Abstract
Energy from biomass is a CO{sub 2} neutral, sustainable form of energy. Anaerobic digestion is an established technology for converting biomass to biogas, which contains around 60% methane, besides CO{sub 2} and various contaminants. Most types of biomass contain material that cannot be digested; in woody biomass, this portion is particularly high. Therefore, conventional anaerobic digestion is not suited for the production of biogas from woody biomass. While wood is already being converted to energy by conventional thermal methods (gasification with subsequent methanation), dung, manure, and sewage sludge represent types of biomass whose energy potential remains largely untapped (present energetic use of manure in Switzerland: 0.4%). Conventional gas phase processes suffer from a low efficiency due to the high water content of the feed (enthalpy of vaporization). An alternative technology is the hydrothermal gasification: the water contained within the biomass serves as reaction medium, which at high pressures of around 30 MPa turns into a supercritical fluid that exhibits apolar properties. Under these conditions, tar precursors, which cause significant problems in conventional gasification, can be solubilized and gasified. The need to dry the biomass prior to gasification is obsolete, and as a consequence high thermal process efficiencies (65 - 70%)
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Citation Formats
Waldner, M H.
Catalytic hydrothermal gasification of biomass for the production of synthetic natural gas[Dissertation 17100].
Switzerland: N. p.,
2007.
Web.
Waldner, M H.
Catalytic hydrothermal gasification of biomass for the production of synthetic natural gas[Dissertation 17100].
Switzerland.
Waldner, M H.
2007.
"Catalytic hydrothermal gasification of biomass for the production of synthetic natural gas[Dissertation 17100]."
Switzerland.
@misc{etde_21318461,
title = {Catalytic hydrothermal gasification of biomass for the production of synthetic natural gas[Dissertation 17100]}
author = {Waldner, M H}
abstractNote = {Energy from biomass is a CO{sub 2} neutral, sustainable form of energy. Anaerobic digestion is an established technology for converting biomass to biogas, which contains around 60% methane, besides CO{sub 2} and various contaminants. Most types of biomass contain material that cannot be digested; in woody biomass, this portion is particularly high. Therefore, conventional anaerobic digestion is not suited for the production of biogas from woody biomass. While wood is already being converted to energy by conventional thermal methods (gasification with subsequent methanation), dung, manure, and sewage sludge represent types of biomass whose energy potential remains largely untapped (present energetic use of manure in Switzerland: 0.4%). Conventional gas phase processes suffer from a low efficiency due to the high water content of the feed (enthalpy of vaporization). An alternative technology is the hydrothermal gasification: the water contained within the biomass serves as reaction medium, which at high pressures of around 30 MPa turns into a supercritical fluid that exhibits apolar properties. Under these conditions, tar precursors, which cause significant problems in conventional gasification, can be solubilized and gasified. The need to dry the biomass prior to gasification is obsolete, and as a consequence high thermal process efficiencies (65 - 70%) are possible. Due to their low solubility in supercritical water, the inorganics that are present in the biomass (up to 20 wt % of the dry matter of manure) can be separated and further used as fertilizer. The biomass is thus not only converted into an energy carrier, but it allows valuable substances contained in the biomass to be extracted and re-used. Furthermore, the process can be used for aqueous waste stream destruction. The aim of this project at the Paul Scherrer Institute was to develop a catalytic process that demonstrates the gasification of wet biomass to synthetic natural gas (SNG) in a continuously operating plant on a laboratory scale (throughput 1 kg/hr, which yields about 200 L{sub SNG}/hr with a thermal heating power of 1 kW{sub th} for a feed concentration of 40 wt %). Ideally, the pilot plant should be capable of conveying solid containing slurries. Various catalysts were selected (some of them were synthesized in-house) and tested for their stability under hydrothermal conditions and for their tolerance towards inorganic salts (sulfate was chosen as model substance for these tests). The