Thomas Kohl

Bio: Thomas Kohl is an academic researcher from Aalto University. The author has contributed to research in topics: Bioenergy & Syngas. The author has an hindex of 4, co-authored 5 publications receiving 176 citations.

The BioSCWG Project: Understanding the Trade-Offs in the Process and Thermal Design of Hydrogen and Synthetic Natural Gas Production

Abstract: 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.

Techno-economic assessment of integrated hydrothermal liquefaction and combined heat and power production from lignocellulose residues

Abstract: 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.

Process modeling, synthesis and thermodynamic evaluation of hydrogen production from hydrothermal processing of lipid extracted algae integrated with a downstream reformer conceptual plant

Abstract: Hydrothermal processing of organics, particularly the supercritical water gasification process, has showed potential in lab-scale records to valorize the chemical energy stored in biomass. The technology manipulates the varying thermo-physical properties around the critical point of water to convert and upgrade the organic content, as well as extract inorganics. This study provides a systematic evaluation to the process upscaling into energetically efficient commercial demonstration. Conceptual plant flowsheets for a lipid extracted algae feedstock were developed on Aspen plus® for 99.9% purity hydrogen fuel production. The advantageous reactor system configuration is integrated within a layout that includes subsequent power generation and gas purification. The process is coupled with a downstream steam reformer block to maximize the poly-generation of hydrogen fuel, power and thermal heat. To thermodynamically evaluate the plant designs, minimum process utility demands were computed with the pinc...

Enhanced biofuel processes utilizing separate lignin and carbohydrate processing of lignocellulose

Abstract: Enhanced biofuel production routes utilizing separate lignin and carbohydrate processing of lignocellulose are analyzed and compared with two conventional routes; the methanol and methane production via syngas from biomass. The enhanced processes studied are: hydrocarbons production by hydrogenation of biomass based sugars by hydrogen obtained from lignin gasification, and ethanol production by biomass hydrolysis and fermentation and conversion of residual lignin into methanol via syngas. The analysis of processes was done by rigorous flowsheet modeling including power production calculations and realistic heat integration and evaluation based on energy yield, greenhouse gas (GHG) reduction and net present value (NPV). The enhanced processes via separate lignin and sugar processing can run in two modes: either being energy self-sufficient or utilizing external low temperature heat and power. The processes can operate with high efficiency as ‘waste heat and power to gas and liquids’ processes for p...

Supercritical water gasification of biomass for hydrogen production Review

Abstract: The paper summarizes the recent developments in the field of supercritical water gasification (SCWG) of biomass. Chemical and chemical engineering studies are introduced and sorted into categories, which are the main factors influencing the chemical reaction pathways of SCWG. These are: the components of biomass (carbohydrates, lignin, ash, proteins and lipids), reaction conditions e.g. concentration and the possible addition of heterogeneous catalysts. Most studies focus on model compounds, here the interference of the components in mixtures give a deeper understanding in view of the conversion of real biomass. Also studies with biomass are reported; here in most cases the effect of salts, catalyzing hydrogen formation, is dominating. The progress in knowledge is evaluated in view of the hurdles to overcome for a wide industrial application. Recent paper hints to a future of hydrothermal gasification as part of a bio-refinery and with an internal use of hydrogen produced.