4 replies to this topic

[mccshaw]

If I have the feed assay and 2 of the 3 product assay, is there any way to determine the properties of the third product stream? Since dealing with hypothetical components, I'm not sure if this can be achieved. 

[Zauberberg]

You need to know their mass flowrates as well. Hysys Unit Op such as MBAL can be used to define composition of the 3rd stream, if compositions and mass flowrates are known for Feed and other 2 products.

[shantanuk100]

Dear MccShaw,

 

1. No you cannot, but it also depends on the property you are looking at (Intensive or Extensive).
It is similar to the study of any property of a mixture.

Though we are talking about assays, look at it this way,

I have a yellow coloured fluid A and a blue colored fluid B.

Now my feed Z is a green colored mixture of A and B.

 

2. Can I now determine the greenness of Z by just knowing the extent of color of A and B alone ?

No. Because, how dark of a green or how light of a green Z becomes is dependent on the amount of A and B you input to the system (Analogous to flowrates).

Similar to Color, the other properties of the assay also vary in a similar manner (irrespective of linear or non linear variation).

So we need at least two out of the three flowrates of the Feed and components.

 

3. Also, it depends on what properties you are trying to determine.
If the property you are trying to determine is intensive (Independent of bulk of fluid), such as density, then yes you can determine them from the assay even without knowing the flowrates of feed and components.
But if it is an extensive property such as enthalpy etc., then you need to know atleast two of the flowrates.

 

Assays are generally used for intensive property determination so check out which category the properties you want to determine fall into.

 

Cheers,

Shantanu

Edited by shantanuk100, 17 March 2016 - 03:45 AM.

[serra]

question is not clear, I presume you know compositions (real and hypothetical components)

of feed and all products except one,

then you should be able to solve mass balance (last product as difference),

note that for both real and hypothetical components values of Mw etc. should be defined,

my copy of Prode Properties allows different methods however, as result,

you obtain a list of components and fractions which is what you need,

from composition (real + hypothetical components) most properties can be estimated,

[Pilesar]

If this is a 'real world' scenario the crude feed is not a constant composition. The feed assay is an approximation of the feed composition which becomes less dependable as time elapses. Product assays are typically more precise because they are over a smaller boiling point range. For this reason, the product assays are sometimes used to determine the pseudo-assay of the feed stream for simulation purposes. How much of the feed analysis is included in the range of the unknown product? For example, if the unknown product stream consists of the lightest 5% of a crude feed, you will not be able to get reasonably useful results by evaluating the feed and the remaining products. Crude distillation often cracks some components so that the material leaving is not quite the same as the material entering.