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MAPCORP YaBB Newbies Offline I love Water and Wastewater.com Posts: 7 Company or Organization: Scidmore	Foam level detection solution for blackwater tank Jun 18^th, 2012, 3:47pm I need a sensor to detect the top of the foam in the blackwater holding tank. The sensor may need to enter the tank from the side. Thanks in advance!
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Jeff Naumann God Member Offline I love Water and Wastewater.com Posts: 1133 Torrance, California Gender: Company or Organization: Jeff Naumann & Associates	Re: Foam level detection solution for blackwater tank Reply #1 - Jun 18^th, 2012, 4:00pm What's the "blackwater holding tank?"
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grrun God Member Offline WaterandWastewa ter.Com is the best! Posts: 3525 Pekin, IL Gender: Company or Organization: Freelance Environmental Engine	Re: Foam level detection solution for blackwater tank Reply #2 - Jun 18^th, 2012, 10:28pm Foam is an interference for ultrasonic level detectors and a combination of a pressure sensor might be the combination that you are looking for to determine both foam and liquid level. grrun
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MAPCORP

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Re: Foam level detection solution for blackwater tank
Reply #3 - Jun 19^th, 2012, 7:31am

The blackwater holding tanks are the VCHT tanks onboard a DDG-52 Arleigh Burke-class guided missile destroyer. There are two such tanks on these ships, each is 490 gallons. The tanks are filled with sewage when the vessels are in regulated water. Greywater is collected separately. The vaccum injectors that move the sewage to the tanks churn bubbles into the blackwater, sometime resulting in a stable foam that can ultimately ends up forced out of the tank vents onto the weatherdeck. The goal is to detect the foam level so intervention can be taken to suppress the foam.

Keith
Maritime Applied Physics Corporation
207-837-6178 x219

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NorCal_Wastewater1

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Re: Foam level detection solution for blackwater tank
Reply #4 - Jun 19^th, 2012, 9:06am

I would suggest a combination of an ultrasonic level transducer & a submersible transducer. Foam causes errors in level readings for ultrasonic sensors so you would take the difference between the two sensors to give you your foam blanket thickness.

If you would like more info please contact me via my email in my file.

Dallas

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Have a great day,

Dallas

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DS

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Re: Foam level detection solution for blackwater tank
Reply #5 - Jun 21^st, 2012, 4:49pm

Hi mapcorp,

some loose thoughts:
if the foam is caused only by the venturi, why not pump the greywater with a regular pump? how/where exactly the air/gas (?) is introduced in the greywater? Is there a leak somewhere that sucks air?
If you detect (enough) foam, what exactly will you do to counter this? What kind of a foam is it anyway? is it an open, unstable foam? Or is it a compact foam like choco-mousse?

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MAPCORP

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Re: Foam level detection solution for blackwater tank
Reply #6 - Jun 22^nd, 2012, 7:55am

The venturi is the method used to create a vacuum for waste to be drawn into the tank. Attempts were made to reduce the oxygen brought in by the pumps previously without success. That's why controlling the foam after it is produced is now the focus of the effort. I strongly suspect that the problem is stable foam, but have no access to verify this. Detecting and suppressing the foam is the focus of our current investigation. Any suggestions?

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Jeff Naumann

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Re: Foam level detection solution for blackwater tank
Reply #7 - Jun 22^nd, 2012, 9:11am

The goal is to detect the foam level so intervention can be taken to suppress the foam.

What method of foam suppression are you using when you do detect foam?

If you are using a defoamer that appears to be effective, maybe just use it routinely when you know the tanks are getting to the point that foam is likely.

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MAPCORP YaBB Newbies Offline I love Water and Wastewater.com Posts: 7 Company or Organization: Scidmore	Re: Foam level detection solution for blackwater tank Reply #8 - Jun 22^nd, 2012, 9:15am If you are using a defoamer that appears to be effective, maybe just use it routinely when you know the tanks are getting to the point that foam is likely. There is currently no foam control system in place. We are in the process of designing one. Is there are defoamer you recommend?
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Jeff Naumann God Member Offline I love Water and Wastewater.com Posts: 1133 Torrance, California Gender: Company or Organization: Jeff Naumann & Associates	Re: Foam level detection solution for blackwater tank Reply #9 - Jun 22^nd, 2012, 9:18am I have no particular knowledge of foam suppression chemicals, other than I know they are sold. How is the generation of foam detected? Is it a backup of sewage into the collector piping, or ??
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MAPCORP

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Re: Foam level detection solution for blackwater tank
Reply #10 - Jun 22^nd, 2012, 9:24am

If you read the initial topic questions, you'll see that foam detection was my original question. We seem to have strayed from that a bit, but that's fine by me. I have some ideas on sensor types, but have not identified specific model numbers yet.

