Periodic Reporting for period 2 - CIRCULAIR (Circular fuel supply for air transport via negative emission HTL conversion)
Reporting period: 2024-07-01 to 2025-06-30
Making Europe a circular and climate-neutral society requires responsible utilisation of residues and wastes, as well as large volumes of sustainable fuels for transport sectors like aviation and shipping. The CIRCULAIR project addresses these challenges by developing an advanced biomass conversion pathway for cost-effective fuel production from abundant agricultural residues through hydrothermal liquefaction (HTL). HTL can convert a wide range of organic feedstocks into fuels and is in particular suitable for wet feedstock.
CIRCULAIR has set four high-level project objectives: (i) to develop and demonstrate a cost-effective pathway to biofuel production from abundant feedstock, (ii) to produce a high share of on-specification jet fuel from HTL biocrudes, (iii) nearly-complete biomass utilisation by coupling with green hydrogen and (iv) to enable negative contributions to the GHG balance of HTL fuel production.
Manure and straw are widely available as agricultural residues. Feedstock costs can be low, especially in areas with regional manure surplus. The challenge of handling HTL process water is addressed by integrating HTL conversion with wet oxidation (WO) of the process water. Thereby, the process water is cleaned-up and thermal integration with exothermic WO reduces the process heat demand of HTL. CIRCULAIR plans to demonstrate autothermal operation of an integrated HTL-WO pilot plant.
The biocrudes that result from HTL conversion can be upgraded to liquid hydrocarbon fuels. Specific challenges for the upgrading towards jet fuel specifications include the residual nitrogen content (CIRCULAIR’s target: < 10 ppm) and the aromaticity of the product as well as the valorisation of distillation residues. CIRCULAIR develops solutions for processing HTL biocrudes through pre-treatment and continuous hydrotreatment. The aim is to obtain a high share of on-specification jet fuel through hydrocracking and targeted hydrofinishing.
The carbon content of the feed biomass is transferred to several product phases. CIRCULAIR develops suitable technologies to derive products from all HTL product phases. HTL conversion yields a biocrude as main product. HTL process water also contains a large fraction of the initial carbon content. Volatile fatty acids are recovered from the process water after WO. Furthermore, CIRCULAIR develops recovery and purification strategies for CO2 streams from HTL conversion and WO. Purified CO2 is combined with green hydrogen for methanol synthesis. Methanol can be used as marine fuel or as a renewable commodity chemical. Finally, a solid phase is evolved. CIRCULAIR investigates the use of HTL chars for soil application and carbon sequestration. The target is to transfer >95% of the initial carbon content to various products.
The CIRCULAIR concept minimizes major emission drivers of HTL conversion: Integration of WO minimizes external process energy demand and the utilisation of green hydrogen minimizes emissions associated with biocrude upgrading. CIRCULAIR investigates opportunities to generate negative contributions to the GHG balance, potentially enabling carbon-negative fuel production. In particular, the long-term carbon sequestration potential of HTL solids is quantified. Further negative contributions may be attributed to avoided burdens in comparison with current manure handling practices.
CIRCULAIR has set four high-level project objectives: (i) to develop and demonstrate a cost-effective pathway to biofuel production from abundant feedstock, (ii) to produce a high share of on-specification jet fuel from HTL biocrudes, (iii) nearly-complete biomass utilisation by coupling with green hydrogen and (iv) to enable negative contributions to the GHG balance of HTL fuel production.
Manure and straw are widely available as agricultural residues. Feedstock costs can be low, especially in areas with regional manure surplus. The challenge of handling HTL process water is addressed by integrating HTL conversion with wet oxidation (WO) of the process water. Thereby, the process water is cleaned-up and thermal integration with exothermic WO reduces the process heat demand of HTL. CIRCULAIR plans to demonstrate autothermal operation of an integrated HTL-WO pilot plant.
The biocrudes that result from HTL conversion can be upgraded to liquid hydrocarbon fuels. Specific challenges for the upgrading towards jet fuel specifications include the residual nitrogen content (CIRCULAIR’s target: < 10 ppm) and the aromaticity of the product as well as the valorisation of distillation residues. CIRCULAIR develops solutions for processing HTL biocrudes through pre-treatment and continuous hydrotreatment. The aim is to obtain a high share of on-specification jet fuel through hydrocracking and targeted hydrofinishing.
