Process for fermentation of syngas from indirect gasification
View Patent ↗Ethanol and other liquid products are produced from biomass using indirect gasification of the biomass to produce a syngas containing CO2, CO, H2 and methane that passes the syngas without substantial removal of the methane to a fermentation zone for the conversion of the CO and CO2 and H2 to ethanol and the production of a methane rich stream followed by the methane reforming of the methane rich stream to produce additional CO and CO2 and H2 that passes to the fermentation zone.
1. A process for the production of liquid products from a biomass feedstock by indirect gasification to syngas comprising CO 2 , CO, H 2 and CH 4 , and bio-conversion of syngas components, said process comprising:
providing a biomass feedstock to a gasifier and indirectly gasifying the biomass feedstock by contact with a heating medium to produce a syngas stream comprising CO 2 , CO, H 2 and at least 10 mole % CH 4 on an anhydrous basis;
passing a feed gas comprising the syngas stream and containing at least 10 mole % CH 4 on an anhydrous basis from the gasifier to a bioreactor to convert CO and CO 2 and H 2 to liquid products by contact with microorganisms therein;
withdrawing a bioreactor effluent stream containing the liquid products from the bioreactor and recovering liquid products from the bioreactor effluent stream;
recovering a tail gas stream from the bioreactor comprising CO 2 and CH 4 ;
separating CO 2 from the tail gas stream to produce a CH 4 rich gas stream;
passing at least a portion of the CH 4 rich stream to a reformer to produce a reformed stream comprising CO and CO 2 and H 2 ; and,
passing at least a portion of the reformed stream to the bioreactor along with syngas from the gasifier to provide the feed gas to the bioreactor.
2. The process of claim 1 wherein the liquid products comprise at least one of ethanol, acetic acid, butanol, or butyric acid.
3. The process of claim 1 wherein a portion of the CH 4 rich stream passes to a combustion heat recovery system for the generation of power or to provide process heat.
4. The process of claim 1 wherein the gasifier comprises a gasification zone that gasifies the carbonaceous feed under substantially anaerobic conditions and a combustion zone that provides heat to the gasification zone.
5. The process of claim 1 wherein the oxygen concentration in the gasification zone is less than 1 mole %.
6. The process of claim 1 wherein the reformer comprises a partial oxidation autothermal reformer.
7. The process of claim 1 wherein the syngas undergoes clean-up for removal of water and particulates before entering the bioreactor.
8. The process of claim 1 wherein the biomass is selected from one or more the group consisting of wood, miscanthus, switchgrass, sugar cane bagasse, corn stover and urban waste.
9. The process of claim 1 wherein the liquid products comprise ethanol.
10. The process of claim 7 wherein the microorganisms in the bioreactor comprises a mono-culture or a co-culture of at least one of Clostridium ragsdalei, Butyribacterium methylotrophicum, Clostridium Ljungdahlii, Clostridium Autoethanogenum, Clostridium Woodii and Clostridium carboxydivorans.
11. The process of claim 1 wherein the syngas on an anhydrous basis comprises 20 to 45 mole % H 2 , 15 to 50 mole % CO, 10 to 20 mole % CH 4 , and 10 to 20 mole % CO 2 and the tail gas comprises at least 25 mole % CH 4 and at least 50 mole % CO 2 .
12. The process of claim 1 wherein the gasifier operates with a temperature of less than 900° C. and a pressure of less than 4 bars absolute.
13. A process for the production of ethanol from a biomass feedstock by indirect gasification to syngas comprising CO 2 , CO, H 2 and CH 4 , and bio-conversion of syngas components, said process comprising:
providing a biomass feedstock to a gasifier and indirectly gasifying the biomass feedstock by contact with a heating medium at a temperature of less than 900° C. and a pressure of less than 4 bars absolute to produce a syngas stream comprising CO 2 , CO, H 2 and at least 10 mole % of CH 4 on an anhydrous basis;
passing a feed gas comprising syngas and containing at least 10 mole % CH 4 on an anhydrous basis from the gasifier to a bioreactor to convert CO and CO 2 and H 2 to ethanol by contact with microorganisms therein;
withdrawing a bioreactor effluent stream containing ethanol from the bioreactor and separating the ethanol in a ethanol recovery section to produce an ethanol product;
recovering a tail gas stream from the bioreactor comprising on an anhydrous basis at least 40 mole % CO 2 and 25 mole % CH 4 ;separating CO 2 from the tail gas stream to produce a CH 4 rich gas stream;
passing a portion of the CH 4 rich gas stream to a combustion heat recovery system for the generation of power or to provide process heat;
passing at least a portion of the CH 4 rich stream to an autothermal reformer to produce a reformed stream comprising CO and CO 2 and H 2 ; and,
passing at least a portion of the reformed stream to the bioreactor along with syngas from the gasifier to provide the feed gas to the bioreactor.