In Ebsilon there are basically two types of substances:

• Substances with a known chemical structure, mostly molecules (H2O, CH2=CH-CH=CH2), but also atoms (noble gases) or ions (MgO, CaSO4). Most of these substances are gaseous, but some are also variable in phase. For these substances, all thermodynamic quantities are well defined, including density and calorific value.
  
• Substances with an unknown chemical structure, mostly solids or liquids, which have been formed from organic material, where bonds from the original organic molecules are partly still present, but whose properties depend on the previous history and therefore cannot be calculated. In Ebsilon, such materials are mainly used as fuels (coal, biomass, oil).

 

For the combustion calculation, Ebsilon needs to know how much heat is released during combustion (i.e. the calorific value must be given) and what exhaust gases are produced.

To know how much CO2 is produced, itmust be known how many C atoms are in the fuel. To know how much H20 is produced, it must be known how many H atoms are in the fuel, etc.

This information is given by the user in the "elemental analysis".

However, this is limited to the elements involved in the combustion reaction, namely C, H, O, N, S and Cl. All other components of the fuel are summarised in Ebsilon as "ash", which are not changed during combustion.

In the case of coal, it is also possible to add chemically bound water (H2OB), which then simply becomes (normal) H2O during combustion. Since the density of this substance cannot be calculated either, it must also be specified as the default value RHOELEM. This specifies the density of the entire unknown substance, i.e. C, H, O, N, S, Cl, ash and H2OB.

However, in a pipeline, for example of the coal type, substances with unknown and known substance can now be mixed, for example when lime is added to the fuel or a carrier air behind a mill. In this case RHOELEM is then used just for the proportion of C, H, O, N, S, Cl, ash and H2OB, for the known substances the densities calculated by the programme are used.

 

Mg and Ca are not part of the elemental analysis, but substances with well-defined composition.

To make this clearer, Release 15 no longer says "atomic" but "metallic". Since there is certainly no metallic Mg or Ca in coal, these must not be specified in the elemental analysis. Mg and Ca in coal are already oxidised and must therefore be specified as components of the ash. If metallic Mg and Ca were to be specified, these substances would be burnt and this would lead to errors in the oxygen demand and possibly also in the calorific value if this is calculated from the composition.