boiler flame failure

  • Thread starter Biswajit Das, Debabrata Dey
  • Start date
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Thread Starter

Biswajit Das, Debabrata Dey

I am working at bakreswar thermal power project in control and instrumentation department. in our unit is suffering from flame failure without any physical change in parameter like coal feeding, total air flow, furnace pressure, primary & secondary air flow and oxygen percentage. it is also observed that flame intensity at all 5 elevation is sharply decreases at the time of flame failure and flame flickering frequency also decrease at that time. after flame failure trip furnace pressure and air flow rapid changes came into service which cleared a combustion problem occurred inside the boiler, our flame scanner is safe flame type.
 
Responding to Biswajit/Debabrata's 06-Apr-09 (06:52) query:

Please furnish some detail on the "Flame Loss" detection system you use:

a) Type and number at each burner!

b) Self-checking?

c) Purging media for flame detector sight-tube, if used?

d) What applicable Standard do you apply: USA, or other?

Regards, Phil Corso ([email protected])

 
D

debabrata dey

> a) Type and number at each burner!<

vortex flow type burner, corner fired boiler,burner no is 4 at each elevation

> b) Self-checking?<

burner checking is done manually.

> c) Purging media for flame detector sight-tube, if used?<

purging media is discharge air of scanner air fan.

> d) What applicable Standard do you apply: USA, or other?<

indian standard
 
1) From the observations made, the most probable cause of tripping is flame-loss detection by just one detector!

2) Can you provide some detail regarding the flame-loss logic? That is, does flame-loss by one detector on any level, initiate trippng?

3) Are the detectors paired, that is, flame-loss detection is required by two on any level?

4) If tripping is done with just one flame-loss detector, then, there is a very simple solution! No, it is not changing the logic so that loss of two burners are need to initiate a trip. This arrangement is very dangerous.

One investigation I participated in involved a boiler with 16-burners, each having paired flame-loss detectors, for a total of 32! Following a total flame-out, one of the detectors failed to detect flame-out and fuel continued to pour into the fire-box, resulting in a boiler explosion. This caused death of many plant personnel in a well known, well operated HPI company. I was tasked to develop a company-wide standard for multi-burner bolers and furnaces!

5) Are the flame-loss detectors equipped with flame-intensity meters?

6) Can you forward a simplified schematic or hand-drawn sketch (pdf format preferred) that can explain the flame-loss logic?

Regards, Phil Corso ([email protected])
 
I am working at bakreswar thermal power project in control and instrumentation department. in our unit is suffering from flame failure without any physical change in parameter like coal feeding, total air flow, furnace pressure, primary & secondary air flow and oxygen percentage. it is also observed that flame intensity at all 5 elevation is sharply decreases at the time of flame failure and flame flickering frequency also decrease at that time. after flame failure trip furnace pressure and air flow rapid changes came into service which cleared a combustion problem occurred inside the boiler, our flame scanner is safe flame type.
Our Power plant in Jamshedpur has got same problem. Boiler tripped on flame failure without any reason, without any prior indication. We face 2-3 trip every year in a particular unit of 67.5 MW. Everytime Furnace pressure dropped before this type of tripping. Can anybody help me out.
 
Our Power plant in Jamshedpur has got same problem. Boiler tripped on flame failure without any reason, without any prior indication. We face 2-3 trip every year in a particular unit of 67.5 MW. Everytime Furnace pressure dropped before this type of tripping. Can anybody help me out.
Why should furnace pressure drop before tripping???? If it is a balanced draft boiler, a drop in furnace pressure means either the fd fan's flow drops or the I'd fan's suction increases ( part of draft control) or if the Fuel flow drops which is a part of combustion control...and if it is a forced draft boiler then either fd fan's flow drops or fuel flow drops or both happens simultaneously...which leads to a drop in furnace pressure...Also any rich air to fuel mix ratio other than recommended by package supplier and as per NFPA 85 can lead to a hazardous explosive condition.
Does your scanner have a flame intensity analog input signal???? If it has,what does it show??
What happens to the O2 indicator before the trip/when furnace pressure drops??
 
