6 replies to this topic

[ELVINA]

Good day!

I am trying to simulate PSA process in Unisim Design (for hydrogen purification). I made model with splitter but I am not sure that this is correct. Did anybody make something like this? Could you help me?

 

[Technical Bard]

That is all you can do.  Thermodynamic simulators like Unisim do not have the capability to model adsorption onto a solid media.  The trick with simulating a PSA unit is to recognize that there is a small heat of absorption/desorption that affects the temperatures of the products.   You would need to ask a PSA vendor for their prediction of performance to get a split (i.e. how much hydrogen is lost in the tail gas) and what the thermal effects are.

[ELVINA]

That is all you can do.  Thermodynamic simulators like Unisim do not have the capability to model adsorption onto a solid media.  The trick with simulating a PSA unit is to recognize that there is a small heat of absorption/desorption that affects the temperatures of the products.   You would need to ask a PSA vendor for their prediction of performance to get a split (i.e. how much hydrogen is lost in the tail gas) and what the thermal effects are.

 

Thank you very much. I have all data about tail gas and it is not a problem. I just thought that there is another way to model it. So will try to do something with splitter and vessels.

[CHEMSTRONG]

I have done it earlier with component splitter for tail gas and 99.99 percent hydrogen in product. We have not done valve switching logic in that .

[ELVINA]

Good day! I am not sure if I understand you correct. I don't know ways to do this process without logic sequence for valves. Because there should be stage for purification for one splitter and stage of regeneration for the others so then some valves should be closed while others should be opened. I have to do this sequence because such points as valves are required in DCS

Edited by ELVINA, 27 February 2018 - 06:12 AM.

[CHEMSTRONG]

Modelling of each PSA adsorption vessel can be done with component splitter with bottom of splitter containing impure tail gas gong to Tail gas Drum and ttop of splitter going to PSA product gas filter and then towards outlet consumers like Hydrocracking (99.99 percent). As far as PSA adsorption, desorption, regeneration sequence, repressurisation is concerned, they can not be modeled in UniSim Design . Valve switching sequence(automatic) can be done in DCS and then UniSim model to be integrated with DCS.

[ELVINA]

Okay, I see. But it seems to me I work in another way)) Firstly I make model and then I should ensure that this model works correct. So I make simulation of sequence in my model using logical operations and spreadsheets which are connected with time. And only after it I start integration with DCS. For DCS I need all these valves because they are in ref files and they should receive commands from DCS/SM. And I cannot imagine model without points which are really necessary for DCS and SM. How did you make your model if for example there are no ESD valves or adjusting valves but there are commands for them from DCS?

Thank you