The Reactor Node is used to select the reactor type and its properties. This node is very similar to the Reactor Node in the Estimation tree.
Reactor Type / Phase Behavior
This grid has the same design as the reactor node under the Estimation tree. Please see the
help document associated with the Estimation tree.
Phases
This grid has the same design as the reactor node under the Estimation tree. Please see the
help document associated with the Estimation tree.
Reactor Properties
This grid displays the reactor properties, which vary depending on the reactor type, namely
Batch,
CSTR or
PFR. The contents of the grid for each reactor are explained below.
Batch
If the reactor type selected in the Reactor Type / Phase Behaviour grid is
Batch, the following properties are listed:
- Volume: Constant - Optimized or Use Density.
If it is Constant - Optimized, the reactor volume is optimized between the specified bounds in Design Values. However, this optimized value is not allowed to change with the batch time.
When Use Density is selected, liquid and solid phase volumes are calculated based on the compounds Molecular Weights and Density Values loaded in Chemistry → Compounds → Properties node.
When Density calculations are enabled for a multiphase batch reactor with a gas phase, the volume of the gas phase along time is given by:
Volume(Gas) = Volume(Total) - [Volume(Liquid) + Volume(Solid) ]
The total volume may be optimized between bounds loaded in Design Values, and the liquid/solid phase volumes are obtained through density model.
You may explore this example to see how to model a reactor with the density option enabled.
- Pressure: Free, Controlled or Fixed at SetPoint. The default option is Free, which is the only option available for single liquid phase. The other options can be chosen for a Single Gas reactor, or for a Multiphase reactor with a gas phase. A more detailed explanation is given below.
- Fedbatch Flows: No, Yes or N/A
- Outflows: No, Yes or N/A
- Volume from Flow Only: No, Yes.
This row only becomes available for a multiphase batch reactor with density calculations enabled in the Volume row and with at least one Fedbatch or Outflow.
This special option is only intended to be used for a liquid-gas system. It allows you to calculate liquid volume using a relaxed density model: the initial liquid volume is set in Design Values node, while its variation along time is obtained by adding/subtracting the equivalent liquid volume of compounds entering/leaving the system through Fedbatch flows/Outflows. Another simplification is that compounds whose density parameters are not loaded are ignored in the volume calculation: this is useful because you need not to provide density parameters for all compounds.
Volume of gas phase is calculated by difference between total volume provided Design Values data and the calculated liquid volume.
- Initial Charge: Optimize Ratio or Fixed Ratio.
The default is Optimize Ratio, meaning that when a optimization run is launched, the initial charge is optimized without any constraints other than the lower and upper bounds defined for each compound in Case Design → Design Values → Initial Charge tab.
When Fixed Ratio is chosen, the Initial Charge for compounds with open bounds is optimized, while keeping the same proportion among them as in the Values provided in the Case Design → Design Values → Initial Charge tab.
When a Simulation is launched, this option does not affect the results, as the Initial Charge is fixed.
- Energy Balance: No, Yes.
The default is No, thus Temperature is an optimized variable between the bounds enforced in Case Design → Design Values → Specifications. If Control Profile is enabled in the Optimization node, the temperature profile may be specified or optimized in the Control Profiles node.
If Energy Balance is set to Yes, the Temperature profile is calculated by heat balance. The bounds entered in the Case Design → Design Values → Specifications node are still enforced. The initial temperature may be optimized between the bounds specified in the Case Design → Design Values → Initial Charge tab.
Explanation of the Pressure options
Free
The pressure for the reactor varies between the bounds entered in Case Design → Design Values.
Controlled
The pressure will be controlled by adjusting a given inflow/outflow. In order to apply this option, one gaseous flow must be defined as Float for Pressure Control in the Reactor → Flows node. This flow will be adjusted in order to minimize the difference between the setpoint and the calculated pressure profile, by using the least square approach.
If Control Profiles is disabled, the pressure setpoint is optimized between the bounds in Case Design → Design Values. The deviation between the setpoint and the actual pressure can be tuned by adjusting the weighting factors in the Optimization-Weights Node.
