1	Feeding pump	2	Beer Pump, 200 hl/h, 9,2 bar
2	Pressure Isolation	3	Shut off Valve
3	Infeed flow	1	Flow Meter, beer 0-200 hl/h
4	Conductivity	30	Conductivity Sensor
5	T supply	13	PT100 Sensor, Tmax = 75° C.
6	Infeed Pressure	10	Pressure sensor 0-10 bar
7	Reg. 1/8	4	Heat Exchanger, Regenerative A = 35 m2
8	T Zone 1	13	PT100 Sensor, Tmax = 75° C.
9	Reg. 2/7	4	Heat Exchanger, Regenerative A = 35 m2
10	Booster Pump	5	Beer Pump, 200 hl/h, 2,2 bar
11	T Zone 2	13	PT100 Sensor, Tmax = 75° C.
12	T Zone 3	13	PT100 Sensor, Tmax = 75° C.
13	Tref Zone 3	13	PT100 Sensor, Tmax = 75° C.
14	T Zone 4	13	PT100 Sensor, Tmax = 75° C.
15	Tref Zone 4	13	PT100 Sensor, Tmax = 75° C.
16	T Zone 5	13	PT100 Sensor, Tmax = 75° C.
17	Tref Zone 5	13	PT100 Sensor, Tmax = 75° C.
18	Zone 3 (past)	7	Heat Exchanger, Pasteurizing
19	Zone 4 (past)	7	Heat Exchanger, Pasteurizing
20	Zone 5 (past)	7	Heat Exchanger, Pasteurizing
21	Zone 6 (past)	7	Heat Exchanger, Pasteurizing
22	T Zone 6	13	PT100 Sensor, Tmax = 75° C.
23	Tref Zone 6	13	PT100 Sensor, Tmax = 75° C.
24	Past.Pressure	10	Pressure sensor 0-10 bar
25	T Zone 7	13	PT100 Sensor, Tmax = 75° C.
26	T Zone 8	13	PT100 Sensor, Tmax = 75° C.
27	Output cooler	21	Heat Exchanger Glycol/Beer
28	T output	13	PT100 Sensor, Tmax = 75° C.
29	Beer flow control	9	Control Valve,Beer
30	Pressure sensor	10	Pressure sensor 0-10bar
31	Pressure Isolation	3	Shut offValve
32	Flow out	1	Flow Meter, beer 0-200 hl/h
33	Filler Flow	1	Flow Meter, beer 0-200 hl/h
40	Fresh Water tohot tank	14	Ball Valve, On/Off
41	HotWater Buffer Tank	16	Tank, Water, 10 hl,Open
42	Cleaning Nozzle	31	Tank Cleaning Nozzle
43	Hot Water Level	32	Tank Level (Pressure)
44	Drain Cold Tank	14	Ball Valve, On/Off
45	Clean Hot Tank	37	Manual Ball Valve
46	Shut offHot Water	37	Manual Ball Valve
47	Water pump	17	Pump, Water, 1200 hl/h, 2 bar
48	HE Hot Water	18	Heat Exchanger, Steam/water.
49	T Water	13	PT100 Sensor, Tmax = 75° C.
50	Hot by-pass	14	Ball Valve, On/Off
51	Heating all zones	14	Ball Valve, On/Off
52	Flow zone 3	38	Flow meter for water 0-1000 hl/h
53	Flow zone 4	38	Flow meter for water 0-1000 hl/h
54	Flow zone 5	38	Flow meter for water 0-1000 hl/h
55	Flow zone 6	38	Flow meter for water 0-1000 hl/h
56	Cooling all zones	14	Ball Valve, On/Off
57	Cooling Zone 6	14	Ball Valve, On/Off
58	T Cold Water	13	PT100 Sensor, Tmax = 75° C.
59	Heat Exchanger Glycol/
	Water	26	Heat exchanger, Glycol/Water
60	Shut off Hot Water	37	Manual Ball Valve
61	Clean Hot Tank	37	Manual Ball Valve
62	Cold Water Level	32	Tank Level (Pressure)
63	Cold Circulation Pump	17	Pump, Water, 1200 hl/h, 2 bar
64	Cleaning Nozzle	31	Tank Cleaning Nozzle
65	Cold Water Buffer Tank	16	Tank, Water, 10 hl, Open
66	Fresh Water to cold tank	14	Ball Valve, On/Off
67	Cold by-pass	14	Ball Valve, On/Off
68	Cold return Zone 6	14	Ball Valve, On/Off
69	Cold return all Zones	14	Ball Valve, On/Off
70	Hot return all zones	14	Ball Valve, On/Off
71	Drain Hot Tank	14	Ball Valve, On/Off
72	T Cold Tank	13	PT100 Sensor, Tmax = 75° C.
73	T Cold Tank	13	PT100 Sensor, Tmax = 75° C.
80	Glycol Shut Off	37	Manual Ball Valve
81	Glycol Shut Off	37	Manual Ball Valve
82	Glycol control valve	22	Control valve 3-way, Glycol
83	Glycol pump	23	Glycol circulation pump
84	Glycol Shut Off	37	Manual Ball Valve
85	Glycol Shut Off	37	Manual Ball Valve
86	Glycol control valve	22	Control valve 3-way, Glycol
87	Glycol Pump	23	Glycol circulation pump
88	Condensate Shut Off	37	Manual Ball Valve
89	Steam Trap	20	Steam Trap
90	Water Take Out, Steam	36	Water Take OUT, Steam
91	Steam Shut Off	37	Manual Ball Valve
92	Strainer Steam	35	Strainer for Steam
93	Steam Trap	20	Steam Trap
94	Steam valve	19	Control valve, Steam

