A new approach to variable pressure cake filtration

Journal of the Chinese Institute of Chemical Engineers

2008

This paper details the capability of a unique, automated filtration apparatus and the newly developed Filter Design Software (FDS) which facilitate equipment selection, scale-up and simulation through an integrated experimental and theoretical approach.By way of example, experimental data were obtained with the apparatus over constant, variable and stepped pressure regimes. Inherent suspension properties were maintained throughout by utilising a computer controlled pressure controller and cake formation was monitored by micropressure transducers capable of providing up to seven independent measures of liquid pressure within 3.3 mm of the filter medium surface. For constant pressure and moderately compressible talc cakes the liquid pressure increased with cake height in a non-linear manner and generally exhibited a concave profile. When a pressure step was applied following a period of constant pressure filtration, the cake structure typically required up to 30 s to reach a new pseudoequilibrium state. During this time the reciprocal filtrate flow rate vs. filtrate volume plot was nonlinear and the liquid pressures in the cake increased rapidly before remaining nearly constant. When the cake was thicker or the pressure step larger, the liquid pressure measured closer to the filter medium remained either constant following the increase in pressure or increased slowly over the 360 s duration of the pressure step which indicates potential difficulties with the stepped pressure test.The filtration data were analysed using FDS to obtain scale-up coefficients and the impact of using incorrect scale-up coefficients on likely filter performance at the process scale is shown. The simulation capabilities of FDS are also highlighted through a case study in which, by way of example, the influence of crystal formation and other operating parameters on the filter cycle for a pharmaceutical product are shown. Simulations quantify how crystal form can detrimentally influence all phases of a cycle and lead to, for instance, slower filtration and wetter filter cakes.

Section: Introductionmentioning

confidence: 99%

Cake filter scale-up, simulation and data acquisition—A new approach

Journal of the Chinese Institute of Chemical Engineers

2008

“…When the probes were connected the computer controlled the switching of the electrode pairs to allow reversing polarity resistance measurements. These were recorded and then converted through calibrations to give real time measures of transient cake thickness and porosity distribution (see also Tarleton andHancock (1997) &Holdich andSinclair (1992) for more details). Wherever possible experiments were repeated to ensure reproducibility.…”

Section: Experimental Procedures and Resultsmentioning

confidence: 99%

“…‡ It is noted in passing that errors in m av tend to become more significant for higher concentration feeds as the effect on calculations of α av is increased. Hancock (1996 and; Tarleton and Willmer (1997); Tarleton (1998))) provides for some progression. The illustrative data presented highlight some of the benefits of routinely monitoring transient cake formation and quantify both the influence of intrusive electrodes on cake formation and the potential scale-up errors which can be introduced by the inappropriate use of filtration test data.…”

Section: Discussionmentioning

confidence: 99%

“…The difficulties of taking representative cake samples and the desire to assess in-situ cake formations has lead researchers to the development, though not widespread adoption, of alternative techniques which in some cases facilitate the near continuous determination of cake structure throughout an experiment. Methods relevant to filtration include the use of intrusive electrodes (Rietema (1953); Baird and Perry (1968); Dobson (1970); Wakeman (1981); Holdich (1990); Tarleton andHancock (1996 and) or pressure probes (Shirato et al (1980); Willis et al (1983); Murase et al (1989);Wu (1994);Fathi-Najafi and Theliander (1995)), flush mounted electrodes (Shirato et al (1971); Shirato and Aragaki (1972)) or pressure probes (Harvey et al (1988)) and X-rays or high energy radiation (Bierck et al (1988); Bierck and Dick (1990); La Heij et al (1996); Tiller et al (1995)). It is noted that similar procedures have also been used to assess related processes such as sedimentation, filter cake deliquoring and microfiltration (Wakeman and Holdich (1984); Wakeman and Vince (1986); Holdich and Sinclair (1992); Shi et al (1993)).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The use of electrode probes in determinations of filter cake formation and batch filter scale-up

1999

Minerals Engineering

Self Cite

A well controlled apparatus was used to obtain new data for constant pressure cake formation in a batch leaf filter which could be fitted with electrode type sensing probes. For aqueous suspensions of calcite and talc, the influence of the intrusive electrodes on cake formation was quantified with respect to filtration parameters. As the electrode length and diameter were altered such that the projected cross-sectional area occupied up to 2.6% of the filter area, the average specific cake resistance (as determined by classical filtration theory) was observed to increase by up to 49% and the average cake porosity decreased by up to 21%. When the electrodes were small relative to the dimensions of the filter cell, their influence on macroscopic cake properties was low. The additional information which electrical resistance measurements provide is discussed in relation to the results and observations by previous researchers and the benefits to filter test analysis and batch filter calculations are highlighted. For moderately compressible cake filtrations it is postulated that the incorrect assessment of cake porosity can typically account for an ~12% error in scale-up calculations for batch filters.

“…The on-line measurement of experimental parameters also allowed a real time display of results on the computer screen as an experiment proceeded. A Ziegler-Nichols analysis and some preliminary experimental investigations showed that a proportional algorithm with a system gain in the region 1-1.5x10 5 was suited to the provision of a constant flow when distilled water alone was used [18]. Initial experiments also showed that the open-loop flow response behaviour of the apparatus was similar to a first order system with a time delay.…”

Section: Methodsmentioning

confidence: 97%

Using mechatronics technology to assess pressure filtration

1999

Powder Technology

Self Cite

This paper describes some recent (initial) developments in laboratory scale cake filtration technology which may ultimately lead to the production of standard equipment for assessing filtration performance. The principles of mechatronics, which integrates electronics, computers, process control and mechanical systems, have been used to provide a state-of-the-art pressure filtration apparatus capable of performing repeatable experiments over a range of pressure/flow regimes commonly encountered in industrial filtrations. Data obtained at constant pressure and proportionally controlled variable pressure are presented to illustrate the scope of the apparatus and the benefits of removing operator interference and damaging pumping operations from filtration experiments. It is shown how scale-up parameters (obtained for aqueous mineral suspensions) can be used to successfully predict constant pressure filtration performance and the problems which can arise when predictions of more compressible variable pressure filtrations are made using data obtained at constant pressure.