"Our newer 7FA's use 4-20mA Reuter-Stokes silicon carbide photo diode scanners which the Mark V and Marak Ve convert to a count. Unfortunately, they require water cooling which has been their Achilles heal."

We have placed a work order for upgrade of our MARK II system. However, the OES suggested to replace our existing Honeywell Flame Scanners (Model No. LG1093AA04; GE P/N: 261A1812P10) with Reuter-Stokes Flame scanners.

But the OES never mentioned about the cooling requirement for R-S Flame Scanners. Can you please provide some more details about these or suggest a web-link for further reading?

Should we insist on using our existing Honeywell Flame Scanners since they have been in operation for last 25 years and without a single replacement till date. Even our MARK V, commissioned in Y2K, uses the same Honeywell Scanners. Will these existing Honeywell scanners be compatible with MARKVI??

au revoir
Rahul

 

Rahul,

I see the fog still exists. It's good to know some things never change.

Why aren't you asking these questions of the OES?

Take a minute and think about the differences between the locations of the flame detectors on the F-class units and those on the older unit with the Mark II.

On the F-class units, the flame detectors are located "inside" the turbine compartment enclosure and are generally fairly close to the combustors. It's very hot in the turbine compartment, even with ventilation fans running. Hence the need for cooling.

On the older units with on-base lagging (enclosure), the turbine compartment enclosures were typically much smaller and the flame detectors were mounted such that they were actually in a small, insulated enclosure, protected from the heat of the turbine compartment. One accessed the flame detectors from outside the turbine compartment in these enclosures.

On older units without any turbine compartment enclosure (open units, usually located in some kind of large, open building) the need for insulating the flame detectors wasn't as great. (Note: We don't know how your units are enclosed or installed.)

There's no way you could know this, but in the early days of DLN (Dry Low NOx) combustion systems, the older Geiger-Mueller (UV, Honeywell) flame detectors were used and they had to have cooling coils because they couldn't be protected in insulated enclosure.

So, all flame detectors require some kind of "cooling", even if it's just being insulated against the heat of the turbine compartment.

As for the problems with the cooling of flame detectors on F-class units, that's usually an operations problem. It's critical to bleed the air from the cooling water tubing at every flame detector (there should be air bleed valves there at every flame detector just for that purpose).

Also, there should be some kind of valves used to control the flow of cooling water to the coils. If there's too much cooling water and the units are in a humid environment and/or have any kind of inlet cooling or evaporative cooling which increases the humidity of the inlet air then the flame detectors can cause the moisture in the air to condense on the lens (sometimes called 'fogging of the flame detector lens') and block the flame sensing.

So, one can't just open the flow control valve fully, it takes some adjustment over time, but once a proper rate has been established the handles are typically removed from the valves to prevent further adjustment.

Operator error is usually the problem with flame detector failures attributed to cooling problems.

But, if you choose, the Geiger-Mueller flame detectors can be used with Mark VI or Mark VIe, just be sure to specify that you wish to retain them instead of replacing them with Reuter-Stokes Flame Trakkers.

 

Many issues are raised in your posting. Let us address them one at a time.

1. Cooling water requirement for flame detectors
Owing to the higher firing temperatures, flame scanners (Honeywell or Reuter-Stokes) used on E-class and later model turbines (that includes your FA class) require cooling water.

2. Outputs of these scanners
Honeywell flame scanners give out pulses, the frequency being determined by flame intensity. Mark V and Mark VI Speedtronic controls can accept these signals directly and convert to logic signals.

With Mark II and Mark IV controls, the logic module is supplied by Honeywell. This module converts pulses from the scanner to an open-collector logic output that is hard-wired to the Mark II or Mark IV panel. The module has an internal frequency threshold, below which the logic output changes state.

3. Using Reuter-Stokes scanner
This scanner has numerous advantages over the other type.
* It requires only 24 VDC supply. Honeywell scanner requires 355 VDC supply.

* Not damaged by polarity reversal

* Much more sensitive under various operating conditions

Mark VI and Mark VIe can accept the scanner's 4-20 mA signal directly. With Mark II, Mark IV and Mark V, external converters are required.

4. OES has not mentioned cooling-water system for the upgrade.

The answer is in item 1 above. In all probability, your turbine with Mark II control is of pre-1984 vintage (that means it is not an E-class unit).

 

>Why aren't you asking these questions of the OES?<

Thanks for answering.....

As for asking the OES is concerned to get the query answered, I think its a very good suggestion, still I was wondering if I can't think of one single post on control.com which cannot be really solved by asking the OES/OEM/Consultant..... Yet posters post.....

Also it would be a mere 'assumption' to 'assume' that the OES wouldn't have been asked before changing the scanner.

My query was posted here cos while surfing control.com I came across this article on MKII to MKVI migration and it got me interested since we are also expecting a MKVI in next few months. It was there that someone had mentioned about the cooling requirements. Naturally, I thought it better to post here and ask alongside rather than query the OES just because some anonymous poster has posted a detail on a non official GE website.

au revoir
Rahul

 

Most of the salespeople selling GE Speedtronic control system upgrades wouldn't know a Speedtronic turbine control panel if they were standing next to it. Almost any question put to them is either answered with a response which would make a politician proud (in other words, a lot of bun but no beef, to quote a famous political response) or it gets passed on to someone else in the organization who may or may not know what's being asked. Worse, when the query is passed along, it usually is way different than what was originally asked.

Yes: most posts here on control.com could be answered by the OES or OEM. But, finding people in those organizations who can answer the questions can be near impossible.

As you have noted, people who have experience operating equipment manufactured by the OES or OEM (who have little operating experience in most cases!) can be more helpful than the OES/OEM.

I was attempting to asking what the OES had told you when you asked them. GE tries to 'upsell' (as most OEMs/OESs do!) and wants to provide R-S Flame Trakkers (which is a company that is owned by GE) whenever they can.

You, as the Customer, don't have to buy them. You can tell them what you want and what you don't want. I can tell you, that if you have on-base lagging with insulated enclosures for the flame detectors (which you also didn't tell us) that you will really like the R-S sensors. They make maintenance and troubleshooting much easier. And, they don't require the 335 VDC which is so terrifying to most people. As you know, they are plug-connected, which is yet another benefit.

You also didn't say if the responses you received on control.com were helpful or not, versus the responses you received from the OES/OEM.