Environmental Engineering Reference
In-Depth Information
Fig. 11 Effect of temperature
on syngas heating value
per unit volume compared to other gaseous fuels such as propane or natural gas.
The relatively low density of syngas is due to the relatively high concentration of
hydrogen, which has the lowest density of any gas. The heating value of gaseous fuels
is usually reported on a volume basis. Hence, the following analysis is given as such.
It is important to keep in mind that heating value presents qualitative information on
the produced syngas and does not inform about the quantity of energy produced.
Figure
11
shows the effect of temperature on the syngas heating value. The
heating value was highest at a reactor temperature of 700
C. At this temperature,
carbon monoxide was the most abundant gas constituent. The maximum heating
value measured was 16.1 MJ/m
3
, occurring at a temperature of 697
°
°
C, S/B of 0.7,
and a residence time of 1.9 s. At this condition, the methane concentration was
13.4 mol%, which its highest measured, and the carbon monoxide concentration
was also near its maximum at 38 mol%. The main reason that the heating was
highest because of the hydrogen concentration being relatively low at 26.3 mol%.
The heating value dropped as the reactor temperature was increased. The minimum
heating value measured was 12.7 MJ/m
3
. This occurred at a reactor temperature of
853
C, S/B of 2.9, and a gas residence time of 4.5 s. The hydrogen concentration
during this particular experiment was the highest measured for un-catalyzed gasi-
°
fication at 51 mol%. The high hydrogen concentration increased the total com-
bustible fraction and volume of the syngas, but decreased the heating value.
3.3 Energy Ef
ciency
One of the most important parameters determining the viability of steam gasi
cation.
is the thermodynamic conversion of energy, or energy ef
ciency (EE). This quan-
titative tool is a good
first estimation of the cost of producing hydrogen-enriched
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