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02588 Experimental comparison of alternative convection suppression arrangements for concentrating integral collector storage solar water heaters
07 Alternative energy sources (bioconversion energy) on the drying performance were also investigated. The goat of this work is to present the experimental results on the drying process of wheat and the effects of the swirling flow field on the drying performance.
05•02586 Energy production from biomass pyrolysis: a new coefficient of pyrolytic valorisation Gu~henneux, G. et al. Fuel, 2005, 84, (6), 733 739. The use of renewable energy sources is becoming increasingly necessary to diminish the greenhouse effect gases production. Biomass is the most common form of renewable energy, widely used in the third world. Pyrolysis, which corresponds to the thermal decomposition of biomass under the action of heat and without any oxidant, is particularly well adapted to the valorization of lignocellulosic products such as wood or straw. The BIOCARB programme of the Commissariat ~t l'Energie Atomique (CEA), to which the Groupe de Recherche sur l'Environnement et la Chimie Atmosphdrique (GRECA) contributes, aims to produce carburant from the gasification of biomass. This fuel can be either pure hydrogen, or gasoil produced by the FischerTropsch process after the pyrolysis and syngas production. It is absolutely necessary to control the different parameters of the pyrolysis (gas composition, formation of tars) to maximize the production of hydrogen or syngas. The new coefficient of pyrolytic valorization presented here helps to meet this requirement. This work presents also experiments on the pyrolysis of straw and rescue in a 550-650°C temperature range with different residence times, on which was based this investigation.
05102587 Evaluation of convective heat transfer coefficient of various crops in cyclone type dryer Akpinar, E. K. Energy Conversion and Management, 2005, 46, (15 16), 2439-2454. In this paper, an attempt was made to evaluate the convective heat transfer coefficient during drying of various crops and to investigate the influences of drying air velocity and temperature on the convective heat transfer coefficient. Drying was conducted in a convective cyclone type dryer at drying air temperatures of 60, 70 and 80°C and velocities of 1 and 1.5 m/s using rectangle shaped potato and apple slices (12.5 x 12.5 x 25 ram) and cylindrical shaped pumpkin slices (35 x 5 ram). The temperature changes of the dried crops and the temperature of the drying air were measured during the drying process. It was found that the values of convective heat transfer coefficient varied from crop to crop with a range 30.21406 and 20.65470 W/m 2 C for the crops studied, and it was observed that the convective heat transfer coefficient increased in large amounts with the increase of the drying air velocity but increased in small amounts with the rise of the drying air temperature.
05102588 Experimental comparison of alternative convection suppression arrangements for concentrating integral collector storage solar water heaters Smyth, M. et al. Solar Energy, 2005, 78, (2), 223-233. An experimental investigation of an inverted absorber integrated collector storage solar water heater mounted in the tertiary cavity of a compound parabolic concentrator with a secondary cylindrical reflector has been performed under simulated solar conditions. The solar water heaters performance was determined with the aperture parallel to the simulator for a range of transparent baffles positioned at different locations within the collector cavity. Results indicate that glass baffles located at the upper portion of the exit aperture of the CPC can reduce thermal losses through convection suppression without significantly increasing optical losses.
05102589 Experimental evaluation of energy and exergy efficiency of a seasonal latent heat storage system for greenhouse heating Ozttirk, H. H. Energy Conversion and Management, 2005, 46, (9-10), 1523-1542. In the following work, a seasonal thermal energy storage using paraffin wax as a PCM with the latent heat storage technique was attempted to heat the greenhouse of 180 m 2 floor area. The system consists mainly of five units: (1) flat plate solar air collectors (as heat collection unit), (2) latent heat storage (LHS) unit, (3) experimental greenhouse, (4) heat transfer unit and (5) data acquisition unit. The externai heat collection unit consisted of 27 m 2 of south facing solar air heaters mounted at a 55 ° tilt angle. The diameter and the total volume of the steel tank used as the latent heat storage unit were 1.7 m and 11.6 m 3, respectively. The LHS unit was filled with 6000 kg of paraffin, equivalent to 33.33 kg of PCM per square meter of the greenhouse ground surface area. Energy and exergy analyses were applied in order to evaluate the system efficiency. The rate of heat transferred in the LHS unit ranged from 1.22 to 2.63 kW, whereas the rate of heat stored in the LHS unit was in the range of 0.65-2.1 kW. The average daily rate of thermal exergy transferred and stored in the LHS unit were 111.2 and 79.9 W, respectively. During the experimental period, it was found that the average net energy and exergy efficiencies were 40.4% and 4.2%,
respectively. The effect of the temperature difference of the heat transfer fluid at the inlet and outlet of the LHS unit on the computed values of the energy and exergy efficiency is evaluated during the charging period.
