Solids Holdup of High Flux Circulating Fluidized Bed at Elevated Pressure

Abstract A comprehensive study of gas-solids flow behaviors was conducted in a novel multi-stage circulating fluidized bed (MCFB). Experiments were carried out in a cold model apparatus (a jetting fluidized bed, JFB, of 0.3 m diameter and 1.95 m tall, a riser of 0.15 m diameter and 12 m tall) at different elevated pressure, solids circulation rates and gas velocities. Geldart group B polystyrene particles of 400 μm in diameter and 1020 kg/m3 in density were used as bed materials. The characteristic of L-valve, axial and radial distributions of solids holdup were systematically tested at elevated pressures by pressure transducers with the frequency of 100 Hz and model PC6M of the optical fiber probes. Operating the L-valve at elevated pressure needs less cross-section average gas velocity compared to that at atmospheric pressure. Experimental results showed that under elevated pressure and high solids flow rate, the MCFB could more easily couple JFB with a riser, where the solids that entered could form three-level step-by-step supplement entrainment and multi-flow regimes formed. Besides, increasing operating pressure led to a higher the apparent solids holdup and local solids holdup. The local solids profiles behaved less uniform distribution at elevated pressure due to decreasing the gas velocity.

Download Full-text

Effect of elevated pressure on gas-solid flow characteristics in a circulating fluidized bed

Powder Technology ◽

10.1016/j.powtec.2020.02.046 ◽

2020 ◽

Vol 366 ◽

pp. 470-476 ◽

Cited By ~ 1

Author(s):

Daoyin Liu ◽

Jinding Hu ◽

Jialong Song ◽

Cai Liang ◽

Chuanlong Xu ◽

...

Keyword(s):

Fluidized Bed ◽

Circulating Fluidized Bed ◽

Flow Characteristics ◽

Elevated Pressure ◽

Solid Flow

Download Full-text

Particle velocity and flow development in a long and high-flux circulating fluidized bed riser

Chemical Engineering Science ◽

10.1016/s0009-2509(01)00200-7 ◽

2001 ◽

Vol 56 (18) ◽

pp. 5295-5303 ◽

Cited By ~ 70

Author(s):

J.H Pärssinen ◽

J.-X Zhu

Keyword(s):

Fluidized Bed ◽

Particle Velocity ◽

Circulating Fluidized Bed ◽

High Flux ◽

Flow Development

Download Full-text

Flow Behaviors in a High-Flux Circulating Fluidized Bed

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.1780 ◽

2008 ◽

Vol 6 (1) ◽

Cited By ~ 6

Author(s):

Xiaofang Wang ◽

Baosheng Jin ◽

Wenqi Zhong ◽

Mingyao Zhang ◽

Yaji Huang ◽

...

Keyword(s):

Pressure Drop ◽

Mass Flux ◽

Total Pressure ◽

Slip Velocity ◽

Circulating Fluidized Bed ◽

High Flux ◽

Flow Ratio ◽

Gas Velocity ◽

Solids Holdup ◽

Superficial Gas Velocity

A high-flux circulating fluidized bed coal gasifier cold model which consists of a vertical riser (0.06m-I.D.×5m-high), two downcomers (0.04m-I.D.×3.5m-high and 0.1m-I.D.×3m-high), an inertial separator, a cyclone and two solid feeding devices were established. Geldart group B particles with mean diameters of 140 ?m and densities of 2700 kg/m3 were used as bed materials. Flow behaviors were investigated with the solid mass flux ranges from 108 to 395 kg/m2 and the superficial gas velocity ranges from 7.6 to 10.2 m/s. The pressure drop, apparent solids holdups, average slip velocity and solids-to-air mass flow ratio under different operating conditions were obtained. The results showed that the riser total pressure drop increased sharply with bed height in the low elevation but slowly in the high elevation, since the solids holdup was higher in the low region than that in the high region. The solids holdup increased with the increasing of solids mass flux while it decreased with increasing superficial gas velocity. A dense suspension upflow flow (DSU) structure was found only existing in the low elevation while the rest upper region was still in the dilute phase, and the length of DSU flow structure increased with solids mass flux. The average slip velocity was found to be the strong function of apparent solids holdup; increasing apparent solids holdup leads to the increase of slip velocity. The riser total pressure drop and apparent solids holdup increase with the solids-to-air mass flow ratio.

Download Full-text

Modeling on High-Flux Circulating Fluidized Bed with Geldart Group B Particles by Kinetic Theory of Granular Flow

Energy & Fuels ◽

10.1021/ef100096c ◽

2010 ◽

Vol 24 (5) ◽

pp. 3159-3172 ◽

Cited By ~ 29

Author(s):

Baosheng Jin ◽

Xiaofang Wang ◽

Wenqi Zhong ◽

He Tao ◽

Bing Ren ◽

...

