GB2247829A - Steam peeling of fruit and vegetables - Google Patents

Abstract

In a steam peeling apparatus, a rotatable pressure vessel 1 accommodates product to be peeled and means are provided for charging the pressure vessel with steam under high pressure and for exhausting steam from the vessel. The pressure vessel is mounted for rotation about a transverse axis so that the vessel passes through an inverted disposition in which its sealing opening is directed downwardly. A selector 46 regulates the period during which the vessel is charged with steam and initiates the exhaust of steam. A speed controller 43 regulates a motor 42 for rotating the pressure vessel 1 such that the vessel will complete an integral number of rotations while it is charged with steam. The control system 48 may also or instead comprise a logic unit 51 responsive to a required rate of product throughput, for setting a batch load weight in dependence on the period for which the pressure vessel is charged with steam. <IMAGE>

Description

Steam peeling This invention relates to steam peeling. In particular, the invention is directed to apparatus and methods for steam peeling fruit and vegetable products contained in a pressure vessel.

Steam peeling is a process in which fruit or vegetable products to be peeled, for example, potatoes, are placed in a pressure vessel, which is then sealed and charged with steam at up to 300 p.s.i. Rapid heating of the surface regions of the product takes place. After a short period of exposure to steam, the pressure within the vessel is released and the steam is allowed to exhaust. Moisture located immediately beneath the skin of the fruit or vegetable product then rapidly evaporates, during this exhaust phase, due to its being at an elevated temperature, causing the skin to be ruptured and lifted off from the flesh of the product, thereby peeling it. In subsequent operations, the peeled skin may be removed fully and separated from the useful product.

The essential objectives of a steam peeling process are therefore twofold, as follows: (a) to remove the peel/skin from the surface of the product, but (b) in carrying out the first objective, (a) above, to nonetheless remove as little as possible of the flesh of the product, thereby providing savings in the cost of raw product.

It is an object of the present invention to improve the efficiency of steam peeling by substantially minimising the time during which the product is in contact with the steam. It is a further object of the invention to further improve the efficiency of steam peeling by substantially optimising the batch size of the product to be peeled.

According to a first aspect of the invention, there is provided steam peeling apparatus comprising a pressure vessel for accommodating product to be peeled, means for charging said pressure vessel with steam under pressure, and means for exhausting steam from said vessel, the pressure vessel being generally cylindrical, having a sealable opening at one end thereof and being mounted for rotation about an axis transverse to its longitudinal axis of symmetry, so that the pressure vessel passes through a substantially inverted disposition during rotation about said transverse axis, in which inverted disposition said opening is directed downwardly, and the apparatus also comprising control means for regulating the duration of the period during which the vessel is charged with steam, for initiating the exhaust of steam from the vessel following the period of charging with steam, and for driving the pressure vessel in rotation during a steam peeling cycle at a speed such that the vessel will complete a substantially integral number of rotations during the period of charging with steam.

Minimisation of the time during which the product is in contact with the steam is thus achieved by matching the pressure vessel rotations to the steaming time and by terminating steaming promptly at the start of the exhaust phase. The exhaust phase commences as rotation comes to an end. In this way, steam time can be optimized.

Preferably the control means comprises a variable speed drive for the pressure vessel and a logic unit responsive to an adjustable input for the steam charging period for setting said speed of rotation of the pressure vessel during a steam peeling cycle. In a preferred embodiment of the steam peeling apparatus of the invention, said control means is also responsive to a position input which may suitably be provided by a detector delivering an output signal when the pressure vessel is in a disposition in which said opening is directed upwardly.

The steam exhausting means may include a steam discharge line and an exhaust chamber selectively connectible to the steam discharge line for withdrawal of steam from the pressure vessel. The steam discharge and other service lines most suitably communicate with the interior of the pressure vessel through bearings supporting it for rotation about said transverse axis, and the substantially inverted disposition of the vessel preferably represents a product discharge orientation thereof.

Said exhaust chamber is suitably connectible to the steam discharge line through suitable valve means, spray means being provided to inject water into the chamber as required to condense steam accumulating therein. Drain means associated with the exhaust chamber allow withdrawal of accumulated condensate as required.