Those skilled in the art will readily understand the possibilities of regulating flows and temperatures on the basis of FIGS.[0197]4-5 and the above listing of elements.

However, those skilled in the art will also readily understand that many modifications are possible as regards the number of sections or zones in the pasteurizing heat exchanger, the number of regenerative zones, the combination possibilities of supplying cold and hot water to the various zones in the pasteurizing heat exchanger and possibilities of adding special heat exchangers for special purposes.[0198]

Those skilled in the art will readily appreciate that the more temperature and flow sensors are installed in the system, the better the possibilities are of monitoring and controlling the uptake of PU's by the liquid product being pasteurized. The important features to keep in mind when modifying or supplementing the shown and described embodiments of a pasteurizing apparatus according to the invention are that the great majority of the uptake of PU's by the liquid product should take place in the pasteurizing zone, and the volume of liquid product contained in the[0199]

conduits

17 and27 leading to the

regenerative zones

12 and13 should be as small as possible.

In the following, methods according to the invention for monitoring and controlling the pasteurizing process will be explained, it being understood that said methods may be applied to many different configurations of pasteurizing apparatus according to the invention and in fact for some of the methods also to conventional pasteurizing apparatus having a holding pipe wherein the pasteurizing takes place without possibility of regulating the temperature during said pasteurization.[0200]

The methods according the invention for monitoring and controlling the uptake of PU's by the liquid product to be pasteurized are based on establishing a mathematical model of the apparatus and measuring temperatures and rates of flow at different points of the apparatus such as indicated in FIGS.[0201]4-5 and defining a number of other points or sections of the flow-paths of the liquid product and/or the flow-paths of the heat transfer fluids. By applying the mathematical model containing parameters for the heat transfer at the different points or sections, the uptake of PU's by the volume of liquid product in said sections or points may be calculated such that the total uptake of PU's by said volumes may be monitored and controlled throughout the pasteurizing process.

Referring now to FIGS. 6 and 7, a[0202]

plate heat exchanger

18 with two strokes has channels between thinvertical plates33 having an embossed pattern, the plates defining channels for heating or cooling water and for beer. Theplate heat exchanger 18 is a well-known conventional plate heat exchanger. The beer and the water flow through the heat exchanger in mutual counter-flow so as to afford the most efficient heat exchange between the beer and the water.

