Design and Construction of a System for Measuring Carbon Monoxide, Hydrogen and Methane Concentrations in a Co-Current Downdraft Biomass Gasifier

Gasification is the process of producing combustible gases from solid materials such as coal, biomass or solid waste. The laboratory of Space Physics and Energy has two experimental gasifiers producing synthetic gases whose natures and concentrations must be determined. To do this, lower-cost sensors were purchased and used for determining the concentration of carbon monoxide with maximum concentration of 1.000 and 2.000 ppm. Hydrogen and methane concentration was not offered by these two commercial gas analyzers. In this paper Metal-Oxide gas sensors were used to extend the measurement range of carbon monoxide up to 4.000ppm. Hydrogen and methane concentrations up to 10.000ppm in synthetic gas produced by a wood fired co-current downdraft gasifier measurements were also enabled. These sensors have a chemical sensing element based on a layer of tin dioxide (SnO2); whose resistivity is sensitive to nature of the gas between two sensing electrodes. This property gives these sensors a resistive electrical model whose measurand is the concentration of the input gas. This study shows that resistor R of the sensor is related to the gas concentration with an equation of the form: log(R/R0) = A log (x) +B. With A= -0.3072, B = 0.921 for methane, A= -0.6527, B=1.3055 for carbon dioxide and A= -1.522, B = 4.5686 for hydrogen.