WO2013012311A1

WO2013012311A1 - Method and apparatus for energy-efficient operation in the sterilization of oil palm fruit

Info

Publication number: WO2013012311A1
Application number: PCT/MY2012/000204
Authority: WO
Inventors: Krishna Moorthy PALANISAMY
Original assignee: Palanisamy Krishna Moorthy
Priority date: 2011-07-18
Filing date: 2012-07-17
Publication date: 2013-01-24
Also published as: GB2507444A; GB201402702D0; BR112014000722A2; CR20140048A; MX351241B; DOP2014000006A; PE20151258A1; CO6920266A2; BR112014000722B1; MY173290A; ECSP14013208A; MX2014000688A; GB2507444B; AP2014007368A0; GT201400008A

Abstract

The apparatus operates with steam above atmospheric pressure. It includes a pressure vessel (40) with an interior (8), at least one movable container (4) holding oil palm fruit with open top exposed to the interior (8). A steam supply conduit supplying steam from an external steam source is connected to the interior (8); the container (4) has a solid floor (11) with at least one open aperture (51) in fluid communication with the interior of the container (4). A channel (15) in fluid communication with the interior of the container (4) is in further fluid communication with another channel (16) which is in fluid communication with exterior of the pressure vessel (40). A method of introducing pressurised steam into the pressure vessel (40) and dispelling trapped air within the stack of oil palm fruit bunches (10) and condensate from the container (4) is disclosed.

Description

Method and Apparatus for Energy-Efficient Operation in the Sterilization of Oil

Palm Fruit

FIELD OF THE INVENTION

The present invention relates generally to method and apparatus for energy-efficient treatment of a porous load of materials particularly plant produce, oil palm and similar fruit bunches, more particularly to a sterilization process that uses steam as a medium of treatment of oil palm fruit bunches. BACKGROUND OF THE INVENTION

Effective heat treatment is usually a critical aspect of many industrial processes in that it can increase the efficiency and effectiveness of downstream processes. It may have a direct impact on product quality and safety. In this instance, a sterilization process that uses hot vapour, such as steam, as a medium for heat treatment of matter in an enclosed vessel is considered. Proper sterilization requires minimum exposure duration at an effective sterilization temperature, depending on the particular matter being sterilized, to attain a particular level of treatment. It is known that trapped air inside a vessel impedes sterilization and several techniques are used to expel the air before proceeding to the actual sterilization stage. Air removal by gravity downward displacement, repeated pressurising-depressurising with the sterilization medium and vacuuming are some of the common methods used to evacuate the air in the vessel. Sterilization of porous materials that contain air in interstices of the material poses a problem due to difficulty in removing the air from within the material. This is even more pronounced in cases where the porous materials are placed in a container within the sterilizing vessel. Sterilization of oil palm (Elaeis Guineensis Jacq.) fresh fruit bunches (FFB), in the palm oil extraction process is an example in point where the fresh fruit bunches stacked in open containers commonly known as cages are charged into a pressure vessel for sterilization using steam as a sterilizing agent.

Conventionally, in a palm oil mill the sterilization process is carried out in a pressure vessel such as a cylindrical vessel, lying in horizontal or vertical position, and filled with steam under certain physical parameters as a batch process. In the case of horizontal sterilizers, open-top perforated wall steel cages stacked with oil palm fruit bunches are pushed on tracks into the pressure vessel for sterilization. Multiple cages would be required for easy handling to achieve a required sterilization batch capacity. After sterilization the cages with the treated bunch are taken out of the sterilizer for further processing of the fruit bunches.

When disposed in a horizontal position, the cylindrical vessel sterilizer has fairly good disposition because oil palm fruit bunches stacked in the cages are more uniformly spread out in this position across the length of the elongated vessel, as opposed to a vertical sterilizer. Thus, when pressurized steam is injected into the interior of the horizontally positioned cylindrical vessel, the steam can reach out to different directions and corners of the contents within the vessel thereby helping treatment of the fruit bunches. However, the conventional design of the horizontal sterilizer has an inherent shortcoming, that is, one of ineffective air removal. The air trapped in the pockets of space within the stacked fruit bunches in the cages renders trapped air difficult to be removed during the initial venting stage of the sterilization process.

