2 replies to this topic

[Clayton]

Hello,
I have to define a Crude stream from assay data from different product streams. I am using HYSYS. I want to know if it is sufficient to put the volumetric flow rate into the blend in order to get the correct composition for the Crude feed. Also, when i put the data into the simulation and ran my atmospheric crude column i was not getting product streams at the desired boiling points i wanted. I am using desired boiling points because these are what the product specifications are based on. At first i thought it was just my column but when installed the individual product stream the data that i entered in the oil environment did not correspond to the data i got in the individual product stream e.g. my kerosene assay data showed that at 95% recovered the boiling point was 235oC but i got 160oC when i calculated the BP of the individual kerosene stream which i installed from the oil environment. I calculated the BP of the individual stream by multiplying the individual component mole fractions against the BP's of the pseudo-components. I would like to know if this makes sense to do and if the temperature of the amount recovered at 95% (or final boiling point) should correspond to the boiling point of the individual stream. Also, if i have the final boiling point should i enter this as 100% recovered in HYSYS.

I would be entirely grateful for your help in this matter as i am a "noob" in HYSYS.

[Andrei]

I am not sure if I fully understand your problem, but here is what I think.
It is perfectly normal to get different boiling points using different calculation methods. The way you calculate manually the boiling points you assume that this property is fully additive and there are no interactions between different pseudo-components.
But still, I don’t think I understood right how you are doing that manual calculation. At the first glance looks to me completely wrong. Maybe you should look at API Databook (old stuff) to see how these things are done properly.
Another thing, there is a certain error involved in the process of pseudo-components generation in Hysys (and any other simulation program). Imagine that you are approximating a continuous curve with an assay. Each cut approximates a certain portion of the curve. You can set up how these cuts (and pseudo-components) are generated, and how the properties of individual cuts are calculated, to minimize these errors. To find out about these settings you have to look into Hysys documentation, there is something there for sure.
As of recoveries, that depends on how did you set up your column in the first place. It may be available some fraction in 95% proportion, but if you set up your column differently your recovery will be different.
Basically I think your problem is difficult to solve without the actual simulation in front and spending some time to look around. Maybe you should submit the file to Aspentech and ask their help.

[Clayton]

Thanks for your help i did get through with the boiling point problem by following steps from the tutorial and finding the boiling point profile of the products