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Material Properties / Streams of classic composition / Streams of type Air, Flue gas, Gas, Crude gas
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    Streams of type Air, Flue gas, Gas, Crude gas
    In This Topic

    Gas Material Value Tables

    You can choose between these different tables:

    In the model options there is a flag for this called “Formulation gas table“ to set the default table to be used for all fluids defined in a model by components 1 and 33.

    An individual specification of the gas table to be used is possible within each component 1 or 33 (sheet "Material Fractions"), where you can specify another table than the one selected as the model option. Which material table has been used for a stream is indicated by the value of its flag FGASFORMULATION. If two different tables "meet" in a mixer, the one at connection point 1 is used for the output stream.
    All tables assume the model of an ideal mixture of the individual gases (even LibHuGas, where the model of an ideal mixture of real gases is used).
    The material tables VDI, NASA and LibHuGas are available for the following gases only:

    All other substances or gases resp. are always calculated by using FDBR polynomials.

    See: Brandt,F.: Wärmeübertragung in Dampferzeugern und Wärmetauschern, FDBR-Buchreihe 1995, Bd.2, Vulkan Verlag Essen

    Real gases - LibHuGas

    LibHuGas by Professor Kretzschmar (University Zittau/Görlitz) can be used for the calculation of real gases. As this library only contains the substances Ar, Ne, N2, O2, CO, CO2, H2O, and SO2, all other substances are calculated as ideal gas according to FDBR. LibHuGas can then consider the water fraction below 0 °C as well (provided that the water fraction is small enough, so that the water remains in the gaseous phase). As using LibHuGas is only possible up to a water content of 99 percent, the LibIF97 will be used in the case of a higher water content.

    To represent other gases, algorithms have additionally been implemented that perform quickly calculable corrections on the ideal gas calculation in order to represent the real gas behaviour by approximation.
    These are the following algorithms:
    In the model options there is a flag for this called “Real gas correction“. It is active when one of the three ideal gas algorithms has been selected and allows either to apply no real gas correction at all or one of the methods mentioned above.
    All algorithms of the real gas correction have been developed exclusively for gases. If one or more components condense, it will be necessary to calculate with more complex algorithms like e.g. the ones provided by the REFPROP library. 
    Often, however, there are only a few streams of a model, for which the real gas correction is significant. An application to all air and flue gas streams with pressures in the range of the atmospheric pressure is usually unnecessary.
    The real gas correction to be applied is specified in Component 1 and 33 respectively (boundary value and start value respectively) in the sheet “Material Fractions”. The definition is then valid
    for the respective stream and is then passed on along the main flow. Which correction has been used can be viewed on the line (tab "Composition") in the result value FREALGC.  If two different real gas corrections meet in a mixer, a warning will be output.

    Water fraction in classical streams in gaseous, liquid and solid phase

    In classical streams (air, flue gas, gas, crude gas, coal, oil, user-defined fluid) Ebsilon calculates the fraction of water of the gaseous phase depending on the corresponding partial pressure. The remaining fraction of the water is liquid above the triple point (0.01°C); below it, it is solid.

    For Ebsilon, the difference between the solid and liquid phase is only in the enthalpy: the enthalpy of the solid phase is decreased by the melting heat. Therefore at T=0.01°C there was a leap in the enthalpy of the flue gas (as long as a liquid or solid fraction of water was present).

    Due to the low partial pressure of the water at these temperatures (0.0061 bar at the triple point), however, the phase equilibrium solid/gaseous (sublimation) only matters in the case of a very low water concentration. At higher concentrations, the gas fraction is negligible, and the behaviour is dominated by the phase transition solid/liquid. Due to the anomaly of the water, with a rising pressure this phase limit will shift to lower temperatures: 0.0026°C at 1 bar, -0.064°C at 10 bar, -0.74°C at 100 bar.

    The LibIce is available in Ebsilon for modeling this behaviour precisely (in the 2-phase-liquid or 2-phase-gaseous stream). For the classical streams, the focus is on the speed of the calculation, so that we have refrained from considering the pressure dependency here (especially as the enthalpy is considered as independent of the pressure).
    The transition point, however, has been shifted from +0.01°C to -0.000001°C from Release 12 on in order to prevent being in the ice phase at T=0°C already. There are two reasons for this:

    The previous value of 0.01°C was only correct at a pressure of 0.0061 bar, and too high for all other pressures. The new value of -0.000001°C corresponds to reality for 1.35 bar; for lower pressures it is slightly too small and for higher ones slightly too high, i.e. more suitable on the whole.

    For streams that contain liquid or solid H2O, however, other enthalpies will now result in the temperature range between -0.000001 and +0.01°C due to the shifting of the transition point. Here the new results will be more useful in most cases. If, however, the solid phase is really desired, the temperature should be decreased to e.g. -0.0000011°C. The results will then be virtually identical with the previous ones.
    The considerations above both apply to free water (“H2O“) and to the bound water existing in the coal (”H2OB“). Ebsilon therefore assumes, that in fact the water bound in the capillaries within the coal cannot evaporate (i.e. there is no phase transition liquid/gaseous), but a phase transition into the solid phase is possible.

    Consideration of non-gaseous components for the specific volume of gases

    Only the gaseous components are considered for the calculation of the specific volume (and thus also the density) of gases (air, flue gas, gas, crude gas), because the fraction of the liquid and solid components to the specific volume is generally negligible due to the higher density.

    Generally the specific volume of these components cannot be calculated because usually only the elementary composition or the general specification “ash“ is specified for this.

    To specify the density for this fraction (liquid and solid parts) use the the specification value “Density for fraction defined by elementary analysis“ (RHOELEM).

    As result values on all streams there are both RHO (mean density of the total flow) and RHOELEM (Density for fraction defined by elementary analysis).

    If a value of 0 is entered for the density (RHOELEM), the fraction of the substances given as elementary analysis will be neglected when determining the specific volume.
    In the case of the non-gaseous components whose chemical composition is known, the specific volume is determined from the corresponding material data. This applies to liquid H2O, NH3, and CO2, for which libraries are integrated in Ebsilon, as well as the substances for the direct desulfurization, for which the following constants are used:

    Heating value definition

    See chapter Heating value.

     

     

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