Aspen Plus tutorial (1) – a practical simulation of a simple flash example

Learn Aspen Plus through an example of flash evaporation. This example introduces a series of operations such as component input, process establishment, physical property selection and actual simulation operation.

Flash evaporation is a common and simple unit process in chemical production. The flash module is located under the separators tab of the model palette:

Detailed explanation of each module:

Module namedescribeobjectiveapplication
Flash2Double outlet flash evaporationBased on the strict vapor-liquid or vapor-liquid equilibrium, the inlet logistics is separated into two export logisticsFlash evaporator, evaporator, separator, single stage separator
Flash3Three outlet flash evaporationBased on the strict vapor-liquid equilibrium, the inlet logistics is separated into two export logisticsDecanter, two-phase single-stage separator
DecanterLiquid liquid DecanterThe inlet stream is separated into two liquid phase outlet streamsDecanter, double liquid phase single stage separator without vapor phase
SepComponent SplitterBased on the specified process or partition ratio, the entrance logistics is divided into multiple export logisticsComponent separation operations, such as distillation or absorption, when separation details are not known or important
Sep2Dual outlet component separatorSeparate the import logistics into two export logistics based on the specified process, split ratio or purityA separation operation, such as distillation or absorption, when the separation details are not known or important

Example 1: methanol / water solution, its mass composition is: water 60% and methanol 40%, feed temperature 40 ℃, pressure 1atm (1atm = 101325pa), flow rate 1000kg / h.

Ask for:

① Calculate the bubble point temperature of the logistics

② Calculate the dew point temperature of logistics

③ The flow was flash evaporated at 85 ℃ and 1 ATM to calculate the flash steam phase fraction. The thermodynamic model is nrtl-rk (NRTL activity coefficient model for liquid phase and rk equation of state for vapor phase)

The following is the detailed solution process:

① Calculate the bubble point temperature of the logistics

Step 1: open Aspen Plus

Enter the component data on the right, that is, the methanol / water components in the example.

First, input the component water, click Find, enter H2O in name or alias, or enter water directly in the component ID of the above interface (it must be an international material name), and then press enter,

Then another component methanol (ch4o) is injected

Step 2: select the physical property method,

Click methods on the left and select nrtl-rk physical property method in base methods,

Confirm the attribute in nrtl-1 under parameters > binary interaction

In fact, you just click it. You don’t need to fill in the data. If the physical property method is wrong at the beginning, there is no data here after correction. At this time, you need to click Reset (Shift + F5) to reset.

Step 3: establish simulation process simulation

Click simulation on the left

Select flash2 under separators

Add logistics, click material, and then add three logistics to the module we just added

Open the f material line under streams, and then enter the parameter of feed rate F. pay attention to select the right unit.

Click B1 under blocks. This B1 represents the name of the flash tank. If the name has been changed when drawing the simulation diagram, it will be the corresponding name after the change.

The vapor fraction is 0 and the pressure is 1 atm,

So far, the data input is complete. Click results under blocks to view, and you can see that the outlet temperature is 79.4928 ℃, which is the bubble point temperature, because the corresponding vapor fraction is 0 (Aspen Plus is generally the molar vapor fraction). The heat load of the flash unit is 11269.1 cal / sec, which means that the flash evaporation process needs to absorb heat. The heat unit here can be replaced by the unit you are familiar with, and you must pay special attention to the unit used in the simulation later.

Click blocks > B1 > stream results to see your logistics information

② Calculate the dew point temperature of logistics

Just change the vapor fraction under blocks > B1 > input to 1 (which means that all the steam changes into steam)

Click Reset on the menu bar to reset, and then click Run to run

The results are the same as the calculation of bubble point temperature. It can be seen that the dew point temperature is 92.6238 ℃ (below).

③ The flow was flash evaporated at 85 ℃ and 1atm to calculate the phase fraction of flash steam.

Other calculation is the same as the bubble point temperature. Modify B1, i.e. the flash device parameter is 80 ℃ and the pressure is 1atm

Reset reset first and then run to view the results in the same way (blocks > B1 > results)

It can be seen that the vapor fraction is 0.0380987 (mole fraction).

Such a simple flash example is introduced, if you have any questions, please leave me a message. The following is an exercise, you can test your mastery.

At the same time, the flow rate of benzene is 100% and the mass fraction is 100 KMPA

① Calculate dew point temperature

② The mixture was flash evaporated at 100KPA to vaporize 60% of the feed. The flash temperature and heat load of the flash process were calculated. Physical property method rk Soave.

You can reply to the “APquestion1” in the weixing MP (PVDesign).

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