Cloud Height in Solids Suspension Agitation

Hicks, Michael Townsen; Myers, Kevin J.; Bakker, A.

doi:10.1080/00986449708936610

Cited by 89 publications

(78 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is worth noting that the experimental values of NjS obtained by direct observation of the tank bottom were found to lie between 85 and 95% of those predicted by Hicks et al (1997), Figure 9 is ogtained, where the data show a slight shift to the right with repect to Figure 8. Use of Figure 9 may be preferable whenever information on the real value of N .…”

Section: D085mentioning

confidence: 65%

Unsuspended mass of solid particles in stirred tanks

Brucato

1998

Can J Chem Eng

View full text Add to dashboard Cite

An original technique for the determination of the fraction of unsuspended solid particles at agitation speeds smaller than NJ, , is proposed. The technique is based on the "twin-systems" concept and is completed by a suitable tracing and detection technique for the solid phase. Results obtained with a fully baffled tank stirred by a Rushton turbine impeller show that the fraction of solids never leaving the tank bottom can be simply correlated to the ratio between agitation speed and Zwietering's complete suspension speed. It is shown that at agitator speeds of about 80% of Zwietering's complete suspension speed, practically all particles but a few, are already suspended. This finding implies that large energy and installation cost savings can be achieved, with respect to current design practices, without significantly affecting the solid-liquid mixing performance.On propose une technique originale pour la determination de Keywords: solids suspension, stirred tanks, partial suspension regime, twin systems.olids suspension in stirred vessels is an operation fre-S quently encountered in the process industry. Relevant examples include multiphase catalytic reactions, adsorption, crystallisation, dissolution, leaching and precipitation. As a consequence solids suspension in stirred vessel has been the subject of a number of investigations, most of which concern experimental methods and predictive correlations for the minimum agitation speed, Njs, required to "just suspend" all the particles, on the basis that this condition corresponds to the lowest specific power input at which all particles surface area is made available for effective processing.Several experimental methods were devised, that were claimed to allow the determination of NjS (Bourne and Sharma, 1974a; Buurman et al., 1986; Rao et al., 1988;Rieger and Ditl, 1994), but the most widely adopted method is still the visual method introduced by Zwietering (1958), by which the just complete suspension speed is defined as the agitator speed at which no solid particle rests on the bottom of the vessel for more than I s. This method clearly requires a transparent bottomed vessel, a feature easily available at laboratory scale but impracticable for large scale installations. The main advantage of this method is its intrinsic simplicity; but it must be pointed out that it is affected by subjective evaluations, so that only with a careful and skilled observation is it possible to get about +5% reproducibility at best in the case of dilute suspensions. No data can be reliably reproduced when solids concentration is above 8% by weight (Oldshue and Sharma, 1993).Zwietering (1958) also proposed a well known heuristic correlation for the estimation of Njs, on the basis of his own data and with the help of dimensional considerations. Similar *Author to whom correspondence should be addressed. E-mail address: abrucato@dicpm.unipa.it correlations were proposed by other authors (Nienow 1968) which were based in some cases on phenomenological models of the suspension phen...

show abstract

Section: D085mentioning

confidence: 65%

Unsuspended mass of solid particles in stirred tanks

Brucato

1998

Can J Chem Eng

View full text Add to dashboard Cite

show abstract

“…The slurry cloud height is loosely defined by the visual interface, occurring at a layer between the dense slurry suspension below, and light low-concentration slurry above. Refer to Hicks et al 13 for an earlier study on this parameter.…”

Section: Stratification As a Methods To Increase Solids Retention Timementioning

confidence: 99%

High solids concentration agitation for minerals process intensification

Wang

Graham

et al. 2010

AIChE Journal

View full text Add to dashboard Cite

in Wiley Online Library (wileyonlinelibrary.com).By using mixing intensification involving high solids concentration as a means to achieve process intensification for the mineral process industry is discussed here. Improving agitator energy efficiency is essential for operating at high solids concentrations. It is shown that improved agitator energy efficiency can be achieved by removing baffles and using higher power number impellers at high solids loadings. Power consumption (50-80%) reductions were demonstrated in the experiments. It is also suggested that slurry stratification in tanks can be used to boost either solids residence time or slurry mass flow. Basic equations related to solids residence time and solids throughput are presented for guidance toward minerals process intensification. An example on doubling throughput via intensification is presented.

show abstract

“…At higher concentration, there is a distinct level (clear interface) to which most of the solid particles are lifted within the fluid at a given impeller speed, this height of the interface from bottom of vessel is called cloud height and above this interface there is only an occasional visit by a few solid particles, however, liquid below this height is solid-rich (Bittorf and Kresta, 2003). Numerous data and literature are available on cloud height (Hicks et al, 1997;Bujalski et al, 1999;Oshinowo and Bakker, 2002;Ochieng and Lewis, 2006). Bittorf and Kresta (2003) derived an equation for cloud height that corroborates best results for solids distribution at low clearance and large impeller diameter:…”

Section: Article In Pressmentioning

confidence: 99%

“…This figure also shows that the impeller speed at which the maximum homogeneity occurred was independent of the impeller position for the given range of clearance. Hicks et al (1997) conducted experiments to study the solid suspension at various off-bottom clearance (T/2.5, T/4, and T/ 10). The mixing was more effective at C = T/2.5 compared to C =T/4 and T/10 for the solid-liquid system.…”

Section: -1500 MMmentioning

confidence: 99%