Oxy-steam gasification of biomass for hydrogen rich syngas production using downdraft reactor configuration

The paper focuses on the use of oxygen and steam as the gasification agents in the thermochemical conversion of biomass to produce hydrogen rich syngas, using a downdraft reactor configuration. Performance of the reactor is evaluated for different equivalence ratios (ER), steam to biomass ratios (SBR) and moisture content in the fuel. The results are compared and evaluated with chemical equilibrium analysis and reaction kinetics along with the results available in the literature. Parametric study suggests that, with increase in SBR, hydrogen fraction in the syngas increases but necessitates an increase in the ER to maintain reactor temperature toward stable operating conditions. SBR is varied from 0.75 to 2.7 and ER from 0.18 to 0.3. The peak hydrogen yield is found to be 104g/kg of biomass at SBR of 2.7. Further, significant enhancement in H-2 yield and H-2 to CO ratio is observed at higher SBR (SBR=1.5-2.7) compared with lower range SBR (SBR=0.75-1.5). Experiments were conducted using wet wood chips to induce moisture into the reacting system and compare the performance with dry wood with steam. The results clearly indicate the both hydrogen generation and the gasification efficiency ((g)) are better in the latter case. With the increase in SBR, gasification efficiency ((g)) and lower heating value (LHV) tend to reduce. Gasification efficiency of 85.8% is reported with LHV of 8.9MJNm(-3) at SBR of 0.75 compared with 69.5% efficiency at SBR of 2.5 and lower LHV of 7.4 at MJNm(-3) at SBR of 2.7. These are argued on the basis of the energy required for steam generation and the extent of steam consumption during the reaction, which translates subsequently in the LHV of syngas. From the analysis of the results, it is evident that reaction kinetics plays a crucial role in the conversion process. The study also presents the importance of reaction kinetics, which controls the overall performance related to efficiency, H-2 yield, H-2 to CO fraction and LHV of syngas, and their dependence on the process parameters SBR and ER. Copyright (c) 2013 John Wiley & Sons, Ltd.

Filter Configuration and PWM Method For Single Phase Inverters with Reduced Conducted EMI Noise

Electromagnetic Interference (EMI) noise is one of the major issues during the design of the grid-tied power converters. Presence of high dv/dt in Common Mode (CM) voltage, excites the parasitic capacitances and causes injection of narrow peaky current to ground. This results in high EMI noise level. A topology consisting of a single phase PWM-rectifier with LCL filter, utilising bipolar PWM method is proposed which reduces the EMI noise level by more than 30dB. This filter topology is shown to be insensitive to the switching delays between the legs of the inverter. The proposed topology eliminates high dv/dt from the dc-bus CM voltage by making it sinusoidal. Hence, the high frequency CM current injection to ground is minimized.

Dopant-configuration controlled carrier scattering in graphene

Controlling optical and electronic properties of graphene via substitutional doping is central to many fascinating applications. Doping graphene with boron (B) or nitrogen (N) has led to p- or n-type graphene; however, the electron mobility in doped-graphene is severely compromised due to increased electron-defect scattering. Here, we demonstrate through Raman spectroscopy, nonlinear optical and ultrafast spectroscopy, and density functional theory that the graphitic dopant configuration is stable in graphene and does not significantly alter electron-electron or electron-phonon scattering, that is otherwise present in doped graphene, by preserving the crystal coherence length (L-a).

Filter Configuration and PWM Method For Single-Phase Inverters With Reduced Conducted EMI Noise

Electromagnetic interference (EMI) noise is one of the major issues during design of grid-tied power converters. A novel LCL filter topology for a single-phase pulsewidth modulation (PWM) rectifier that makes use of bipolar PWM method is proposed for a single-phase to three-phase motor drive power converter. The proposed topology eliminates high dv/dt from the dc-bus common-mode (CM) voltage by making it sinusoidal. Hence, the high-frequency CM current injection to the ground and the motor-side CM current are minimized. The proposed filter configuration makes the system insensitive to circuit non-idealities such as mismatch in inductors values, unequal turn-on and turn-off delays, and dead-time mismatch between the inverter legs. Different variants of the filter topology are compared to establish the effectiveness of the proposed circuit. Experimental results based on the EMI measurement on the grid side and the CM current measurement on the motor side are presented for a 5-kW motor drive. It is shown that the proposed filter topology reduces the EMI noise level by about 35 dB.

Study of a four-level system in vee plus ladder configuration

We present the results of a theoretical study of a four-level atomic system in vee + ladder configuration using a density matrix analysis. The absorption and dispersion profiles are derived for a weak probe field and for varying strengths of the two strong control fields. For specificity, we choose energy levels of Rb-87, and present results for both stationary atoms and moving atoms in room temperature vapor. An electromagnetically induced absorption (EIA) peak with negative dispersion is observed at zero probe de-tuning when the control fields have equal strengths, which switches to electromagnetically induced transparency (ET) with positive dispersion (due to splitting of the EIA peak) when the control fields are unequal. There is significant linewidth narrowing in thermal vapor. (C) 2015 Elsevier B.V. All rights reserved.

