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Single Stage Desalter Mass Balance Started by sjam shid, Feb 23 2013 10:49 AM

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sjam shid

H i Guys,

I am trying to perform a sim ple m ass balance on a single stage desalter. I have 60000 BPD of oil with 4000 ptb, and 5% wash

water with 400 ptb. I know that water effluent is 6667 BPD and crude oil effluent contains 0.2% water.

Posted 23 February 2013 - 10:49 AM

Page 1 of 6Single Stage Desalter Mass Balance - Student - Cheresources.com Community

10/19/2014http://www.cheresources.com/invision/topic/17297-single-stage-desalter-mass-balance/

I know it should be a pretty sim ple and straightfowrard calc, but cannot wrap m y m ind around it. Can anyone please give

som e guidance?

Thanks in advance,

J

(http://www.cheresources.com /invision/index.php?

app=core&m odule=attach&section=attach&attach_id=6480) Single_Stage_Desalter.jpg(http://www.cheresources.com /invision/index.php?app=core&m odule=attach&section=attach&attach_id=6480)

28.12KB 82 downloads

ankur2061

sjam shid,

Refer the attached sketch. The various term s in he sketch are defined as follows:

A = inlet water flow rate in oil, BPD

E = m ixing efficiency

K

a

= salinity of inlet water in oil, lb/bbl

K

c

= salinity of outlet water in oil, lb/bbl

K

y

= dilution water salinity, lb/bbl

Y = dilution water flow rate

C = flow rate of residual water in the outlet oil, BPD

V = disposal water flow rate, BPD

K

v

= disposal water salinity, lb/bbl

k = salinity, ppm

SG

w

= water specific gravity, dim ensionless

Q

0

= oil flow rate, BPD

X

a

= inlet water cut, expressed as fraction

X

c

= outlet water cut, expressed as fraction

Z = oil salt content, PTB

Now try solving the m ass balance. This should be enough guidance to give you a start.

Good luck in perform ing the m ass balance calculations.

Regards,

Ankur.

Attached Files

Posted 23 February 2013 - 01:43 PM

kkala

Probably som e data is m issing, as following can indicate. "BPD", "ptb" quantities are supposed at som e "standard"

tem perature.

1. Crude in : 60000 BPD (blue figures are given quantities).

W ater in: 60000x5% = 3000 BPD

W ater effluent (brine): 6667 BPD

Crude out : 60000+3000-6667 = 56333 BPD (assum ed sam e as "crude oil effluent").

2. Salt with crude in : 60x4000 = 240000 lb/d (ptb=pounds per thousand barrels).

Salt with water in : 4x400 = 1600 lb/d

Total salt in : 240000+1600 = 241600 lb/d

Assum ed salt content in brine out: 33000 ptb, figure m issing (red figures arbitrarily supposed for an exam ple).

Salt with brine out : 6.667x33000 = 220011 lb/d

Salt with crude out : 241600 - 220011 = 21589 lb/d (*)

Extent of salt rem oval from crude: 1-21589/240000 = 0.91, or 91%

3.1 "Desalting of Crude oil" can be seen in Nelson, Petroleum Refinery Engineering, M cGraw-H ill, 1958), pages 265-268.

Posted 25 February 2013 - 06:14 PM



3.2 One could m easure another quantity (e.g. salt content of crude out) instead of salt content of brine.

3.3 (*) W ater content of 0.2% in crude out would m ean 56333x0.2% =112.7 BPD of water. Assum ing all diluted salt is in

water, its salt content would be ~190000 ptb, which is unrealistically high (expected around 33000 ptb). Or probably 0.2%

water is too low.

On the other hand usual salt rem oval efficiency is ~ 90% (per 3.1). If the data is experim ental, new m easurem ent with

additional data has to be realized, to clarify the balance.