In a further aspect of the invention, there is provided a steam peeling method in which product to be peeled is exposed to high pressure steam for a controlled time period, wherein the pressure vessel is rotated according to a predetermined programme for at least a portion of the time period during which the product is exposed to high pressure steam and the rotation of the pressure vessel is matched to said time period of exposure to high pressure steam so that a substantially integral number of rotational cycles is completed during said time period during which the product undergoing peeling is exposed to high pressure steam.

Thus a particular improvement afforded by the present invention in a first aspect thereof, which may be referred to as a "rotational programme", is an enhanced efficiency of steam peeling, both in respect of removal of peel and skin from the surface of product, and also in respect of removing as little as possible of the flesh of the product.

The rotational programming feature of the present invention ensures that the pressure or processing vessel is always in its upright disposition at the end of the steaming period, irrespective of the duration of the steaming time.

A number of advantages flow from this improvement. There is a reduction in the exhaust time and the period of unwanted product heating which is typically associated with the pressure decay phase of the exhaust period is reduced, thereby reducing waste of useful product.

The invention allows reduction in overall cycle time, thereby enabling the processing of smaller batch loads. Reduction in batch loads in turn enables the use of shorter steam times and as a result less peel loss. The use of rotational programming enables the system to take full advantage of large bore steam inlet and outlet pipework and valving. Finally, rotational programming enables soft start and stop to be provided, thereby enabling smoother machine operation and longer machine life to be achieved.

In a further aspect, which may be combined with the first-mentioned aspect of the invention above or may be applied independently to steam peeling apparatus comprising a pressure vessel for accommodating product to be peeled, means for charging said pressure vessel with steam under pressure, and means for exhausting steam from said vessel, the pressure vessel being generally cylindrical, having a sealable opening at one end thereof and being mounted for rotation about an axis transverse to its longitudinal axis of symmetry, so that the pressure vessel passes through a substantially inverted disposition during rotation about said transverse axis, in which inverted disposition said opening is directed downwardly, the control means of the apparatus may comprise a logic unit responsive to an adjustable input indicative of a required rate of product throughput, for setting a batch load weight value in dependence on the duration of the period during which the vessel is charged with steam. The throughput of product may be defined by product input to the apparatus, in terms of quantity per hour or indeed quantity per any other unit of time.

To this end, said control means may regulate operation of a product delivery means to terminate product in-feed to the peeling apparatus when the weight of the current batch load as held in charging or supply means for the pressure vessel reaches a predetermined value.

The product delivery means is suitably an in-feed conveyor forwarding product to be peeled to a load-cell mounted hopper for the pressure vessel. Typically, the in-feed conveyor is driven by an electric motor, and the control means is responsive to the weight of the current batch load held within the supply hopper to terminate drive of the in-feed conveyor when the batch load reaches the value established by the control means for the particular value of line capacity or throughput required, in terms of product quantity or weight per hour or other unit of time.

The invention will now be described having regard to the accompanying drawings, in which Figure 1 is a diagrammatic representation of steam pressure versus time during a peeling operation using a conventional method and apparatus, Figure 2 is a diagrammatic sectional representation of a pressure vessel for use in the steam peeling apparatus and method of the present invention, Figure 3 is a schematic diagram of a steam peeling system in accordance with the invention, Figure 4 is a schematic diagram showing control features of a steam peeling system according to the invention, and Figure 5 is a schematic diagram incorporating control features of Figure 5, together with certain further control features relating to regulation of batch size.

Figure 1 is a diagrammatic representation of a typical conventional steam peeling cycle, in graphical terms. During the first two to three seconds of the cycle, the steam peeling pressure vessel is charged up to a pressure of approximately 300 p.s.i. with steam. This pressure of approximately 300 p.s.i. is maintained for a further seventeen or eighteen seconds, to about the twenty-first second of the cycle for the example shown, at which time the pressure is relieved and the steam exhausts from the pressure vessel during a further phase of the cycle extending over approximately the next twenty seconds, that is up to about the forty-second second of the cycle. During this time, there is continuing decay of steam pressure at a decreasing rate until the pressure finally approaches atmospheric.

Peeling is known to take place most efficiently at pressures of the order of 300 p.s.i. If lower pressures are used, longer steam times are required, and the result is the removal of greater amounts of product flesh than would be the case if a pressure of the preferred level were used. Referring again to Figure 1, efficient peeling will take place, for the cycle represented, during the steaming phase of the cycle, i.e. the period during which the pressure vessel is charged with a substantially constant steam pressure of the order of 300 p.s.i.

