Abstract:
An apparatus for the heat treatment of a product, in particular a product contained within a hermetically sealed pouch or other plastic container, the apparatus having, a heating unit to contain a product as product is brought towards a treatment temperature and pressure, a sterilization unit to contain product at a pre determined treatment temperature and pressure to sterilize product, and a cooling unit to bring a product from the treatment temperature and pressure towards ambient; each unit being selectively sealable from another unit, the apparatus further having: a plurality of conduits carrying heat-exchange fluids allowing heat to be transferred between units; and having a heater, preferably producing steam, to supply heat to the apparatus; a heat-exchange unit enabling heat energy to be transferred from one conduit to another; and a hot well to retain a reservoir of heat exchange fluid at the highest temperature required by the apparatus.

Description:
FIELD OF THE INVENTION 
     The present invention is concerned with a retorting apparatus used in the heat treatment of food products and in particular with a heat exchange system incorporated therein. 
     BACKGROUND TO THE INVENTION 
     The heat exchange system as herein described is useful in conjunction with any continuous retorting apparatus in order to control the particular heat transfer fluids used within that apparatus. Nevertheless, the system is especially suited and described with reference to the retorting apparatus described in International (PCT) Patent Application No. PCT/GB08/01146. In order to improve the functioning of a retorting apparatus, the invention described in PCT/GB08/01146 utilises a plurality of enclosed volumes, each separately sealable from other volumes, the product moving serially from one volume to another. 
     With increasing energy prices and also a desire to reduce so-called greenhouse emissions, minimising energy wastage is increasingly important. Prior art batch retorts are not on the whole energy efficient, and the ineffective usage of the energy in the heating fluids results in a large amount of energy and water being wasted. 
     Continuous retorts can be significantly more energy efficient, but have failed to become commercially acceptable due principally to excessive complexity, size and cost compared to existing batch retorts. 
     The present invention therefore seeks to address the above problems and produce a retorting apparatus incorporating a heat exchange system which provides optimised energy usage as well as providing the means of transporting the product through the retort, thereby significantly reducing the complexity and cost of the retort. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention there is provided an apparatus for the heat treatment of a product, in particular a product contained within a hermetically sealed pouch or other plastic container, the apparatus comprising, a heating unit to contain a product as product is brought towards a treatment temperature and pressure, 
     a sterilisation unit to contain product at a predetermined treatment temperature and pressure to sterilise product, 
     and a cooling unit to bring a product from said treatment temperature and pressure towards ambient; 
     each unit being selectively sealable from another unit, the apparatus further comprising: 
     a plurality of conduits carrying heat-exchange fluids allowing heat to be transferred between units; 
     and comprising a heater, preferably producing steam, to supply heat to the apparatus; 
     a heat-exchange unit enabling heat energy to be transferred from one conduit to another; 
     a hot well to retain a reservoir of heat exchange fluid at the highest temperature required by the apparatus. 
     Preferably the apparatus comprises a plurality of heating units, enabling the heating to be carried out in staged steps and increasing the efficiency of energy usage. 
     Optionally, the heat-exchange unit includes a heat pump. 
     The apparatus preferably includes a plurality of cooling units enabling the cooling to be carried out in staged steps, and again increasing the efficiency of energy usage. 
     Preferably, the hot well retains water at a temperature of greater than 110 C and further preferably below 130 C. 
     Conveniently the apparatus includes a magazine to retain a product combining pouch convey a product containing pouch through the apparatus. Further conveniently the magazine is rotably mounted about a central shaft, said shaft being so configured to receive a plurality of magazines. 
     Preferably, heat is conveyed through the apparatus by a liquid. Further preferably, the fluid acts to exert a force on product to facilitate motion of product through the apparatus. The shaft and magazines are advantageously surrounded by a casing, further advantageously of tubular construction to allow easier handling of product. The casing optionally has one or more apertures in the wall of the casing to enable fluid to circulate within the casing and about the product. Advantageously, the casing includes pins or baffles on the outer surface to increase the force felt by the casing due to flow of heating fluid. 