05•02590 Life cycle assessment (LCA) of an integrated biomass gasification combined cycle (IBGCC) with CO2 removal Carpentieri, M. et al. Energy Conversion and Management, 2005, 46, (11-12), 1790-1808. Based on the results of previous studies, the efficiency of a Brayton/ H i m combined cycle fuelled with a clean syngas produced by means of biomass gasification and equipped with CO2 removal by chemical absorption reached 33.94%, considering also the separate CO2 compression process. The specific CO2 emission of the power plant was 178 kg/MW h. In comparison with values previously found for an integrated coal gasification combined cycle (ICGCC) with upstream CO2 chemical absorption (38-39% efficiency, 130 kg/MW h specific COz emissions), this configuration seems to be attractive because of the possibility of operating with a simplified scheme and because of the possibility of using biomass in a more efficient way with respect to conventional systems. In this paper, a life cycle assessment (LCA) was conducted with presenting the results on the basis of the Eco-Indicator 95 impact assessment methodology. Further, a comparison with the results previously obtained for the LCA of the ICGCC was performed in order to highlight the environmental impact of biomass production with fossil fuels utilization. The LCA shows the important environmental advantages of biomass utilization in terms of reduction of both greenhouse gas emissions and natural resource depletion, although an improved impact assessment methodology may better highlight the advantages due to the biomass utilization.
05•02591 Numerical modeling of straw combustion in a fixed bed Zhou, H. et al. Fuel, 2005, 84, (4), 389-403. Straw is being used as main renewable energy source in grate boilers in Denmark. For optimizing operating conditions and design parameters, a one-dimensional unsteady heterogeneous mathematical model has been developed and experiments have been carried out for straw combustion in a fixed bed. The straw combustion processes include moisture evaporation, straw pyrolysis, gas combustion, and char combustion. The model provides detailed information of the structure of the ignition flame front. Simulated gas species concentrations at the bed surface, ignition flame front rate, and bed temperature are in good agreement with measurements at different operating conditions such as primary air-flow rate, pre-heating of the primary air, oxygen concentration, moisture content in straw, and bulk density of the straw in the fixed bed. A parametric study indicates that the effective heat conductivity, straw packing condition, and heat capacity of the straw have considerable effects on the model predictions of straw combustion in the fixed bed.
05102592 On the intrinsic reaction rate of biomass char gasification with carbon dioxide and steam Klose, W. and W61ki, M. Fuel, 2005, 84, (7-8), 885-892. The gasification of beech wood char and oil palm shell char with carbon dioxide and steam was studied. To avoid heat and mass transport limitations during gasification, the amount of char, particle size and flow rate were varied in isothermal experiments. A rate expression of the Langmuir-Hinshelwood-type was applied to match the experimental data at different partial pressures and reaction temperatures in the intrinsic regime. Furthermore, the reactive surface area (RSA) of the biomass chars was determined as a function of the degree of conversion by the temperature-programmed desorption technique (TPD). The results show that the reaction rate is in general proportional to the RSA. The surface related reaction rates for the studied biomass chars are comparable to surface related reaction rates for coal chars at similar reaction temperatures.
