5 replies to this topic

[Sandeep sailesh kumar]

Do need help in simulating transient tank filling. The idea is quite simple but aspen hysys seems to not execute it as well as we want it to. I need to fill in hydrocarbon liquid at 41 c and 110 mbarg to a tank filled with inert and see the response in the vapor phase. I kept a valve to first regulate inert gas for some time and then close the valve and open hydrocarbon valve . but I am getting weird result at outlet, plus sometimes negative molar rate in inlet .

It will be helpful if someone can let me know a way ….

 

thanks in advance

 

[AlertO]

Hi Sandeep

 

Please give us the simplified sketch of your system including with process boundary condition you have input in your dynamic simulation. Otherwise, it is difficult to make any recommendations against your problem.

[Sandeep sailesh kumar]

thanks for the prompt reply

 

I have attached the schematic diagram .some od the conditions are in the diagram

using inert inlet valve, we fill in the inert gas keeping the valve VLV-102 closed for a certain amount of time . after that time we will close the inert valve and start filling it with hydrocarbons(mostly liquid) to tank meanwhile  keeping valve VLV-102 open. there will be a small fraction of flash. tank is about 163950 m3 in dimension. i need to see the behaviour of outlet vapor . any doubt feel free to let me know.

Attached Files

•  schematic diagram tank.png   406.47KB   18 downloads

[tushargoel]

Sandeep,
if the schematic you shared is actually representative of your HYSYS model then there's a lot of modelling missing in my opinion. My recommendation is for you to first define your system in detail before you start simulating.
Try to model the system as a replica of actual tank operation and control system.

1) The inlet of Inert should be having a PIC and a PV to control the pressure inside the tank. If you do not want the inside pressure to be controlled via a valve, then remove the Inert inlet line altogether and initiate the tank with the composition of your inert gas at the starting of your simulation.

2) Similarly, the outlet line for vapor phase release should either be an PIC controlled PV system to regulate the pressure or it should be an Restriction orifice. The restriction orifice would not prevent back flow and hence it may see negative flow.

3) Liquid inlet flow can be manually controlled by you. However, provide sufficient upstream pressure so that the line does not see reverse flow on opening the valve.

4) Ensure liquid outlet valve is open only when the level is non-zero. Keep a track of liquid level in the tank.

 

Always keep a track of the pressure inside the tank. Simulator always respects the Pressure-Flow dynamics. The outlet lines battery limit pressure should be low enough to allow forward flow.

Also, keep an eye on the composition of the the liquid. There might be dissolution of vapor phase components in the liquid phase which may cause pressure drop and reverse flow.  

Edited by tushargoel, 24 February 2019 - 05:57 PM.

[AlertO]

Hi Sandeep

 

Your inlet pressure at boundary is quite strange. 110-kPa flow is unable to continue feed if your pressure in the tank is a little grow-up. This is why you faced with negative flow. At least you need to put more realistic number (e.g. pump discharge pressure) to this stream to see any changes in the tank.

 

Hope this may help you.

[Sandeep sailesh kumar]

thanks both of you for the valuable suggestions. i am going to try it now