through understanding of fouling (for example Georgiadis et al., 1998;
Petermeieret al., 2002;Grijspeertet al., 2004).Thisapproach might be com-
binedwithcleaningschedule optimisation to optimiseoverall plant operation.
Smailiet al. (1999)considered CIP of sugarprocessplants, and investigatedthe
scopefor reducing the cost of cleaning by optimisingthe foulingand cleaning
cycle,including scheduling and minimising the length of the cleaningperiod
(Smaili et al., 2001, 2002a,b). Starling and Nicol(2001)investigated CIP
systems to determine the optimallayout of different plants.
29.1.3 Cost of fouling and cleaning
Foulingand subsequentcleaning of foodproductionplantshas botheconomic
and environmentalimpact. The directcostsof foulingand cleaninghavebeen
categorised as the following (Pritchard,1988):
∑ Lossof production: reduced processefficiencyand the needto shut downto
clean.
∑ Maintenancecosts: due to the necessity to installcomplex cleaningprocesses.
∑ Fuel costs: increased heating and pumping power to maintain process
conditions.
∑ Capitalexpenditure: overestimatingheatexchangerareaand installation of
extrapumpcapacityto allowfor fouling.
Environmentaleffects are increasinglyimportant.There are increasing global
concerns to reduce the amount of waste fromfoodproduction.Solutionsusedfor
dairycleaningmustbe neutralisedto a pH rangebetween 6.5 and 10 before
beingreleased, so the products of this neutralisationstep are of mainly environ-
mentalconcern(Grasshoff,1997).Products includesodium carbonates, sodium
hydrocarbonates and sodiumsaltsof nitricand phosphoric acid.Phosphates
(addedto cleaningagents to reducewaterhardness) are of known ecologicalrisk
due to excess waterphytilication/eutrophication.Complexingagents addedto
cleaning solutionsmayalso remobilise heavymetals(Grasshoff,1997).Other
possible additives(e.g.activeoxygenand activechlorine) are also of concern,
despitethe increasein cleaning rateson theiraddition.Activeoxygencan cause
splittingof waterand molecular oxygenon addition to hot cleaningsolutions
(Grasshoff,1989).Addition of suchchemicals to increasecleaning ratesshould
be keptto a minimum untilmoreis known of theirenvironmental effect.
Recovery and reuse of CIP chemicals are usedin some cases to reducethe load
on sewerage,althoughin all casesthe effluent mustat some pointbe released.
Thiscan take placeby: (1) processingof the wasteon site and directdisposal to
an outfall ditch,or (2) release to a localsewerage plantfor processing, i.e.
indirect disposal.
29.1.4 Understanding cleaning
If fouling did not occurthere would not be a need to clean;however, extensive
research has not yet founda preventionmethodand so cleaningmuststill take
Improvingthe cleaning of heatexchangers 471