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Mechanical Engineering Department, Seminar April 2008
Fluidization Characteristics of Rice Husk in a Fluidized Bed
Abdussalam AbuadalaPh.D Candidate
Supervisor: Prof. Prabir Basu
Mechanical Engineering Department
Dalhousie University
Halifax, Nova Scotia
B3J 2X4 Canada
Mechanical Engineering Department, Seminar April 2008
Outline• What is the fluidization?
• Why do need to fluidize rice husk?
• Experimental setup
• Results
• Conclusion
Mechanical Engineering Department, Seminar April 2008
This work is a part of my PhD research
Mechanical Engineering Department, Seminar April 2008
What is the fluidization?
It is a technique used to
make solid behaves like
fluid. This technique will be used
in biomass gasification.
Mechanical Engineering Department, Seminar April 2008
Why do we need to fluidize rice husk as received?
1. Conserve energy that need in pretreatment operation to improve its flow properties.
2. Rice husk has 20% ash, silica consists 95% and its properties could be affected when mixed with other bed material.
3. Reduce operating cost of plant.
Mechanical Engineering Department, Seminar April 2008
•Presently we do not know if husk can be fluidized without mixing it with sand.
•So, we explore fluidization potential of husk: in bubbling fluidized bed (BFB)in circulating fluidized bed (CFB)
Mechanical Engineering Department, Seminar April 2008
Experimental setupPressure Tap No.
Height(cm)
0 17
1 37
2 73
3 110
4 195
5 248
6 348
7 452
8 493
Mechanical Engineering Department, Seminar April 2008
Bed materialRice husk from: Rice Hull Specialty Products Incorporation, Stuttgart, Arkansas, USA. The
properties were measured in the lab.
Material HuskBulk density(kg/m3) 156
Particle density(kg/m3)
1139
Sphericity 0.175
Voidage in static bed
0.86
dp(µm) 1550
Mechanical Engineering Department, Seminar April 2008
Bubbling Fluidized Bed
• This experiment used: Sandwich distributorThree different bed cross
sectionsDifferent bed depths
Mechanical Engineering Department, Seminar April 2008
Results
Mechanical Engineering Department, Seminar April 2008
Pressure drop across the bed against superficial gas velocity
W = 6 kg; A = 0.15 m²; Hst = 0. 37m; Wg/(pmA)= 1.12
Pressure drop across the bed against superficial gas velocity
W = 6 kg; A = 0.15 m²; Hst = 0. 37m; Wg/(pmA)= 1.12
A (m2) W (kg) Hst (m) Wg/(pmA)
0.15 6.0
9.2
12.9
0.37
0.54
0.73
1.12
1.2
1.29
0.35 17.3
28.4
37.6
0.37
0.54
0.73
2.42
1.59
1.33
0.50 24.2
36.3
50.5
68.0
0.37
0.54
0.73
0.87
1.05
1.09
1.23
1.16
Ratio of pressure due to weight and that from experiment
BFB; A= 0.5 m2; Hst= 0.54 m u = 0.5 m/s, Wg/(PA)=2.6 u = 0.8 m/s, Wg/(PA)=1.53
Mechanical Engineering Department, Seminar April 2008
BFB A =0.5 m2; u =1.75 m/s; Wg/(AP) =1.3
Front view Top view
Mechanical Engineering Department, Seminar April 2008
Mechanical Engineering Department, Seminar April 200815
Observations in BFB• Ratio of weight and pressure drop is
always greater than 1 though in BFB it is equal to 1.
• It suggests the weight of husk particles was never supported by fluid friction.
• Yet appearance of fluidized bed suggests creation of constantly shifting mini channels.
• It could also suggest formation of husk agglomerates whose size might be change.
15
Mechanical Engineering Department, Seminar April 2008
Fast Fluidized Bed•Objective:To explore if husk could be in circulating fluidization unaided•Experiments:Measured density profile at constant loop seal aeration to study effects of:
Superficial gas velocity Bed inventories
Suspension density profile for 30 kg bed inventory for three superficial velocities
Density is small above 1.0 m and below 4.5 m.
Exponential decay trend similar to fast bed of granular solids.
Only a minor effect of velocity noted.
Loop aeration was unchanged.
Mechanical Engineering Department, Seminar April 2008
Effect of superficial velocity on suspension density by using 45.5 Kg as bed inventory
Mechanical Engineering Department, Seminar April 2008
Effect of superficial velocity on suspension density by using 68 Kg as bed inventory
Mechanical Engineering Department, Seminar April 2008
Effect of superficial velocity on suspension density by using 91 kg as bed inventory
Mechanical Engineering Department, Seminar April 2008
Mechanical Engineering Department, Seminar April 2008
Effect of bed inventory on suspension density (at U =2.6 m/s and across height 0.17 – 1.10 m)
2121
Mechanical Engineering Department, Seminar April 2008
CONCLUSIONS• It is possible to achieve fast fluidization with
rice husk and without mixing it with other solids.
• Pressure drop across ‘fluidized’ husk was below that need for complete support.
• It suggests formation of micro-channeling or husk agglomerates.
• The weight over pressure drop ratio increased with bed depth (0.5m2 & 0.15m2 beds) suggesting channeling at higher Hst/A ratio.
2222
Mechanical Engineering Department, Seminar April 2008