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00996 A solution of the neutron diffusion equation for a hemisphere with mixed boundary conditions
05 Nuclear fuels (scientific, technical) 05100991 Natural gas in Brazil's energy matrix: demand for 1995-2010 and usage factors Fernandes, E. et al. Energy Policy, 2005, 33, (3), 365-386. This paper describes and analyses the constraints hampering achievement of the 12% share planned for natural gas in Brazil's energy matrix by 2010, and advises policies for reaching that goal on the basis of forecasts and three probable scenarios for the development of the Brazilian economy. The 12% share goal was established in 1993 by the Ministry of Mines and Energy and confirmed in 2000, and is now in full development. The figures used to represent the estimates of natural gas demands in the three scenarios were obtained from the Integrated Energy Planning Model (MIPE-Modelo Integrado de Planejamento Energ6tico), which is a technical and economic forecasting model developed by a group of researchers linked to the Energy Planning Program run by the Graduate Engineering Programs Coordination Unit at the Rio de Janeiro Federal University (COPPE-UFRJ) under the sponsorship of Petrobras (a Brazilian enterprise operating in the oil and gas segment) and Eletrobrfis (a Brazilian enterprise in charge of electricity demand planning). The analysis of the constraints takes place under the aegis of the objective proposed by the Brazilian Government. The authors suggest specific actions to be taken in four application areas of natural gas: industrial, electric power generation, domestic distribution and vehicular fleet conversions. All the actions proposed encourage the use of a fuel with low environmental impacts and high calorie power, replacing firewood and other polluting fuels and are evaluated relative to the impacts occurring in society, especially from the standpoint of social welfare in a developing country. The necessity of developing the goods and services infrastructure in the country to support the natural gas insertion in the Brazilian energy matrix is also addressed.
Derived gaseous fuels 05•00992 A new type of coal gas fueled chemical-looping combustion Jin, H. and Ishida, M. Fuel, 2004, 83, (17-18), 2411 2417. A new type of coal gas fuelled chemical-looping combustion is experimentally investigated by means of a fixed-bed reactor operated at elevated pressure. Chemical-looping combustion may be carried out in two successive reactions between two reactors, a reduction reactor (coal gas with metal oxides) and an oxidation reactor (reduced metal with oxygen in the air), which may lead to a breakthrough in clean coal technology by simultaneously allowing efficient use of energy and greenhouse gas control. The study experimentally examined the kinetic behaviour between solid looping materials and coal gas in a highpressure fixed bed reactor. On the basis of the development of suitable material and the good reactivity with the fixed bed reactor, the study identified that the coal gas fuelled chemical-looping combustor has much better reactivity than natural gas combustors, and this phenomenon is completely different from direct combustion with natural gas. The promising results obtained here will be valuable for the design of a practical reactor.
05100993 mixture
Hydrogasification of coal and polyethylene
Yasuda, H. et al. Fuel, 2004, 83, (17-18), 2251-2254. The hydrogasification of coal and polyethylene (PE) mixtures was carried out at 1073 K under 7.1 MPa of hydrogen. The product distribution and temperature profile were analysed. The yield of methane reached 90% (carbon basis) after 80 s when PE was used alone. A significant synergistic effect was found when coal and PE were mixed and used in hydrogasification. This synergistic effect may have been partly due to compensation of the endothermic process in coal pyrolysis by heat from the hydrogenation of PE when the coal and PE were mixed. Temperature drop in the early stage in coal hydrogasification was prevented by the mixing and the carbon conversion to methane from coal was enhanced. It is suggested that waste plastics could be mixed as a feedstock in a coal hydrogasification processes.
04
BY-PRODUCTS RELATED TO FUELS
05/00994 Bench-scale experimental evaluation of carbon performance on mercury vapour adsorption Yan, R. et al. Fuel, 2004, 83, (17-18), 2401-2409.
