Firetube Operation Basics
1-2
750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
FIGURE 1-2. Firetube Boiler Cutaway View
The low emission option for the Promethean line of Firetube Boilers reduces Nitrogen
Oxide (NOx) emissions, a major contributor to ozone pollution (smog). Carbon Monox-
ide (CO) emissions also tend to be lower due to increased turbulence caused by the addi-
tion of the flue gases into the combustion air stream, thereby improving combustion.
The Promethean Firetube Boiler line is designed to incorporate Induced Flue Gas Recir-
culation (IFGR) when firing either natural gas and/or light oil, and is compatible with
both hot water and steam systems.
The IFGR system mixes a portion of the relatively cool flue gas from the exit of the
fourth-pass tubes with the incoming combustion air to reduce the furnace flame temper-
ature, thereby reducing NOx emissions. In this approach, the combustion air fan handles
both the combustion air and the recirculated flue gases.
FIGURE 1-3. Induced Flue Gas Recirculation (IFGR)
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