Pekka Simell - Academia.edu (original) (raw)

Papers by Pekka Simell

Research paper thumbnail of Closing energy cycle: Power-to-Methanol and Methanol-to-Power

Research paper thumbnail of Pure aromatics from biomass

Research paper thumbnail of Experimental Bench-Scale Study of Residual Biomass Syngas Desulfurization Using ZnO-Based Adsorbents

Energy & Fuels, 2020

Dry-bed adsorptive desulfurization of biomass-based syngas with a low-to medium sulfur content us... more Dry-bed adsorptive desulfurization of biomass-based syngas with a low-to medium sulfur content using ZnO was studied as an alternative to conventional wet-scrubbing processes for a small-to medium-scale biomass-to-liquid process concept. Following laboratory-scale long-term H 2 S breakthrough experiments in a previous study, desulfurization tests were scaled-up to bench-scale with actual bio-syngas to verify the lab-scale results under more realistic process conditions. A desulfurization unit was constructed and connected to a steam-blown atmospheric pilot-scale fluidized bed gasifier. Two successful 70+ h test campaigns were conducted with H 2 S removal below the breakthrough limit using full-sized ZnO adsorbent particles. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy elemental analysis, and Brunauer−Emmett−Teller (BET) surface area characterization of the fresh and spent adsorbent pellets were performed. SEM micrographs displayed the outward enlarging particle size in the sulfided layer. Characterization showed significant core−shell sulfidation behavior with a few hundred micron-thick sulfided layer leaving the majority of ZnO unutilized. Adsorbents lost most of their porosity in use, which was evident from BET surface area results. Simultaneous COS removal was found possible by the hydrolysis reaction to H 2 S. Furthermore, evidence of minor chlorine adsorption was found, thus highlighting the need for a dedicated HCl removal step upstream of desulfurization.

Research paper thumbnail of Method and Process for Cleaning a Productgas of a Gasification Reactor

Research paper thumbnail of Method for the purification of gasification gas

Research paper thumbnail of Effect of pressure on tar decomposition activity of different bed materials in biomass gasification conditions

Fuel, 2015

h i g h l i g h t s The tested bed materials were sand, dolomite, MgO, olivine and olivine/kaolin... more h i g h l i g h t s The tested bed materials were sand, dolomite, MgO, olivine and olivine/kaolin. Dolomite and MgO had the highest tar decomposing activities. The catalytic activities of dolomite and MgO reduced with increasing pressure.

Research paper thumbnail of High Efficiency Biomass to Power Operation Experiences and Economical Aspects of the Novel Gasification Process

15th European Biomass Conference and Exhibition, from Research to Market Deployment. Berlin 2007

Research paper thumbnail of Synthesis Gas Characterization at VTT laboratories and test facilities

Research paper thumbnail of Behaviour of tars on the filter in high temperature filtration of biomass-based gasification gas

Fuel, 2015

Abstract Behaviour of tars in high temperature filtration was studied at atmospheric pressure in ... more Abstract Behaviour of tars in high temperature filtration was studied at atmospheric pressure in steam and air/steam gasification conditions. Wood pellets and bark pellets were used as feedstock and silica sand and dolomite (Myanit B) as bed materials. Experiments were carried out in a bench-scale bubbling fluidised-bed gasifier coupled with a hot gas filter unit. Interestingly, it was found that filter could act, in a sense, as a prereformer when it was operated at 800 °C. The total amount of tars in the gas was reduced on the filter in all tests regardless of the used feedstock, bed material or gasifying agent. Highest reduction, in the order of 50 wt% of total tars, was obtained in steam gasification tests when dolomite was used as bed material. It was concluded that the changes in tars are derived from thermal tar reactions due to long residence time at high temperature on the filter but also from catalytic reactions induced by the presence of unreacted biomass char and carry-over dolomite on the filter surface. Tar reduction on the high temperature filter could be beneficial for downstream units and improve their operability, especially the reformer where the lower tar level could reduce coking tendency on the catalyst.

