Global Change Abstracts The Swiss Contribution - SCNAT

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194 Global Change Abstracts – The Swiss Contribution | Mitigation and Adaptation Technologies 4 Mitigation and Adaptation Technologies 08.1-412 Thermo-economic optimization of a solid oxide fuel cell, gas turbine hybrid system Autissier N, Palazzi F, Marechal F, van Herle J, Favrat D Switzerland Engineering , Energy & Fuels Large scale power production benefits from the high efficiency of gas-steam combined cycles. fit the lower power range, fuel cells are a good candidate to combine with gas turbines. Such systems can achieve efficiencies exceeding 60%. High-temperature solid oxide fuel cells SOFC) offer good opportunities for this coupling. In this paper a systematic method to select a design according to user specifications is presented. The most attractive configurations of this technology coupling art? identified using a thermoeconomic multi-objective optimization approach. The SOFC model includes detailed computation of losses of the electrodes and thermal management. The system is integrated using pinch based methods. A thermo-econonnic approach is then used to compute the integrated system performances, size, and cost. This allows to perform the optimization of the system with regard to two objectives: minimize the specific cost and maximize the efficiency Optimization results prove the existence of designs with costs from 2400 $ / kW for a 44% efficiency to 6700 $ /kW for a 70% efficiency. Several design options are analyzed regarding, among others fuel processing, pressure ratio, or turbine inlet temperature. The model of a pressurized SOFC-mu GT hybrid cycle combines a state-of-theart planar SOFC with a high- speed micro-gas turbine sustained by air bearings. Journal of Fuel Cell Science and Technology, 2007, V4, N2, MAY, pp 123-129. 08.1-413 Effect of pressure and fuel-air unmixedness on NOx emissions from industrial gas turbine burners Biagioli F, Güthe F Switzerland Energy & Fuels , Engineering The effect of fuel-air unmixedness on NOx emissions from industrial lean premixed gas turbine burners fueled with natural gas is analyzed in the pressure range from 1 to 30 bar. The analysis is based on a model where NOx production is split, according to a Darnkohler number criterion, into a “prompt” (fast) contribution generated within the very narrow instantaneous heat release region (flamelet) and a “postflame” (slow) one, generated in the combustion products. Using GRIM chemical kinetics, it is found that (a) the prompt NOx contribution is approximately a factor of 3 less sensitive to adiabatic flame temperature variations than postflame NOx and (b) prompt and postflame NOx change with pressure respectively according to an exponent alpha(PR) similar or equal to -0.45 and alpha(PF) similar or equal to 0.67. It is shown that total NOx emissions change from being mostly of prompt type at 1 bar to being mostly of postflame type at 30 bar, so that the effect of fuel-air unmixedness on NOx emissions significantly increases with increasing pressure. The combination of these findings yields a negative NOx pressure exponent under fully premixed conditions across a rather large range of equivalence ratios but a positive one for levels of fuel-air unmixedness typical of industrial burners. This result is confirmed by the application of the NOx model in the large eddy simulation of the ALSTOM EV double cone burner, which gives, in line with experimental data, an NOx pressure exponent growing, with equivalence ratio, from similar or equal to 0.1 to similar or equal to 0.67. Combustion and Flame, 2007, V151, N1-2, OCT, pp 274-288. 08.1-414 Consumption and efficiency of a passenger car with a hydrogen/oxygen PEFC based hybrid electric drivetrain Büchi F N, Paganelli G, Dietrich P, Laurent D, Tsukada A, Varenne P, Delfino A, Koetz R, Freunberger S A, Magne P A, Walser D, Olsommer D Switzerland Meteorology & Atmospheric Sciences, Engineering, Energy & Fuels The main factors for reducing the consumption of a vehicle are reduction of curb weight, air drag and increase in the drivetrain efficiency. Highly efficient drivetrains can be developed based on PEFC technology and curb weight may be limited by an innovative vehicle construction. In this paper, data on consumption and efficiency of a fourplace passenger vehicle with a curb weight of 1 850 kg and an H-2/O-2 fed PEFC/Supercap hybrid electric powertrain are presented. Hydrogen consumption in the New European Driving Cycle is 0.67 kg H-2/100 km, which corresponds to a gasoline equivalent cosumption of 2.51/100 km. When including the energy needed to supply pure oxygen, the calculated consumption increases from 0.67 to 0.69-0.79 kg H-2/100 km, depending on the method of oxygen production. Fuel Cells, 2007, V7, N4, AUG, pp 329-335.
