Simultaneous drying and pyrolysis of solid fuel particles

Saastamoinen, Jaakko; Richard, Jean-Robert

doi:10.1016/0010-2180(96)00001-6

Cited by 81 publications

(45 citation statements)

References 27 publications

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“…These include the i) first order kinetic evaporation model [12,33,36,[41][42][43], ii) equilibrium model [29,[44][45][46], and iii) a constant temperature model (also known as the heat sink model) [34,39,40,[47][48][49]. The first order kinetic approach is a simplified approach which treats the evaporation rate as a thermally activated process described with a first order Arrhenius rate equation.…”

Section: Dryingmentioning

confidence: 99%

Modeling kinetics-transport interactions during biomass torrefaction: The effects of temperature, particle size, and moisture content

Bates

Ghoniem

2014

Fuel

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ABSTRACT:A comprehensive one-dimensional model accounting for the effects of heat and mass transfer, chemical kinetics, and drying was developed to describe the torrefaction of a single woody biomass particle. The thermochemical sub-models depend only on previously determined or measured characteristics, avoiding the use of fitting or tuning parameters and enabling a rigorous energy balance of the process. Moreover, a high temperature drying sub-model is introduced which overcomes the difficulties associated with existing approaches to give physically consistent results, smooth implementation, and numerical stability. The particle model was validated against experimental data from the literature for intraparticle temperature profiles, particle mass and energy yields over a range of particle sizes and reaction temperatures. The modeling results describe well the three distinct stages observed during the torrefaction of large particles including the heatup, drying, heat release due to exothermic reactions resulting in thermal overshoot, followed by thermal equilibrium where conversion is governed by mass loss kinetics. The nonlinear effects of particle size, temperature, moisture content, and residence time on the mass and energy yields are quantified and explained. Larger particles exhibit a significant internal temperature gradient and strong temperature overshoot especially at the centerline. The magnitude of the overshoot is a function of the conductivity, particle size, and average heat release rate. Because of the rise in the reaction rate, higher temperatures increase the sensitivity of the process to particle size. Due to the dependence of drying rate on heat transfer limitations, the sensitivity of torrefaction to initial moisture content increases strongly with particle size. Highlights: 1D coupled model describes the dynamics of drying and torrefaction of a single particle  Model predicts particle temperature overshoot, elemental, and energy balance  Validated against single particle experimental results from literature  Larger particles convert more non-uniformly with higher thermal overshoot.  Higher temperatures and increased moisture content exacerbate particle size effects

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Section: Dryingmentioning

confidence: 99%

Modeling kinetics-transport interactions during biomass torrefaction: The effects of temperature, particle size, and moisture content

Bates

Ghoniem

2014

Fuel

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“…A model, in which the driving force is the difference between the instantaneous density and the final density at that temperature, ρ-ρ f (T p ), instead of commonly applied difference between instantaneous density and the final density at some indefinite future temperature T f , ρ-ρ f (T p ), better describes the real situation [41]. In this case the rate of pyrolysis is modelled by Eq.…”

Section: Heating Drying and De-volatilization Of A Biomass Particlementioning

confidence: 99%

“…The drying delays devolatilization and the processes become overlapping [41] for large particles. This is illustrated in Figure 4.…”

Section: Heating Drying and De-volatilization Of A Biomass Particlementioning

confidence: 99%

“…For small particle heating up and drying take place before significant pyrolysis takes place and much of the volatiles can be released above the bed. For a large particle drying and pyrolysis can be overlapping [41]. Then more volatiles can be released in the bed, since moister particle is also heavier.…”

Section: Division Of Combustion Of a Particle In The Dense Bed And Abmentioning

confidence: 99%

“…However, particles may be completely dried before pyrolysis and before reaching the critical weight and then drying will have no effect on the release profile. Models can be used to estimate, if drying and pyrolysis are overlapping [41,50].…”

Section: Division Of Combustion Of a Particle In The Dense Bed And Abmentioning

confidence: 99%

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Release Profile of Volatiles in Fluidised Bed Combustion of Biomass

Saastamoinen¹

2014

J Fundam Renewable Energy Appl

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A simplified model for the release profile of volatiles in fluidised and circulating fluidised beds is presented. The location of the release of volatiles in the furnace depends on the interplay of flow of fuel particles affecting their location and heating of fuel particles affecting rates of drying and pyrolysis and consequently the mass of fuel particles. The coupled equations describing heating, de-volatilization including drying, elutriation and movement of particles are solved to find the release profile. Large heavy particles remain in the dense bed whereas light particles are entrained by the gas and elutriated from the bed to the riser. The situation is dynamic, since fuel particles lose weight due to release of moisture and volatiles and decrease in size due to shrinkage affecting their movement and escape from the lower dense bed to the riser. The model is based on the following the fate of a small batch of fuel particles undergoing de-volatilization and elutriation from the dense bed. The model predicts the location of the release of volatiles and the profile of the release of volatiles in the riser. Part of volatiles is released in the dense bed and the rest above the bed in the riser.

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