17 replies to this topic

[Celopsin.Khan]

My question is:

 

that Fig 5.1 Nelson 1958 (attached). It gives a correction scale for K factor, now if we know the K factor of crude oil ... would the same factor be used for its refined products (e.g Naphtha, Kerosene, LGO, HGO, FFO) ... 

 

For example I have a crude oil of API gravity 44.28 (K factor = 10.91) and its products are

Naphtha (API = 60.4)

LWK (API = 42.91)

LGO (API = 32.15)

HGO (API = 22.27)

FFO (API = 19.50)

 

Now would all the products have separate K factor values?????? Which I think so is a YES ... so is there any means we can calculate the K factor of the products?????

 

Attached Files

•  E- 301.jpg   279.04KB   40 downloads

[PingPong]

It would have been better for future reference if you had added this question to the other topic, as it is related.

 

Different fractions will have different UOP-K values. Calculation is only possible if you have boiling curve and specific gravity of fraction.

Naphtha will have higher K than crude, maybe Kero also slightly higher, gasoils about the same, residues have lower K than crude.

 

If you have an assay for your specific crude then maybe in there are K-values given for various fractions.

 

For your purpose of estimating Cp you should not worry to much about the exact value of K. For example: you could take for Light Naphtha K=13, for Heavy Naphtha average of 13 and that of crude, kero and gasoils about the same as crude, atmospheric residue 0.5 points lower than crude.

Edited by PingPong, 03 February 2014 - 10:11 AM.

[Celopsin.Khan]

Thanks  ... I really found it helpful

[PingPong]

For example I have a crude oil of API gravity 44.28 (K factor = 10.91)

It is very strange that a crude with such high API gravity has such low UOP-K factor. Something seems wrong here.

Which crude oil is this supposed to be?

Edited by PingPong, 03 February 2014 - 11:56 AM.

[Celopsin.Khan]

For example I have a crude oil of API gravity 44.28 (K factor = 10.91)

It is very strange that a crude with such high API gravity has such low UOP-K factor. Something seems wrong here.

Which crude oil is this supposed to be?

 

Actually I dont know the exact K factor value, I only know the API gravity values, The API of crude is 44.28. So I did a random search on internet with the keywords "Meyal"(crude well: which is the source of my API + "k factor" and I got a PDF. In which they had listed different physio chemical properties of Crude Oils in Pakistan.

 

K type (API = 44.18) was the most close to my value ..... and for that type k value is 10.91

Attached Files

•  Physico-Chemical Analysis of Some Pakistani Crude Oils.pdf   243.09KB   111 downloads

[PingPong]

I am sorry to say, but the persons who calculated those K-values must have done something wrong.

 

Unfortunately for crude K the Distillation data are not complete, but they are for H (and some others).

For H you should use the Distillation data and specific gravity to calulate K-value and you will find a much higher number than that 11.09 reported for H.

[Celopsin.Khan]

you should use the Distillation data and specific gravity to calulate K-value

 

can u guide me through the process of calculation K value using Distillation Data. I have read it in API Technical Databook and Maxwell (1950) but I just cant get it right. The formula mentioned is

 

((MEABP)^1/3 )/Sp Gr @ 60 F/60 F

[PingPong]

Calculating the MeABP is not easy, but you can estimate it using API method 2B1.1 and figure 2B1.2

 

For example: if VABP = 515 ^oF and 10%-90% slope is 6.25 ^oF/% then MeABP = 515 - 60 = 455 ^oF

 

So UOP-K = (455 + 460 ^oR)^0.3333 / 0.8112 = 11.97

Edited by PingPong, 04 February 2014 - 01:52 PM.

[Celopsin.Khan]

Calculating the MeABP is not easy, but you can estimate it using API method 2B1.1 and figure 2B1.2

 

For example: if VABP = 515 ^oF and 10%-90% slope is 6.25 ^oF/% then MeABP = 515 - 60 = 455 ^oF

 

So UOP-K = (455 + 460 ^oR)^0.3333 / 0.8112 = 11.97

 

It is said that API gravity classifies the crude oils ... Now if we know the API gravity of crude oil and the products yield %ages and their respective API gravities, is there any way we can estimate the TBP of that crude oil.

I tried it for myself back calculating the assay using the product yields ... but I failed :| 

 

Actually, I got design manual of a Distillation Unit of a Refinery, the data is of 1980, and their design temperatures and pressures are based on the product yeild tests of the Oil Field Meyal. 

 

Now I dnt know how or why, the refinery officials themselves dnt have that assay data. And their have been modifications in the refinery (e.g addition of a preflash, they are nt producing 5 products now) which leaves me in a no land with exactly 5 days before my presentation (if not delayed or otherwise).

Edited by Celopsin.Khan, 06 February 2014 - 08:18 PM.

[PingPong]

API gravity says something (but not everything) about a crude: high API means more recoverable distillates than low API.

Therefor high API crudes has higher market price than low API crudes.

 

If you know the TBP cutpoints of all products, or the ASTM D86 distillation of all products, then you could make a rough TBP curve.

 

If not, you could use the D86 Distillation data of those Pakistani crudes with similar API as your Meyal, and convert those to TBP using the procedure in the API Technical Data Book. Maybe Nelson also gives procedure for that, I am not sure.

 

What do you need the TBP curve for? It is a little (too) late to start a simulation of the unit with only a few days before your presentation.

[Celopsin.Khan]

Actualy I dont need the TBP curve, neither am I making a simulation (that wd be the next phase which is abt 2 months later). 

