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Waste biomass as a mean for global carbon dioxide emissions mitigation remains under-utilized. This is mainly due to the low calorific value of virgin feedstock, characterized generally with high moisture content. Aqueous processing, namely hydrothermal liquefaction in subcritical water conditions, has been demonstrated experimentally to thermally densify solid lignocellulose into liquid fuels without the pre-requisite and energy consuming drying step. This study presents a techno-economic evaluation of an integrated hydrothermal liquefaction system with downstream combined heat and power production from forest residues. The utilization of the liquefaction by-products and waste heat from the elevated processing conditions, coupled with the chemical upgrading of the feedstock enables the poly-generation of biocrude, electricity and district heat. The plant thermal efficiency increases by 3.5 to 4.6% compared to the conventional direct combustion case. The economic assessment showed that the minimum selling price of biocrude, based on present co-products market prices, hinders commercialization and ranges between 138 EUR to 178 EUR per MWh. A sensitivity analysis and detailed discussion on the techno-economic assessment results are presented for the different process integration and market case scenarios.

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This article presents a summary of the main findings from a collaborative research project between Aalto University in Finland and partner universities. A comparative process synthesis, modelling and thermal assessment was conducted for the production of Bio-synthetic natural gas (SNG) and hydrogen from supercritical water refining of a lipid extracted algae feedstock integrated with onsite heat and power generation. The developed reactor models for product gas composition, yield and thermal demand were validated and showed conformity with reported experimental results, and the balance of plant units were designed based on established technologies or state-of-the-art pilot operations. The poly-generative cases illustrated the thermo-chemical constraints and design trade-offs presented by key process parameters such as plant organic throughput, supercritical water refining temperature, nature of desirable coproducts, downstream indirect production and heat recovery scenarios. The evaluated cases favoring hydrogen production at 5 wt. % solid content and 600 • C conversion temperature allowed higher gross syngas and CHP production. However, mainly due to the higher utility demands the net syngas production remained lower compared to the cases favoring BioSNG production. The latter case, at 450 • C reactor temperature, 18 wt. % solid content and presence of downstream indirect production recorded 66.5%, 66.2% and 57.2% energetic, fuel-equivalent and exergetic efficiencies respectively.

The author was responsible for the design and execution of the study. The author performed the literature review, data collection, model development and validation, and conducted the subsequent analysis of the technical and economic findings. Mika Järvinen contributed with guidance and knowledge on the black liquor and recovery boiler modelling approach, and assisted with the analysis for the integration study with pulp mill operation. This introductory chapter briefly explains the potential role of biomass as a source for renewable carbon and hydrogen carriers in matching near-term energy demand, while also mitigating global climate change. The chapter then lists some of the technical and commercial challenges facing biomass conversion practices, as well as drivers for further development. Figure 4. Key liquid and gaseous bio-carrier production pathways (developing and commercial).

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As CO2 emissions from traffic must be reduced and fossil-based traffic fuels need to phase out, bio-based traffic fuels alone cannot meet the future demand due to their restricted availability. Another way to support fossil phase-out is to include synthetic fuels that are produced from circular carbon sources with renewable energy. Several different fuel types have been proposed, while, methanol only requires little processing from raw materials and could be used directly or as a dropin fuel for some of the current engine fleet. CO2 emissions arising from fuel production are significantly reduced for synthetic renewable methanol compared to the production of fossil gasoline. Methanol has numerous advantages over the currently used fossil fuels with high RON and flame speed in spark-ignition engines as well as high efficiency and low emissions in combustion ignition engines. Feasible options for engine development or upgrading for methanol have been presented separately in the past work but not considering the whole value chain. The results indicate that high concentration methanol blends will increase significantly tank-to-wheel efficiency, lower energy consumption and CO2 emissions, while their volumetric fuel consumption will increase compared to gasoline, due to the low calorific content of methanol. The work visualizes the impact on CO2 emissions for methanol-fueled transport applications and overall suitability for propulsion. For marine sector, successful demonstrations reveal high maturity of engine technology using methanol fuel. This work also highlights further development needs of synthetic renewable methanol to become a sustainable future transport fuel.