Specific setup issues for predicting phase equilibrium curves using the Flash2 module
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I want to use Aspen’s Flash2 module to predict the phase equilibrium curve for MDEA-PZ absorbing CO2. The phase equilibrium data in the literature are the CO2 partial pressure-CO2 liquid phase concentration data at a constant temperature. The literature does not provide the total pressure or specific amounts of the gas and liquid phases; only temperature, partial pressures, and concentration data are given. My question is: Are the temperature and pressure of the gas-liquid phase feed set at normal temperature and pressure? Are the temperature and pressure of the gas-liquid feed identical to those in the flash module? After assuming a value for the liquid flow rate, should the gas flow rate be set at a value high enough to saturate the liquid before conducting sensitivity analyses on the module’s temperature and pressure, or can it be set at any value prior to reaching that saturation level? Finally, could you provide detailed instructions on the specific settings required to use the Flash2 module for predicting phase equilibrium data in multi-component systems? Looking forward to replies from experts! Thank you!
When using Aspen Plus’ Flash2 module to predict the phase equilibrium curve for MDEA-PZ absorbing CO2, you need to follow these steps for setup: 1. Selection of property model: Choose a property model suitable for describing the MDEA-PZ-CO2 system, such as the Electrolyte NRTL model. 2. Feed condition settings: Since the literature only provides temperature, partial pressure, and concentration, the CO2 partial pressure of the gas-phase feed can be set to match those values in the literature, while the temperature is set to the value given in the literature. If the total pressure is not specified in the literature, a common pressure value can be used, such as atmospheric pressure or the experimental pressure mentioned in the literature. If there are liquid-phase components, their concentrations should also be set to the corresponding values given in the literature. 3. Flash conditions setting: Set the operating conditions of the Flash2 module to the same temperature and pressure as those of the feed. 4. Flow rate settings: Assuming a reasonable liquid phase flow rate, the gas phase flow rate can be set at a certain excess to ensure sufficient contact between the gas and the liquid, thereby achieving an approximately saturated state. The excess gas ratio should not be set too high; it can generally be determined using the excess factor commonly used in laboratories or industrial installations. 5. Sensitivity analysis: For sensitivity analysis regarding temperature, pressure, and gas phase excess, after establishing a set of baseline conditions, by changing these parameters, the changes in the phase equilibrium curves can be observed in order to verify the robustness of the simulation results. The specific setup steps are as follows: a. Open the Aspen Plus software and create a new flow diagram. b. Add the Flash2 unit operation to the flow diagram and set appropriate property methods. c. Enter information such as the fluid feed flow rate, temperature, pressure, and component concentration. d. Set the operating conditions and select the variables to be analyzed (such as temperature, pressure, etc.) for sensitivity analysis. e. Run the simulation, check for convergence, and analyze the results. It is crucial to ensure that a property model capable of accurately describing the interactions between MDEA-PZ-CO2 is selected, as this is essential for predicting phase equilibrium curves. If possible, refer to other literature or experimental data to assist in determining the initial set values and operating conditions, as well as to verify the accuracy of the simulation results. .