To achieve optimal brewing results, the brewing water must have a specific hardness. A so-called brewing gypsum must therefore be added as ultra-pure gypsum mineral to increase the hardness of water. This calcium sulphate must be added to the brewing process as a suspension with up to 10 % concentration via a dosing system.
The abrasive properties of these suspensions and their tendency for sedimentation thereby present highest requirements on the dosing system. A relatively high flow rate must be maintained in the system to prevent sedimentation of the solids during the dosing process; this velocity, in turn can lead to high wear in the pumps and fittings because of the abrasive medium employed.
In regard to the preparation tank for the suspension, it is impor¬tant here that, on the one hand, complete drainage of the tank is possible and, on the other hand, the agitator, which is constantly driven, always remains submerged in the liquid and the solids the¬reby remain suspended. This task is normally solved through tanks – made of thermoplastics (PP or PE) – with an inclined bottom and an agitator equipped with a stripping agitator mechanism.
The latter is positioned only a few millimetres above the tank bottom thereby ensuring that the tank can be emptied almost completely even during the dosing process.
In addition, ultrasonic level measuring ensures that the actual filling level is always reliably recorded preventing the system from running dry. Filling the preparation tank with brewing gypsum is normally a manual process and takes place via a filling device. Common preparation volumes for the suspensions are 1 or 2 m³.
While the management of wear and the tendency to sedimenta¬tion in the tank can be handled relatively easily, dosing requires a clearly greater effort to ensure the operational reliability and availability of the entire system in the long term.
The dosing pump is clearly the centre of considerations in this process. Piston diaphragm pumps equipped with valves that were especially designed to deliver liquids with high-wearing properties have proven successful. The common hard seat of the valve ball is thereby replaced by an elastic seat.
On the pressure side of the dosing pump, a hose pulsation
damper ensures a uniform low-pulsation flow and takes care that pressure peaks, resulting from the delivery characteristics of oscillating displacement pumps, are reduced. This also simplifies flow rate measuring (usually handled by magnetic-inductive flow meters).