China
Africa
Explore chapters and articles related to this topic
Fluidized Bed Combustion
Published in Kenneth M. Bryden, Kenneth W. Ragland, Song-Charng Kong, Combustion Engineering, 2022
Kenneth M. Bryden, Kenneth W. Ragland, Song-Charng Kong
A fluidized bed is a bed of solid particles that are set into motion by blowing a gas stream upwards through the bed. The velocity of the gas stream must be large enough to locally suspend the particles (fluidize the bed) but small enough to ensure that particles are not blown out of the bed. The bed is similar to a liquid in that it appears to be boiling and exhibits buoyancy and a hydrostatic head. Hence it is called a fluidized bed. The main components of a fluidized bed are the air plenum, the air distributor, the bed, and the freeboard as shown in Figure 17.1. The freeboard is used to disengage the particles that are thrown up above the bed and to complete the combustion of volatiles and fine particles that do not burn completely in the bed. This type of fluidized bed is called a bubbling fluidized bed. A second type of fluidized bed—a circulating fluidized bed—operates at a higher gas velocity that entrains part of the fuel and bed particles and recirculates them back into the lower part of the bed.
The Inception, Evolution and Theory of Spray-freeze-drying
Published in S. Padma Ishwarya, Spray-Freeze-Drying of Foods and Bioproducts, 2022
Later, researchers came up with an alternative approach of contacting the atomized feed with cold, dry gas in a fluidized bed at atmospheric pressure (Mumenthaler & Leuenberger, 1991) or sub-atmospheric pressure (Anandharamakrishnan et al., 2008; Anandharamakrishnan, Rielly, & Stapley, 2010). Fluidization was adopted to apply uniform heat to the frozen particles during the freeze-drying process, by leveraging the small sample dimensions, thereby reducing the drying time without the risk of particle melting and collapse. However, this is not possible to obtain with the conventional freeze-drying, wherein the latent heat of sublimation is supplied by conductive or radiative heating. Moreover, fluidized bed has the advantage of excellent heat and mass transfer due to good contact between the particles and fluids. This renders the SFD suitable for large-scale operations with good mixing between particles that lead to fast drying at a low capital cost of construction. This marked the beginning of atmospheric spray fluidized bed freeze-drying (ASFBFD) and vacuum spray fluidized bed freeze-drying (VSFBFD) (Ishwarya et al., 2015).
One-Dimensional Fluidized Bed Furnace Model
Published in Maria da Graça Carvalho, Woodrow A. Fiveland, F. C. Lockwood, Christos Papadopoulos, Combustion Technologies for a Clean Environment, 2021
Fluidized bed technology can be utilized in a wide variety of processes, such as the combustion or gasification of coal, dry exhaust-gas cleaning, drying, calcination and roasting, as well as ore-reduction processes. The modelling of two-phase flow is extremely significant in terms of the thermal design of fluidized bed combustors, and crucial for calculating combustion kinetics and kinetics of pollutant formation and reduction. Previous studies of fluidized bed models generally used a mean particle diameter; only in a few instances has the particle size distribution been mentioned. It is acknowledged, however, that there is a sorting effect in a fluidized bed as well. With this fact in mind, one can develop a simple one-dimensional model. This model can be used to calculate very plausible porosity and pressure distributions in a fluidized bed. This simultaneously facilitates the determination of circulating solid mass flow.
Advances in dewatering and drying in mineral processing
Published in Drying Technology, 2021
Benitta A. Chaedir, Jundika C. Kurnia, Agus P. Sasmito, Arun S. Mujumdar
Some advantages offered by fluidized bed drying include easy material transport, good solids mixing, high heat and mass transfer rates, high thermal efficiency, and low maintenance cost. Generally, heat input required in fluidized bed dryers is less than double the latent heat of the water evaporated, demonstrating superior thermal efficiency compared to other dryer types. The inherent drawback of huge energy consumption of fluidized bed dryers are compensated by lesser mechanical complexity and smaller footprint.[34] The performance of a fluidized bed dryer (FBD) relies on many factors such as drying temperature, fluidizing gas flow rate, fluidization velocity and overflow outlet height. The minimum fluidization velocity Umf and terminal settling velocity Ut are two key parameters for the design and operation of FBDs.
Investigation of rough rice drying in fixed and fluidized bed dryers utilizing dehumidified air as a drying agent
Published in Drying Technology, 2021
Drying rice with the use of desiccants in a closed environment can be a prolonged exchange of moisture. Therefore, there is a necessity to study the effects of desiccants on drying air along with the effects of a rapid drying system such as a fluidized bed dryer. Fluidized bed drying is seen as one of the most available technologies to achieve a higher drying rate.[19,20] In this technique, the air is blown at high speed to support the weight of the drying material, and drying takes place in a fluidized state.[21] In a fluidized bed, moisture is removed by evaporation from the grain kernels; heat is supplied for evaporation through convection from the drying air to the surface of the grain, and through conduction, the heat is supplied to the center of the grain.[22] Moisture travels in the opposite direction and evaporates in the environment through convection. Fluidized bed drying offers many advantages that include ease of handling of grains, uniform drying, and enhanced drying rate.[23–25]
A variational method for determining the hydrodynamic parameters of simplified fluidized bed equations
Published in Particulate Science and Technology, 2020
Hamid Reza Nazif, Amir Hossein Javadi
One of the most important parameters in this process is to determine the minimum fluidization velocity. This quantity is the minimum velocity where solid particles are suspended in the fluidized bed. Different methods have been used to detect this parameter so far. Caicedo et al. (2002), by performing different experiments on two-dimensional fluidized beds, have indicated that the minimum fluidization velocity is the function of the fluidized bed weight, solid diameter, and width of the column.