Hi,

I am working in a gas fired boiler (300MW) and we are using fireeye flame scanners.

At times our scanner cannot detect the flame due to:
-lens dirty
-scanner faulty (most probably due to the heat)
-cable problem that cause marginal relay.

One thing that we could not really understand is that when we do replacement of the scanners on load (unit running) we can feel the hot air coming from the windbox. Should it be vacuum inside the windbox? Might be that the case our scanners lens tend to get dirty and trip the gas burners? by the way we are using flame scanner cooling fans to cool the scanners.

Anybody can explain?

 

Hello,

A boiler can be designed to have a positive or negative furnace pressure. Does your unit have an induced draft (ID) fan or only a forced draft (FD) fan? (A fan than supplies air and a fan that removes air).

If you do have an ID fan then yes I would not expect to have air coming out of the flame scanner sight pipe.

I assume the scanner cooling air fan is piped in correctly to each scanner.

Good luck,

Mark
http://www.peakhmi.com/

 

Sonicjco...

1) Hot air leaking from combustion chamber, then fire-box is overpressured. I don't believe this is a safe condition! (Once I was bodily carried out of a refinery when I dared comment to ref management that the CO-boiler was being over-fired!

2) How is scanner being cooled? Is ambient air or instrument air being blown through the scanner sight-tube?

3) Replace cable with mineral-insulated (MI) type.

Regards, Phil Corso (Cepsicon [at] aol.com)

 

Hi Phil,

We use flame scanner cooling fans to cool our scanners. We are not using our instrument air compressor.

Our flame scanner cooling fans pressure is 68.10mBar, while our windbox pressure is 17.92mbar. our furnace pressure is -0.58mbar. dP furnace/windbox is 20.15mbar.

 

Hello,

So the furnace pressure is negative.

And I assume the flame scanner sight tube passes though the windbox to the furnace with out any holes.

So, I would not expect air to be coming out of the sight tube.

If you stop the air from the scanner air fan do you still have air coming out the sight tube?

If the scanner air inlet to the sight tube at a angle less that 90 degrees?

Good luck,

Mark
http://www.peakhmi.com/

 

Hi,

The scanner air inlet is less than 90 degrees. Currently the unit is running, shutting down the scanner cooling fan will cause MFT so I cannot really comment.

 

Hello,

I assume each scanner does not have a scanner air valve.

1. Is there a flexible hose between the hard pipe of the scanner air system and the connection to the sight pipe that can be squeezed to stop the scanner air?

2. Can the scanner air pipe to the scanner sight pipe be disconnected?

Looking for some method to stop the air to this one scanner without tripping the unit.

Good luck,
Mark
http://www.peakhmi.com/

 

Hi Mark,

Yes there is a flexible hose connectiong to the sight tube.

Hmmm..we might try to disconnect it during on load. But are you trying to measure flow here?

True, our scanner does not have a valve.

 

Hello,

If you stop the scanner air from entering the sight pipe and you still have air coming out the sight pipe then the air is coming from the windbox.

Since the furnace is under a vacuum that is the only remaining source.

If air is not coming out then all is well.

Do you have an air filter on your scanner air fan inlets?

Good luck,

Mark
http://www.peakhmi.com/

 

Hello Sonic,

Your System is correct.Generally Saperate Fans are used for cooling scanner.Somtimes isolation valve is provided on scanner cooling line. That may be ok but you have add in your SOP (standard operating procedure) or check list to ensure opening of this valve prior to boiler start up.

1)you need to check Scanner air pressure. As due to less pressure than furnace combustiable gases may have reverse flow and scanner getting dirty (if its a carbon like deposit)

2)you need to increase scanner cooling pressure or Check for any chocking of piping/connection. Is the fan capacity appropriate for cooling/sealing?

3)How is the combustion? Flame condition?

regards,
CPPguy

 

Hi CPPguy,

True we might need to check the fan air pressure and also the piping system.

But our atmosferic pressure supposed to suppress the windbox pressure if we do open the scanner from the sight tube on a running unit, right?

Mark,

we do not have any air filter installed at our air inlet at our scanner. We do have one installed at our fans though

 

Hello,

>---But our atmosferic pressure supposed to suppress the windbox pressure if we do open the scanner from the sight tube on a running unit, right? ---<

That depends. One of my first questions was does the sight pipe pass through the windbox to the furnace? The next question, if it does pass through the windbox to the furnace does it have any holes?

