Transcript Fluidization Characteristics of Rice Husk in a Fluidized Bed Abdussalam Abuadala
Fluidization Characteristics of Rice Husk in a Fluidized Bed
Abdussalam Abuadala Ph.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
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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 setup
Pressure Tap No.
0 1 2 3 4 5 6 7 8 Height(cm) 17 37 73 110 195 248 348 452 493
Mechanical Engineering Department, Seminar April 2008
Bed material
Rice husk from: Rice Hull Specialty Products Incorporation, Stuttgart, Arkansas, USA. The properties were measured in the lab.
Material Bulk density (kg/m 3 ) Particle density (kg/m 3 ) Sphericity Voidage in static bed Husk 156 1139 0.175
0.86
d p (µm) 1550
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Bubbling Fluidized Bed
•
This experiment used:
Sandwich distributor
Three different bed cross sections
Different bed depths
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Results
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Pressure drop across the bed against superficial gas velocity
W = 6 kg; A = 0.15 m²; H st = 0. 37m; Wg/(
p m A)= 1.12
Mechanical Engineering Department, Seminar April 2008
Ratio of pressure due to weight and that from experiment
A (m 2 ) W (kg) H st (m) Wg/(
p m A) 0.15
6.0
0.37
1.12
9.2
12.9
0.54
0.73
1.2
1.29
0.35
0.50
17.3
28.4
37.6
24.2
36.3
50.5
68.0
0.37
0.54
0.73
0.37
0.54
0.73
0.87
2.42
1.59
1.33
1.05
1.09
1.23
1.16
BFB; A= 0.5 m 2 ; H
st
= 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 m 2 ; u =1.75 m/s; Wg/(A Front view
P) =1.3
Top view
Mechanical Engineering Department, Seminar April 2008
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.
Mechanical Engineering Department, Seminar April 2008
Fast Fluidized Bed
•
Objective: To explore if husk could be in circulating fluidization unaided
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Experiments: Measured density profile at constant loop seal aeration to study effects of:
Superficial gas velocity
Bed inventories
Mechanical Engineering Department, Seminar April 2008
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.
550 500 450 400 350 300 250 200 150 100 50 0 0
U= 2.6 m/s U=3.2 m/s U= 3.7 m/s
10 20 30 40 50 60 70 80 90 100
(kg/m 3 )
Mechanical Engineering Department, Seminar April 2008
Effect of superficial velocity on suspension density by using 45.5 Kg as bed inventory 550 500 450 400 350 300 250 200 150 100 50 0 0
U = 2.6 m/s U= 3.7 m/s U=3.2 m/s
10 20 30 40 50
(kg/m 3 ) 60 70 80 90 100
Mechanical Engineering Department, Seminar April 2008
Effect of superficial velocity on suspension density by using 68 Kg as bed inventory 550 500 450 400 350 300 250 200 150 100 50 0 0
U= 2.6 m/s U=3.2 m/s U= 3.7 m/s
10 20 30 40 50 60
(kg/m3) 70 80 90 100 110 120
Mechanical Engineering Department, Seminar April 2008
Effect of superficial velocity on suspension density by using 91 kg as bed inventory 550 500 450 400 350 300 250 200 150 100 50 0 0 U= 2.6 m/s U= 3.2 m/s 10 20 30 40 50 60
(kg/m 3 ) 70 80 90 100 110 120 130 140
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)
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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 (0.5m
2 & 0.15m
2 beds) suggesting channeling at higher H st /A ratio.
Mechanical Engineering Department, Seminar April 2008
Mechanical Engineering Department, Seminar April 2008