Building a pilot biorefinery to produce Sustainable Aviation Fuels (SAFs) in Wisconsin

By Mingxin Zhang and Unni Kurumbail

Problem Statement: Petrochemicals is a linear economy

Current chemicals production stems primarily from fossil fuel feedstocks. While a breathtaking wealth of value-added chemical transformations have enabled the modern economy, the linear nature of this industry (take-make-dispose) is not sustainable in the long run. It is critical to develop circular pathways for the production of critical fossil fuel products that can not otherwise be replaced. Aviation fuel represents such a product because the unique energy-density requirements inherent in flight make it a challenging product to replace. In this proposal, we put forth an idea for a Wisconsin-based pilot biorefinery. This involves taking advantage of Wisconsin’s strong agricultural and manufacturing roots, as well as geographic and educational advantages, to jumpstart SAFs in our own backyard.

Background: Decarbonization role of SAFs & premises of gasification

Decarbonization role of SAFs

The human desire and need for airline travel will not disappear. The time-distance theory of human mobility suggests that across cultures and eras, humans have always tried to travel as much as they can inside fixed monetary and time windows (Schafer, 2006). As human development flourishes across the globe, it will be accompanied by an insatiable demand for cost-effective travel and experiences far away from one’s home. Global aviation fuel demand currently exceeds 340 billion L/yr, and at current rates of increase is expected to generate 5% of global greenhouse gas (GHG) emissions by 2050 (Shahabuddin et al 2020). There is a clear need for a sustainable aviation fuel that can propel us into a future of unlimited, environmentally-conscious travel. 

Almost no aviation fuel comes from renewable resources, due to the energy density requirements. The only other reasonably competitive technology is battery-powered aircraft from renewable electricity. To fuel a Boeing 747 or Airbus A320-size aircraft up to 600 nautical miles, a battery needs an energy density of 800 watt-hours/kilogram (Schäfer, 2019). However, lithium-ion batteries as state-of-the-art energy storage technologies have an energy of 250 Wh/kg. By contrast, jet fuel has an energy density of 11,890 Wh/kg. There is no indication that batteries can become technically viable in time to decarbonize long-haul flights on pace with our global decarbonization goals. Another challenge with all-electric aircraft is the variability in the decarbonization of the local electricity production mix. For example, with a 57% coal, and 37% nuclear energy mix in the Czech Republic, the difference in CO2 emissions between jet fuel and electricity is only 25% (Hospodka et al.). 

In these ways, if SAFs could be made affordably and on a large scale, they would represent  the most realistic pathway to rapidly decarbonize air transport. We believe that gasification is one avenue for SAF production that deserves particular attention from Wisconsin legislators.

Premises of Gasification

Gasification is a mature technology with the capability for developing aviation-fuel blends from circular economy feedstocks such as municipal solid waste, used plastics, and biomass. During gasification, a feedstock such as forest residue is heated to 800-1200°C temperatures in the presence of oxygen and steam, producing a mixture of carbon monoxide and hydrogen known as syngas (see Fig.1). Syngas can then be converted via the well-established Fischer-Tropsch process into longer-chain hydrocarbons that are refined into synthetic fossil fuel products of choice (gasoline, diesel, aviation fuel, lubricating oils, commodity chemicals, etc.). Some of the major challenges that prevent gasification from being used more often today include:

  1. Variability of the feedstock: differing moisture content, carbon content, and impurities make it challenging to run an optimal process that can be cost-competitive with other technologies. 
  2. Dispersed feedstock: A significant portion of the cost associated with gasification is the collection of suitable resources from dispersed locations. For example, the main feedstocks of gasification, lignocellulosic biomass from agricultural wastes, is often widely dispersed in rural communities.
  3. Lack of large-scale infrastructure: Petrochemical refineries are the locations where fossil fuels like oil are converted into gasoline, diesel, and the major commodity chemicals that we build our world out of today. They dominate the industrial landscape because they outcompete cottage industries through economies of scale. Small biomass gasification plants simply cannot compete with large petrochemical refineries.

Figure 1: Schematic of a typical biomass-to-aviation-fuel process

Source: M. Shahabuddin et. al 2020

It is no secret that Wisconsin’s manufacturing and agricultural sectors have suffered in recent decades, due to forces such as globalization and commoditization. Wisconsin’s population has been declining and it is not immediately obvious that Wisconsin has a path forward to provide quality jobs for working-class and middle-class citizens in the decades to come. We would like to offer a vision to the Wisconsin legislature for how Wisconsin can use gasification technologies to make inroads into the dual problems of local economic challenges and global sustainability goals.

