Devolatilization, biomass pyrolysis

Devolatilization (or pyrolysis) This step consists of the thermochemical decomposition in the absence of oxidizing agents of the cellulose, hemicellulose, and lignin compounds present in the original biomass with production of volatiles and char (Beneroso et al., 2014 Liu et al., 2009). Volatiles are produced until temperature reaches approximately 350—400° C, and include H2O (v), CO2, oxygenated vapor species, and primary oxygenated liquids. 

Our methods and experiments (UW) previously addressed composition effects in pyrolysis of RDF (Lai, et al 1993) and wood (Krieger-Brockett, et al 1997). In those papers and this one, even minor components are shown to alter pyrolysis slate when appropriate statistical methods are used. This paper briefly summarizes our work on pyrolysis product slates resulting from large- or macro-particle devolatilization (in which heat transfer is a slow process) of native biomass compositions in under-utilized species. The method has general applicability and owing to the limited scope of this article, the reader is referred to Somasundaram (1990), Lai (1991) and Rodriguez (1996) for details and extensive literature reviews with only a few relevant articles mentioned here,... 

ABSTRACT The radiative pyrolysis of wood (thick cylinders and chip beds) has been investigated experimentally for external radiative heat fluxes in the range 28-80kW/m, resulting in maximum sample temperatures of 600-950K. Radial temperature profiles, product yields and composition, and devolatilization rates have been measured. The influences of wood variety (hardwoods and softwoods) on the pyrolysis characteristics are discussed and comparisons are made with biomass (agricultural residues). 

Another direct measure of reactivity is the determination of maximum volatile yield from pyrolysis or devolatilization of any fuel. Figure 4-5 compares the maximum volatile yield of urban wood waste and sawdust to the maximum volatile yield of Black Thunder and Pittsburgh 8 coal. Note that the maximum volatile yield for both woody biomass samples exceeded 90 percent. This is in direct contrast to the coals, and to the petroleum coke as shown in Chapter 2. 

Slow pyrolysis of biomass operates at relatively low heating rates (0. l-2°C/s) and longer solid and vapor residence time (2-30 min) to favor biochar yield (Nanda et al., 2014b). Slow pyrolysis operates at temperature lower than that of fast pyrolysis, t q)ically 400 10°C and has a gas residence time usually > 5 s. Slow pyrolysis is similar to carbonization (for low temperatures and long residence times). During conventional pyrolysis, biomass is slowly devolatilized facilitating the formation of chars and some tars as the main products. This process yields different range of products with their properties dependent on temperature, inert gas flow rate and residence time. 

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