For the purposes of the mathematical model mentioned above, the[0203]heat exchanger 18 is considered as consisting of a number of sections, cells or finite elements as shown in FIG. 7, where finite element n is bounded by two cross-sections through an entire stroke of the heat exchanger such that the volume in said finite element n of water and beer, respectively, is considered for that finite element. The number of finite elements into which each stroke or for that matter the entire heat exchanger may be considered as being sub-divided for the purposes of the mathematical model is chosen considering a trade-off between the accuracy of the mathematical model and the calculation of the PU-uptake for each volume of beer in each finite element and the calculating capacity of a computing means employed to perform the necessary calculation with a frequency also determined by such a trade-off.

The element n contains beer from all the beer plate spaces in one stroke and water from all the plate spaces in the same stroke as well as the stainless steel of all the plates in the stroke comprised between said boundaries. It is supposed that the temperature of the beer, of the water and of the steel plate does not vary across the stroke, i.e. that the flow of beer and water is evenly distributed in all the channels. Therefore the volumes of beer and water and steel may be added together within the boundaries of given element n.[0204]

Referring now to FIG. 6[0205]a,the flow of beer and water through the system of heat exchangers shown in FIGS. 3, 4 and5 so as to illustrate the flow of water and beer through the system in another way.

Referring now to FIG. 8, the volume Vb of beer, Vp of steel plate, Vw water represents the total volume of beer, plate and water within the boundaries of element n. Therefore each calculation element is characterized by a constant beer volume (VB), water volume (VW) separated by a plate with width equal to the thickness of a single plate and an area corresponding to the areas of all the plates in the element n, as well as a heat transfer coefficient. The element has four operational data, accumulated PU-uptake (PU) for the beer, the temperature of the beer (Tb), the temperature of the water (Tw) and the temperature in the center of the plate (Tp). Each element furthermore contains the PU-values of a number of ideal PU-curves (ideal set curve 1-X) for a number of ideal curves as discussed in the following.[0206]

The heat transfer coefficient is calculated based on a supposition that both the flow of water and beer is very turbulent and thereby maintains the same temperature in the whole element. The heat transfer thus consists of a heat transmission from beer to the plate, a heat transmission through the plate to the center of the plate, a heat transmission from the center of the plate to the surface of the plate and a heat transmission to the water. This is shown by the temperature gradient uppermost in FIG. 8 and the arrows at the bottom part of FIG. 8. The heat transfer coefficient is determined by experiments as a function of beer flow-rate and water flow-rate as will be explained in the following in connection with the explanation of the “adaptive adjustment of the heat transfer coefficient”.[0207]

The calculation of the operational data in the elements is updated for each sample (calculation cycle). The calculation is to be performed as often as necessary to be able to suppose that the heat transmission is constant, i.e. that the temperatures only change slowly compared to the frequency of sampling or calculation.[0208]

After each calculation/sample the liquid and fluid volumes are moved a number of finite elements in the flow direction corresponding to the measured flow and the frequency of calculation/sampling. The calculated number of elements that the volumes are to be moved in the flow-direction is rounded up or down to the closest integral number. The error introduced by this rounding up or down is stored and is added to a next calculation before said calculation is rounded up or down, and so on.[0209]

The calculation is carried out as follows for each finite element and for each sample/calculation:[0210]

Calculate the heat transmission from beer to plate based on the start temperatures.[0211]

Calculate the heat transfer from the plate to water based on the start temperatures.[0212]

Calculate the total energy transmission in the course of one sample ([0213]3.1 and3.2 are assumed to be constant during the sampling period).

