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Design Of A Atmospheric Crude Tower?


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#1 Celopsin.Khan

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Posted 15 May 2014 - 09:36 AM

Can anyone help me here with the proper direction of where and which book or what steps can I follow to design the Fractionator (Multi Draw Distillation Column)?

By far I hav studied Nelson, but the steps are quite confusing and also not everything is mentioned like

 

Plate Spacing of Rectifying Section =
Top Flooding Velocity =
Top Volumeteric Flow Rate =
Top Net Area Requirment =
Top Coloum Crossectional area =
Top Diameter of Coloum =
Downcommer Area =
Net Area =
Active Area =
Weir Length =
Weeping Velocity =
Actual Vapor Velocity =
Total Back up in DownCommer =
Total Back up in DownCommer in =
Top Residance Time =
 

 

How or where can I get started with a complete design (internal & external). Thanks



#2 PingPong

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Posted 16 May 2014 - 05:12 AM

First of all you need to have the tray loadings: the flowrate (and properties) of the vapor entering each tray, and the liquid flowrate (and properties) of the liquid leaving each tray.

Normally one obtain those by doing a column similation using Hysys or PRO/II or Aspen Plus or ........

 

When looking at the tray loadings you divide the column in sections with similar loadings and design the trays in each section using software from Sulzer or KochGlitsch or another source. That will give you the required column diameter of each column section, as well as all the other tray parameters such as tray spacing, number of downcomers, downcomer width, outlet weir height, et cetera.

 

Before running tray software I suggest you read Coulson & Richardsen Volume 6, Henry Kister (Distillation Design) and Perry, and Ludwig to have some understanding of tray design. If you can find a copy of the good old Glitsch Ballast Tray Design Manual that would also help to enhance your insight.


Edited by PingPong, 16 May 2014 - 05:18 AM.


#3 Celopsin.Khan

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Posted 16 May 2014 - 07:47 AM

Ok lets assume that I cant use any simulation software and I have to do the calculations theoretically. What I know right now about the distillation column is the 

 

Tower Feed Mass Flow rate - 26652.715 kg/hr

Entering Temperature (Crude Oil) - 324 C 615 F

Entering Pressure - 20 psig 138 KPa

 

Steam Entering Pressure - 110 psig 758 KPa

Steam Flow Rate - 189.01 kg/hr

 

Top Reflux Ratio - 0.72

Top Temperature - 140 C 284 F

Top Pressure - 13 psig 90 KPa

 

Bottom Temperature - 311 C 592 F

 

Other Info Known:

Side Draws Temperatures

Side Draws Mass Flow Rates

and API gravities of Entering Crude and the Products.

 

Now how do I get started? with calculation of Diameter first. The books u told me, am consulting them.


Edited by Celopsin.Khan, 16 May 2014 - 07:59 AM.


#4 PingPong

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Posted 16 May 2014 - 09:14 AM

You always need tray loadings to design a distillation column.

 

The fact that you don't have them (yet) does not change anything.

With only the above numbers you cannot dimension the column.

 

I suppose you can try to estimate the tray loadings using the methods in Watkin's book, preferably the 2nd edition.

I don't know any other book to use for that.

 

Note also that:

- a crude column usually has pumparounds, but you don't mention any.

- an atmospheric distillation column for only 26653 kg/h crude is very small, only about 5000 BPSD. I get the impression that this is the  V-301 you posted about in januari? Isn't that an existing column? So what are you trying to do? Verifying its length and diameter? In any case: you first need te obtain tray loadings.



#5 Celopsin.Khan

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Posted 16 May 2014 - 10:38 AM

Note also that:

- a crude column usually has pumparounds, but you don't mention any.

- an atmospheric distillation column for only 26653 kg/h crude is very small, only about 5000 BPSD. I get the impression that this is the  V-301 you posted about in januari? Isn't that an existing column? So what are you trying to do? Verifying its length and diameter? In any case: you first need te obtain tray loadings.

 

Yup it is the same project working on phase II i.e Design. The plant is of 5000 BPSD capacity. It does have pumparounds and I have temperatures and flow rates of those too. 

 

Yes you can say that I am verifying its length. Its a University Project, so its just an approximation. I have the book you mentioned. Let me study it ... 

 

What exactly u mean by Tray Loadings ... the Liquid and Vapor Flow rate? ... L and V?



#6 PingPong

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Posted 16 May 2014 - 11:31 AM

Yes, you need the flowrate (and properties) of the vapor entering each tray (through the sieve holes or valves), and the flowrate (and properties) of the liquid leaving each tray (over the outlet weir into the downcomer).



#7 Celopsin.Khan

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Posted 16 May 2014 - 04:49 PM

Yes, you need the flowrate (and properties) of the vapor entering each tray (through the sieve holes or valves), and the flowrate (and properties) of the liquid leaving each tray (over the outlet weir into the downcomer).

 

Can u refer to a topic or page number for quick reference ... Please. Thanks



#8 PingPong

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Posted 17 May 2014 - 05:20 AM

Quick reference about what? Tray loadings?

 

I only know Watkins 2nd edition for doing manual column calculations, but it is a hell of a job.

 

I now notice that Watkins lists tray loadings as Vapor From Tray and Liquid To Tray, which is stricly speaking not correct for tray sizing, but let's not worry about that. Simply take largest vapor flow and largest liquid flow in each column section for tray sizing.



#9 Celopsin.Khan

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Posted 17 May 2014 - 08:07 AM

Yes I had a look at the book (Watkins) and it was scary (would surely need time to read and understand)

 

I managed to find an example on Page 892 of Nelson' Petro Refinery Engg ... in this example, he calculates the no of stages in a very funny manner .... but after reading the 16th chapter of this book, I dont see any way No of Stages can be calculated except through equilibrium data.

 

Following this example? Is it a good option for a study project. I mean he just takes the no of stages using previous designs .. as simple as that ... so what u say?


Edited by Celopsin.Khan, 17 May 2014 - 08:09 AM.


#10 PingPong

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Posted 17 May 2014 - 10:29 AM

V-301 is an existing column, right? So you know already the number of actual trays and so you can massage your calculations towards that (preferred) result.

 

I am not familiar with Nelson's book, but in Watkins there are the socalled Packie correlations in the form of charts (figures 2.6 and 2.7) which one can use to determine required amount of actual trays for a certain ASTM gap or overlap in combination with vapor and liquid flows. Obviously there is a correlation between separation, number of trays and L/V ratio in a column section and that is what Packie figured out.






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