Proposed Solution: Build a state-supported biomass-gasification pilot plant to produce SAFs

We propose that the Wisconsin Legislature commission a Request for Proposal (RFP) for a state-supported biomass-gasification pilot plant with the primary purpose of developing an economically viable biomass-to-aviation-fuel gasification industry. The plant would have to be built within Wisconsin, but would be allowed to source biomass from surrounding states as well, utilizing Wisconsin’s unique location at a crossroads of numerous great plains states and well-established waterways. The plant would serve as a biorefinery and biobattery, producing a variety of saleable products, including electricity, on the open market. However, its main target would be the development of a robust biomass-to-SAFs process, selling aviation fuel to local airline hubs as a primary market. Below we outline some of the major environmental, economic and social aspects of this policy that cause us to support it strongly.

Environmental: Gasification offers an avenue to meet Wisconsin’s environmental goals.

Renewable aviation fuels are the path forward for decarbonizing heavy air travel. Only a few methods of renewable aviation fuel production are currently approved under ASTM 7566 aviation fuel requirements (Alternative Fuels Data Center). Two of these produce various products from Fischer-Tropsch upgrading of wood residues for blending ratios up to 50%. Gasification is a promising technology for the upstream production of bio-oils that can undergo the Fischer-Tropsch process, and thus represent a logical expansion of SAFs  production into a wider range of feedstocks. 

A gasification industry has powerful implications beyond SAF production. Wisconsin currently has a 10% renewable portfolio standard for electricity providers. This will likely increase in the future as state RPS standards are increased to meet national goals such as the Paris agreement and Biden administration goals. However, Wisconsin’s electricity grid is one of the dirtiest in the country — coal-fired power plants provide around half of Wisconsin’s net electricity generation. (EIA, 2020). Electricity co-production at a biomass gasification plant can enhance the process of decarbonizing Wisconsin’s grid. Biomass gasification is well-suited for application to electricity production-major power plants (200MW+) run off a version of gasification that is tailored for electricity production (ETIP Bioenergy, 2019).  Furthermore, it is clean. Previous life cycle analysis (LCA) of integrated biomass gasification combined cycle with CO2 removal found that the use of biomass has the potential to reduce the life cycle GHG emissions by 77%-99% in comparison to fossil fuel combustion, depending on the types of feedstock and the combustion technology (Kadiyala et al.). LCA results also show the advantage of utilizing biomass over coal (a major current Wisconsin feedstock) in terms of fossil fuel depletion and GHG emissions avoidance (Carpentieri et al.).  Biomass represents a dispatchable electricity generation source that could serve as a ‘biobattery’ as Wisconsin transitions to a wind and solar-heavy future. This can replace our current coal and natural gas assets, while still providing their large capacity and reliability.

There are incredible opportunities for synergy in these two processes. Because a significant fraction of the overhead involved in gasification is the collection of suitable feedstock, the combination of biomass gasification for products and biomass gasifier combustion for electricity would be a strong candidate for an energy and cost-efficient manufacturing base for Wisconsin.

An environmentally responsible state program should sustainably deploy this technology. Issues that are often faced by incinerators, such as water pollution, disposal of ash, and other byproducts like tar, char, and alkaline compounds, can come into play while gasifying biomass. Current cleaning technologies mitigate pollution levels by reducing tar production (and therefore reducing water contamination) and cleaning the effluent gas from the gasification reactor (Menya,, 2014). R&D continues to reduce the environmental effects, with national programs engaged in developing more efficient and environmentally sound gasification technologies. There are promising benefits to using biochar from gasification as a soil amendment, carbon sequestration technology, and saleable product (Hansen et. al, 2015). Local institutions such as the Great Lakes Bioenergy Research Center can perform targeted research to expedite environmental protection technologies to sustainably develop a Wisconsin gasification industry. 

One unintended benefit that may emerge from a clear state commitment to innovate solutions to environmental problems is its attractiveness to young people. Sustainability is a core value for millennials, and a state-wide commitment to sustainability can attract talented and productive workers to the state. This effect is observed in Madison, which contrasts the state of Wisconsin and continues to expand in population as young people flock to the city in no small part because of its bike paths, sustainable shopping, and dining options, and embrace of its natural beauty. 

Economic: Wisconsin is well-suited to meet the already present demand for SAFs.

The demand for SAFs is promising. Reuters reported that US airlines are lobbying the Biden Administration to support sustainable aviation fuel subsidies, and Chicago-based Boeing has committed to fly with 100% sustainable aviation fuels by 2030. The tendency to greener aviation fuels displays the potential demand for gasification plants. We envision a future where Wisconsin-based SAFs are sold to airlines in commercial, private, and military end-uses to blend with current jet fuel. This is a particularly attractive idea, given Wisconsin’s proximity to the major international air hub at O’Hare.

Wisconsin is in other ways as well an ideal state to build biomass-gasification plants. According to the Bioenergy Feedstock Assessment from Wisconsin Bioenergy Initiative, six types of available biomass in the state include roundwood, wood processing residuals, wood harvest residuals, corn stover, grasses from fallow pastures, and dairy manure. For instance, approximately 1.5 million dry tons of wood residuals could be utilized in combustion or gasification every year in the state, which could produce around 125 million gallons of biofuel (Wisconsin Bioenergy Initiative, 2012). More broadly, building biomass-gasification plants could create an industrial symbiosis whereby various biomass sources in Wisconsin are combined to efficiently produce a variety of value-added products.

