Chemical and Process Engineering Research www.iiste.org ISSN 2224-7467 (Paper) ISSN 2225-0913 (Online) Vol.28, 2014 1 Numerical Investigation of the Effects of Reactor Pressure on Biomass Devolatilization in Thermally Thick Regime Pious O. Okekunle 1* , Daniel I. Adeniranye 1 , Emmanuel A. Osowade 2 1. Department of Mechanical Engineering, Faculty of Engineering and Technology, Ladoke Akintola University of Technology, P.M.B. 4000, Ogbomoso, Oyo state, Nigeria. 2. Department of Mechanical Engineering, Faculty of Technology, Obafemi Awolowo University(O.A.U.), Ile- Ife, Osun state, Nigeria. *Email of the corresponding author: pookekunle@lautech.edu.ng Abstract Effects of reactor pressure on biomass devolatilization in thermally thick regime were numerically investigated in this study. Wood pellet ( = 400   3 ⁄ , ∅ 10  and length 20 ) was modeled as a two-dimensional porous solid and pyrolysis was simulated at a heating rate of 30 K/s and final reactor temperature of 973 K for five different reactor pressures [vacuum; 0.0001 and 0.01 atm, atmospheric;1 atm and pressurized; 10 and 100 atm, regions]. Transport equations, kinetic models, intra-particle pressure generation equation and energy conservation equation were coupled and simultaneously solved to simulate the pyrolysis process. Solid mass conservation equations were solved by first order Euler Implicit Method. Darcy’s law was used to estimate intra - particle flow velocity. Finite Volume Method was used to discretize the transport, energy conservation and pressure generation equations. Results showed that even in thermally thick regime, increase in reactor pressure does not affect the rate of primary tar generation. Findings also revealed that the rates of generation of secondary products at atmospheric and pressurized regions are not significantly different. Further increase in reactor pressure in the pressurized region resulted in a slight reduction in the peak of secondary products generation rate. Results further showed that increase in reactor pressure reduced intra-particle temperature gradient especially in the pressurized region, thereby causing process time elongation. As would be expected, tar release rate decreased with increase in reactor pressure while gas release rate increased in both atmospheric and pressurized regions. Keywords: Biomass, pyrolysis, pressure effects, thermally thick regime, intra-particle secondary reactions 1. Introduction The need for alternative sources of energy, which are environmentally friendly, has been realized the world over. Aside from the fact that fossil fuels threaten the environment by emitting greenhouse gases, their reserves are getting depleted. This has made energy analysts uncertain about the possibility of fossils meeting future energy demand. Subsequently, biomass energy has been receiving attention and many research works are still ongoing to explore its potentials. Pyrolysis and gasification are thermochemical routes to recover energy locked up in biomass and agricultural residues. Many research works have been carried out for better understanding of the effects of various process parameters, physical phenomena and sample nomenclature on these processes [1-13]. Of recent, we have investigated the effects of reactor pressure on pyrolysis in thermally thin regime [14]. It was found out that pressure increase within vacuum region (0.0001 - 0.01 atm) and within pressurized region (10 – 100 atm) has no significant effect on the rate of primary tar production, primary tar intra-particle secondary reactions rates, and gas and tar release rates. However, increase in pressure from vacuum to atmospheric, and from atmospheric to pressurized region increased primary tar residence time within the pyrolyzing solid, thereby enhancing intra-particle secondary reactions. In most commercial boilers and gasifiers, biomass samples used are usually within the thermally thick regime [15]. In this regime, there exists a significant intra-particle temperature gradient which will affect various physical phenomena and the kinetics of chemical reactions taking place during pyrolysis. Therefore, this study invesigates the effects of reactor pressure on pyrolysis in thermally thick regime.