16 Fuel science and technology (fundamental science, analysis, instrumentation)

irradiation. PAHs are formed during the flame period. The PAH specified here are those formed inside the flame at the brick surface. In the case of an industrial application, it must be emphasized that these PAHs are likely to react downstream depending on the furnace conditions. The density of the fuel and the size of the elements have no impact on these emissions. Our results show that this is the percentage of PE that controls the emissions. We showed that the introduction of more than 30% of PE (expressed in micrograms per gram of PE) leads to very high PAH emissions. Moreover, for mass fractions of PE larger than 30%, heavy PAH, which are more toxic than light PAH, are formed in majority. In conclusion, if PE mass fractions lower than 30% are used, such substitution fuels allows one to recover the available energy of these materials, while solving the environmental and technical problems usually encountered when burning these materials individually.

04/02126 Determination of selenium by ICP-MS and HG- iCP-MS in coal, fly ashes and sorbents used for flue gas cleaning Dfaz-Somoano, M. et al. Fuel, 2004, 83, (2), 231 235. The determination of selenium in solid materials related with the use of coal for energy production was evaluated by two methods; ICP-MS and HG-ICP-MS. Coals, fly ashes and various solids used as sorbents in gas cleaning processes (kaolin, limestone, alumina, metal oxide mixtures and activated carbons), were the materials analysed. In several of these materials, selenium could be determined by either method with similar results. However in coal, fly ashes and some activated carbons, the use of a HG-ICP-MS is necessary in order to avoid interferences. The results obtained by both methods in samples

1 1 whose selenium content ranges from gg g to mg g- , are discussed. In general, good (±2-4%) to excellent (4-1-2%) agreement between the reference and the obtained concentrations was achieved in the analysis of the certified and reference samples, the relative standard deviation being lower than 10% in all cases.

04•02127 DF'I" and MM calculation: the performance mechanism of pour point depressants study Zbang, J. et al. Fuel, 2004, 83, (3), 315-326. Adding pour point depressants (PPDs) to lower the cold filter plugging point (CFPP) of oils has been widely used as the most valuable way in the world. To develop the new type of PPDs according to the oils of different kinds, many researchers have tried to study the performance mechanism of PPDs with different methods. In this article, we have carried out this study with density function theory and molecular mechanics calculation methods. From the results of different systems, we have found that: (1) Alkane molecule is non-polar but the methyl groups on the chain ends have higher electronegativity than all the methylene groups. (2) The EVA (copolymer of ethylene and vinyl acetate) molecule is divided into segments by the polar groups, and the segments are composed of carbon chains, while at the joint points of the segments are ester groups. Calculation results show that the non- polar parts of EVA molecule have good affinity to the adjacent alkane molecules. The rigidity of the carbon bonds neighboring to ester groups is enhanced by the introduction of ester groups, which can also help the next segments to get into the next crystal units and accelerate the growth rate of the planes perpendicular to (001) plane. (3) The alkane molecules absorbed on the PPD molecules can be bent, and the bending conformation brings steric hindrance effect to the molecules to deposit on the surface near the PPD molecules. The relatively higher electronegativity of the methyl groups, which are bent out of the crystal units, can also bring more repulsion effect to the alkane molecules to deposit. This helps to restrict the high growing velocity of (001) plane and results in the uniformity growing rate in three dimensions. (4) If we want to get the good performance properties of PPDs, the carbon number should be a little lower than the mean carbon number of the wax crystals. Then the acetate percent of EVA molecules should be around 30% and the concrete value should be determined according to the oils used.

04•02128 Discrete formulation for two-dimensional multigroup neutron diffusion equations Vosoughi, N. et al. Annals of Nuclear Energy, 2004, 31, (3), 231-253. The objective of this paper is to introduce a new numerical method for neutronic calculation in a reactor core. This method can produce the final finite form of the neutron diffusion equation by classifying the neutronic variables and using two kinds of cell complexes without starting from the conventional differential form of the neutron diffusion equation. The method with linear interpolation produces the same convergence as the linear continuous finite element method. The quadratic interpolation is proven; the convergence order depends on the shape of the dual cell. The maximum convergence order is achieved by choosing the dual cell based on two Gauss ' points. The accuracy of the method was examined with a well-known IAEA two- dimensional benchmark problem. The numerical results demonstrate the effectiveness of the new method.

