Tuesday, May 17, 2011

Why Bio-Energy Continues to Take a Backseat to Hydrocarbons

Society will require crucial transportation fuels for several more decades. Over that time period, synthetic fuels produced from renewable biomass will become more and more competitive with fuels derived from fossil fuel hydrocarbons. But for now, the infrastructure for biomass feedstock production and fuel processing is virtually nonexistent. And the economic justification for building and scaling that biomass fuels/chemicals infrastructure will require time to fall into place.
Researchers from the Stevens Institute of Technology, BASF Catalyst and Golden BioMass Fuels Corporation report on their investigation of an energy balance, in broad outline, for the production of a high-quality synthetic diesel from residual crop biomass via a Fischer-Tropsch route in a paper published in the ACS journal Energy & Fuels.
The particular process explored in the paper consists of:
harvesting surplus biomass (such as crop residue);
locally pyrolyzing the biomass into pyrolysis oil (PO), char, and noncondensable gas (NCG);
transporting the PO to a remote central processing facility;
converting the PO at this facility by autothermal reforming (ATR) into synthesis gas (CO and H2); and
Fischer–Tropsch (FT) synthesis of the syngas into diesel fuel.
...The team found that the process considered, in which a portion of the char and noncondensable gas are used to supply heat to the drying and pyrolysis steps and under the assumptions made, has an energy efficiency to liquid fuel on the order of 40%—i.e., 40% of the initial energy in the biomass will be found in the final liquid fuel after subtracting out external energy supplied for complete processing, including transportation as well as material losses.

...Using the process modelled, replacing ~15% of current petroleum consumption in the United States would require the gathering of biomass from a substantial portion of the land area of the major crop-producing states...
ACS Abstract of biomass FT study

Due to the relatively low energy density of biomass, a large growing area must be devoted to producing biomass feedstock for whichever energy densification and refining process is chosen.

The study above is based upon a reasonable process, and probably represents nearly the state of the art for biomass to diesel conversion at this time. Local pyrolytic densification of biomass allows for more efficient shipping to a central gasification and F-T catalytic refinery. It would not be a bad method of producing diesel except for one thing: It is much more economical at this time to use either crude oil using conventional refineries -- or even coal or natural gas, using F-T approaches.

Fischer-Tropsch technologies are improving for the use of either gas or coal as gasification feedstocks. Here are a few items from recent F-T news stories:

Altona Energy has inked a cooperation agreement for application of Rentech's technologies in gasification of coal and biomass at its Arckaringa project located in South Australia. [Keep in mind that the biomass component would not be included except for reasons of governmental mandate, rebate, or other top-down incentive. The biomass component is not yet economic when compared to coal.]

Jacobs to Collaborate on Commercialisation of BP/Davy Fischer Tropsch

Completed semi-commercial demonstration of the low temperature Fischer-Tropsch technology at Mossel Bay gas-to-liquids plant

Oxford Catalysts Moving Toward Commercial Launch

And so on... Fischer Tropsch is an old technology which is being improved and adapted for a wide range of feedstocks and syngas mixtures. Using biomass with F-T and other thermochemical processes is necessarily a second choice, after hydrocarbons, due to the energy density factor. If governmental incentives, regulations, taxes, mandates, rebates, etc. become so topheavy as to shift the economics toward biomass, a wide range of societal and economic repercussions would necessrily follow -- not all of them ultimately for the better.

Over time, alternative means of producing scalable volumes of advanced liquid fuels from biomass are being devised. Some of these methods are likely to achieve economic competitiveness with hydrocarbons, as the incentives landscape shifts and alters. In the long run, F-T is unlikely to survive as a viable process except for production of certain high value chemicals which are difficult to produce bio-synthetically (or bio/nano-synthetically) at lower temperatures and higher efficiencies.

Liquid fuels will be important to society for some decades, and high value industrial scale chemicals will be important for much longer.

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