Agriculture Reference
In-Depth Information
Impact of changes in the cross section of pipelines on the flow
characteristics
Flow as source of mechanical energy in CIP processes
Laminar flow in a pipe (
v
= flow velocity
)
Many liquid layers pass the pipe at different velocities increasing
towards the centre without any significant exchange between them.
Diameter:
80 mm
65 mm
Volume flow:
36 000 l/hour
36000 l/hour
Flow velocity:
2 m/s
3 m/s
v
1
v
v
v
4
v
3
v
v
1
Pressure drop:
0.55 bar/100 m1.6 bar/100 m
Acceptable
Diameter:
80 mm
100 mm
Turbulent flow in a pipe
A complete exchange takes place within the flowing liquid.
Volume flow:
36 000 l/hour
Flow velocity:
2 m/s
1.2 m/s
Pressure drop:
0.55 bar/100 m
Not acceptable
Figure 5.9
Diagrammatic representations of laminar and turbulent flow in different pipe diameters (Reproduced with permission from
Ecolab. © Ecolab).
Mechanical cleaning effect in tank cleaning
Spraying geometry of spray balls (spray pattern)
20-35 l/min/m circumference of the tank
According to the specific requirements spray balls show a different
spraying geometry. Different sizes are available so as to adopt the
sprayed volume of the cleaner solution to the specific requirements.
In tank cleaning a sufficient mechanical effect is
provided by a closed falling film of the cleaning
solution running down the tank walls.
The films are usually 0.4-0.6 mm thick
The most important factor here is the volume flow.
Depending on amount and nature of soil the
volume flow should range between
20 and 35 l/min/m (= 1.5-2 m
3
/hour/m)
Figure 5.10
Spray ball types and mechanical cleaning effects in tank cleaning (Reproduced with permission from Ecolab. © Ecolab).
at the boundary layer close to the pipe surface, with little
or no mechanical energy to help the cleaning (Fig. 5.9).
Spray pressure and pattern
- Spray balls or rotating jets
are used for the interiors of large tankers or vessels.
Again, if impingement is too gentle or blind spots are
protected from the impact of the spray, there will be
insufficient energy to have an effective clean. Typical
pressures are 1-3 bar for low-pressure systems and 6 bar
for high-pressure systems. Flow rates of approximately
20-35 l/min/m circumference of the vessel are normally
needed to achieve the desired results (Fig. 5.10).
Temperature
- Generally, temperatures of 70-85°C are
used which has a high bearing on the rate of the cleaning
reaction.
Detergent control
- Typically driven by a temperature-
compensated conductivity probe and pump. Conductivity
closely follows free caustic levels in CIP solutions and
allows for fully automatic control. Manual dosing, in con-
trast, runs the risk of chemical strength being too high or
too low.
Chemical energy and foam control
- The main deter-
gent in CIP is normally an alkali, frequently caustic
based. The additional components, such as surfactants
for preventing foam and aiding wetting and chelating
agents for removing scales such as calcium phosphate,
may be included in the detergent formulation as sup-
plied; this is called a built detergent. The additional com-
ponents may also be supplied separately as a specialist
additive product. For formulation reasons, additives are
technically superior and more economical but require
parallel dosing pumps for caustic and additive.
Recycling
- Detergent solutions may be used more
than once; it is economical and environmentally friendly
and reduces the loading on effluent plants. Solutions