Mercury emission in combustion flue gases is a significant environmental concern due to its toxicity and high volatility. The problem is particularly severe for elemental mercury (Hg0) in vapour since it cannot be effectively removed using current air pollution control devices. Activated carbon (AC) adsorption is a technology that offers a great potential for the control of gas-phase mercury emissions. This paper outlines the results of a parametric study conducted with a bench-scale fixed bed, on the capture of trace mercury vapour from simulated flue gas using ACs. The performances of five commercially available ACs, which are claimed to be effective sorbents of mercury, are evaluated. The parameters investigated include carbon loading, reaction temperature, inlet mercury concentration, and particle size of ACs. A full screening of the physical properties of the five carbons using BET, SEM, XRF, and XRD, facilitates a better understanding to the nature of adsorption. The experimental data suggest that the adsorption of mercury is greatly dependent upon the operation conditions. For sulphur-impregnated carbon, adsorption involves both physical and chemical processes. With increasing temperature, physical adsorption decreases due to the nature of exothermal adsorption process whilst chemisorption might be enhanced, evidenced by the better performance of carbon at a higher temperature. The external surface area of AC has a significant contribution to the high performance of ACs. This study provides a good reference for screening the commercial carbon candidates to be used for treating vapour Hg in the actual exhausted flue gas over a wide range of conditions.
05/00995 The silicate/non-siUcate distribution of metals in fly ash and its effect on solubility Kim, A. G. and Kazonieh, G. Fuel, 2004, 83, (17-18), 2285-2292. In a study at D O E ' s National Energy Technology Laboratory, 32 Class F fly ash samples from pulverized coal (PC) power plants were dissolved in concentrated nitric acid and in hydrofluoric acid to estimate the distribution of metals in non-silicate and silicate matrices. Nineteen cations occurred to some extent in both phases. Using a column leaching method, the release of the metals was determined with four leachant solutions; the pH of the leachants ranged between 1.2 and 12. Although the amount of an element extracted from the fly ash was low, solubility in alkaline leachants was correlated with elements in non-silicate compounds. Solubility in acid solutions was correlated more strongly with silicate phase concentration.
05
N U C L E A R FUELS Scientific, technical
05/00996 A solution of the neutron diffusion equation for a hemisphere with mixed boundary conditions Cassell, J. S. and Williams, M. M. R. Annals of Nuclear Energy, 2004, 31, (t7), 1987-2004. An analytic solution of the diffusion equation for a hemisphere of fissile material is presented with mixed boundary conditions. This allows one to study the bare hemisphere with radiation boundary conditions and also the interaction between two hemispheres with opposing flat faces. Numerical results are given for one-speed fast neutrons in 23Su. The procedure for multi-group calculations was also developed.
05/00997 A systematic method to identify nonlinear dynamics of BWR by using the reactor noise Liu, W. et al. Progress in Nuclear Energy, 2003, 43, (1-4), 209-216. For the identification of the dynamics of the Vermont Yankee B W R with the reactor noise, different parametric models have been tested. The widely used A R M A model is unable to identify the non-linearity in the noise data. A systematic method by using the N A R M A model, which takes advantage of both the A N N and A R M A , is developed. Comparisons are made between the identification results with A R M A and N A R M A model. The advantages of identification with N A R M A model over A R M A model are demonstrated. The linear-kernels of the identified N A R M A models are extracted so that the natural frequency, damping ratio and time constants of the B W R are obtained. The values of those characteristics are well corresponded with the eigenvalues calculated by the differential equations of the Vermont Yankee BWR. The damping ratio with negative value is found to be a criterion for the existence of limit-cycle, which can be seen from the impulse response on the (Xt, X, 1) plane, in stable non-linear system.
Fuel and Energy Abstracts May 2005
153
Derived gaseous fuels 05•00992 A new type of coal gas fueled chemical-looping combustion Jin, H. and Ishida, M. Fuel, 2004, 83, (17-18), 2411 2417. A new type of coal gas fuelled chemical-looping combustion is experimentally investigated by means of a fixed-bed reactor operated at elevated pressure. Chemical-looping combustion may be carried out in two successive reactions between two reactors, a reduction reactor (coal gas with metal oxides) and an oxidation reactor (reduced metal with oxygen in the air), which may lead to a breakthrough in clean coal technology by simultaneously allowing efficient use of energy and greenhouse gas control. The study experimentally examined the kinetic behaviour between solid looping materials and coal gas in a highpressure fixed bed reactor. On the basis of the development of suitable material and the good reactivity with the fixed bed reactor, the study identified that the coal gas fuelled chemical-looping combustor has much better reactivity than natural gas combustors, and this phenomenon is completely different from direct combustion with natural gas. The promising results obtained here will be valuable for the design of a practical reactor.
