Periodic Reporting for period 1 - CIRCULAIR (Circular fuel supply for air transport via negative emission HTL conversion)
Reporting period: 2023-01-01 to 2024-06-30
Making Europe a more 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, where direct electrification is not viable. 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 of the process water. Thereby, the process water is cleaned-up and thermal integration with exothermic wet oxidation reduces the process heat demand of HTL. CIRCULAIR plans to demonstrate autothermal operation of a continuous HTL process with integrated wet oxidation at pilot-scale.
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 that result from HTL conversion. CIRCULAIR develops suitable technologies to derive marketable 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 wet oxidation. Furthermore, CIRCULAIR develops tailored recovery and purification strategies for CO2 streams resulting from HTL conversion and the wet oxidation. 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 state-of-the art HTL conversion: Integration of wet oxidation minimizes external process energy demand for HTL, utilisation of green hydrogen minimizes emission associated with biocrude upgrading. CIRCULAIR investigates opportunities to generate negative contributions to the GHG balance, potentially enabling carbon-negative fuel production. In particular, the performance of HTL solids for soil amendment is investigated and their long-term carbon sequestration potential is quantified. Furthermore, negative contributions may also 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 of the process water. Thereby, the process water is cleaned-up and thermal integration with exothermic wet oxidation reduces the process heat demand of HTL. CIRCULAIR plans to demonstrate autothermal operation of a continuous HTL process with integrated wet oxidation at pilot-scale.
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 that result from HTL conversion. CIRCULAIR develops suitable technologies to derive marketable 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 wet oxidation. Furthermore, CIRCULAIR develops tailored recovery and purification strategies for CO2 streams resulting from HTL conversion and the wet oxidation. 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 state-of-the art HTL conversion: Integration of wet oxidation minimizes external process energy demand for HTL, utilisation of green hydrogen minimizes emission associated with biocrude upgrading. CIRCULAIR investigates opportunities to generate negative contributions to the GHG balance, potentially enabling carbon-negative fuel production. In particular, the performance of HTL solids for soil amendment is investigated and their long-term carbon sequestration potential is quantified. Furthermore, negative contributions may also 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. Existing pilot plants, both for HTL and wet oxidation have been operated in order to provide samples to further project partners who investigate the utilization of these product stream. In terms of HTL synergetic advantages of co-liquefaction of manure and straw were evaluated, another focus of the investigation was the wet oxidation of process waters. The design phase of a thermally coupled HTL and wet oxidation system was completed, preparing the demonstration of coupled HTL-WO in the next phase of the project.
The work performed on upgrading of HTL biocrudes has focussed on the development of pretreatment and conditioning methods that will allow for continuous fixed bed hydroprocessing of biocrudes from manure and straw. The investigations of valorisation of aqueous and gaseous side-streams demonstrated the feasibility of the process of extraction and stripping of volatile fatty acids using synthetic waters. The compositions of the HTL gases have been determined in batch and pilot plant experiments. The suitability of biochars resulting from the HTL process for CO2 adsorption was evaluated. CIRCULAIR also investigated treatment methods for HTL chars to investigate their soil application and carbon sequestration potential in the next project phases.
An initial process model for system analyses of HTL conversion and wet oxidation (WO) of HTL process waters was established. This initial process model allows to derive energy and mass balances for a CIRCULAIR baseline configuration, which foresees distributed HTL-WO plants and a centralized upgrading facility. Denmark was chosen as regional context of this initial evaluation due to high biogenic feedstock densities and favourable conditions for green hydrogen generation from wind power.
The work performed on upgrading of HTL biocrudes has focussed on the development of pretreatment and conditioning methods that will allow for continuous fixed bed hydroprocessing of biocrudes from manure and straw. The investigations of valorisation of aqueous and gaseous side-streams demonstrated the feasibility of the process of extraction and stripping of volatile fatty acids using synthetic waters. The compositions of the HTL gases have been determined in batch and pilot plant experiments. The suitability of biochars resulting from the HTL process for CO2 adsorption was evaluated. CIRCULAIR also investigated treatment methods for HTL chars to investigate their soil application and carbon sequestration potential in the next project phases.
An initial process model for system analyses of HTL conversion and wet oxidation (WO) of HTL process waters was established. This initial process model allows to derive energy and mass balances for a CIRCULAIR baseline configuration, which foresees distributed HTL-WO plants and a centralized upgrading facility. Denmark was chosen as regional context of this initial evaluation due to high biogenic feedstock densities and favourable conditions for green hydrogen generation from wind power.
The main results of the CIRCULAIR project will be generated in the second and third reporting period. Nevertheless, the CIRCULAIR consortium is at the forefront of European HTL research and the preparatory work in the first reporting period may be considered beyond state of the art from project start. In particular, investigations of co-liquefaction of manure and straw as well as wet oxidation of the HTL aqueous phase increased the scientific understanding in the field of HTL conversion. Similar conclusions can be drawn for HTL biocrude upgrading as well as product recovery from aqueous, gaseous, and solid side streams.
Early indication from wet oxidation of HTL process waters might be of particular importance with respect to future uptake of commercial HTL fuel production. The initial research and development indicate that WO is an effective process to remove organic compounds and thereby cleans up HTL process waters. Initial analyses indicate that autothermal operation may be achieved, i.e. all external heat demand for HTL conversion is met by WO of the HTL aqueous phase.
Early indication from wet oxidation of HTL process waters might be of particular importance with respect to future uptake of commercial HTL fuel production. The initial research and development indicate that WO is an effective process to remove organic compounds and thereby cleans up HTL process waters. Initial analyses indicate that autothermal operation may be achieved, i.e. all external heat demand for HTL conversion is met by WO of the HTL aqueous phase.