In-situ Measuring Technique for Heat Capacity Determination of Steam-gas Mixtures at High Enthalpy Geothermal Sites

Abstract

High enthalpy geothermal sites provide hot steam, which can directly be used in flash power plants for electricity generation. In order to dimension the steam turbine it is essential to know the steam enthalpy expressed in isobaric heat capacity and Joule Thomson coefficient. Geothermal steam is a mixture of both water vapour and non-condensable gases like carbon dioxide, methane and other volatile light hydrocarbons as well as hydrogen sulphide. This gas composition determines the thermodynamic properties of the steam flow. Usually at operating power plant pressure, the gas/steam mixture is far from being an ideal mixture, which makes it difficult to calculate the fluid enthalpy. Here in-situ measurements could help to close the gap of knowledge concerning the influence of the volatiles. For thermal water, heat capacity is already measured by in-situ measuring technique of KIT. In a further step, it is considered to adopt this technique to compressible fluids and to test it on-line at high enthalpy geothermal sites.