International Conference on Applied Energy ICAE 2013, Jul 1‐4, 2013, Pretoria, South Africa Paper ID: ICAE2013‐656 FIRST PRINCIPAL MODELING OF THE PYROLYSIS OF A THICK BIOMASS SLAB EXPOSED TO THERMAL RADIATION: A TANSIENT STUDY FOR TAR, CHAR AND HYDROCARBON FORMATION Syed Shabbar Raza Masdar Institute of Science and Technology Abu Dhabi, United Arab Emirates Isam Janajreh Masdar Institute of Science and Technology Abu Dhabi, United Arab Emirates ABSTRACT A first principal modeling of thick wooden slab is performed to investigate the degradation and evolution of tar, char and light hydrocarbon using thermal radiations. Using the governing mass, momentum transport and energy balance equation, a one dimensional model is defined. The governing equations are solved using the finite element method subjected to the initial conditions and boundary conditions. The modeled physical time is 3.5 minutes in which the lumped and discrete quantities are calculated. The wooden slap is exposed to 25 kW/m 2 of thermal radiation that contributes to the temperature gradient across the thick wooden slab. The result shows the exponential decrease in wood mass with respect to time and temperature. The decrease in wood mass directly related to the evolution of char and gas, that are evolving according to Arrhenius based kinetics. Thus the mass of char and gas are also calculated that gives the increasing exponential trend. Finally, the temperature distribution inside the slab is also calculated using the energy equation. Results are compared with the data available in the literature and found in good agreement. INTRODUCTION Biomass fuel is always a promising route to produce charcoal/bichar, tar and light hydrocarbon. The light hydrocarbon is normally in the form of CO, CO 2 and C 1 -C 5 compounds [1]. The conversion of biomass in the form of solid, liquid and gaseous mixtures provide the source of energy to the world in the form of generating electricity, heating homes, increasing soil fertility, and providing process heat for industrial facilities. The direct combustion of biomass to produce steam that can be used to generate electricity using rankine cycle [2] or to convert biomass into combustible gases using gasification to drive high efficiency gas turbine [3]. Also the thermochemical conversion of biomass into ethanol and methanol [4] is off great interest for the transportation fuel and other fuel using fisher-Tropsch process [5]. Unlike the other hydrocarbons i.e. rock oil, coal and natural gas, the biomass termed as a carbon neutral fuel [6, 7] that can be a key factor to reduce greenhouse gas emission that is the most difficult aspect of climate change mitigation [8]. The major problem of biomass to attain its position as front line energy source is due to its lower power generation efficiency [9-11]. In order to increase the efficiency of biomass conversion the fundamental understanding of each unique conversion of biomass fuel is necessary. Pyrolysis of wood is one of the emerging fields that are used to convert biomass in fuel [12-14]. Pyrolysis involves heating of raw biomass components or organic materials in the absence of oxidizer. Thermal degradation of the biomass components is accomplished by mass transport of the de-volatilization products through advection and diffusion and escape of products at the surface of the particle. The volatile yield from pyrolysis includes a complex mixture and more than one hundred hydrocarbons were found [15-17]. In the following research the modeling of biomass (wood) pyrolysis is performed. In the list of volatile solid fuel conversion, the research performed to model the coal is relatively mature as compare to biomass. The modeling of coal devolatilization, combustion and gasification in the form comprehensive model and CFD code are already performed in waste to energy lab at Masdar institute, Abu Dhabi with variety of different feedstock [18-21]. The similar modeling techniques that are used for coal cannot be use directly for biomass due to the large difference in the physical and chemical properties, as given in Table 1. Table 1: Comparison of physical and chemical properties of coal and biomass [22] Property Coal Biomass Density (kg/m 3 ) ~1300 ~500 Size (mm) ~0.1 ~0.3 Shape Spherical Irregular H/C (molar) 0.8 1.5 O/C (molar) 0.02~0.4 0.4~1.0 Heating value (MJ/kg) ~25 ~16 The most illustrative representation of the difference between the O/C and H/C ratio of coal and biomass is provided in Van Krevelen diagram, is given in Figure 1 that clearly shows the increased hydrogen in oxygen contents in biomass.