Environmental Engineering Reference
In-Depth Information
Assuming HHV
O
2
= 0.014 GJ/kg O
2
,
CO
2
in tons per GJ of energy input can be reduced to
RQ
0
:
1
:
ð
17b
Þ
where the approximate sign is due to assumption of constant HHV
O
2
= 0.014 GJ per
kg of O
2
consumed. For RQ = 1 (pure carbon), CO
2
is about 0.1 tons per GJ or
100 g per MJ.
In order to validate approximate expression for CO
2
, actual measured heating
values of fuels for which compositions are well known (e.g., CH
4
,C
8
H
18
,C
12
H
23
,
C
2
H
5
OH, coal, and biomass) are used to estimate CO
2
in tons per GJ. Results are
shown in Fig.
11
. It is apparent from Fig.
11
that CO
2
in tons per GJ of energy input
has a slope of 0.1 which con
rms the approximation.
The RQ factor for fuels of known composition can be estimated using Eq. (
12
).
Table
5
shows the variation of RQ factor for different fuels.
In general, the RQ factor increases with decrease in hydrogen-to-carbon ratio.
Methane which has a H/C ratio of 4 has the lowest RQ factor for pure fuels with
RQ = 0.5. It can be observed from Table
5
that the solid fuels have comparatively
higher oxygen content. Higher oxygen content results in higher RQ factor for solid
fuels. Gasoline and diesel fuels which are used in the automobiles have a com-
paratively lower RQ when compared to that of solid fuels. Lower O/C ratio of the
liquid fuels is one of the factors behind the lower RQ values.
It is seen that most solid fuels (pure carbon RQ = 1, biomass fuels (mesquite and
juniper) RQ = 0.94
-
0.97, most sweet sorghum sources = 0.98
-
1.0 (TAMU
2013
),
0.095
0.090
0.085
y= 0.1101 x - 0.0045
R
2
= 0.90
0.080
0.075
y= 0.0941 x + 0.0039
R
2
= 0.99
0.070
0.065
0.060
0.055
Curve fit - Boie Eq
Curve fit - actual HHV
0.050
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
RQ
Fig. 11 CO
2
emitted in tons per GJ of energy input for fuels with different RQ factors. Fuel
measured heating value and composition data was used in estimation of CO
2
. Slope of both the
trend lines (actual heating value and heating value estimated using Boie equation) was 0.1 which is
same as the approximate value derived using Eq. (
17b
)
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