Gas detection in heat exchanger

Switchman,

I assume you check industrials suppliers for sniffers.

I also assume you follow NFPA 86 for start up, might be a good idea to review it,

I do it, keeps me updated and less complacent?

Your very lucky, on a tangent since this oven was not in use do you not have a main manual shut off for this oven when not in use?

phoenix911

Phoenix911,

Thanks for your reply. I do have a couple of good Bacharach sniffers and a full range of test equipment such as combustion gas analyzers, pressure testers, flame circuit meters, etc. I have both a weekly and monthly PM where all safeties are verified, CO ppm and % of O₂ is checked and adjusted, and everything is cleaned.

I have a copy of NFPA 86 on the shelf next to me, and portions as part of a quarterly training session, as well as a link to the online version in my list. We do several inspections every year ranging from the local fire captain to our insurance guy.

I do have two manual shutoff valves on each unit. One on top, 6" down of the main line. Then I have one right before the electrically operated gas valve. After yesterdays situation I have my guys going out and shutting off the manual valve until I can resolve this.

But I still want to add a gas sensor permissive to the pre-ignition safeties. I don't believe the pre purge...at 30 seconds...would have cleared this exchanger.

Switchman,

sounds you have the safety in place, although purge is only a safety proceedure, it does not solve or detect your leak,

And as you know the purge is not time constraint but air exchange believe it to be 4x volume, (do not have NFPA 86 at my side at this time, so this is off of my memory, and not a reliable source)

May have to reprogram your logic, sorry I was'nt any help.

good luck,

phoenix911

Sorry, guess I was'nt trying too hard for you,

These people have been good to me,

http://www.eclipsenet.com/products/products.aspx?pid=259780

I'll dig through eclipsenet and see if they have a sensor.

NFPA 86 sec 8.4 does call for a pre-ignition time...but I can find no specific time period, mine is 30s. The next line down calls for at least 4 standard cubic feet (scf) of air or inert gas to be introduced during the purge. Although,I have not calculated out...I'm sure all this is as it should be. My ovens don't cough, sputter, rumble, or worse...backfire on start.

I have flow 'sail' switches in my burners as well as diaphragm pressure switches for constant burner air blower monitoring.

These units have been in service plenty of time...work great and we put lots of product through. I just want to prevent ignition in the situation like yesterday. No way pre purge would have cleared this.

You didn't specify the temperature in your heat exchangers. By natural gas, I presume you mean methane...........

Have a look at http://www.tectra.hu/pdf-docs/Thermox-WDG-iv_atex_6-06_lo.pdf

This is probably overkill (1600^oC!) for a bakery operation. If so, you will have to extract a continuous gas sample from each oven, cool it down to an acceptable temperature - around 60^oC - (an interesting little engineering exercise itself) and run the samples through conventional sensors. Frontline Safety UK have a combustible gas detector rated up to 200^oC but I don't know if methane is included.

Yes, I think the natural gas is a mix of methane and other gases...not quite sure of the composition...but if necessary our utility will give me a breakdown, I'm sure.

These ovens have a max temp of 500^o f so I would think a sensor rated for 1000 would be safe.

I looked at the file you attached and it's a bit different from what I'm after...I saw this one and it's more a flue gas process control. I have an account with Ametek so I'll send them an email also and see if they have something.

What I'm looking to do is essentially use a sniffer sensor in the exchanger so that if gas is present above a certain level (due to a leak) I will block ignition prior to igniting a bomb. The sensor will be disabled once I enable the ignition sequence.

Hi¡

instead of measuring temperature you can use other 2 systems more reliables and quicker, these are ionization flame detection and UV (ultraviolet) flame detection,anyway you have to buy special gas controller and valve

Have a look at Honeywell

Sensors:

http://europe.hbc.honeywell.com/oem/combustion/residential_heating/gas/sensors.htm

Controllers: http://europe.hbc.honeywell.com/oem/combustion/residential_heating/boilers/boiler_electronics.htm

Sorry guest...you misunderstand...

You're talking just opposite of what I need. I currently have proper and correct ignition modules which have built-in µA flame sensing and control the valve.

The issue is that I had a gas valve leak into the exchanger when off. I need to put in a gas sensor. Prior to firing the oven off I will use the gas sensor in the exchanger to enable the firing cycle. If my oven is full of leaked fuel I do not want to fire it.

Thanks

Try Bacharach Inc. 625 Alpha Drive, Pittsburg, PA (412) 963-2000.

Fax (412) 963-2091

Don't know how often you check for CO etc , but you should perform a leakdowd test at the gas valve every 4 months or so(assuming you run the ovens 24/7).... [ monthly would be sweet ]gas valves are rated for about 100,000 cycles..then need to be replaced...I perform a leakdown test on all gas appliances , each time I service one , and write the date of the first test if I don't know the history of the equipment...I always run the model and serial# to see how old the unit is..and assume that the gas valve has never been changed..

As a side note...also get into checking your draft at the burner and at the draft inducer..should be pretty much equal..if you are .05 at the burner and .02 at the inducer...your heat exchanger is is impacted (obstructed) and needs to be cleaned..