Oil Vapor Sensor

[horsefeather]

I'm looking for a sensor that detects the presence of oil vapor, not necessarily a measurement of the amount present but that oil is present above a specified threshold. The application is in a 5000 psi Nitrogen stream. The oil contamination is 30Wt compressor oil.

My fallback position is to find a low spot in the system and mount a level sensor horizontally to detect oil accumulation.

Thanks!

 

[waross]

How is your budget??
You may be able to detect an oil mist with a radiation type consistency instrument.
The first smoke detectors on the market, in the early 70's, would sometimes trigger if a nearby motor bearing overheated. This happened long before failure or visible smoke.
You would be looking for an instrument more sophisticated than a smoke detector and less pricey than the radiation consistency transmitters used to monitor the consistency of the black liquor feed to a recovery boiler.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[horsefeather]

Hmm, I'll look into that. The N2 moves at 750 scfm so I'm not sure if the vapor remains stationary for a sufficient time to absorb the alpha radiation and interrupt the charged flow.

Operations just contaminated $125K of membrane filters because of a collapsed oil coalescing filter so a $250 sensor is justifiable.

The more I think about it the more I'm leaning towards a sensor mounted vertically on the bottom of the vessel to detect any oil that accumulates. I was thinking of taking an ultrasonic level detector, but the one from Omega needs 1.25 cm inch of fluid between the gap to work. I'm thinking more on the order of a .5 to 1mm oily film. I'm still researching other ultrasonics.

In short I am now looking for a sensor that detects an oily film between the electrodes. I haven't gotten the spec sheet on the oil yet so I cannot provide the conductivity.

Thanks for the reply

 

[waross]

The conductivity of oil varies from very low to very high depending on the amount of disolved metal in the oil. Good new oil should have excellent insulating properties. If a compressor is wearing, the microscopic dissolved metal particles will drop the insulating properties dramatically.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

What about capacitive effects of oil between plates? Does oil have a dielectric constant worth using?

Is there ANY chance of water in this stream?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[GTstartup]

what about a VOC detector? I think i've seen them for about $600

 

[horsefeather]

I was thinking some sort of thin film capacitance sensor, but I haven't been able to find one. There are a number of capacitance based level detectors, but by the time I have accumulated enough oil for these to measure, I'm screwed. I remember seeing a twisted pair water leak detector a while ago but the oil dielectric constant may not be sufficient for it to work. I'll get the oil specs on Wednesday. There is no water present.

The final N2 stage is a cylinder about a meter long with a 30 cm diameter. It is pressurized to 350 bar. The sensor I am looking for would be inserted into a drilled and tapped port on the bottom of the cylinder laying down. Any oil present coalesces and collects at the bottom of the cylinder along the longitudinal axis. So I'm looking to detect the presence of oil not the quantity; a .3mm film should do it.

I'm still researching VOC detectors.

I appreciate all the help I'm geeting.

 

[DRWeig]

Horsefeather,

I suggest you look up the folks in your area who install underground fuel storage tanks. If you're in the US, look on a gasoline pump and see who installed them -- there should be an obvious label. In Memphis, it's The Southern Company.

Leak detection systems for gasoline and diesel (and other hydrocarbons, including lube oils) for double-wall tanks typically include a twisted wire pair specifically designed for what you're trying to do. Veeder-Root is one manufacturer that springs to mind. Maybe Google "UST Leak Detection Systems" to find others... Or if you're in a big city, the EPA or health department might have info.

Let us know what you find!!

Good on ya,

Goober Dave

 

[roydm]

I remember seeing a sensor that relied on oil swelling some sort of material to operate a switch.
What happend to your membrane filters, perhaps something there could be used e.g. pressure drop to make a small detector upstream.
Regards
Roy

 

[morg]

I seem to remember some automotive sensors in the far infrared spectrum {4200 nm} used to detect the prescence of oil vapor.

Another method would use a microwave cavity in the 10Ghz freq. Most oil has a dielectric around 2.5 the difference in resonance to air would be a factor of the square root of the dielectric of the oil. Monitoring the frequency shift and the amplitude change would answer the vapor questions if the cavity is temperature stable.

Morg

 

[horsefeather]

Thanks for the many answers.

RoyDMatson - The membranes are a series of tubes with holes poked in them small enough to let O2 molecules out, but not the N2. Any oil clogs up the pores and significantly reduces efficiency. Short story - By the time there is a peressure difference the damage is done. At $112K a replacement set it's too expensive too wait.

DRWeig - A lot of the sensors use a swelling medium similar to what RDM suggested, and there are some that are capacitance related, the swellers require replacement when alarmed, and the capacitance requires a long run of wire. Both would require installation and sealing to operate in a pressurized environment.

morg - Good idea but sounds expensive, I'll pursue it further. With air rushing through at 750 scfm, I think I would have to insert some sort of pneumatic cul-de-sac to slow the flow. Let me give that one more thought.

I've got a couple level sensors, one works on oil filling a gap and the other is electro-optic. What I am leaning towards is putting in a sump before the membranes, perhaps with a baffle and mount the sensor vertically from the bottom. The idea is that when the system is turned off, any oil would drain into the sump and raise the alarm. Theres a number of particulate filters, heaters and a charcoal filter before the membranes; I'll locate a place in there.

Thank you for all the ideas!

 

[DRWeig]

Cool, Horsefeather!

Thanks for the feedback.

Good on ya,

Goober Dave

 

[badservo]

I did a some searching and found this,

http://www.beko.de/221.0.html?&L=8

I will try to get more info about it tomorrow.

 

[horsefeather]

badservo -

Good catch - I'll call them tomorrow

Thanks!