Research paper thumbnail of Effect of process conditions on tar formation from thermal reactions of ethylene

Fuel, 2015

ABSTRACT Thermal reactions of ethylene were studied to understand better the effect of process co... more ABSTRACT Thermal reactions of ethylene were studied to understand better the effect of process conditions on tar formation in biomass gasification. The effects of pressure, residence time and temperature on thermal reactions of ethylene were studied. The analysis of products from methane up to pyrene was performed by the novel online GC method. Ethylene conversion increased linearly as a function of pressure and residence time. Tar formation increased exponentially in the pressure range 1–3.5 bar and linearly with the residence time. The fraction of heavier tar compounds was found to increase with temperature and pressure. The tar composition was compared with different biomass gasification tar compositions, and the compositions were found to resemble each other. The obtained tar-laden product gas could be used as a realistic tar model when the cleaning of biomass gasification gas is studied.

Research paper thumbnail of Clean syngas from biomass—process development and concept assessment

Biomass Conversion and Biorefinery, 2014

This paper summarises the long development work done at VTT for gas clean-up for various synthesi... more This paper summarises the long development work done at VTT for gas clean-up for various synthesis applications. The development work has covered the most challenging and costly steps in biomass gasification based processes: high-temperature gas filtration and reforming of hydrocarbon gases and tars. The tar content of product gas is one of the main factors defining the temperature window in which the hot-gas filter can be operated, which in the case of fluidized-bed gasification is at 350–500 °C. Research is ongoing to achieve higher and thus more economical operation temperatures. Optimal operation of a catalytic reformer can be achieved by using a staged reformer where zirconia-based catalysts are used as a pre-reformer layer before nickel and/or precious metal-based catalyst stages. The temperature of the reformer is optimally increased in subsequent stages from 600 up to 1,000 °C. According to the techno-economic analysis, increasing the hot-gas filtration temperature by 300 °C or methane conversion in the reformer from 55 to 95 % both lead to about 5 % reduction the liquid fuel production cost.

Research paper thumbnail of Steam reforming of pyrolysis oil aqueous fraction obtained by one-step fractional condensation

International Journal of Hydrogen Energy, 2015

The aqueous fraction of pyrolysis oil, which was produced and fractionally condensed in VTT's 20 ... more The aqueous fraction of pyrolysis oil, which was produced and fractionally condensed in VTT's 20 kg/h fast pyrolysis Process Development Unit, was successfully steam reformed in a fixed-bed reactor over a commercial nickel catalyst without any additional steam. As a result of the one-step fractionation process, the aqueous pyrolysis oil, which had a water content of 72.7 wt%, contained only limited amounts of thermally unstable sugar-type compounds that typically hinder the performance of catalytic steam reforming. An average hydrogen yield of 81% was achieved over two hours at relatively mild process conditions: 650 C, steam-to-carbon ratio of 3.84 and gas hourly space velocity of 5000 h À1. When the reaction temperature was varied between 600 and 750 C, clear catalyst deactivation was only observed at 600 C. In theory, by utilizing the one-step fractional condensation scheme and subsequently steam reforming the aqueous pyrolysis oil, sufficient amounts of hydrogen could be generated for significantly deoxygenating the organic pyrolysis oil via catalytic hydrodeoxygenation.

Research paper thumbnail of Formation and Removal of Nitrogen Compounds in Gasification Processes

Advances in Thermochemical Biomass Conversion, 1993

ABSTRACT

Research paper thumbnail of Nitrogen Compounds in Peat and Wood Gasification and Gas Combustion

Research in Thermochemical Biomass Conversion, 1988

ABSTRACT

Research paper thumbnail of Carbon formation in catalytic steam reforming of natural gas with SOFC anode off-gas

International Journal of Hydrogen Energy, 2015

Natural gas was reformed with anode off-gas of a solid oxide fuel cell (SOFC) in a laboratory rea... more Natural gas was reformed with anode off-gas of a solid oxide fuel cell (SOFC) in a laboratory reactor using model gases. Nickel and precious metal catalysts were tested at 650 C and 700 C inlet temperature. The oxygen to carbon (O/C) molar ratio of the inlet gas was varied between 0.3 and 2.0 to find out the limit O/C ratio for carbon formation. Two natural gas compositions were used: low purity Danish gas and high purity Russian gas. The experimental limit was found to be 0.9e1.25 for nickel catalyst and 0.5e0.75 for precious metal catalyst. The limit was higher with Danish gas than with Russian gas in the experiments with nickel catalyst but this effect was not observed with the precious metal catalyst. A good correlation between experimental results and thermodynamic calculations was found using the principle of actual gas: the calculations estimated the O/C limit ratio for nickel at 1.0 and for precious metal catalyst between 0.5 and 0.7.