04/02129 Effect of calcium ion and montmorillonite clay on bitumen displacement by water on a glass surface Basu, S. et al. Fuel, 2004, 83, (1), 17-22. Experiments were conducted to study the effect of calcium ion and montmorillonite clay on bitumen displacement by an aqueous phase on a glass surface. Upon exposure to an aqueous environment containing calcium ion and clays, a thin coating of bitumen on a glass surface displaced spontaneously in the inward radial direction. The initially circular bitumen disk took the shape of a spherical droplet. The dynamic and static contact angles of bitumen on the glass surface were estimated by measuring the contact radius of bitumen with time. The dynamic and static contact angles in the presence of calcium ion and clays are compared with the case when no calcium ion and clays are present. At pH 9, the static contact angle decreased significantly in the presence of calcium ion having a concentration higher than 25 ppm, For a given temperature and at a pH of 9, the initial dynamic angle variation with time was affected less by the presence of clays than with the case of calcium addition. There was no synergetic effect on the dynamic and static angles due to the presence of both calcium ion and clays. In the presence calcium and clays, the results would suggest a negative impact on bitumen liberation from sand grains in the industrial process of bitumen extraction from oil sands. In all cases, the contact angle is measured through the bitumen phase.

04•02130 Ethyl acetate oxidation in flame condition: an experimental study Gasnot, L. et al. Fuel, 2004, 83, (4 5), 463-470. For a better knowledge of the oxidation process of volatile organic compounds, the experimental study of Ethyl Acetate (EA) oxidation in CH4/EA/Oz/N2 low pressure flames has been investigated. Molecular species concentration profiles have been obtained by coupling microp- robe sampling with gas chromatography (GC/TCD/FID, GC/MS) analysis. The addition of EA to a reference methane/air flame induces (1) an enhancement of the C2 and C3 hydrocarbon oxidation pathways and (2) the formation of oxygenated intermediate compounds such as aldehydes, alcohols and ketones. The experimental results are discussed to point out the kinetic processes involved in the high temperature oxidation of EA, which may contribute to the develop- ment of a detailed chemical mechanism. To our knowledge, we present the first experimental study concerning EA oxidation in flame conditions.

04/02131 Experimental measurement of gas permeability through bitumen: results for H2, N2 and 02 Favre, E. et al. Fuel, 2004, 83, (l), 89-96. This study reports experimental results concerning the transport of permanent gases (H2, 02, N2) through bitumen between 15 and 25°C. A pressure differential technique, already used in membrane science in order to determine the permeability of gases through dense polymeric films, has been attempted with bitumen samples. It is shown that reproducible permeability data can be obtained thanks to this strategy, providing that bitumen mechanical resistance is improved by a support paper and a low leak module is used. Experimental results are analysed in terms of permeability value and temperature dependency (activation energy) in comparison with other dense and permeable organic solids (polymers). The limitations of the technique as well as its potential extension to diffusion coefficient determination are discussed.

04/02132 Exploiting special structure in interior-point algorithms for power generation dispatching Jabr, R. A. International Journal of Electrical Power & Energy Systems, 2004, 26, (1), 65-71. Different mathematical models of the power generation dispatching problem can be solved using interior-point algorithms for linear programming. The efficiency of these algorithms is related to the effort required to factorize the matrix used to solve for the search direction at each iteration. In this paper, it is shown that when the problems are formulated in symmetric form, two mathematically equivalent forms for the search direction can be obtained. These are the primal form and the dual form, both involving positive definite matrices. By analysing the fill-in in both forms prior to factorization, a form with the least fill-in is found for each of the dispatching problems. Simulation results on standard IEEE test systems and on a practical network confirm that the primal form is most advantageous for unconstrained scheduling problems but for constrained problems with a DC network model, the dual form is superior.

04/02133 Freezing time calculations for various products Mokheimer, E. M. A. et al. International Journal of Energy Research, 2003, 27, (12), 1117 1130. This article presents a numerical simulation that estimates the freezing time for different products. In this regard, the freezing process is mathematically modelled by transient heat conduction equations that incorporate the physical properties of the three distinct regions that exist during a freezing process. These regions are namely, the solid

Fuel and Energy Abstracts July 2004 293