     Preferably excess water in excess of that needed by the retort is returned to the heat well. Further preferably, a valve is included preventing flow of water having a temperature of greater than 125 C into the hot well. 
     The apparatus preferably includes one or more fans to draw air through a unit to aid heat transfer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the accompanying drawings which show by way of example only, two embodiments of a retorting apparatus and heat exchange system. In the drawings: 
         FIG. 1  is a diagrammatic illustration of a retort and heat exchange system incorporating a heat pump; 
         FIGS. 2   a  and  2   b  are diagrammatic illustrations of product-containing cassettes secured within magazines passing through the apparatus; and 
         FIGS. 3   a - 3   d  illustrate passage of cassettes into a heating chamber as well as details of heat transfer fluid flows and hydraulic rotation. 
         FIGS. 4   a - 4   f  are diagrammatic illustrations of the same retort without the heat pump but utilising a simple heat exchanger instead and showing the various stages of heat exchange and hydraulic transfer along with the associated conduits; 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The retorting apparatus as shown in  FIG. 1  is suitable for sterilising food products retained within a sealed container and particularly suitable where the container is formed of a plastics material. 
     The product being processed through the apparatus is subjected to a heating and a pressurising cycle in which the product is brought from ambient conditions to elevated temperature and pressure conditions to accomplish sterilisation before being returned to ambient. 
     In general, the system for controlling the temperature and pressure comprises a heat source in the form of a boiler, which provides steam directly to a number of elements of the system. A heat exchanger enables energy to be transferred from one fluid conduit to be transferred to another without the risk of bacterial contamination being passed over. In addition a heat pump provides energy savings by enabling partially cooled water to be cooled to ambient and distributing the energy removed from that water to another volume of water which requires heating. A hot well, including a supply of steam heating direct from the boiler, is also provided to deal with the handling of water at the hottest temperatures used by the system, above 110 C, and the heating and storage of such water at the maximum required at around 130 C. 
     By providing for energy to be movable between areas of energy deficit and surplus, the energy efficiency of the retort apparatus is improved. 
     Referring in detail to the embodiment shown in  FIG. 1 , this shows a retorting apparatus in which batches of food product held within a container are progressively heated and then cooled, prior to being packaged for sale. The product is typically mounted in a magazine which then passes from one chamber (labelled T 1 , T 2  and T 7 -T 10 ) to the next. Within the main sterilisation chamber  10  the magazine is mounted on a housing for rotation about the central axis of the retort between positions T 3 -T 6 . Whilst undergoing this larger scale rotation of movement, the magazine can also rotate relative to the housing thereby increasing the overall rotation to ensure even heating of product, or improved ingredient mixing, or improved internal heat transfer. Alternatively, the magazine can be counter rotated to eliminate or reduce such rotation where this is of benefit to the product, such as in products where compaction can reduce quality. 
     In  FIG. 1 , chamber T 1  is used to load magazines or cassettes of product containers into a position from which they can be carried through the continuous retort and within which initial heating can commence by direct contact heat transfer from hot water at approximately 60 C circulating within. The magazines in chamber T 1  can be rotated by the support shafts, or by the hydraulic action of pressurised water impinging upon fins attached to the magazines to allow any trapped air to be evacuated by gravitational displacement and to permit mixing of ingredients if needed. 
     Once the first chamber contains the required number of magazines the gate valve connecting chambers T 1  and T 2  is opened so that the magazine full of cassettes can be transported by the drive chain located between the two rotational shafts, or by the hydraulic action of heat transfer fluids being sucked from T 1  into the primary heating chamber T 2 . 
