lowering the productivity of these systems. Thus, a rational approach was developed for
controlling proper operation of true solid/gas systems, involving a thermodynamic
control of the different molecular species present in the gaseous phase thus insuring the
true solid/ gas characteristics.
Controlling the thermodynamic parameters of a gaseous phaseIf one considers a solid gas bioreactor based on a packed bed, the following
representation can be made, as depicted on Figure 9.1. This allows very simple
parameters controlling the thermodynamic activity of each compound to be easily
identified.
The inlet gas will be characterised by its molar composition, the inlet temperature and
the total pressure of the system. For poorly charged gas, if one assumes that it can be
considered an ideal gas, these few parameters allow a complete definition of the
thermodynamics of the gas entering the reactor.
While the molar composition of the inlet gas and the total pressure are known, it is
possible to calculate easily the partial pressure of each compound (Ppx), resulting from
the following equation:
assuming that nx is equal to the number of moles of X in a finite gas volume containing a
total of ntotal moles at the absolute pressure of Pa. For continuous systems, the molar flow
Q can be used instead of n. Then, the thermodynamic activity (ax) can be calculated using
Solid/gas systems, theory and applications 265