Measurement of Two Kinds of Granular Temperatures, Stresses, and Dispersion in Bubbling Beds

2005 ◽  
Vol 44 (5) ◽  
pp. 1329-1341 ◽  
Author(s):  
Jonghwun Jung ◽  
Dimitri Gidaspow ◽  
Isaac K. Gamwo
Keyword(s):  
Bubbling Beds

CFD simulations of bubbling beds of rough spheres

2008 ◽  
Vol 63 (23) ◽  
pp. 5653-5662 ◽  
Author(s):  
Shuyan Wang ◽  
Huilin Lu ◽  
Xiang Li ◽  
Long Yu ◽  
Jianmin Ding ◽  
...  
Keyword(s):  
Cfd Simulations ◽  
Bubbling Beds

A local transient approach to monitoring fluidization quality in freely bubbling beds

2008 ◽  
Vol 180 (3) ◽  
pp. 296-306 ◽  
Author(s):  
Clay R. Sutton ◽  
John C. Chen
Keyword(s):  
Bubbling Beds

Measurement and Computation of Turbulence in Risers Using Kinetic Theory

2003 ◽  
Author(s):  
Mehmet Tartan ◽  
Dimitri Gidaspow ◽  
Jonghwun Jung
Keyword(s):  
Particle Velocity ◽  
Circulating Fluidized Bed ◽  
Flow Region ◽  
Granular Temperature ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Cfd Models ◽  
Viscous Heat ◽  
Fluidization Regime ◽  
Bubbling Beds

Detailed experimental velocity, particle concentration and stresses for flow of particles in a vertical pipe, riser are needed for verification of various CFD models for multiphase flow in the industrially important circulating fluidized bed (fast fluidization) regime. This study provides such information for flow of 530 μm glass beads in the fully developed flow region of a 7 m symmetric riser with a splash plate. Instantaneous particle velocity distributions were obtained using a particle velocity imaging technique and a probe inserted into the riser, while the particle concentrations were measured with a gammaray densitometer. Time averaged particle velocity distributions can be well represented by a parabolic velocity distribution, with the mean velocity obtained from flux divided by the measured bulk density. The radial granular temperature profiles agree with an analytical expression similar to the thermal temperature distribution in Poiseuille flow with viscous heat generation. A solution to the complete CFD model shows that the assumptions made in the analytical solution are valid. Our measurements of stresses in the risers and bubbling beds show the existence of two types of random kinetic energies or granular temperatures. The true granular temperature is due to oscillations of particles, while the second is the average of the normal Reynolds stresses. In the core of the riser, the true granular temperature is much larger than the Reynolds type granular temperature. The reverse is true in the bubbling bed.

The Modeling and Analysis of a Package-Scale Circulating Fluidized Combustor

2001 ◽  
Author(s):  
Matthew J. Kremer ◽  
Savas Yavuzkurt
Keyword(s):  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Gas Temperature ◽  
Complex Flow ◽  
Modeling And Analysis ◽  
Commercial Code ◽  
Carbon Burnout ◽  
Recirculation Zones ◽  
Primary Velocity ◽  
Bubbling Beds

The preliminary analysis of a package-scale circulating fluidized bed (CFB) combustor through modeling and experimentation was performed to help determine particle trajectories and carbon burnout efficiency. The CFB consisted of a primary fast fluidizing bed and two bubbling beds. The fluidized bed models found in literature and a freeboard model utilizing a commercial code, FLUENT, were used in simulations. Primary gas velocity of the fast fluidizing bed was varied between 4.9 and 12.2 m/s and gas temperatures were varied between 800 and 1200 K. For comparison with computations of hydrodynamics, a scaled down version of the combustor was run using granulated plastic particles at 300 K. The results of computations showed that the freeboard has a very complex flow with many recirculation zones that usually become larger and move away from the walls with increasing primary velocity. There was less particle movement in the experiments than in the simulations due to the differences in particle diameters, the type of particles, the gas temperature, and the scaling geometry.

