Ljungstrom Air Heater Fire Detection Systems?

[xcbeast944]

Can anyone tell me where I could find some information/options for fire detection or "hot spot" detection systems for Ljungstrom Air Heaters? The infrared detectors aren't doing the job so I'm thinking of switching to a stationary thermocouple design. Any help would be appreciated. Thanks,

Dan

 

[rmw]

What is your process and what is your fuel? Most Lungstrum APH's I have ever had experience with were far enough downstream of the heat transfer equipment that they operated well below the ignition temperatures of any fuel particles that might build up in the baskets. The problems I saw were more toward the end of condensation in the cold end baskets causing build up and plugging. A fire might have been nice to burn some of that crap out of there facetiously speaking of course.

rmw

 

[xcbeast944]

It's a coal-fire plant with a tri-sector rotary air preheater. The cold end corrosion is of course a bigger issue but upon startup there is a potential for fire, and I guess thats where the need for the detection system comes. The in-line infrared detectors aren't functional anymore and we want to move towards a design without any moving parts and easily maintained. I've had a design proposed by one vendor but I'm having trouble finding any competative designs (or any designs) from other vendors. There just doesn't seem to be many resources to turn to. Any guidance would be helpful...

Dan I

 

[dpc]

I have no solution, but rest assured, these can catch fire and burn up quite nicely. I witnessed a primary air heater fire about thirty years ago caused by oil carryover during startup and testing of a 600 MW coal-fired plant. Took a lot of ductwork and supporting steel along with it.

 

[RRaghunath]

I think if purging is carried out religiously before every start, that would ensure the safety of these air pre-heaters. Another thing is monitoring the pressure drop across the heater and cleaning up using soot blowers.

There are sensors which can be mounted in the duct walls (so that the same are not affected by the fly ash etc.), but may not be as sensitive.

Asking Steam generator vendors like BHEL (in India) or B&W can be helpful.

 

[wde0665]

My experience with the HSDS was the ongoing failure of the drive system and not so much the infrared scanner itself. This posed problems as maintenance could not be performed while the boiler fans were on.

Just tossing this out, but was thinking about utilizing an extra sootblower lance/drive setup with the infrared scanner attached. That's about as far as I got down that line.

Would have to resolve many challenges such as a port large enough to get the sensor out when needed, safety for personnel if maintaining online, seal air, mechanics of the extraction process for maintenance, etc.

But at least the drive system should be fairly reliable and easy to maintain, even with the multiple bump-and-wait-one-rotation duty on the contactor.

The challenge with multiple stationary sensors is that if one fails, you're essentially blind in that area and relying on statistics that the remaining functioning ones would catch any issues.

The hazard with fires in our case, was the carry-over of unburned carbon from the gas-outlet side to the air-inlet side where oxygen becomes available to sustain combustion should the ember temperature still be sufficient.

Hasn't been an issue yet, but it would be tough to explain why the detection system wasn't working in the event of a problem.