Tying in a chlorine residual analyzer to a VFD metering pump 3

[EngDon]

I would like to know what would be the most proficient way to set up a Hypo injection system utilizing a chlorine residual analyzer and a Variable Frequency Drive(VFD) pump. The current system utilizes the VFD metering pump (metered according to flow rate); however, I believe that tying in a chlorine residual analyzer will be a much more effective method to control the VFD according to chlorine residual. Any suggestions would be appreciated.
Thank You.

 

[jOmega]

On the assumption that the analyzer measures PPM......

You would need a VFD with PI or PID Closed Loop capability.

Then you would need to provide it with an adjustable setpoint that is scaled in proportion to the units of applicability.... i.e. PPM, etc ...
for analog... 0-10v 10v = xx PPM
or analog ..... 4-20mA 20mA = xx PPM
or digital setpoint capability within the VFD and scaling capability of the feedback.

Next, the Chlorine Analyzer must be able to provide a feedback of the correct proportionality to match the setpoint range.

ex. analyzer provides output range 0-10v where 10v = xx PPM, etc...

Next you would need to be able to adjust the response of the closed loop to accommodate the transport delay of the analyzer. Transport delay is the the time that it takes to report a change, once a change has been made.. This could be anywhere from milliseconds...to seconds.... to minutes... depending upon how fast the selected analyzer processes a sample and how many samples are required to arrive at the correct measurment.

And you would need to correlate metering pump flow... to PPM ....

That's the basic framework.



jO

 

[jbartos]

Suggestion: More information is needed. There may be various pumps involved. Is the VFD pump a chlorine booster pump? Is the chorine metering pump the same as the chlorine booster pump? Is the magnetic flow meter with ON-OFF function? Is the flow meter differential?

 

[jOmega]

JB

I think that Don succinctly stated that it was a metering pump being operated by the VFD.

Metering Pumps are NOT Booster pumps, JB.

In this type of application, JB.... there isn't any call for a "Booster Pump".... there is no need to increase the flow or the pressure.

What is required is to meter the amount of chlorine being added to the process.

It is basically, a very simple system, JB.

 

[EngDon]

Thank you for your advice; subsequently, I don't know if using a residual analyzer alone to control the addition of chlorine will suffice. The current system is fed using a feed forward control scheme proportional to flowrate, which does not adequately provide the right residual. I am concerned about the mixing and aging problems involved with sodium hypochlorite and the ability of the residual analyzer to compensate for such problems. If a residual analyzer is installed can I be assured that a 15 Million-Gallon basin will maintain a determined residual? What should be the lag between the injection point of the chlorine and the sample point of the analyzer, or would it not make a difference in a holding basin?

 

[jbartos]

Comment: Reference:
1. Theodore Baumeister "Mark's Standard Handbook for Mechanical Engineers," 8th Edition, McGraw-Hill Book Co., 1978, page 16-17
The metering pump is an accurately calibrated positive-displacement pump which provides both measurement and control of fluid-flow rate. Obviously, the control implies reduction of the flow as well as boosting.

 

[jbartos]

Suggestion: Visit

http://www.instrument.org/res.htm

http://www.instrument.org/Article_CompndCosts.htm

(notice special sample pumps there)

http://www.controlmagazine.com/Web_First/ct.nsf/ArticleID/PSTR-54EQ9G/

http://www.dkktoa.net/news4.html

http://sgcbookstore.safeshopper.com/78/12.htm?427

http://www.yokogawa.com/cms/com/ep/...dual+Chlorine+Analyzer+RC400G&currentPageNo=1

http://www.capitalcontrolsindia.com/pg01.htm

http://www.gliint.com/catalog/pdf/data/ds-accl2.pdf

http://www.ryanherco.com/Industries/VendorArticles/Walchem/ChlorineDisinfectionControl.pdf

(for a choice of methods)

Please, also try Civil/Environmental Engineering Forum
e.g.

http://www.eng-tips.com/viewthread.cfm?spid=164&newpid=164&sqid=64180

 

[quark]

Why should you go for a pump with VFD? Standard chlorine dosing systems are with diaphragm pumps where you can control both stroke and no. of strokes per minute. You can do manual setting or give analog input for automatic setting as well.

