Gasification of liquids derived from Direct Thermochemical Liquefaction

Mar 2024

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Biomass residues and waste streams can be used as feedstock for direct thermochemical liquefaction (DTL) technologies to produce a renewable energy carrier in liquid form. DTL techniques include Fast Pyrolysis to produce Fast Pyrolysis Bio-Oil (FPBO) and hydrothermal (or solvent) liquefaction (HTL) for the production of biocrudes.

Gasification of DTL-oils and by-products for the production of renewable fuels, chemicals and materials through the syngas intermediate platform allows the utilization of biomass residues in current (refinery) processes. While direct gasification of biomass residues and waste streams to syngas is also intensively investigated and implemented on commercial scale, the gasification of DTL-oils can have some distinct advantages from a logistic, economic, and technical point of view.

In this report, produced in the frame of IEA Bioenergy Task 34 (Direct Thermochemical Liquefaction), an overview is presented on the status of DTL-oil gasification on pilot- and demo-scale (TRL ≥ 5). Moreover, potential alternatives such as the gasification of DTL by-products and hybrid gasification systems are briefly discussed. Finally, the requirements for standards and analysis methods are shortly assessed and an outlook for the future potential of DTL-oil gasification is given.

While a lot of combinations of liquefaction and gasification technologies can be considered, only the use of FPBO (slurry) in entrained flow gasifiers has been tested on MW scale. Based on the results published in open literature the technical feasibility of the route can be considered as a rather low-risk option. Gasification as such is a technology that is widely implemented in refinery operations worldwide and DTL oils are not considered technologically challenging to be applied as feedstock. The syngas product composition depends on the fuel and applied gasification technology, but generally the dry gas contains 25-50% H2, 25-45% CO and 20-30% CO2, which is similar to the gas obtained by direct biomass gasification. The energy efficiency of the DTL-oil gasification is comparable to direct biomass gasification. The main hurdles which need to be taken is to establish the commercial viability of the route and to increase the availability of DTL-oil (market size). To establish a viable business case, the potential advantages of DTL-oil gasification should outweigh the costs of the added liquefaction step.

  • For gasification processes the scale of operation is a very important factor in the economic feasibility; large scale installations of several hundred MW input are desired to minimize the production costs. The feedstock quantity required at a single location – particularly low energy-density biomass residues and waste streams – however is challenging to secure. Decentralized conversion of the low-energy-density feedstocks in DTL-oils is a way to improve the logistics of the value chain, improving the economic feasibility as well as limiting the GHG emission during transport.
  • From a technical point of view, the initial conversion by DTL is advantageous as the liquid can be fed more-easily in a pressurized gasifier compared to a solid fuel. Depending on the process details, the inorganic contaminants (ash) present in biomass residues and waste streams can be separated during DTL as well, avoiding expensive technical solutions to deal with these components in the gasifier (slag formation) and gas cleaning systems. Furthermore, DTL-oils are much more uniform compared to the original biomass residues and wastes, allowing a single gasifier unit to operate on various feedstocks at the same time.

Combining the gasification process with water electrolysis to form a hybrid process, in which oxygen from electrolysis is used as oxidant in the gasifier and hydrogen is added to the syngas before product synthesis, could provide an optimal synergy between the simultaneous production of advanced biofuels and e-fuels.

Currently there is no fuel standard for DTL-oils to be used as feedstock for gasifiers. Based on the experience with DTL oil gasification an indicative list of quality parameters is suggested in the report as input for future standardization activities. Specific attention needs to be paid to the suitability of analysis standards in combination with the complex nature of DTL-oils.

Figure: bioliq® process flowsheet. Source: Karlsruhe Institute of Technology.