The Role of Inorganics in Biomass Gasification: Catalytic Effects on Char Reactions and Toxic Emissions
Kramb, Jason (2017)
Tampere University of Technology
2017
Luonnontieteiden ja ympäristötekniikan tiedekunta - Faculty of Science and Environmental Engineering
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Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-15-3897-1
https://urn.fi/URN:ISBN:978-952-15-3897-1
Tiivistelmä
This thesis studied the role of inorganic elements in biomass gasification, focusing on catalytic effects in char gasification and removal of toxic metals from the product gas. A combination of experimental, including gasification using thermogravimetric analysis and fluidized beds, and modeling techniques were used.
Spruce and birch woods were leached of the naturally occurring ash forming elements and loaded with varying amounts of calcium or potassium. These woods were then gasified in either an isothermal thermogravimetric analysis device or a bubbling fluidized bed reactor. In the case of the spruce wood gasified using the thermogravimetric analysis device, char conversion models were evaluated against the measured data and an empirical model was developed which uses the concentration of calcium and potassium in wood to predict the conversion rate behavior of the char when gasified in CO2 . The results from the fluidized bed gasification tests of birch wood showed that calcium was the primary active catalyst in the wood and the increased reactivity resulting from calcium doping was clear even in the much larger scale of a fluidized bed compared to the thermogravimetric analysis. The potassium doped samples did not exhibit increased reactivity in the fluidized bed due a nonreactive layer of secondary char being deposited on the char surface.
The behavior of arsenic in the product gas of chromated-copper arsenate wood was modeled using equilibrium calculations and measured experimentally in a bubbling fluidized bed. The equilibrium model accurately predicted that the product gas could be cleaned by cooling the gas below 260°C and filtering to remove condensed arsenic.
While there are methods for modeling the effects of inorganics in catalyzing char gasification, further research into interconnected issues of surface area, pore sizes, pyrolysis conditions and inorganic concentrations is needed. Similarly, while equilibrium modeling has been shown to predict the behavior of arsenic during gasification in some cases, there are many gaps in understanding which arsenic compounds are most relevant.
Spruce and birch woods were leached of the naturally occurring ash forming elements and loaded with varying amounts of calcium or potassium. These woods were then gasified in either an isothermal thermogravimetric analysis device or a bubbling fluidized bed reactor. In the case of the spruce wood gasified using the thermogravimetric analysis device, char conversion models were evaluated against the measured data and an empirical model was developed which uses the concentration of calcium and potassium in wood to predict the conversion rate behavior of the char when gasified in CO2 . The results from the fluidized bed gasification tests of birch wood showed that calcium was the primary active catalyst in the wood and the increased reactivity resulting from calcium doping was clear even in the much larger scale of a fluidized bed compared to the thermogravimetric analysis. The potassium doped samples did not exhibit increased reactivity in the fluidized bed due a nonreactive layer of secondary char being deposited on the char surface.
The behavior of arsenic in the product gas of chromated-copper arsenate wood was modeled using equilibrium calculations and measured experimentally in a bubbling fluidized bed. The equilibrium model accurately predicted that the product gas could be cleaned by cooling the gas below 260°C and filtering to remove condensed arsenic.
While there are methods for modeling the effects of inorganics in catalyzing char gasification, further research into interconnected issues of surface area, pore sizes, pyrolysis conditions and inorganic concentrations is needed. Similarly, while equilibrium modeling has been shown to predict the behavior of arsenic during gasification in some cases, there are many gaps in understanding which arsenic compounds are most relevant.
Kokoelmat
- Väitöskirjat [4865]