Skip to main content

Hydrothermal liquefaction: Enhanced performance and feedstock flexibility for efficient biofuel production

Periodic Reporting for period 2 - HyFlexFuel (Hydrothermal liquefaction: Enhanced performance and feedstock flexibility for efficient biofuel production)

Reporting period: 2019-04-01 to 2020-03-31

The European Union set ambitious climate targets, by 2030 at least 14% of the final energy consumption in transport should be renewable. Furthermore, the European Green Deal aims at a 90% reduction in transport emissions to achieve net-climate neutrality by 2050. In this context, hydrothermal liquefaction (HTL) is emerging as feedstock-flexible biofuel technology to produce various renewable transportation fuels.

HyFlexFuel is dedicated to the development of a cost-competitive production pathway for liquid fuels based on HTL. The specific objectives of HyFlexFuel include:
1) Demonstrating compatibility of the process with a diverse feedstock base
2) Maturing HTL-based fuel production from technological readiness level TRL 2-4 to TRL 5
3) Increasing heat integration and product recovery
4) Understanding the relation between feedstock and process conditions vs. product yield and quality
5) Efficient valorisation of residual process streams
6) Quantification of techno-economic and environmental performance potentials, risks and benefits
7) Demonstrating drop-in capability of HyFlexFuel products
8) Identification and quantification of technology gaps

The scope of HyFlexFuel covers the entire production chain to finished fuels, as well as the utilisation of further process streams. The availability of a broad range of biomass feedstock is studied in detail. The project demonstrated and optimized the liquefaction of lignocellulosic biomass, microalgae and wet wastes into biocrudes. The biocrudes are subsequently upgraded into transportation fuels, such as gasoline, jet fuel and diesel. The substantial content of organic compounds in HTL process water is converted via catalytic hydrothermal gasification (cHTG) and anaerobic digestion (AD). Both processes yield methane, e.g. for on-site electricity and heat generation. Valuable inorganic nutrients are recovered from the process and can be used as fertilisers.
After 30 of 48 project months, the HyFlexFuel project has already produced many significant results, including:
(i) The quantification of residue and waste availability in Europe
(ii) The production of biocrudes in a unique HTL pilot plant from various biomasses
(iii) The successful upgrading of HTL biocrudes from algae and sewage sludge to hydrocarbon fuels
(iv) The valorisation of further process streams to improve the economics of the process via energy generation and nutrient recovery
(v) The development of a process model to quantify the economic and environmental performance in the further course of the project.
The achievements of the HyFlexFuel project are discussed in more detail in the following paragraphs.

The availability of sustainable biomass streams in Europe was investigated by project partner DBFZ (German biomass research centre). DBFZ quantified the potential availability of waste streams such as sewage sludge, biogenic municipal wastes, manure, and various kinds of agricultural residues such as straw and sugar beet leaves. Feedstock density maps were compiled for each biomass to identify suitable locations for HTL plants in Europe.

The unique pilot-scale HTL plant at Aarhus University demonstrated the hydrothermal liquefaction of three model feedstocks, the microalgae spirulina, miscanthus, and sewage sludge under industrially relevant conditions. Further experimental campaigns with a variety of biomasses demonstrated the feedstock flexibility of HTL conversion. During these campaigns more the 300 kg of biocrude were produced. In parallel, HTL models were developed based on screening experiments with smaller reactors to optimize the biocrude yield and quality. Thereby it was found that the co-processing of different biomasses can improve the performance. To understand the complex HTL reaction pathways, HyFlexFuel partners developed and applied sophisticated analytical techniques to reveal the chemical composition of biocrudes and other product phases.

The chemical composition of biocrude varies depending on feedstock and process conditions. The HyFlexFuel project developed specific strategies to remove solid particles and minerals from the respective biocrudes prior to the upgrading. For the upgrading itself, Aalborg University and Haldor Topsoe derived multi-step strategies, including an appropriate use of catalysts. So far, HTL biocrudes from the microalgae Spirulina and sewage sludge were successfully upgraded to a mixture of hydrocarbon fuels. First analyses showed that the quality of the resulting fuel mixture is promising for gasoline, jet fuel and diesel production. Project partner Eni investigated the alternative option to co-feed HTL biocrudes in refineries. It was found that specific properties of biocrudes limit the co-feeding ratios to few percent. However, mildly upgraded biocrudes may improve this significantly.

The biocrudes are not the only product from HTL conversion, typically 90% of the output of a HTL plant is process water, which contains a significant amount of minerals and organics. HyFlexFuel investigates the production of methane from the organic content via catalytic hydrothermal gasification (cHTG) and anaerobic digestion (AD). First cHTG experiments were carried out on a pilot facility at the Paul Scherrer Institute, strategies for the separation of salts and of sulfur-containing species were developed. AD experiments at project partner OWS (Organic Waste Systems) showed substantial biogas production for HTL process water from miscanthus, while process waters from sewage sludge and Spirulina proved to be more challenging. The University of Hohenheim successfully recovered nitrogen and phosphorus in form of struvite, a fertilizer product, from the process water and from solids that also form during HTL.

In the system analysis workpackage Bauhaus Luftfahrt established a numerical process model covering all abovementioned process steps. This model will now serve as a basis to evaluate the economic and environmental performance of HTL fuel production.
The intermediate results of the HyFlexFuel project, which are described in the previous section, already reach well beyond the state of art of HTL conversion before project start. The ambition to transform Europe to a net-carbon neutral society by 2050 requires a change from conventional transportation fuels towards renewable alternatives. This transformation is underway and advanced conversion technologies for biofuel production from a broad range of feedstock can have a crucial impact here. The HyFlexFuel technology enables such feedstock flexible fuel production, also from wet waste streams such as sewage sludge, manure or food waste, which need to be disposed otherwise. Therefore, the process provides various distinct market opportunities for fossil fuels replacement, to create employment in rural development, but also for fertilizer as a by-product from the conversion of feedstocks, which are rich in nitrogen and phosphorus. One example is the integration of the HyFlexFuel process in wastewater treatment plants, to destroy micro-pollutants in sewage sludge, to recover phosphorus, and to produce fuels. HTL-based fuel production is still in the development phase, HyFlexFuel is advancing key process steps and thereby demonstrates the potential to produce drop-in capable fuels in a scalable, sustainable and economically competitive way.
The HyFlexFuel process