NZ506380A - A method of pasteurisation of liquid food products (milk) wherein there are two heating steps with the second heat step having a temperature less than the first heating step - Google Patents

Abstract

A liquid processing plant and a method of heat treating a liquid such as milk. The liquid is treated in a two stage heating process separated by a flash-cooling step. A flow meter and a temperature sensor monitor the liquid. In response to the conditions monitored by the sensors, the liquid can be directed to a recovery station or be redirected to the heating chambers for reprocessing.

Description

INTELLECTUAL PROPERTY OFFICE OF N.Z. 2 6 SEP 2001 RECEIVED Patents Form No. 5 Our Ref: 502593 NEW ZEALAND PATENTS ACT 1953 Complete After Provisional No. 506380 Filed: 16 August 2000 COMPLETE SPECIFICATION LIQUID PROCESSING PLANT AND METHOD OF HEA T TREA TING A LIQUID We, DOWNER MBL LIMITED, a New Zealand company of 26 Liverpool Street, Hamilton, New Zealand hereby declare the invention, for which We pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described and by the following statement: PT0512177 ,11. 2 6 SEP 2001 2 RECEIVED LIQUID PROCESSING PLANT AND METHOD OF HEAT TREATING A LIQUID Technical Field The present invention relates to a liquid processing plant. More particularly, but not exclusively it relates to a liquid processing plant for the heat treatment of a liquid product.

Background Art There are many standards for the heat treatment of liquid food products such as milk around the world. A feature common to the majority of standards is the requirement for pasteurisation of the liquid food product. Pasteurisation is the process of applying heat to the product for a specified time to destroy harmful microorganisms or other undesirable species. The pasteurisation process typically involves heating of the liquid food product to a stated pasteurisation temperature, holding the liquid food product at this temperature for a specified time period, cooling and recovery. In many countries, to comply with set-down standards or codes, it is often a requirement that the liquid food product be tested to ensure that it was pasteurised according to the process and if not, be able to be diverted, usually to the feed stream for re-processing.

In preparation of a dry product by evaporation of a liquid source, the ultimate dry product must also have passed through a pasteurisation stage in its processing. A conventional evaporation system typically consists of a feed tank, a preheat system to raise the temperature to boiling (for the evaporation), a holding section or sections, where the pasteurisation process takes place, calandrias where the evaporation takes place, and a final drying step.

With some feedstocks such as milk, it is desirable to also heat treat the milk feed at a temperature in excess of that required for evaporation. This heat treatment, which causes denaturing of the protein in the milk, imparts different functional properties to the ultimate powder product. The heat treatment step is usually incorporated into the preheat system. Following the heat treatment the feed temperature is reduced to a temperature close to the boiling temperature prior to entering the calandrias for 50638 0 evaporation. In the same way as before, there must usually be a diversion path allowing diversion of product back into the feed stream, which does not meet the pasteurisation and/or heat treatment criteria. The diversion valves are located after the preheat system and before the evaporator.

A number of disadvantages with this conventional system exist. Heat treatment is at a temperature in excess of pasteurisation temperatures. To streamline the processes, the feed is also typically held for the length of time required by the pasteurisation process at this elevated temperature, thereby incorporating both processes in one. With products such as milk, which are heat 10 sensitive, heat damage may occur as a result of holding the milk for these lengths of time at these elevated temperatures. It is preferable to have the product at the elevated temperature for the minimum time necessary.

Further, the use, as described, of diversion valves immediately upstream of the evaporator can cause problems. If it is necessary to divert product back into the 15 feed stream then a supply of hot water must be fed through the evaporator in order to keep it operational. The use of water in this way causes interruption of the operation, and can make it difficult to restart processing product. If water were not used then the evaporator may block requiring a period of downtime whilst the blockage is cleared.

It is an object of the present invention to provide a liquid processing plant which overcomes or at least ameliorates some of the abovementioned disadvantages, or which at least provides the public with a useful choice.