catalysts were characterized by numerous techniques (such as TG/FTIR, TPO/TPR, TOC, BET, XRD, XPS, ICP, TEM, HAADF-STEM, and SEM-EDXS). The biomass was analyzed for its constituents in order to get a reliable estimate of its energy content, which is essential for the calculation of the process economics. The lower heating value of concentrated swine manure was found to be 16.3 MJ/kg{sub dry} {sub matter}. Skeletal nickel catalysts, which are widely used in the industry due to their attractive price, gasified wood suspensions (conc. 10 - 30 wt %) in a batch reactor completely to SNG. The methane yield was 0.33 g{sub CH{sub 4}}/ g{sub wood,} {sub dry}, which corresponds to the maximum yield governed by thermodynamics. Manure suspensions were also gasified in the hydrothermal environment. The highest methane yield achieved was only 0.21 g{sub CH{sub 4}}/ g{sub dry,} {sub matter}, which is 80% of the maximum yield by thermodynamics. The reason for this were the salts present in the manure, which had not been separated before the experiments and caused the deactivation of the catalyst. Thus, the importance of an integrated salt separator in a demonstration plant cannot be emphasized enough. The most promising catalyst systems (nickel, ruthenium) were tested for their activity and stability in the hydrothermal environment in a continuously operating test rig, where due to the applied pump only liquids could be fed. A mixture of five organic substances (formic and acetic acid, ethanol, phenol, and anisole) that approximates hydrolyzed wood served as feed. The skeletal nickel catalysts turned out to be active but not stable, as they deactivated within a few hours. The attempt to stabilize them by co-doping of other metals (Ru, Mo, Cu) was not successful. Ru/TiO{sub 2} was not active enough, but Ru/C completely gasified the mixture at high space velocities over a period of more than 200 hours; the product gas composition corresponded at all times to the thermodynamic equilibrium composition. This catalyst was tested for its tolerance towards sulfate, which turned out to be low: the addition of a few ppm to the feed led to a deactivation within hours. The deactivation mechanism was identified as chemical poisoning. The poisoning species which is present in situ in the hydrothermal environment (sulfate vs. sulfide) is not clear. The experimental evidence can be explained by both hypotheses. A heating system for quartz capillaries rendered the visual examination of hydrothermal processes possible. Due to the required low amounts of feed material (a few hundred milligrams) and frequent capillary explosions, the usage of the system was discontinued. The conveying of solid containing slurries on the laboratory scale turned out to remain an unsolved problem. Thus, only liquid type biomass can be fed with the process demonstration unit that was built. A suitable feedstock was found with palm oil pyrolysis condensate, a problematic waste stream very common in Indonesia, that has a high organic content (exceeding 40 wt %). Preliminary gasification experiments with ethanol and salt separation experiments with sodium sulfate were successful. (author)}
place = {Switzerland}
year = {2007}
month = {Jul}
}
title = {Catalytic hydrothermal gasification of biomass for the production of synthetic natural gas[Dissertation 17100]}
author = {Waldner, M H}
abstractNote = {Energy from biomass is a CO{sub 2} neutral, sustainable form of energy. Anaerobic digestion is an established technology for converting biomass to biogas, which contains around 60% methane, besides CO{sub 2} and various contaminants. Most types of biomass contain material that cannot be digested; in woody biomass, this portion is particularly high. Therefore, conventional anaerobic digestion is not suited for the production of biogas from woody biomass. While wood is already being converted to energy by conventional thermal methods (gasification with subsequent methanation), dung, manure, and sewage sludge represent types of biomass whose energy potential remains largely untapped (present energetic use of manure in Switzerland: 0.4%). Conventional gas phase processes suffer from a low efficiency due to the high water content of the feed (enthalpy of vaporization). An alternative technology is the hydrothermal gasification: the water contained within the biomass serves as reaction medium, which at high pressures of around 30 MPa turns into a supercritical fluid that exhibits apolar properties. Under these conditions, tar precursors, which cause