 

[EngDon]

jbartos, Thank you for all of the helpful links.

 

[jOmega]

Quark:

I'm curious: How would you do that in a Closed Loop system with a diaphragm type pump... i.e. how would you control the stroke and the number of strokes per minute... in a closed loop system with the analyzer as an integral part of the loop.

Suggestions .... ? ? ? ?

 

[quark]

jOmega!!

I give up. My explanation on this to you will be like translating a Chinese literary work into German commoners language (funnily I don't know both the languages). I took all the sarcasm and still, no crossing swords (coz you sure are an expert guy - ref. your previous posts)

What I intended to mean is a pump driven by a solenoid and not by motor. Prominent is the manufacturer of these pumps and we did this for one of our water treatment plants.

Next time, I think, I should restrict myself from generalizing a specific thing.

Sincerely,

 

[jOmega]

JB:

You almost got it right;

"Obviously, the control implies reduction of the flow as well as boosting."

Not really, JB.

Here are a couple of definitions for you:

1. from Webster's New World Dictionary ...

Booster..... an auxiliary device for increasing force, power, pressure, or effectiveness.

2. from Vicker's Hydraulic Handbook...

At a given speed, Positive Displacement pumps deliver constant volume {flow} independent of discharge pressure.

NO BOOSTING, JB.

Metering Pumps, JB, deliver a specific volume.....

I located a primer for you on Positive Displacement pumps:

http://www.engineeringtoolbox.com/34_414.html

Here's a quote from within the above reference:

"Positive Displacement Pumps are constant flow machines".

In the world of positive displacement pumps, JB, boosting is not a term that applies; rather, it is appropriate for pressure boosting applications, which a metering pump application is not.

 

[jOmega]

Quark:

I asked the question of you, because I was hoping to gain some insight into how such a task is accomplished. I was not aware that there are such things as ELECTRONIC STROKE CONTROL.... which, your last post motivated me to crank up the search engine.

I found the following :

http://www.neptune1.com/pumps/e-stroke.htm

to be an epiphany... and a welcome addition to my applcation library.

Perhpas you'd care to share some insight into how the application was accomplished ....and is it a closed loop or open loop system.

Thanks

jO

 

[panelman]

sone the rigs we have set up we use process flow to set speed (stroke/min) and then use feedback from an analyzer to control the stroke length

 

[jbartos]

Suggestions to jOmega (Electrical) Sep 18, 2003 marked ///\\JB:
You almost got it right;
"Obviously, the control implies reduction of the flow as well as boosting."
Not really, JB.
Here are a couple of definitions for you:
1. from Webster's New World Dictionary ...
Booster..... an auxiliary device for increasing force, power, pressure, or effectiveness.

///Unfortunately, I do not see a word "booster" in my posting. All what is see is "boosting" meaning "increasing" or "raising". See Webster New World Thesaurus.\\
2. from Vicker's Hydraulic Handbook...
At a given speed, Positive Displacement pumps deliver constant volume {flow} independent of discharge pressure.
NO BOOSTING, JB.
Metering Pumps, JB, deliver a specific volume.....

///Please, see my quote from the referenced Mechanical Handbook. Take it up with the referenced Mechanical Handbook Editor.\\
I located a primer for you on Positive Displacement pumps:

http://www.engineeringtoolbox.com/34_414.html

///Thank you. Good to know.\\
Here's a quote from within the above reference:
"Positive Displacement Pumps are constant flow machines".

///I did not post anything to the contrary.\\\

In the world of positive displacement pumps, JB, boosting is not a term that applies; rather, it is appropriate for pressure boosting applications, which a metering pump application is not.

///I cited the controls that implies increases and decreases within controls margins.\\