Calculate PU-uptake and add same to the accumulated value of PU-uptake for the finite element in question.[0214]

Calculate the PU-error as the difference between the actual PU-value and an ideal PU-value.[0215]

Calculate the new temperatures of the beer, the water and the plate.[0216]

Move the beer (Tb, PU) and the water (Tw) a number of finite elements in the flow-direction thereof corresponding to the respective flow-rates thereof.[0217]

The above calculation sequence is repeated for each element and for each sample.[0218]

In this manner data is constantly generated for allowing monitoring of the PU-uptake of all the volumes defined by the finite elements n such that various strategies for controlling the pasteurizing process may be implemented.[0219]

The “adaptive adjustment of the heat exchange coefficients” mentioned above takes place as described in the following.[0220]

The heat transfer coefficient can be determined by operating the pasteurizing apparatus while adjusting the heat transfer coefficient with the purpose of minimizing the difference between the calculated and the measured output temperatures at the discharge of each heat exchanger. Manual adjustment of the heat transfer coefficient can be done during commissioning or at any time in order to minimize the errors. Adaptive adjustment (auto tuning) can be done during normal operation or in a specially designed start-up sequence. The purposes of a regular adaptive adjustment of the heat exchange coefficients are:[0221]

Adapt to any minor changes in the system due to scaling, wear etc.[0222]

In case of a major change in the coefficients, the system will go into alarm mode.[0223]

The development over time will provide information about necessary cleaning and maintenance.[0224]

Referring now to FIGS. 9 and 10, the graphs therein illustrate the uptake of PU by the liquid product as a function of the position of the finite element along the flow-path of the liquid product, in this case the number of finite elements being[0225]300. In both graphs anideal curve34 for the uptake of PU's as a function of the position of the portion of liquid product in question along the path flow of the liquid product is shown. Thecurve35 shows the actual PU-uptake, and thedip36 indicates a certain volume of the liquid product that has received too few PU's because of some anomaly such as a stop or a sharp reduction in flow-rate of the liquid product. In the conventional control system for conventional pasteurizers having a holding pipe, the temperature will be measured at the entrance to the holding pipe and it will be assumed that all beer in the pasteurizer will be treated correctly. If an anomaly such as36 occurs, the control will not have any possibility to react and, as illustrated in FIG. 9, acertain volume36 will be under-pasteurized when it exits the pasteurizer.

In the control system according to the invention, an[0226]

ideal curve

34 is calculated for a given flow and the flow-rate of the liquid product and/or of the heat transfer fluid as well as the temperature thereof may be controlled such that the volume being treated having the worst discrepancy as regards PU-uptake compared with the ideal value is compensated for by increasing the PU-uptake generally in the pasteurizer with a value just sufficient to bring the volume with the worst discrepancy up to the ideal curve. The control system according to the invention will calculate that there is liquid product that does not follow the ideal curve and will for instance decrease the flow-rate thereof until the worst portion is on the ideal curve.

The ideal curve employed may be calculated or measured. The measured ideal curve can be established in the following manner.[0227]

The pasteurizer is operated with a constant flow until thermal balance is obtained and the correct PU-uptake is calculated in the simulation for the pasteurized beer. The calculated PU-uptake value and the measured treatment temperature for all the positions in the pasteurizer are stored in the computer whereby an ideal curve is established.[0228]

Alternatively a calculated ideal curve can be used, the calculated ideal curve being established by a simulation of the system or a traditional calculation of the heat transfer.[0229]

It is necessary to use different ideal curves corresponding to different flows as the shape of the curve changes with varying flow-rate. This will be explained more detailed in the following.[0230]

Referring now to FIGS. 11, 12 and[0231]13, two different ideal curves for a flow-rate of 380 hl/hr and 120 hl/

hr

37,38, respectively, are shown for different positions along the flow-path of the beer to be pasteurized, the flow-path being sub-divided into 1,600 finite elements. The number of PU's taken up is indicated multiplied by 5 for better clarity. The graphs also show the temperature of the beer as a function of the position along the flow-path, i.e. in each of the 1,600 finite elements. The ends of the two heating regenerating zones, the four pasteurizing zones and the two cooling regenerative zones are shown with respect to the position, i.e. the end of the first pasteurizing zone, reference No.18 in FIGS. 3 and 4 and “past.3” in the table in FIG. 13 is positioned at position or finite element No.640, and similarly, the temperature curves39 and40 in FIGS. 11 and 12, respectively, show that the temperature of the beer along the flow-path is different for different flow-rates, and consequently, the ideal curves for PU-

uptake

37,38, respectively, are also different.

