| dc.description.abstract | This study developed two gas chromatographic (GC) systems: one is to monitor the chemical composition of stack gas from factories, and the other is to analyze the composition of biogas from biomass torrefaction. Both methods have a common ground; that is they both measure methane and non-methane hydrocarbons (NMHCs). However, the first method only separates NMHCs as a group from methane, whereas the second method performs elaborate separation of more than 10 gases.
To allow long-term operation with minimal downtime and maintenance, both GC systems adopted isothermal and back-flush design, involving a 10-port, 2-position switching valve and several column sets with each set consisting of a pre-column and analytical column kept at a constant oven temperature.
Two methods were tested for the first application; they are back-flush and split methods. Because the back-flush method caused the undesired peak tailing with the NMHC peak, the split design was adopted and tested by inter-comparing with the catalytic method which is widely used for the EPA air quality monitoring stations. Although both readings were very similar, the catalytic instrument was found to be susceptible to incomplete catalytic removal of NMHCs resulting in systematic bias, especially when ambient air contained high levels of NMHCs. By contrast, this problem can be fully avoided by our GC method.
In the application of biogas analysis, a GC system with the similar back-flush isothermal concept was built to separate more than 10 species, i.e., N2, O2, CO, CO2, CH4 and C2-C4 NMHCs, for each injection. The system was first tested in the off-line mode, and later adapted to a biomass torrefaction chamber for on-line monitoring gas composition. Both the off-line and on-line results appeared to be very similar, proving that the GC system can perform on-line analysis as planned. Basing on the instantaneous chemical compositional information provided by the on-line GC, the process parameters for a given type of biomass can be optimized accordingly. | en_US |