Energy flow in the bioliq process based on the stoichiometric reaction equations. Source: Henrich et al. Click to enlarge.

Bioliq is a three-stage process, envisioning the use of distributed fast pyrolysis (FP) plants in combination with a large centralized gasification and fuel production facility. Biomass is pyrolized to a pyrolysis oil. The pyrolysis oil is mixed with pyrolysis coke from the process to create a biocrude slurry for transport and subsequent gasification to syngas and subsequent catalytic conversion to chemicals and/or fuels.

A key technology in the process is the centralized oxygen-blown, slagging-entrained flow gasifier operating at high pressure above the downstream synthesis pressure to avoid expensive intermediate syngas compression, according to FZK. The reaction chamber is enclosed by a membrane wall, cooled with pressurized water and can accommodate feed with much ash. Because of the high gasification temperature (above ca. 1,200 °C), the raw syngas is practically tar-free and has a low CH₄ content; thus simplifying downstream syngas cleaning.

In principle, they note, any pumpable fluid feed, which can be pneumatically atomized with oxygen and has a heating value above 10 MJ/kg, is suited as the feed for the entrained flow gasifier feed. The pre-conversion of biomass into the biosyncrude slurry via the distributed FP plants increases the feedstock flexibility considerably. The biosyncrude is well suited for energy-dense storage and transport, resulting in lower transportation costs and large biomass delivery areas.

Because of the complex technology to be applied, BTL plants for biosynfuel production can only be economic in large facilities, the researchers say. Furthermore, given the limitations on biomass conversion to biosynfuel, the FZK team sees an ongoing role for coal and natural gas derived synthetic fuels, likely combined with BTL in very large integrated XTL complexes.

The energy efficiency of biomass conversion to biosynfuel via syngas as intermediate is only about 40%. A substitution of the present 2008 global motor fuel consumption of 2 Gtoe/a would therefore require a biomass harvest of 4 Gtoe/a. This is four times the present global bioenergy consumption of 1 Gtoe/a and will probably be at the limit of a sustainable level. In view of the still-growing motor fuel consumption and many other competitive uses of biomass, a complete substitution of fossil motor fuels by biosynfuel is not only rather unlikely but almost impossible. A sufficient and sustainable long-term supply with liquid hydrocarbon fuels seems possible only for special applications where liquid fuels are hard to replace e.g., as aviation fuel. This sustainable level probably is less than a quarter of the future transportation energy consumption.

It is therefore likely, that during the inevitable development and transition to new transportation techniques, the still-abundant coal and also natural gas reserves will play an important intermediate role for several decades. Corresponding CTL and GTL technologies for oil substitution are available already today and can be combined with BTL technology in huge and more economic mixed XTL complexes.

...In a BTL plant, practically all biocarbon can be converted into biosynfuel in an environmentally safe way, if the required additional H₂ is supplied from other sources, e.g., via coal gasification, and the produced fossil CO₂ is completely disposed of with little additional technical effort. The biosynfuel production can at least be doubled in this way and the huge XTL complex can contribute via the economy of scale. The Karlsruhe bioliq concept is well suited for large XTL concepts with mixed feedstock.

—Henrich et al. (2009)

Resources

• Edmund Henrich, Nicolaus Dahmen and Eckhard Dinjus, (2009) Cost estimate for biosynfuel production via biosyncrude gasification. Biofuels, Bioprod. Bioref. 3:28–41 doi: 10.1002/bbb.126