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Steam limpet pressure drop 1

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Vishal Kumar

Vishal Kumar

Chemical
Nov 23, 2019
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Dear all,
Please find the attachment where we are using steam Saturated (3.5kg/cm2g) for heating through limpet to keep internal material in liquid state (melting point 63C). I have two doubts , considering the size of this tank the height , is it a good idea to use one single limpet through the body because the number of turns and flow path will be huge and result in significant pressure drop (not calculated yet), and anyone has any experience with use of load cell for a flat bottom tank pls share.
 
 https://files.engineering.com/getfile.aspx?folder=6aaf2788-c4d9-454d-9118-3d4dd8aeb322&file=IMG_20240210_100538.jpg
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Insulation all over the tank is a must, but why heat the tank above the maximum liquid level? Does material evaporate/sublime and form stalactites or whiskers, or does it have a different bad habit?

Yes, on the side, I would have multiple zones. I would check reasonable flow/pressure drops for steam and CW, in case the tank gets repurposed in the future. I've seen it happen, a lot!

At first glance your design is overkill, but I don't have all the facts. Why not determine how much heat is needed for steady-state heat losses given some good insulation? I bet the heat can easily be provided by just a bayonet pipe coil that bolts into/onto a manway. Use pumps already in the design for recirculation. Much cheaper!

Load cells on flat bottom tank work fine. Use 3 if possible, self-leveling. You may need a stiffer base than usual for this. Talk to your ME and tank fabricator.

Good Luck,
Latexman

 
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Thanks for the valuable input , max liquid level ? I didn't mention anything about that. Material has a melting point of 63 so we are unloading it into a tanker so it has to be kept at 80-85 C all the time.
I missed to show insulation which will be there over the tank.
It's a final product hence storage capacity is high given our product demand and timeline to produce it.

I have calculated the heat loss from the tank and a 2 inch steam line is coming out to be good for just maintaining the temperature.

We want limpet to at least heat internally if the material has solidified back , it takes time but will be flow able.
 
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Be very careful with the thermal and hydraulics design of these external coils - you've got internal condensation of steam with significant portion of the tubes more or less liquid flooded. And will you be taking credit for the heat transfer component due to subcooling of the hot condensate ?
Pressure in the tubes will be a reflection of the backpressure induced by the range in return steam condensate header pressure at this location. So check if some surface area will be taken up for de superheating rather than condensation. De superheating htc will be much lower than that for condensation.
 
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Hi,
I don't know the reliability of your power station but I 've bad experience with outage and tank frozen (phenol). You may want to consider electrical heat tracing instead of steam tracing. Management of steam trap and condensate need to be carefully analyzed. We have no indication about your product but make sure that is not going to freeze on the sky because of N2 and make your safety device obsolete.



My 2 cents
Pierre
 
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With these external coils and given the viscosity of phenol, would suggest it is difficult to get the centre and floor of the tank heated. Thermal convection currents will be localised to the tank side walls only.

See also this for operator TWA exposure limits for phenol vapor : 1ppmw in Australia.


Gas dispersion studies during tank filling operations should not result in ground level (or any elevated structures where operators may be present) exceeding 1ppmw.
 
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Vishal Kumar said:
, max liquid level ? I didn't mention anything about that.
Click to expand...

In my experience, limpet coils on the cone-top section of an API-type tank are extremely rare. API tanks are not designed for liquid level to enter the cone-top section. Steam/electrical tracing may be a better choice there.

Good Luck,
Latexman

 
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My concerns are , although on a daily basis we are thinking but have to close soon for fabricator to start working :-
1. Pump is 20m3/hr for product unloading & so didn't use circulation HE as it will take a lot of time for heating through only circulation. (Can keep it for emergency though) No other form of agitation is possible I feel.
2. As already pointed out , heating to reach the center due to convection ( product has viscosity 3.6 cP)
3. For steam condensation we can manage by providing separate coils I feel. Although heat loss won't be very high due to limpeting and insulation.
4. Top cone point by Latex man is I feel right observation, liquid won't be filling till that much height but just if ever happens to de scale the material tracing can be enough.
5. Can you please elaborate the N2 point as I didn't get it , do you mean N2 flow will cool down the material in the top cone and may result in safety device nozzle choking?
Thanks for all your points , pressure drop in limpet I will revert back by tomorrow.
 
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Find a way to run some pump to enable internal agitation during tank heating with this external coil setup. Else use internal floor coils spread well over the floor.
What is your reason for external coils rather than internal coils ? Is it a concern with steam leak into phenol if there was a rupture in the internal floor coils ? With SS316L floor coils, this should not be a concern?
 
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