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High Visocosity In Very Long Pipe


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#1 ramram

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Posted 02 September 2020 - 02:59 PM

Hi Everyone,

 

I've asked by a client to calculate a pump for a new project.the client would like to transfer mineral oil

from a new pump to a spraying nozzle.the desired flow rate is 1.5m3/hr.the pipe length from the pump discharge to the desired location - a spraying nozzle is about 770 meters long.

when i first tried to calculate the pump TDH @ 20degC was very high and is about 220barg!which is impossible to achieve.the mineral wool density is 860kg/m3 and 182cP @ 20degC.

my idea was to install a heat exchanger to raise the temperature from 20degC to 90degC in order to lower the viscosity (11cP @ 90degC) which lowers the TDH to about 16barg which is fine for the client.

The issue is that i'm abit worried about the pipe length-the pipe will require tracing and insulation which maintain high temperature but the incase of failure the oil will be cooled and remain inside the pipe which then will be very difficult to drain.the pipe will have some pockets and it will be impossible to drain the pipe back to the pump or vessel.

I wonder whether it will be possible to install few drains valve and steam injection for cleaning incase of failure and will it be good solution or rather to install a new vessel and pump very near the spraying nozzle?

 

Kind Regards,



#2 breizh

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Posted 02 September 2020 - 06:57 PM

Hi,

On operation point of view you are right to worry about material stuck in the pipe .  You need to be able to drain and clean the line in case with sufficient enough points to do so , including flanges for easy dismantle . 

You also need a close monitoring of the tracing system temperature all along the pipe . Big issues are safety if the pipes are installed on rack and the maintenance of insulation in good condition after repair (availability of workers and cost).

note : Make sure that your power source is always available and be able to flush the entire line in case of trouble ( steam or liquid flush) .

 

This is valid for short and long distance.

 

note : You mentioned spray  nozzle , this very much depends to the pressure applied .

 

Lobe pump should be suitable for your application 

 

My view 

Breizh 


Edited by breizh, 03 September 2020 - 11:20 PM.


#3 ramram

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Posted 03 September 2020 - 12:05 AM

Thank you Breizh,

 

I've thought to install a pressure reducing valve to achieve the required inlet pressure for the spraying nozzle.



#4 Chemitofreak

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Posted 03 September 2020 - 04:55 AM

Just some questions

 

Has the Client asked you to size only the pump ?

 

Has he given you the liberty to add additional equipment? Can you increase the temperature of the fluid to reduce the viscosity?


Edited by Chemitofreak, 03 September 2020 - 04:55 AM.


#5 thorium90

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Posted 03 September 2020 - 08:17 PM

Might I suggest for consideration, to pump the fluid to an atmospheric tank near the spray nozzle. Size the main transfer pump to this tank only.

Then from this tank, have a second set of spray pumps just to supply the spray nozzle.

Do take note that with high viscosity fluids, adding a few elbows here and there will throw off the calculations significantly...

Also what type of pump are you proposing?


Edited by thorium90, 03 September 2020 - 08:18 PM.


#6 ramram

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Posted 04 September 2020 - 07:12 AM

Might I suggest for consideration, to pump the fluid to an atmospheric tank near the spray nozzle. Size the main transfer pump to this tank only.

Then from this tank, have a second set of spray pumps just to supply the spray nozzle.

Do take note that with high viscosity fluids, adding a few elbows here and there will throw off the calculations significantly...

Also what type of pump are you proposing?

 

Even if I i suggest additional pump for the spray nozzle only the long distance remains.

I calculated to raise the temperature to 90degC which will reduce the viscosity to 11cP from 182cP

the required pump will be be 16barg.I suggested for the client to choose a screw pump.



#7 ramram

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Posted 04 September 2020 - 07:14 AM

Just some questions

 

Has the Client asked you to size only the pump ?

 

Has he given you the liberty to add additional equipment? Can you increase the temperature of the fluid to reduce the viscosity?

Not only the pump but give a complete solution.

I suggested to add an electrical heat exchanger to raise the temperature to 90degC,temperature tracing and insulation.

 

But my question was how i can handle with a failure of the pump or tracing?



#8 breizh

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Posted 04 September 2020 - 07:19 AM

Hi,

You may consider  a pigging system to ensure the line is clean at the end of the operation . To me you cannot keep the line full of  product  .

My view 

Breizh 



#9 ramram

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Posted 04 September 2020 - 07:25 AM

Hi,

You may consider  a pigging system to ensure the line is clean at the end of the operation . To me you cannot keep the line full of  product  .

My view 

Breizh 

what is the cost of such pigging system?

the pigging system is able to work @80-90degC?



#10 breizh

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Posted 04 September 2020 - 07:32 AM

Hi ,

For point 2  YES , use the right material for the pig .I 've attached an article .

For point 1 , check with the references attached in  the brochures .

Good luck

Breizh 

Attached Files



#11 latexman

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Posted 04 September 2020 - 08:08 AM

Is the pipe existing?  What size and schedule pipe?

 

Is the mineral oil produced on site?  If not, how is it supplied and the logistics?


Edited by latexman, 04 September 2020 - 08:10 AM.


#12 Jiten_process

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Posted 14 September 2020 - 03:05 AM

I remember the similar instance during early days of my career. I went for commissioning of fired heater / burner system. Normally a fuel gas is used for firing and incase fuel gas is not available, as a back up fuel oil system provided. It was dual fired burner system. Since, this fuel oil system is normally remained idle, the similar issue we faced during start-up. Although heat tracing was provided, since the system remains idle, most of the times, no operator usually pays attention. And when it has to actually work, heat tracing was out most of the times due to either thyrester trip or any other reason. It resulted one small accident also, despite of low temperature, operator started the pump which was positive displacement pump and keep pushing the fluid only unable to do it (due to very high viscosity), resulted in gasket failure of one the discharge filter and oil spilled out. Fortunately, no one was harmed. What we had to do is, take steam hose and heat the entire system from outside manually. This worked for timebeing but for sure this is not the safe way to do it and not an SOP. Not recommended as designed system. 

 

I think, your system is designed to operate continuously. So you may not face big issues. I dont have full picture of your system design, hence can give you some general design points as below.

 

1) Heat tracing failure should alarm in the control room and shall be designated as "high priority" alarm

2) Provide one recirculation line downstream of heat exchanger back to suction vessel to establish heated oil profile. your pump and heat exchanger should be near to suction vessel. Moreover, as you rightly said, try to reduce your system volume as much as you can. have your suction vessel, electric heater and pump near to discharge point as much as you can. 

3) provide back-up electric heater inside your suction vessel from which pump is taking suction. 

4) Provide heat conservative insulation. Failure of heat tracing will not cool down the inventory in a short time. Heat conservative insulation will help you to get sometime to solve the issue. Also, if your tracing is working fine, failure of pump / tripping of pump, may not lead any operation issue as oil temperature is still maintained. 

5) Better to consider steam tracing. Make sure standard steam trap arrangements have bypass. so that, you can manually ensure the condensate is drained and steam is available inside the tracing. If your system is so critical, consider providing electrical tracing in parallel with steam tracing, as a back-up. 

6) make sure all dead legs and drain points are adequately heat traced. if possible, provide additional tracing points. 

7) your heat exchanger design is also critical. Design the heat exchanger taking conservative oil viscosity and at low oil velociy. Although, actual velocity during normal operation is higher, it will result in improved HTCoefficient in operation. This will give you some margin for upsets. 

 

Hope this helps. 


Edited by Jiten_process, 16 September 2020 - 02:20 AM.





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