The current foam detection method is noticing that foam is coming from the tank vent pipe onto the weatherdeck. Not the best detection method. Wink

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Jeff Naumann

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Re: Foam level detection solution for blackwater tank
Reply #11 - Jun 22^nd, 2012, 9:35am

MAPCORP wrote on Jun 22^nd, 2012, 9:24am:

If you read the initial topic questions, you'll see that foam detection was my original question. We seem to have strayed from that a bit, but that's fine by me. I have some ideas on sensor types, but have not identified specific model numbers yet.

The current foam detection method is noticing that foam is coming from the tank vent pipe onto the weatherdeck. Not the best detection method. Wink

Is there any type of check valve on the tank vent? I was just thinking that maybe a light-weight ball check MIGHT be able to suppress foam from being discharged from the vent...........maybe made of foam plastic. If that would work perhaps the presence of foam could be keyed to the ball check level?

How is the tank level measured?

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MAPCORP YaBB Newbies Offline I love Water and Wastewater.com Posts: 7 Company or Organization: Scidmore	Re: Foam level detection solution for blackwater tank Reply #12 - Jun 22^nd, 2012, 9:39am Currently there are point sensors on the tank that measure the liquid level. Because of the way this system operates, a check valve in the vent could result in an uncontrolled pressure buildup in the tank.
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DS

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Re: Foam level detection solution for blackwater tank
Reply #13 - Jun 23^rd, 2012, 3:43am

Hi mapcorp,

maybe you can put a conductivity (electrical) sensor in the vent pipe. as soon as the foam rises and "touches" the electrodes, currrent will be detected and puts into action a dosing pump with Anti-foam (AF).

This may work, but I do not like this kind of solutions since it acts on the consequences and not on the causes.

which type & amount of AF to be used strongly depends on the type of foam you want to fight. stable foams are often pretty tricky... probably that has to be found by trial and error...

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almar1965 God Member Offline Composting is the work of Satan !! Posts: 1269 Santiago Gender: Company or Organization: Sinquiver Ltda	Re: Foam level detection solution for blackwater tank Reply #14 - Jul 5^th, 2012, 5:15pm Hi DS is spot on with this !! Struktol do a device exactly like this. Contact Lars Herwaegehr via lherwaegehr@struktol.de Tell him Alistair sent you ! regards Alistair
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Re: Foam level detection solution for blackwater tank
Reply #15 - Jul 6^th, 2012, 1:46am

Hi Mapcorp,

You could try a E&H Liquicap FMI51, or similar capacitive sensor.

The probe can be calibrated to your foam and non foam situation. Basically the whole probe is sensitive so as the foam rises the capacitance rises and can be set to alarm.

Having said that you may struggle if it's horizontally installed. Although I guess it would just trip instantly. The problem with a horizontal install that I can see is that you may need a hysteresis setting.

Also how deep is the foam? if it's a couple of inches you may as well read the liquid level and trigger an alarm at a lower set-point.

Call E&H (Endress & Hauser) I'm sure they could come up with something.

Hope that helps.

Regards,
argfin

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argfin Full Member Offline I love Water and Wastewater.com Posts: 145 Company or Organization: None	Re: Foam level detection solution for blackwater tank Reply #16 - Jul 6^th, 2012, 1:48am Oops, just read DS's reply!
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DS God Member Offline sapere aude Posts: 1581 Company or Organization: Indept. Freelance Consultant	Re: Foam level detection solution for blackwater tank Reply #17 - Jul 6^th, 2012, 2:48am Forgot to mention that an optical sensor with an adaptable trigger level would also be a possibility. A requirement would be that the thing is easily and fully cleanable.
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almar1965 God Member Offline Composting is the work of Satan !! Posts: 1269 Santiago Gender: Company or Organization: Sinquiver Ltda	Re: Foam level detection solution for blackwater tank Reply #18 - Jul 6^th, 2012, 4:13am and that the operator actually carries this job out.............
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MAPCORP YaBB Newbies Offline I love Water and Wastewater.com Posts: 7 Company or Organization: Scidmore	Re: Foam level detection solution for blackwater tank Reply #19 - Jul 6^th, 2012, 7:48am All, Thanks for the help. I completed my proposal, so now it is time to wait. This topic could come alive again in 6 months if the contract is awarded. Best! KS
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