Dipl. Ing. Matthias Mayerhofer Technische Universität München ...

Results and Discussion 53
7.2 Sampling and Gas Analysis
The product gas was online monitored in order to determine its composition at different operating
conditions. The sampling point was after the catalyst bed, in order to have a clear picture of how it
is affected by the presence of the catalyst. With the results of these measurements further values
were calculated to define the potentials of the syngas. The compounds that were measured were
CO, CH4 and H2 which constitute the fuel of the product gas and of course the CO2 and the water
content. The gas yield before the throughput of the gas in the catalyst bed can be seen below
Figure 26. After the decomposition of the tar inside the catalyst bed the composition changes significantly.
24,5
11,8
5,7
11,0
Figure 26: Gas composition before catalyst test rig
Dry product gas Lower Heating Value (LHV) was calculated for the different operating conditions.
The results can be seen below in Table 6, Table 7 and Table 8. For the iron based catalysts, it can
be seen that as the temperature increases the heating of the value increases too, whereas as the
space velocity increases the heating value decreases. This is expected as the temperature and the
residence time of the gas in the catalyst are two essential factors that define the value of the product
gas. The higher the activity of the reactions that take place the higher the richness of the gas
composition in H2, CH4, and CO. For the iron based catalysts, the highest heating value of the gas
is obtained at 860°C and SV=6584 1/h. But this value is very close to the one obtained for 800°C
and SV=4488 1/h, which is important as these catalysts are supposed to be used in situ were the
maximum temperature reached is 800°C. For the nickel based catalysts, the LHV is slightly affected
by the changes in the SV. These catalysts were sufficiently active in all the different operating
conditions, so the differences in the residence time didn’t affect a lot the gas composition. For the
precious metal catalysts the influence of the SV is not very evident either. The LHV of these two
catalysts don’t differ a lot but the products gas in their presence has significantly higher heating
value compared to the iron ones.
To calculate the LHV first the wet concentration of every compound was found with the following
equation
Then taking into consideration the molar mass of every compound and its heating value the LHV
was calculated, and the results can be seen below. It is obvious that although the operating conditions
vary significantly the heating value of the gas didn’t range a lot, because the composition of
the gas was affected enough by the presence of the catalyst.
4,0
42,9
H₂O
CH₄
CO
CO₂
H₂
N₂