Cereals processing technology

194 Cereals processing technology
provide an automatic system to wash the upper walls and ceiling of the vessel. The
requirement of cleanliness and a good standard of hygiene is high on the Maltster’s
agenda, and the modern design eliminates earlier problems in under-floor access
and adequate cleaning. During germination, the temperature and humidity of the
air provide ideal conditions for the formation of bacterial fungal growth.
It is now common practice to provide germinating vessels which are
completely automated. Both loading and unloading can be achieved in this way,
and during processing of the grain the provision of appropriate sensors can
control air volumes, humidity, temperature, etc.
9.6.3 Kilning vessels
As with germinating vessels, all recent major kiln developments in the UK have
been based on circular stainless steel vessels. Although construction is generally
similar to that of germinating vessels, a more complicated system of large
ducting is required, for the greater air flow, the larger fans, recirculation of the
process air, and heat recovery.
One significant difference between the germinating vessel and the kiln lies in
the layout of the loading/unloading unit. While, once again, the boom can be
fixed, with the floor rotating, or vice versa, turning of the material after loading
is not required in a kiln, hence the vertical spirals of the germinating vessel are
absent. In their place is a horizontal loading/levelling screw conveyor, which can
be adjusted to vary its height above the floor, so that pre-selected depths can be
adopted for loading or stripping (see Figs 9.4 and 9.8).
A further factor to be taken into account in kiln construction is the need for a
higher standard of insulation, to minimise heat loss. The kilning operation uses
more energy, both in the form of heat and electrical power than any other part of
the malting process, perhaps up to 85 to 90 per cent. Most kilns incorporate
some form of energy conservation, although with current fuel prices, it is
doubtful if the retro-fitting of heat recovery to existing kilns can be justified. In
most cases, the principal heat source is gas supplied on an ‘interruptible’ basis,
with oil storage being provided as a standby. Ambient air is drawn into the main
heating system (after pre-heating, if heat recovery has been fitted) and thence
through a variable speed fan, or fans, into the plenum chamber below the
perforated floor on which the grain has been loaded and levelled.
To minimise energy costs, albeit at higher capital cost, it is desirable to
reduce the grain bed depth compared with germinating vessels, and an ideal
figure for a new kiln design would be around 350 to 450 kg/m 2 of original
barley, which in the case of a 300 t capacity kiln would give a diameter of about
30 m. This compares with about 26 m diameter for a similar batch size
germinating vessel.
If a single kiln is used in the design for the malting process, and on the basis
of a 24-hour cycle, it is necessary to size the fans, heating equipment, ducting,
etc., to allow drying and cooling to be completed in approximately 20 hours,
allowing approximately four hours for loading, unloading and cleaning.