Other objects of the invention may become apparent from the following description which is given by way of example only.

Disclosure of the Invention In a first aspect of the invention there is provided a liquid processing plant including: •a heat treatment section for receiving liquid from a liquid supply and applying heat treatment to received liquid; ',SJT nl-^VAL PROPERTY OrFICc OF n.z. ' 2 MAR W3 REEEIVEB 4 06 • one or more sensors for monitoring one or more pre-selected characteristics the heat treatment section, or of the liquid within the heat treatment section; • an evaporator section downstream of the heat treatment section; • a diversion valve system arranged downstream of the evaporator section; and • a recovery section; wherein dependent on the output of the one or more sensors the diversion valve system either directs liquid from the evaporator section to the recovery section for further processing and/or recovery, or directs liquid from the evaporator section to the heat treatment section for re-processing.

Preferably, the one or more sensors includes a temperature sensor and a flow meter.

Preferably, the evaporator section in use provides a condensate and wherein the diversion valve system includes a condensate communication path for selectively communicating said condensate to said heat treatment section via said liquid supply or to said recovery section dependent on said output of the one or more sensors.

Preferably, the condensate communication path passes through the heat treatment section, thereby allowing heat transfer from the condensate to liquid from said liquid supply.

Preferably, the heat treatment section includes a holding section for holding liquid after application of heat thereto, the holding section located upstream of the evaporator section. of Preferably, the heat treatment section includes a first heat treatment section 30 with associated first holding section for applying a first heat treatment of a first 506 duration at a first temperature to a liquid and a second heat treatment section with associated second holding section for a second heat treatment of a second duration at a second temperature to a liquid from said first heat treatment section.

Preferably, the plant is adapted to hold the liquid in the first holding section for substantially the minimum duration required by the first heat treatment process.

Preferably, the liquid processing plant further includes an intermediate cooling section that in use actively cools the liquid between the first heat treatment section 10 and second heat treatment section.

Preferably, the first temperature is substantially between 80°C to 120°C and wherein the actual temperature is selected depending on the heat treatment requirements for the liquid.

Alternatively, the first temperature may be substantially between 80°C to 100°C.

Alternatively, the first temperature may be substantially between 80°C to 90°C.

Preferably, the second temperature is substantially between 72°C to 75°C and the second duration is substantially 15 seconds.

Preferably, the diversion valve system includes a first and a second valve, 25 wherein the second valve is located, and operated to direct liquid as required upon failure of the first valve.

" INTELLECTUAL OFFICE Or N.Z. 1 2 MAR 2003 5063 6 Preferably, the liquid is a food product and the liquid processing plant is adapted to pasteurise the food product.

Preferably, the food product is a milk product.

In a second aspect of the invention there is provided a method of heat treating id including the steps of: • providing a supply of liquid; • heating the liquid to a predetermined temperature; • holding the liquid in a holding section at substantially the predetermined temperature for a pre-selected period of time; • monitoring the conditions of the liquid in the holding section and/or the conditions of the holding section with one or more sensors; • concentrating liquid from the holding section in an evaporator section; and • controlling a diversion valve system downstream of the evaporator section, in response to the conditions monitored by the sensors, to advance the liquid to a recovery station for further processing or to divert it back to the supply.

Preferably, the steps of heating and holding the liquid include: • holding the liquid in a first holding section at substantially a first temperature for a first pre-selected period of time which is selected to impart predetermined heat related properties to the liquid; • holding the liquid in a second holding section at substantially a second temperature for a second pre-selected period of time; .NTEuinCVdML pKCi-v/fY ' OFFICE OF N.Z. " L 1 2 MAR ~M3 I a liqui n pr rr p p p ^ 5063 7 and wherein the step of monitoring the conditions of the liquid includes monitoring the conditions of the liquid in the either or both of the holding sections.