3.4 Salt content of 35636 ptb in brine would result in "salt with crude out" 241600-6.667x35636 = 4015 lb/d, and salt

content 4015/0.1127 = 35625 ~ 35636 ptb in the water of crude out. This could close the salt balance in theory, but salt

rem oval efficiency from crude would be (240000-4015)/240000 = 98.3 % , which seem s too high.

3.5 Com m ents on all above text are welcom ed. Desalter brine m et in local refinery had salt content ~1.5 g/l = 526 ptb,

differing to present picture.

Edited by kkala, 25 February 2013 - 06:35 PM.

ankur2061

sjam shid,

W hen doing desalter calculations the wash water (dilution water) is generally not an input. It is a calculated value based on

the m ixing effciency of the wash water. If it were so sim ple as an input = output and with convenient assum ptions then

anybody with basic understanding of m ass or m aterial balance could do it.

As per the sketch I have provided with the notations, the wash water qty thus becom es:

Y = A*(Kc - Ka) / E*(Ky - Kc)

where:

Y = wash water flow rate, BPD

A = oil stream flow rate, BPD

E = m ixing efficiency as a fraction (input, generally between 0.7 to 0.8)

Ka = salt content of water in inlet crude oil, lb/bbl (input)

Kc = salt content of water in outlet crude oil, lb/bbl (the desired value or desired output))

Ky = salt content of the wash water, lb/bbl (input)

Once you calculate Y, the water balance of the desalter gets solved

The brine disposal flow rate can be easily calculated:

V = A + Y - C

Once you know the values of A, Y, C & V, the salt content of the disposal (brine) stream becom es sim ple as per the salt

balance provided below and you don't have to m ake any assumptions.

Kv = A*Ka + Y*Ky - C*Kc / V

where:

Kv = salt content of the brine (waste stream ), lb/bbl

Desalter calculations are thus done with the wash or dilution water as an unknown entity and not as an input.

Regards,

Ankur.


kkala

Concerning post no 4 (by ankur2061), following notes could be helpful for those seeking clarification of the query.

1. The m atter concerns m ass balance, not desalter design considerations.

2. W ash water input (stream Y on the thum bnail of post no 2) is given as 5% of crude oil input (localrefinery: 3-5% of volum etric

flow of crude).




3. To clarify stand of post no 4, please apply it using the specific num bers given in post no 1. Specific issues will get m ore

clear.

4. Com m ents on post no 3 (by kkala) have also to be specific, preferably on calculated num bers (wrong, right?), to help

readers and reality.

Edited by kkala, 26 February 2013 - 04:56 AM.

ankur2061

Basis of assum ption of 33000 ptb salt content in brine has not been explained in post# 3. kkala is requested to provide the

sam e. Post# 4 provides the basis for the wash water or dilution water calculated quantity based on the m ixing efficiency

which is how a m ass balance is done for a desalter.

Nowhere post# 4 has tried to design the desalter (design, if som ebody has the concept of it, m eans sizing of the desalter

vessel). Only the m ass balance is provided based on sound logic and with no assum ptions. The m ass balance provided in

post#4 is based on the following inputs:

1. Flowrate of incom ing oil

2. W ater content of incom ing oil

3. Salt content of incom ing oil

4. Salt content of wash water

5. Desired output of salt in outgoing oil

6. W ater cut of outgoing oil from the desalter

7. M ixing effciency

The outputs of the m ass balance are as follows:

1. W ash water flow rate

2. Brine solution flow rate

3. Salt concentration of waste brine solution

No assum ptions have been m ade as regards to the content of salt in the brine solution which post#3 has so conveniently

m ade without providing any explanation. No further explanation is required that this is how a m ass balance across desalter

needs to be done.


kkala

Post no 6 (by ankur2061) is noted, but let the status be cooled before a brief response. M eanwhile it m ay worth while looking

into post no 3 (by kkala). Views can be of course different, readers can judge and take the useful part of each.