 

1. What I need is the UOP K characterization factor to do energy balance on the Distillation Column, using the Fig from Nelson attached.  20140130074514889_0004.tif.jpg   520.23KB   10 downloads

 

The procedure in my mind to apply energy balance is that I need to calculate the Heat Contents of all the Input Streams and Output streams of the column.

 PFD.png   215.1KB   9 downloads

Now If I get my system boundary as shown in fig. I need the K values to use the Graph of Nelson to calclate Heat Contents of Products.

 

2. For the pump arounds, the strategy in my mind is that I would subtract the Heat Duty of the Heat Exchangers, so I get the difference of Heat Content between draw off and return stream of both the pump arounds, But do I need to calculate the pumping power added???

 

3. The overhead of Column, I don't know its API gravity so I cant use the graph. Any suggestions how do I carry energy balance on the overhead condensor?

Edited by Celopsin.Khan, 07 February 2014 - 11:32 AM.

[PingPong]

1. As I showed in message #8: the UOP-K factor of Pakistani crude 44 ^oAPI is about 12.0

For liquid products see my message #2

 

 

2. Stricktly speaking, yes, but that will be small compared to exchanger duties. Moreover there will be heat loss through the insulation of the column, exchangers, piping, so if you really want to drive yourself crazy you should also include that....

Serious: don't overdue accuracy, or you will waste too much time (that you don't have anymore) with details.

 

3. The overhead vapor from the column going to the condensor is not only hydrocarbon vapor but also includes steam. The hydrocarbon vapors will have a UOP-K of about 13 because it is mainly Light Naphtha. For the steam part use steam data.

 

However: Note that absolute value of enthalpy has no meaning, only enthalpy difference has. So I don't see how you can do a proper heat balance over the columns only. Frankly I don't see the point of that either.

 

And how are you going to handle the partly vaporized crude entering the column? You don't know how much vapor and how much liquid is present there.

 

Earlier I thought you were doing a heat balance over the whole CDU, but now .....

Edited by PingPong, 07 February 2014 - 02:15 PM.

[Celopsin.Khan]

1.  

For your purpose of estimating Cp you should not worry to much about the exact value of K. For example: you could take for

Light Naphtha K=13

Heavy Naphtha average of 13 and that of crude

kero and gasoils about the same as crude,

atmospheric residue 0.5 points lower than crude.

 

Really helpful reply, any reference for the above would really help me strengthen my defense.

 

2.

However: Note that absolute value of enthalpy has no meaning, only enthalpy difference has. So I don't see how you can do a proper heat balance over the columns only. Frankly I don't see the point of that either.

 

And how are you going to handle the partly vaporized crude entering the column? You don't know how much vapor and how much liquid is present there.

 

Earlier I thought you were doing a heat balance over the whole CDU, but now .....

 

actually I wd be taking a reference temperature obviously for the enthalpies.   (so they wd nt be absolute values)

 

How am I going to handle the partially vaporized crude? ...   I still haven't figured out. I need to know the percentage vaporized? then I can use the same Nelson graph for vapor heat contents ... is there any general range of percentage vaporized feed??? (that should help)

 

 

Actually the heat balance is over the whole plant, that I have divided section wise. 

Edited by Celopsin.Khan, 07 February 2014 - 05:49 PM.

[PingPong]

Really helpful reply, any reference for the above would really help me strengthen my defense.

I showed the calculation for one of those Pakistani crudes in message #8. The K-values of products relative to crudes are my personal experience based on data from other crude assays that I have seen through the years. No specific reference, I am afraid.

But you should not worry too much about the exact K of each fraction as the impact on the Cp is small anyway.

 

actually I wd be taking a reference temperature obviously for the enthalpies.

OK.

 

How am I going to handle the partially vaporized crude?

All the distillates (HGO and lighter) withdrawn above the crude feed nozzle, plus the dirty wash oil (overflash) from the last tray above the feed are vaporised by the Charge Heater H-301, and by stripping steam in the column bottoms. I can't tell here how much is the result of the stripping steam, but very roughly speaking the vapor from the feed heater is usually a few percent more than the sum of all distillates.

 

Actually the heat balance is over the whole plant, that I have divided section wise.

Does not that make your work only more complicated?

I do not know what exactly your assignment is, but I would first do the heat balance over the whole plant. And make a mass balance over the whole unit.

That would allow me to calculate the H-301 absorbed duty by the crude, simply from the overall heat balance. And from that I could calculate vaporization (kg/h) and see whether that makes sense in relation to all distillates (kg/h).

[Celopsin.Khan]

What is the right method to do material balance against a side stripper of Crude Distillation Unit?

Edited by Celopsin.Khan, 12 February 2014 - 05:27 AM.

[PingPong]

The right way be to use a simulator, but you probably want to do it by hand. In that case you should read chapter 2 in the book

Petroleum Refinery Distillation by R.N. Watkins (Gulf Publishing Company, 1979, 2nd Edition).

[Celopsin.Khan]

The right way be to use a simulator, but you probably want to do it by hand. In that case you should read chapter 2 in the book

Petroleum Refinery Distillation by R.N. Watkins (Gulf Publishing Company, 1979, 2nd Edition).

 

I have the book, u r referring to Chapter titled "Vacuum Tower"?

[PingPong]

No, I was referring to the chapter on Atmospheric Tower.

In my book (2^nd edition, 1979) that is Chapter 2 (and Vacuum Tower is Chapter 3).