May-2025

Woody residue gasification: a dual solution for decarbonisation

Utilising woody residue from forest thinnings can support new fuel production and mitigate wildfire risk.

Shrinivas Lokare and Andrew Kramer, SunGas Renewables Inc.
Bryan Tomsula, CPFD Software

Article Summary

As the world confronts growing energy demands through the first quarter of the 21st century, the shift from traditional fuels to renewable and cleaner fuels continues to grow. These renewable fuels can help companies meet their carbon reduction obligations and comply with specific government requirements. Solid feed gasification is a proven and established process that can be a major component in expanding the production of these renewable fuels and presents a viable option for conversion of renewable feedstocks into fuels and chemicals at scale (see Figure 1).

Biomass residues and municipal solid waste (MSW) feedstocks are two abundant feedstocks that can produce alternatives to conventional fuels. Biomass, comprising organic materials such as agricultural residues, energy crops, and forestry residues, offers a renewable and abundant source of energy. MSW consists of non-recyclable organic waste, such as food scraps, low-grade plastic, and garden waste.

However, MSW faces challenges like contamination and the need for sorting and cleaning. Sourcing and processing MSW is further complicated by inconsistent segregation, high transportation costs, and limited infrastructure for advanced waste treatment. Although advanced technologies are being developed and put into practice to improve MSW quality and conversion efficiency, these difficulties adversely impact project feasibility as feedstock cost is directly proportional to the extent of pretreatment it requires before feeding it to the gasifiers.

Forest residues – a low-hanging fruit
Woody biomass – primarily sourced from forest thinning and wood processing industry – offers a lower cost and practical option for renewable fuels and chemicals manufacturing, as it is a clean and readily available feedstock. According to the US Department of Energy’s 2023 Billion-Ton Report, nearly 150 million dry short tons of forestry wood are currently used each year for energy (DOE, 2023). This quantity alone can produce about 20% of the total sustainable aviation fuel (SAF) demand of the US or about 10% of the total methanol demand of the world.

Traditionally, forest thinnings are a significant source of feedstock for the pulp and paper industry. Removing the younger trees and underbrush allows the remaining trees to grow larger, producing high-quality material for construction lumber. The woody residues generated from the thinning provide a sustainable raw material source for the pulp and paper industry to produce various types of pulp, including kraft and thermomechanical pulps (TMP), suitable for paper products. With the rise of digital technologies, the pulp and paper industry has seen its market shrink, prompting the closure of many facilities and a search for new uses for forest thinnings. At the same time, limited thinning and forest management – particularly in private, non-working, and public forests – has worsened an already serious environmental concern. Renewed forest management and forest thinning are beginning to result in additional feedstock availability.

Forest thinning is also a crucial wildfire prevention strategy that involves selectively removing trees and underbrush to reduce combustible material and wildfire risk (see Figure 2). Private working forest practices have demonstrated how to use thinning to control the risk of wildfires and result in healthier and larger timber. Improved forest management practices in non-working forests will minimise carbon emissions, reduce fire risks, and lead to an increase in standing forests.

Dual challenges: one sustainable solution
The dual challenges of needing alternatives to fossil fuels and preventing wildfires can be addressed through a complementary solution: utilising woody residue from forest thinnings in gasification processes to produce renewable fuels and chemicals.

SunGas Renewables (SunGas), a company dedicated to transforming organic waste into advanced clean fuels, has designed a system that offers this solution.

SunGas’ technology uses a bubbling fluidised bed gasifier and cyclone as core components. This process has been proven across a variety of process conditions, including solid feedstocks, scale, operating pressure and temperature, and bed materials. Based on the extensive developmental work and feedback from 21 commercially operating gasifiers, SunGas has established sophisticated process and computational fluid dynamics (CFD) models. The Aspen-based process modelling tool is used to establish gasification cases for all the various conditions as referenced earlier and validated against the experimental/field data. The comparative analysis, as shown in Figure 3, highlights the robustness of process models in predictions of product quality (H2/CO) and yield (H2+CO).

In fluidised bed reactors, the interaction between the solids and gas is very important to enhance contact between reactants and maintain a consistent thermal profile throughout the bed. The commercial CFD software, Barracuda Virtual Reactor, developed by CPFD Software, is a robust tool used throughout industry to study these complex fluidised bed systems.

The CPFD models help provide insight into the fluidisation behaviour under various conditions and verify key design and scale-up considerations during commercial product development. Figure 4 shows sample results for key process variables, which are used to generate an insight into reactor performance and scale-up.

SunGas’ integrated solution for decarbonisation
SunGas’ S1000 product is an integrated system consisting of key components engineered to provide excellent performance (see Figure 5).

The process starts with drying biomass to the required moisture content. The dried biomass is fed into a fluidised bed gasifier, reacting with steam and oxygen at 850°C. Inside the gasifier, biomass undergoes pyrolysis, breaking down into volatile gases and char. The char reacts with steam and oxygen to produce syngas, a mixture of hydrogen, carbon monoxide, carbon dioxide, methane, and other trace gases. The fluidised bed ensures thorough mixing and heat transfer, promoting greater than 95% conversion of the carbon in the feedstock. The resulting syngas is cleaned of impurities and can be used for power generation or processed into advanced clean fuels and chemicals.

In the quest for advanced clean fuels, one of the challenges is the heterogeneous nature of feedstocks, requiring tailored pretreatment for consistent quality. High moisture content reduces conversion efficiency, and impurities like ash and sulphur require additional treatment and processing steps. Reliable feedstock supply chains and economic viability are also concerns, needing robust logistics.