Preferably, the second temperature is less than the first temperature and greater than or equal to a predetermined minimum required temperature to effect a required heat treatment on liquid in the heat treatment section.

Preferably, the first pre-selected period of time is substantially that required for 10 passage of the liquid through the first holding section, and the liquid temperature is changed to the second temperature substantially immediately after the first preselected period has elapsed using a cooling means.

Preferably, the cooling means is a flash cooling unit that in use cools the liquid 15 to substantially the second temperature.

Preferably, the first temperature is between substantially 80°C and 120°C depending on the heat treatment requirements for the liquid.

Alternatively, the first temperature may be between substantially 80°C and 100°C.

Alternatively, the first temperature may be between substantially 80°C and 90°C.

Preferably, the second temperature is substantially between 72°C to 75°C and the second pre-selected period of time is substantially 15 seconds. "^~e^Cl'iJAL pro^E:2ty1 Oi-Fice of N.Z. 1 2 MAR M3 8 ii.

Preferably, the liquid is a food product and the method of heat treating is adapted to pasteurise the food product.

.MTb"' 'JCVL'.AL PROP3.1TY c r .'c:- OF n.z. I 1 2 HAH W3 RISfilSHfEU Preferably, the liquid is a milk product.

According to a third aspect of the invention there is provided a heat treatment plant substantially as herein described and with reference to the accompanying drawings.

According to a fourth aspect of the invention there is provided a method for heat treatment of a liquid substantially as herein described and with reference to the accompanying drawings.

Other aspects of the invention may become apparent from the following 15 description which is given by way of example only and with reference to the accompanying drawings.

Brief Description of the Drawings is a schematic of a liquid processing plant of the invention, is a detailed schematic of a preferred form of the evaporator plant of Figure 1.

Modes for Carrying Out the Invention Figure 1 provides a generalised schematic of a liquid processing plant according to one preferred form of the invention. A heat treatment section of the 25 invention is shown as A with associated holding tubes D, and an evaporator section B. The other principal components are a sensing system E, a diversion system C and a balance tank F.

Figure 1: Figure 2: The product of the heat treatment section A and associated holding tubes D is sensed by the sensing system E, before passage into the evaporator system B. The product emerging from the evaporator system B is communicated to either the M,6J 8 0 9 balance tank F, and ultimately returned to the heat treatment system A> for further processing and/or drying as indicated by arrow G. The diversion system C controls the communication of the product to the balance tank F or advanced for further processing depending upon the result of the sensing by the sensing system 5 E.

..M i Ei ^1 J/hL i' t<u'■ i v7 i omci Or N.Z. 1 2 MAR 2003 With reference to Figure 2, in which a more detailed schematic of a liquid processing plant according to the preferred form of the invention is shown, operation of the evaporator plant is as follows. Liquid product is received into a supply tank 1, and pumped to the heat treatment section A, by a pump P1. The supply tank 1 provides the 5 balance tank of Figure 1. It will be appreciated by those skilled in the art that the number, location and type of pumps or other pumping means used may be varied depending on the particular requirements of the plant.

The heat treatment section A includes a number of unit operations to raise and or lower the temperature of the liquid to be heat treated. With reference to Figure 2, these I operations include heating means including heat exchangers 2, 3 and a heating unit 4, which heats the liquid product by the injection of vapour (vapour 1). A control valve 24 is provided to enable control over the amount of heating in the heating treatment section A.

Although Figure 2 shows a particular arrangement of the heating and cooling unit 15 operations, there are many different methods of heating suitable for use in liquid processing systems and the number and type of heat exchangers used may be varied. The particular method of heating employed preferably requires no use of the actual heat-treated product (or concentrate) from down stream of the holding section 9 for heating the feed in the heat treatment section A. This minimises complications associated with 20 ensuring no leakage between the streams of liquid, such as the use of a positive pressure in the downstream heat treated regions. However, other arrangements of heating operations will be possible as can be envisaged by one skilled in the art including in some cases, use of downstream product in the heat exchange processes of the heat treatment system.

