Bulletin 4343 Page 2
Maximum TwinBed II Capacities with Conical Regenerators, 3/8" Diameter Media, 2300°F Furnace Temperature
Pressure Drop Firing ("w.c.)
Pressure Drop Exhausting ("w.c.)
Exhaust Temp. (°F)
HHV Available Heat
TwinBed
Maximum Capacity
80%
100%
80%
100%
80%
100%
80%
100%
Size
SCFH Air MMBtu/h
Extraction
Extraction Extraction
Extraction
Extraction
Extraction
Extraction
Extraction
4343-7-A 4343-7-B 4343-8-A 4343-8-B
22000 44000 55000 78100 121000
2.0 4.0 5.0
355 325 310 310 310
630 590 575 570 570
75% 75% 75% 75% 75%
80% 80% 80% 80% 80%
24.0 29.0 32.0 35.0 29.5
24.0 29.0 32.0 35.0 29.5
16.5 20.0 22.5 24.0 19.0
27.5 33.0 37.5 40.0 32.0
7.1
4343-9
11.0
LOW NOx EMISSIONS TwinBed II uses low NOx technology developed by Tokyo Gas Co. Ltd. of Japan. North American is the exclusive worldwide licensee for use of this technology with regenerative burners. To minimize NOx formation, two different air-fuel mixing techniques are used depending on furnace temperature. TwinBed II is operated as a conventional regenerative high velocity burner when furnace temperature is below 1450°F (788°C). Above 1450°F fuel is switched to strategically placed nozzles adjacent to the burner tunnel port. Low NOx Injection of fuel (LNI) into the furnace chamber allows inspiration of combustion products into the air and fuel streams reducing the rate and temperature of the combustion reaction, thus significantly suppressing the formation of NOx. This "in- furnace" direct NOx control method maintains highest potential efficiency. There is no efficiency loss as with flue gas recirculation (FGR) that is frequently used to reduce NOx emission from regenerative burners.
FGR involves adding furnace exhaust gas to the combustion air where the inert constituents reduce the rate and temperature of the combustion reaction. If added after the combustion air flows through the regenerator, FGR can reduce system thermal efficiency up to 15%. If added prior to the regenerator system, efficiency can be maintained, but larger regenerators are required to accept the additional volume. Other regenerative burners use up to 50% FGR. A very practical advantage of TB-II low NOx technology is the simplicity of construction of the burner and tile. Burners that use air staging to reduce NOx require internal refractory baffles that the TB-II design eliminates.
800
700
Regenerative No FGR
600
500
Regenerative 20% FGR
400
Gas injectors reduce NOx emissions.
300
Regenerative 50% FGR
200
100
0 1400 1600 1800 2000 2200 2400 2600 Furnace temperature, F Twin Bed II No FGR
Conventional regenerative burner NOx levels vs. TwinBed II
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