Tips for Working with Gas Fermentation: Scale up Considerations for Gas Handling
Introduction to Gas Fermentation
Gas fermentation technology has potential to be a profitable carbon-recycle/utilization technology, allowing for the sustainable production of chemicals, fuels, and food while simultaneously addressing the increasing social and economic pressure surrounding carbon emissions. This fermentation technology converts gases such as carbon dioxide, carbon monoxide, hydrogen, and methane into valuable products using microorganisms. One appealing feature of gas fermentation is its versatility, specifically to substrates and feedstocks which include industrial waste gas, gasified municipal/landfill biomass, and gasified lignocellulosic biomass. This flexibility creates an attractive platform and generates a new value chain for transforming low-value waste streams into higher-value feedstocks for sustainable products.
(Left): Waste Gas Emissions (Right): Gas Fermenter, Source: Forbes via LanzaTech
Recycling carbon from waste emissions is one particularly interesting application of gas fermentation. Waste gas-rich streams containing CO, CO2, and CH4 can be captured from a variety of emissions sources (steel mills, refineries, chemical plants, etc.) and used as a carbon feedstock to produce polymers, fuels, protein-rich animal feed and other products via gas fermentation.
While there are many examples of successful scale up of traditional fermentation processes, gas fermentation is still relatively new. Although lessons scaling up traditional fermentation processes can provide some guidance, the scaling of gas fermentation from laboratory to commercial scale presents unique economic and engineering challenges. Examples of these challenges include gas handling, gas to liquid mass transfer, fermenter design, management of potentially flammable or explosive gases, and selection and integration with waste gas producers.
In this article we will focus on challenges related to gas handling, but stay tuned for more in our series on how to tackle the challenges of gas fermentation!
Gas Handling
For a commercial scale waste gas fermentation process where feed gas is supplied by industrial waste gas, the composition and quality of the waste gas can be very difficult to predict and control at the point of emission. Therefore, the varying compositions of carbon feedstocks and hydrogen, as well as temperature and pressure, require careful design in the front end of the fermentation process. These variations can significantly affect the performance and yield of a microbial gas fermentation process, both of which are important factors to account for when assessing the technoeconomic feasibility of a commercial scale process.
The capital cost of gas handling and conditioning equipment can be significant and must be carefully evaluated when determining the economic feasibility of scaling a gas fermentation process or designing a new facility. In many cases gas compression equipment is required for delivering waste-gas to the fermentation process to achieve sufficient operating pressures in upstream/downstream equipment (e.g. separation/purification during pre-treatment). In some scenarios, waste-gas may need to be concentrated to achieve sufficient mass transfer and performance in the fermenter.
Impurities should also be expected in these waste gas streams (e.g. hydrogen sulfide). These impurities can impact the fermentation process and damage downstream processing equipment if left untreated. Pre-treatment systems consist of a variety of technologies, such as gas scrubbers, chemical absorption, membrane-based separation, pressure swing adsorption and physical absorption. However, it is important to note that the requirements for gas pre-treatment are specific to process and site. Therefore, you must evaluate these requirements at each stage of scale up as well as during any site selection assessment.
The CapEx/OpEx, feasibility and risks of each gas handling and pretreatment technology will vary depending on scale, gas fermentation process, and site selection. Understanding all these subtleties and how they impact technology selection and commercial feasibility at various stages is critical during scale up of a gas fermentation process.
How we can help
Next Rung Technology provides engineering, execution, operations, and consulting services to companies developing sustainable technologies. We have experience scaling a variety of processes and products across many different fermentation platforms (including gas fermentation!).
We have helped clients succeed with everything from early-stage road mapping and techno-economic assessment, to full FEL1/2/3 design support on Pilot, Demo, and Commercial facilities.
If you would like to learn more about how we can support you, reach out to us via our contact page. We would love to learn more about what you are working on with your gas fermentation process!
Meanwhile, tune in for our next installment of the gas fermentation series where we will dive deep on another unique scale up challenge of gas fermentation. Sign up for our quarterly newsletter to be informed of the next installment.