minutesniroklarSauerflu»ssig1.0%nitricacidproductfromthe Chemischen
FabrikDr. Weigert, Hamburg, Germany).Aftercareful intermediate rinsing (pH
controlin the outflow) the plant was filledwithwater.A ready-mixed enzyme
solutionwas addedto the circulationvolumeof 1500 L. The pH value,which
shouldbe in a rangebetween 9.0 and 9.5 due to the addedformula,reached
approx. 8.2 and had thus to be slightlycorrectedby adding a smallquantity of
NaOH.The enzyme-containing cleaningsolutionwas circulated for 45 minutes
throughthe circuit,and subsequently discharged to drain. Aftersix minutes
waterrinsingthe cleaningwas stoppedand the heatexchangeropened.All the
product flowpaths of the platedevicewerevisually clean(Fig.32.10). Wipe
testswitha cleanwhitelinenclothdid not hint of possiblefouling residues. In
the sameway, but without dailydisassembly,the heatexchangerwas operated
consecutively for 4 days between 7 and 10 hours, to be subsequently
enzymaticallycleaned.At the end of day 4, the plateheatexchangerand the
Fig. 32.10 High-temperaturesectionof a milkheater(ZE 23 WP1,Alfa-Laval,
Germany),enzymaticallycleaned.Enzymatic cleaning in foodprocessing 533