Installation | Rasert™
NOx SUPPRESSION TECHNOLOGIES The annular combustion in the North American RASERT™ burner inherently results in lower combustion temperatures hence lower NOx emissions. Additionally, other NOx suppression techniques, including air staging and self recirculating FGR (flue gas recirculation) are used. Air staging works by adding the air to the fuel in controlled "stages" which delays combustion, and reduces the concentration of oxygen in the hottest part of the flame. It also helps maintain temperature uniformity on the radiant tube. The 4748 design internally entrains FGR into the combustion air streams. The addition of FGR lowers the peak flame tempera- ture by reducing the concentration of oxygen in the combus- tion air. The reduction of peak temperature greatly lowers the amount of NOx generated in the flame. The graph below shows typical NOx in the flue of a 4748-650 RASERT burner, operating with 140 cfh natural gas. The flue gases exit the burner at approximately 1050°F and the burner combustion air is preheated to approximately 1200°F.
FLAME SUPERVISION An air purged sight tube is available that will allow UV flame detectors to be used with the North American 4748 RASERT. The sight tube is purged with air from a small tube attached to the burner body. The use of the air purge will increase the NOx by approximately 10%. The sight tube has a ½ " NPT male fitting which will fit many UV flame detector cells without additional adapters. See Bulletin 8832 for additional choices of flame detectors and adapters, which must be ordered separately. The RASERT burner has been tested as explosion resistant as defined in NFPA86 2003 Section 3.3.16. spark is required. Spark distributor systems and half wave transformers are not as reliable as conventional continuous ignition transformers. The 4748 can not be lit with a torch at the exhaust exit in a cold tube. LIGHTING ARRANGEMENTS Ignition on the 4748 burner is provided by a direct spark igniter located on the main burner body. The spark should be turned on before opening the burner gas valve. After the burner is lit, the spark must be turned off for proper burner operation. During the ignition period, a continuous 6000 volt (minimum) INSTALLATION CONSIDERATIONS The radiant tube mounting flange should be located 26 inches from the hot face of the furnace wall. This will ensure that the stabilizer is "inside the furnace" and not in the furnace wall. If the radiant tube is not long enough to meet this requirement, a spool piece should be added to the radiant tube to make up the distance. The fire tube inside the radiant tube must be engineered for each application. Besides identifying the proper material, it must be sized for the outlet of the burner, the length of the furnace, and the inside diameter of the radiant tube. The flue gas exits the burner from a connection on the main burner body, and is sized to fit standard pipe. To find the specific size see the dimension chart on sheet 4748-1. The exhaust connection will typically be a "stub stack", discharging at an air break into a collection header. Additional exhaust system back pressure should be avoided as it will effect burner capacity and NOx suppression .
Typical NOx vs. Radiant Tube Temperature
10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0
0.0 5.0
0 250 500 750 1000 1250 1500 1750 Average Radiant Tube Temperature, °F
Bulletin 4748 Page 4
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