Research paper thumbnail of The Effect of Sulfur on ZrO2-Based Biomass Gasification Gas Clean-Up Catalysts

Topics in Catalysis, 2009

The effect of sulfur on biomass gasification gas clean-up over ZrO2, Y2O3–ZrO2 and SiO2–ZrO2 cata... more The effect of sulfur on biomass gasification gas clean-up over ZrO2, Y2O3–ZrO2 and SiO2–ZrO2 catalysts was examined. Experiments were carried out at the temperature range of 600–900 °C with sulfur free and 100 ppm H2S containing simulated gasification gas feeds. A mixture of toluene and naphthalene was used as a tar model compound. Results revealed that the sulfur addition affected positively on

Research paper thumbnail of Solid Oxide Fuel Cell System Development in VTT

Journal of Fuel Cell Science and Technology, 2007

The Finnish solid oxide fuel cell (SOFC) project (FINSOFC) was initiated in 2002 as a five-year p... more The Finnish solid oxide fuel cell (SOFC) project (FINSOFC) was initiated in 2002 as a five-year project. It forms the core of the publicly funded SOFC research in Finland. The purpose of the project is to support the industry in its development of SOFC systems and components and other possible SOFC-based business to be created in the future. The project is coordinated by the VTT Technical Research Centre of Finland in cooperation with universities and industrial enterprises. The project is executed in close cooperation with several European partners both bilaterally and within Real-SOFC. The focus is to construct and run a natural gas-fueled 5kWe SOFC power plant demonstration connected to heat and electricity grids. The power plant demonstration contains a stack and all BOP components from fuel processing to power conditioning and grid connections. The aim is also to thoroughly understand the behavior of the system. The subprojects needed to do this are (i) fuel processing, (ii) te...

Research paper thumbnail of Effects of gasification gas components on tar and ammonia decomposition over hot gas cleanup catalysts

Research paper thumbnail of Catalytic purification of tarry fuel gas with carbonate rocks and ferrous materials

Research paper thumbnail of Catalytic clean-up of gasification gas with precious metal catalysts – A novel catalytic reformer development

Fuel, 2010

Several precious metal catalysts were prepared on modified zirconia and tested for the selective ... more Several precious metal catalysts were prepared on modified zirconia and tested for the selective catalytic clean-up of the gasification gas. The activity of the precious metal catalysts were compared to that of the modified zirconia supported nickel catalyst and to the support. The activities of the catalysts were tested in a monolithic form in a quartz laboratory reactor at temperatures of 600-900°C under atmospheric pressure using synthetic sulfur containing gas mixture. In addition, the stability of the Ni and Rh catalysts was examined by measuring the activities at 800°C for 10 h using sulfur containing gas. The simulated gas contained CO, CO 2 , CH 4 , C 2 H 4 , H 2 , N 2 , H 2 O, H 2 S, NH 3 and a tar model compound, i.e. a mixture of naphthalene and toluene. The addition of metal on the support promoted the activity in tar model compound decomposition only at the temperature range of 850-900°C. The order of activity was Rh % Ni > Pd > Ir > Ru > Pt. Almost complete tar model compound conversion was achieved with Rh, as well as with Ni, at 900°C. At lower temperatures, the support showed higher activity in tar model compound decomposition compared to the metal/support catalysts tested. Only Ni and Ru showed moderate activity in ammonia decomposition. In regard to sulfur tolerance at 800°C, Rh was activated during the 10 h experiment while the activity of Ni decreased. The performance of both was restored after the overnight N 2 flush and the conversion of the tar model compound was higher for Rh (64%) than for Ni (46%).

