COCO - CAPE-OPEN to CAPE-OPEN simulation environment

Gibbs minimization reactor

The Gibbs minimization reactor is a simplified reactor model for which the reaction equilibrium is calculated by minimizing the Gibbs free energy (at specified temperature and pressure) or maximizing entropy (at specified pressure and heat duty).

One can specify - as with other reactors - a reaction package that defines the reactions that the Gibbs minimization reactor should consider. This is however not required; one can also indicate the reactive compounds. To specify the reactive compounds, edit the reactor, and put a check mark in front of all compounds that will take part in the reaction equilibrium at the Reactive Compounds tab (this can only be done when the reactor knows which compounds are present; for this it may be required to first connect one of the material ports of the reactor). A set of linearly independent reactions will be automatically derived from the element and charge balances.

The Gibbs minimization reactor is a single-phase reactor. The reactor phase must be specified. The specified phase must be defined by the thermodynamic system by which the connected material streams are defined. The Gibbs minimization reactor is suitable for use when reaction equilibrium constants are not known in advance and when the reaction phase is known (otherwise, the CSTR or Equilibrium Reactor can be used instead).

The Gibbs minimization reactor requires knowledge of enthalpy and enthalpy that include the formation terms. Properties "enthalpyF" and "entropyF" must be defined in the simulation for the Gibbs minimization reactor to properly work.

Energy balance

The Gibbs minimization reactor can be modeled either as an isothermal process, or as process with external heating or cooling. In the first case, reactor temperature is specified. In case of specified heat duty, the reactor temperature is calculated from the energy balance; the energy balance is based on the enthalpy that includes formation heats and does not require specification of heats 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.

Other options

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

The Gibbs minimization reactor is solved iteratively. Convergence tolerance and maximum number of iterations can be specified.

Solution details

The solution methodology is roughly described in van Baten, J.M., Szczepanski, R., A thermodynamic equilibrium reactor model as a CAPE-OPEN unit operation, Computers and Chemical Engineering 35 (2011) 1251-1256. However, the projection method described in that article is no longer used. Instead the compositions are determined by truncation of flow rates that violate non-negativity constraints, and the goal function is solved subject to the non-negativity constraints.