If Control Profiles is enabled, you may dynamically simulate or optimize the pressure set point profiles. Information on dynamic profile optimization is available in the following documents:
Fixed at Setpoint
The pressure setpoint is optimized, however the actual pressure is forced to be equal to the pressure setpoint, by adjusting the flow set as Float for Pressure Control. However, due to this tight specification, convergence problems may occur. This can happen due to other constraints on the model leading to an overspecified system. In such cases, it would be worth trying the Controlled option for the pressure.
When Control Profiles is disabled, the pressure setpoint is optimized between the bounds in Case Design → Design Values. That also means that the actual pressure will be a constant, whose value will be located between the bounds loaded in Case Design when optimizing. When simulating, the pressure setpoint (and the actual pressure) will be fixed to the Value entered in the Design Values node.
If Control Profiles is enabled, you may dynamically simulate or optimize the pressure set point profiles. Information on dynamic profile optimization is available in the following documents:
CSTR
If the reactor type selected in the Reactor Type / Phase Behaviour grid is
CSTR, the following properties are listed:
- Flow:
Optimized, Float for Pressure Control (only for Single Gas or Multiphase with a Gas Phase defined), plus Use Density for Single Liquid or Multiphase system.
Optimized is the default option, for which the reactor flow is optimized between the specified bounds in Case Design → Design Values node.
In case of selecting Float for Pressure Control, the Gas Flow is calculated in order to match the Pressure to the experimental values.
When Use Density is selected, liquid/solid flows are calculated based on the compounds Molecular Weights and Density Values loaded in Chemistry → Compounds → Properties node.
- Pressure: Free, Fixed to Setpoint by Flow, Fixed to Setpoint by IF, Fixed to Setpoint by IS.
When Free is selected, pressure will be calculated using ideal gas law if the reactor is Single Gas or Multiphase with a gas phase, otherwise no pressure is reported.
Fixed to Setpoint by Flow option appear for Single Gas or Multiphase reactor with a gas phase. When selected, pressure setpoint is optimized, so the actual pressure is forced to be equal to the pressure setpoint, by adjusting the flow of the gas phase leaving the reactor.
The options Fixed to Setpoint by IF / IS appear only when Intermediate Feed/Separation are enabled, thus allowing to adjust the IF/IS streams to keep pressure fixed to its setpoint. For the special case of Gas - Gas Membrane reactor, this option is not allowed.
When Pressure if Fixed to Setpoint by IF, the Initial Charge and the Intermediate Feed for each subsequent reactor are calculated to match the Pressure Setpoint at each reactor.
When Pressure if Fixed to Setpoint by IS, the Initial Charge and the Intermediate Separation for each subsequent reactor are calculated to match the Pressure Setpoint at each reactor.
In Simulation mode, to control the pressure, we allow only one degree of freedom. Therefore, if pressure is fixed by IF (Intermediate feed), in general, there are as many degrees of freedom as compounds. To ensure that there is only one degree of freedom, we force the ratio among the compounds to be the same as that provided in the initial values. Thus, the intermediate feed and initial charge are calculated, but with the fixed ratio assumption. This means Initial Charge and Intermediate feed will have the compounds with open bounds calculated, while keeping the same proportion among them as in the provided values in the Initial Charge and Intermediate feed tabs.
Likewise, if Intermediate Separation is enabled, for overall based separation, the separation factors are calculated while keeping the same proportion among them. For phase based separation, there is only one degree of freedom, which is the removal percentage of the gas phase. The liquid phase separation factors are kept fixed to the initial values.
Some other caveats about this implementation can be seen below in the Fixed Ratio section.
- Intermediate Feed: No(default) or Yes.
By enabling this option, you can define intermediate feed between CSTR units.
- Intermediate Separation: No, Overall Based and Phase Based.
When Intermediate Separation is enabled, you can perform separations using a component splitter, between consecutive CSTR reactors in the CSTR series. By selecting Overall Based, you may specify the percentage of each compound removed at the end of the CSTR unit; if Phase Based is chosen, a fraction of one or more phases leaving a reactor can be removed. Graphical help for entering such data is provided by clicking on the Description tab in data entry sheets for the Intermediate Separations.
- Initial Charge / IS / IF : Optimize Ratio or Fixed Ratio.
