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Unformatted text preview: Fig. 3 (a) Co-production of liquid FT transportation fuels and SNG from biomass;
(b) Production of FT liquids from biomass.
Boerrigter and Zwart have evaluated the co-production of 50 PJ of FischerTropsch transportation liquids and 150 PJ of SNG per year (i.e. 10% of the 2001 Dutch
consumption of these energy-carriers), leading to an annual CO2 emission
reduction of approximately 12.5 Mtonne. A part of the SNG in these concepts is
produced by methanation of the FT off-gas, which already contains significant amounts
of C1-C4 SNG compounds, however, the amount of SNG produced by methanation of
the off-gas is not sufficient to comply with the 150 PJ per year goal. Additional SNG
has to be produced either by "integrated co-production", in which a side-stream of the
product gas of the gasifier is used for dedicated methanation (figure 4a), or by "parallel
co-production", in which part of the biomass is fed to a second gasifier coupled to a
dedicated stand-alone methanation reactor (figure 4b). Operating the FT-synthesis at
conditions where more SNG is produced at the cost of transportation fuels is not
desirable (from both economic and product quality viewpoints). ECN-RX--04-085 8 FT liquids
Biomass Methanation Gasification SNG
(a) FT liquids
Gasification #1 FT synthesis Methanation Biomass SNG
Gasification #2 Methanation
(b) Fig. 4 (a) integrated co-production of FT liquids and SNG; (b) parallel co-production
of FT liquids and SNG.
In general, pressurised O2-blown CFB gasification and atmospheric indirect
steam-blown gasification are identified to be the most suitable technologies for coproduction (figure 5), with CO2 reduction costs in the range of the energy tax
exemption for “green power” in the Netherlands of 100 €/tonne. The overall
efficiencies (FT liquids plus SNG) are higher for CFB and indirect gasification
concepts compared to EF gasification as already much CH4 and C2 compounds are
present in the product gas. On the other hand, the efficiency to FT l...
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- Spring '08
- Chemical Engineering