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Theoretical and experimental study of the influence of particle shrinkage on the thermal treatment of particulate solids in fluidized bed

A.V. Mitrofanov, N.S. Kasatkina, Y.S. Ryzhakova

Vestnik IGEU, 2016 issue 5, pp. 49—54

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Abstract in English: 

Background: Biofuel is one of promising directions of thermal power engineering development. Biofuel from agricultural and forest industry wastes can be quite efficient. However, in many cases these materials have high humidity and require deep drying before combustion, which leads to additional energy costs. Effective drying of such materials can be realized in the apparatuses with fluidized bed. But the choice and reliable justification of the process regime parameters are impossible without adequate mathematical modeling of the process. The essential feature of the process is significant variation of particle properties under thermal treatment, in particular of their mass and shrinkage, which is practically not taken into account in the known models and urges us to modernize them.

Materials and methods: The modeling of moisture content and heat distribution evolution in fluidized bed was based on the Markov chains approach. The model includes two parallel chains of cells for particles and air with the intermutual influence of transition probabilities in homologic cells. Besides, the homologic cells can exchange heat and moisture with each other at each time transition. The sizes of particles in the cells are additionally adjusted according to the current moisture content. The experimental validation of the proposed model was done on a lab fluidized bed reactor with potato cubes as a convenient test material.

Results: A model of drying kinetics in gas-solid systems has been suggested and verified. The model allows describing the evolution of the solid bed expansion and moisture content during drying. The calculation results are presented for the cases of particle shrinkage and those with constant size of particles.

Conclusions: The obtained results have shown the necessity of taking into account shrinkage phenomenon for adequate modeling of heat and mass transfer in fluidized bed.

Key words: fluidized bed, state vector, matrix of transition probabilities, particle settling velocity, heat transfer, mass transfer, moisture content, solid fuel.

References in English: 

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Ключевые слова на русском языке: 
псевдоожиженный слой, вектор состояния, матрица переходных вероятностей, скорость витания частицы, теплоотдача, массоотдача, содержание влаги, твердое топливо
Ключевые слова на английском языке: 
fluidized bed, state vector, matrix of transition probabilities, particle settling velocity, heat transfer, mass transfer, moisture content, solid fuel
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