Cleaning of Storage Equipment
Appropriately designed storage tanks with
properly installed spray devices are essential
for effective spray cleaning. The fixed-based
spray that is permanently installed has become
more prominent in the industry than the rotat-
ing and oscillating spray devices. It requires
less maintenance, is constructed of stainless
steel without moving parts, and endures. Per-
formance of this unit is not affected by minor
variations in supply pressure, and spray is con-
tinuously applied to all of the surfaces. Cylin-
drical and rectangular tanks can be properly
cleaned when sprayed with 4 to 10 L/min/m^2
of internal surface, with patterns designed to
spray the upper one-third of the storage con-
tainer. Because the equipment contains heat-
ing or cooling coils with complex agitators, a
special spray pattern is normally required, as is
a subsequent increase in pressure and volume
to cover all of the surfaces.
The vertical silo-type tank requires flow
rates of 27 to 36L per linear meter of tank cir-
cumference. Because of the difficulty in
reaching the spray devices for occasional
inspection and cleaning, non-clogging disc
sprays are normally used in this type of stor-
age vessel. Although most spray cleaning is
conducted with standard sprays, special
devices such as disc sprays, ball sprays, and
ring sprays are available for use with vacuum
chambers, dryers, evaporators, and complex
vessels with special processing features.
Cleaning of large tanks that use spray
devices differs from line cleaning applications
because prerinsing and postrinsing are gener-
ally accomplished through use of a burst tech-
nique in which water is discharged in three or
more bursts of 15 to 30 seconds each, with
complete draining of the tank between suc-
cessive bursts. This procedure is more effective
in removing sedimented soil and foam than is
continuous rinsing, and it can be accom-
plished with less water consumption.
The soil deposited in storage tanks and
processing vessels is more variable than that
associated with piping circuits; thus, cleaning
techniques for this equipment are more
diverse. For lightly soiled surfaces, such as
those of storage tanks for milk or low-fat
milk by-products, effective cleaning can be
accomplished through a three-burst prerinse
of tempered water. Recirculation of a chlori-
nated alkaline detergent of 5 to 7 minutes at
55 °C, application of a two-burst postrinse at
tap water temperature, and recirculation of
an acidified final rinse for 1 to 2 minutes at
tap water temperature also contribute to
effective cleaning. Recirculation time and
temperature may be increased slightly for
more viscous products with a higher content
of fat and total solids.
Soil components from cold surfaces differ
from those of burned-on deposits, which
contain higher protein and mineral contents.
Burned-on soil requires increased cleaning
compound concentration and solution tem-
peratures of up to 82°C, with an application
time of up to 60 minutes. Excessive amounts
of burned-on deposits can also be cleaned
effectively with application and circulation
of a hot alkaline detergent and a hot acid
detergent solution.
Table 16–3 lists the typical concentration
of cleaning compounds and sanitizers for
various cleaning applications. Although
variations can exist, the suggested concen-
trations should be considered.
Cleaning programs depend on the proper-
ties of the product passing through the sys-
tem during production. In addition to
cleaning applications previously discussed,
the following approach is recommended for
the following processing systems:
Milk, skim milk,and low-fat products pro-
cessing equipment. Because of the mineral
content of these products, the equipment can
be cleaned effectively by recirculation of an
acid detergent for 20 to 30 minutes, with fol-
low-up by direct addition of a strong alka-
line cleaner, which is then recirculated for
approximately 45 minutes. An intermediate