05100993 mixture
Hydrogasification of coal and polyethylene
Yasuda, H. et al. Fuel, 2004, 83, (17-18), 2251-2254. The hydrogasification of coal and polyethylene (PE) mixtures was carried out at 1073 K under 7.1 MPa of hydrogen. The product distribution and temperature profile were analysed. The yield of methane reached 90% (carbon basis) after 80 s when PE was used alone. A significant synergistic effect was found when coal and PE were mixed and used in hydrogasification. This synergistic effect may have been partly due to compensation of the endothermic process in coal pyrolysis by heat from the hydrogenation of PE when the coal and PE were mixed. Temperature drop in the early stage in coal hydrogasification was prevented by the mixing and the carbon conversion to methane from coal was enhanced. It is suggested that waste plastics could be mixed as a feedstock in a coal hydrogasification processes.
04
BY-PRODUCTS RELATED TO FUELS
05/00994 Bench-scale experimental evaluation of carbon performance on mercury vapour adsorption Yan, R. et al. Fuel, 2004, 83, (17-18), 2401-2409.
Mercury emission in combustion flue gases is a significant environmental concern due to its toxicity and high volatility. The problem is particularly severe for elemental mercury (Hg0) in vapour since it cannot be effectively removed using current air pollution control devices. Activated carbon (AC) adsorption is a technology that offers a great potential for the control of gas-phase mercury emissions. This paper outlines the results of a parametric study conducted with a bench-scale fixed bed, on the capture of trace mercury vapour from simulated flue gas using ACs. The performances of five commercially available ACs, which are claimed to be effective sorbents of mercury, are evaluated. The parameters investigated include carbon loading, reaction temperature, inlet mercury concentration, and particle size of ACs. A full screening of the physical properties of the five carbons using BET, SEM, XRF, and XRD, facilitates a better understanding to the nature of adsorption. The experimental data suggest that the adsorption of mercury is greatly dependent upon the operation conditions. For sulphur-impregnated carbon, adsorption involves both physical and chemical processes. With increasing temperature, physical adsorption decreases due to the nature of exothermal adsorption process whilst chemisorption might be enhanced, evidenced by the better performance of carbon at a higher temperature. The external surface area of AC has a significant contribution to the high performance of ACs. This study provides a good reference for screening the commercial carbon candidates to be used for treating vapour Hg in the actual exhausted flue gas over a wide range of conditions.
05/00995 The silicate/non-siUcate distribution of metals in fly ash and its effect on solubility Kim, A. G. and Kazonieh, G. Fuel, 2004, 83, (17-18), 2285-2292. In a study at D O E ' s National Energy Technology Laboratory, 32 Class F fly ash samples from pulverized coal (PC) power plants were dissolved in concentrated nitric acid and in hydrofluoric acid to estimate the distribution of metals in non-silicate and silicate matrices. Nineteen cations occurred to some extent in both phases. Using a column leaching method, the release of the metals was determined with four leachant solutions; the pH of the leachants ranged between 1.2 and 12. Although the amount of an element extracted from the fly ash was low, solubility in alkaline leachants was correlated with elements in non-silicate compounds. Solubility in acid solutions was correlated more strongly with silicate phase concentration.
05
N U C L E A R FUELS Scientific, technical
05/00996 A solution of the neutron diffusion equation for a hemisphere with mixed boundary conditions Cassell, J. S. and Williams, M. M. R. Annals of Nuclear Energy, 2004, 31, (t7), 1987-2004. An analytic solution of the diffusion equation for a hemisphere of fissile material is presented with mixed boundary conditions. This allows one to study the bare hemisphere with radiation boundary conditions and also the interaction between two hemispheres with opposing flat faces. Numerical results are given for one-speed fast neutrons in 23Su. The procedure for multi-group calculations was also developed.
05/00997 A systematic method to identify nonlinear dynamics of BWR by using the reactor noise Liu, W. et al. Progress in Nuclear Energy, 2003, 43, (1-4), 209-216. For the identification of the dynamics of the Vermont Yankee B W R with the reactor noise, different parametric models have been tested. The widely used A R M A model is unable to identify the non-linearity in the noise data. A systematic method by using the N A R M A model, which takes advantage of both the A N N and A R M A , is developed. Comparisons are made between the identification results with A R M A and N A R M A model. The advantages of identification with N A R M A model over A R M A model are demonstrated. The linear-kernels of the identified N A R M A models are extracted so that the natural frequency, damping ratio and time constants of the B W R are obtained. The values of those characteristics are well corresponded with the eigenvalues calculated by the differential equations of the Vermont Yankee BWR. The damping ratio with negative value is found to be a criterion for the existence of limit-cycle, which can be seen from the impulse response on the (Xt, X, 1) plane, in stable non-linear system.
Fuel and Energy Abstracts May 2005
153