During the exhaust phase, during which the steam pressure decays continually towards atmospheric pressure, undesired continued "cooking" of the flesh of the product takes place. This potentially useful product is removed with the skin at the separating stage, and thus an extended exhaust phase leads to waste of useful product. The terms steaming and exhaust phases are defined more fully in regard to Figure 3, where the operation of a steam peeling system in accordance with the invention is described.

It will be apparent from the diagrammatic representation of Figure 1 that if the exhaust time is reduced, then the period of further exposure of the product to steam is similarly reduced and waste of useful product is minimised. Accordingly the present invention is directed inter alia not only to minimising steam time but also to achieving a reduction of the exhaust time by applying improvements to the peeling process as effected in a rotatable pressure vessel.

Figure 2 is a schematic sectional representation of a rotatably mounted pressure vessel I for a steam peeling system according to the invention, depicted in an upright configuration with the vessel loading and discharge opening 3 directed upwardly. During the steaming phase of a peeling cycle, this pressure vessel rotates about a horizontal axis, designated by reference 31 in Figure 2. Reduction in steam exhaust time for the pressure vessel 1 of Figure 2 may be achieved by one or more of the following methods: (a) Ensuring that the vessel is in the upright position, shown in Figure 2, during exhaust. In this configuration, the exhaust port 34 of the vessel is not covered by product and the flow of steam from the vessel may therefore take place in an unrestricted manner.

(b) Ensuring that the exhaust system is sufficiently large to ensure that the flow of exhaust steam from the vessel is not unduly restricted.

(c) Use of small batch loads, coupled with short cycle times.

This has the advantage that only a very small quantity of condensate is formed during steaming. This small quantity of condensate flashes off therefore very quickly during the exhaust phase. The use of short total cycle times enables plant line production rates to be maintained.

Proceeding from this last-mentioned requirement, efficient steam peeling is thus established by running at minimum batch load at all times. Batch load is determined by dividing the required output per hour by the number of batches per hour. The throughput or capacity of the peeling system is generally predetermined by the size of the peeler unit and the line throughput, while the number of batches per hour is determined by the overall cycle time, i.e. the time required by the peeling machine to fully process one batch of product.

Cycle time is made up of a number of individual time periods required to deal with each of the following steps: Fill time, close vessel door, steam time, exhaust time, open vessel door, and dump product.

Of these times, the fill and dump times and the door close and door open times are substantially invariable for a particular installation. Thus the main variables in the total cycle time are steam time and exhaust time, these also being to some extent interdependent, in that exhaust time increases if steam time is increased.

Steam time is determined by the product quality, which typically has also a seasonal aspect. In general, at the start of a product season, steam times are typically short, while towards the end of the season, steam times may rise by as much as 250%. Within this general rising trend in steam time over the season, steam and exhaust times also vary from day to day, depending on the product quality coming into the plant. Indeed, if product is being sourced from a number of different locations, it may be necessary to vary steam time even within a production period as short as a single day.

It will be apparent from the foregoing that the optimum or smallest batch load required to meet a particular constant line capacity will rise from an initially low figure for early season product to a higher figure, perhaps as much as 50% higher, for late season product.

In present day peeling installations, batch weight changes are generally made manually by the operator, batch weight being typically regulated by load cells which monitor the weight of the in-feed offered to the peeler and terminate delivery of product to the peeler when the required batch weight is reached. In order to provide optimum peeling conditions, the operator should therefore adjust the batch size or load whenever a change is made in the steam time. In other words, if steam time is reduced for a particular batch of product, then the batch size should also be reduced so as to minimise loss and achieve optimum peeling.

The complexity of these inter-related manual adjustments frequently result in the two variables, namely steam time and batch load, not necessarily being changed in conjunction with one another, batch load typically remaining the same irrespective of the adjustment in steam time. As a result, as for example steam times go down, batch loads remain high, and the possible improvement in peel loss which would result if the batch load were reduced, is foregone. Thus typically the batch load is set at a value that will ensure sufficient output of peeled product to meet the line capacity even under the longest or most adverse steam times. If steam times can be reduced, because of a higher quality batch of product, line capacity continues to be met, but the potential for achieving improved efficiency in the peeling step is foregone.