The heat exchangers 2, 3 and heating unit 4 provide a first heat treatment process, by which the liquid product may be heated to a temperature in excess of pasteurisation temperatures.

A first holding section 18 is provided if it is necessary to hold the liquid product at a particular temperature in this process for a particular length of time. However, the 30 liquid product may pass directly through the first holding section 18, which in the limit may simply be in the form of an interconnecting pipe between the heating section and the next processing unit, without being held for any time period. The time that the liquid is held at this elevated temperature is dependent on the requirements for the liquid and is chosen to impart heat related properties to the liquid. For heat sensitive liquids, which may be adversely affected by prolonged exposure to these temperatures, this time is preferably pre-selected as the minimum time to impact these properties to the liquid. Energy and efficiency savings may also result in minimising this period.

The liquid product exits from the first holding section 18 and passes to a cooling section 7, wherein the temperature of the liquid product is actively reduced, in this case, to that required for pasteurisation. The cooling section 7 is preferably a flash cooling unit allowing rapid cooling. Alternatively, a heat exchanger may be used to provide the cooling, utilising any liquid at a cooler temperature. Liquid from downstream of the holding section 9 may be used provided adequate protection against contamination is provided.

If a flash cooling unit is used, the liquid product is pumped from the cooling section 7 using a pump P2 to the second holding section 9, wherein the liquid product is held at the desired flow rate for at least a minimum holding time. When the liquid product is milk this pasteurising process may involve holding the liquid product in the range 72°-75°C for approximately 1 5 seconds. The temperature and duration used may be dictated by legislation.

The second holding section 9 may alternatively be located upstream of the first holding section 18 and first heat treatment process if required. A system configured in this way may also be used as a pasteuriser. However, this is a less preferred form of the invention due to resulting increased complexity, attributable largely to the additional means of heating required. The first and second holding sections 18, 9 provide the holding tubes D of Figure 1.

A flow meter 8 is located in the pipeline between the cooling section 7 and the holding section 9. The flow meter 8 can be used to verify that the maximum flow rate is not exceeded. This ensures that the liquid product has been held in the second holding section 9 for at least the specified time. The flow meter 8 may alternatively be located between the second holding section 9 and the evaporator section B as indicated by flow meter 8'. A temperature transmitter 10 located downstream of the second 12 holding section 9 is used to verify that the product has been held at or above the required temperature. In the preferred embodiment of Figure 1, the flow meter 8 and the temperature transmitter 10 together provide the sensing system E of Figure 1.

It will be appreciated by those skilled in the art that sensors may also or 5 alternatively be provided to monitor the conditions of the holding section 18 and that the sensors may be located internal or external to the holding sections 18, 9. Furthermore, additional sensing may be performed if required, for example obtaining a pressure measurement, viscosity measurement or any other measurement of the liquid characteristics.

The evaporator section B includes one or more evaporator calandrias 20 where the liquid product is concentrated to produce "concentrate" and the moisture which is evaporated (vapour) is condensed in a cooling unit 21 to form vapour condensate. The vapour condensate may be used for preheating the feed product in the heat exchangers 2 and/or 3 prior to disposal or further treatment, as indicated by path 22. The vapour 15 condensate may be pumped to the heat exchangers by pump P4 and is preferably, either returned to the supply tank 1, or discarded to reduce the risk of contamination of the liquid output.

In the event that the temperature at the end of the second holding section 9, as monitored by the temperature transmitter 10, is other than that required for the heat ^^20 treatment process, or the flow rate as monitored by the flow meter 8, is higher than the required flow rate, then the liquid feed product has not received the prescribed heat treatment. Either or both of the temperature transmitter 10 and flow meter 8 may then actuate the diversion system C to prevent the product that has not been sufficiently treated from proceeding to further processing or drying.

