Investigation on Complex Pressure Fluctuations in a Gas-Solids Circulating Fluidized Bed Rieser

2012 ◽  
Vol 538-541 ◽  
pp. 610-615
Author(s):  
Jun Xu ◽  
Xing Xing Chen ◽  
Gui Lei Wang ◽  
Yao Dong Wei
Keyword(s):  
Fluidized Bed ◽  
Pressure Fluctuation ◽  
Circulating Fluidized Bed ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Axial Direction ◽  
High Amplitude ◽  
Solid Mass ◽  
Two Phase ◽  
Mass Fluxes

The experiment is carried out in a 13-meter-high circulating fluidized bed(CFB) to investigate gas-solid two-phase flow by pressure sensor. The axial pressure and pressure fluctuation are measured in different solid mass fluxes. With the solid mass flux increasing, pressure gradually increases, and pressure gradually decreases along the riser upwards. The characteristic of pressure fluctuation in the riser is analyzed, which indicates that pressure fluctuation in the riser originates from the inlet. The intensity of the pressure fluctuation decreases along the riser upwards. This pressure fluctuation is composed of two types: one is of low frequency and high amplitude, which is resulted from unstable feeding to the riser and keeps coherent along the axial direction. And the other is of high frequency and low amplitude, which is the result of a variety of factors, such as cluster movement, gas-solid interaction and gas velocity fluctuation.

scholarly journals Systematic Study of Pressure Fluctuation in the Riser of a Dual Inter-Connected Circulating Fluidized Bed: Using Single and Binary Particle Species

Processes ◽  
2019 ◽  
Vol 7 (12) ◽  
pp. 890 ◽  
Author(s):  
Yusif A. Alghamdi ◽  
Zhengbiao Peng ◽  
Caimao Luo ◽  
Zeyad Almutairi ◽  
Behdad Moghtaderi ◽  
...  
Keyword(s):  
Fluidized Bed ◽  
Pressure Fluctuation ◽  
Circulating Fluidized Bed ◽  
Pressure Fluctuations ◽  
Single Species ◽  
Terminal Velocity ◽  
Operating Conditions ◽  
Cold Flow ◽  
Fluidization Regime ◽  
Spectrum Density

This study systematically investigates the pressure fluctuation in the riser of a dual interconnected circulating fluidized bed (CFB) representing a 10 kWth cold-flow model (CFM) of a chemical-looping combustion (CLC) system. Specifically, a single-species system (SSS) and a binary-mixtures system (BMS) of particles with different sizes and densities were utilized. The pressure fluctuation was analyzed using the fast Fourier transform (FFT) method. The effect of introducing a second particle, changing the inventory, composition (i.e., 5, 10 to 20 wt.%), particle size ratio, and fluidization velocity were investigated. For typical SSS experiments, the results were similar to those scarcely reported in the literature, where the pressure fluctuation intensity was influenced by varying the initial operating conditions. The pressure fluctuations of BMS were investigated in detail and compared with those obtained from SSS experiments. BMS exhibited different behaviour; it had intense pressure fluctuation in the air reactor and in the riser when compared to SSS experiments. The standard deviation (SD) of the pressure fluctuation was found to be influenced by the fluidization regime and initial operating conditions, while the power spectrum density (PSD) values were more sensitive to the presence of the particles with the higher terminal velocity in the binary mixture.

The Local Heat Balance in a Stationary Fluidized-Bed Furnace Burning Biomass Fuels

2003 ◽  
Author(s):  
Fredrik Niklasson ◽  
Filip Johnsson
Keyword(s):  
Fluidized Bed ◽  
Combustion Rate ◽  
Heat Balance ◽  
Circulating Fluidized Bed ◽  
Local Heat ◽  
Splash Zone ◽  
Two Phase ◽  
Bed Temperature ◽  
Temperature Constant ◽  
The Vertical Distribution

This work investigates the influence of biomass fuel properties on the local heat balance in a commercial-scale fluidized bed furnace. Experiments with different wood based fuels were performed in the Chalmers 12 MWth circulating fluidized bed boiler, temporarily modified to run under stationary conditions. A two-phase flow model of the bed and splash zone is applied, where the combustion rate in the bed is estimated by global kinetic expressions, limited by gas exchange between oxygen-rich bubbles and a fuel-rich emulsion phase. The outflow of bubbles from the bed is treated as “ghost bubbles” in the splash zone, where the combustion rate is determined from turbulent properties. It is found that a large amount of heat is required for the fuel and air to reach the temperature of the bed, in which the heat from combustion is limited by a low char content of the fuel. This implies that a substantial fraction of the heat from combustion of volatiles in the splash zone has to be transferred back to the bed to keep the bed temperature constant. It is concluded that the moisture content of the fuel does not considerably alter the vertical distribution of heat emitted, as long as the bed temperature is kept constant by means of flue gas recycling.

