Retrofitting the High Stability Pilot

Critical Dimensions    

Since the high stability pilot utilizes a larger than normal end cap, there may be spatial constraints caused by existing equipment.  Please check the following for proper igniter clearance:

• Typically there is about 5" of exposed guide pipe.

• At the end of guide pipe the end cap is:

  • diameter:  5"

  • width:  2"

• Electrodes extend 7" out from the end cap.

• Ignition cable connections (1/2") extend 1" off the end of the electrode.

• Total clearance length should be approximately 15" from the point of mounting.

• Along with the required clearance for the end cap there must be room for two 1/2" NPT connections:  located at 12 (gas) and 9 or 3 o'clock (air). 

• The insertion length of the pilot in inches must be provided.  The insertion length is defined to be the length of the pilot inside the duct burner from the point of mounting.

Mounting Plate

Coen understands that adapting an existing mounting plate to the High Stability Pilot will be unique to each customer.  If the existing mounting plate can be field modified to accept the 2-/1/2" guide pipe  and a 3-7/8" diameter bolt pattern (4-hole), Coen highly recommends our standard mounting flange and gasket.  If the existing mounting plate can not be used, Coen will be happy to customize a new mounting plate.  It is also possible to seal weld the igniter into the duct, however this prevents any future removal of the High Stability Pilot. 

Air

Supplied air is required for the High Stability Pilot to achieve a reliable light-off.  The air, once inside the pilot, mixes with the gas creating a mixture which is easily ignited.

• The air supplied can be delivered continuously or only during ignition.  Delivering air continuously will keep moisture and particulate matter from collecting within the pilot, without a noticeable drop in performance of the overall system.

• Air can be supplied from the scanner cooling air blower if the blower can meet this added capacity.  If the user elects not to deliver air continuously, an additional solenoid valve would need to be purchased.

• For automatic operations a solenoid valve and a regulating valve is required to control air pressure to the pilots.  During light-off some air will be diverted to the pilots for approximately 20 seconds.

• If the existing blower or plant air cannot be used a new blower would need to be purchased.

• The necessary air requirements to achieve 0.5 million Btu/hr are:  25 scfm @ 2.0 psig.

Firing Rate                                     

For most applications, to achieve a stable flame with the High Stability Pilot, the firing rate should be between 300,000 - 500,000 million Btu/hr.  Coen recommends that all retrofit pilots be sized for 500,000 million Btu/hr, thus if oversized the pilot has the potential for some turndown.  Here are the necessary requirements for a 500,000 million Btu/hr High Stability Pilot:

• 6000 V and 20 mA transformer

• Natural Gas:  8.4 scfm @ 3.4 psig.

If the desired firing rate is not 500,000 million Btu/hr, a chart can be used to determine the required air and gas pressure at another firing rate.

With the required pressures known, flow rates for gas and air can be determined from the following graphs.  For example, if the gas pressure is 3.4psig and air pressure is 2.5psig, the respective flows would be:

• Gas Flow:  8.4 scfm
• Air Flow:  30 scfm

High Stability Pilot Parts

*XX -- Entire pilot length = Insertion length, in inches, + 5 inches, minimum. 

ZZ = Insertion length in inches.

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