Rapid wort cooling is nowadays performed exclusively with plate heat exchangers, sometimes more briefly called plate coolers. In these, the wort is cooled by cold water. The heat exchange occurs through thin chrome-nickel steel plates.
About plate heat exchangers
A plate heat exchanger consists of a large number of thin metal plates, arranged behind one another, between which wort and cold water flow alternately. Because, in the case of each plate, wort flows through channels on one side and cold water through channels on the other, a basic clement (flow path) always consists of two plates. To obtain good heat exchange in every case:
- very thin metal plates are used,
- the plates have a profile that will produce turbulence,
- the gap between the plates is very small,
- the countercurrent flow of wort and cold water is used,
- the direction of the flow is changed frequently.
Method of operation of the plate heat exchanger
In the plate heat exchanger, the hot wort is cooled by cold water from about 98 to 95°C to the 6 to 8°C pitching temperature. The cooling water is thereby heated to a temperature that can be controlled by the velocity of the water throughflow.
Cooling may be performed in one or two stages. Two stage cooling was previously customary. In the larger pre-cooling section the wort transfers heat to cold process water. Whilst the wort is cooled to about 3 to 4°C above the water temperature, the cooling water is heated to 80 to 88°C. In the smaller low temperature cooling section the wort is cooled by ice water at 1 to 2°C to the desired pitching temperature. The ice water is thereby warmed but remains below the temperature of the process water and is so fed back into the ice water cooler again.
One stage cooling is increasingly being used. In this process cooled ice water at 1 to 2°C is heated in the plate heat exchanger to 80 to 88°C whilst the hot wort at 95 to 98°C is cooled to the pitching temperature. The ice water which is used for this must be replaced by fresh water.
The energy requirement is less with two stage cooling than with one stage cooling. Nevertheless, many breweries prefer one stage cooling because
- its construction and operation are simpler,
- it costs less to buy,
- it is incorrectly assumed that the energy requirement is the same as with two stage cooling.
The permitted operating pressure of a plate cooler is in general 10 bar overpressure. Between the water side and the wort side of the plates, there is a pressure difference which is normally about 2 bar and at most 4 bar. This pressure difference must not be increased since it can lead to the deformation of the plates and gaps in the seals. The heat exchange plates have to be arranged to accommodate the maximum pressure difference which can occur (possibly up to 20 bar).
Advantages of plate heat exchangers
There is no alternative to the plate heat exchanger because other possible cooling methods are not used for various reasons. Nevertheless, the following advantages should be mentioned:
- a plate heat exchanger requires very little floor space,
- it provides very good heat transfer with little pressure loss,
- it is easy to clean and can be connected to a CIP system,
- wort remains only a very short time in the cooler, and
- it introduces no risk of contamination.
The plate heat exchanger can be adapted to changed operating conditions, the specific structural configuration can be adjusted according to your needs. The above is Tiantai’s introduction to plate heat exchangers. If you need beer brewing equipment, remember to contact us.