The Hydrodynamics Studies on Loop Seal in CFBC Boiler Using CFD Analysis

2019 ◽  
Vol 15 (1) ◽  
Author(s):  
M. Vivekanandan ◽  
N. Anantharaman ◽  
M. Premalatha
Keyword(s):  
Pressure Drop ◽  
Circulating Fluidized Bed ◽  
Unit Length ◽  
Mechanical Valve ◽  
Sand Particle ◽  
Cfd Analysis ◽  
Solid Mass ◽  
Mass Fluxes ◽  
Computational Fluid Dynamics Cfd ◽  
Good Agreement

Abstract In a circulating fluidized bed (CFB), the loop seal is an important component which recirculates the solids captured by the cyclone to the bottom of the riser and avoids the direct flow of gas from high-pressure riser to the low-pressure cyclone. Most of the CFBC systems employ a Non-Mechanical valve, and its function has been investigated by many researchers. In this work, the flow of solid particle within the loop seal has been studied elaborately, and various design and operating parameters of the loop seal were analyzed in detail using Computational Fluid Dynamics (CFD). The CFD study has handled a loop-seal of dimension 110 mm × 430 mm × 400 mm high. This analysis has been done with a 200 µm sand particle and it is checked for its flow ability through various sizes and by altering the L/H ratio for three solid mass fluxes and for three L/H ratios of loop seal. The rate of solid mass flux depends on the length of the horizontal passage connecting the recycle cycle compartment of the loop seal with the supply chamber and hence the solid flow rate and the pressure difference per unit length are directly proportional to the length of the chamber or passage. Hence, L/H ratio is taken as a driving variable for the optimum performance of loop seal. The CFD analysis results reveal that the aeration of the solid to be used within the loop-seal should be higher than the Minimum Fluidization velocity. Also, keeping the length of the horizontal passage constant and varying the height of the passage will reduce the pressure drop. The pressure drop across the horizontal passage decreases up to a certain L/H ratio after which it increases. By comparing the three L/H ratios, L/H ratio of 2.62 is having a lesser pressure drop for the three mass fluxes. L/H ratio of 2.62 is having a good fluidization phenomenon and also the flow from the recycle chamber is more in comparison to the other L/H ratios. Experimental data from the literature is in good agreement with the CFD results.

Liquid–solid mass transfer in a two phase fluidized bed bioreactor

2008 ◽  
Vol 135 (1-2) ◽  
pp. 135-140 ◽  
Author(s):  
L. Prasanna Lakshmi ◽  
Y. Pydi Setty
Keyword(s):  
Mass Transfer ◽  
Fluidized Bed ◽  
Solid Mass ◽  
Two Phase ◽  
Fluidized Bed Bioreactor

Detection of gas-solid flow faults of a circulating fluidized bed using pressure fluctuations in wind caps

2016 ◽  
Vol 33 (7) ◽  
pp. 2240-2251 ◽  
Author(s):  
Hua-wei Jiang ◽  
Jian-qiang Gao ◽  
Hong-wei Che ◽  
Jun-fu Lu ◽  
Fu-mao Wang ◽  
...  
Keyword(s):  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Pressure Fluctuations ◽  
Solid Flow

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.

Flow behaviors in the downer of a large-scale triple-bed combined circulating fluidized bed system with high solids mass fluxes

2011 ◽  
Vol 66 (18) ◽  
pp. 4212-4220 ◽  
Author(s):  
Guoqing Guan ◽  
Chihiro Fushimi ◽  
Masanori Ishizuka ◽  
Yu Nakamura ◽  
Atsushi Tsutsumi ◽  
...  
Keyword(s):  
Fluidized Bed ◽  
Large Scale ◽  
Circulating Fluidized Bed ◽  
High Solids ◽  
Mass Fluxes

Characteristics of Circulating Fluidized Bed Evaporator with Vapor-Liquid-Solid Three-Phase Flow

2012 ◽  
Vol 455-456 ◽  
pp. 1618-1626 ◽  
Author(s):  
Ji Tian Song ◽  
Jun Chi ◽  
Han Fei Zhang ◽  
Zhen Ying Liu
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Research Work ◽  
Correlation Equation ◽  
Evaporation Process ◽  
Two Phase ◽  
Heat Transfer Efficiency ◽  
Three Phase ◽  
Three Phase Flow

In this paper, pumpkin juice concentrations were carried out using a three-phase circulating fluidized bed evaporator. The flow and heat transfer characteristics of this evaporation process were investigated and parametric studies were conducted to identify the governing parameters in the process. It was found that compared with two-phase evaporation process, addition of inert particles improved the heat transfer efficiency by 35% and also inhibit forming and clean fouls during the pumpkin juice concentration. A correlation equation of boiling heat transfer coefficient was established for the three-phase circulating fluidized bed evaporator. This research work improves the understanding of the three-phase circulating fluidized bed evaporator and benefit to its wider application in foodstuff field.

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