The heat of reaction is related to the heat of formation by:
For COUSCOUS reactors, three options are available for calculation of the heat balance:
- use enthalpyF: the heat balances will use the property enthalpyF. This property is sure to include the heat of formation, and heat of reaction is therefore automatically taken into account. This is the default option. This option however requires the simulator or thermodynamic package to support the property enthalpyF.
- use enthalpy and heat of reaction: the heat balance will include the enthalpy difference between in- and outlets, as well as the heat of reaction of each of the reactions. The heat of reaction (at reference conditions of the Property Package!) must be known through the reaction package. Also, the user must make sure that the property Enthalpy does not include heats of formation, or the heat of reaction is effectively taken into account twice.
- use enthalpy and do not use heat of reaction: this will assume that the heat of reaction term is not required as the heat of formation is included in the Enthalpy property. The user must make sure that the latter is the case, or effectively the heat of reaction is ignored.
It is not possible for the reactor unit operation to tell whether heat of formation is included in property Enthalpy. It is therefore up to the user to determine whether it is included. For some property packages one can configure this. For others a choice cannot be made. In this case, often heats of formation are excluded from Enthalpy, as to prevent large round-off errors in enthalpy calculations (heats of formation are often order of magnitude higher than difference in enthalpy w.r.t. the reference state).
When using Enthalpy from TEA, heat of formation is not included. TEA supports the property enthaplyF, so when using reactors in combination with TEA it is advised to add enthalpyF to the list of supported properties using the property package configuration window, and use EnthalpyF for the enthalpy balance of reactors.