4 replies to this topic

[bridgerlady]

Good morning community,

 

I am a current Undergraduate student, and I am working with Aspen Plus to model the emptying of a full tank. To my knowledge, Aspen Plus is used to determine steady state calculations. However, the process I would like to model is transient. I am looking to analyze the temperature and the pressure inside the tank as it empties at a specified flow rate and pressure. Is there a way to use Aspen Plus to attain transient data? In this process, a tank needs to be filled, flow to the tank needs to be shut off, and then an outlet valve needs to be opened.

Regards

[Lucian Gomoescu]

Hello,
 

You can export the file from Aspen Plus with Aspen Dynamics format.

You may follow these steps:

1. Go to Data Browser>Setup>Specifications and change Input mode to "Dynamic".

 

2. Define the streams and for the tank (separator block) go to Dynamic>Vessel and change type "instantaneous" with "vertical" or "horizontal" and insert its dimensions.

 

3. Go to tank Input>Specifications and choose Pressure and Heat Duty (at least this is what i understood from your topic).

4. Run the simulation. You can make a dynamic simulation only after the run is succesful.

 

5. Go to File>Export> and save file as either "Flow Driven Dyn Simulation", either as "P Driven Dyn Simulation" (from the topic i didn't understand 100% the scenario).

 

Observation:

In a flow driven dynamic simulation, the stream flows are manipulated directly, pressures result from the hold up dictated by the flow rates.

 

In a P driven dynamic simulation, the stream flow rates are defined implicitly by pressure-flow relations  and pressure differences (you no longer define streams flow rates directly). Pressures dictate hold up implicitly via pressure-flow relations. Thus, in a P driven simulation you'll have to define pressure changers (e.g. pipes, valves, pumps etc) between operations blocks.

 

So far, your scenario seems to be solvable with a simple flow driven dynamic simulation (you mentioned "specified flow rates", which sounds as "fixed flow rates", in my opinion).

[ankur2061]

Hi,

 

While I understand the need of your assignment being implemented in Aspen Plus (Dynamic module), you may want to understand the physical laws of mass / momentum flow of a liquid-filled tank being emptied out through a small opening. If you desire so, please refer the excel workbook available at the following link:

 

http://www.cheresour...ndrical-vessel/

 

Regards,

Ankur.

[bridgerlady]

Thank you Ankur and Lucian for the input.

I should have included that the simulation is for a gas. Also, Lucian, I have a working steady state simulation. The setup is simply a flash drum with the required input and output flows. My concern is that I would like to retrieve information about the temperature and pressure of the gas within the tank. Currently, within Aspen Plus, I am required to supply a feed stream along with two of the following: temperature, pressure, or heat duty, specified for the flash drum. For my specific situation, a tank with one inlet/outlet valve would be allowed to empty at a specified pressure and mass flow. No heat, would be supplied, and the temperature and pressure within the tank would fall as the gas leaves. I hope this clarifies the situation. I am new to Aspen Plus and may be misunderstanding portions of the simulation setup.

[ankur2061]

Hi,

 

If it is gas and you need to know the temperature and pressure over time as the gas releases from a vessel then have a look at this:

 

http://www.cheresour...through-a-hole/

 

Regards,

Ankur.