The present invention is directed to improvements in the programming of process events during rotation of the pressure vessel, with the objective of enabling incorporation of the preferred features identified above into the steam peeling system, and their use to the maximum extent possible. The invention is further directed to automating the computation of batch load and interlinking this computation with the setting of steam time, for automatic increase or reduction in batch load in conjunction with variation in steam time.

The vessel 1 of Figure 2 rotates about its axis 31 during the steaming period. In conventional steam peeling installations, the rotational speed of the vessel during this portion of a peeling cycle is typically 6 r.p.m. This corresponds to one revolution of the pressure vessel every ten seconds. Depending however on the nature of the product and on the quality of the particular batch of product, the actual steaming time required during a peeling cycle may vary from ten to fifty seconds. If, in a conventional steam peeling installation, a steaming time of ten seconds is in question, the pressure vessel will undergo exactly one revolution during the steaming phase. Thus it returns to the upright disposition of Figure 2 just as the ten second steaming phase expires. The pressure vessel is then in a position to exhaust in its upright disposition.As indicated, this is an ideal configuration for the exhaust phase.

If however, the steam time is eleven seconds, the vessel commences a second revolution just as the steaming time is completed and will continue to rotate for a further nine seconds before returning to the upright position. Consequently, the exhaust phase will be initiated and take place during a time period for at least part of which the vessel is not in an upright disposition. This represents a less than ideal situation, for a number of reasons.

Firstly, since the vessel is not in the upright position at the start of and during the exhaust phase, product may cover the exhaust port 34 of the vessel, which is aligned with its horizontal axis, and the flow of steam from the vessel may therefore be restricted. This may result in a less rapid decrease in pressure than would be the case if the vessel were in the upright position with no product in the vicinity of the exhaust port 34. Also, if the flow of steam from the vessel is restricted at this point, i.e. the exhaust port 34 from the vessel, by the presence of product, no advantage can be gained from using large bore exhaust piping and valves.

Such a slowdown in exhaust time has an additional adverse effect on overall production, since the total machine cycle time is also increased. The plant line production rate per hour may be calculated by multiplying the batch size per cycle by the number of cycles per hour, to give a throughput figure for each hour of operation. It will be immediately apparent therefore that if the cycle time is increased, the batch size per cycle must also be increased to maintain a given level of line production output throughput. However, this in turn itself leads to further extended exhaust times, so that there is an adverse circular effect or closed loop.

The second less than ideal consequence of exhaust while the vessel is not in its upright position arises from the length of time which the vessel takes to rotate and arrive at the upright position once again. For example, if the vessel is not in the upright position when exhaust time begins, but has only moved away from the upright position to a small extent, it may take up to almost ten seconds for the vessel to complete a full rotation and again arrive in the upright configuration. If the required exhaust time is only six seconds, for example, then a further four seconds are inevitably wasted before the vessel returns to the upright position. Only when the vessel is in this orientation, can the door be allowed to open for subsequent discharge of the product. In an average cycle time lasting for example fifty seconds, four seconds represents an extension of 8% in total cycle time. As already indicated in the foregoing paragraph, extension of the cycle time has the adverse effect of requiring larger batch sizes to maintain a given line rate, and consequently the use of longer exhaust times with consequent loss or waste of potentially useful product, for the reasons previously set forth.

The application of rotational programming to a rotatably mounted pressure vessel which is a special feature of the present invention ensures that the vessel is always in the upright position at the end of the steam phase and the start of the exhaust period. In this way the invention overcomes the problems associated with conventional equipment and provides the advantages described in the following paragraphs.

The advantages of exhausting while the vessel is in the upright position may be explained having regard to Figure 2. When the vessel 1 is in this position, the product occupies the bottom portion of the vessel, designated by reference 32, and the greater part of the steam will take up position in the upper part of the vessel, reference 33.

Consequently, as soon as the exhaust valve is opened, the steam has an uninterrupted passage to the exhaust port 34 and out of the vessel 1, thereby reducing the exhaust time and also providing a very rapid drop in pressure within the vessel. This more rapid exhaust provides more efficient peeling by minimising product waste.

A further advantage resides in the fact that the installation may be fitted with large bore exhaust piping to take full advantage of the high flow rate achieved on account of the unrestricted flow of steam from the vessel, occasioned by the absence of product at the vessel exhaust port. This gives a further reduction in the exhaust time and a further reduction in waste of useful product.

In addition to reducing the exhaust time, the large bore pipe and the steam distribution system enable a rapid rise in steam pressure in the vessel at the start of the peeling cycle to be achieved1 thereby also enhancing the efficiency of peeling at this stage of the peeling operation also.

