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Franks and Seiberling
the number of sprays required for proper coverage of simple vessels. As spray
cleaning was applied to dryers and evaporators, other configurations including
tubes with bubbles and small half-spheres were developed. These have been further
refined to provide the pinpoint coverage to address the numerous issues found in
biopharmaceutical and pharmaceutical process equipment. This chapter can
address only the most basic aspects of design and application.
Coverage Criteria
The early users of tank CIP quickly learned that it was easier to pump water into a
tank than to remove it, reliably,under automatic control. Field experience suggested
that horizontal, cylindrical, and rectangular tanks could be effectively cleaned at
flow rates of 0.2 to 0.3 gpm/sq ft (30–35 Lpm) of the upper third ofthe surface
for vessels in general and for all other applications of permanent spray devices.
Other criteria include (1) run agitators and (2) spray both sides of all baffles. The
advent of the large dairy silo in the early 1960s resulted in findings that 2.0 gpm/ft
(25 Lpm/m) of circumference for vertical vessels, applied to the dish head only,
would clean vessels of nearly any size, if the tank head contained no nozzles. When
spray CIP was applied to biopharmaceutical and pharmaceutical industry vessels
in the late 70s and early 80s, it was quickly discovered that standard spray designs
used successfully in dairy, beverage, brewing, and food facility vessels would not
work, primarily because of the number of head nozzles and other interruptions to a
continuous surface. Directionally drilled sprays became the solution, by addition of
streams to specifically target nozzles, manway and agitator collars, dip tubes, etc.
Successful experience suggests the need for 1.0 to 1.5 gpm (3.8–5.7 Lpm) being
required for each head nozzle and that the 2.0 gpm/ft (25 Lpm/m) of circumference
based on diameter is needed for manway and agitator collars in addition to the
2.0 gpm/ft (25 Lpm/m) of vessel circumference. The total flow rate for vessels
using this approach typically averages close to 3.0 gpm/ft (38 Lpm/m)
of circumference.
Fixed spray devices have been found to perform very effectively at 25 psi
providing good spray ricochet and coverage while avoiding excessively high
system pressure requirements.
Flow Rate and Turbulence Considerations
When cleaning pipelines, the recommended velocity of 5ft/sec (1.5 m/sec) is to
assure afull line in horizontal runs and this velocity provides Reynolds numbers
( Re) well above that required for Turbulent flow ( ReO 2100). The velocity of afilm
passing down the sidewall of avessel is governed only by gravity,but Re is affected
by viscosity and temperature. Hyde (1) calculated the Re of turbulent falling films at
2.5 gpm/ft (38 Lpm/m) of circumference as 2060 for ambient water (208C), 4360 for
acaustic wash at 608 C, and 5668 for awater-for-injection (WFI) rinse at 808 C. Greene
(2) previously cited areference to Principles of Chemical Engineering (3) as the means
of determining the Re for afilm running down the sidewall of atank and noted that
temperature, via it’s impact on viscosity,affected Re significantly.Hesuggested that
for a7.5-in. (2.3 m) diameter tank, aflow rate of 75 gpm (17 m 3 /hr) would be
required for acold rinse as compared to only 25 gpm (5.5 m 3 /hr) for ahot (808 Cor
1808 F) wash to achieve the Re of O 2100 considered adequate for turbulent flow.The
higher flow in avessel of this diameter would equate to approximately 3.0 gpm/ft
(38 Lpm/m) of circumference suggested above as the average design flow rate, and