a b s t r a c tA new method based on the Young-Laplace equation for measuring contact angles and surface tensions is presented. In this approach, a first-order perturbation technique helps to analytically solve the Young-Laplace equation according to photographic images of axisymmetric sessile drops. When appropriate, the calculated drop contour is extended by mirror symmetry so that reflection of the drop into substrate allows the detection of position of the contact points. To keep a wide range of applicability, a discretisation of the drop's profile is not realised; instead, an optimisation of an advanced image-energy term fits an approximation of the Young-Laplace equation to drop boundaries. In addition, cubic B-spline interpolation is applied to the image of the drop to reach subpixel resolution. To demonstrate the method's accuracy, simulated drops as well as images of liquid coal ash slags were analysed. Thanks to the high-quality image interpolation model and the image-energy term, the experiments demonstrated robust measurements over a wide variety of image types and qualities. The method was implemented in Java and is freely available [A.F. Stalder, LBADSA, Biomedical Imaging Group, EPFL,

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Several volatile inorganic species are of concern in future integrated gasification combined cycle (IGCC) power systems because of their relation to erosion, corrosion, fouling, and slagging. The aim of this work was to obtain more information on the influence of the temperature on the release of Na, K, Cl, and S species during gasification. Therefore, six hard coals were gasified in lab-scale experiments in a helium/oxygen atmosphere at 1100, 1400, and 1700 °C. The results represent conditions in an entrained-flow gasifier. Hot-gas analysis was performed by molecular beam mass spectrometry. Species of interest were HCl, H2S, COS, SO2, NaCl, Na2SO4, KCl, and KOH. In principle, the results show a strong influence of the temperature and the coal composition on the release of the species under investigation; e.g., the release of KOH is strongly increased with an increasing temperature.

The global demand for reduced CO 2 emission from power plants can be answered by coal gasification techniques. To develop integrated gasification combined cycles that incorporate hot syngas cleaning facilities, detailed knowledge of the thermophysical properties of coal ashes is imperative. Currently, the surface tension of liquid coal ash slags in a reducing environment was studied by means of the sessile drop method. Three different algorithms were employed to analyze the acquired drop images. The slags under consideration were obtained from black and brown coals as well as from an experimental gasification reactor. Typically, a sharp surface tension decrease with temperature was found in the melting interval of the ashes. This was followed by a temperature range of smooth drop contours during which a slight rise of the surface tension could mostly be observed. Bubbles at the circumference of the drops started to appear when approaching the measurement temperature limit of 1550 °C. With regard to the temperature regime of uncorrugated drop profiles, coal ash slags exhibited surface tension values between 400 and 700 mN/m.

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