Furthermore1 because the vessel is always in the upright position during exhaust, the vessel door may be opened and the product discharged immediately on completion of the exhaust phase. There is no delay in waiting for the vessel to return to its upright position1 as can be the case with conventional equipment employing rotatable pressure vessels.

All of these positive features together result in its being possible to reduce the total cycle time to a minimum, which as already indicated, means that smaller batch sizes can be used. This has a consequent reduction in exhaust time and thereby further enhances peeling efficiency with minimisation of waste.

The present invention provides a control system for steam peeling apparatus which enables achievement of the various advantages set forth above. To this end, according to the present invention, the control features of the steam peeling system cooperate with the pressure vessel drive in such a way as to ensure that the pressure vessel is always in its upright position at the end of the steaming phase in a steam peeling operation, ready for the start of the exhaust phase, irrespective of the steaming time. This is achieved by the control features of the invention incorporating a rotational programme which determines the number of revolutions the pressure vessel requires to complete during the steaming phase for a particular band of steam time values.For example, for steam times between eight and fifteen seconds, inclusive, the vessel is driven in a manner such as to complete one revolution during the steam time. If the steam time is between sixteen and twenty-five seconds, then the vessel is driven so as to complete two revolutions during the steam phase. Thus the rotational speed of the pressure vessel during this steam phase is varied to match the required steam time.

This rotational programme is achieved by use of an electrical frequency inverter which is controlled by an analogue output from an industrial computer. For each steam time selected, the computer software generates a set of output parameters which are inputted to the frequency inverter so as to drive the vessel in rotation at a speed ensuring that it will end up in the vertical position at the end of the steaming time.

A further feature of the rotational programme provided by the invention is a built-in soft start and soft stop facility, solving the familiar problem of gently starting and stopping an out of balance load of up to one ton. This enables a dramatic increase in the mechanical life of the machine to be achieved.

A steam peeling system in accordance with the invention and its control features will now be described having regard to Figures 3 and 4. Turning first to Figure 3, which is a diagrammatic representation of steam peeling apparatus in accordance with the invention, a generally cylindrical pressure vessel 1, which typically has a capacity of some fifteen hundred litres, is mounted on trunnion bearings 2 for rotation about an axis transverse to its longitudinal axis of symmetry, which axis of symmetry is the vertical axis of the vessel 1 when it is in an upright disposition. Service lines for fluid and control communication with the pressure vessel are carried between the rotatable unit 1 and control equipment of the apparatus through the trunnion bearings, which are provided with rotating couplings.A loading and discharge opening 3 is located at the upper end of vessel 1 in the orientation in which it is depicted in Figure 3. This disposition of the pressure vessel represents a top dead centre or upright position, and, for discharge, the vessel 1 is rotated into a substantially inverted disposition. A sealing door 4 closes off opening 3 when the pressure vessel is placed under steam pressure during a peeling operation.

A steam charging and discharge line 5 communicates between a steam supply 6 and the interior of pressure vessel 1 through lefthand trunnion bearing 2. A main steam valve 7 in a steam line leading to line 5 controls the flow of steam from the source or supply 6 into line 5. An exhaust valve 8 located in line 5 controls discharge of steam from pressure vessel 1 to an exhaust chamber 9. Condensation of exhaust steam takes place in chamber 9, this being furthered by the injection of water under control of water valve 10. An exhaust duct 11 communicates between the interior of chamber 9 and atmosphere, while a water drain 12 allows any excess condensate and water building up within the lower region of chamber 9 to flow away to drain.

Operation of the system of Figure 3 will now be described for a complete cycle. The pressure vessel 1 is moved into an upwardly opening disposition with the door 4 clear of opening 3. The product to be peeled is discharged into vessel 1 from an overhead hopper 13. Door 4 is then closed. An electrical safety interlock switch which verifies that the door is closed is then made, after which the following further events take place: Exhaust valve 8 is closed and steam inlet valve 7 is opened to allow high pressure steam to enter the vessel. This is the start of the steaming phase of the cycle.

Simultaneous with the closing of valve 8 and the opening of valve 7, the vessel also begins to rotate in accordance with the rotational programme. A particular rotational programme is selected to ensure that the vessel will be in an upright position at the end of the steam time, irrespective of the length of the steam time.