The diversion system C shown in Figure 2, which receives product from the evaporator calandrias via pump P3, includes two diversion valves 13, 14. Actuation of the diversion system C causes the concentrate to be directed back to the supply tank 1. The diversion system C includes a primary diversion valve 13, and optionally, although preferably a secondary diversion valve 14. The secondary diversion valve 14 acts as a 30 leak detector so that in the event of failure of the primary diversion valve 13 no product can flow down stream of the diversion system C. There is further provided a third 13 diversion valve 1 5, which is actuated so that vapour condensate is directed to the supply tank 1 when either of the concentrate diversion valves 13, 14 are actuated. This ensures that the feed to the evaporator section B remains similar during the diversion mode as the forward flow mode. Alternatively, the condensate diversion may be 5 replaced by an alternative water supply when either of the concentrate diversion valves 13, 14 are actuated.

If the liquid feed product has not received the prescribed heat treatment within the second holding section 9 and the diversion system C is actuated, then the entire system must be sanitised before conforming product can be produced once more. To 10 sanitise the system all three diversion valves 13, 14, 15 are actuated to divert the concentrate and vapour condensate streams back to the feed tank 1. During this circulation the temperature of the system between the heat treatment section A and the primary diversion valve 14 is increased so that it is above the required holding temperature for the required time. The temperature is monitored by the temperature 15 transmitter 10 and a second temperature transmitter 12.

Following sanitising, the evaporator parameters may be re-set to the production set points and heat treatment and evaporation may recommence.

In an alternative embodiment, the heat treatment section may have only a single heating section and single holding section, with the diversion valves downstream of the '20 evaporator controlling whether the liquid is forwarded for drying or further processing or returned to the supply tank.

Where in the foregoing description reference has been made to elements or integers having known equivalents, then such equivalents are included as if they were individually set forth.

Although the invention has been described by way of example and with reference to particular embodiments, it is to be understood that modifications and/or improvements may be made without departing from the scope or spirit of the invention.

OrhlCt OF N.Z. 14 1 2 MAR 2jP

Claims (20)

Claims

1. A liquid processing plant including: • a heat treatment section for receiving liquid from a liquid supply and 5 applying heat treatment to received liquid; • one or more sensors for monitoring one or more pre-selected characteristics of the heat treatment section, or of the liquid within the heat treatment section; • an evaporator section downstream of the heat treatment section; 10 • a diversion valve system arranged downstream of the evaporator section; and • a recovery section; wherein dependent on the output of the one or more sensors the diversion valve system either directs liquid from the evaporator section to the 15 recovery section for further processing and/or recovery, or directs liquid from the evaporator section to the heat treatment section for re-processing.

2. The liquid processing plant of claim 1, wherein the one or more sensors includes a temperature sensor and a flow meter.

3. The liquid processing plant of either claim 1 or claim 2, wherein the 20 evaporator section in use provides a condensate and wherein the diversion valve system includes a condensate communication path for selectively communicating said condensate to said heat treatment section via said liquid supply or to said recovery section dependent on said output of the one or more sensors. 25

4. The liquid processing plant of claim 3, wherein the condensate communication path passes through the heat treatment section, thereby allowing heat transfer from the condensate to liquid from said liquid supply.

5. The liquid processing plant of any one of claims 1 to 4, wherein the heat treatment section includes a holding section for holding liquid after 30 application of heat thereto, the holding section located upstream of the evaporator section. 15 5063 5 7. 10 8. 9. 15 10. 20 25 12. 13. 30

The liquid processing plant of claims 5, wherein the heat treatment section includes a first heat treatment section with associated first holding section for applying a first heat treatment of a first duration at a first temperature to a liquid and a second heat treatment section with associated second holding section for a second heat treatment of a second duration at a second temperature to a liquid from said first heat treatment section.

The liquid processing plant of claim 6, wherein the plant is adapted to hold the liquid in the first holding section for substantially the minimum duration required by the first heat treatment process.

