750-91 (revised 2009)
Model CB-LE Packaged Boiler Manual
1-3
1.2 — The Boiler
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 temperature, thereby reducing NO
X
emissions. In this
approach, the combustion air fan handles both the combustion air and the recirculated flue gasses. Accordingly,
this method is called Induced Flue Gas Recirculation (IFGR) because the flue gas is “induced” into the fan inlet.
The LE Option, with its various levels of IFGR systems, can affect the selection of the combustion air fan, motor,
burner, and other components. Several different system configurations are available, depending on the require-
ments for NO
X
emissions and the fuels used. All systems use similar primary components, but may have different
linkage controls, IFGR damper, fan, and motor sizes.
When firing heavy oil in a gas/oil CBLE boiler, the heavy oil isolation valve is required in order to protect the
IFGR system from soot buildup and corrosion. See CB manual 750-171 for operating details on the Heavy Oil Iso-
lation system.
Always order genuine Cleaver-Brooks parts from your local Cleaver-Brooks authorized representative.
The boiler and related equipment installation are to be in compliance with the standards of the National Board of
Fire Underwriters. Installation should also conform to state and local codes governing such equipment. Prior to
installation, the proper authorities having jurisdiction are to be consulted, permits obtained, etc. All boilers in the
above series comply, when equipped with optional equipment, to Industrial Risk Insurers (IRI), Factory Mutual
(FM), or other insuring underwriters requirements.
1.2 — The Boiler
The Model CBLE boiler is a packaged firetube boiler of welded steel construction and consists of a pressure vessel,
burner, burner controls, forced draft fan, damper, air pump, refractory, and appropriate boiler trim.
The horsepower rating of the boiler is indicated by the numbers following the fuel series. Thus, CB700-250 identi-
fies a gas-fired 250 hp boiler.
The firetube construction provides some characteristics that differentiate it from other boiler types. Because of its
vessel size, the firetube contains a large amount of water, allowing it to respond to load changes with minimum
variation in steam pressure.
Firetube boilers are rated in boiler horsepower (BHP), which should not be confused with other horsepower mea-
surements.
Hot water is commonly used in heating applications with the boiler supplying water to the system at 180º F to 220º
F. The operating pressure for hot water heating systems usually in 30 psig to 125 psig.
Steam boilers are designed for low pressure or high pressure applications. Low pressure boilers are limited to 15
psig design, and are typically used for heating applications. High pressure boilers are typically used for process loads
and can have a design pressure of 75 to 350 psig.
Steam and hot water boilers are defined according to design pressure and operating pressure. Design pressure is the
maximum pressure used in the design of the boiler for the purpose of calculating the minimum permissible thick-
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