The steaming part of the cycle continues, during which time the vessel rotates until the expiry of the steam time as inputted to the machine computer or controller by the machine operator.

Immediately the steam time expires, i.e. the steaming phase finishes, the exhaust part of the cycle begins, i.e. the exhaust phase. This happens in the following manner.

At the end of steaming, the vessel will have again arrived in its upright position. The operation of valves 7 and 8 is now reversed. Valve 7 closes, shutting off the supply of steam to the pressure vessel 1, while valve 8 opens to allow high pressure steam into the exhaust chamber 9 via line 5. Valve 10 is also opened at this time to allow water into exhaust chamber 9 as a spray to condense the exhaust steam. The pressure in the vessel is thus reduced from approximately 300 p.s.i. to less than 3 p.s.i., i.e. a pressure at which door 4 can safely be opened.

The sealing door 4 is then opened, the vessel 1 goes through one further rotation during which the product is discharged, and it then returns to its upright position. The cycle is now complete and the pressure vessel is ready to accept a further charge of product for peeling.

The control and drive features of the system of the invention are shown in Figure 4 of the drawings. Pressure vessel 1 is driven in rotation by a motor and gearbox 42, fed with a three phase supply from a variable speed controller 43 in the form of a variable frequency inverter fed by a three-phase mains supply 43a. The input to controller 43 comes from a programmable line controller 45 through an analogue output module 44. Unit 45 has two inputs, the first of which is provided by a steam time selector designated by reference 46 and the second of which is a pressure vessel position input provided by a transducer 47. An output signal is delivered from transducer 47 when the pressure vessel 1 is in a particular orientation relative to the sensor, this triggering orientation being the upright vertical disposition for the steam peeling system represented.Unit 45 is in essence an industrial computer, suited to factory floor and plant use, and adapted by appropriate software or programming to provide a digital output which is a function of the inputs applied to it. Units 43, 44, 45 and 46 are suitably housed within a control module or board 48 of the peeling apparatus of the invention.

Operation of the control features shown in Figure 4 can now be described by way of example. For this purpose, two assumptions may be made in regard to the steam peeler1 which have been found to be practically relevant in most installations. The first assumption is that the minimum steam time required for the vast majority of products will be approximately 8 seconds. The second assumption is that the maximum desirable speed of rotation of vessel 1 is 7.5 r.p.m.

Experience has shown that faster speeds lead to reduced machine life and possible damage to product. However, the invention may nonetheless also be adapted for application in situations where different underlying criteria prevail.

In accordance however with the criteria set forth above, the electric motor and gearbox unit 42 are therefore designed and/or selected to drive the vessel at 7.5 r.p.m., when supplied with a 100% output from the variable speed controller 43. This equates to direct connection of drive unit 42 to a three phase mains power supply. When a steam time of 8 seconds is selected, the vessel is therefore driven at 100% of its maximum rotational speed, so that it performs one rotation and returns to the upright position at the end of the steam time. This 100% speed of rotation of the vessel of 7.5 r.p.m. corresponds to one rotation every 8 seconds. This drive speed is selected by the control programme equipment for this specified steam time.

If the steam time is 12 seconds, it then becomes necessary to drive the vessel at 8/12 x 100% of its maximum speed, i.e. 66% of its maximum speed, so that it will rotate and return to its upright position again as the steam time comes to an end. The percentage speeds, in terms of maximum speed, required for a variety of steam times, may readily be computed.

The control system functions as follows to achieve this variable speed drive of the pressure vessel. Before commencing a peeling operation, the operator enters a steam time in the selector unit 46. The time entered into unit 46 is seen as a discrete input by the programme line controller or PLC 45, where it activates an individual section of software within a programme contained in the PLC. The PLC then outputs to the analogue module 44, a digital signal appropriate to the steam time input. This PLC digital output signal is converted by the digital to analogue converter or module 44 to an analogue or continuously variable signal, which in turn forms the input to the speed controller 43. This input may be a O to 20 ma current signal or a O to 10 volt voltage signal.Variable speed controller 43 adjusts the electrical frequency of the incoming three phase mains supply, to provide an output of different frequency to drive motor 42. The frequency of supply to motor 42 is thus determined in accordance with the control signal received from the PLC 45 and the analogue module 44.

