Dutch Researchers Conclude Large-Scale Biomass-to-Liquids Processing Can be Economically Feasible Even with Imported Feedstock
|General schematic lineup of the complete integrated system for FT crude production from pretreated biomass. Click to enlarge.|
Europe is working with a long-term vision of having 30% or more of the total transportation fuels consumption of the EU-25 come from biofuels by 2040.
Asserting that one of the most promising options for producing the requisite fuel is the Fischer-Tropsch synthesis of biomass feedstocks (Biomass-to-Liquids, BTL), and noting that much of that feedstock would need to be imported to Europe, three Dutch researchers evaluated the impact of pretreatment of biomass on the feasibility of overseas biomass conversion to FT products.
Syngas can be produced from biomass by either noncatalytic high-temperature entrained-flow (EF) or catalytic low-temperature gasification technologies. Unlike the already widely demonstrated high-temperature EF gasification technology, the catalytic technologies do not yet exist commercially. Furthermore, they include two conversion steps, making them more expensive. However, most importantly, they are not fuel-flexible, which is considered to be of vital importance in the case of large-scale production facilities.
The EF gasification technology is therefore identified as the optimum process for the production of syngas from a variety of solid biomass streams, for example, woody biomass, and straw and grassy material.
Pre-treatment of biomass allows the efficient feeding of the feedstock into an entrained flow gasifier, and thus is an important part of such a BTL process. In an import scenario, however, it offers the additional important benefit of reducing transport costs by densification.
The team assessed 10 different BTL production routes from overseas biomass to the FT product in Rotterdam on the basis of different pretreatment options: chipping, pelletization, torrefaction, and pyrolysis.
They concluded that pretreatment of the biomass at the front end of the BTL route significantly increases the economic feasibility and that overseas torrefaction is the most attractive pretreatment option.
Torrefaction is a process that slowly heats biomass in an inert atmosphere to a maximum temperature of 300° C. The treatment yields a solid uniform product with a lower moisture content and a higher energy content compared to those in the initial biomass.
They also found that dedicated overseas pretreatment (i.e., torrefaction and pyrolysis) is more attractive than conventional pelletization. A large-scale, central, overseas BTL synthesis plant would be the most attractive route for BTL production—only the finished product would be shipped.
However, local logistic aspects require the construction of several small-scale synthesis plants, causing significant economical disadvantages due to economy of scale, according to the researchers.
They calculated that the final FT product can be produced from overseas biomass for €15/GJ (US$19/GJ) (or €0.55/liter (US$2.65/gallon) of diesel equivalent). They conclude that at crude oil prices of around $60/bbl, large-scale BTL is economically feasible.
“The Impact of Biomass Pretreatment on the Feasibility of Overseas Biomass Conversion to Fischer-Tropsch Products”; Robin W. R. Zwart, Harold Boerrigter, and Abraham van der Drift; Energy Fuels, 20 (5), 2192 -2197, 2006. 10.1021/ef060089f S0887-0624(06)00089-2