methanol synthesis loop, fed with the make-up syngas and producing crude methanol;   a section where said crude methanol is processed to obtain methanol of a required purity;   means for recovering at least one CO 2 -containing stream separated from processing said crude methanol, and   means feeding said CO 2 -containing stream to said reforming section.   
     
     
         14 . A method according to  claim 13 , where the provision of said means for recovering a CO 2 -containing stream, and feeding said stream to the reforming section, comprises the step of re-routing the piping of a flash gas separated by de-pressurization of crude methanol from the synthesis loop, and re-routing the piping of a further CO 2 -containing stream recovered from distillation of crude methanol, said re-routing being directed to a CO 2  compressor ( 106 ) feeding the reforming section. 
     
     
         15 . A method according to  claim 13 , further comprising the step of providing a compressor for the recovered CO 2 -containing stream.