     The chamber T 2  is sealed by the closure of this gate valve and the 90 C water contained therein is replaced by hotter pressurised water over a period of minutes to take the product up to the final sterilisation temperature and overpressure. The magazines in chamber T 2  can also be rotated by mechanical or hydraulic means to allow further mixing of ingredients if needed. After the required time the gate valveconnecting T 2  with chamber  10  is opened so that the magazines can be transported by either mechanical or hydraulic means into the chamber  10   
     The main chamber  10  comprises a main substantially cylindrical pressure vessel. During operation of the chamber  10 , a body of water  11  is maintained at such a level that the product passes therethrough. Within the main chamber  10  is disposed a large rotational frame holding four tubular compartments into which the product container magazines are loaded. It should be evident to the skilled observer that the number of tubular compartments fitted into the chamber  10  is chosen to suit the user and expected product. The tube can have a central spargepipe along its length enabling heating fluid to flow along its length, or alternatively the hollow centres of each cassette can act collectively as a sparge pipe. The chamber  10  is kept at the required sterilisation temperature and pressure by the introduction of steam at a pressure of 5 bar via the two upper sparge pipes which are above the water level. If necessary compressed air can also be used to augment or help the control of overpressure. The temperature and pressure are maintained at these constant values during a full normal period of operation of the retort, which could easily be several days in duration. 
     Loading of magazines into the chamber  10  from the chamber T 2  takes place such that the magazines enter the lower half of the chamber  10  below the water level maintained within the chamber  10 . After a preset time within the pressurised water a magazine, is rotated upwardly, in the direction indicated by the arrow A between positions T 3  and T 6 , out of the water (indicated by the shaded region  11 ) and into the pressurised steam above the water surface. Alternatively, the entire chamber  10  may be flooded with pressurised water. 
     Independent rotational means are provided, either mechanical or hydraulic, to provide additional rotation of product at positions T 3 -T 6  or to counter rotate to eliminate the effect of the rotation of the magazine carrier or to provide pre programmed rotation or counter rotation as required. 
     Before unloading from T 6  can commence the first cooling chamber T 7  needs to be filled with high temperature water and pressurised to sterilisation over pressure by closing its gate valves and transferring its contents to T 2  to heat the incoming product at the same time as filling it from the chamber  10 . The water pumped from chamber  10  is made up from the hot well. 
     As soon as the pressures and temperatures are equal in both chamber  10  and T 7  the interconnecting gate valve can be opened. Once the gate valve is fully open the product magazine in position T 6  is transferred to the chamber  17  by either mechanical or hydraulic means. 
     When the chamber T 7  has received its product magazine, the gate valve closes and the high temperature water is pumped back into the lower section of the baffled hot well  27  and replaced with water from T 8  at around 60 C, thereby cooling the product to around 90 C. 
     The chamber T 8  is the location of the second stage of cooling where the product is cooled from 90 C to 60 C by pumping in water at 40 C from the chamber T 9 . 
     From the chamber T 8 , the product then passes into two further chambers T 9 , T 10  in which it is further cooled to 40 C and 30 C respectively. In the final chamber T 10  a fan  35 , axially located with respect to the chamber T 10  dries and cools the product by evaporative cooling of the water on the outside of the product containers. 
     Dealing now with the heating and cooling system in more detail, unprocessed product enters the chamber T 1 . Water from the chamber T 2  which is at a temperature of around 90 C is pumped, via the valve V 2 , into the chamber T 1 . This preheats the product to around 80 C. In doing so, the energy lost to the product causes the temperature of the water to fall to around 60 C. This cooler water is pumped via a conduit  20  to a heat exchanger, which in the described embodiment comprises a heat pump  21 , and in particular to the evaporator  22  of the heat pump  21 . Here the water is cooled to 20 C by means of a refrigerant contained within a coil  23  of the evaporator  22 . The energy now held in the refrigerant is passed via a compressor  24  to a heating section (see below) of the heat pump  21 . The chilled water is either returned directly to the chamber T 9  via conduit  34  or is circulated through a heat exchanger (not shown) to keep segregation of product cooled heating water (which may be contaminated) from the heat treated product which is being cooled. 
