Modeling and simulation of biomass pyrolysis processes
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abstract
Pyrolysis is a thermochemical process where organic matter is decomposed into gaseous products,
oils constituted by tars, and non-volatilized residual char, through the elevation of the system
temperature (400-800°C), in the absence of oxygen. This process can be modeled and simulated for
deeper analysis and optimization. However, since the process is clearly influenced by a high number
of operational parameters such as temperature, pressure and dozens of simultaneous parallel
reactions, its simulation becomes significantly complex. Thus, the aim of this work is the modeling of
a more robust pyrolysis process, considering more components present in tar composition, as well as
the evaluation of pyrolysis products distribution under different pyrolysis temperatures: 400, 500 and
600°C. Hence, a model was developed based on second-order equations [1], using pyrolysis
temperature as the main variable, achieving as result the yield of three macro components: gases, tar
and residual char. The gas fraction is composed by: carbon monoxide (CO), carbon dioxide (CO2),
methane (CH4) and hydrogen (H2); tar fraction is constituted by: benzene (C6H6), toluene (C7H8) and
naphthalene (C10H8), and the residual char is accompanied by ash in its composition. Simulation was
implemented using biomass data based on the composition of olive residues applying the chemical
process simulation software UniSim Design. The modeling first step is biomass decomposition in a
conversion reactor, applying the yields obtained using the previous equations, while the second step
is the decomposition of residual char in a yield reactor, resulting in the elemental constituents: carbon
(C(s)), hydrogen gas (H2), oxygen gas (O2), nitrogen gas (N2), solid sulfur (S(s)), and ash.
It is possible to note that the pyrolysis model results (see Table 1), implemented with the Software
UniSim Design, show, in general, compatibility with the results available in the literature [2, 3]. The
model reveals low sensitivity for the yield results, when using different sources of biomass with similar
compositions, possibly due to the use of the temperature as the main variable
This work is funded by the Portuguese Foundation of Science and Technology (FCT) within the framework of the
SUBe Project, ref.: PCIF/GVB/0197/2017. The authors are grateful to the Foundation for Science and Technology
(FCT, Portugal) for financial support through national funds FCT/MCTES (PIDDAC) to CIMO (UIDB/00690/2020 and
UIDP/00690/2020) and SusTEC (LA/P/0007/2021