The development of a gasification pilot plant represents a ‘technology push’ program from the state of Wisconsin, where we take a loss on the technology initially in order to bring it down the cost curve and make it feasible for private actors. By developing a market for SAFs, the WI government can spur private corporations to develop their own gasification technologies or a myriad of other SAFs platforms that are unknown a priori.

A study by Mustafa et al. suggests that the payback period for a gasification plant in local regions is around four years. The analysis included the capital cost, operational and maintenance (O&M) costs for the biomass pretreatment processes, the gasification plant, and the gas to liquid plant. Furthermore, the Southern Research Institute also proves that small-scale biomass plants (200 ton/day) and medium-scale biomass gasification plants (500-1000 ton/day) have the potential to overcome technical and logistical challenges for biomass to liquid fuels. The internal rate of return is around 16.8%, which means the annual rate of growth of the gasification investment is expected to generate 16.8% interest (Sangwal).

Considering the carbon emission goals of O’Hare Airport and Midway Airport in Chicago in the past three years, the SAF market available for such plants is promising. Furthermore, SAFs could also be sold to states like California and Oregon that have a statewide “clean fuel standard” policy.  California, for example, currently imports biodiesel from Singapore. This could be directly replaced through competitive Wisconsin-based biofuels.

Finally, the benefits of a SAF economy extend into local communities. Farmers could collaborate with gasification plants to provide their extra agricultural or animal waste, and as a result, earn extra income.  Fuels would be made close to the sources of the feedstocks to reduce  transportation costs, bringing economic opportunities and investment to rural communities. A manufacturing economy can bring jobs to the state more broadly, and is in keeping with Wisconsin’s historic industrial base and agricultural sector. There is symbolic and real economic value to investing in shared renewable energy projects that take advantage of our natural advantages. 

Social: A gasification industry can strengthen interstate collaboration, boosting local success through coherent regional effects.

SAF production needs multifaceted effort, and interagency collaboration is necessary to build biomass-gasification plants for SAFs. The federal government created a SAFs Interagency Working Group aiming to develop and scale best practices to support the success of SAFs in commercial, business, and military aviation sectors. Similarly, the Great Lakes Biomass State and Regional Partnership (GLBSRP) is an instance of interagency collaboration at the state level and guides the U.S. heartland to increase production and use of bioenergy and biobased products throughout the midwest. We believe that, with Wisconsin leading the way, we can harness the incredible wealth of research and technological development that has been put into biofuels development to successfully develop a SAFs industry in Wisconsin. The key is leveraging these unique partnerships to provide technical guidance, feasibility studies, and community engagement. 

The Midwest has a strong tradition of research and development into biofuels. A state technology push can provide opportunities for researchers at varied institutions to connect on pilot-scale projects in Wisconsin that drive SAFs down the cost curve. This is a unique opportunity to connect researchers with larger-scale plants they don’t normally have access to. In doing so, they can tailor research to optimize Wisconsin’s technology.

Residents close to selected locations for gasification plants would probably have concerns about noise, air and water quality, and safety issues of plant construction. Thus, education, knowledge dissemination, and outreach are important to support the policy proposal. The government and industry could educate and disseminate knowledge about alternative fuels and gasification plants. For instance, the Wisconsin Department of Transportation could publish research reports about alternative aviation fuels and their impacts on decarbonizing the aviation industry and integrate the concepts of SAFs with youth and adult aviation education programs. The Wisconsin Department of Natural Resources could also hold public meetings and hearings to guide local communities to understand the site selection process and the potential economic, environmental, and societal effects on local communities.

We propose that Wisconsin’s legislature reach out to the GLBSRP to utilize their resources and expertise during the RFP process. Take, for instance, Dynamic Group Inc. in Brown County. The company, together with the Public Service Commission (PSC), Department of Natural Resources (DNR), and Department of Agriculture, Trade and Consumer Protection (DATCP) announced a $20 million grant program for digester projects in the Lake Michigan watershed. The program built a Green Pastures ZBio Energy Center and collaborated with utility companies, dairy producers, renewable energy research institutions, and engineering companies to utilize around 189 million gallons of manure in Brown County and produce about 500,000 MMBtu of renewable biogas. The program illustrates a viable mechanism for pilot gasification plants in Wisconsin.

Wisconsin has a proud history of progressivism and union activity that stems from its manufacturing roots. These traditions can be applied soon to the development of a gasification industry. In the 21st century, progressivism involves leading on sustainability. By incorporating this aspect of sustainability into its state policies, WI has the opportunity to renew the manufacturing and agricultural traditions that have made it unique and successful in the past and chart a greener path into the future.


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