Coal Fired Boiler Flame Scanners 1

[Konstantinov]

We have a stoker fed, moving grate coal fired boiler, which has a backup gas fired auxiliary/emergency backup burner. In order for the gas burner to fire immediately on the start command, a scanner looking at the coal fire has to sense the presence of a coal flame. If no flame is detected, the gas burner will go through a 5 minute purge cycle before lighting off. This is the safety feature that assures the gas burner can not light if there is no boiler flame present. Obviously, a 5 minute purge is required when lighting the gas burner on a cold boiler. In an emergency, with the coal fired boiler operating, we do not want to wait 5 minutes before getting the gas burner in operation. We have tried a variety of scanner types, IR, near IR, UV, etc. I understand that a coal fire operates in the range of 3,500 to 5,500 Angstroms.

There are two components to the flame we are sensing; the DC component which is the energy level sensed from the brightness of the flame, and the AC component, which is the flicker frequency of the flame. Having a large burning surface ~ 20' x 20', this is a "lazy fire" compared to forced air combustion systems. The problem that I am experiencing is that I can tune the scanner for the AC and DC components of the flame for normal load conditions, but when the boiler goes to low load conditions, such as when production is down for the weekend, the scanner does not respond well to the reduction or difference in the AC and DC component. I have also found that there are several significant AC flicker frequencies at any given load, making it difficult to lock the scanner in on a predominant frequency. Does anyone have any success stories with an installation similar to ours?

 

Dear Sir.
We are searching the market for an alternative heating for our 100,000 sq. ft. greenhouse facility in Chilliwack, BC., Canada. Could you please contact us by phone or email.
Our phone number is 1-604-795-3555
Email: bosch@uniserve.com
Fax # 1-604-793-0355

We use about 20,000 GJ og natural gas per year.
December 2000 we used 2900 GJ. per month
Our peak usage in that month was 108 GJ per day.

Looking forward in hearing from you
Peter Van Den Bosch
Van Den Bosch Greenhouses.

 

[reggie]

If the temperature of the chamber is above 760 deg C, you can do a "purge bypass" according to NFPA 86. You need a separately derived temperature sensor and a stand alone controller. We use this system in industrial gas fired furnaces.

 

[joecontrol]

You could try a flame rod type of sensor but locating it on the boiler may be a problem. Why not add a pilot to the gas burner and have it run all the time I am sure the cost of the gas would not be too much.That way a purge would not be needed just a monitor on the pilot. Pilot on start burner this would fix the need for purge. This might be a simple fix. well good luck ,Joe

 

[EngineerBSME]

Flame detection which can distinguish between coal flame and oil or gas ignitors has been a fleeting task for several years. It is mostly an art rather than a science.
Physical arrangement of the detectors is important. However, the experts in the area as we speak are as follows:

Flicker Flame - Intensity (AC/DC) using photo-diode cell sensor:
Mr. Bob McWhorter (technology passed down through three generations of McWhorters)
Bailey Controls Corp
Cleveland, Ohio

A successful user of this technology is:
Mr. Dave Simpkins
Cumberland Steam Plant
Tennessee City, Tennessee
1300 Mw, B&W, Opposed Fired, Dual Units, Pulverized Coal, Oil Ignitors

Photo-diode Sensor:
Each type fuel has a fingerprint which can be plotted and distinguished. For computer based flame frequency discrimination between various fuel sources contact:
Tri-hedral

http://www.trihedral.com

Canada

Proprietary Sensor:
There is a new proprietary method of easily discriminating between any type flame but more importantly actually measures the rate at which combustion is presently occurring. The system was successfully tested at B&W, Top Fired, 235 Mw, Coal Fired, Oil Ignitor, Clinch River Plant, Cleveland, Virginia. Testing was completed in August 2002. Proper use of the system improved the boiler combustion efficiency 5-10% at full load. With improved combustion, boiler effluents improved considerably (NOx, CO, LOI). Contact haclift@yahoo.com for additional information and a source for the cost effective equipment.

 

[mbbmcs]

I would look more into cadmium for flame detection if your haveing problems at change over from coal to gas.
because when cadmium is exposed to visible light it emits
electrons (and it dont take much light and the coal will continue to give off light during change over)with the strength of the visible light.