The ideal curves may be calculated or measured. A measured ideal curve can be established by operating the pasteurizer with a constant flow until balance has been obtained, and the correct PU-uptakes are calculated in the simulation for the pasteurized beer. The calculated PU-uptake value and the measured heat treatment temperature (the temperature of the water flowing in) for all positions in the pasteurizer are stored in the memory of the calculator whereby an ideal curve is established. Alternatively, a calculated ideal curve can be employed, said calculated ideal curve being established by simulating the pasteurizer or by a traditional calculation of heat transmission.[0232]

For different flow-rates, a number of ideal curves and heat treatment temperatures are stored, and the ideal curve and treatment temperature corresponding to a specific flow-rate is found by interpolating between the thus established ideal curves, whether they be measured or calculated.[0233]

The table in FIG. 13 shows, as mentioned above, possible ideal curves with a nominal flow-rate of 380 hl/hr, and 120 hl/hr with a desired PU-uptake value of 10.[0234]

During stable operation at a certain flow-rate of beer, the actual PU-uptake curve for the beer will follow the ideal curve for that flow-rate. However, if for instance a stoppage occurs, several strategies may be employed. For instance the flow-rate may be reduced and the last pasteurizing zone (past.[0235]6) is cooled so that the PU-uptake level in the first three zones are raised and at the same time a colder pasteurized beer flow is created to the first cooling regenerative zone (reg.7/2) having the highest temperatures. During re-start after a stop all four pasteurizing zones (past.6) may be used to heat at constant temperature such that a “flat” curve results for ensuring that finite elements with PU-uptake values higher than the required minimum holds back the flow-rate from increasing.

As mentioned above, many different strategies may be employed depending on the situation, the number of pasteurizing zones, the required minimum PU-uptake, the character of the liquid product to be treated and so on.[0236]

Referring now to FIG. 14, the graph shows the ideal curve for a flow-rate of 380 hl/hr and the[0237]

corresponding temperature curve

39. Thecurve40 shows the actual uptake of PU's after the flow-rate suddenly is reduced from 380 hl/hr to 300 hl/hr. The control system is then allowed to automatically adjust for this sudden decrease in flow-rate and it can be seen from thecurve40 that the actual uptake of PU's is above the ideal curve at the outlet of the last pasteurizing heat exchanger (past.6) while the PU-uptake at the inlet to the first pasteurizing heat exchanger (past.3) is very proximate to the ideal curve. The control method or system according to the invention regulates the flow-rate of the beer and of the heat transfer fluid such that the actual PU-uptake curve40 quickly moves back to coincide with the ideal PU-uptake curve38.

In the following, one embodiment of control loops pertaining to the PU-uptake control method according to the invention will be described in connection with FIG. 15, which is a block diagram of three novel control loops for controlling a pasteurizer according to the invention.[0238]

The control loops shown in FIG. 15 are applicable to the pasteurizing apparatus shown in FIGS.[0239]4-5.

Flow demand/set-point [[0240]4]:

The flow demand from the filler station [[0241]2] is added to the flow demand form the level regulator in the buffer tank [1] [3]

Temperature set-point[0242]1 (optimal) [6]

From the above flow demand the control will interpolate [[0243]5] between the flow-value for the ideal curves and find the corresponding temperature, called temp set-point1 [6].

Temperature set-point[0244]2 (limited) [8]

Limitations to temperature changes [[0245]7] are made in order to ensure that the physical system can follow thesetpoint2 with a small temperature error. This is important to ensure stable temperatures and a stable PU-uptake.

Hot water temperature [[0246]9]

The regulator for the steam heat exchanger controls the temperature of the hot water. The set-point for the regulator is the above set-point[0247]2 (limited) [8]

The ideal PU-curve [[0248]14] is interpolated [13] from the temperature set-point2 (limited) in order to make the ideal curve match the actual conditions as well as possible.

The PU error [[0249]15] is found as the actual calculated value [12] minus the interpolated ideal PU-value [14].

The most important PU error [[0250]15] is the smallest value of the PU error present in the pasteurizer within the current sample time.

