I am measuring sealed quench furnace atmosphere using 3-gas analyser and CO2 readings is about 2.0-2.8%. It indicates water or air leak to the furnace chamber.
I did check fan cooling jacket(been replaced), quench rack seal for air leak.
Oil analysis done few days ago indicates less than 150 ppm of water. Door seals are ok. When I open the sampling tube valve, water is dripping like from the tap. What other options are to check water/air source? Is it water/air leak or is it oxygen which can react with hydrogen (from endothermic gas)creating "crystal water"?

In order to answer you question, it would be helpful to know a few additional facts. First, what type of atmosphere are you running inside the furnace - Endothermic gas, nitrogen/methanol or something else? Second, are you adding a hydrocarbon enriching gas and if so, which one? Third, what is the dew point of the incoming gas (at the generator? at the furnace?) Fourth, what temperature is the furnace at when you are taking your readings? Also, what size furnace do you have and what are the gas flows? Next, what type of material (steel grade) are your processing? Lastly, are you trying to control the furnace atmosphere with a system that adds both air and gas to the atmosphere?

If you are opening the gas sample tube and find water dripping out, it is a clear indication that you have an extremely high dew point (> +70F) inside the furnace. In cases such as these your 3-gas sampling readings (CO, CO2, CH4), dew point and oxygen probe values are probably not accurate given the conditions you describe.

There are a number of problems that could cause this situation. For example, (a) your incoming gas atmosphere might be out of control, (b) the gas lines to the furnace might be leaky and allowing air to infiltrate into the gas line, (c) your atmosphere control systems may be malfunctioning (d) you may have an air leak due to a faulty seal or cylinder, (e) you may have a water leak from a fan bearing casting or water cooled component, etc.

Is it possible to run the furnace under 100% nitrogen and check the dew point? This would help isolate whether you have a leak or not. Water or air leaks in integral (sealed) quench furnaces can be extremely difficult to track down. You mentioned that the fan cooling jacket has been replaced - this is a common source of water introduction into a furnace due to the fact that some water cooled fan bearing castings are porous.

Please get back to us and we will provide additional insights.

Furnace is using Endothermic gas, and methane as an enrichment gas.
We do not measure dew point, endo generators and furnaces are checked with 3 gas analyzer.
Furnace temperature during measurements was 900°C, CO-18.00%, CO2-2.821%, CH4-10.0-15.0%.
Furnace size(load size)is 0.42m3.
Endo flow-8.0-10.0 m3/h.
CH4 flow -2.0 m3/h.
Air flow -20 SQFH.
We are using this furnace as a carburising unit for 8620/EN36 materials and carbonitriding of EN32 etc. Sometimes we are using this furnace for solution treatment of Titanium which is without protective atmosphere (followed by water quench but into the external water tank). To control atmosphere we are using methane and air.

I can run furnace under Nitrogen but I have not got equipment to check dew point.

Could you explain in details what do you mean by "incoming gas is out of control" and how to detect leak on the gas line?

One more thing I noticed during my checks. When I turn the furnace fan off, carbon potential starts to build up quite quick and vice versa, when fan is turned on carbon potential drops down suddenly.

I hope it helps.

Endo generator produce:
CO-19.45%, CO2-0.534%, CH4-0.06%. It is running at 1000°C and coarbon potential is 0.15%C. Do you think endo gas dew point might me an issue in this case?

Yes.

Most Endothermic gas generators are designed to run in the temperature range of 1040C - 1065C (1900F - 1950F). The fact that you are running the generator at 1000C (1832F) is a concern. I would definitely check with the manufacturer to determine the recommended operating temperature and run the unit at this temperature.

Most OEM manufacturers recommend running an Endothermic gas generator between +40F to +50F dew point. I personally prefer keeping the generator around +40F and making gas additions at the furnace. Under these conditions here is a typical set of values (based on natural gas feed stock):

CO: 19.02 - 19.66
CO2: 0.252 - 0.260
CH4: 0.01 - 0.04
Dew Point +40
Carbon Potential 0.40%C

Finally, in looking at your 3-gas analysis numbers, the methane CH4 value (> 0.05%) indicates that the generator is in need of being burned out.
Modified By Daniel Herring on 11/6/2009 at 6:22 PM

My earlier comment about "incoming gas is out of control" has to do with the generated Endothermic gas. If its composition varies over time (because the generator is not running under ideal conditions) the atmosphere chemistry inside your furnace will fluctuate significantly.

Your 3-gas analysis values have me concerned and the amount of free methane seems very high. Is your infrared analyzer properly calibrated?

Regarding gas lines, these are normally checked using a commercially available soap solution.

One additional suggestion would be to rent (or buy) a portable dew point analyzer. One good source (there are others) is Super Systems, Inc. (www.supersystems.com).

Feel free to contact me at dherring@heat-treat-doctor.com or +1 (630) 834.3017 if you need more help than can be provided via postings such as this one.


Modified By Daniel Herring on 11/6/2009 at 6:31 PM