     The product, when at a temperature of around 80 C passes to the chamber T 2 . Here, water from the chamber retort  10 , at a temperature of around 130 C passes by the conduit  25  to the chamber T 2 . Energy from the water is used to heat the product. In doing so, the temperature of the product is raised to around 125 C and the temperature of the water falls to around 90 C, ready to be pumped into T 1  as described above. The product then passes into the retort  10  at position T 3 . The water  11  is at a temperature of 130 C and is maintained in liquid form by the pressure within the retort  10 . The temperature of the water  11  acts to commence sterilisation of the product. Part or all of the loss of heat energy of the water  11  occasioned by this step is replaced by that from the steam above the water level. 
     The temperature within the retort  10  is maintained at 130 C by heat from two sources. Firstly, steam is obtained directly from the boiler  26 . Secondly, heated recycled water is obtained from the hot well  27 . 
     Once the sterilisation process is complete, product passes from the retort  10  to the chamber T 7  where the product is cooled by water having a temperature of around 60 C and obtained from the chamber T 8  via the conduit  28 . The product temperature therefore falls from 130 C to around 90 C. The water, before cooling, passes via a conduit  29  and the valve V 1  to the hot well  27  to be heated to 130 C ready for re-use to heat the chamber  10 . 
     Initially, when the product is at a 130 C having just exited the chamber  10 , the water flowing along the conduit  29  is above 125 C and the valve V 1  directs the water directly into the hot well  27 . As the temperature of the product falls however, the water temperature in the conduit  29  also falls. Below a temperature of 125 C, the valve V 1  directs the water to the condenser  30  of the heat pump  31 . Here heat is removed from the refrigerant bringing the water to around 130 C, which water than passes via a conduit  31  to the hot well  27 . It should be noted that whilst the water from the conduit  29  is being passed by the valve V 1  directly into the hot well  27 , water at around 90 C is drawn via a conduit  32  from the chamber T 2  into the condenser  30 . When required, water in the hot well  27  can be heated by heat taken from the steam drawn from the steam boiler  26  by means of a coil  33 . Alternatively, in applications using heat pumps with refrigerant fluids which are more suited to lower temperatures, the heat pump is used mainly to augment efficient heat transfer from the cooling water and the steam boiler is the only means to add heat energy to the medium to high temperature water in the 65 to 90 C range which is then heated to 130 degrees C. 
     The product in the chamber T 7 , once it has reached a temperature of around 90 C is transferred to the chamber T 8 , where further cooling to around 60 C takes place. The cooling is achieved by pumping water from the chamber T 9 , the water having a temperature of around 40 C into the chamber T 8 . Similarly, on passage to the chamber T 9 , the product is cooled to a temperature of around 40 C. In order to achieve this, cooling water from the evaporator  22  at a temperature of around 20 C, is pumped via a conduit  34 , or via the segregating heat exchanger, into the chamber T 9 . Finally, the product is transferred from the chamber T 9  to the chamber T 10  where the product is dried, through evaporative cooling by air drawn through the chamber T 10  by the axially oriented fan  35  mounted thereto. Water losses are made up by running water from a potable mains supply via a break tank into the chamber T 9  to the required level. 
     Turning now to  FIGS. 2 ,  3  and  4 , a further feature of the apparatus is hereby exemplified. The movement of the product-bearing magazines is illustrated in simplified form in  FIGS. 2   a  and  b . In summary, the product containing magazines  57  are loaded into the apparatus at location A. They then pass through a series of chambers in the direction shown by the arrows before exiting the apparatus at position B. The chambers are shown in  FIG. 2   a  as being five in number, although it will be recognised that this number can be chosen to suit the intended application. The chambers  1 - 5  are separated from one another by a series of gate valves  1 - 4  which can isolate chambers from each other when closed. 
     The heating and heat exchange system described above assists in movement of product between chambers, as exemplified in  FIGS. 3   a - 3   d . The entry and exit points  60  and  61  are so located that heating or cooling fluid flows through a chamber  52  in the direction of movement of the magazines  57  which contain cassettes  40  which bear product. The magazines  57  retain the cassettes  40  by means of end caps  55  which are of larger diameter than the magazines  57 . When the magazine  57  has to be moved within the retort the pressure in conduit  60  in increased relative to that in conduit  61  by a pump. The force generated by differential pressure on the end caps  55  thereby causes the magazines to move in the required direction. The efficiency of this process along with the product treatment process in general, is improved through the segregation of ‘slugs’ of water which can be at different temperatures in  60  and  61  and are effectively kept from mixing by the end caps. This is particularly useful where the next set of conditions in the newly vacated chamber are designed to be different to those being used prior to the transfer of the magazine out of the chamber. 