For an Optimization run in which Optimize Ratio is selected, the initial charge and the Intermediate Feed/Separation are optimized without any other constraint than the lower and upper bounds defined for each compound and/or phase, as defined in Design Values node.
On the contrary, for an Optimization run with Fixed Ratio selected, the Initial Charge will have the compounds with open bounds optimized while keeping the same proportion among them as in the provided Values in the Initial Charge tab. Similar logic applies for Intermediate Feed and Intermediate Separation (Overall base) if they are enabled.
There are some special situations that deserve mention here for the Fixed Ratio option. For example, if there are 3 compounds [A, B, C] and if C has the same lower and upper bounds, then REX fixes the value of C, but the values of A and B are optimized while keeping their proportion to be the same as the initial value.
Furthermore, if C has an initial value of zero, with open bounds, REX fixes the value of C to zero in the Fixed Ratio case. A and B are again optimized while keeping their proportion to be the same as the initial value.
When a Simulation run is launched, this option does not affect the results at all. For Pressure control reactor Simulation, when the Pressure is set by IF or IS, the fixed ratio implementation as described above is automatically applied irrespective of whether Optimize ratio or Fixed ratio is chosen.
- Energy Balance: No, Yes.
This option is similar the explanation earlier here for the batch reactor. Selecting No allows for free optimization of the temperature. Selecting Yes means only the initial temperature is optimized and the outlet temperatures are calculated by energy balance.
PFR
If the reactor type selected in the Reactor Type / Phase Behaviour grid is
PFR, the following properties are listed:
- Pressure: Free is the Default option, and the only option for Single Liquid Phase. For Single Gas Phase or Gas - Gas reactor, the Fixed at SetPoint option is available, where the flow along the PFR reactor is calculated in order to have pressure to be exactly the user-specified values. More explanation is given below.
- Flow:
Constant-Optimized is the default option, for which the reactor flow is optimized between the specified bounds in Design Values and is kept at this optimum value for the length of the PFR.
When the Phase Behavior is chosen as Single Gas or Gas - Gas, there is also the option of Float for Pressure Control, implying that the flow along the reactor will be adjusted along the reactor to satisfy the user-provided pressure values, while honoring the lower and upper bounds on the flows as entered in the Case Design → Design Values node.
When the phase is Single Liquid, there is also option Use Density, so the liquid flow will be obtained by the density model, while also satisfying lower and upper bounds on the flow as entered in the Case Design → Design Values node.
- Initial Charge: Optimize Ratio or Fixed Ratio.
The default is Optimize Ratio, meaning that when a optimization run is launched, the initial charge is optimized without any other constraint than the lower and upper bounds defined for each compound in Case Design → Design Values → Initial Charge tab.
When Fixed Ratio is chosen, the Initial Charge for compounds with open bounds is optimized but keeping the same proportion among them as in the values provided in the Case Design → Design Values → Initial Charge tab.
When a Simulation is launched, this option does not affect the results, as the Initial Charge is fixed.
- Energy Balance: No, Yes.
This option is similar the explanation earlier here for the batch reactor. Selecting No allows for free optimization of the temperature. Selecting Yes means only the initial temperature may be optimized and the temperatures profiles are calculated by energy balance.
Explanation of the Pressure options
Free
The pressure for the Single Gas or Gas - Gas reactor varies between the bounds entered in Case Design → Design Values.
Fixed at Setpoint
The pressure setpoint is optimized, however the actual pressure is forced to be equal to the pressure setpoint, by adjusting the flow (that you must select as Float for Pressure Control).
When Control Profiles is disabled, the pressure setpoint is optimized between the bounds in Case Design → Design Values. That also means that the actual pressure will be held constant between the bounds loaded in Case Design when optimizing. When simulating, the pressure setpoint (and the actual pressure) will be fixed to the Value entered in the Design Values node.
If Control Profiles is enabled, you may simulate the pressure profile along the PFR reactor. Information on profile specification is available in the document Case Design → Profiles Specify
Load Reactor Data
This action is useful when an Estimation has been performed before and you would like to transfer the reactor configuration from Estimation to Optimization. The
Load Reactor Data action fills all the reactor Properties and Values from the Estimation study.
If no Estimation has been performed, this action loads the default reactor, which is the Single Liquid Batch reactor.