For installations over 2000 ft elevations, a derate schedule is applied. The boiler input rating must be reduced by
4% per 1000 ft.
This is illustrated using the following graph.
55
Harsco Industrial, Patterson-Kelley Technical Service 1.877.728.5351
a
PP
e
N
d
IX
2
Gas Fired Boiler
Derate procedure is as follows:
With the boiler at high fire, adjust the gas valves (
as described in section 3.10.4
) to get 5% O2 in the flue gas.
If this cannot be achieved, perform the following steps:
•
If the O2% is too high, then the inlet gas pressure should be adjusted to the minimum pressure allowed,
typically 5” wc The gas valve should be adjusted to obtain approximately 5% O2. If the O2% is still too high, the
fan speed may be lowered. This procedure should only be performed by factory trained personnel.
•
If the O2% is too low, then the gas valve settings should be reduced.
This procedure is also described in Bulletin 06-08.
a
ppendIx
2: b
oIler
a
lTITude
d
eraTe
s
Chedule
