Filtration filter aid

The majority of the volume of beer in the world is processed by filter aid filtration. This technology relies on adding powders to the beer that form a very porous bed when they impinge on the filter surface. This is achieved by slurrying the filter aid in water, deaeration and pumping the slurry into the beer. Thus the prefilter beer on reaching the filter surface encounters a fresh layer of filter aid as the bed develops. This prolongs the filtration mn. 

Filter vessel technologies include plate and frame, leaf and candle. The latter two are preferred today because they are easier and faster to clean and restart than the plate and frame. Candle filters are simpler constructions but leaf filters are probably more flexible (Hermia Brocheton, 1994). 

The filtration operation is preceded by precoating of the filter. This comprises recirculation of deaerated water around the vessel while adding filter aid slurry. Thus an initial bed of filter aid exists at the start of beer filtration. This means that the brewer has options to optimise the process other than simply the selection of the main 

---

FIG. 18-109 Filter-aid filtration system for precoat or body feed. (Schweitzer, Handbook of Separation Techniques for Chemical Engineers, p. 4-12. Copy-light 1979 hy McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company.)... 

Pressure leaf filters are used to separate much the same lands of slurries as are filter presses and are used much more extensively than filter presses for filter-aid filtrations. They should be seriously considered whenever uniformity of production permits long-time operation under essentially constant filtration conditions, when thorough washing with a minimum of hquor is desired, or when vapors or fumes make closed construction desirable. Under such conditions, if the filter medium does not require frequent changing, they may show a considerable advantage in cycle and labor economy over a filter press, which has a lower initial cost, and advantages of economy and flexibility over continuous vacuum filters, which have a higher first cost. 

Pressure leaf filters are used to separate much the same kinds of slurries as are filter presses and are used much more extensively than filter presses for filter-aid filtrations. They should be seriously considered whenever uniformity of production permits long-time operation... 

Phase separation Use filter aid Filtration, centrifugation Optimize stirring regime... 

A pressure leaf filter is required for the clarification of a vegetable oil, operating at a constant flowrate of 3 m /h. Afler pre-coating the filter medium with a suitable filter aid, filtration ensues up to a maximum pressure difiEerential of 4.5 bar. 

Filtration processes may be classified as either depth filtration or surface filtration. Depth filtration relies on a layer of porous media in which suspended particles in the beer are trapped within the media. Examples in brewing include filter aid filtration, sheet filtration and some forms of filter cartridge. Surface filtration normally refers to membrane technology. A thin layer of membrane has pores throughout the structure. This means that it is possible to achieve very exact filtration, perhaps enabling sterilisation, but typically the quantity of suspended beer particles that may be removed is less than for depth filtration. 

Precoat, or filter aid, filtration is used to promote the formation of more porous filter cakes whose particles would otherwise cause severe filter medium blinding (see Chapter 2 for details). Standard filter aids include diatomaceous earth or diatomite, which is the most common, perlite and cellulose based products. These are used as filtration precoats and/or included as body-feed within otherwise standard filter arrangements. 

Gerdes, E., Precoat filtration with organic filter aids . Filtration Separation, 1040-1043 (December 1997)... 

Hutto, F. B., What the filter man should know about filter aid filtration . Filtration... 

In general, filter aid filtration should be used only for systems that meet two key requirements. First, the desired product is the filtrate, not the cake. Second, the filter aid is acceptable in the filter cake or the filter cake can be easily repulped and refiltered to remove the filter aid. In addition, the particle-settling rate should be less than 0.012 m/min and the particle concentration lower than 0.1 wt% (< 0.3% for rotary drum precoat). 

---