CSTR

The CSTR (Continuously Stirred Tank Reactor) is a simplified reactor model in which the reactor content is assumed single phase and well mixed. It has one inlet and one outlet. Before running the CSTR, it needs to know about reactions. A reaction package must therefore be assigned to the CSTR reactor.

From the assigned reaction package, you can specify equilibrium reactions as well as kinetic reactions. Kinetic reactions have a reaction rate that is specified either as homogeneous (mol/s/m³) or heterogeneous (mol/s/kg catalyst).

The CSTR is implemented a single phase reactor. The reactor phase must be specified. Only reactions that take place in the specified phase can be selected. If you want to calculate the reactions in combination with the phase equilibrium and you have only equilibrium reactions, you can use the Equilibrium Reactor. For single-phase equilibrium systems in which the equilibrium constants are not known in advance, you can use the Gibbs minimization reactor.

If homogeneous kinetic reactions are selected, the reactor volume needs to be specified.

If heterogeneous kinetic reactions are selected, either the catalyst mass needs to be specified, or the catalyst density and volume must be specified. The catalyst mass is then calculated as the product of catalyst density and catalyst volume.

If both homogeneous and heterogeneous reactions are selected, the reactor volume needs to be specified. Also, two out of three must be specified for catalyst volume, catalyst density and catalyst mass (the third one will be calculated from the relation catalyst mass = catalyst density times catalyst volume). The catalyst volume will be subtracted from the reactor volume to obtain the effective reaction volume.

There is no specification for catalyst porosity; if the reactive phase exists inside the catalyst pores, catalyst density or volume must be specified to reflect this.

Energy balance

The CSTR 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, r_j the reaction extents and (-ΔH_R,j) the heat of reaction for the j-th reaction (see enthalpy balance details below for heat of reaction).

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.

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.

After the reactor is solved, the outlet will be flashed at specified pressure (after pressure drop) and at the specified (in case of isothermal) or calculated temperature. If the phase equilibrium is such that phases appear that are not the specified reaction phase, warnings are generated. In this case, the specified heat duty will not be met, as the reactor was solved for enthalpy of a single phase. The enthalpy change resulting from the flash will cause the enthalpy not to be balanced.

Other options

Pressure drop can be specified. The reaction takes place at the pressure after taking into account the pressure drop.

The CSTR is solved iteratively. Convergence tolerance and maximum number of iterations can be specified.

Report

The last run report will show the extent of the reactions as they have taken place, the equilibrium constants and reaction rates as calculated at reaction conditions, the basis for which the equilibrium constants hold, and the heat balance details.