Hydrogen-rich gas production from biomass air and oxygen/steam gasification in a downdraft gasifier

Biomass gasification is an important method to obtain renewable hydrogen, However, this technology still stagnates in a laboratory scale because of its high-energy consumption. In order to get maximum hydrogen yield and decrease energy consumption, this study applies a self-heated downdraft gasifier as the reactor and uses char as the catalyst to study the characteristics of hydrogen production from biomass gasification. Air and oxygen/steam are utilized as the gasifying agents. The experimental results indicate that compared to biomass air gasification, biomass oxygen/steam gasification improves hydrogen yield depending on the volume of downdraft gasifier, and also nearly doubles the heating value of fuel gas. The maximum lower heating value of fuel gas reaches 11.11 MJ/ N m(3) for biomass oxygen/steam gasification. Over the ranges of operating conditions examined, the maximum hydrogen yield reaches 45.16 g H-2/kg biomass. For biomass oxygen/steam gasification, the content of H-2 and CO reaches 63.27-72.56%, while the content Of H2 and CO gets to 52.19-63.31% for biomass air gasification. The ratio of H-2/CO for biomass oxygen/steam gasification reaches 0.70-0.90, which is lower than that of biomass air gasification, 1.06-1.27. The experimental and comparison results prove that biomass oxygen/steam gasification in a downdraft gasifier is an effective, relatively low energy consumption technology for hydrogen-rich gas production.

Kinetics of picosecond laser pulse induced charge separation and proton transfer in bacteriorhodopsin

Bacteriorhodopsin (BR) films oriented by an electrophoretic method are deposited on a transparent conductive ITO glass. A counterelectrode of copper and gelose gel is used to compose a sandwich-type photodetector with the structure of ITO/BR film/gelose gel/Cu. A single 30-ps laser pulse and a mode-locked pulse train are respectively used to excite the BR photodetector. The ultrafast failing edge and the bipolar response signal are measured by the digital oscilloscope under seven different time ranges. Marquardt nonlinear least squares fitting is used to fit all the experimental data and a good fitting equation is found to describe the kinetic process of the photoelectric signal. Data fitting resolves six exponential components that can be assigned to a seven-step BR photocycle model: BR-->K-->KL-->L-->M-->N-->O-->BR. Comparing tests of the BR photodetector with a 100-ps Si PIN photodiode demonstrates that this type of BIR photocletector has at least 100-ps response time and can also serve as a fast photoelectric switch. (C) 2003 Society of Photo-Optical Instrumentation Engineers.

Ultra-dry oxygen atmosphere to protect tellurite glass fiber from surface crystallization

In this study we report on surface crystallization phenomena and propose a solution for the fabrication of long and robust tellurite glass fibers. The bulk tellurite glasses of interest were prepared by melting and quenching techniques. Tellurite glass preforms and fibers were fabricated by suction casting and rod-in-tube drawing methods, respectively. The surfaces of the tellurite bulk glass samples and of the drawn fibers prepared under different controlled atmospheres were examined by X-ray diffraction. When the tellurite glass fibers were drawn in ambient air containing water vapor, four primary kinds of small crystals were found to appear on the fiber surface, alpha-TeO(2), gamma-TeO(2), Zn(2)Te(3)O(8) and Na(2)Zn(3)(CO(3))(4)center dot 3H(2)O. A mechanism for this surface crystallization is proposed and a solution described, using an ultra-dry oxygen gas atmosphere to effectively prevent surface crystallization during fiber drawing. (C) 2010 Elsevier B.V. All rights reserved.

Charge Separation in Wurtzite/Zinc-Blende Heterojunction GaN Nanowires

The electronic properties of wurtzite/zinc-blende (WZ/ZB) heterojunction GaN are investigated using first-principles methods. A small component of ZB stacking formed along the growth direction in the WZ GaN nanowires does not show a significant effect on the electronic property, whereas a charge separation of electrons and holes occurs along the directions perpendicular to the growth direction in the ZB stacking. The later case provides an efficient way to separate the charge through controlling crystal structure. These results have significant implications for most state of the art excitonic solar cells and the tuning region in tunable laser diodes.

OXYGEN ANALYSES IN HIGH-TC SUPERCONDUCTING FILMS BY MEV PROTON ELASTIC BACKSCATTERING

A technique for analysis of total oxygen contents in high-T(c) superconducting films is demonstrated. It uses elastic backscattering (EBS) of 1.5-2.5 MeV protons. By comparing the H EBS spectra from substrate materials, the absolute oxygen content in the films can be easily calculated. It is estimated that the analysis can be accurate to better than 5% for YBCO films with thicknesses from several hundred angstroms to several microns. Comparisons with RBS are given and advantages of this technique are shown.

OXYGEN IN INXGA1-XASYP1-Y GROWN ON GAAS

The measurement of DLTS on the alloy InxGa1-xAsyP1-y (0 less-than-or-equal-to y less-than-or-equal-to 0.3; 0.5 greater-than-or-equal-to x greater-than-or-equal-to 0.35) shows a new signal, labeled as E2, with an activation energy of E(c) - 0.61 eV and the SIMS signals show a large number of oxygen. To clarify is further, the energy of the deep level E2 is quantitatively calculated by using Vogl's tight-binding theory and Hjalmarson's deep level theory. As a result, the deep A1-symmetric level associated with an oxygen on the anion site of InxGa1-xAsyP1-y locates deeply in the band gap. Thus, the level E2 is considered to be induced by the oxygen impurity.

DEFECT MODEL OF PHOTOCONVERSION BY OXYGEN IN SEMIINSULATING GAAS

The basic idea of a defect model of photoconversion by an oxygen impurity in semi-insulating GaAs, proposed in an earlier paper, is described in a systematic way. All experiments related to this defect, including high-resolution spectroscopic measurements, piezospectroscopic study, and recent measurements on electronic energy levels, are explained on the basis of this defect model. The predictions of the model are in good agreement with the experiments. A special negative-U mechanism in this defect is discussed in detail with an emphasis on the stability of the charge states. The theoretical basis of using a self-consistent bond-orbital model in the calculation is also given.

ELECTRICAL CHARACTERS OF OXYGEN DEFECTS IN SILICON SUBJECTED TO INTRINSIC GETTERING TREATMENT

The influence of oxygen defects on the resistivity and mobility of silicon wafers is discussed. Grinding processes were performed on the surfaces of samples in order to obtain the information on interior defects of the samples. Spreading resistivity and Hall measurements prove that SiO(x) complexes alone result in resistivity increase and mobility decrease. Deep level transient spectroscopy experiments prove that SiO(x) complexes alone are electrically active. A mechanism of carrier scattering by electrically active SiO(x) complex is proposed to explain the changes of resistivity and mobility.

AN ANALYSIS OF CHARGE STATES FOR LOCAL VIBRATIONAL-MODES BY OXYGEN DEFECTS IN SEMI-INSULATING GAAS

The high-resolution spectral measurements for new local vibrational modes near 714 cm-1 due to the oxygen defect in semi-insulating GaAs are analyzed on the basis of a model calculation by self-consistent bond orbital approach. Two charge states of oxygen atom with 1 and 2 extra electrons are assigned to be responsible for these local modes. The observed frequencies are explained by the properties of Ga-O-1 and Ga-O-2 bonds and the calculated cohesive energy indicates that the O-2 state is stable. The results are in good agreement with the kinetic analysis.