Numerical and Experimental Investigation of Intra-Particle Heat Transfer and Tar Decomposition during Pyrolysis of Wood Biomass

Abstract

Pyrolysis of cylindrical woody biomass has been investigated both numerically and experimentally with emphasis on intra-particle heat transfer and tar decompostion. In experiment, wood cylinder of 8 mm diameter and 9 mm length was pyrolyzed in an infrared reactor exposed to both convective and radiative heat fluxes in argon environment. The final reactor temperature was 973 K, and heating rate was 5, 10 and 30 K/s. Three K-type thermocouples were located in the sample to measure intra-particle temperature history. The weight fraction history and intra-particle temperature profiles were measured at different runs. Tar was obtained at a cold trap. In calculation, a two-dimensional, unsteady state single particle model was developed and used to simulate the pyrolysis process. Wood cylinder was modeled as an isotropic porous solid. Solid mass conservation equations were solved by using first-order Euler Implicit Method. Gas phase mass conservation equations and energy conservation equation were discretised by finite volume method. In order to investigate the effect of intra-particle heat transfer, simulations were carried out, first, by considering temperature gradient and second, by assuming uniform temperature within the sample. When temperature gradient was considered, simulation results were in good agreement with experimental data. When uniform intra-particle temperature was used in the simulation, simulation results were quite different from experimental measurements, the degree of difference increasing with increase in heating rate. Both calculation and experiment showed tar yield decreased with increasing heating rate. This was because tar formation reaction and intra-particle tar decomposition reactions were enhanced by increase in heating rate but the latter was dominant. It was shown that intra-particle heat transfer and tar decomposition played an important role in pyrolysis characteristics of wood cylinder.

Effect of Biomass Size and Aspect Ratio on Intra-Particle Tar Decomposition during Wood Cylinder Pyrolysis

“…A schematic diagram of experimental setup is shown in our previous report (13) . The experimental set-up essentially consists of a thermo-balance (ALVAC, TGD-9600) and tar trap.…”

“…Because the mathematical model, equations, assumptions, and calculation procedures used for this study are the same as used in our previous work (13) , a brief summary is included in this section.…”

“…The primary tar further undergoes secondary reactions. The kinetic and thermodynamic parameters are the same as those used in our previous work (13) . Figure 1 Pyrolysis model used in this study (13) …”

“…As mentioned above, intra-particle transport phenomena are important factors to consider during biomass pyrolysis; however, little effort has been made to study intra-particle tar decomposition. Recently, we investigated intra-particle tar decomposition experimentally and numerically, and have shown that tar decomposition is possible using an intra-particle tar decomposition process (13) . Biomass size and aspect ratio might be important factors in intra-particle reaction; however, the effects of those factors have not been discussed well from the point of view of intra-particle tar decomposition, although recent research has shown that biomass shape and size influence biomass particle dynamics, including drying and reaction rates (14) .…”

Optimized Heating Rate and Soot-catalyst Ratio for Soot Oxidation over MoO3 Catalyst

“…The particulate concentrations are referred to as 5 wt%, 10 wt%, and 15 wt%. The loose contact was achieved by manually mixing catalysts with the carbon black in a mortar with a spatula for 3 minutes till a homogeneous state [8,9].…”