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Dear Expert,

My Gas Turbine is using 4 Honeywell Flame Detector with no cooling media & no Denox injection.

1. Is it normal to have inconsistent intensity among the 4 detectors (1 can be 180CNT, the other can be 380CNT).

2. What can be the cause of this detector reduce its intensity reading gradually, sometimes until it become 0 CNT.

3. Any better practice i.e. install cooling system, change type/model or etc.???

Thank you.

1. Yes. Condition of the flame detectors, age, heat, wiring, can all contribute to issues. I've also seen very fine dust particles collect in the sight tubes of the flame detectors, completely blocking the lens. Also, some flame detector mounts get bent/damaged during maintenance outages and this causes the detector to not be properly aimed at the flame. Also, the type of fuel and the condition of the fuel nozzles also affects flame detector feedback intensity. But, if you're not experiencing any higher than normal exhaust temperature spreads when this problem is occurring, it's likely a mechanical or a wiring or printed circuit card/flame detector module issue, or a problem with the detector. Have you tried exhanging flame detectors to see if the problem follows the flame detector or stays in the same combustion can?

2. It might be heat-related; we don't know how the flame detectors are mounted on your unit (inside the turbine compartment; in insulated insets of the compartment enclosure. I saw an exhaust leak once that was directing hot gases in the vicinity of a flame detector cause that flame detector to have problems. The technicians and operators wouldn't go in that area when the unit was running because they knew about the leak, and they didn't relate that the flame detector that was getting hot from the leak was the one that was intermittently and continually failing. Water cooling is usually only used on flame detectors which are located inside the turbine compartment and not in some kind of insulated "compartment". The amount of water flowing to the cooling coils of the detector can cause moisture (even ambient humidity; it doesn't have to be from foggers or evap coolers) to condense on the lens, so be careful with installing cooling coils.

3. Silicon carbide flame detectors have proven to be much more sensitive than comparable UV Geiger-Muller flame detectors. Reuter-Stokes is one manufacturer of the SiC detectors, called "Flame Trakkers."

It is not abnormal to see discrepancies such as the one you listed. Count is an indication of the flame intensity and the state of the detector tube itself. Typically, the threshold is 64, below which it will be no-flame condition.

Differences in the combustion pattern and combustion efficiency can also be the causes of these different count values.

If your unit is EA-class or later ones, the higher firing temperature requires the flame detectors be water-cooled. This will be implemented in the original package.

The new units will have Reuter-Stokes flame scanners that are beter than the ones you have, in many respects:

* 4-20 mA output
* 24 VDC power supply
* Not damaged by polarity-reversal.
* More sensitive than the tube-types

With Mark VI Speedtronic control system, the change over is rather simple. With Mark V, additional hardware is required to convert the signal to frequency.