Stochastic bubble developing model combined with Markov process of particles for bubbling fluidized beds

Целью данного исследования является проверка корреляционного метода Коутса Редферна и разработка нового метода анализа кинетических характеристик для брутто процесса термического разложения пиролизной смолы при неизотермических условиях. Указанный процесс термического преобразования был исследован экспериментально методом термогравиметрического анализа. Существует несколько кинетических моделей, чтобы анализировать механизм пиролиза в терминах формальных реакций. В рамках этого подхода кинетические параметры процесса пиролиза могут быть оценены по данным полной потери массы в процессе нагрева (термогравиметрический анализ – ТГА). Процедура термогравиметрического анализа может проводиться как в изотермических, так и в неизотермических условиях, но всегда экспериментальные данные, полученные в ее процессе, должны быть преобразованы в подходящие корреляционные соотношения. Полученные результаты показали, что реакция пиролиза протекает в диапазоне температур от 540 К до 700, К и индукционный период процесса составляет примерно 224 мин. Кинетические параметры были установлены традиционным методом Коутса –Редферна. Для снижения трудоемкости идентификационных процедур по сравнению с методом Коутса–Редферна и учета наличия индукционного периода реакции был предложен новый метод расчета кинетических параметров. В результате исследования было показано, что по сравнению с методом Коутса –Редферна предложенный способ дает более достоверную зависимость для расчета кинетических параметров. Предложенный метод использует алгоритм Коутса–Редферна для оценки механизма реакции, но величина постоянной скорости реакции определяется непосредственно из получаемых экспериментальных данных о скорости термического превращения.

/pdf/an-innovate-method-of-thermogravimetric-data-analysis-2a3zk6zp69.pdf

An innovate method of thermogravimetric data analysis

Dynamic Monte Carlo reactor modeling of calcium looping with sorbent purge and utilization decay

A one-dimensional mathematical model of particulate solids thermal treatment in a fluidized bed based on the theory of Markov chains is proposed. A feature of the model takes into account the variation of particle properties that takes place during the fluidization. This variation occurs due to thermo-physical and chemical processes that take place during particulate solids treatment in the fluidized bed. These variations affect the particle settling velocity which is the main parameter that forms the bed expansion and local velocity of flow around the particles that strongly influences the thermo-physical and chemical processes in the bed. A generalized correlation for the drag force coefficient is proposed and tested for various materials. It was necessary to have more precise calculation of the particle settling velocity in the model. The model was developed to describe the drying process in the bed. A good correlation between computed and experimental data was achieved.

A markov chain model to describe fluidization of particles with time-varying properties

Solid circulation rate (Gs) represents the mass flux of circulating particles in circulating fluidized bed (CFB) systems and is a significant parameter for the design and operation of CFB reactors. Many measuring technologies for Gs have been proposed, though few of them can be applied in industrial units. This paper presents a comprehensive study on measuring technologies, and the results indicate that though the accumulation method is most widely applied, it is constrained by the disturbance of normal particle circulation. Some publications have proposed mathematic models based on pressure drop or other parameters to establish Gs measurement models; these necessitate the accurate modeling of complicated gas-solid flows in industrial devices. Methods based on certain measurement devices to specify parameters like velocity require device endurance in the industrial operation environment and stable local gas-solid flow. The Gs measuring technologies are strongly influenced by local gas-solid flow states, and the packed bed flow in standpipes make the bottom of standpipes an ideal place to realize Gs measurement. 

/pdf/measuring-technologies-for-cfb-solid-circulation-rate-a-2vu54pdg.pdf

Measuring Technologies for CFB Solid Circulation Rate: A Review and Future Perspectives

A one-dimensional mathematical model of particulate solids fluidization based on the theory of Markov chains is proposed. Transition probabilities that form the matrix and control the migration of particles over the bed are subdivided into two types, convection and diffusion. The convection transition probabilities depend on the local particle concentration in cells of the chain and mainly define the bed expansion at certain hydrodynamic conditions. The diffusion transition probabilities form particle concentration distribution over the bed height. On the basis of the model, the heat exchange between gas and particulate solids is described. The batch fluidization model is generalized to the case of continuous fluidization that allows predicting a connection between throughput and hold-up, as well as particle residence time distribution in a bed. Some aspects of the approach are verified experimentally.

Modeling of Particle Concentration Distribution in a Fluidized Bed by Means of the Theory of Markov Chains

Theoretical Study of Particulate Flows Formation in Circulating Fluidized Bed

The objective of the study is to develop a simple yet informative model to investigate the features of the process of particulate flows formation in a circulating gas-solid fluidized bed. The propo...

Andrey V. Mitrofanov

Papers

An innovate method of thermogravimetric data analysis

Modeling of Particle Concentration Distribution in a Fluidized Bed by Means of the Theory of Markov Chains

A markov chain model to describe fluidization of particles with time-varying properties

Theoretical Study of Particulate Flows Formation in Circulating Fluidized Bed

Application of the theory of Markov chains to theoretical study of processes in a circulating fluidized bed