Simulated long-term climate response to idealized solar geoengineering

Solar geoengineering has been proposed as a potential means to counteract anthropogenic climate change, yet it is unknown how such climate intervention might affect the Earth's climate on the millennial time scale. Here we use the HadCM3L model to conduct a 1000year sunshade geoengineering simulation in which solar irradiance is uniformly reduced by 4% to approximately offset global mean warming from an abrupt quadrupling of atmospheric CO2. During the 1000year period, modeled global climate, including temperature, hydrological cycle, and ocean circulation of the high-CO2 simulation departs substantially from that of the control preindustrial simulation, whereas the climate of the geoengineering simulation remains much closer to that of the preindustrial state with little drift. The results of our study do not support the hypothesis that nonlinearities in the climate system would cause substantial drift in the climate system if solar geoengineering was to be deployed on the timescale of a millennium.

Influence of the Configuration of Obstacles on Premixed Flame Acceleration in a Tube

在一端封闭、一端开口的火焰传播管中均匀布置障碍物,研究了障碍物结构对管道中预混火焰传播的影 响。结果表明,由于障碍物的扰动,火焰不断加速,在阻塞比相同的条件下,最终的火焰稳态速度与障碍物的形状 和间距基本无关,其中障碍物间距仅仅影响火焰的加速速率,在障碍物间距约等于火焰传播管内径( W/ D≈1. 0) 时,平均火焰速度达到最大值,火焰到达稳态传播的距离最短。同时,本文用一维简化模型模拟了火焰在障碍物管 道中的加速过程,计算结果与实验测试结果在定性上比较吻合,说明在管内火焰速度较低的情况下,用一维可压缩 流动近似处理能初步揭示管内火焰的加速机制。

Contingent sensitivity to configuration in a nonlinear evolution system

A trans-scopic sensitivity of macroscopic failure to slight differentiation in the meso-scopic structure of a system with nonlinear evolution is reported. A periodical chain following a non-local load-sharing evolution was applied as a propotype in failure study. The results demonstrate that there is a transition region composed of globally stable (GS) and evolution induced catastrophic (EIC) modes. That is different from a critical threshold as predicted by percolation and renormalization group theories. Moreover, the EIC mode shows a distinctive sample specific behaviour. For instance, some neighbouring initial states may evolve into completely different final states, though different initial states can evolve into the same final states. As an example, a marginal configuration of EIC mode, a quasi-Fibonacci skeleton, is constructed.

Analytical Study of Idealized Two-Dimensional Cellular Detonations

In this study, the idealized two-dimensional detonation cells were decomposed into the primary units referred to as sub-cells. Based on the theory of oblique shock waves, an analytical formula was derived to describe the relation between the Mach number ratio through triple-shock collision and the geometric properties of the cell. By applying a modified blast wave theory, an analytical model was developed to predict the propagation of detonation waves along the cell. The calculated results show that detonation wave is, first, strengthened at the beginning of the cell after triple-shock collision, and then decays till reaching the cell end. The analytical results were compared with experimental data and previous numerical results; the agreement between them appears to be good, in general.

Analysis of Dislocation-Induced Strain Field in an Idealized Wafer-Bonded Microstructure

The localized dislocation at the interface induces uneven strain distribution in two wafer-bonded layers. Because of the different elastic properties of two bonding layers and this uneven strain distribution, the bilayered microstructure deflects and deflection relaxes the strains. Depending on the microstructure dimensions, elastic properties and lattice parameters, the contribution of deflection to strain field can be very significant. The interface condition also plays an important role in relaxing strain. Two models capable of describing different interface conditions are used for the analysis and offer a more comprehensive study on the dislocation-induced strain field in a wafer-bonded bilayered microstructure. The combined effect of microstructure dimensions and interface condition on the strain is presented and compared.

Modeling Ammonothermal Growth of GaN Single Crystals: The Role of Transport

Single crystal gallium nitride (GaN) is an important technological material used primarily for the manufacture of blue light lasers. An important area of contemporary research is developing a viable growth technique. The ammonothermal technique is an important candidate among many others with promise of commercially viable growth rates and material quality. The GaN growth rates are a complicated function of dissolution kinetics, transport by thermal convection and crystallization kinetics. A complete modeling effort for the growth would involve modeling each of these phenomena and also the coupling between these. As a first step, the crystallization and dissolution kinetics were idealized and the growth rates as determined purely by transport were investigated. The growth rates thus obtained were termed ‘transport determined growth rates’ and in principle are the maximum growth rates that can be obtained for a given configuration of the system. Using this concept, a parametric study was conducted primarily on the geometric and the thermal boundary conditions of the system to optimize the ‘transport determined growth rate’ and determine conditions when transport might be a bottleneck.

NUMERICAL ANALYSIS OF THE FLOWFIELD IN A SUPERSONIC COIL WITH AN INTERLEAVED JET CONFIGURATION AND ITS EFFECT ON THE GAIN DISTRIBUTION

In a supersonic chemical oxygen-iodine laser (COIL) operating without primary buffer gas, the features of flowfield have significant effects on the Laser efficiency and beam quality. In this paper three-dimensional, multi-species, chemically reactive CFD technology was used to study the flowfield in mixing nozzle implemented with a supersonic interleaving jet configuration. The features of the flowfield as well as its effect on the spatial distribution of small signal gain were analyzed.