Bulletin 8061 Page 2
HOW IT WORKS StepFire™ directs the firing of a multiple burner furnace. It ad- justs the thermal input by sequentially switching burners from high-to-low for controlled periods of time, providing uniform heat release. As the heat demand decreases, each burner's on-firing time shortens, while its rotation time--the burner's combined high fire and low fire time--lengthens. Conversely, as the de-
mand increases, the burner's on-firing time lengthens, while its rotation time shortens.
Each zone's burners are controlled by solenoids on their air input valve. The fuel valves are pneumatically cross linked to the air via a ratio regulator (see Figure 2).
Example Burner Firing Operation: 2 burners operating under a (32-second) rotation time at 50% and 75% heat demands.
At 75% demand, burner one runs at high fire at the beginning of the time interval. Burner two gœs to high fire 8 seconds after burner one. Burner one switches to low fire at the 24-second point. Burner two switches to low fire at 32 seconds, the end of the base period, as shown in Figure 4.
At 50% demand, burner one is at high fire for 16 seconds, while burner two is at low fire. After 16 seconds, burner one switches to low fire and burner two switches to high fire, as shown in Figure 3.
1
Low
High
Low
High
1
High
Low
Low
High
2
2
0 4 8
0 4
Rotation Time (Seconds) 8 12 16 2024 2832 (repeat)
12 16 20 24
28
32 (repeat)
Rotation Time (Seconds)
Figure 4. StepFire Operation–2 burners, 75% demand, 32-second rotation time.
Figure 3. StepFire Operation–2 burners, 50% demand, 32-second rotation time. Example Burner Firing Operation: 4 burners operating under a (24-second) rotation time at 50% heat demand.
If step firing four burners in a zone, each burner would be raised to high fire for their 50% time intervals in equal increments within the base rotation period (see Figure 5).
1
Low
High
2
Low
Low
High
3
High
Low
Low
High
High
4
0
22 24
2 4 6 8101214161820
(repeat)
Rotation Time (Seconds)
Figure 5. StepFire Operation–4 burners, 50% Demand, 24-second rotation time.
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.
CONTACT fna.sales@fivesgroup.com T +1 800 626 3477 - F +1 216 373 4237
Fives North American Combustion, Inc. 4455 East 71st Street - Cleveland, OH 44105 - USA www.fivesgroup.com
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