The decision
by a brewery to use a particular optimum process depends upon several
important criteria. These include purchase costs, space requirements,
process flexibility, operational and consumption costs, energy usage
and environmental protection as well as achievable technological brewing
conditions for optimum wort and beer quality.
Wort boiling
processes with energy recovery systems, which are uncomplicated in use
and operate with a high degree of functionality, have significant advantages.
The operational characteristics and selection criteria from the energy
point of view are described here.
Wort
boiling
The functions
of wort boiling are:
In order
to achieve acceptable heating rates and evaporation figures with conventional
plants using internal calendria, it is necessary to provide high steam
pressures and large heating surfaces. High steam temperatures of up
to 150 degrees Celsius have such an adverse thermal effect on the wort
that valuable components are destroyed and quality deteriorates.
Reducing
energy usage
With the
advent of modern boiling systems, the required overall evaporation can
be lowered to about 6.5 per cent without any technological disadvantages.
Various
processes are used and additional equipment installed which recover
and/or recycle the energy contained in the vapours. These include evaporative
condenser, vapour compressor, low-pressure boiling and energy storage
system.
Evaporative
condenser: Vapours are condensed in a plate or shell and tube heat
exchanger, and water heated in counter-current flow.
Vapour
compressor: Thermal and mechanical vapour compressors are in use.
The pressure of the vapour (generated during wort boiling) is increased
either in a thermo-compressor or a mechanical vapour compressor, and
then reused for heating the wort in a wide gap plate or shell and tube
type heat exchanger.
Low-pressure
boiling: Boiling in some systems takes place at a slightly positive
pressure in order to raise wort temperature and accelerate chemical
reactions. Undesirable flavour substances are stripped off on expansion
to atmospheric pressure.
Energy
storage system: The warm water generated in the evaporative condenser
is heated up to over 97 degrees Celsius and then used for wort preheating
from 78 to 92 degrees Celsius during the worth collection from lauter
tun to wort kettle.