Keyword(s):

Kinetic Theory ◽

Fluidized Bed ◽

Granular Flow ◽

Circulating Fluidized Bed ◽

High Flux ◽

Group B

Download Full-text

Effects of Riser Diameter on Solids Holdup and Particle Velocity Profiles in Circulating Fluidized Bed Riser Systems

Journal of Energy Resources Technology ◽

10.1115/1.4046139 ◽

2020 ◽

Vol 142 (7) ◽

Author(s):

Ronald W. Breault ◽

Steven L. Rowan ◽

Justin M. Weber ◽

Jingsi Yang

Keyword(s):

Fluidized Bed ◽

Particle Velocity ◽

Circulating Fluidized Bed ◽

Velocity Profiles ◽

Small Scale ◽

Sauter Mean Diameter ◽

Particle Size Range ◽

Cold Flow ◽

Solids Holdup ◽

Radial Profiles

Abstract Tests were performed in a 0.1-m diameter small circulating fluidized bed (SCFB) and 0.3 m diameter cold flow circulating fluidized bed (CFCFB) riser systems located at the National Energy Technology Laboratory (NETL) to study the effects of riser diameter on the riser hydrodynamics. These tests were performed at solids circulation rates of Gs = 20 and 75 kg/m2 s and superficial gas velocities of Ug = 5.8 and 6.5 m/s using high-density polyethylene (HDPE) pellets with a density of 0.863 g/cm3, particle size range of 600–1400 µm (with a Sauter mean diameter of 871 µm, placing them in the Geldart B classification). Comparisons of riser axial pressure and solids fraction profiles, radial particle velocity profiles, and radial profiles of higher statistical moments and select chaos analysis parameters were considered. The results showed that for a given Ug and Gs, the smaller diameter riser exhibited characteristics associated with more dilute solids flow than that observed in the larger diameter riser. Additionally, the larger diameter riser exhibited a downward flow of solids near the wall under all test conditions, whereas the smaller diameter riser data exhibited little or no indications of solids downflow near the wall. These findings suggest that, from an industrial standpoint, a direct scaleup of small-scale tests cannot readily be accomplished as the solids holdup and the solids velocity profiles in small units (those normally tested in the laboratory) are not similar to those of large units and the performance of large units can therefore not be predicted from small-scale tests.

Download Full-text

Hydrodynamic experiments on a small-scale circulating fluidized bed reactor at elevated operating pressure, and under an O2/CO2 environment

Thermal Science ◽

10.2298/tsci150921068s ◽

2017 ◽

Vol 21 (2) ◽

pp. 1093-1104 ◽

Cited By ~ 1

Author(s):

Yerbol Sarbassov ◽

Azd Zayoud ◽

Pinakeswar Mahanta ◽

Sai Gu ◽

Panneerselvam Ranganathan ◽

...

Keyword(s):

Pressure Drop ◽

Fluidized Bed ◽

Atmospheric Pressure ◽

Circulating Fluidized Bed ◽

Elevated Pressure ◽

Small Scale ◽

Operating Pressure ◽

Hydrodynamic Parameters ◽

Hydrodynamic Experiments ◽

Promising Development

Pressurized circulating fluidized bed technology is a potentially promising development for clean coal technologies. The current work explores the hydrodynamics of a small-scale circulating fluidized bed at elevated operating pressures ranging from 0.10 to 0.25 MPa. The initial experiments were performed at atmospheric pressure with air and O2/CO2 environments as the fluidization gas to simulate the hydrodynamics in a circulating fluidized bed. A comparison between the effects of air and O2/CO2 mixtures on the hydrodynamics was outlined in this paper for particles of 160 ?m diameter. A small but distinct effect on axial void-age was observed due to the change in gas density in the dense zone of the bed at lower gas velocity, while only minimal differences were noticed at higher gas velocities. The hydrodynamic parameters such as pressure drop and axial voidage profile along the height were reported at two different bed inventories (0.5 and 0.75 kg) for three mean particle sizes of 160, 302, and 427 ?m and three superficial gas velocities. It was observed that the operating pressure had a significant effect on the hydrodynamic parameters of bed pressure drop and axial bed void-age profiles. The effect of solids loading resulted in an exponential change in pressure drop profile at atmospheric pressure as well as at elevated pressure. The experimental results on hydrodynamic parameters are in reasonable agreement with published observations in the literature.

Download Full-text

3D CPFD Simulation of Circulating Fluidized Bed Downer and Riser: Comparisons of Flow Structure and Solids Back-Mixing Behavior

Processes ◽

10.3390/pr8020161 ◽

2020 ◽

Vol 8 (2) ◽

pp. 161

Author(s):

Yancong Liu ◽

Yingya Wu ◽

Xiaogang Shi ◽

Chengxiu Wang ◽

Jinsen Gao ◽

...

Keyword(s):

Fluidized Bed ◽

Residence Time ◽

Circulating Fluidized Bed ◽

Operating Conditions ◽

Solids Holdup ◽

The Difference ◽

Large Clusters ◽

Small Clusters ◽

Cluster Behavior ◽

Back Mixing

The difference of gas-solids flow between a circulating fluidized bed (CFB) downer and riser was compared by computational particle fluid dynamics (CPFD) approach. The comparison was conducted under the same operating conditions. Simulation results demonstrated that the downer showed much more uniform solids holdup and solids velocity distribution compared with the riser. The radial non-uniformity index of the solids holdup in the riser was over 10 times than that in the downer. In addition, small clusters tended to be present in the whole downer, large clusters tended to be present near the wall in riser. It was found that the different cluster behavior is important in determining the different flow behaviors of solids in the downer and riser. While the particle residence time increased evenly along the downward direction in the downer, particles with both shorter and longer residence time were predicted in the whole riser. The nearly vertical cumulative residence time distribution (RTD) curve in the downer further demonstrated that the solids back-mixing in the downer is limited while that in the riser is severe. Solids turbulence in the downer was much weaker compared with the riser, while the large clusters formation near the wall in the riser would hinder solids transportation ability.

Download Full-text