Research paper thumbnail of Closing energy cycle: Power-to-Methanol and Methanol-to-Power

Research paper thumbnail of Pure aromatics from biomass

Research paper thumbnail of Experimental Bench-Scale Study of Residual Biomass Syngas Desulfurization Using ZnO-Based Adsorbents

Energy & Fuels, 2020

Dry-bed adsorptive desulfurization of biomass-based syngas with a low-to medium sulfur content us... more Dry-bed adsorptive desulfurization of biomass-based syngas with a low-to medium sulfur content using ZnO was studied as an alternative to conventional wet-scrubbing processes for a small-to medium-scale biomass-to-liquid process concept. Following laboratory-scale long-term H 2 S breakthrough experiments in a previous study, desulfurization tests were scaled-up to bench-scale with actual bio-syngas to verify the lab-scale results under more realistic process conditions. A desulfurization unit was constructed and connected to a steam-blown atmospheric pilot-scale fluidized bed gasifier. Two successful 70+ h test campaigns were conducted with H 2 S removal below the breakthrough limit using full-sized ZnO adsorbent particles. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy elemental analysis, and Brunauer−Emmett−Teller (BET) surface area characterization of the fresh and spent adsorbent pellets were performed. SEM micrographs displayed the outward enlarging particle size in the sulfided layer. Characterization showed significant core−shell sulfidation behavior with a few hundred micron-thick sulfided layer leaving the majority of ZnO unutilized. Adsorbents lost most of their porosity in use, which was evident from BET surface area results. Simultaneous COS removal was found possible by the hydrolysis reaction to H 2 S. Furthermore, evidence of minor chlorine adsorption was found, thus highlighting the need for a dedicated HCl removal step upstream of desulfurization.

Research paper thumbnail of Method and Process for Cleaning a Productgas of a Gasification Reactor

Research paper thumbnail of Method for the purification of gasification gas

Research paper thumbnail of Effect of pressure on tar decomposition activity of different bed materials in biomass gasification conditions

Fuel, 2015

h i g h l i g h t s The tested bed materials were sand, dolomite, MgO, olivine and olivine/kaolin... more h i g h l i g h t s The tested bed materials were sand, dolomite, MgO, olivine and olivine/kaolin. Dolomite and MgO had the highest tar decomposing activities. The catalytic activities of dolomite and MgO reduced with increasing pressure.

Research paper thumbnail of High Efficiency Biomass to Power Operation Experiences and Economical Aspects of the Novel Gasification Process

15th European Biomass Conference and Exhibition, from Research to Market Deployment. Berlin 2007

Research paper thumbnail of Synthesis Gas Characterization at VTT laboratories and test facilities

Research paper thumbnail of Behaviour of tars on the filter in high temperature filtration of biomass-based gasification gas

Fuel, 2015

Abstract Behaviour of tars in high temperature filtration was studied at atmospheric pressure in ... more Abstract Behaviour of tars in high temperature filtration was studied at atmospheric pressure in steam and air/steam gasification conditions. Wood pellets and bark pellets were used as feedstock and silica sand and dolomite (Myanit B) as bed materials. Experiments were carried out in a bench-scale bubbling fluidised-bed gasifier coupled with a hot gas filter unit. Interestingly, it was found that filter could act, in a sense, as a prereformer when it was operated at 800 °C. The total amount of tars in the gas was reduced on the filter in all tests regardless of the used feedstock, bed material or gasifying agent. Highest reduction, in the order of 50 wt% of total tars, was obtained in steam gasification tests when dolomite was used as bed material. It was concluded that the changes in tars are derived from thermal tar reactions due to long residence time at high temperature on the filter but also from catalytic reactions induced by the presence of unreacted biomass char and carry-over dolomite on the filter surface. Tar reduction on the high temperature filter could be beneficial for downstream units and improve their operability, especially the reformer where the lower tar level could reduce coking tendency on the catalyst.

