Flow Meters for Gases

Im looking for some new flow meters for our systems. Currently we use a waukeetronic flow meters (it works like a measuring light curtain). The problem we have is most of the gases we use are generated, so they contain soot and such. This quickly can foul the flow meters ability to read. The gases are usually 60% nitrogen, 20% hydrogen and 20% CO. There are other gases as well, but they all follow a pattern similar to that. Normally the ranges are 100 to 12,000 CFH. I was wondering what other people use, and if anyone has any recommendations for flow meters. Thanks

Matt

We have just installed OSI flowmeters in a dirty stack and they look good so far.

They have a positive air supply option that we haven't required to help keep them clean.

Brian.

I dont think these would work in our situation. They appear to be for large flues and such. Ours are for controlling flows and mix ratios of these gases. Also, our pipes tend to be 6" or less. Thanks tho!

matt

Matt,

We use thermal dispersion FCI flowmeters for natural gas flow, which may be more to your scale.

Brian.

Thats definetly the type of thing im looking for thanks. Any other suggestions?

You've left out a critical piece of data, how hot are the gases?

If the thermal dispersion works for you, let me know. I've tried a couple brands, not FCI, and the claims that thermal dispersion works at high temeperatures or at varying temperatures seems to be based more on a single case than in general.

Thermal dispersion works great for room temperature gas or cold gas coming out of liquid phase. I've used Thermal Instruments, Rotronics (on liquids), and IFM. But when gas gets over 250 or thereabouts ,I haven't had much luck getting them to work. I suspect that the ability to supply enough heat to measure it's removal at higher temperature has something to do with it.

I've used Kurz and Sierra thermal dispersion (insertion hot wire probe style) for clean cool gas, too. I'm not sure if a sooty gas would bother them or not, or what the temp limitations are.

Dan

The gases range from about 45F to 250F. One system may have 2 that read gases before mix and cracking (60F) and one that reads the cracked gas (200F) for example.
What about the corilolis based meters?[font=Arial, Helvetica, sans-serif]
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I would encourage you to pursue thermal dispersion for the low temperature gases. It fits well there.

The 250° level is where I'd had consistent problems though. Again, I never used the brand first mentioned though.

I have no experience with Coriolis on gases. I would definitely consider it though. A quick check of spec sheet should tell what the maximum medium range is for it. Coriolis is very subject to vibration, so mounting is a big factor in proper operation.

Dan

We always use endress + hauser flow meters. http://www.us.endress.com/

We use a lot of thermal mass flow meters. FCI meters are good, but have a
slow response time that is a problem for some applications. We use Sage Metering a lot: contact Jack Sheldahl 866-677-7243

Thermal mass meters are great but I've experienced fouling of the thermal element in a not-so-dirty gas environment. The fouling acts as an insulator on the element which causes performance degradation. (So, make sure the salesperson has a very convincing story and references).

Consider too what turndown you require and what your budget is.

Ive contacted the suppliers from several companies with a description of our process. Thanks for the tips guys.

Anyone ever use the flow meters that use an orifice plate and pressure transducer?

matt

Orifice plates and venturi flow tubes with DP transmitters are the "old reliable" method. They have a few drawbacks. If your environment is dirty enough to foul a thermal meter, you may also be fouling the pressure taps. Also, they are usually limited to a 10:1 turndown - below 10% of max flow rate they don't give a reading. Finally, they only give a volumetric flow rate, so if you want standard cubic feet per minute (normalized to standard temperature and pressure, usually 68°F and 14.7 psi) or mass flow rate you need to add temperature and pressure transmitters as well.