Piping Manufacturer for Chlorine Contact Time

[sjsiok]

I am looking for a pipe manufacturer that specifically has pipe made for chlorine contact time. I was searching the internet recently and found one...i think it was polyethylene and blue in color. The company even made special u-shaped bends to run the piping like a snake. Any help would be appreciated.

 

[hydrae]

Any type of pipe will do just be mindful of all the other issues.

I have found the most cost effective size in ductile and PVC for large projects is 30" and if loop is needed reducers and 12" bends are cheaper than full size 90° in the 30". For smaller sizes the cost of end caps may result in the most effective size less than 30"

Fusion welded PE is fine as long as you know you will never need to work on the pipe...

Spiral welded steel in 8.5ft diameter was cheaper but other issues with steel dropped it from contention.

Make sure on the large sizes Re is > 4000 otherwise laminar flow will reduce the effectiveness by 75%

Hydrae

 

[rconner]

You may be interested in the prior thread at

http://www.eng-tips.com/viewthread.cfm?qid=101285&page=10

 

[BobPE]

Hydrae:

Just curious. When you say keep Re>4000 are you intending the contactor be used to provide velocity gradient too? If you use the pipe as contact and go to laminar then you are in a short length of large diameter vrs turbulent flow that will require longer lengths of smaller diameter for the same flows. There is a trade off the in the economy of diameter vrs. length and if you mix effectively upstream of the contactor you could then size the contactor for economy rather than for hydraulics.

Again, just curious what your thoughts were....

Take care...

Bob

 

[rconner]

I have noticed federal and state EPA sites discuss some aspects of these matters e.g. (see e.g.

http://www.epa.gov/safewater/mdbp/pdf/profile/lt1profiling.pdf

). Along with other information the section in Appendix G. Baffling Factors, near the end of this site is some interesting in that it appears that tanks with a larger length to width ratio (like a cylindrical pipe) have close to a "perfect" baffling factor, I guess with regard to the assumption of "plug flow" in calculation of contact time, as opposed to other more squat, at least unbaffled tank shapes that can apparently more "short circuit" the flow.
Perhaps another non-obvious to some aspect that also bears mentioning is that some designers and references suggest or require the use of an "injection fitting" or "quill" designed for disinfection injection (I think various types searchable through USABlueBook etc.) that passes through and seals to the pipe wall so that the relatively more concentrated disinfection solution or slurry is discharged into the turbulent region of flow and away from the pipe/lining wall (see e.g. requirements for hypochlorite injection per pg 25 Section 4 of the state EPA site at

http://www.epa.state.oh.us/ddagw/Documents/greenbook.pdfthe

section,
<<< 4.1 Disinfection
A. Requirements
All community public water systems and major non-community water systems (those serving 1,000 or more persons for any 60 days out of the year) must provide disinfection. Gaseous chlorination should not be considered for small water systems and is not covered by this manual. Non-Community public water systems with large or complex distribution systems should consider the installation of a chlorination system. Chlorination of an unsafe source is unacceptable treatment, surface water treatment must be provided.
B. Design Procedure for Hypochlorite Feed System
1. Equipment: A hypochlorinator feed system consisting of a solution tank and a small diaphragm pump with a four-way valve placed on the discharge side of the pump or a peristaltic type pump is used to inject a chlorine solution into the water. Injection ports should be 45 degrees from the bottom of the pipe and protrude 1/3 of the pipe diameter into the pipe.>>>

 

[hydrae]

Bob

My concern is not in the mixing of the disinfectant, I would always inject at a nominal pipe size then enter the CT pipe. I would want Re’s at the injection point significantly higher than 4000, otherwise the injection point will need some additional mixing device before CT credit begins such as an elbow, multi-point quill or static mixer.

Laminar flow is very rare, so it is typically not a problem as a CT pipe goes, 43 gpm in a 30 pipe has an Re of 4000, most muni wells I work with are at least 100 gpm, so using a 30 pipe is ok...

What are my thoughts on CT theory, as I understand the one drop of water that received the least amount of time is what the time is based upon, so when a pipe has laminar flow the center travels exactly twice the average speed, and when the velocity profile is integrated over the area it ends up flowing 4 times the volumetric speed, since there is no mixing that center water went through 4 times faster than a plug flow example. So a 30 inch pipe in laminar flow is equal to a 8 pipe in plug flow (the water in the center of each pipe received the same CT in both pipes. Moral, if your source is less than 43 gpm, do not size the pipe for maximum economy (30 inch), size it for turbulent flow at least, then size for economy. Since knowing if the flow is turbulent or laminar at Re between 2000 and 4000 is unpredictable stay above 4000.

Turbulent flow has a velocity profile that is nearly flat, except for a very narrow cylinder at the edge of the pipe.

CT’s calculate a log factor in disinfection, so to use the tables, the worst case has to be the sample calculation, since a small amount of failed material has a large effect on the log value.

An Re of 4000 will not keep particles in suspension, research has shown a velocity of 2 ft/sec is required for that through flushing programs (no mater what size pipe)

Does this answer your question?

Hydrae

 

[BobPE]

You know it did Hydrae, I was jut curious on how you were thinking, I have seen a lot of different approaches and it is nice to see one as thought out as your...

Thanks...

Bob