Global Change Abstracts – The Swiss Contribution | Mitigation and Adaptation Technologies 08.1-415 Flame-synthesized LaCoO3-supported Pd 2. Catalytic behavior in the reduction of NO by H-2 under lean conditions Chiarello G L, Ferri D, Grunwaldt J D, Forni L, Baiker A Italy, Switzerland Engineering , Meteorology & Atmospheric Sciences A 0.5 wt% Pd/LaCoO3, prepared by flame-spray pyrolysis (FP), was tested as catalyst for the low-temperature selective reduction of NO by H-2 in the presence of excess O-2. In particular, the effect of the precalcination and prereduction temperature on catalytic activity was compared with that of a similar Pd/LaCoO3 sample prepared by impregnation with a Pd solution of FP-prepared LaCoO3. The FP-made catalyst allowed full NO conversion at 150 degrees C, with 78% selectivity to N-2, thus outperforming the catalytic behavior of the corresponding sample prepared by impregnation. The higher activity of the FP-made catalyst has been attributed to the formation of segregated Co metal particles, not present in the impregnated sample, formed during the precalcination at 800 degrees C, followed by reduction at 300 degrees C. Two reaction mechanisms can be deduced from the temperature-programmed experiments. The first of these, occurring at lower temperatures, indicates cooperation between the Pd and Co metal particles, with formation of active nitrates on cobalt, successively reduced by hydrogen spillover from Pd. The second, occurring at higher temperature, allows 50% conversion of NO, with >90% selectivity to N-2, and involves N adatoms formed by dissociative NO adsorption over Pd. Prereduction at 600 degrees C led to a slight increase in catalytic activity, due to the formation of a Pd-Co alloy, which is more stable on reoxidization compared with Pd alone. Moreover, the cooperative reaction mechanism seems to be favored by the proximity of Co and Pd in metal particles. Journal of Catalysis, 2007, V252, N2, DEC 10, pp 137-147. 08.1-416 Flame-synthesized LaCoO3-supported Pd 1. Structure, thermal stability and reducibility Chiarello G L, Grunwaldt J D, Ferri D, Krumeich R, Oliva C, Forni L, Baiker A Italy, Switzerland Engineering , Meteorology & Atmospheric Sciences Nanosized LaCoO3 (LCO) and 0.5 wt% Pd/LaCoO3 (PdLCO) were synthesized in a single step by flame-spray pyrolysis (FP) and characterized by N-2 adsorption-desorption at 77 K (BET), electron microscopy (HRTEM, STEM-EDXS), in situ XRD, in situ fluorescence XANES and EXAFS (around the 195 Pd K-edge), EPR, and H-2 TGA-TPR. The stability of the perovskite structure under different treatments and the location of Pd were addressed by calcination at 600 and 800 degrees C and successive reduction in 10% H-2/He to 300 and 600 degrees C. The as-prepared Pd LCO exhibited a high surface area (ca. 100 m(2)/g). Palladium appeared to be finely dispersed on the FP material and was partially incorporated in the perovskite lattice. Calcination at 800 degrees C caused sintering and substantial incorporation of Pd at the B-site of the ABO(3) framework. EXAFS revealed that the Pd-O distance was shorter than in PdO and further decreased with increasing calcination temperature, simultaneously with the appearance of a Pd-La contribution. The reduction process involved both Pd and Co. In the 100-300 degrees C range, the reduction of Co3+ to Co2+ (from LaCoO3 to La2CO 2O 5) and the segregation of Pd in the form of metal particles occurred. The reduction of Co was already reversible at 120 degrees C, and the perovskite structure was restored after exposure to oxygen. In contrast, Pd remained in the metallic state. Therefore, the final structure of PdLCO after mild reoxidation consisted of Pd and Co particles supported on LaCoO3- In contrast, reduction at 600 degrees C led to the formation of a Pd-Co alloy. The composition of PdLCO reduced at different temperatures is likely to strongly influence the catalytic processes involved in combustion exhaust after treatment. Journal of Catalysis, 2007, V252, N2, DEC 10, pp 127-136. 08.1-417 Increase of passenger car engine efficiency with low engine-out emissions using hydrogen-natural gas mixtures: A thermodynamic analysis Dimopoulos P, Rechsteiner C, Soltic P, Laemmle C, Boulouchos K Switzerland Engineering , Energy & Fuels In this study a state of the art passenger car natural gas engine was optimised for hydrogen natural gas mixtures and high exhaust gas recirculation (EGR) rates in the part load domain. With optimal combinations of spark timing (ST) and EGR rate the achievements are significant efficiency increase with substantially lower engine-out NOx while total unburned hydrocarbons or CO-engineout emissions are not affected. Comprehensive investigations of the parameter space using design of experiments (DoE) algorithms provided a complete picture of the potential of such applications. Combustion analysis on the other hand allowed to
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