Mechanical Engineering Department, Seminar April 2008 Fluidization Characteristics of Rice Husk in a Fluidized Bed Abdussalam Abuadala Ph.D Candidate Supervisor:

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


Outline• What is the fluidization?

• Why do need to fluidize rice husk?

• Experimental setup

• Results

• Conclusion


This work is a part of my PhD research


What is the fluidization?

It is a technique used to

make solid behaves like

fluid. This technique will be used

in biomass gasification.


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.


•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)


Experimental setupPressure Tap No.

Height(cm)

0 17

1 37

2 73

3 110

4 195

5 248

6 348

7 452

8 493


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


Bubbling Fluidized Bed

• This experiment used: Sandwich distributorThree different bed cross

sectionsDifferent bed depths


Results


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


BFB A =0.5 m2; u =1.75 m/s; Wg/(AP) =1.3

Front view Top view



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


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.


Effect of superficial velocity on suspension density by using 45.5 Kg as bed inventory


Effect of superficial velocity on suspension density by using 68 Kg as bed inventory


Effect of superficial velocity on suspension density by using 91 kg as bed inventory



Effect of bed inventory on suspension density (at U =2.6 m/s and across height 0.17 – 1.10 m)

2121


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.

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Documents

Mechanical Engineering Department, Seminar April 2008 Fluidization Characteristics of Rice Husk in a Fluidized Bed Abdussalam Abuadala Ph.D Candidate Supervisor: