Distribution of gas flow in a fluidised bed

✍ Scribed by M.J. Lockett; J.F. Davidson; D. Harrison

• Publisher: Elsevier Science
• Year: 1968
• Tongue: English
• Weight: 106 KB
• Volume: 23
• Category: Article
• ISSN: 0009-2509
• DOI: 10.1016/0009-2509(68)89012-8

✦ Synopsis

WE HAVE the following comments to make in reply to the communication by Mr. Godard and Professor Richardson: I. Equation (I) in our paper [ I] refers to a bubbling fluidised bed with constant voidage fraction between bubbles. Most liquid-solid systems are non-bubbling and of course fall outside the scope of our paper. But most gas-solid systems bubble, particularly at gas flows of practical interest, and our paper is relevant to their behaviour. It is true, as Davies and Richardson show[2], that beds of fine particles (5% 142 u) and low densities (SP. P;T. 0.95-1.27) can be fluidised at low velocities (up to 3 c,,)without visible bubbling. But at higher flow-rates such beds do exhibit bubbling, and under these conditions the voidage fraction E between the bubbles may revert to a value nearer E", as suggested by Davies and Richardson [3]. 2. As pointed out by Godard and Richardson, our results would still be valid if the superficial velocity in the particulate phase took a value Ul, greater than U,, due to the voidage fraction between bubbles having a constant value r,!, greater than E; U,!, would then be the uniform velocity needed to support the bed weight with no bubbles and a voidage cb. U,, is the lowest value of the superficial velocitv to support . . the bed weight. at voidage E,,. 3. Experimental work both at Harwell I41 tusina X-ravs) L > and ai Cambridge [5, 61 (using a capacitance technique) has shown that. when bubbling first occurs at a flow-rate close to U,,. the voidage fraction l between bubbles is very nearly constant and equal to c,,, except near the bubble where c may be about IO per cent greater than e,,.