05•02593 Performance of a concentrating photovoltaic/ thermal solar collector Coventry, J. S. Solar Energy, 2005, 78, (2), 211 222. The performance of a parabolic trough photovoltaic/thermal collector with a geometric concentration ratio of 37× is described. Measured results under typical operating conditions show thermal efficiency around 58% and electrical efficiency around 11%, therefore a combined efficiency of 69%. The impact of non-uniform illumination on the solar cells is investigated using purpose built equipment that moves a calibrated solar cell along the line of the receiver and measures short circuit current. The measured illumination flux profile along the length shows significant variation, despite the mirror shape error being less than 1 m m for most of the mirror area. The impact of the illumination non-uniformities due to the shape error, receiver support post shading and gaps between the mirrors is shown to have a significant effect on the overall electrical performance. The flux profile
Fuel and Energy Abstracts
November 2005 379
05•02586 Energy production from biomass pyrolysis: a new coefficient of pyrolytic valorisation Gu~henneux, G. et al. Fuel, 2005, 84, (6), 733 739. The use of renewable energy sources is becoming increasingly necessary to diminish the greenhouse effect gases production. Biomass is the most common form of renewable energy, widely used in the third world. Pyrolysis, which corresponds to the thermal decomposition of biomass under the action of heat and without any oxidant, is particularly well adapted to the valorization of lignocellulosic products such as wood or straw. The BIOCARB programme of the Commissariat ~t l'Energie Atomique (CEA), to which the Groupe de Recherche sur l'Environnement et la Chimie Atmosphdrique (GRECA) contributes, aims to produce carburant from the gasification of biomass. This fuel can be either pure hydrogen, or gasoil produced by the FischerTropsch process after the pyrolysis and syngas production. It is absolutely necessary to control the different parameters of the pyrolysis (gas composition, formation of tars) to maximize the production of hydrogen or syngas. The new coefficient of pyrolytic valorization presented here helps to meet this requirement. This work presents also experiments on the pyrolysis of straw and rescue in a 550-650°C temperature range with different residence times, on which was based this investigation.
05102587 Evaluation of convective heat transfer coefficient of various crops in cyclone type dryer Akpinar, E. K. Energy Conversion and Management, 2005, 46, (15 16), 2439-2454. In this paper, an attempt was made to evaluate the convective heat transfer coefficient during drying of various crops and to investigate the influences of drying air velocity and temperature on the convective heat transfer coefficient. Drying was conducted in a convective cyclone type dryer at drying air temperatures of 60, 70 and 80°C and velocities of 1 and 1.5 m/s using rectangle shaped potato and apple slices (12.5 x 12.5 x 25 ram) and cylindrical shaped pumpkin slices (35 x 5 ram). The temperature changes of the dried crops and the temperature of the drying air were measured during the drying process. It was found that the values of convective heat transfer coefficient varied from crop to crop with a range 30.21406 and 20.65470 W/m 2 C for the crops studied, and it was observed that the convective heat transfer coefficient increased in large amounts with the increase of the drying air velocity but increased in small amounts with the rise of the drying air temperature.
05102588 Experimental comparison of alternative convection suppression arrangements for concentrating integral collector storage solar water heaters Smyth, M. et al. Solar Energy, 2005, 78, (2), 223-233. An experimental investigation of an inverted absorber integrated collector storage solar water heater mounted in the tertiary cavity of a compound parabolic concentrator with a secondary cylindrical reflector has been performed under simulated solar conditions. The solar water heaters performance was determined with the aperture parallel to the simulator for a range of transparent baffles positioned at different locations within the collector cavity. Results indicate that glass baffles located at the upper portion of the exit aperture of the CPC can reduce thermal losses through convection suppression without significantly increasing optical losses.
05102589 Experimental evaluation of energy and exergy efficiency of a seasonal latent heat storage system for greenhouse heating Ozttirk, H. H. Energy Conversion and Management, 2005, 46, (9-10), 1523-1542. In the following work, a seasonal thermal energy storage using paraffin wax as a PCM with the latent heat storage technique was attempted to heat the greenhouse of 180 m 2 floor area. The system consists mainly of five units: (1) flat plate solar air collectors (as heat collection unit), (2) latent heat storage (LHS) unit, (3) experimental greenhouse, (4) heat transfer unit and (5) data acquisition unit. The externai heat collection unit consisted of 27 m 2 of south facing solar air heaters mounted at a 55 ° tilt angle. The diameter and the total volume of the steel tank used as the latent heat storage unit were 1.7 m and 11.6 m 3, respectively. The LHS unit was filled with 6000 kg of paraffin, equivalent to 33.33 kg of PCM per square meter of the greenhouse ground surface area. Energy and exergy analyses were applied in order to evaluate the system efficiency. The rate of heat transferred in the LHS unit ranged from 1.22 to 2.63 kW, whereas the rate of heat stored in the LHS unit was in the range of 0.65-2.1 kW. The average daily rate of thermal exergy transferred and stored in the LHS unit were 111.2 and 79.9 W, respectively. During the experimental period, it was found that the average net energy and exergy efficiencies were 40.4% and 4.2%,
respectively. The effect of the temperature difference of the heat transfer fluid at the inlet and outlet of the LHS unit on the computed values of the energy and exergy efficiency is evaluated during the charging period.
