A Mathematical Model of Biomass Combustion Physical and Chemical Processes

Abstract

The numerical simulation of biomass combustion requires a model that must contain, on one hand, sub-models for biomass conversion to primary products, which involves calculations for heat transfer, biomass decomposition rate, product fractions, chemical composition, and material properties, and on the other hand, sub-models for volatile products transport inside and outside of the biomass particle, their combustion, and the char reduction/oxidation. Creating such a complete mathematical model is particularly challenging; therefore, the present study proposes a versatile alternative—an originally formulated generalized 3D biomass decomposition model designed to be efficiently integrated with existing CFD technology. The biomass decomposition model provides the chemical composition and mixture fractions of volatile products and char at the cell level, while the heat transfer, species transport, and chemical reaction calculations are to be handled by the CFD software. The combustion model has two separate units: the static modeling that produces a macro function returning source/sink terms and local material properties, and the dynamic modeling that tightly couples the first unit output with the CFD environment independently of the initial biomass composition, using main component fractions as initial data. This article introduces the generalized 3D biomass decomposition model formulation and some aspects related to the CFD framework implementation, while the numerical modeling and testing shall be presented in a second article.

A Numerical Model of Biomass Combustion Physical and Chemical Processes

“…The maximum concentrations of the species are: CO = 4.84%, CO 2 = 5.45%, and H 2 O = 0.3%, three to four times lower compared to the previous time. Carbon oxides are dominant again, as expected, water resulting from methane, ethylene, and hydrogen burning and coal decomposition (which contains a certain fraction of H and O, as seen in [1]). CO distribution is much narrower and its conversion into CO 2 occurs on a longer range, with a lower flame temperature (1300 K).…”

“…After t = 25 s the flame continually lost intensity, reaching a minimum at 55 s (T = 1300 K), after which, with accelerating decomposition of the carbon residue reached ≈1500 K at the end of the process. Figure 13 shows how the flame finally covers the entire particle, char combustion making the transition from decomposition regime II to regime I [1]. Although there are no experimental data published by Lu for this case, we have performed combustion modeling and simulation for a particle with the L/D ratio = 4, all other parameters being identical to the previous case.…”

“…The work presented herein is entirely founded on the mathematical model of biomass combustion physical and chemical processes explained in great detail in [1]. For a more complete understanding and easier assessment of this effort, we strongly encourage the reader to take it into consideration.…”

Pyrolysis of Pruning Residues from Various Types of Orchards and Pretreatment for Energetic Use of Biochar

“…Comparison of the slow and fast heating rates indicated the lower amount of solid fraction formed during FP. During SP, the dynamics of the biomass degradation was reduced, and secondary oxidation and possible combustion processes may have occurred [ 44 ]. The combination of both parameters; namely, higher heating rate and higher temperature of the pyrolysis, resulted in increased volatile fraction generation, and thus a lower biochar yield.…”

Some network models related to heat and mass transfer during thermal conversion of biomass

“…There is a wide array of mathematical models for biomass combustion, gasification, torrefaction [8,9]. Since the biomass is a porous medium, pore network models offer an alternative to continuous medium approach, see [10] for historical account and [11; 12] for more recent developments.…”