Fractionation of fat 213 8.2.1 Flat-bed vacuum band filter Florentine continuous filter The Tirtiaux process(Tirtiaux, 1980; Ricci-Rossi and Deffense, 1984)for fractionation of fats by gradual and selective cooling followed by filtration on their patented, continuous belt 'Florentine, vacuum filter is probably the most widely used flat-bed system. Crystallisation is normally carried out in two stages(Kreulen, 1976). The plant layout includes a recrystallisation stage where the feed is first cooled slightly to reach nucleation. It is then pumped into crystallisation tanks, The vertical tanks are jacketed and fitted with an agitator or a coil or both, depending on their size, varying between 12 and 50 tonnes. The agitator provides convection movements without scraping the wall during the whole cooling stage for efficient crystallisation. The oil is cooled under con trolled conditions, whereby it is the temperature of the oil that actually controls the rate of cooling. This slow crystallisation enables control of the latent heat of crystallisation and avoids supercooling. When crystallisation is complete and the filtration temperature is reached, the slurry is filtered on the Florentine continuous-belt filter(Fig. 8. 4) Air conditioning Scraping Recycling Fig.8.4. Florentine filter(courtesy of Tirtiaux, Belgium). The Florentine is a horizontal type, flat-bed filter. The filtration takes place on a continuous perforated stainless steel belt operating at a vacuum of 50-200 mbar. The filter is fitted with a recycling device which enables the filtrate from the first filter section to be recycled. This facilitates filtration on a preformed stearin cake and increases the quality of the filtrate. The filter is self-cleaning, and the filtration area is enclosed and air conditioned. The latter helps to maintain the feed slurry at the temperature of fractiona- tion until separation of the fractions is completed. Filtration is possible at temperatures as high as 45C(tallow)or as low as 2 C (lightly hardened soyabean oil The Tirtiaux process was first developed in Europe for the fractionation of beef tallow. This was later extended to palm oil when they installed the first commercial plant inHot water I > I I1 Y system / Heating it