The beer flow [[0251]18] is controlled by a regulator [16] which uses the most important PU error (15) as input. If the most important PU error is negative, the flow is reduced and if the error is positive, the flow is increased.

Hereby an embodiment of an automatic PU-uptake control system according to the invention has been described, but as mentioned above, other possible control systems will be obvious to those skilled in the art based on the principles of the invention.[0252]

Thus, a much simpler control method could be by basing the control system on a pre-determined sequence under certain anomalous conditions while utilizing the monitoring method for PU-uptake according to the invention such that for example under a stop, a pre-determined sequence for closing down the flow of beer and cooling of the pasteurizing zone may be utilized, the sequence being developed based on a series of test runs where the finite element mathematical model is used to monitor the result and ensure that no beer is under-pasteurized. Under operation the monitoring method according to the invention based on the finite element mathematical model will also monitor the operation and give an alarm if the chosen pre-determined sequence results in under-pasteurization of the beer.[0253]

Referring now to FIGS. 16 and 17 which are isometric views from two sides of a pasteurizing apparatus according to the invention and generally corresponding to the flow-diagram or diagrammatic view in FIGS. 4 and 5 with the difference that in this embodiment shown in FIGS. 16 and 17 cooling and heating, respectively, may only take place in all the pasteurizing heat exchanger (past.[0254]1-past .4) simultaneously. The flow of water and beer, respectively, is shown by means of the arrows. The apparatus is quite compact and is mounted on abase plate50 having acabinet51 for all the regulating and computing equipment, thebase plate50 being of a size allowing the entire apparatus to be transported in a commercially available 40 ft marine container. This is of great importance for the economical aspects of the apparatus according to the invention as the compactness allows shop-floor construction, trial operation and even part commissioning which entails large savings both as regards installation time and costs.

Referring now to FIG. 18, an apparatus for the pasteurizing of liquid products in a continuous flow, as for example fluid foodstuffs and beverages, consists of a[0255]

regenerative part

102 into which the product is fed by asupply pump101.

After the[0256]

regenerative part

102, the product is led further to the pasteurizingpart106 which cannot only heat the product to the pasteurization temperature, but also cool the product down in the event of a stop in production. Both theregenerative part102 and the pasteurizingpart106 consist of heat exchangers. Heating or cooling takes place by supplying hot or cold water via a mixingvalve116 to the pasteurizingpart106.

Temperature sensors

105,111 are placed before and after the pasteurizingpart106, so that the pasteurization process can be controlled. Between theregenerative part102 and the pasteurizingpart106 there are also placed booster pumps104,112 which ensure that the product has constant over-pressure in the apparatus.

The product is now led back to the[0257]

regenerative part

102 where it transfers its heat to the product in the inlet. Hereafter, the product is led to anoutlet18 where, for example, a filling plant (not shown) can be placed.

The apparatus can be produced in several configurations, depending on demands regarding temperatures and pasteurizing. The temperatures used in the following are thus only examples, since each product has its own specific temperature requirements.[0258]

The apparatus taken here as starting point (see FIG. 19) is intended for the pasteurizing of beer. The apparatus consists of two main heat exchangers, i.e. a regenerative heat exchanger which is divided into two[0259]

zones

102,103, and a pasteurizing heat exchanger which is divided into three

zones

106,108,110.

The product is led into the[0260]

regenerative zone

102 by means of asupply pump1, where the product at 2° C. is heated to 33° C. The product is now led further to the secondregenerative zone103 where it is heated to 65° C. A

booster pump

104 and112 ensures that there is an over-pressure, partly in the pasteurizing

heat exchanger

106,108,110 and partly in the cooling part of the

regenerative heat exchanger

102,103. This over-pressure ensures that in the event of a possible leakage, air or fluid does not come into the pipe system, but only out. In this way it is avoided that bacteria capable of survival are transferred to the pasteurized product.

A[0261]

temperature sensor

105 is provided before the inlet to the pasteurizing heat exchanger.