Two examples may be cited. If for example the operator enters a steam time of 14 seconds1 the software in PLC 45 generates a current signal at the output of analogue unit 44 as follows: 8/14 x 20 ma = 11.4 ma.

This current signal is interpreted by speed controller 43 as representing 11.4/20, i.e. 57%, of the maximum signal. Controller 43 responds to this input by appropriately adjusting the frequency of the supply to the motor 42. This ensures that motor 42 operates at 57% of its maximum speed, i.e. 57% of 7.5 r.p.m. = 4.275 r.p.m., to provide one revolution of the vessel every 14 seconds.

In a second example, the operator enters a steam time of 30 seconds. The output from PLC 45 via analogue module 44 then provides an 80% of maximum speed signal to the controller 43. Motor 42 is then driven by controller 43 at 80% of its maximum speed, i.e. 0.8 x 7.5 r.p.m. = 6 r.p.m., to provide one revolution every 10 seconds. Under these conditions, vessel 1 performs three revolutions during the steaming time of 30 seconds, before it returns to a final upright position for the third time, ready for discharge.

The number of revolutions is controlled as follows. For steam times of 8 to 15 seconds inclusive, the PLC 45 stops the vessel 1 the first time it passes detector 47. For steam times of 16 to 23 seconds, the PLC 45 stops the vessel 1 the second time it reaches the detector 47, while for steam times of 24 to 31 seconds, the PLC 45 stops vessel 1 the third time detector 47 is triggered. As shown in the drawing, the position of activation of detector 47 corresponds to the upright disposition of the vessel, and accordingly detector 47 is activated each time the vessel 1 passes into or through this orientation during its rotation. A further sensor, not pertinent to the present invention and not illustrated, which indicates a partially-tilted filling disposition of the vessel 1, may be mentioned for the sake of completeness.

During the peeling cycle, the pressure vessel is therefore driven in rotation under the command of the rotational programme. The speed of rotation during the steam peeling process is variable, to provide the required matching of steam time with integral rotations.

The rotation programme may also not necessarily be continuous and it may include starts or stops at various dispositions of the pressure vessel, depending on the total cycle time and the product being handled. The total cycle time may thus also be varied by providing for stopping and starting of the vessel during the cycle, but the vessel preferably turns at a constant rate or revolutions per minute during its actual drive periods. With this arrangement, if, for example, the cycle time is fifteen seconds, then the vessel may be stopped for one or more short periods so that the cycle will correspond overall to one rotation only of the pressure vessel. If the steam cycle time is twenty seconds or greater, then the pressure vessel may either be driven at an appropriate speed to complete two rotations within the required time, or one or more stops may be incorporated in the rotational cycle, if required, but always so that the final disposition of the pressure vessel will be upright when the steam cycle terminates. Steaming may also be started and stopped to match vessel rotation.

The apparatus of the invention, also employed in carrying out the method of the invention, may also include further process control equipment for regulating the operation of the various valves and drive motors at appropriate times during the operating cycle. This further control equipment is preferably also driven by a programmable microprocessor, so that the various parameters of operation may be changed at will to suit diferent products and different operating requirements. The apparatus and method of the invention are therefore highly flexible and capable of being adapted to a multiplicity of operating cycles and a diversity of products.

The aspect of the invention by which automated batch size selection is effected will now be described having regard to Figure 5, which corresponds to Figure 4 with the addition of certain further control features. As shown in. Figure 5, programmable line controller (PLC) 45 is now provided with two further inputs, the first of which comes from a capacity selection entered at selector unit 51, while the second input is a weight signal transmitted from load cells 52 supporting hopper 13. A further direct output from PLC 45 controls the drive of in-feed conveyor 53 by actuating conveyor motor 54.

The operation of this further aspect of the invention takes place as follows. A required line throughput or capacity figure in typically lbs/hr is input at unit 51. Controller 45 then establishes the overall cycle time, taking account of the particular steam time currently selected by unit 46. This overall cycle time is then compared with the entered capacity figure at unit 51, and controller 45 establishes the lowest batch weight capable of meeting the capacity requirement. Whenever the weight of product within loading or batching hopper 13 reaches this target batch weight, as reported to controller 45 by load cells 52, controller 45 acts to terminate drive of in-feed conveyor 53 by stopping conveyor drive motor 54.

