Investigating the flow structures in semi-cylindrical bubbling fluidized bed using pressure fluctuation signals

2019 ◽  
Vol 30 (6) ◽  
pp. 1247-1256
Author(s):  
Seyedeh Mahsa Okhovat-Alavian ◽  
Jamshid Behin ◽  
Navid Mostoufi
Keyword(s):  
Fluidized Bed ◽  
Pressure Fluctuation ◽  
Flow Structures ◽  
Bubbling Fluidized Bed

Horizontal Pressure Fluctuation in Bubbling Fluidized Bed

2003 ◽  
Author(s):  
Vesa V. Walle´n
Keyword(s):  
Pressure Gradient ◽  
Fluidized Bed ◽  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
Middle Part ◽  
Biomass Combustion ◽  
Bottom Part ◽  
Pressure Transducers ◽  
Bubbling Fluidized Bed ◽  
Horizontal Pressure

Pressure measurements were conducted in a two-dimensional hot atmospheric bubbling fluidized bed reactor in the laboratory of Energy and Process Engineering at Tampere University of Technology. A set of six fast pressure transducers was used to detect the rapid pressure fluctuations inside the bubbling bed of the reactor. These pressure transducers were placed both vertically and horizontally into the reactor. From these measurements it was found that the vertical pressure fluctuation took place at the same time at different levels of the bed. Also the same fluctuation could be seen under the air distributor. The horizontal pressure fluctuation was found to vary both by place and time. At the bottom part of the bed the highest pressure peaks was found at centre of the bed. Most of the time there was a pressure gradient the highest pressure being in the centre of the bed. This gradient creates horizontal flow of gases from middle to the sides. The velocity of this flow varies with the size of the pressure gradient. The opposite effect can be found in the upper part of the bed. The highest pressure was no more in the middle part of the bed. Instead, it was found to be between the centre of the bed and left and right walls. The pressure was low at the walls but also rather low at the middle of the bed. There must be flow towards the walls and to the centre axis. These pressure fluctuations can provide an explanation for the well-known “wandering plume” effect. They can also give a tool to better describe the mixing inside a bubbling fluidized bed. This kind of tool is needed when biomass combustion is modelled in bubbling fluidized bed.

Characterization of the flow in a gas-solid bubbling fluidized bed by pressure fluctuation

2017 ◽  
Vol 174 ◽  
pp. 93-103 ◽  
Author(s):  
Jie Xiang ◽  
Qinghai Li ◽  
Zhongchao Tan ◽  
Yanguo Zhang
Keyword(s):  
Fluidized Bed ◽  
Pressure Fluctuation ◽  
Bubbling Fluidized Bed

Gas-Mixing in Bubbling Fluidized Bed Combustors: Hydrodynamics and Macromixing Associated With Bubble Bursting at the Bed Surface

2003 ◽  
Author(s):  
R. Solimene ◽  
A. Marzocchella ◽  
P. Salatino ◽  
R. Ragucci
Keyword(s):  
Fluidized Bed ◽  
Fluid Dynamic ◽  
Volatile Matter ◽  
Solid Fuels ◽  
Flow Structures ◽  
Specific Reference ◽  
Gas Mixing ◽  
Fluidized Bed Combustion ◽  
Bubble Bursting ◽  
Bubbling Fluidized Bed

Gas-mixing phenomena may play a significant role in fluidized bed combustion of solid fuels. Issues associated with gas mixing include: a) effectiveness of mass transfer between the bubble and the emulsion phases in the bed; b) degree of mixing between segregated gaseous streams in plume-like or bubbly flow in the bottom bed; c) extent of mixing between segregated gaseous pockets/streams in the splashing zone or in the upper freeboard. Among the others, issues b) and c) turn out to be relevant to fluidized bed combustion of high-volatile solid fuels (biomass, RDF, etc.). In this case, the rate of gas mixing often overcomes intrinsic kinetics as the rate-controlling step in volatile matter burn-out, especially under “stratified” combustion conditions. Despite several and significant contributions to the subject, understanding of gas-mixing in bubbling fluidized beds is still poor and calls for additional investigation. The present work aims at investigating gas-mixing in bubbling fluidized bed with specific reference to the above issue c). A laser assisted imaging technique has been used to characterize the hydrodynamic patterns associated with the bursting of either isolated bubbles or couples of closely time-delayed bubbles at the surface of a fluidized bed. Quantitative image analysis procedures were exploited in order to assess parameters defining the general fluid-dynamic behaviour and macromixing of the bubble-generated gas pockets with the mainstream gas. The formation of toroidal flow structures upon bubble bursting is highlighted in the case of isolated bubbles. The toroidal pockets entrain mainstream gas and grow accordingly while rising along the splash zone. Toroidal flow structures are observed also in the case of couples of closely time-delayed bubbles, but interference between leading and trailing pockets leads to more complex structures characterized by multiple incoherent eddies. The relevance of macromixing to volatile matter burning under conditions of stratified fluidized bed combustion is assessed and discussed.

Experimental Study of Defluidization by Continuous Water Injection into a Gas-Solid Fluidized Bed Using Pressure Fluctuation Measurements

2015 ◽  
Vol 798 ◽  
pp. 160-164 ◽  
Author(s):  
Flavia Tramontin Silveira Schaffka ◽  
Giulia Kaminski Tramontin ◽  
Maria Regina Parise
Keyword(s):  
Fluidized Bed ◽  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
Water Injection ◽  
Fixed Bed ◽  
Experimental Tests ◽  
Flow Rates ◽  
Bubbling Fluidized Bed ◽  
Inner Diameter ◽  
Bed Material

This work studies the induced defluidization condition of a gas-solid fluidized bed system when distilled water is continuously injected into the bed of particles. Experimental tests carried out to different water flow rates were analyzed through a technique based on pressure signals measurements. The bed material used was glass beads (Geldart D particles), with mean diameter of 1.55 mm. Experiments were performed in an acrylic Plexiglas tube with 0.11m in inner diameter and 1.0 m in height, with the bed led from an initially bubbling regime up to attain a fixed bed condition. Pressure fluctuations were acquired and processed using LabVIEW 10.0TMsoftware. Results showed that the defluidization condition promoted by water injection in a bubbling fluidized bed can be efficiently identified using pressure fluctuation measurements.

Analyzing dominant particle-flow structures inside a bubbling fluidized bed

2019 ◽  
Vol 77 ◽  
pp. 232-241
Author(s):  
Mohammad Reza Haghgoo ◽  
Donald J. Bergstrom ◽  
Raymond J. Spiteri
Keyword(s):  
Fluidized Bed ◽  
Particle Flow ◽  
Flow Structures ◽  
Bubbling Fluidized Bed
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