Civil Engineering Reference
In-Depth Information
Fig. 6.7
Typical relationship between stack gas concentrations of CO
2
(%) and O
2
(%) and excess
air (%)
t
s
t
a
CO
2
%
• Total stack gas losses
where
K
s
is called Hassenstein coefficient
(see Table
6.5
where only the Lower Heating Value is assumed as reference),
t
s
is the stack gas temperature and
t
a
is the ambient temperature (typical values of
CO
2
% less than 10 %). This formula is acceptable if incombustibles are kept
low;
• Losses for unburned combustible
%
¼
K
s
CO
where
K
c
equals 50.5 for
fuel oil, 37.9 for natural gas, 59 for coal if the Lower Heating Value is assumed
as reference (typical values of CO% less than 0.1 %).
Examples of evaluation are given in Sect.
6.12
.
In Fig.
6.10
the main combustion parameters are correlated by a set of curves
called the Ostwald triangle. In particular, if CO
2
% and O
2
% are known, it is
possible to check whether the combustion is complete, and if it is not, to determine
the CO%. Otherwise, if only CO
2
%orO
2
% is known, by introducing CO%
(measured or estimated), it is possible to determine the other. Other sets of
correlation curves also exist for use according to local practice.
%
¼
K
c
%
CO
2
%
þ
CO
%
