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Sizing Of Min. Flow Line With Ro And Isolating Valve


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#1 Ankit_Kumar

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Posted 25 August 2015 - 03:58 AM

Hi 

 

I need to do calculations regarding sizing of  min. flow line with RO for a pump. Appreciate if anyone can guide me & check my calculations are right or not? 

Attached please find data for installation of min. flow line of pump with RO.

 

Following steps were followed. 

·         Pump Data Sheet is provided for refrence. Please note that fluid is TMA (Trimethyl Amine)

 

Data_Sheet.jpg
 
Data_Sheet_1.jpg
 
 

·         1st I did the line sizing, based on velocity through the pipe. i.e. 1-3 m/s. 4 inch dia pipe was selected based on it as shown

 

http://s1.postimg.or...7wcrj/image.jpg

 

·         As existing discharge piping is of 40 SCH so I selected inner dia of pipe of 102.3 mm for a pipe of 4” 40 SCH (kindly see if this selection is right because I am confused regarding it)

 

·         Orifice dia was calculated through spreadsheet with a flow of 55 Nm3/hr (more than min. flow to counter friction losses due to piping & bends). 

Kindly guide for liquid, Nm3/hr to be used or m3/hr. I think for liquid, it remains the same.

 

I found this spreadsheet on internet (i don't know exact location, my apology) and calculated RO dia 

 

http://s16.postimg.o...5it/Orifice.jpg

 

·         Requested to kindly check it at your end from another sheet if this spread sheet has calculated it rightly, if possible



#2 breizh

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Posted 25 August 2015 - 11:49 PM

http://www.pipeflowc...ns.com/orifice/

 

To support your calculation . I'm not clear about what you want to achieve. Is it to prevent overheating ?

 

Note : Always attach a sketch to avoid misunderstanding .

 

Good luck .

 

Breizh 


Edited by breizh, 26 August 2015 - 12:59 AM.


#3 Ankit_Kumar

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Posted 26 August 2015 - 01:26 AM

At present on our plant, pumps are installed without min. flow line. Due to this during changeover or parallel run, pumps got damaged several times. So I m trying to do sizing of a line for min. flow of pump. This line should hv an isolating valve and Restricted orifice.

 

I posted my calculations for review purpose. If you can review & provide guidance

 

For min. flow, i calculated line inner dia from Q = vA with velocity value in the range of 1-3 m/sec.

4" dia pipe was selected based on it.

 

Sch number of 40 was selected as discharge pipe of pump has the same SCH number. Therefore, 4" 40 Sch pipe inner dia was selected, (Kindly see if this selection is right ? )

 

Then I put the values in a spreadsheet for RO and from there i got orifice dia. Now i am not sure about the authencity of spreadsheet. 

To counter pressure loss due to i/v, pipe & fittings i assumed flow through the orifice to be 55 Nm3/hr which is more than req. min. flow 50 Nm3/hr.

 

If you can cross check it , i'll be grateful. There are two more issues;

 

I read Orifice thickness can be selected based on design pressure of piping but i don't know how?

 

Selection of i/v ? Gate valve or plug valve?  Criteria? 



#4 Ankit_Kumar

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Posted 26 August 2015 - 01:59 AM

ok


Edited by Ankit_Kumar, 23 December 2015 - 02:57 AM.


#5 fallah

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Posted 26 August 2015 - 03:09 AM

Anit_Kumar,

 

You should take the minimum stable flow of pumps from relevant vendors. Then the sizing the line/valve in minimum flow line would be done based on such flow rate...Have you gone this way?


Edited by fallah, 26 August 2015 - 03:11 AM.


#6 Ankit_Kumar

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Posted 26 August 2015 - 03:24 AM

Yeah it is providied as 50 Nm3/hr. For both thermal & stable flow.



#7 breizh

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Posted 26 August 2015 - 06:37 AM

Hi ,

With the data provided , I can confirm that your calculator is working well . Same result .

 

For isolation valve refer to the document attached .

 

 

Good luck .

 

Breizh



#8 Bodhisatya

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Posted 26 August 2015 - 10:13 AM

Breizh Sir

 

Can you please provide literature/spreadsheet pertaining to RO sizing so that we can try preparing the same of our own.

 

Ankit Kumar can u please share ur spreadsheet.

 

Bodhisatya


Edited by Bodhisatya, 26 August 2015 - 10:15 AM.


#9 ankur2061

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Posted 26 August 2015 - 12:50 PM

Ankit Kumar,

 

Why do you describe your liquid flow as "Nm3/hr"? Gas flow is described at some standard conditions (NTP / STP) since it is compressible flow and not liquid flow which is incompressible flow.

 

50 m3/h is a large minimum safe flow. Providing an RO is wastage of energy. You would be better served to provide a control valve in the minimum recycle line to conserve energy. To understand about the various schemes for minimum safe flow refer the following link and the schemes for minimum flow:

 

http://www.cheresour...trifugal-pumps/

 

Regards,

Ankur.



