Ignition Options & Installation | 4950 Flame Grid
PILOTS, FLAME SUPERVISION. Options available: Option 1 — raw gas pilot/flame rod Option 2 — raw gas pilot/UV Option 3 — premix pilot/flame rod Option 4 — premix pilot/UV
Turning vanes
3 duct diagonals
Elbow
Fume flow
If UV is specified, an adapter nipple is furnished, but detector must be purchased separately. Flame rods are furnished when Option 1 or 3 is specified. Raw gas pilots require combustion air from the fume stream. A spark electrode ignites gas and air as they mix. Gas pressure at the pilot inlet must exceed duct pressure by at least 3"w.c. (7.5 mbar) Raw gas pilots should be ignited with normal air. After the main burner flame is ignited, the fume-laden reduced-oxygen air can be introduced into the duct.
Duct downstream of burner must be enlarged and refractory- lined. See Figure 2. Always install one or more observation ports downstream of the burner for observation of the complete grid surface. See bulletin 8790 for observation port options. Flame Grids can be installed in horizontal or vertical ducts. If fume stream contains particulate matter, burner duct should be horizontal to prevent particulate accumulation on the grid. Exces- sive buildup can require frequent cleaning. 4950 Burners with “A” dimension 20" or greater have support plates near the free end of the grid. These plates should be attached to duct wall or suitable structural members to support free end.
Dirty effluent might foul the raw gas pilot igniter. In these appli- cations a premix pilot is recommended.
If effluent is “clean,” either a flame rod or UV detector is suitable. High particulate loads may foul a flame rod. Dense smoke may blind a UV detector. Choose flame supervision based on specific conditions. An interrupted pilot must be used. A constant pilot is a safety hazard and causes uneven heating of the burner. When spark igniting raw gas pilots, flame detection system must interrupt spark. Spark can dissociate raw gas into carbon compounds that over time could ground the spark plug.
Figure 2. Typical Flame Grid installation.
Continuous weld this mounting plate to duct, centered and square with 1⁄8 " clearance between grid and duct wall or silhouette plate. Burner has provision for removing from mounting plate if necessary.
PREMIX PILOTS
Ignition flame supervision and Grid Plates on downstream side
A premix pilot requires at least 4 osi/7.0"w.c./17.2 mbar combus- tion air from an external source blower or compressed air re- ducer, a 3070 compressed air reducer converts a small amount of compressed air into low pressure air source that can be use to supply combustion air to a small burner or pilot. See sheet 3070-1 for details. Most existing 4950 burners with premix pilots use 4027 style pilots but 4021 pilots can also be used. See bulletin 4011/4021 for instructions on installing and operating premix pilot tips.
Weld mounting to duct wall
Insulation
9 3⁄8 " (238)
See
Fume/Air
Dwell chamber
Flow
8" to 10" (203 to 254)
I NSTALLATION. Flame Grids are inserted through duct wall cutouts (see dimension page for cutout sizes).
Insulation by customer
Steel duct wall
Fume flow pattern to the burner must be as uniform as possible to assure complete incineration. Therefore, locate Flame Grids at least 3 duct diagonals downstream from any elbow or fan; turning vanes are recommended in elbows.
Observation port
Inside duct dimensions for first 8-10" downstream of Flame Grid must conform to burner dimensions A and B (e.g., 14" 12" for 4950-1412). Dwell chamber cross sectional area must be at least twice nominal burner area (dimension A dimension B).
Bulletin 4950 Page 5
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