Methods and apparatus for recycling tail gas in syngas fermentation to ethanol
Inventors
Winter, John D. • Hohman, Jerrod
Assignees
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Publication Number
US-11857923-B2
Publication Date
2024-01-02
Expiration Date
Abstract
The invention present provides a method (and suitable apparatus) to convert biomass to ethanol, comprising gasifying the biomass to produce raw syngas; feeding the raw syngas to an acid-gas removal unit to remove at least some CO2 and produce a conditioned syngas stream; feeding the conditioned syngas stream to a fermentor to biologically convert the syngas to ethanol; capturing a tail gas from an exit of the fermentor, wherein the tail gas comprises at least CO2 and unconverted CO or H2; and recycling a first portion of the tail gas to the fermentor and/or a second portion of the tail gas to the acid-gas removal unit. This invention allows for increased syngas conversion to ethanol, improved process efficiency, and better overall biorefinery economics for conversion of biomass to ethanol.
Core Innovation
The invention describes a method of converting a carbonaceous feedstock to a syngas-fermentation product by gasifying the feedstock with an oxidant to form a raw syngas stream comprising CO, H2, and CO2, optionally producing an intermediate syngas stream via a syngas-cleanup unit. The raw syngas stream and/or the intermediate syngas stream are fed to an acid-gas removal unit to remove at least some of the CO2 and produce a conditioned syngas stream.
The conditioned syngas stream is fed to a fermentor under fermentation conditions with microorganisms and nutrients to biologically convert one or more of CO, H2, or CO2 to a fermentation product, generating a product stream and a tail gas stream comprising at least CO2 and unconverted CO or H2. The method then recycles portions of the tail gas either back to the fermentor, to the acid-gas removal unit, or to both.
The recycle split of the first portion of the tail gas and the second portion of the tail gas is used to control the acid-gas molar ratio in the fermentor feed, expressed as (CO+H2)/(CO2+H2S). Recycling is tuned through defined recycle ratios and associated control of CO2 content and conversion behavior, including reported improvements in syngas conversion when recycling is applied.
Claims Coverage
Independent claim 1 covers the overall process flow for syngas fermentation from carbonaceous feedstock with split tail-gas recycling to both the fermentor and the acid-gas removal unit. The claim set further refines this independent claim with additional independent-parameter controls and quantitative performance constraints in dependent claims, while maintaining the core recycling architecture.
Tail-gas split recycling to fermentor and acid-gas removal
Recycling at least a first portion of the tail gas to the fermentor, at least a second portion of the tail gas to the acid-gas removal unit, or both, while generating the tail gas from fermenting conditioned syngas in the presence of microorganisms.
Conditioning syngas via acid-gas removal prior to fermentation
Feeding at least a portion of the raw syngas stream and/or at least a portion of the intermediate syngas stream to an acid-gas removal unit to remove at least some of the CO2 and produce a conditioned syngas stream for biological conversion to a fermentation product.
Biological conversion in a fermentor to produce product and tail gas
Feeding at least a portion of the conditioned syngas stream to a fermentor, under suitable fermentation conditions and in the presence of suitable microorganisms and nutrients to biologically convert one or more of CO, H2, or CO2 to a fermentation product and generate a tail gas stream comprising at least CO2 and unconverted CO or H2.
Raw syngas generation from carbonaceous feedstock with oxidant and gasifier
Introducing a carbonaceous feedstock and an oxidant to a gasifier under suitable gasification conditions to produce a raw syngas stream comprising CO, H2, and CO2.
Overall, claim coverage centers on producing CO/H2/CO2-containing raw syngas, conditioning it by acid-gas removal to generate a conditioned syngas stream, fermenting to a fermentation product while producing CO2-containing tail gas with unconverted CO or H2, and then recycling portions of that tail gas to both the fermentor and the acid-gas removal unit as part of the claimed conversion architecture.
Stated Advantages
Recycling can improve syngas conversion of CO and H2, with reported values such as ~90–98% with recycling versus <90% without recycling.
Compressed tail-gas recycle can increase fermentor pressure and improve mass transfer/liquid-phase syngas availability.
Documented Applications
Producing an ethanol syngas-fermentation product from biomass/carbonaceous feedstock using syngas fermentation with tail-gas splitting and recycling.
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