The carbon content of the feed biomass is transferred to several product phases. CIRCULAIR develops suitable technologies to derive products from all HTL product phases. HTL conversion yields a biocrude as main product. HTL process water also contains a large fraction of the initial carbon content. Volatile fatty acids are recovered from the process water after WO. Furthermore, CIRCULAIR develops recovery and purification strategies for CO2 streams from HTL conversion and WO. Purified CO2 is combined with green hydrogen for methanol synthesis. Methanol can be used as marine fuel or as a renewable commodity chemical. Finally, a solid phase is evolved. CIRCULAIR investigates the use of HTL chars for soil application and carbon sequestration. The target is to transfer >95% of the initial carbon content to various products.
The CIRCULAIR concept minimizes major emission drivers of HTL conversion: Integration of WO minimizes external process energy demand and the utilisation of green hydrogen minimizes emissions associated with biocrude upgrading. CIRCULAIR investigates opportunities to generate negative contributions to the GHG balance, potentially enabling carbon-negative fuel production. In particular, the long-term carbon sequestration potential of HTL solids is quantified. Further negative contributions may be attributed to avoided burdens in comparison with current manure handling practices.
The first phase of the project was focused on the preparation of the implementation, especially during the second reporting period (up to month 30) an increasing number of project results became available. Existing pilot plants, both for HTL and WO were operated in order to improve the understanding of these processes and to provide samples to further project partners who investigate the utilization of various product streams. In terms of HTL, synergetic advantages of co-liquefaction of manure and straw were evaluated, another focus of the investigation was the WO of process waters. A pilot plant for the demonstration of thermally coupled HTL and WO was designed and constructed; this pilot plant is now in the commissioning phase.
The work performed on upgrading of HTL biocrudes has focussed on the development of pretreatment and conditioning methods that allowed first runs both for continuous fixed bed hydroprocessing and slurry hydrotreating towards the end of the second reporting period. The investigations of valorisation of aqueous and gaseous side-streams demonstrated the feasibility of processes for the recovery of volatile fatty acids from HTL process waters. The compositions of the HTL and WO gases have been determined, both streams contain a high share of CO2 (more than 90%) that may be utilized for green methanol production. Based on the gas compositions, adsorption-based clean-up procedures for these CO2 streams were evaluated. CIRCULAIR also investigated and developed treatment methods for HTL chars to evaluate their soil application and carbon sequestration potential.
A pre-evaluation of fuel production cost and live-cycle greenhouse gas emissions was conducted based on an initial process model. These initial results indicate deep reductions in greenhouse gas emissions (> 80% compared to fossil fuels) at estimated fuel production costs in-between current jet fuel prizes and fuel production costs of current aviation biofuels.
The work performed on upgrading of HTL biocrudes has focussed on the development of pretreatment and conditioning methods that allowed first runs both for continuous fixed bed hydroprocessing and slurry hydrotreating towards the end of the second reporting period. The investigations of valorisation of aqueous and gaseous side-streams demonstrated the feasibility of processes for the recovery of volatile fatty acids from HTL process waters. The compositions of the HTL and WO gases have been determined, both streams contain a high share of CO2 (more than 90%) that may be utilized for green methanol production. Based on the gas compositions, adsorption-based clean-up procedures for these CO2 streams were evaluated. CIRCULAIR also investigated and developed treatment methods for HTL chars to evaluate their soil application and carbon sequestration potential.
A pre-evaluation of fuel production cost and live-cycle greenhouse gas emissions was conducted based on an initial process model. These initial results indicate deep reductions in greenhouse gas emissions (> 80% compared to fossil fuels) at estimated fuel production costs in-between current jet fuel prizes and fuel production costs of current aviation biofuels.
The main demonstration activities of the CIRCULAIR project will take place in the final third reporting period. The intermediate results of CIRCULAIR are at the forefront of European HTL research and clearly beyond state of the art from project start. This refers in particular to an increased scientific understanding of the co-liquefaction of manure and straw, WO of HTL aqueous phases, modelling and designing plants for coupled HTL and WO, pre-treatment procedures for HTL biocrude upgrading, product recovery from aqueous and gaseous side streams, characterisation of HTL solids and procedures to utilize HTL solids for soil amendment and carbon sequestration, as well as refined process models for system analyses of HTL fuel production.
Coupling HTL with a WO of HTL process waters might be of particular importance with respect to future uptake of commercial HTL fuel production. CIRCULAIR results indicate that WO is an effective process to remove organic compounds and thereby clean up HTL process waters. Modelling shows that autothermal operation may be achieved, i.e. all process heat demand for HTL conversion may be met by WO of the process water.
Coupling HTL with a WO of HTL process waters might be of particular importance with respect to future uptake of commercial HTL fuel production. CIRCULAIR results indicate that WO is an effective process to remove organic compounds and thereby clean up HTL process waters. Modelling shows that autothermal operation may be achieved, i.e. all process heat demand for HTL conversion may be met by WO of the process water.