Testing of cold scaled bed modeling for fluidized-bed combustors

The overall objectives of this project are to develop experimental techniques for measuring the forces of fluidized particles, and to predict the solid-gas performance in fluidized beds by using data analysis system, and by elucidating the intrinsic mechanism of erosion and attrition phenomena in fluidized beds. The reduction of erosion and attrition rates is one of the critical engineering problems for the design and operation of fluidized bed combustors. Specifically, the objectives are to: (1) develop the experimental techniques to measure the forces of solid particles prevailing in fluidized beds: (2) measure and characterize the forces of solid particles in various types of fluidized beds with various configurations (conventional and spouted fluidized beds) and with different scales (10, 20, and 30cm) under various fluidization conditions (particle size, bed aspect ratio and gas velocity); (3) find and verify the mechanism of erosion rates of in-bed tubes and attrition rates of fluidized particles by forces of solid particles in fluidized beds. We developed three different kinds of measurement methods, i.e., fracture sensitive sensor, piezoelectric sensor and gas pressure fluctuation method. By using these methods the exact forces of solid particles, including the transient corporate in fluidized beds, were systematically measured. Simultaneously, the erosion rates of in-bed tubes and attrition rates of fluidized particles were measured. 69 figs., 9 tabs.

The objective of this work is to recognize and interpret the signals of transient motion of bubbles (slugs) in fluidized beds by measuring and utilizing the signals of transient motion of solid particles. The two signals were measured simultaneously and also synchronized by using the TTL signal technique in the same fluidized beds. Also, a simultaneous study of video bubble image, transient force and pressure signals was initiated in a two dimensional fluidized bed. we successfully synchronized three signals so that the relationship of bubble behavior and force pressure signals can be identified and characterized. It has been found that bubble image can well be correlated to the transient force signal of solid particles under certain conditions in three dimensional fluidized beds. Accordingly, it seems that the transient force signals can significantly help understanding the transient motion of bubbles (slugs), which is important to design the fluidized beds.

Data science integrated with computational fluid dynamics for particle collision modeling in fluidized bed

The objective of this research is to predict the erosion rates of in-bed tubes of specific materials in fluidized beds by using a novel approach that we have recently developed. This technique assesses the erosion rates of in-bed tubes by considering two key factors: the peaks of the transient forces of solid particles and the characteristic erosion properties of tube materials concerned. We developed a simple characterization method to assess the erosion rates of in-bed tubes. With this method, an erosion index considering the surface area, weight loss of in-bed tubes, and the operating time, was used. A systematic study was carried out in a 411 rectangular fluidized bed to study the relationship between erosion rate and maximum transient forces of solid particles in fluidized beds. Three different kinds of metal tubes, with well defined tensile strength (at) and elasticity modulus (E), were used. They are copper, aluminum and stainless steel. By considering the tensile strength and elasticity modulus, together with the peaks of transient forces of solid particles, a characteristic erosion function was introduced. This characteristic function was found to have a good correlation with the erosion rate. Thus, the prediction of in-bed tube erosion rates was achieved, when the peaks of transient forces of solid particles and tube material`s characteristic properties are known.

A technique for determining devolatilization rates of large coal particles in a fluidized bed combustor

A technique has been developed to give a quantitative measure of the contacting efficiency of liquid feed onto particles in a hot fluidized bed for petroleum applications. Copper naphthenate was used as a tracer to measure the coating of atomized bitumen feed onto solid coke particles in a fluid coking pilot plant. The pilot plant consisted of a reactor vessel, where bitumen was injected into the reactor as feed, and a regeneration vessel, where coke particles were heated and circulated back to the reactor. Atomized bitumen droplets were injected through a feed nozzle into the reactor section. A small concentration of copper naphthenate tracer, pre-diluted with bitumen, was injected upstream of the nozzle, following a step function with time. As the bitumen reacted, the copper formed solid deposits on the surface of the particles, effectively labeling the particles that had been contacted by the bitumen droplets. Frequent coke samples from the solids exiting and entering the reactor were taken during and after the injection of the tracer.Two types of measurements were conducted on the coke samples; bulk copper concentration in the samples, using Inductively Coupled Plasma (ICP), and copper concentration on individual coke particles using energy-dispersive X-ray (EDX) analysis. The data for bulk copper concentration confirmed that the solids were mixed rapidly in the reactor, approximating a Continuous Stirred Tank Reactor (CSTR). The EDX analysis of individual coke particles demonstrated, however, that a significant fraction of the coke particles within the samples were not labeled with copper. This result indicated that many of the particles in the fluidized bed were not contacted by bitumen in the reactor. Consequently, the tracer technique was used to compare the coating efficiency of bitumen on coke particles by operation of different nozzle designs.

