Mechanical Engineering Department, Seminar April 2008 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 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. Height(cm)

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 Husk Bulk density (kg/m 3 ) 156 Particle density (kg/m 3 ) 1139 Sphericity Voidage in static bed 0.86 d p (µm) 1550

Mechanical Engineering Department, Seminar April 2008 Bubbling Fluidized Bed This experiment used:  Sandwich distributor  Three different bed cross sections  Different 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; H st = 0. 37m; Wg/(  p m A)= 1.12 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

A (m 2 )W (kg)H st (m) Wg/(  p m A) Ratio of pressure due to weight and that from experiment

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  P) =1.3 Front view Top view Mechanical Engineering Department, Seminar April 2008

15 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

Effect of bed inventory on suspension density (at U =2.6 m/s and across height 0.17 – 1.10 m) 21

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 (0.5m 2 & 0.15m 2 beds) suggesting channeling at higher H st /A ratio. 22

Mechanical Engineering Department, Seminar April 2008