750-368
CBEX Elite 100-1200 HP
6-11
6.12 — Adjusting Combustion
As an example, assume that a 600 horsepower boiler is installed at 2,000 feet above sea level, is equipped with
a standard gas train and burner, and that 1,000 Btu natural gas is available with an incoming gas pressure of 3
psig. The pressure and flow requirements can be determined as follows:
Pressure
Correction for the 2,000 feet altitude must be made since altitude has a bearing on the net regulated gas pres-
sure. The standard gas train requires 37.5” WC gas pressure at sea level, Table 6.1. Table 6.2 indicates a correc-
tion factor of 1.07 for 2,000 feet. Multiplying the results in a calculated net regulated gas requirement of
approximately 40.1” WC. This is the initial pressure to which the regulator should be adjusted. Slight additional
adjustment can be made later, if necessary, to obtain the gas input needed for burner rating.
Flow
Since the gas flow rate is based on standard conditions of flow, correction must be made for the supply pressure
through the meter of 3 psig. Determine the flow rate by dividing the Btu content of the gas into the burner input,
Table 6.3, and “correct” this answer by applying the correction factor for 3 psig, Table 6.4.
Btu/hr input
= CFH (Cubic feet/hour)
Btu/cu. ft.
or
25,100,000
= 25,100 CFH (at 14.7 lb, atmospheric base 1,000 pressure)
then
25,100
= 21,271 CFH
1.18
This is the CFH (at line pressure) that must pass through the meter so that the equivalent full input requirement
of 25,100 CFH (at base pressure) will be delivered.
6.11.4 — Checking Gas Flow
Your gas supplier can generally furnish a gas meter flow chart from which gas flow can be determined. After a
short observation period, the information aids in adjusting the regulator to increase or decrease flow as required
to obtain the rating.
The information given in this section is for all practical purposes sufficient to set and adjust controls for gas input.
Your gas supplier can, if necessary, furnish exact correction factors that take into consideration Btu content, exact
base pressure, specific gravity, temperature, etc., of the gas used.
6.12 — Adjusting Combustion
Combustion settings are made using the Hawk control system. Refer to manual included with the boiler con-
trols.
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