Author index

Modelling and experimental validation of a fluidized-bed reactor freeboard region: Application to natural gas combustion

Biomass energy has attracted considerable attention as a renewable and clean energy source that can be stored and transported effectively. A critical component in this context is the fluidized bed, which plays a vital role in biomass energy utilization. An in-depth understanding of the flow characteristics of non-spherical biomass particles within the fluidized bed is essential for improving energy efficiency. This study utilizes a combination of numerical simulations and experimental analysis to explore the flow patterns of biomass particles under eight distinct drag correlations. The investigation covers various flow regimes in the fluidized bed, concentrating on critical parameters such as flow evolution, gas-phase pressure distribution, particle phase velocity vectors, bed pressure drop, particle mixing characteristics, bed expansion height, and the energy-dynamic behavior of the particles. The results indicate that the Ergun resistance model closely matches the experimental data, particularly regarding the flow evolution of the particles. This model shows a more uniform mixing of the particles and greater stability in the magnitude and frequency of pressure fluctuations at the bed surface. This stability is reflected in the average pressure drop, highlighting the enhanced performance of the fluidized bed. Overall, this research sheds light on the intricate dynamics of non-spherical biomass particles in fluidized beds and provides valuable insights for optimizing particle design. By focusing on design enhancements, it is possible to achieve higher combustion efficiency, supporting the broader objective of sustainable energy utilization. In summary, this study emphasizes the significance of precise modeling and understanding of flow characteristics in the fluidized bed, which is crucial for advancing biomass energy technologies.

Comparison of hydrodynamics and operational characteristics of a multistage fluidized bed with high-density and low-density powders

Collison of sand particles in fluidized bed plays a very important role in determining hydrodynamics of fluidized bed. Effect of coefficient of restitution on hydrodynamics on 300 µm particles in gas-solid fluidized bed was investigated. Eulerian-Eulerian model was used for simulating hydrodynamics of fluidized bed. For investigation, different values of coefficient of restitution which correspond to different values of elasticity of particles were used. No bubbles were found for perfectly elastic collisions. With decrease in the value of coefficient of restitution from 1 to 0.8, bubble formation shows a positive effect.

Gas–solid fluidized beds are complex particle systems, and the electrostatic behavior of particles in fluidized beds is even more complex, which is influenced by numerous factors such as particle properties and operating conditions. Current studies focus on the effect of a certain factor on particle charging without a global picture. Furthermore, there is no mathematical model that can describe the interaction of multiple factors on particle charging because it is difficult to build a model for such a complex system. Therefore, a new approach is needed. In this study, a model capable of accurately predicting the surface charge density of particles in monodispersed gas–solid fluidized beds within a certain range was developed based on the literature and experimental data through several machine learning methods including kernel ridge regression (KRR), support vector machine regression (SVR), and multilayer perceptron (MLP). SVR and MLP models gave the best results with R2 equal to 0.980 and 0.979, respectively. However, the sensitivity analysis showed that the MLP model was more reliable than the SVR model. In conclusion, the feasibility of using machine learning to analyze the charging behavior of particles in fluidized beds is demonstrated, and the proposed MLP model can serve as an accurate correlative tool for fast and effective estimation of particle surface charge density in gas–solid fluidized beds.

Axial mixing of fine particles in fluidized beds

Pulsating flow effect on the segregation of binary particles in a gas–solid fluidized bed

Mass transfer in fluidized beds is an important operation for separation processes. Two effects can be achieved by using fluidized beds in mass transfer processes increasing interface area and relative movement between the phases. These effects are both desirable because they lead to greater process rates. This paper presents an experimental investigation regarding mass transfer from the wall of a column to the fluid in a fluidized bed of inert spherical particles. The experiments were conducted in column 40 mm in diameter with spherical particles 0,8-3 mm in diameter and water as one fluidizing fluid. The method of dissolution of benzoic acid was used to provide very low mass flux. The average wall-to-fluid mass transfer coefficients were determined for two systems: single-phase fluid flow and a fluidized bed of inert particles The measurements encompassed a Reynolds number range from 100-4000 for single-phase flow and 600-4000 in fluidized beds. The mass transfer coefficients for both systems were calculated from weight loss of benzoic acid. The effects of superficial liquid velocity and particle diameter on the mass transfer coefficient were investigated. It was found that mass transfer was more intensive in the fluidized bed in comparison with single phase flow. The best conditions for mass transfer were reached at a minimum fluidization velocity, when the mass transfer coefficient had the greatest value. The experimental data were correlated in the form: jd = f(Re), where jd is the dimensionless mass transfer factor and Re the Reynolds number.