GB952754A - Process and plant for refining fats - Google Patents

Abstract

<PICT:0952754/C3/1> <PICT:0952754/C3/2> Fats are continuously refined by a process in which a stream of the fat is passed to the base of a vertical column of alkali lye and then passed up into the column in interspaced substantially <PICT:0952754/C3/3> <PICT:0952754/C3/4> equal fine streams distributed over the horizontal cross-section of the column under streamline conditions so that the streams divide into substantially equal drops of size not less than 0.1 mm. soon after entering the column of lye and pass straight up through a substantially constant height of lye to the surface thereof. The drop size is suitably 0.5-2 mm., preferably about 1 mm., and may be controlled either by controlling the size of the outlets, or more preferably by controlling the rate of flow of fat from outlets of equal and constant size. It is also preferred that the excess pressure exerted on the fat passing to the column be low or zero. The lye, which suitably has an alkali concentration of 0.1-1.5 N, preferably 0.3-0.8 N, generally also contains a small amount of an alkali resistant surface tension depressant, e.g. an alkylaryl sulphonate detergent; an additional electrolyte, e.g. NaCl, KCl, NH4Cl, or Na2SO4, may also be added to assist separation of the fat from the lye. Fat entering the column may suitably previously have been purified by treatment with phosphoric acid as described in Specification 887,885; such fats may, for example, be hardened whale, peanut or cottonseed oils, tallow or lard. Other fats, e.g. coconut oil, do not require this preliminary treatment. After refining the refined oil may be treated with citric acid to remove soap and alkali residues. In a preferred embodiment (see Fig. 2), fat from a filter chamber 32 associated with the apparatus for the preliminary treatment of suitable fats with phosphoric acid as described in Specification 887,885 is passed by line 37 to the base of container 38 which is full of lye. The fat stream enters the container 38 just below perforated false bottom 39 and forms a layer 74 above a layer 75 of lye. Lye displaced from the container 38 passes by lines 50 to tank 51 whence it can be repumped back to container 38 through line 52. So that the excess pressure on the layer 74 of fat should be low or zero, the layer 75 of lye is connected directly to the column of lye above false bottom 39 by pipe 42. In order to prevent turbulence a system of vertical partitions 40 is provided in the column of lye. The fat stream passes through perforated false bottom 39 through perforations 41 and breaks up into a series of uniformly sized drops which rise in non-turbulent flow to the top of the lye column where they coalesce. When float 48 in funnel 46 rises to a certain level, valve 49 is opened and refined fat is drawn off through line 47 to container 57 (see Fig. 3), the fat being introduced by spray device 58. Container 57 is maintained at low pressure (about 6 mm. Hg) by evacuation through line 59. The lower part of container 57 is surrounded by steam jacket 60, and is fitted with an agitator. Citric acid solution is added to the fat from tank 61, and a filter aid, e.g. kieselguhr, may also be added. This treatment with citric acid is suitably carried out in the presence of a reducing agent, e.g. 0.1-0.3% by weight of the fat of sodium bisulphite, or gaseous hydrogen which is bubbled through the mixture, and is described in Specification 920,349. Until the filter aid has been deposited on filter supports in filter 65, the mixture leaving container 57 is pumped by lines 63, through filter 65 and back to container 57 by line 68. After the filter aid has been deposited, however, fat leaving filter 65 passes by line 66 and safety and rest filter 67 to a storage tank (not shown) or to deodorization as desired. Figs. 4 and 5 illustrate a preferred means of forming the stream of fat drops at the base of the column of lye. Above each line of perforations 41 (see Fig. 5) is positioned an inverted gutter 76 with side walls 78 of dentate form (see Fig. 4, which is a section along IV-IV of Fig. 5). The fat collects under gutter 76 and emerges in streams 79 between teeth 78; these streams soon break up into uniform streams of drops.