6843-25 Hot Spot Burners are offered in -3 and -4 sizes. These burners produce short, intense flames when operating on either natural gas or distillate oil. During oil firing, 8 psi of compressed air is required at the burner for atomization. During gas operation, 2 psi of compressed air is required to protect the atomizer, but 8 psi can be used if it is necessary to maintain the same burner capacity as during oil operation. The 60% Alumina burner tiles withstand furnace temperatures to 2800°F, and are grooved to provide a tight seal when mounted in either the furnace roof or wall. The tiles are reinforced with stainless steel needles, and require suitable hand protection be used during handling. For natural gas operation, the pressure required at the gas connection is approximately one half the main air pressure at the air connection. For oil operation, each burner must be equipped with an air/ oil Ratiotrol™ regulator and Sensitrol™ oil valve. This Sensitrol oil valve is not included with the burner assembly and must be ordered separately. As the atomizer nozzles are precision machined, a 100 mesh strainer must be installed in the oil line supplying the burners. In addition, to prevent damage, handling of the atomizers should be kept to a minimum. When shutting down the burners or switching over to gas operation, completely purge the oil atomizers of oil to prevent coking. North American Dual-Fuel ™ Hot Spot Burners
Sheet 6843-1
Standard burners are supplied with a flangeless mounting plate for installation in a furnace roof. Optional flanged mounting is available (at additional cost) for installation in a furnace wall. Add the letter "C" at the end of the burner designation when ordering the flange, i.e. 6843-3-25-C. A 4011-12 pilot set is recommended for individual burner ignition. When multiple burners share a single pilot pre-mix header, a 4021-12 pilot tip per burner with an appropriately sized air/gas mixer is recommended. A UV Detector should be used for flame supervision. While it is strongly recommended that the burners be lit at low fire, the maximum main air pressure for lighting when firing oil is 8 osi. The Dual-Fuel™ hot spot burners will perform well when coupled with an air/fuel ratio control system that is capable of controlling within the stability range of the burners. The extremely fast mixing characteristics of this burner limit excess air, and excess fuel should be limited to less than 10% Caution must be taken when calculating burner inputs. Due to expansion changes in the burner at different firing rates, air flow dœs not follow the square root law. In addition, burner air flow decreases as the furnace temperature increases, resulting in a change in air/fuel ratio. As a result, the final burner air/fuel ratio settings must be made with the furnace at operating temperature. This results in the burners firings lightly lean during a cold start-up and reaching ratio as the furnace reaches temperature.
COMBUSTION AIR CAPACITIES in scfh (for Btu/h HHV, multiply by 100)
air pressure drop across the burner in osi
Burner designation 6843-3-25 6843-4-25
0.5
1
2
4
9
16
30
scfh
psig
540 920
780
1100 1830
1590
2450
3340 5600
4570
230 230
8 8
1250
2700 4050
7700*
Air rates are for burners operating on natural gas on ratio. Cold air capacity when not burning will be approximately 7% greater.
* Gas only. 16 osi is maximum air rate for oil on 6843-4-25.
WARNING: Situations dangerous to personnel and property may exist with the operation and maintenance of any combustion equipment. The presence of fuels, oxidants, hot and cold combustion products, hot surfaces, electrical power in control and ignition circuits, etc., are inherent with any combustion application. Components in combustion systems may exceed 160°F (71°C) surface temperatures and present hot surface contact hazard. Fives North American Combustion, Inc. suggests the use of combustion systems that are in compliance with all Safety Codes, Standards, Regulations and Directives; and care in operation.
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