Flare Pilot Indication Reliability 1

[JohnBradf]

Our facility operates several flares, which are subject to the pilot monitoring requirements of 40 CFR 60.18(f)(2). Our delema is that we chose to use ionization detection to indicate flame presence. This system is either off (0) when in normal operation or on (1) when in an alarm state. The problem is that we are constantly having problems with the indication swinging from 0 to 1 within a span of minutes (this is continuously monitored on the DCS) so that we generate records of non-compliance. In reality the pilots are lit as evidenced by the fact that reignition is not necessary.

The instrument department can't find anything significant to fix (or so they say). As a consequence, we continually write work orders to have them sent back saying nothing abnormal was noted.

My question is, does anyone know of another technology that is more reliable other than thermocouples, IR, and UV? Our experience with TCs is better than IR or UV, but we still burn the wires off from time to time. We have tried IR, but have the same problem as the ionization detection. We are currently experimenting with UV, but getting similar results. I'm in a quandary???

To muck the situation even more we expect issuance of our Title V Permit shortly which will require deviation reports. Currently we are having literally hundreds of deviations per month.

Thanks in advance for the help.

John

 

[Flareman]

You say flares - is this an enclosed ground flare (like a furnace or an elevated flare?

I'll first assume an elevated flare

in my opinion, the best overall method is to use thermocouples. I know they have a bad "rap" but, in my experience that's because of the lack of attention paid to the associated "stuff".
- make sure the thermocouple tip itself is protected in a thermowell. I know it slows down the response time but it's usually only a minute or two.
- use a long thermocouple which uses a MIMS sheath, at least 310SS quality / Chrome at least 20%, don't use regular SS. You can get high chrome/nickel sheaths at very little extra.
- run the upper part of the thermocouple inside a pipe (could be the pilot pipe)
look at the selected location for the "head", the further away from the top of the tip the better - if you are within 12 ft for a small tip or up to 40 ft for a big tip (depends on expected flows) protect the head with a thermal shield
- don't use thermoplastic terminal blocks
- run any extension cable in a hot zone (sketch in a paper I have, send me an email to flareman_xs@netzero.net) using SS covered MIMS (make sure you seal the ends whilst they are dry)

Ionisation rods ground off far too easily in inclement weather and are still subject to suspicious electrical connections. As you say, they also go in and out frequently whereas the t/c lag avoids that, and you can set down the temperature to "hot" rather than "ridiculously hot".

You can go for a remote ground mounted IR system, there is a good one on the market for just this purpose, but the best chance you have is to see 2 out of 3 or 4 pilots and if there is any other attachment on the tip (steam rings and wind shields for example) you may have no line-of-sight.

The fact that you say UV (UV?? I hope you have no steam injection) makes me wonder if it isn't a ground flare. Local optical sensors like conventional UV and IR "peepers" are OK and, even good, as long as the flame is inside and they are outside looking in through a sighting tube.
Otherwise forget it.

Does this help or am I way off base with my understanding.
Have you asked the vendor what he suggests?


David

 

[JohnBradf]

You assume correctly, all of our systems are elevated. We have three air assist and two steam assist flares. One air assist and one steam assist utilize TCs. The others use ionization detection with IR backup (which as I indicated are unreliable).

Your suggestions and assumptions are valid in that with the current configuation of the IR cameras, I suspect we are not seeing the pilot flame as we should considering meterologic disturbances (primarily wind).

I also agree that TCs are the most reliable technology to date and will suggest we re-evaluate the position of and proper shielding of existing devices as well as, the modificaiton of current ionization devices to TCs as well.

As for vendors, while some offer very good suggestions, I have found that a sales pitch for additional hardware is more often the norm.

You have helped, thanks; additionally I will send you email for the paper you have offered.

John