CleaverBrooks CB-LE Series - Page 106

Chapter 6 — Adjustment Procedures
6-18 Part No. 750-184
Figure 6-7 Flue gas analysis chart for Natural Gas
!
Caution
Turndown in excess of the burner design may damage the burner
diffuser and/or the burner housing. Failure to follow these
instructions could result in damage to the equipment.
It is important to understand what the readings shown on an
instrument refer to when setting combustion in a boiler. To assist
with this understanding Figure 6-7 shows the relationship between
O
2
levels (excess air) and the products of combustion for a typical
flue gas analysis (natural gas).
One of the products of combustion is CO
2
(Carbon Dioxide). This is
shown in percentage.
Another product of combustion is CO (carbon monoxide) and is
shown in both percentage and parts per million (ppm). The
maximum CO level standardly allowed is less than 400 ppm.
However, this may change subject to local regulations.
The percent O
2
recorded on an instrument equates to percent
excess air, i.e. 3% O
2
is approximately 15% excess air and 4% O
2
PER CENT O
2
OCTNECREPSAGEULFNI
PER CENT EXCESS AIR
1020
3040
5060
5
6
7
8
9
10
11
12
1123243545 6
67
809
PER CENT CO
2
IN FLUE GAS
FIRST VISIBLE TRACE OF STACK HAZE
1/10 of 1% CO = 1,000 PPM
15