     The tubular magazine arrangement  57  comprises a cylindrical portion  53  into which an array of five product carrying cassettes  40  is passed. The cylinder  53  includes perforations which enable heating fluid to freely circulate within and pass through the cylinder  53  to heat or cool product. 
     Once the product is located within the cylinder  53 , end plates  55  are secured over the ends of the cylinder  53  and the complete magazine  57  is loaded into the chamber  51 . The pressure in chamber  51  is now increased relative to that in chamber  52 . When the gate valve  58  on the exit end of chamber  51  is opened, the magazine containing the product is moved into the next chamber  52  in the direction shown by Arrow C in  FIG. 3   b  by the pressure differential now acting on the end caps  55  which in turn produces a translational force. 
       FIG. 3   c  shows that this transfer of magazines can be actuated from within a single chamber by flow from 60 to 61 as described above. 
     The energy efficiency of the apparatus is thereby increased as the heat exchange fluid doubles as the motive force fluid. Moreover, the requirement for additional mechanical features to cause this motion is also reduced. 
     It will be appreciated that although the end plate of  55  must be solid the other elements of the end cap can be open and can include features to improve engagement and force exerted on the cylinder  53  by the fluid flow. Moreover, the end cap can also include features such as fins  56  or baffles to increase or redirect the said force, distribute heat exchange fluids more efficiently, or enable rotation or counter rotation of the cylinder. 
       FIG. 3   d  shows two such features. When heat transfer fluids are directed via conduit  62  they enter the end cap between two end plates, the inner one of which has an open centre which aligns with the hollow core of the product bearing cassettes which directs the fluid into the said core in the direction of arrow D. As the outlet  63  is inboard of the other end cap it can only accept fluids which have been forced between the individual product pouches or containers in an outwardly radial flow as shown by the eight smaller arrows. Of course this flow is in fact taking place over 360 degrees, not just in one plane as shown here. The second drawing shows the effect of adding an extra inlet and canting them now shown as  64 . The inlet fluids now impinge on the fins  56  and cause a rotational effect in the direction of arrow E. It can therefore be seen that the retort designer now has multiple options to make use of the heat transfer fluids in the detailed management of the product as it passes through each stage of the continuous retort. 
       FIGS. 4   a - f  shows the same retort as  FIG. 1  but with different pipework to permit hydraulic transfer of product magazines or ‘cassettes’ and shows the progression of cassettes  1  to  8  passing through that retort. The four stages of loading, heating, cooling and unloading are managed in this embodiment alongside the flow of heat transfer fluids for both heat transfer as well as physical transfer of cassettes. 
       FIG. 4   a  shows stage  1  with gate valves GV 1  and GV 3  open. The cassette  3  (Cas 3 ) is being transferred from the chamber T 10  to the chamber T 7  by the pumping of 130 C water from chamber T 7  to the inlet chamber of piston pump P 1  via conduit c. At the same time the discharge side of the piston pump P 1  is transferring water at 130 C to the hot well via conduit b. The water entering the hotwell at the lower section displaces water from the top section back into chamber T 10  via conduit a. All of these transfers are taking place from a base pressure of 3 bar with the pumping action of P 1  providing sufficient over/under pressure to ensure hydraulic force sufficient to provide the necessary transfer of the two cassettes being moved. 
     At the same time the cassette Cas 6  is being transferred from chamber T 1  to chamber T 2  by the action of the piston pump P 2  which is sucking water at 90 C from the chamber T 10  side of the chamber T 2  via conduit d and at the same time is pumping water at 90 C through a conduit e into the newly loaded cassette  7  via its hollow central core, thereby increasing the head in both chambers T 0  and T 1  which completes the hydraulic circuit and forces the cassette  6  to move into chamber T 2 . 
