Perforated Pipe Distributor 3

[jproj]

I am looking for a good reference regarding perforated pipe distributors. I have Perry's, but the section on perforated pipes is rather limited.

More specifically, I'm trying to calculate pressure drop of steam across the perforated pipe (based on number & size of holes). I have done liquid pressure drop calculations (based on flow through an orifice) and am confident they are correct.

I'm having trouble with calculations involving steam (specifically the density changes as pressure drops). I know that part of the orifice equation for a non-compressible fluid uses a material balance:
(A*V*rho)in = (A*V*rho)out (with density canceling out)

(A = area, V = velocity, rho = density)

I assume I need to include the density changes, but I also think there is be more to it than that.

If someone could point me in the right direction (good text / website / info) it would be much appreciated.

jproj

 

[butelja]

Look at Crane 410 technical paper for compressible flow equations.

 

[TD2K]

Are you talking about the flow of steam down the distribution header itself or across the holes or both?

I'd suggesting finding a copy of Crane's technical paper 410C, flow of fluids through valves, fittings and pipes. They handle compressible fluids using a similar equation for incompressible flow but adjusted for compressible flow by means of an expansion factor (Y).

 

[jproj]

Sorry if I was unclear. I am trying to find info on perforated pipe distributors (steam flowing from a steam header, through some piping, to a perforated pipe and into a unit, say a storage tank).

Specifically, I would like to find information on how to calculate the pressure drop through the holes (perforations) in the pipe. This is a straightforward calculation for liquid since it is nearly incompressible, but as TD2K stated, the problem lies in dealing w/ incompressible flow.

I appreciate your responses, but I'm unsure if I can get a copy of Crane's technical paper (although I'm going to try considering it is listed as a good reference in half the posts I read!). Does anyone have any alternate references?

Thanks!

jproj

 

[KernOily]

jproj, is this a sparger, like a tank steam sparger? Is it built on a header-lateral arrangement? Thanks!
Pete
P. J. (Pete) Chandler, PE
Principal Engineer
Mechanical, Piping, Thermal, Hydraulics
Processes Unlimited International, Inc.
Bakersfield, California USA
pjchandl@prou.com

 

[jproj]

Pete:

It's a horizontal pipe that would be inserted into the bottom of a tank with the holes discharging steam in the vertical direction (see example below... 6 holes):

(------Steam Outlets-------)
================= ==== ==== ==== ==== ==== ====
Steam Inlet----> ] <-Pipe end
===============================================

There are not any sparger nozzles on the pipe, just holes. Thanks for the response, any help / references are appreciated!

jproj

 

[jproj]

ouch, that one got mangled... hope you get the point though (pipe end should be on the right end)

jproj

 

[KernOily]

Nice ASCII artwork... just like the old days! ;-)

When I did this I used the procedure in Perry's. I designed a gas sparger, not steam, but the procedure is the same. I've also done it without Perry's, i.e. use your favorite orifice flow equation to size the holes since it's likely you know what flowrate (mass or volumetric) you want through each hole. You assume the pressure is constant inside the header since the holes are in parallel relative to the header itself. That means the velocity has to decrease as you go down the nozzle, thus you should probably decrease pipe size as you go down the header. I think you would be well within a reasonable defensible design if you assumed the fluid properties to be constant over the length of the header.

I am currently working a project that sparges gas into an iron chelate solution in a contactor vessel for H2S removal. There are 64 sparge nozzles in this 12' Ø vessel on a header-lateral arrangement. In this vessel, the header is a 10&quot; and the laterals are all 2&quot;. It operates at low pressure (3 psig) and the gas distribution/contact time in the solution is perfectly acceptable, so that tells me the assumption of constant fluid properties inside the sparge header is OK. Thanks!
Pete
P. J. (Pete) Chandler, PE
Principal Engineer
Mechanical, Piping, Thermal, Hydraulics
Processes Unlimited International, Inc.
Bakersfield, California USA
pjchandl@prou.com

 

[TD2K]

If you want to post your email address here or drop me a note at testdog2000@yahoo.com, I can send you the relevant pages (5 or 6) out of Crane. It is a nice reference book.

 

[TBP]

Try Spirax Sarco. They publish (or at least used to publish) a booklet called &quot;Direct Steam Injection&quot;. It may be like some of their other stuff, only available in the UK.

It does state that a large number of smaller diameter holes are preferable to a small number of larger holes. Avoid a single row of holes along the bottom of the steam pipe, but rather drill two rows, at 45* angles.

There is a chart showing the approx steam flow from holes of various diamters with a range of differential pressures.

With a 10 psi differential pressure, a 1/16&quot; hole will pass about 2 #/hr, a 1/8&quot; hole 8 #/hr and a 3/16&quot; hole 20# hr.

With a 20 psi diff, the numbers are 3, 12, and 28 #/hr respectively, and with a 30 psi diff, they go to 4, 16 and 36 #/hr.

There are 11 of these little booklets listed, and I've only got 3 of them. I was given these about 15 years ago by a Spirax Sarco rep who was originally from the UK, and I hadn't seen them before - and haven't since.

E-mail me your fax number, and I'll get you the chart.

tpbindustrial@on.aibn.com

 

[jproj]

TBP:

Is you e-mail correct? I cant seem to get anything to go through.

jproj

 

[TBP]

Sorry jproj - typo. I got the 'p' and 'b' transposed. Try this one:

tbpindustrial@on.aibn.com

 

[gearjammer]

try the department of energy web site
or the

http://www.osti.gov

site

 

[grimma]

jproj,

I have quite the same problem as you - plus, even after reading the topic on &quot;pipe or tube&quot; I'm even more confused on what termm should I use, as English is not my mothertongue language.
I have a tank of activated sludge, and I want to provide air in it, through a series of pipes (!), with perforations.
So, did you manage to get sthg relevant about it?

As you've been here for longer than me, maybe you know if the following topics have already been answered:
- Is there any tip on the size of the holes I should make? (knowing I want bubbles around 4 mm in diameter)
- Also for the distance between each hole: enough so that agitation and aeration is optimal, but not too many, as I don't want the bubbles to &quot;join&quot; and form bigger ones

Thanx a lot

 

[KernOily]

Here's a reference for you all: &quot;Designing Gas-Sparged Reactors&quot;, Chemical Engineering, July 1967.

I have been working on a similar problem since May and I found out that the design of these things is not a trivial issue. A lot rides on this design. If it doesn't work, my name is Mud.

I studied the procedure in Perry's and it was a little too watered down to suit me. So, I built a PipePhase model of the entire distribution lateral system. This system consists of a header-lateral system of 8 laterals of varying lengths in the bottom of a circular vessel. If you can imagine the grill on a barbecue, you get the picture of what it looks like, sans the ring around the OD of the grill.

For a first cut, I assumed each hole behaved as a pipe exit. My main concern was to ensure the distribution of the gas was approximately equal across the ID of the vessel because this maximizes the contact time of the gas with the liquid. I set the hole diameter at 3/4&quot; (a single row of holes on the bottom of the pipe) because this process is a precipitation reactor and the precipitate tends to agglomerate at the sparger holes, so we use large holes. If the holes are any smaller, they tend to plug off rapidly. I used the 90% area reduction rule of thumb to set the maximum number of holes. So I ran the model and it gives really good gas distribution across the laterals with reasonable pressure drop.

I then changed the pipe exit to an orifice, and the results were the same except I got a bit more dP. So, we are proceeding with detailed design of the new internals.

In response to the question above about 4mm bubble size - don't the bubbles coalesce into their natural maximum large size&quot; as they rise? Thanks!
Pete