2 Dezember 2009

nova-Buchbesprechung: Outwitting the Dilemma of Scale

Cost and Energy Efficient Scale-down of the Fischer-Tropsch Fuel Production from Biomass.

In his book “Outwitting the Dilemma of Scale” the author Stefan Fürnsinn from the Vienna University of Technology shows a competent analysis on the current discussions on small-scale plants for the Fischer-Tropsch process for biomass conversion. He shows the needs for second generation biofuels due to the CO2 accumulation in the atmosphere and the security of supply of crude oil and natural gas and shows how FT-processes should help. To produce low-cost FT-biofuels he proposed a design small-scale production and disagrees with the concept that synfuel plants have to be of enormous scale to allow cost-competitive production.

Cover_Outwitting.jpgThe aim of this book is to show a concept for a small-scale and low-cost way to produce FT-biofuels. Stefan Fürnsinn discusses the state-of-the-art of the conventional Fischer-Trosch syntehsis process with a detailed economic assessment based on his reserch at the Vienna University of Technology and shows the problems and challenges of a biomass-based production. His assessment leads hin to a new concept of small-scale and low-cost design based on a normal pressure synthesis and ends with a comparison of his concept with the state-of-the-art FTS.

Presentation of the publisher
There is hardly any topic in the renewable energy sector that is as dynamic as the world of biofuels. Due to growing concerns about CO2 emissions, the importance of the transport sector in everybody’s life as well as concerns about security of fuel supply in Europe and the US biofuels are an interesting field of research. One of the most fascinating questions particularly in synthetic biofuels is the debate about the “ideal” scale of production plants. On the one hand, fossil fuel supply is based on large and centralized facilities, on the other, bioenergy systems are typically characterized by small and decentralized technologies. The question is: Which way to go in biomass-based Fischer-Tropsch fuel production? As the author disagrees with common wisdom that synfuel plants have to be of enormous scale to allow cost-competitive production, an unconventional and innovative process design is proposed that combines small-scale and low-cost fuel production. Consequently, the production based on “polygeneration” and a revival of the historic “normal pressure synthesis” could open the door to decentralized, biomass-based Fischer-Tropsch synfuel technology.

Abstract
As a result of increasing concerns about both CO2 accumulation in the atmosphere and security of supply of crude oil and natural gas especially in Europe, biofuels play an increasingly important role. In order to combine high fuel qualities with maximized yields per acre of land, so-called second-generation, synthetic biofuels have been identified as advantageous for the future. Fischer-Tropsch fuels which are obtained via biomass gasification and subsequent catalytic conversion of the syngas compounds H2 and CO are one highly promising technology in this field, since they offer two distinct advantages: compatibility with the existing infrastructure, both in
relation to vehicles and distribution channels, as well as outstanding fuel qualities that compare to and even exceed those of conventional fossil fuels.

Besides these benefits, Fischer-Tropsch fuel production costs have to be kept to a minimum so as to guarantee lowest possible CO2 avoidance costs. For this reason, it is commonly argued that FT-production facilities must be very large so as to take advantage of economies of scale, which lead to decreasing specific fixed costs with increasing plant size. However, at the same time there is great interest in small scale facilities, as there not only risks are minimized, regional development is enhanced, and flexibility is gained, but also CO2-savings are amplified. The latter is due to the fact that in smaller facilities, low temperature heat that is otherwise cooled off into the atmosphere, can be recovered and utilized for district heating purposes. Hence, small plants are generally attractive, but typically high production costs have hampered their success.

Given the advantages of small scale biofuel production, in this work the challenge of finding ways for a cost and energy efficient down-scale of the Fischer-Tropsch synthesis was taken on. As obviously the commonly employed FT-conversion system that is based on entrained-flow oxygen gasification is not applicable in the small scale, in a first step other gasification options were analyzed. As a result of the high hydrogen and low nitrogen content of the producer gas, steam gasification as realized in Guessing/Austria, was identified as most suitable. With adequate process design, including the introduction of the so-called “polygeneration” strategy that involves co-generating fuels, power and district heat, the production costs were reduced significantly.

However, full competitiveness with gigawatt-scale plants was not achieved. Thus, fast pyrolysis of biomass was investigated, as this way decentralization of the fuel production can be achieved. Furthermore, pyrolysis may serve as a means of using low-cost feedstocks that can otherwise not be converted directly in a gasification process. And indeed, the results obtained are highly promising. Still, many uncertainties remain especially with respect to the quality of pyrolysis oils produced from inferior raw materials. Finally, as a means of outwitting the dilemma of scale, a radical break with conventional downscaling approaches was introduced: In contrast to all previous attempts, which aim at optimizing syngas production so as to match the requirements of the coal-based Fischer-Tropsch technology, costs can be significantly cut if the opposite is done, i.e., the synthesis is actually adapted to the synthesis gas generation via atmospheric steam gasification. This implies a change in the pressure level of the FT-synthesis, which can be achieved through the “normal pressure synthesis”. Hence, an entirely atmospheric conversion chain results. In combination with a polygeneration product strategy, consequential improvements of the economic performance and the ecologic impact are accomplished. Thus, the scale-down to systems that preserve the advantages of small scale and are competitive with Gigawatt-scale plants was achieved.

Product details
Stefan Fürnsinn, 2009: Outwitting the Dilemma of Scale: Cost and Energy Efficient Scale-down of the Fischer- Tropsch Fuel Production from Biomass. VDM Verlag Dr. Müller, 592 pages, hardback, €79.00, ISBN 978-3-8364-5097-3

Source: VDM Verlag Dr. Müller, 2009

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