The advantages of chlorinedioxidedisinfectionincludea shorterduration and
reduced energy and water consumption. Experience with optimised new
sanitation procedurehas shownno majorproblems in beer quality. Furthermore,
interruptions into the production havebeenreduced and equipment is subjected
to less thermal stress(Agiuset al., 2004).Hanet al. (1999)showedthat 10 mg/L
of chlorine dioxidegas wereeffectivein reducing spoilageorganismsin fruit
juiceproductionin epoxy-linedstoragetankswhenthe exposure was 30 min at
9±28ÎC witha highrelative humidity (>90%)or at 25±28 ÎC withthe relative
humidity > 69%.
Thedesignand operation of spray ballshavebeenimproved to enhance
cleaning and todaymany suppliers can produce customisedsystemswithan
excellent cleaning efficiency. Sprayballsare hollowand usuallyspherical, with
diameters from35 to 150 mm withan inlettubeof about25±50mm.A number
of holes, typically witha diameterfrom1.6 mm to 2.4 mm,are drilledin the
bodyin positionsthat givethe desired spraydistribution (Morison and Thorpe,
2002).The traditionalstaticsprayball providesa simple meansof distributing
the cleaningfluidontothe tankwalls. Rotating sprayheadsspraythe wallsin a
uniformpattern and this combination of cleaning patternand mechanicalimpact
removesresiduesin a shortertimeand withless waterthana staticspray ball.
The rotatingnozzle headis particularly suitable for tanks that havecomplicated
internals because a single rotatingjet hits the varioustank componentsfromboth
sidesbecauseof its horizontal rotation(Mu»ller, 2001). In general, the processof
soil removal involves the initialwettingand subsequentsoftening or dissolution
of the fouledmaterial, followedby complete removal by impingement or
irrigation.The cleaningby a jet witha stablediameter of less than 4 mm was not
performed by direct impingement alone. The effectiveness of a spray ball
depends on the wettingareaaround and below the pointof impingement.
According to the studiesby Morisonand Thorpe(2002), the temperatureof the
waterand the additionof a small quantityof detergent weretwo of the most
significantvariables to affectthe wetting rate.Increasingthe pressureof the jet
also enhancesthe surfacewetting.
30.3 Hygienicdesign test methods
Hygienic designtest methodscan be usedto find the challengingcriticalspots in
cleaning equipment.These testsare intended as basicscreeningtestsfor the
hygienicdesign of equipment and are not indicativeof performancein industrial
cleaning situations. Thesemethodsare basedon standardisedprocedures.They
are verysensitive, so that it is possible to indicate evenverysmallpoorly
designedor defectiveareas,suchas crevicesarisingfrom,e.g., the wrong design
of a gasket (EHEDG,1993b). The hygienic design test methodsalwayshave
threesteps.Firstlythe equipmenthas to be soiledwitha standardisedsoil
containing a tracersubstance.The soil is dried to the equipmentsurfaceand it is
cleanedafterwards withan adaptedcleaning procedurethat shouldleavesome
Improvingthe cleaningof tanks 501