05•02590 Life cycle assessment (LCA) of an integrated biomass gasification combined cycle (IBGCC) with CO2 removal Carpentieri, M. et al. Energy Conversion and Management, 2005, 46, (11-12), 1790-1808. Based on the results of previous studies, the efficiency of a Brayton/ H i m combined cycle fuelled with a clean syngas produced by means of biomass gasification and equipped with CO2 removal by chemical absorption reached 33.94%, considering also the separate CO2 compression process. The specific CO2 emission of the power plant was 178 kg/MW h. In comparison with values previously found for an integrated coal gasification combined cycle (ICGCC) with upstream CO2 chemical absorption (38-39% efficiency, 130 kg/MW h specific COz emissions), this configuration seems to be attractive because of the possibility of operating with a simplified scheme and because of the possibility of using biomass in a more efficient way with respect to conventional systems. In this paper, a life cycle assessment (LCA) was conducted with presenting the results on the basis of the Eco-Indicator 95 impact assessment methodology. Further, a comparison with the results previously obtained for the LCA of the ICGCC was performed in order to highlight the environmental impact of biomass production with fossil fuels utilization. The LCA shows the important environmental advantages of biomass utilization in terms of reduction of both greenhouse gas emissions and natural resource depletion, although an improved impact assessment methodology may better highlight the advantages due to the biomass utilization.
05•02591 Numerical modeling of straw combustion in a fixed bed Zhou, H. et al. Fuel, 2005, 84, (4), 389-403. Straw is being used as main renewable energy source in grate boilers in Denmark. For optimizing operating conditions and design parameters, a one-dimensional unsteady heterogeneous mathematical model has been developed and experiments have been carried out for straw combustion in a fixed bed. The straw combustion processes include moisture evaporation, straw pyrolysis, gas combustion, and char combustion. The model provides detailed information of the structure of the ignition flame front. Simulated gas species concentrations at the bed surface, ignition flame front rate, and bed temperature are in good agreement with measurements at different operating conditions such as primary air-flow rate, pre-heating of the primary air, oxygen concentration, moisture content in straw, and bulk density of the straw in the fixed bed. A parametric study indicates that the effective heat conductivity, straw packing condition, and heat capacity of the straw have considerable effects on the model predictions of straw combustion in the fixed bed.
05102592 On the intrinsic reaction rate of biomass char gasification with carbon dioxide and steam Klose, W. and W61ki, M. Fuel, 2005, 84, (7-8), 885-892. The gasification of beech wood char and oil palm shell char with carbon dioxide and steam was studied. To avoid heat and mass transport limitations during gasification, the amount of char, particle size and flow rate were varied in isothermal experiments. A rate expression of the Langmuir-Hinshelwood-type was applied to match the experimental data at different partial pressures and reaction temperatures in the intrinsic regime. Furthermore, the reactive surface area (RSA) of the biomass chars was determined as a function of the degree of conversion by the temperature-programmed desorption technique (TPD). The results show that the reaction rate is in general proportional to the RSA. The surface related reaction rates for the studied biomass chars are comparable to surface related reaction rates for coal chars at similar reaction temperatures.
05•02593 Performance of a concentrating photovoltaic/ thermal solar collector Coventry, J. S. Solar Energy, 2005, 78, (2), 211 222. The performance of a parabolic trough photovoltaic/thermal collector with a geometric concentration ratio of 37× is described. Measured results under typical operating conditions show thermal efficiency around 58% and electrical efficiency around 11%, therefore a combined efficiency of 69%. The impact of non-uniform illumination on the solar cells is investigated using purpose built equipment that moves a calibrated solar cell along the line of the receiver and measures short circuit current. The measured illumination flux profile along the length shows significant variation, despite the mirror shape error being less than 1 m m for most of the mirror area. The impact of the illumination non-uniformities due to the shape error, receiver support post shading and gaps between the mirrors is shown to have a significant effect on the overall electrical performance. The flux profile
Fuel and Energy Abstracts
November 2005 379