Fouling and UHT Processing

Fouling and UHT Processing

DEPARTMENT OF FOOD SCIENCE AND READING

THE UNIVERSITY OF

ABSTRACT

has been designed and ~~·nal~~"~+'A~ a and a cooler. It has a variable rate it is t'\~'' '~t1~+-a to between 100 and few seconds. Flow tellll'P~erlilt\Jlre's are monitored through a system. A has been which allows real calculations heat transfer • The can be used to monitor the extent of fouling and cleaning the of cleaning for UHT processes.

INTRODUCTION

is the adhesion of material on surfaces of heat milk there are two distinct which is formed between has content 30-40%,

are are calcium

of the passage, DESIGN OBJBCTIVBS

163

and

3000 ~ ....

.t"L..I"L ~

~

-0--

...n.

1.J

...!J..

~

.....

--

J'"L""

..., '"'

...

2000

1000

o

10

20

30

50

90

Figure 1. The Overall Heat Transfer Coefficient (OHTC) the sterilizer when soft water is heated to a temperature 140°C proving its long- and short-term stability.

often The effects of some time become obvious when of the two or three a few hours more. This progress of the will be and means that a will be . The therefore the with even a small cost of milk for a £100 whereas with the commercial heat In order to minimise the miniature UHT that a maximum amount of flowrate necessary. The effects of on and on flowrate have to be measured in order to be able to measure the cnanqes of overall heat transfer coefficient which has been chosen as the characteristic parameter of the process. DBSCRIPTION OF THB APPARATUS

The

exchaDqers

cooler The

is hot water, heated is controlled with an accuracy The water comes an external source and has no tendencies. The dimensions of the 1. The can raise the from ambient (lS±2 up to 8SOC when The he.ter (sterilizer) is heated pressure (O-S 1. At the steam exit of the heat a thermostatic It is to and use the heat

~

21 1) Product 21 Water Tank 31 Three·way valve

5'

41

Valve 61 Pre-heater 7) Hot Water In 8t Hot Waler Out 9) POSition of Thermocouple 10) Main Heater Steam Outlet Steam Inlet 13) Position of Thernloc:ouple 141 Position of Thern~oc:ouple un Position or Thefl'1rloc;oIJlpie 161 Cooler

6

17, Cooling Water Inlet 18) Cooling Water Outiet

1

19)

, 19 24... ~.r." w":

..

201 211 221

231 24)

Valve Valvel Flow Meter Position Pressllre Transdure IPll Position of Pressure Transdme (P2) posirion of PressufC lransdUle (P3) Posltion 0# Press! Transdure Cf4)

0'

tl:! ~.

~

5'

1

.a. ~

lOj:

a "'tI

Figure 2. Block Diagram of the miniature UHT plant. The flow-path of the product is the dotted tine.

a

~

Fouling and UHT Processing

165

Table 1. Dimensions of the Heat Preheater 0.445 (10') m)

(10.3 m)

72.3

Heater 0.985 72.5

Cooler 0.48 72.3

2.667

2.667

2.667

0.254

0.254

0.254

2

2

at alower controlled a pressure pressure there is a condensed to drain from the rotate the heater and have it in a horizontal . The dimensions of heater are 1. The Pd~~dQe tube is extended before the heat excnan,ge:r for more than in the heat excn.anigetr heat flow is counter-current tube in order to reduce the from the milk raise the temperat,ur'e maximum which the instruments The heat to allow tubes removed and of the heater is before each and the external surface of the tubes is tested for or corrosion. The outer surface of the shell is to minimise heat losses. The cooler uses mains water as shell-side medium with a of 1 0 ° C with no The dimensions of cooler are tubes when more is moves under the action of a multi-lobe pump which with a needle pressure valve maintains inside to avoid and . Before there

maintains the same diameter and number of bends is to a material of construction is 316 stainless steel.

2.667'

Bio,che1nist,ry of Milk

166

INSTRUMENTATION

The telmpE:!rel.tl.llre at the heater exit of the via

a

pressure in accurate The calibrated with water and milk at ambient additional calibration was done with water at in order to check if the difference in te~mt)el~a1~u:re the calibration line and it was found that it 3000

2000 ~--------~~----------------------------------~

1000

o

o

50

100

TIME (min)

150

200

Figure 3. The Overall Heat Transfer Coefficient (OHTC) of the steriliser when reconstituted skimmed milk (pH:6.761 is heated to UHT temperature (140°C). The OHTC calculated Equation

allows real

water

Coefficient (U)

and

(1)

U=

where G

A

CLEANING

A combination of the standard _~,,~~_u and the Almas-Lund nrot:.OCOl achieve maximum removal • At the end of each run the st:.anaara and before the start when the flow is the to

there are It has been observed at a rate at the its value at the

.,,_~~._

REFERENCES 1. _~n~iu;

2.

Tissier J.P, Lalande M. milk on Progress, 2, 4, p.218-229 Sandu C, heat

device for surface,t Almas K.

(1984

in

"A

168

Biochemistry of Milk Products

and .. ed. 3.. Almas of stainless

p.29-39.

__ ~wu.u~

and Characterisation 23,