Handbook of Brewing, Third Edition by Stewart Graham G.; Russell Inge; Anstruther Anne

Handbook of Brewing, Third Edition by Stewart Graham G.; Russell Inge; Anstruther Anne

Author:Stewart, Graham G.; Russell, Inge; Anstruther, Anne
Language: eng
Format: epub
ISBN: 9781351230810
Publisher: CRC Press
Published: 2017-09-04T16:00:00+00:00

Figure 11.22 Whirlpool operators and their separation: (a) whirlpool types and (b) relationship of wort entry velocity to vessel height/diameter.

The separation of the solids from the liquid is achieved by sedimentation due to gravitational and centrifugal forces and the “teacup” effect. Due to the tangential entry of the wort into the cylindrical vessel, a parabolic flow is established, which causes an increasing pressure gradient across the radius from the middle to the walls of the vessel. Friction between the fluid and the walls and base of the vessel causes the formation of a fluid layer where the centrifugal force on a particle is diminished, which the force on the particle directed toward the vessel center exceeds, causing the particle to move and settle there. In order to aid this process, vessels are designed with large diameters and reduced height to speed up settling. Thus, the height to diameter ratio (H/D) is important. A range of 0.5 to 1.0 is normal, with a trend toward lower values for new installations. The volume stream of the entering wort should be in relation to the H/D ratio28 (Figure 11.22b). The wort entry velocity should not be too high because hot trub flocs can be damaged, influencing their sedimentation properties.

Wort should be transferred to the whirlpool as soon as boiling is complete, at a flow rate of less than 2.4 m/s. It should enter the whirlpool at a speed of 3.5 to 5 m/s, at an angle of 20ºC to 30º to the vessel tangent at a height of 1 m from the vessel floor, which gives the maximum efficiency of energy conversion. A vessel with an H/D ratio of 0.6 would fill in about 10 min. The spin time in the vessel is 20 to 30 min before transfer to the wort cooler begins. To avoid the cone of trub collapsing, the stand time should not exceed the rotation time.27 Furthermore, the stand time should be minimized to avoid DMS formation from DMS precursors. Whirlpools cannot be used with whole hops unless a separate hopback or strainer is used before entering the whirlpool. High-gravity worts do clarify slower compared to worts of lower extract because the difference between the density of the particles and the wort is smaller (Stokes’ law). If no hop material is present, separation is poorer; the best results have been claimed with hop powder.29 Anaerobic conditions are also said to increase the amount of material deposited, particularly by injecting carbon dioxide or nitrogen into the wort line when pumping into the whirlpool.

There are two general types of whirlpool separators (Figure 11.22a). The first is a flat-bottomed vessel that has an angle of 1 in 50 to allow easy removal of solids. There should be three wort draw-off points at 50%, 10% to 15%, and 0% of the full level. Initial collection should be from the top point, then from that positioned at 10% to 15% as the vessel is emptied. Flow should then be reduced to avoid damage to the trub cone.


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