Ujjal Naskar
You said "Both boiler are designed by the same manufacturer."
Without discussion revealing data there never will be a solution. So then, let's start with...
1) What did the Mfg say!
2) What did the your instrumentation reveal other than "Furnace-Pressure dropped"? Can you confirm that "Pressure-Drop" is not unwittingly part of the trip-logic? Was "Fuel-Cutoff coincident with "Pressure-Drop" or did it occur several seconds later?
Regards, Phil Corso
 
Why should furnace pressure drop before tripping???? If it is a balanced draft boiler, a drop in furnace pressure means either the fd fan's flow drops or the I'd fan's suction increases ( part of draft control) or if the Fuel flow drops which is a part of combustion control...and if it is a forced draft boiler then either fd fan's flow drops or fuel flow drops or both happens simultaneously...which leads to a drop in furnace pressure...Also any rich air to fuel mix ratio other than recommended by package supplier and as per NFPA 85 can lead to a hazardous explosive condition.
Does your scanner have a flame intensity analog input signal???? If it has,what does it show??
What happens to the O2 indicator before the trip/when furnace pressure drops??
ID Fan & FD Fan is stable, no such movement in current and gude vane control before the trip. Fuel flow is also stable, absolutely no interruption before trip. Flame intensity is going down before trip. Prior to that furnace pressure dip observed. No such change in O2 also.
 
ID Fan & FD Fan is stable, no such movement in current and gude vane control before the trip. Fuel flow is also stable, absolutely no interruption before trip. Flame intensity is going down before trip. Prior to that furnace pressure dip observed. No such change in O2 also.
What does the first out alarm & SOE readings say? You are saying that the flame intensity is going down...so if we consider your flame scanners to be correct, so that means obviously the fireball inside the furnace is not stable and that is the reason why the flame intensity is dipping...also you are saying that the furnace pressure dips...so next we need to find why the pressure dips...and what might be the causes of it...right?? I want to ask you...what do you think might be the reason of furnace pressure going down?? Because you have an upper hand over the readings and datas at site and with your systems...I will be glad if you can tell.
Is the dip in the furnace pressure has got any coherency with the fireball not being stable ???
Is the reading of the furnace pressure taken from a single transmitter only or is there a averaging function being done from multiple transmitters??
Is there a windbox to furnace differential pressure transmitter?? If so, what is the reading of it before the flame intensity dips...?? Is it also going down similarly like the furnace pressure is???? Also for a stable reading ,transmitters are generally damped and also SCADA update times are present for data logging. So, whatever is happening in the field, and what you are seeing on the screen, there is a time lag to it...and also dcs/plc scan cycles are in milliseconds and so is the trip command.So before you can trust the readings on your screen for fault findings or root cause analysis, be fully sure and aware of what you are trusting upon. Saying everything is showing normal wont lead us anywhere..
Also, what has the maintenance team done as a collective effort to find the cause of the spurious trips.?? See, whatever you are stating, calls out for a root cause analysis to be done thoroughly and the amount of data that is required for it to be done properly can be very exhaustive and overwhelming when done like this through forums...The best way is to be present at the site...and so, only you can do that...For us, we can only suggest something which might give you hints or clues...but then only you(with your colleagues or seniors or maybe just alone) will have to do the challenging part or maybe the better part of finding out the root cause , else all this is just a waste of time and words.
Cheers & Good Luck!!
 
Ujjal Naskar
One simple question... How long have the boilers been in operation?
The reason I asked about the Intensity-meters and now age, follows:
Since this is a Tangentially-Fired furnace, and unless the swirling ball of flame is exactly centered, the intensity-meter for each flame-detector should vary as the ball comes closer, then moves away. However, if all intensity-meters are pegged to max, it means the furnace is being Over-Fired!

None of what I said above has anything to do with unwarranted trips unless there is an "Over-Fired" condition tied into the tripping-logic! And one of the intensity-meters operating erratically is causing the spurious trip. If such is the case, then single flame-loss tripping is in violation of NFPA-85 !

An aside:
I investigated such an incident once ! The unit was very old and all meters were pegged to max ! After years of operation plant personnel had gotten so used to it they thought it was "normal" !

In closing, I agree with Udshred, "Saying everything is showing normal won't lead us anywhere" !
Regards, Phil Corso
 
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