A valve[0262]121 (see FIG. 20) is placed as close as possible to the pasteurizing heat exchanger. During normal operation, this valve121 ensures that the inlet and the outlet from theregenerative heat exchanger103 on the nonpasteurized side are held separate. During a stop in production, the valve121 is opened, whereby re-circulation is made possible in this side of theregenerative heat exchanger103. This valve is optional and is not used in the cases/configurations where the outlet temperature from theheat exchanger103 is below the temperature limit for the recording of PU.

At the inlet to the[0263]

first zone

6 of the pasteurizing heat exchanger, the product at 65° C. is heated on the primary side to 72° C., this temperature being held through the

zones

108 and110.

A valve[0264]122 is placed as close as possible after the pasteurizing heat exchanger. Under normal operation, this valve must ensure that the inlet and outlet from theregenerative heat exchanger103 are held separate on the pasteurized side. During a stop in production, the valve is opened, whereby re-circulation becomes possible in this second side of theregenerative heat exchanger103. When the product leaves thelast pasteurizing zone110, it is pumped via thebooster pump112 into the cooling part of theregenerative part103 and is cooled down to approx. 40° C., and further to the lastregenerative zone102 where the product is cooled down to 9° C. A flow-control valve113 can be placed after the regenerative part. Hereafter, the product flows through a cooler114 and further to anoutlet118 where a possible buffer tank and/or a bottling or containerising plant is placed. With an embodiment having a minimal buffer tank, the flow-control valve113 ensures that the buffer tank does not get over-filled, i.e. that the flow is controlled by the level in the buffer tank.

In an apparatus without buffer tank, it is the filling plant (not shown) which determines the flow through the apparatus.[0265]

The cooler[0266]114 is used only if the outlet temperature of the product becomes too high, e.g. as a result of a stop in operations and subsequent restarting.

A[0267]

temperature sensor

107,109,111 is placed after each pasteurizing

part

106,108,110. Atemperature sensor115 is also placed after the cooler114. These sensors register whether or not the necessary temperatures have been achieved, so that heating and cooling respectively can be controlled on the secondary side of the pasteurizing

heat exchanger

106,108,110.

The heating/cooling sources in the[0268]

regenerative part

102,103 consist of the product itself (hence regenerative), and in the pasteurizing

part

106,108,110 of hot and

cold water

19,20 respectively, where the amount of heat in the water is determined by signals from the

temperature sensors

107,109,111 in the

individual pasteurizing zones

106,108,110. The regulation of the water supply itself is effected in a mixingvalve116 of commonly known type. The return water from the secondary side of the pasteurizing heat exchanger is led away via areturn pipe117, possibly for heating with a view to re-use in the heat exchanger.

The following is a description of the apparatus during a stop in production.[0269]

The regenerative heat exchanger can be divided into two[0270]

zones

102 and103 as shown, or constitute a single zone. In the event of a stop in production, the temperature profile in the first zone will be constant for the first minutes, after which the temperature will slowly approach the average temperature for the heat exchanger. In the second zone, or if there is only one zone, the temperature in the last part of the exchanger and in the pipe connections hereto will be so high that PU is recorded. To avoid this, re-circulation takes place in both the regenerative zones and pipe connections until a constant average temperature is achieved below the temperature limit for the recording of PU (e.g. 53° C.). The re-circulation is effected by opening the valves121 and122.

The pasteurizing[0271]

zones

106,108,110 will be cooled down to e.g. 56° C. during a production stop, so that the recording of PU is stopped.

The following is a description of the apparatus when re-started after a stop in production.[0272]

After a stop in production, ail of the pasteurizing zones are re-heated to the normal temperatures to ensure that no under-pasteurization occurs, and also that over-pasteurizing is limited as much as possible.[0273]

When re-starting an apparatus without buffer tank, the process is controlled by raising the temperature on the secondary side of the pasteurizing[0274]

heat exchanger

106,108,110 depending on the speed of flow.

The above embodiments and the apparatus according to the invention have been described by way of example, and various modifications and amendments will be obvious to those skilled in the art without departing from the scope of the appended claims.[0275]