#10 Ankit_Kumar

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Posted 26 August 2015 - 03:46 PM

Dear Ankur & Breizh

 

Many Thanks for your valueable input. I have noted some problems in my calculations, appreciate if u can help in them

 

As per data sheet, unit of flow is Nm3/hr mentioned. I also noted it but Thanks to Ankur for highlighting it. Now what to do? Assume it is m3/hr or convert it. If conversion, how to convert in case of liquid? Assume I can't ask from vendor 

 

Vap pressure of liq at operating temp of 92 C is 12.2 kg/cm2 while pump suction pressure is 12.5 kg/cm (Orifice d/s pressure also) so i think should design R with DP of less than 3.9 (say 1,5) to avoid vaporization. Kindly give comments regarding it.

If yes, i think no need to do line sizing again.... only orifice sizing is required? 

 

Ankur _ This min. flow line will be used only in case of pump startup or changeover .... I guess in that case this energy loss is not much of big value. For continuous flow through line, either to install control valve or schroedahl valve. Right?

 

1 more thing ... May b the discharge pressure at 50 m3/hr flow is different as per curve. The delta of 3.9 might be for rated flow case only. (I am not in office now so don't know exactly). If yes, then what to do?

 

Kindly give your comments for better understanding 



#11 Ankit_Kumar

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Posted 26 August 2015 - 03:58 PM

Dear Bodhisatya 

 

Kindly guide how to attach excel or any other sheet here so that i can share spreadsheet.

 

I know only image pasting. 



#12 breizh

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Posted 26 August 2015 - 06:54 PM   Best Answer

Bodhisatya ,

 A good reference is Flow of fluid through Valves , fittings and Pipe . TP N .410M by Crane .

The calculator attached  is based on document in reference .

 

 

Hope this helps.

 

Breizh


Edited by breizh, 27 August 2015 - 12:46 AM.


#13 ankur2061

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Posted 26 August 2015 - 11:47 PM

Ankit,

 

Although I have not encountered liquid flow in Nm3/hr, the conversion at the operating temperature is simple. Convert the volume flow in mass flow by multiplying with the density of the liquid at NTP (0 deg C). Once you have the mass flow in kg/h, divide the mass flow by the density @operating temperature to get the volume flow in m3/h.

 

Every time the pump flow at pump discharge drops below the minimum safe flow, the control valve in the minimum flow recycle line will open to maintain the minimum safe flow. At all other times, the control valve is supposed to remain closed. An economic analysis is required to evaluate whether a control valve is justified vis-a-vis a RO in terms of the excess power required for continuous recycle through an RO. Remember that with an RO there will be continuous recycling through the minimum flow recycle line.

 

Regards,

Ankur.



#14 fallah

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Posted 26 August 2015 - 11:58 PM

An economic analysis is required to evaluate whether a control valve is justified vis-a-vis a RO in terms of the excess power required for continuous recycle through an RO.

 

As an accepted rule of thumb which confirmed by some reputable oil and gas companies, up to 15 KW installed power for pump it would be more efficient having permanent recirculation line fitted with a RO...
 



#15 Bodhisatya

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Posted 27 August 2015 - 12:45 AM

Dear Bodhisatya 

 

Kindly guide how to attach excel or any other sheet here so that i can share spreadsheet.

 

I know only image pasting. 

 

Please hit the more Reply options,you will get the necessary instructions ,choose attach files and upload the same

 

Bodhisatya



#16 Bodhisatya

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Posted 27 August 2015 - 12:53 AM

 

Although I have not encountered liquid flow in Nm3/hr, the conversion at the operating temperature is simple. Convert the volume flow in mass flow by multiplying with the density of the liquid at NTP (0 deg C). Once you have the mass flow in kg/h, divide the mass flow by the density @operating temperature to get the volume flow in m3/h.

 

 

Regards,

Ankur.

Ankur Sir

 

In Air Separation Units we always imply Liquid flow in Nm3/hr (equivalent to Gas).This is for maintaining homogeneity while performing the mass balance.

 

Bodhisatya 



#17 Ankit_Kumar

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Posted 27 August 2015 - 02:57 AM

Thanks to all for ur guridance. Some questions still left unanswered. Appreciate if you can answer abt them also;

 

Vap pressure of liq at operating temp of 92 C is 12.2 kg/cm2 while pump suction pressure is 12.5 kg/cm (Orifice d/s pressure also) so i think should design R with DP of less than 3.9 (say 1,5) to avoid vaporization. Kindly give comments regarding it.

If yes, i think no need to do line sizing again.... only orifice sizing is required?

Ankur if we design it at less delta P, i think this will be economical also. 

 

May b the discharge pressure at 50 m3/hr flow is different as per curve. The delta of 3.9 might be for rated flow case only. (I am not in office now so don't know exactly). If yes, then what to do?



#18 Ankit_Kumar

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Posted 28 August 2015 - 06:13 AM

Guys i am almost done with this issue. Kindly help for completions.

Thanks in advance.






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