Thus typically in operation of a system incorporating this further feature of the invention, a target capacity is set by a line supervisor, typically at the start of a day's production. Steam time is also selected for the first batch of product to be handled, but may be varied during the day's operations, depending on the quality of the product. Irrespective however of the actual value of steam time selected at unit 46, the system of the invention regulates the charging of pressure vessel 1 from hopper 13 so that the batch size is always optimised for best possible peeling performance. Thus the invention ensures that the peeling system always runs at maximum efficiency and loss of time due to excessively large batch sizes is obviated. The system may also incorporate further feedback to adjust batch size in the event of the feed rate decreasing, for example due to slow supply of product. Instead of the pressure vessel lying idle until such time as hopper 13 fills, the system may be adapted to run immediately pressure vessel 1 becomes available to receive product with whatever batch size is appropriate to the current real-time in-feed rate of product from conveyor 53.

Claims (12)

1. Steam peeling apparatus comprising a pressure vessel for accommodating product to be peeled, means for charging said pressure vessel with steam under pressure, and means for exhausting steam from said vessel, the pressure vessel being generally cylindrical, having a sealable opening at one end thereof and being mounted for rotation about an axis transverse to its longitudinal axis of symmetry, so that the pressure vessel passes through a substantially inverted disposition during rotation about said transverse axis, in which inverted disposition said opening is directed downwardly, and the apparatus also comprising control means for regulating the duration of the period during which the vessel is charged with steam, for initiating the exhaust of steam from the vessel following the period of charging with steam, and for driving the pressure vessel in rotation during a steam peeling cycle at a speed such that the vessel will complete a substantially integral number of rotations during the period of charging with steam.

2. Steam peeling apparatus according to Claim 1, wherein the control means comprises a variable speed drive for the pressure vessel and a logic unit responsive to an adjustable input for the steam charging period for setting said speed of rotation of the pressure vessel during a steam peeling cycle.

3. Steam peeling apparatus according to Claim 2, wherein said control means is also responsive to a position input provided by a detector which delivers an output signal when the pressure vessel is in a disposition in which said opening is directed upwardly.

4. Steam peeling apparatus according to any of Claims 1 to 3, wherein the steam exhausting means includes a steam discharge line and an exhaust chamber selectively connectible to the steam discharge line for withdrawal of steam from the pressure vessel.

5. Steam peeling apparatus according to Claim 4, wherein said exhaust chamber is connectible to the steam discharge line through suitable valve means, spray means being provided to inject water into the chamber as required to condense steam accumulating therein.

6. Steam peeling apparatus according to any preceding claim, wherein said control means comprises a logic unit responsive to an adjustable input indicative of a required rate of product throughput for setting a batch load weight value in dependence on the duration of the period during which the pressure vessel is charged with steam.

7. Steam peeling apparatus comprising a pressure vessel for accommodating product to be peeled, means for charging said pressure vessel with steam under pressure, and means for exhausting steam from said vessel, the pressure vessel being generally cylindrical, having a sealable opening at one end thereof and being mounted for rotation about an axis transverse to its longitudinal axis of symmetry, so that the pressure vessel passes through a substantially inverted disposition during rotation about said transverse axis, in which inverted disposition said opening is directed downwardly, and the apparatus also comprising control means including a logic unit responsive to an adjustable input indicative of a required rate of product throughput, for setting a batch load weight value in dependence on the duration of the period during which the pressure vessel is charged with steam.

8. Steam peeling apparatus according to any preceding claim, wherein the control means regulates operation of a product delivery means to terminate product in-feed to the peeling apparatus when the weight of the current product load as held in charging means for the pressure vessel reaches a predetermined value.

9. Steam peeling apparatus according to Claim 8, wherein said product delivery means is an in-feed conveyor for delivering product to be peeled to a loading hopper for the pressure vessel and the control means regulates operation of a drive motor for said conveyor.

10. A steam peeling method in which product to be peeled is exposed to high pressure steam for a controlled time period, wherein the pressure vessel is rotated according to a predetermined programme for at least a portion of the time period during which the product is exposed to high pressure steam and the rotation of the pressure vessel is matched to said time period of exposure to high pressure steam, so that a substantially integral number of rotational cycles is completed during said time period during which the product undergoing peeling is exposed to high pressure steam.

11. Steam peeling apparatus substantially as described herein with reference to and as shown in Figures 3 and 4 or Figures 3 and 5 of the accompanying drawings.

12. A steam peeling method substantially as described herein with reference to the accompanying drawings.