16 replies to this topic

[owe]

Good day!

I saw many things concerning steam sparger on the forum, but I miss one thing to be sure of my design! If you can help me it will be really appreciated!

I need to inject in a water tank around 660 lbs/h (300 kg/h) of steam (around 6 barg and 200°C). The pressure in the tank at sparger level is 2,9 psi (0,2 bar) because it is just an atmospheric tank.

typically I have done a sparger with small holes and my calculation give a result of 30m/s IN the sparger and the pressure drop through the sparger is only 0,02 bar. This is low to keep a velocity through the holes around 35-40m/s. The pressure drop is very low. And finally I can not find a criteria on the speed of steam in the holes.

Can you just tell me what is the criteria for the holes velocity please? I think the 25-30m/s inside the pipe is high but good. I just want to see with you the velocity and pressure drop to be sure.

Once again, many thanks for your support as usual!!

 

 

[latexman]

Make the sum of the area of all the holes ~ 1/2 the cross-sectional area of the pipe. That usually leads to good distribution.

[breizh]

Hi,

Consider this link to support your work:

https://www.cheresou...g-calculations/

 

More sophisticated equipment is available on the market; you may want to ring or email these guys to get a customized solution.

You will find a datasheet at the end of the document to support your query.

 

another reference:

https://www.pro-soni...ct-your-boiler/

 

last resource (TBP rule of thumb -8)

https://www.eng-tips...-design.233068/

 

High velocity means risk of erosion .

 

Good luck

 

Breizh

Attached Files

•  sparging.pdf   559.09KB   5 downloads
•  sparger_design_guide.pdf   472.99KB   7 downloads

[katmar]

The main problem with this type of steam injector is noisy cavitation, and this is made worse by having large bubbles of steam with low interface area with the water. So it is better to use small diameter (3mm or less) holes in the sparger to generate small bubbles and good mixing. From this perspective it would be better to have a high velocity through the holes, but of course within reason.

You can get off-the-shelf steam injectors from companies like Spirax Sarco. These units work on Bernoulli's principle sucking the water into the steam and mixing it well.

If you do make your own sparger remember to have a couple of holes at the bottom of the sparger so that the water can be driven out at start up.

[latexman]

owe,

Consider this link:

https://simpliengine...n-manifold/3480

[owe]

Thank you all, as usual.

After reading all the posts (I read often yours Breizh), for around 250  kg/h of steam (around 200°C), for a sparger inside an open water tank (1m deep) I used a 3,5 inch sch 40 (90 mm ID).

I have 14 mbar of pressure drop through the holes. 168 holes diameter 4mm.

The speed inside the RO is 65 m/s.

if you think this is not so bad, I can share my calculation for other people if they want to use it

 

(Note: katmar: Yes, 2 holes will be used to drain water at start up. Thanks!)

Thank you for your feedback

[breizh]

Hi,
Feel free to share your work with the community.
Breizh

[latexman]

To put a finer point on it, the exit thrust from each hole, although small, should be balanced by having a hole on the opposite side of the diameter. I saw several spargers with 4 rows of holes (top, bottom, and both sides of pipe).

[owe]

Thanks Latexman. I am doing like this. I am just having a look on the drawing to do like this. For the diameter, Steam orifice diameter (4mm) is not too big?

[owe]

Hello again and thank you for your time.

For the velocity i used the formula: velocity=cd*(2*DP*100000/density)^0,5. In my particular case (low pressure), I add 0.5 kg/m3 of steam. Considering a CV of 0,65, my velocity is very high. Around 100m/s. That is why I want to know if possible the max speed in the orifice itself (the speed will decrease quickly after but I don't know if there is a criteria). For a pressure drop of 1,7 psi I have more than 140m/s inside the nozzle

That is why I am looking at the design criteria for velocity or minimum pressure drop.

Thank you a lot.

[breizh]

Hi,

Review your calculation, you are in choked flow condition (sonic condition).

Breizh

Attached Files

•  fermilab-d0-en-173.pdf   183.56KB   5 downloads

[breizh]

Hi,

Another reference for sparger.

Breizh

Attached Files

•  Design gas distributors.pdf   1.02MB   5 downloads

[owe]

Thanks a lot. I am sorry but I can not upload my file but herebelow a copy of the exact data. (if someone knows how to upload an excel file let me know )

I am not in chocked flow as pressure drop is very small and inlet pressure is 1.08 barabs.

As you can see, what I try to explain is that with so low pressure drop, I have already a high steam velocity inside the nozzle.

 

 

flow of steam 250 kg/h

pressure at sparger outlet 1,0646 bar abs (water tank atmo with around 40cm of water)

steam temperature at inlet 182 °C

 

sparger hole diam 4 mm

number 180

pressure inside sparger 1,0878 bar abs

 

pressure drop of sparger holes : 23,2 mbar 0,3248 psi

(sparger pipe pressure drop of 1 m lenght not calculated)

 

velocity inside hole 59 m/s

 

sparger tube ID (4 inch) 102 mm

sparger tube velocity 16 m/s

 

[breizh]

Hi,

To add document, click on more Reply options button (bottom right), select choose file and attach.

That's it.

Note: My understanding from your initial input data is the following 

P steam 7 bara, 200C, Pressure discharge nozzle 1.2 bara (liquid static head +Patm),

about 300 kg/h of steam.

I definitely don't buy your calculation. Review the documents posted.

 

Psteam inside sparger/P outlet = 7/1.2 > {(k+1)/2}^k/(k-1), choked flow.

k being cp/cv steam at 7 bara or 1.3035 

 

right now, I'm thinking the OD of the sparger is too big for 300 kg/h steam and the hole size is also too big. I would not comment about the number of holes because we don't have idea about the diameter of the tank and the length of the sparger.

note : velocity in the sparger (pipe) is about 4m/s 

Good luck.

Breizh 

[katmar]

What reference has caused you to want to limit your velocities so much? Keeping the velocities low (and therefore the pressure low) is what is causing you to need so many holes. Unless your vessel is very small the steam velocities will have completely dissipated long before the stream of bubbles can reach the wall.

I have used spargers inside pipes where the distance to the wall was relatively small, and they worked successfully for many years without problems. I appreciate that the liquid in the pipe was being constantly renewed and resulted in better mixing than you would get in a tank but I don't think the steam velocity would be a problem.

In tanks, where the mixing is less than in a pipe, it is more important to take advantage of the mixing effect of the injected steam and this will be better with smaller holes. The number of holes would be unreasonable if they were smaller when using your low pressures, but I have seen spargers work at higher pressures with the orifice holes choked without problems.

Once the tank is hot the mixing is less critical, but at start up the tank can vibrate quite badly when injecting steam into cold water. Be careful to allow for slow injection of steam at start up.

[owe]

Oh sorry for the confusion. The steam is 7 barg but we have a control valve etc.

But the inside pressure of the sparger is 1.0878 bar abs!

 

The tank is very small (2 meters long for 1m diameter, horizontal). 

That is why I provide so many orifices to have a better mixing.

 

I attached the file.

[owe]

with the file...

Attached Files

•  orifice example.xlsx   49.18KB   6 downloads