Experimentelle Bestimmung und numerische Simulation der Oberflächenspannung von Schlackesystemen unter Vergasungsbedingungen

摘要

Due to the global aims of climate protection the emission of CO2 should be reduced tremendously in the next decades. This goal can be reached by the reduction of the use of fossil fuels and by the sequestration of CO2 in the fuel converting process. Therefore the gasification technology offers the option to separate the CO2 before converting the synthesis gas to further products. Afterwards the CO2 can be stored or used in processes like the “Enhanced Oil Recovery”.To get a better understanding of the gasification process in detail and to increase the efficiency of this process it can be fully or partly reproduced as a detailed computer model by computational fluid dynamics. One important part of the process is the slag layer on the refractory line of the gasifier. To get a good model of the flow and the growth of the slag layer a good knowledge of the thermophysical properties like the viscosity or the surface tension is required. To get a better understanding of the surface tension behavior of coal slags the surface tension of different synthetic slag systems and of real coal ashes and slags was measured successfully in this work. For the measurements the sessile drop method was used. At first a sample of the slag was molten in a furnace under argon atmosphere up to a temperature of ca. 1500 °C. From the shape of the molten sample the surface tension was calculated afterwards by a computer algorithm.In total samples in eleven synthetic slag systems with different compositions and six real coal ash and slag systems, which were compared to similar composed synthetic slag systems were measured. For the synthetic systems surface tension values between 200 mN/m and 600 mN/m were found. It was shown that alkali species, especially potassium oxide and phosphor oxide will decrease the surface tension and that earth alkali species and alumina oxide will increase the surface tension of silicate slag systems. For the real coal slags surface tension value in a range of 375 mN/m to 425 mN/m were obtained. Next to the measurements it was shown that it is possible to model complex slag systems containing surface active species with the ionic radius model and the model can be improved by using the associated species model if the input data is available.