The liquid processing plant of claim 6 or claim 7, further including an intermediate cooling section that in use actively cools the liquid between the first heat treatment section and second heat treatment section.

The liquid processing plant of any one of claims 6 to 8, wherein the first temperature is substantially between 80°C to 120°C and wherein the actual temperature is selected depending on the heat treatment requirements for the liquid.

The liquid processing plant of any one of claims 6 to 8, wherein the first temperature is substantially between 80°C to 100°C and wherein the actual temperature is selected depending on the heat treatment requirements for the liquid.

The liquid processing plant of any one of claims 6 to 8, wherein the first temperature is substantially between 80°C to 90°C and wherein the actual temperature is selected depending on the heat treatment requirements for the liquid.

The liquid processing plant of any one of claims 6 to 11, wherein the second temperature is substantially between 72°C to 75°C and the second duration is substantially 15 seconds.

The liquid processing plant of any one of claims 1 to 12, wherein the diversion valve system includes a first and a second valve, wherein the second valve is located, and operated to direct liquid as required upon failure of the first valve. 16 ..MTELLIECTUAL PROP^TY OFFICE OF N.Z. 1 2 MAR 2003

14. The liquid processing plant of any one of the precearng'craims, whi#i|h| liquid is a food product and the liquid processing plant is adapted to pasteurise the food product.

15. The liquid processing plant of claim 14, wherein the food product is a milk 5 product.

16. A method of heat treating a liquid including the steps of: • providing a supply of liquid; • heating the liquid to a predetermined temperature; • holding the liquid in a holding section at substantially the predetermined 10 temperature for a pre-selected period of time; • monitoring the conditions of the liquid in the holding section and/or the conditions of the holding section with one or more sensors; • concentrating liquid from the holding section in an evaporator section; and • controlling a diversion valve system downstream of the evaporator 15 section, in response to the conditions monitored by the sensors, to advance the liquid to a recovery station for further processing or to divert it back to the supply. 20

17. The method of claim 16 wherein the steps of heating and holding the liquid include: • holding the liquid in a first holding section at substantially a first temperature for a first pre-selected period of time which is selected to impart 25 predetermined heat related properties to the liquid; • holding the liquid in a second holding section at substantially a second temperature for a second pre-selected period of time; and wherein the step of monitoring the conditions of the liquid includes 30 monitoring the conditions of the liquid in the either or both of the holding sections.

18. The method of claim 17, wherein the second temperature is less than the first temperature and greater than or equal to a predetermined minimum 17

19. 5

20. 40 10 21. 22. 15 23. 24. • 20 25. 25 26. 27. 28. 30 required temperature to effect a required heat treatment on liquid fthQ ^ heat treatment section. The method of either claim 17 or claim 18, wherein the first pre-selected period of time is substantially that required for passage of the liquid through the first holding section, and the liquid temperature is changed to the second temperature substantially immediately after the first pre-selected period has elapsed using a cooling means. The method of claim 19, wherein the cooling means is a flash cooling unit that in use cools the liquid to substantially the second temperature. The method of any one of claims 17 to 20, wherein the first temperature is between substantially 80°C and 120°C depending on the heat treatment requirements for the liquid. The method of any one of claims 17 to 20, wherein the first temperature is between substantially 80°C and 100°C depending on the heat treatment requirements for the liquid. The method of any one of claims 18 to 20, wherein the first temperature is between substantially 80°C and 90°C depending on the heat treatment requirements for the liquid. The method of any one of claims 17 to 23, wherein the second temperature is substantially between 72°C to 75°C and the second pre-selected period of time is substantially 15 seconds. The method of any one of claims 16 to 24, wherein the liquid is a food product and the method of heat treating is adapted to pasteurise the food product. The method of any one of claims 16 to 24, wherein the liquid is a milk product. A heat treatment plant substantially as herein described and with reference to the accompanying drawings. A method for heat treating a liquid substantially as herein described and with reference to the accompanying drawings.