7 replies to this topic

[dhns]

Dear all,

could anyone can explain about the "SELECTION OF MODES(DYNAMIC / STEADY STATE) IN HYSYS"
for which case wehave to select the dynamic simulations ?for which case wehave to select the steady state simulation ?

thanks in advance


regards,
Dhnsekaran

[Padmakar Katre]

Dear,

This is a bit confusing question - at least for me. Still, I will try to reply your query. If you don't get convinced, please ignore my reply.

From your question what I could reply is that you need to have a steady-state simulation to get the mass and energy balance of a plant for which you have modelled in Hysys. Now, if you have any change in boundary streams say inlet feed conditions which you can change and converge the model of your unit by making changes which you will give you the steady state mass and heat balance. As well, in steady state you could change the conditions and effects of that change will reflect on your model wherever its applicable.

Now, in case of Dynamics you will have the real feel of the running unit. In the dynamic model you can model the different events and check the effects which will always be changing with the time. As well you could check the responses of the modeled control loops and conclude the needed changes to be made to your controllers. The event scheduler is a good tool in Hysys where you could configure the events like the Bottom Pump should stop/trip at LLL of the vessel from where it takes the suction. Now, if the pump fails what happens to the plant that you could check in dynamics. The releif scenarios you could model in dynamics.

I hope this could help you a little.

[Steven_Zhu]

Steady state simulaiton can finish process design, process optimization, process analysis. Dynamic simulaiton focus on Process control analysis, Operator training, unit beheavy analysis. You can make sure which kind of simulaiton you can use according to what you want to do.

Best regards.

[dhns]

Dear katr!,

Thanks for your valuable information,and reply. If am using one EOS (EX.Peng Robinson Equation) for Steady state, is it applicable for the Dynamic state also ?

Please advice,
REgards,
Dhnsekaran

[JoeWong]

Steven,
Good response.

Steady state simulation focus on system balance (heat + mass).
Dynamic simulation focus on scontroller & control device response and hence system behavior.

Steady state simulation could be seen as a snapshot of one moment of Dynamic simulation. Dynamic simulation is used when transient phenomenon is more preferable for study. System hold up should be considered in dynamic simulation.

[joerd]

If am using one EOS(EX.Peng Robinson Equation) for Steady state,Is applicable for Dynamic state also ?

Certainly, the EOS describes thermodynamic behavior for the system. You should use the same package regardless of whether your simulation is time based or not.

[Andrei]

Fundamentally both Steady State and Dynamic perform some sort of balance.
The differences between them are:
1. In Steady State Time parameter is not present, while in Dynamic is;
2. In Steady State there is no accumulation or holdup factor
You can take snap-shots of the dynamic simulations each one of them resembling one different steady state.
If the balance is in a stable zone the system will stay more or less at that steady state. If the balance is in an unbalanced zone, the system will evolve to a new steady state. Balanced or unbalanced zone is determined by the size of the accumulation factor: zero accumulation means stable zone.
All steady state equations, not only thermodynamics, are valid in dynamic mode.