Edited by kkala, 26 February 2013 - 05:51 AM.


narendrasony

Derivation of the form ula provided by Ankur for calculating W ash water flow rate (BPD)

Use following m ass balance equations (Refer Post-2 by Ankur for Nom enclature):

Water (or brine) balance: A + Y = C + V - (1)

Deslater inlet water: A + E * Y = B - (2)

From (1) & (2): C + V = B + Y * (1-E) - (3)

Salt balance: A * Ka + E * Y * Ky = Kb * B = Kb * (A + E*Y) - (4)

Note that Kb = Kc - (5) Therefore A*Ka + E*Y*Ky = Kc * (A + E*Y) - (6)

Or Y = A*(Ka - Kc) / E*(Kc - Ky) as given by Ankur.




Back to Student

M echanical Energy Balance

Started by Guest_W ereSheep_* , 14 Oct 2014

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14 Oct 2014

Regards

Narendra

kkala

Negative feedback on post no 7 today by ankur2061 indicates that the status has not been cooled. Reasons are not apparent to

kkala, thinking that stand of post no 3 is clear and helping for clarification of the truth. Im partiality is needed for this.

Ankur2061 is kindly requested for public explanation.

Brief response on technical m atters by kkala, as said in post no 7, will com e later.

Posted 04 M arch 2013 - 08:27 AM

ankur2061

As requested basis for assum ption of 33,000 ptb in brine has not been provided. As m entioned in post #6 no assum ptions

have been m ade whereas post #3 m akes an assum ption which cannot be substantiated or has any basis. Thus the negative

feedback.

Posted 04 M arch 2013 - 10:38 AM

kkala

ankur2061, on 04 Mar 2013 - 17:46, saidAs requested basis for assum ption of 33,000 ptb in brine has not been provided. As m entioned in post #6 no assum ptions

have been m ade whereas post #3 m akes an assum ption which cannot be substantiated or has any basis. Thus the negative

feedback.

kkala, on 26 Feb 2013 - 02:54 AM, said:

Probably som e data is m issing, as following can indicate.

...............................................................................................................

Assum ed salt content in brine out: 33000 ptb, figure m issing (red figures arbitrarily supposed for an exam ple).

................................................................................................................

3.2 One could m easure another quantity (e.g. salt content of crude out) instead of salt content of brine.

..................................................................................................................

3.4 Salt content of 35636 ptb in brine would result in "salt with crude out" 241600-6.667x35636 = 4015 lb/d, and salt content 4015/0.1127 =

35625 ~ 35636 ptb in the water of crude out. This could close the salt balance in theory, but salt rem oval efficiency from crude would be

(240000-4015)/240000 = 98.3 % , which seem s too high.

kkala, on 26 Feb 2013 - 2:28 PM, said:

Post no 6 (by ankur2061) is noted, but let the status be cooled before a brief response. M eanwhile it m ay worth while looking into post no 3

(by kkala). Views can be of course different, readers can judge and take the useful part of each.

Im partial reading of kkalas posts, especially of the points above, gives evidence that argum entation by ankur2061 in post no

10 is groundless. Nevertheless this is now subject to judgm ent of independent reader.

Looking into specific responses needs patience, it is not so easy to trace the m ass balance problem . Generic directions are of

little help, arithm etic application of given data could really help, and post no 3 has tried for it. Fair criticism should have

studied the other view beforehand, or at least asked for clarifications; and not been in hurry.

Arithm etic application requested from ankur2061 would help sim plify variables and probably go to the theoretical solution

of about 35636 ptb of salt in brine (after adopting Kb=Kc, by naredrasony). One such solution has been already addressed in

post no 3, para 3.4, by kkala, expressing also skepticism . Com m ents on it, or on resulting high salt content in brine, would

have helped the query, contrary to politics and negative feedback.

Edited by kkala, 04 March 2013 - 06:29 PM.

Posted 04 M arch 2013 - 05:44 PM



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