Fixed conversion reactor
The fixed conversion reactor is a simplified reactor model for which the extent or conversion of one or more reactions are specified. It has one inlet and one outlet. Before running the fixed conversion reactor, it needs to know about reactions. A reaction package must therefore be assigned to the fixed conversion reactor.
For a set of reactions, the fixed conversion reactor considers two scenarios: either the reactions are assumed to be in series or parallel.
For parallel reaction, the extent rj, or conversion ζi,j of component i, for the reaction j, is specified. Using this definition we obtain for the overall conversion of component i:
where Lin and Lout are the in- and outlet streams. It is sufficient to specify only one conversion ζi,j per reaction since this fixes the effective rate of the reaction under consideration:
The definition as above requires consistent inputs; only a single extent, rj, or conversion, ζi,j is allowed per reaction. Invalid specifications may yield negative compositions and the unit will return with an error.
The conversion for serial reactions are defined by:
where the intermediate total flow rates, Li, are obtained from a total mass balance. This equation is evaluated sequentially in the same order as the reactions appear in the "reactions" tab of the unit operation's configuration window.
The fixed conversion reactor can be modeled either as an isothermal process, or as process with external heating or cooling. In the first case, outlet temperature is specified. In case of specified heat duty, the reactor temperature is calculated from the energy balance:
where H denotes the mixture enthalpy, Q the specified heat duty, rj the reaction rates and (-ΔHR,j) the heat of reaction for the j-th reaction (see enthalpy balance details below for heat of reaction).
The heat duty can be specified directly or via an energy inlet stream. If heat duty is not specified via an energy inlet stream, an energy outlet stream can be connected that will receive the heat duty for the reactor.
For the enthalpy balance, three options are available: use enthalpyF, use enthalpy and heat of reaction, or use enthalpy and do not use heat of reaction. See reaction enthalpy for details.
Pressure drop can be specified as well. Since conversions are specified, pressure does not influence the reaction rates or equilibria.