Issues Impacting Refractory Service Life in Biomass/Waste Gasification Page: 4 of 10
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New gasification projects which target fuel flexibility (i.e., the ability to process variable
feedstock) must take into consideration the anticipated ash fusion temperature, gasifier temperature,
and the type of gas feed desired for the turbine or chemical feedstock when designing their facilities [9].
With any carbon feedstock, the gasifier should be strategically located to minimize transportation costs
and maximize raw material availability. Other factors, such as those associated with carbon feedstock
processing (grinding and beneficiation), must also be considered because of equipment costs and
limitations. Interest has been gathering worldwide in the use of biomass, or other high carbon industrial
wastes, as gasifier feedstock for a number of reasons, including: 1) it is considered a renewable energy
source and helps meet Kyoto targets for reduced CO2 emissions [10,11]; 2) many types of biomass are
considered industrial wastes and have a disposal cost which helps offset the cost of gasification; and 3)
biomass is available in most parts of the industrial world, including developing countries that have no
coal or oil resources. Because significant issues remain with feedstock processing and ash
chemistry/refractory liner interactions [12], the gasification of biomass is still considered a developing
technology. The balance of this paper will focus on biomass and waste slag/refractory interactions.
BIOMASS AND WASTE GASIFICATION
Biomass is defined by Higman and van der Burgt [13] as any material that can be used as a
fuel, or as a raw material for a fuel, that is derived from a recently living organism - a definition that
excludes fossil fuels, but includes materials like agricultural and forestry wastes, black liquor, sewage
sludge, and animal refuse. A partial listing of biomass and waste feedstock is given in table 2. Although
not considered a major industrial fuel, biomass supplies 15-20 percent of the total fuel used in the
world, primarily as a heating and cooking source in non-industrialized countries [13].
Table 2 - Biomass and waste feedstock used in gasification
Biomass - Tree bark, timber block, sawdust, wood powder
- Crop residue, husk, straw, corn stalks, soy straw, rice hulls
- Coconut shell, ground nut shells, coffee husks, cocoa husks
- Cotton residues
- Palm oil shells, fibers, stems
- Animal meat and bone, poultry litter
- Black liquor
- Marine crops
Waste - Municipal solid landfill
- Industrial solid and liquid by-product
The severe operating environment created by the gasification of biomass and other high-carbon
waste materials creates a number of operational issues which limit the application of this technology.
These issues are summarized in table 3. The source of biomass or waste feedstock must be
consistently available in the quantity and consistency needed for gasification, with the additional
requirement that shipping distances for biomass should not be greater than 50 km from collection
points [14]. Gasifiers, such as those shown in figure 2, require a carbon feedstock with a high energy
density and with an appropriate particle size for feeding into the gasifier. A number of gasifier designs
have been developed that are capable of processing biomass, and are similar to those shown in figure
3. They can accommodate a coarse feedstock and are generally designed to operate at temperatures
below 900 C. The low gasification temperature is preferred for biomass and waste because of the low
melting point and highly aggressive nature of the residual ash, the reactivity of which increases with
temperature. To keep the biomass ash from melting, some fluidized bed reactors operate at
temperatures as low as 650 C. Fluidized bed reactors are also used instead of entrained flow gasifiers
because the short residence time (seconds) in entrained flow gasifiers can result in incomplete
combustion of the biomass. Tar formation, as mentioned earlier, is an issue in the low operating
temperature fluidized bed gasifiers, which results in clogged particle filters, impacts combustion
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Bennett, J. P.; Kwong, K. -S. & Powell, C. A. Issues Impacting Refractory Service Life in Biomass/Waste Gasification, article, March 1, 2007; Houston, Texas. (https://digital.library.unt.edu/ark:/67531/metadc891367/m1/4/: accessed May 5, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.