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Min. Tube Dia. For Hex In Slurry Duty To Avoid Plugging


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#1 curious_cat

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Posted 31 August 2015 - 05:14 AM

Is there a recommended practice about min. tube dia for Heat Exchangers in slurry duty (5% solids w/w)  to avoid plugging of tubes? 

 

I've seen velocity recommendations of 2m/s to 4 m/s so I will definitely keep my velocities in that range but is there an independent tube size suggestion too? 

 

Perhaps based on ease of cleaning if plugging occurs? I was considering a 1.25" tube. Comments?

 

This is a vertical steam heated, titanium tube evaporator for boiling (18 ft tubes). Crystalline inorganic salt is the dissolved component. 



#2 Bobby Strain

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Posted 31 August 2015 - 07:11 PM

It depends on the slurry character. Some instances use spiral plate exchangers which are less prone to pluggage.

 

Bobby



#3 breizh

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Posted 31 August 2015 - 08:10 PM

Hi,

 

Based on my experience , consider High Pressure  cleaning to recover the performance of the unit.  This requires access to remove the bottom part of the HX and to introduce the lance and other hoses.  Another good tool to assist the cleaning is an endoscope (tiny camera) to be purchased or rented.  

 

Hope this helps

 

Breizh



#4 Bobby Strain

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Posted 31 August 2015 - 10:13 PM

Is this a forced circulation, upflow design? Thermosyphon? Or a falling film. I think this is something that I would send to a vendor with experience in handling like material. Give them a duty spec to quote to.

 

Bobby



#5 curious_cat

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Posted 31 August 2015 - 10:31 PM

It depends on the slurry character. Some instances use spiral plate exchangers which are less prone to pluggage.

 

The slurry is essentially a NaCl brine. Hence the Titanium tubes. The solids are hard, crystalline, brittle. They are not slimy or film forming. 



#6 curious_cat

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Posted 31 August 2015 - 10:33 PM

 

Based on my experience , consider High Pressure  cleaning to recover the performance of the unit.  This requires access to remove the bottom part of the HX and to introduce the lance and other hoses.  Another good tool to assist the cleaning is an endoscope (tiny camera) to be purchased or rented.  

 

Thanks breizh!  I was hoping you'd reply since you seem to have worked with similar units to the one I'm describing. 

 

We too have planned high pressure water jet cleaning. Access to both top & bottom heads of the HEX has been provided. 

 

Is there an optimal minimum tube dia for lancing the tubes?

 

Alternatively, can you tell what dia tubes you have worked with in slurry duty Heat Exchangers? 


Edited by curious_cat, 31 August 2015 - 10:34 PM.


#7 curious_cat

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Posted 31 August 2015 - 10:48 PM

Is this a forced circulation, upflow design? Thermosyphon? 

 

Forced circulation, upflow design.  

 

With a 5% slurry my impression is that both thermosiphons & falling films become quite impractical. 

 

Even with forced circulation we anticipate water-jet lance cleaning due to plugging issues like breizh described. 



#8 breizh

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Posted 01 September 2015 - 12:35 AM

curious-cat ,

I need to dig in my files , the only thing I found so far  is the diameter of the bundle which  is increasing from 600 mm to 650 mm and eventually to 700 mm for the last effect for the same length of tubes 7000 mm.

 

tube diameter : 38 mm

 

Breizh


Edited by breizh, 01 September 2015 - 01:21 AM.


#9 curious_cat

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Posted 01 September 2015 - 01:31 AM

 

I need to dig in my files , the only thing I found so far  is the diameter of the bundle which  is increasing from 600 mm to 650 mm and eventually to 700 mm for the last effect for the same length of tubes 7000 mm.

 

tube diameter : 38 mm

 

Thanks breizh! That helps a lot. 

 

Our tubes are 6000 mm length. The vendor was offering a quick lead time on 29 mm tubes but I think it's too small. 

 

I'm going in for the 38 mm tubes based on my intuition and now supported by what you've been using too. 

 

It'd be great to hear any other parameters you could get. e.g. What velocities do you guys use? 2 to 4 m/s is a broad range so I'd be curious to hear what has worked out for you. 



#10 breizh

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Posted 01 September 2015 - 02:55 AM

Hi ,

Some data :

Viscous liquid : 3 m/s

 

Multiple effects : final effect : 2 to 2.7 m/s ; intermediate : 1.5 to 1.8 m/s ; first effect : 1.2 to 1.5 m/s .

 

 

Breizh



#11 curious_cat

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Posted 01 September 2015 - 03:22 AM

Hi ,

Some data :

Viscous liquid : 3 m/s

 

Multiple effects : final effect : 2 to 2.7 m/s ; intermediate : 1.5 to 1.8 m/s ; first effect : 1.2 to 1.5 m/s .

 

Thanks again breizh!

 

I'm thinking of using 3 m/s design velocity since the tubes are Ti and hence can take higher velocities. 

 

Do any of your effects have multiple passes? Any experience whether twin passes are ok for slurry duty? 


Edited by curious_cat, 01 September 2015 - 03:23 AM.


#12 breizh

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Posted 01 September 2015 - 03:32 AM

Hi ,

Single pass effects .

 

Note : As an option for your project , did you consider using MVR ( mechanical vapor recompression ) ? This came to my attention after completion of my last project .

 

Good luck.

 

Breizh


Edited by breizh, 01 September 2015 - 11:25 PM.





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