The Rise and Combustion of Particles of Sewage Sludge and Petroleum Coke in a Slugging Fluidized Bed

2005 ◽  
Author(s):  
A. C. Rees ◽  
J. F. Davidson ◽  
J. S. Dennis ◽  
A. N. Hayhurst
Keyword(s):  
Sewage Sludge ◽  
Petroleum Coke ◽  
Volatile Matter ◽  
Fuel Particle ◽  
Single Particles ◽  
Volatile Material ◽  
Fixed Temperature ◽  
Burn Out ◽  
Inert Particles ◽  
Bubbling Beds

The rise-times, from just above the base to the top of the bed, of single particles of dried sewage sludge and of two types of petroleum coke were measured in a slugging bed of sand fluidized by air. The sewage sludge and the petroleum cokes contained, on an as received basis, 49.5, 9.0 and 0.5 wt.% volatile matter, respectively. The bed (i.d. 25.5 mm; height 1300 mm) was electrically heated to a fixed temperature between 700 and 900°C. Two sizes of sand were fluidized: +212, −300 μm and +710, −850 μm. The expansion of the bed was held constant by keeping the excess gas velocity at (U − Umf) = 190 mm/s. In a bed of the coarser sand, it was found that the time of rise of single particles of sewage sludge (< 4 mm diam.) was large enough to allow devolatilization and char burn-out to be complete before the particle reached the upper surface of the bed. The measured times of rise are significantly longer than those found in bubbling beds [12, 13]. Thus, a slugging bed, of say 2 m in depth, would have significantly better heat retention and contact of the volatile material with the particulate phase than a bubbling bed of the same depth. With the finer sand, particles of sewage sludge and of petroleum coke containing volatile material rose rapidly to the top of the bed, well before combustion was complete. Published theory [6] was used to predict the rise-times of inert particles in a hot slugging bed. The predictions compare favourably with measurements using petroleum coke containing negligible amounts of volatile material and moisture. The use of a modified form of Stokes’s law to predict the velocity of rise of inert particles is shown to compare well with experiments. The experimental results suggest that once a minimum rate of gas evolution (from volatiles or moisture) is achieved a bubble forms which is large enough to lift a fuel particle to the surface. For particles meeting this criterion, the rise-time appears to be independent of the size of the fuel particle.

Dynamic model of calcium looping carbonator using alternating bubbling beds with gas switching

Fuel ◽  
2017 ◽  
Vol 208 ◽  
pp. 522-534 ◽  
Author(s):  
Shady Emad ◽  
Ahmed A. Hegazi ◽  
Salah H. El-Emam ◽  
Farouk M. Okasha
Keyword(s):  
Dynamic Model ◽  
Calcium Looping ◽  
Bubbling Beds

scholarly journals Devolatilization of Residual Biomasses for Chemical Looping Gasification in Fluidized Beds Made up of Oxygen-Carriers

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 311
Author(s):  
Andrea Di Giuliano ◽  
Stefania Lucantonio ◽  
Katia Gallucci
Keyword(s):  
Fluidized Beds ◽  
Oxygen Carrier ◽  
Reaction Model ◽  
Chemical Looping ◽  
Oxygen Carriers ◽  
First Order ◽  
Fluidizing Agent ◽  
Mitigate Climate Change ◽  
Bubbling Beds ◽  
Better Than

The chemical looping gasification of residual biomasses—operated in fluidized beds composed of oxygen-carriers—may allow the production of biofuels from syngas. This biomass-to-fuel chain can contribute to mitigate climate change, avoiding the accumulation of greenhouse gases in our atmosphere. The ongoing European research project Horizon2020 CLARA (G.A. 817841) investigates wheat-straw-pellets (WSP) and raw-pine-forest-residue (RPR) pellets as feedstocks for chemical looping gasification. This work presents experimental results from devolatilizations of WSP and RPR, in bubbling beds made of three different oxygen-carriers or sand (inert reference), at 700, 800, 900 °C. Devolatilization is a key step of gasification, influencing syngas quality and quantity. Tests were performed at laboratory-scale, by a quartz reactor (fluidizing agent: N2). For each pellet, collected data allowed the quantification of released gases (H2, CO, CO2, CH4, hydrocarbons) and mass balances, to obtain gas yield (ηav), carbon conversion (χavC), H2/CO ratio (λav) and syngas composition. A simplified single-first order-reaction model was adopted to kinetically analyze experimental data. WSP performed as RPR; this is a good indication, considering that RPR is similar to commercial pellets. Temperature is the dominating parameter: at 900 °C, the highest quality and quantity of syngas was obtained (WSP: ηav = 0.035–0.042 molgas gbiomass−1, χavC = 73–83%, λav = 0.8–1.0); RPR: ηav = 0.036–0.041 molgas gbiomass−1, χavC = 67–71%, λav = 0.9–1.0), and oxygen-carries generally performed better than sand. The kinetic analysis suggested that the oxygen-carrier ilmenite ensured the fastest conversion of C and H atoms into gases, at tested conditions.

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