Infrared Spectroscopy for Online Measurement of Tars, Water, and Permanent Gases in Biomass Gasification

Online measurements of the raw gas composition, including tars and water, during biomass gasification provide valuable information in fundamental investigations and for process control. Mainly consisting of hydrocarbons, tars can, in principle, be measured using Fourier transform infrared (FT-IR) spectroscopy. However, an instrument subjected to raw gas runs the risk of condensation of tars on optical components and subsequent malfunction. Therefore, an external cell, heated to at least 400 ℃, has been designed to ensure that tars remain in the gas phase during FT-IR measurements. The cell was used for on-line FT-IR measurements of permanent gases (CO, CO2, CH4), water, and tars during the operation of a lab-scale downdraft gasifier using wood pellets, bark pellets, and char chips. Based on calibration, the measurement error of permanent gases was estimated to be 0.2%. Concentrations evaluated from spectral signatures of hydrocarbons in tar are in good agreement with results from solid-phase adsorption measurements and correlated well with operational changes in the gasifier.

Parametric study of corn cob biochar (CCBc) yield via microwave pyrolysis

In the long-run, microwave pyrolysis can be a simpler and low energy-requiring alternative to conventional pyrolysis for the thermochemical conversion of biomass to useful products. However, there are still research gaps in its mechanism. Thus, this study investigated the various factors affecting the biochar yield using a half resolution (2k-1) factorial design on the microwave pyrolysis of corn cob wastes. A viable biochar product was produced within minutes of the reaction; wherein, the statistical analysis confirmed the exposure time, microwave output power and their interaction as significant in the CCBc yield. The highest yield obtained was 52.87% when exposure time and output power were set to 5 min and 450W, respectively. A general decreasing effect on the yield was observed from increasing exposure time and output power. This was due to the rapid heating experienced by the corn cob wastes causing the hydrocarbons to react and transform into permanent gases at higher temperatures. To confirm the carbon content of the CCBc, elemental analysis showed an average of 67.11% C at low time-low power (LTLP) of 450 W for 5 min and 81.32% C for the samples operated at high time-high power (HTHP) of 700 W for 10 min.

Solubility Parameters of Permanent Gases

The solubility parameters,δH(Tb), of nonreactive permanent gases at their boiling pointsTb(<290 K) are calculated from individually discussed values of their molar enthalpies of vaporization and densities obtained from the literature. These values are tabulated and where available the coefficients of the temperature dependence expressionδH(T)are also tabulated. The trends noted in theδH(Tb)values are dealt with and the values are compared with those reported in the literature and derived from the solubilities of the gases in various solvents. TheδH(Tb)values are shown to correlate linearly with the depths of the potential wells (attractive interaction energies,ε/kB) for binary collisions of the gaseous molecules and with the surface tensions,σ(Tb), of the liquefied gases.