significant problems in conventional gasification, can be solubilized and gasified. The need to dry the biomass prior to gasification is obsolete, and as a consequence high thermal process efficiencies (65 - 70%) are possible. Due to their low solubility in supercritical water, the inorganics that are present in the biomass (up to 20 wt % of the dry matter of manure) can be separated and further used as fertilizer. The biomass is thus not only converted into an energy carrier, but it allows valuable substances contained in the biomass to be extracted and re-used. Furthermore, the process can be used for aqueous waste stream destruction. The aim of this project at the Paul Scherrer Institute was to develop a catalytic process that demonstrates the gasification of wet biomass to synthetic natural gas (SNG) in a continuously operating plant on a laboratory scale (throughput 1 kg/hr, which yields about 200 L{sub SNG}/hr with a thermal heating power of 1 kW{sub th} for a feed concentration of 40 wt %). Ideally, the pilot plant should be capable of conveying solid containing slurries. Various catalysts were selected (some of them were synthesized in-house) and tested for their stability under hydrothermal conditions and for their tolerance towards inorganic salts (sulfate was chosen as model substance for these tests). The catalysts were characterized by numerous techniques (such as TG/FTIR, TPO/TPR, TOC, BET, XRD, XPS, ICP, TEM, HAADF-STEM, and SEM-EDXS). The biomass was analyzed for its constituents in order to get a reliable estimate of its energy content, which is essential for the calculation of the process economics. The lower heating value of concentrated swine manure was found to be 16.3 MJ/kg{sub dry} {sub matter}. Skeletal nickel catalysts, which are widely used in the industry due to their attractive price, gasified wood suspensions (conc. 10 - 30 wt %) in a batch reactor completely to SNG. The methane yield was 0.33 g{sub CH{sub 4}}/ g{sub wood,} {sub dry}, which corresponds to the maximum yield governed by thermodynamics. Manure suspensions were also gasified in the hydrothermal environment. The highest methane yield achieved was only 0.21 g{sub CH{sub 4}}/ g{sub dry,} {sub matter}, which is 80% of the maximum yield by thermodynamics. The reason for this were the salts present in the manure, which had not been separated before the experiments and caused the deactivation of the catalyst. Thus, the importance of an integrated salt separator in a demonstration plant cannot be emphasized enough. The most promising catalyst systems (nickel, ruthenium) were tested for their activity and stability in the hydrothermal environment in a continuously operating test rig, where due to the applied pump only liquids could be fed. A mixture of five organic substances (formic and acetic acid, ethanol, phenol, and anisole) that approximates hydrolyzed wood served as feed. The skeletal nickel catalysts turned out to be active but not stable, as they deactivated within a few hours. The attempt to stabilize them by co-doping of other metals (Ru, Mo, Cu) was not successful. Ru/TiO{sub 2} was not active enough, but Ru/C completely gasified the mixture at high space velocities over a period of more than 200 hours; the product gas composition corresponded at all times to the thermodynamic equilibrium composition. This catalyst was tested for its tolerance towards sulfate, which turned out to be low: the addition of a few ppm to the feed led to a deactivation within hours. The deactivation mechanism was identified as chemical poisoning. The poisoning species which is present in situ in the hydrothermal environment (sulfate vs. sulfide) is not clear. The experimental evidence can be explained by both hypotheses. A heating system for quartz capillaries rendered the visual examination of hydrothermal processes possible. Due to the required low amounts of feed material (a few hundred milligrams) and frequent capillary explosions, the usage of the system was discontinued. The conveying of solid containing slurries on the laboratory scale turned out to remain an unsolved problem. Thus, only liquid type biomass can be fed with the process demonstration unit that was built. A suitable feedstock was found with palm oil pyrolysis condensate, a problematic waste stream very common in Indonesia, that has a high organic content (exceeding 40 wt %). Preliminary gasification experiments with ethanol and salt separation experiments with sodium sulfate were successful. (author)}
place = {Switzerland}
year = {2007}
month = {Jul}
}