I have seen installation where the sight pipe is very short and the scanner is looking through the windbox or part of the windbox into the furnace. And I have seen them go through the windbox to the furnace.

We are missing some data.

Does the sight pipe pass through the windbox to the furnace? That has to be determined first.

If the sight pipe passes through the windbox, with the scanner cooling air removed from the system, with a valve, or clamping down on a flexible hose or disconnecting the piping, does air come out the scanner sight pipe?

If that test proves air comes out and the furnace is in a vacuum state the sight pipe is leaking air from the windbox into the sight pipe. Something is broken.

If the test proves air does NOT come out, the air reported earlier was coming from the scanner cooling air fan.

One of my questions was the connection for the scanner air inlet to the sight pipe less than 90 degrees? The answer back was yes. The idea is that the scanner cooling air is blowing toward the furnace not the scanner.

And finally, if the sight pipe does NOT pass through the windbox to the furnace, removing the scanner I would expect air to come out the scanner sight pipe depending on the length of the scanner pipe. And a dirty scanner can be from flarebacks - furnace panting- NOT A GOOD THING - or dirty scanner cooling air or not piped in correctly.

Good luck,

Mark
http://www.peakhmi.com/

 

Hi Mark,

I have checked into our boiler drawings. Its true that our sight pipe is assembled only half of the windbox only. It does not go through till the furnace.

I guess that really explains the situation we are facing.

We are having many problems with our scanners until we had to jumper the main flame signals. One of the observation seen is the burner gallery area is hot.

 

Hello,

Very good.

The next area I would look into is the scanner cooling air AT the scanner.

1. Is the piping large enough?

2. Are there any restrictions?

3. What is the volume of air flow at the scanner head?

4. What is the temperature of the scanner cooling air at the scanner head?

5. Are the scanner and scanner mounting air tight?

6. What is the scanner air pressure at the scanner head?

If the scanner cooling air pressure is high enough, at the scanner head, air from the windbox will not be coming up the sight tube.

And assuming the scanner cooling air pressure is high enough then the dirt is coming from the scanner cooling air fan system. That leads to dirty or missing filters at scanner air fan inlets or the filter is not fine enough.

Good luck,

Mark
http://www.peakhmi.com/

 

SonicJoe...

1) What is the fuel?

2) How many burners?

3) How many scanners per burner?

4) What is Boiler MFT philosophy? trip on loss of one scanner? One burner? Or other logic?

5) Do you use NFPA Standards?

6) Is your goal to eliminate, yes I said eliminate... not just reduce.... false trips, without jeopardizing safety?

Regards, Phil Corso (cepsdicon [at] aol [dot] com)

 

Phil,

>1) What is the fuel?
Gas or Oil

>2) How many burners?
16

>3) How many scanners per burner?
3 scanners (1 for igniter,1 for oil and 1 for gas)

>4) What is Boiler MFT philosophy? trip on loss of one scanner? One burner? Or other logic?

MFT happens if last burner trip. Will fail as main flame failure trip

>5) Do you use NFPA Standards?
Yes

>6) Is your goal to eliminate, yes I said eliminate... not just reduce....false trips, without jeopardizing safety?
Yes

 

SonicJoe... send me your email address and I will send you a series of papers covering a patented SIS/ESD System.

I will begin with one presented in the "Journal of System Safety Society!" Called, "Probabilistic Risk Assessment of Equipment Safety Systems" for rotating-machinery, fired-equipment, and critical-processes.

The system operated for well over 600 million hours without failure... but, and here is my The Caveat, without software!!!

Regards, Phil Corso (Cepsicon [at] aol [dot] com)

 

Hello,

> The system operated for well over 600 million hours without failure... but, and here is my The Caveat, without software!!! <

It is late in the night for me and I sometimes fail to duplicate what someone is saying and I sometimes make very simple arithmetic errors.

Hours of operation 600,000,000 Hours

Equals
Days of operation 25,000,000 Days

Equals
Years of operation 68,493 Years

If it was 600 concurrent systems that ran for 1,000,000 hours

Equals
Days of operation 41,667 Days

Equals
Years of operation 114 Years

I am confused. Could you help me understand?

Mark

 

Phil,

My email add is fadzril_idzham [at] yahoo [dot] com

>SonicJoe... send me your email address and I will send you a series of papers covering a patented SIS/ESD System. <

 

Certainly Mark... great pickup. The 600 million hours referred to the I/O/F count.

BTW, "success" means zero unwarranted trips, and always tripping when required!

Phil