       FIG. 4   b  shows the beginning of stage  2 . All four gate valves are now closed and piston pump P 2  is now on its return stroke pumping water at 90 C from its new discharge side (which had been taken from chamber T 2  in stage  1 ) into the core of the cassette  7  via conduits n and m and the un-sterilised water side of heat exchanger x, thereby further heating the product within the cassette  7 . This water is being heated in the heat exchanger by hot water on the sterilised water side which is being circulated by centrifugal pump P 3  via conduits i and l through the core of cassette  3  within chamber T 7 , thereby cooling the product contained in cassette  3 . 
     Product in cassette  6  is being heated from 90 C to over 110 C and around 2.2 bar by the action of both the discharge and inlet sides of piston pump P 1  via conduits j and k. 
     Cassette  1  is being withdrawn from chamber T 9  and mains water is introduced to the core of cassette  1  to further cool the product contained therein from 40 C to 30 C. The excess water drains into chamber T 9  by gravity, cooling the water in chamber T 9  to between 20 C and 40 C. 
       FIG. 4   c  shows the end of stage  2 , some two minutes after its start. The product in the cassette  7  is now around 60 C, an increase of 40 C from ambient and that in cassette  3  is now around 90 C, 40 C lower than sterilisation temperature. The temperature of product in the cassette  6  is now at almost 130 C and the pressure in chamber T 2  has been increased to 3 bar. 
     The final cooling and drying of cassette  1  and its product is achieved by forced air from the axial fan through its core. 
       FIG. 4   d  shows stage  3 . The pressures in T 7  and T 6  are now equalised enabling the gate valve GV 4  to open and cassette  3  to be transferred by the hydraulic action of water being pumped from the discharge side of piston pump P 1  at 1.2 bar against the lower pressure head of 1.1 bar in chamber T 8 . The water flow into chamber T 8  is drawn into the suction side of centrifugal pump P 3  via conduit m and the heat exchanger x and thence via conduit s into the core of the newly loaded cassette  8  which is at 20 C. 
     The pressures in chambers T 10  and T 2  are also equal at 3 bar enabling gate valve GV 2  to open and the hydraulic action of water at 90 C and 3 bar being pumped from P 2  via conduit q to the chamber T 0  side of chamber T 2  to transfer cassette  6  into chamber T 10 . Overflow water at 130 C from chamber T 10  is returned to the hotwell via conduit a. The cassette  1  is now ready for removal from the retort.  FIG. 4   e  shows the start of stage  4 . All gate valves are again closed. The chamber T 7  is pressurised from 1.2 bar up to 3 bar by the opening of conduit y which then allows the transfer of water at 130 C into chamber T 7 , mixing with the water at 90 C contained within chamber  17  which in turn is drawn into the inlet side of piston pump P 1  via conduit v at an aggregate temperature of 110 C. 
     The water contained in chambers T 9  and T 8  is circulated through the heat exchanger and cassettes  2  and  3  via conduits h, g and m by piston pump P 3  until the temperature in conduit h exceeds that in T 9 . 
     The 90 C water in the discharge side of piston pump P 2  is pumped into the core of cassette  8  to heat it from 60 C. Excess water at 90 C is drawn into the inlet side of piston pump P 2  from chamber T 1 . 
     The 110 C water in the discharge side of piston pump P 1  is pumped into the base of the hot well where it is heated to 130 C by the boiler (not shown). Mixing of water at 110 C and 130 C is avoided through the use of baffles within the hot well. Water at 130 C is thereby pumped via conduit a into the core of cassette  6  within chamber T 10 , heating the product contained therein from 110 C to 130 C. 
       FIG. 4   f  is the end of stage  4 . Chambers T 0 , T 1  and T 2  are all now at 90 C. The excess pressure in chamber T 2  is bled into chamber T 0  via the core of cassette  8  via conduit z. The cycle of 4 stages is now ready to be repeated. 
     It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention.