Hot Gas Conditioning: Recent Progress with Larger-Scale Biomass Gasification Systems; Update and Summary of Recent Progress Page: 47 of 103
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need for a separate sulfur-removal step. Since raw biomass gases are generally deficient in
hydrogen, water shift gas reactions would adjust the H2/CO ratio. Following scrubbing to
remove CO2 and acid gases, the final synthesis gas would be converted using commercial
technologies.
Experimental data has also been collected for biomass systems. In bench-scale tests using
commercial nickel-based catalysts, it has been reported (Berg, et al, 1997) that steam
reforming over nickel catalysts can potentially be effective even in the presence of some
sulfur-containing species. In these tests, hydrogen sulfide present at levels of 100 and 200
ppm partially deactivated the catalyst, but activity could be retained in part by increasing
the reaction temperature.
Related work on steam reforming of biomass gas for production of hydrogen has been
reported (Czernik, et al, 2000; 1999). Pyrolysis products similar to tars from biomass
gasifiers were vaporized and reacted with steam over a nickel-based catalyst (U91) used
commercially in the reforming of natural gas. In bench-scale experiments, yields
approached 80% of the theoretical value with some carbon formation on the catalyst surface.
In biomass gasification systems, the amounts of tar would be significantly lower than in the
reported system, which had different goals. However, the work suggests that shifting the
biomass gas and dealing with residual amounts of tar in the product gas is potentially
feasible using commercial catalysts.
Recent interest has also been expressed in the use of biomass thermal gasification to provide
a hydrogen-rich fuel gas for fuel cells (see, for example, Amos, 1998). The issues of gas
cleanup are closely related to those of producing a synthesis quality product. Removal of
particulates and tar from the gas stream is essential, and reforming of the gas is also
required. Care must also be exercised to ensure low sulfur content in the fuel gas. The
overall compatibility of the gasification and fuel cell technologies has not been well
characterized, but the gas cleanup demands of the fuel cells will likely be similar in
magnitude to those for synthesis gases. Fuel cell requirements are discussed more in
Section 4 of this report.
While the production of fuels and chemicals from biomass synthesis gases is technically
feasible, the economic feasibility is more difficult. The subject of integrated biomass
gasification systems for synthesis gas and for hydrogen production with fuel cells is
discussed in more detail in Section 4 of this report.
3.4 Survey of Biomass Gas Conditioning Technologies
As part of the ongoing IEA Bioenergy Agreement Task on biomass gasification (IEA
Bioenergy, 2000), a survey of technologies available for biomass gas conditioning was
developed in 1999. The survey was developed for participants to distribute to industries in
their own countries. The responses were to be used to develop a listing of available
technologies and the companies capable of providing them. As the IEA Bioenergy Task
proceeded, it was decided that a world-wide compilation of the capabilities of individual
companies was lower priority than other efforts, and the survey was not widely distributed.
The survey developed through that effort is attached to this document as Appendix A and
can freely be distributed if individuals wish to compile a directory of capabilities for their
own country.34
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Stevens, D. J. Hot Gas Conditioning: Recent Progress with Larger-Scale Biomass Gasification Systems; Update and Summary of Recent Progress, report, September 1, 2001; Golden, Colorado. (https://digital.library.unt.edu/ark:/67531/metadc715374/m1/47/: accessed April 27, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.