Research paper thumbnail of Effect of process conditions on tar formation from thermal reactions of ethylene

Fuel, 2015

ABSTRACT Thermal reactions of ethylene were studied to understand better the effect of process co... more ABSTRACT Thermal reactions of ethylene were studied to understand better the effect of process conditions on tar formation in biomass gasification. The effects of pressure, residence time and temperature on thermal reactions of ethylene were studied. The analysis of products from methane up to pyrene was performed by the novel online GC method. Ethylene conversion increased linearly as a function of pressure and residence time. Tar formation increased exponentially in the pressure range 1–3.5 bar and linearly with the residence time. The fraction of heavier tar compounds was found to increase with temperature and pressure. The tar composition was compared with different biomass gasification tar compositions, and the compositions were found to resemble each other. The obtained tar-laden product gas could be used as a realistic tar model when the cleaning of biomass gasification gas is studied.

Research paper thumbnail of Clean syngas from biomass—process development and concept assessment

Biomass Conversion and Biorefinery, 2014

This paper summarises the long development work done at VTT for gas clean-up for various synthesi... more This paper summarises the long development work done at VTT for gas clean-up for various synthesis applications. The development work has covered the most challenging and costly steps in biomass gasification based processes: high-temperature gas filtration and reforming of hydrocarbon gases and tars. The tar content of product gas is one of the main factors defining the temperature window in which the hot-gas filter can be operated, which in the case of fluidized-bed gasification is at 350–500 °C. Research is ongoing to achieve higher and thus more economical operation temperatures. Optimal operation of a catalytic reformer can be achieved by using a staged reformer where zirconia-based catalysts are used as a pre-reformer layer before nickel and/or precious metal-based catalyst stages. The temperature of the reformer is optimally increased in subsequent stages from 600 up to 1,000 °C. According to the techno-economic analysis, increasing the hot-gas filtration temperature by 300 °C or methane conversion in the reformer from 55 to 95 % both lead to about 5 % reduction the liquid fuel production cost.

Research paper thumbnail of Steam reforming of pyrolysis oil aqueous fraction obtained by one-step fractional condensation

International Journal of Hydrogen Energy, 2015

The aqueous fraction of pyrolysis oil, which was produced and fractionally condensed in VTT's 20 ... more The aqueous fraction of pyrolysis oil, which was produced and fractionally condensed in VTT's 20 kg/h fast pyrolysis Process Development Unit, was successfully steam reformed in a fixed-bed reactor over a commercial nickel catalyst without any additional steam. As a result of the one-step fractionation process, the aqueous pyrolysis oil, which had a water content of 72.7 wt%, contained only limited amounts of thermally unstable sugar-type compounds that typically hinder the performance of catalytic steam reforming. An average hydrogen yield of 81% was achieved over two hours at relatively mild process conditions: 650 C, steam-to-carbon ratio of 3.84 and gas hourly space velocity of 5000 h À1. When the reaction temperature was varied between 600 and 750 C, clear catalyst deactivation was only observed at 600 C. In theory, by utilizing the one-step fractional condensation scheme and subsequently steam reforming the aqueous pyrolysis oil, sufficient amounts of hydrogen could be generated for significantly deoxygenating the organic pyrolysis oil via catalytic hydrodeoxygenation.

Research paper thumbnail of Formation and Removal of Nitrogen Compounds in Gasification Processes

Advances in Thermochemical Biomass Conversion, 1993

ABSTRACT

Research paper thumbnail of Nitrogen Compounds in Peat and Wood Gasification and Gas Combustion

Research in Thermochemical Biomass Conversion, 1988

ABSTRACT

Research paper thumbnail of Carbon formation in catalytic steam reforming of natural gas with SOFC anode off-gas

International Journal of Hydrogen Energy, 2015

Natural gas was reformed with anode off-gas of a solid oxide fuel cell (SOFC) in a laboratory rea... more Natural gas was reformed with anode off-gas of a solid oxide fuel cell (SOFC) in a laboratory reactor using model gases. Nickel and precious metal catalysts were tested at 650 C and 700 C inlet temperature. The oxygen to carbon (O/C) molar ratio of the inlet gas was varied between 0.3 and 2.0 to find out the limit O/C ratio for carbon formation. Two natural gas compositions were used: low purity Danish gas and high purity Russian gas. The experimental limit was found to be 0.9e1.25 for nickel catalyst and 0.5e0.75 for precious metal catalyst. The limit was higher with Danish gas than with Russian gas in the experiments with nickel catalyst but this effect was not observed with the precious metal catalyst. A good correlation between experimental results and thermodynamic calculations was found using the principle of actual gas: the calculations estimated the O/C limit ratio for nickel at 1.0 and for precious metal catalyst between 0.5 and 0.7.

