Nitrogen Saturation Sensors?

I was thinking of that earlier but would that give me an absolute nitrogen level or just the non-existence of O2? to what level of O2 is the minimum for these sensors? I need a guaranteed assured of absolutely no O2 in the environment .

<...need a guaranteed assured of absolutely no O2 in the environment....>

Measuring zero is extraordinarily difficult!

All that can be done is the assure that the oxygen level is below a certain point. There are any number of instrument manufacturers that can offer suitable equipment.

Nitrogen has nothing to do with your manufacturing process. Oxygen is the chemical that disturbs the metallurgical process you are attempting to achieve. Use an oxygen sensor (or dual instrumentation) to 1) verify that all the O2 is gone, and 2) verify that no O2 is reentering the process through the cracks in your bells. You can use a vacuum pump and any purge gas that does not contain O2, but you need to also verify positive pressure and I would imagine your customer would like to have temperature logs of the steel along with the metallurgical reports. Why don't you automate your whole process? We supply better electronic control packages down here in Austin than the stuff you have from 1950, and we supply better annealing bells and bases up here in Cleveland than the stuff you have from 1910. Call for help; we may be able to provide info that the cost of changing your process is less than the cost of continuing in the same manner.

Welcome xstek99!

Looking forward to your contributions here on CR4.

The points that you made re Oxygen / nitrogen in your post were relevant. The points that you made regarding process upgrades would be "good answers" if there was credit available for manufacturers to upgrade processes. Currently, there is not.

Nice to read your contributions.

milo

I agree with the observation that you really want to use an O2 sensor because O2 is the contaminate you are trying to minimize. You need to know the flow rate of N2 into the chamber. At 452 cubic feet of volume and a purge flow rate of 452 cfh, O2 level after 1 hour will be about 10% or 100,000 ppm. After 2 hours it will be about 5% or 50,000 ppm, etc. It might be helpful if you knew the dew point of the incoming N2 purge gas. If it contains moisture, you will be adding O2 from the purge itself. Even if the source of purge gas is dry, moisture can be picked up by water diffusing through organic inlet tubes. Also, you might achieve low O2 levels faster if you pump the air out of the bell before you backfill with N2.

Thank you everyone for you valued answers. Being at work this morning I have had the chance to go over the bell area and have a little more information about the N2 , Fist off the N2 incoming pressure is @ 27 p.s.i. at a flow rate of 4.25 SCFM. After looking up the actual original rawings of the retort's (bells) the dimensions are 6'2 1/2 " I.D with a inside height of 6' 11" . Therefore if my calculations are correct it should be around 187.94 cubic feet. with a flow rate of 4.25 SCFM it should take aproximately 45 min for 188 cubic ft of nitrogen to flow into the bell. So does this mean that in 45 min the nitrogen has displaced the O2 in the bell or has it just filled and needs to purge longer to ensure that as much O2 as possible has been forced out. This current process from what I gathered in conversations this morning was calculated many many years ago prob like 10-15 I would guess. So it is definately time to reassess this process SOP Also noting XSTEK99's reply I am already automating this process this is why I was looking for the N2 senors but looks like going to have to go with O2 sensors instead. I was thinking of putting one sensor inside the annealing area under the protective plate for the fan, and also one on the exhaust line th detect the nn-presence of O2 there as well and see how they match up. I will be using Rockwell Automation SLC5/05 PLC,s with either AB Panelview 900 or better or a Maple Systems HMI for operator control. And just for the record most of my current controls are less the 15 years but close and am using multiple Honeywell UDC process controllers for this and most temperature control in plant. I hope this helps . Thankx to all once again

<...does this mean that in 45 min the nitrogen has displaced the O2 in the bell or has it just filled and needs to purge longer to ensure that as much O2 as possible has been forced out...Rockwell Automation SLC5/05 PLC,s with either AB Panelview 900 or better or a Maple Systems HMI for operator control....>

All the PLC equipment will do is to provide a pre-programmed recipie, i.e. a set of conditions that will permit the process to run.

The oxygen level depends upon whether there is any mixing of the incoming gas with the gas that is already there. If there isn't, then 45min might be enough. If there is good mixing, then it could take 5 times that for the oxygen level to drop to 1% of its original level.

The only way to ensure that the oxygen level is low enough for the process to proceed safely is to measure it.

N2 and O2 mix easily with eash other. That probably accounts for why you don't find O2 rich or lean environments on earth. You have to create them. So if you want an O2 lean environment to anneal parts you either must dilute and purge the existing O2N2 mixture with pure N2, which implies many changes, or you must pump out all the gas with a vacuum pump and replace the mixture with pure N2. As previously mentioned, O2 gettering can assist, but is not normally used to pump large volumes. You could also separate the gasses with cryogenics, but I don't believe that's very practical.

http://digital.ni.com/worldwide/singapore.nsf/web/all/0E3D370EB82DEDAA862574D700241161 The nice thing about National Instruments is that someone's probably done it B4, or is doing it now. If not, we have a small army here in Texas. There's a LabView developer within 50 miles of you, contact your local NI Rep and ask for his input. Hope this helps out.

A vacuum pump can be used to evacuate the bell (it is common practice), this would speed up the process and make sure that the oxygen levels are minimal when the nitrogen is introduced.

The obvious question that has not been asked is, at what temperature is the bell atmosphere when the bell is purged.

If the temperature is high the gas been purged will need to be put through a heat exchanger, to avoid damage to the vacuum pump and oxygen or nitrogen sensing equipment.

Nitrogen can be purchased with different levels of purity depending on the requirements.

From my past experience some of the annealing bell processes operate at high temperatures

I hope this gives you some additional information.