Research paper thumbnail of The Effect of Sulfur on ZrO2-Based Biomass Gasification Gas Clean-Up Catalysts

Topics in Catalysis, 2009

The effect of sulfur on biomass gasification gas clean-up over ZrO2, Y2O3–ZrO2 and SiO2–ZrO2 cata... more The effect of sulfur on biomass gasification gas clean-up over ZrO2, Y2O3–ZrO2 and SiO2–ZrO2 catalysts was examined. Experiments were carried out at the temperature range of 600–900 °C with sulfur free and 100 ppm H2S containing simulated gasification gas feeds. A mixture of toluene and naphthalene was used as a tar model compound. Results revealed that the sulfur addition affected positively on

Research paper thumbnail of Solid Oxide Fuel Cell System Development in VTT

Journal of Fuel Cell Science and Technology, 2007

The Finnish solid oxide fuel cell (SOFC) project (FINSOFC) was initiated in 2002 as a five-year p... more The Finnish solid oxide fuel cell (SOFC) project (FINSOFC) was initiated in 2002 as a five-year project. It forms the core of the publicly funded SOFC research in Finland. The purpose of the project is to support the industry in its development of SOFC systems and components and other possible SOFC-based business to be created in the future. The project is coordinated by the VTT Technical Research Centre of Finland in cooperation with universities and industrial enterprises. The project is executed in close cooperation with several European partners both bilaterally and within Real-SOFC. The focus is to construct and run a natural gas-fueled 5kWe SOFC power plant demonstration connected to heat and electricity grids. The power plant demonstration contains a stack and all BOP components from fuel processing to power conditioning and grid connections. The aim is also to thoroughly understand the behavior of the system. The subprojects needed to do this are (i) fuel processing, (ii) te...

Research paper thumbnail of Effects of gasification gas components on tar and ammonia decomposition over hot gas cleanup catalysts

Research paper thumbnail of Catalytic purification of tarry fuel gas with carbonate rocks and ferrous materials

Research paper thumbnail of Catalytic clean-up of gasification gas with precious metal catalysts – A novel catalytic reformer development

Fuel, 2010

Several precious metal catalysts were prepared on modified zirconia and tested for the selective ... more Several precious metal catalysts were prepared on modified zirconia and tested for the selective catalytic clean-up of the gasification gas. The activity of the precious metal catalysts were compared to that of the modified zirconia supported nickel catalyst and to the support. The activities of the catalysts were tested in a monolithic form in a quartz laboratory reactor at temperatures of 600-900°C under atmospheric pressure using synthetic sulfur containing gas mixture. In addition, the stability of the Ni and Rh catalysts was examined by measuring the activities at 800°C for 10 h using sulfur containing gas. The simulated gas contained CO, CO 2 , CH 4 , C 2 H 4 , H 2 , N 2 , H 2 O, H 2 S, NH 3 and a tar model compound, i.e. a mixture of naphthalene and toluene. The addition of metal on the support promoted the activity in tar model compound decomposition only at the temperature range of 850-900°C. The order of activity was Rh % Ni > Pd > Ir > Ru > Pt. Almost complete tar model compound conversion was achieved with Rh, as well as with Ni, at 900°C. At lower temperatures, the support showed higher activity in tar model compound decomposition compared to the metal/support catalysts tested. Only Ni and Ru showed moderate activity in ammonia decomposition. In regard to sulfur tolerance at 800°C, Rh was activated during the 10 h experiment while the activity of Ni decreased. The performance of both was restored after the overnight N 2 flush and the conversion of the tar model compound was higher for Rh (64%) than for Ni (46%).