As a preconditioning of the pressure vessel for effective sterilization air is evacuated commonly by gravity downward displacement whereupon introduction of steam through the top of the vessel, denser air gets stratified to a lower layer and subsequently discharged from the pressure vessel through air dispersal perforated pipes positioned at the bottom region of the vessel to the exterior of the vessel. To improve air removal effectiveness, double or triple peak sterilization is practised where the vessel containing the stacked fruit bunches in the cages is subjected to ^' repeated pressure releases after partial pressurisation with steam to displace and evacuate the residual air before beginning the actual sterilization process. While improvement in sterilization is achieved by multiple peak sterilization, the disadvantages include a significant amount of steam being wasted by the pressurization and depressurization steps in the repeated venting of steam and heating of the relatively extensive mass of metal of the vessel and the fruit cage carriages. Longer overall sterilization batch time is also required because of the multiple peak steps thereby reducing the throughput capacity of the sterilizer. More importantly, pressure pulsing to remove air is particularly disturbing to a steady state upstream process where the supply steam comes from, like power generation by a back pressure steam engine. In conventional sterilizers, the initial de-aeration step expels air from the internal spaces of the vessel by gravity downward displacement through proper bottom air dispersal perforated pipes and it typically takes about 5 minutes of the total cycle time. Subsequent two de-aeration peak steps partially expel pockets of air trapped within the interior space of the fruit bunches stacked in the cages and these take about 25 minutes of the total cycle time.

Evacuating the air from a pressure vessel by vacuuming prior to the sterilization cycle as practised in smaller sterilizers employed in the heath care industry is not practical and economical for large sterilizers used in the palm oil extraction process where the volume of the pressure vessel can be up to about 180 cubic meters. To compensate for inefficient air removal a longer period of treatment under steam conditions or a higher steam pressure or a combination of both is employed. The detrimental effects of trapped air requiring a longer period of sterilization and/or a higher steam pressure to meet the process requirement demand a higher thermal energy as a consequence. Current practice uses an external source of saturated steam at about 4 bar (400 kPa) pressure and at about 144 ^eC as the heating medium in triple-peak sterilization and this typically takes more than 90 minutes to complete a full cycle for satisfactory results. Accordingly, the rapid and effective removal of air is the key to raising thermal energy utilisation efficiency.

SUMMARY OF INVENTION

The invention discloses a method and an apparatus to heat treat a porous load of material which porous load of material includes plant produce, more particularly oil palm fresh fruit bunches. The invention is applicable to all plant produce that needs heat treatment by steam, like in the processing of almonds, cashew nuts and peanuts. The method to heat treat a porous load of material in a pressure vessel includes the steps of transporting at least one open topped container containing the porous load into the pressure vessel. The container is mounted on a carriage on tracks within the pressure vessel. The pressure vessel is then sealed followed by the admission of steam into the interior of the pressure vessel whilst releasing air from the pressure vessel. As steam is admitted into the pressure vessel, the temperature of the porous load is raised until it reaches a sufficient temperature for heat treatment and is maintained at that level sufficiently long to complete the process of heat treatment of the porous load. Raising the temperature of the porous load includes the step of inducing a flow of steam through the porous load across the container between the interior and an exterior by developing a pressure differential across the container. Said pressure differential is between a first pressure (P1 ) prevailing in the interior and a second pressure (P2) prevailing in a first fluid pathway at perforation at he surface of the container wherein the second pressure (P2) varied by inducing a fluid flow between the first fluid pathway and the exterior of the pressure vessel, thereby substantially dispelling residual air from within the porous load of material. The flow of steam through the porous load of material is substantially turbulent and the pressure differential between P1 and P2 is between 100 Pa and 2000 Pa. Where the porous load of material is oil palm fruit bunches the saturation steam temperature corresponding to the pressure in the interior is less than 10 ^SC above the predetermined sterilisation temperature of the oil palm fruit bunches.

The invention also discloses a sterilizer operable with pressurised steam for heat treatment of a porous load of material. The steriliser comprises a horizontally positioned cylindrical pressure vessel with at least one steam inlet port and at least one open topped container mounted on a carriage transportable along a pair of tracks mounted within the pressure vessel. The sterilizer further includes a first fluid pathway mounted on the carriage and extending from the surface perforation of the container to at least one first aperture to be in fluid connection with a second fluid pathway. The second pathway is secured to the pressure vessel extending from at least one second aperture to at one first discharge port to be in fluid connection with the exterior of the pressure vessel. The fluid connection between the first fluid pathway and the second fluid pathway is effected via an engageable connection formed by way of a resilient sealing gasket between peripheral lips surrounding the first and second apertures when the carriage is in registration at predetermined position on the tracks. Alternatively the fluid connection between the first fluid pathway of a carriage and the second fluid pathway which is secured to the pressure vessel is effected via an axially engageable connection between conduit ends forming the first and second apertures and wherein the fluid connection between adjacent carriages in tandem is effected via an axially engageable connection between conduit end forming the first apertures and the conduit end forming a third aperture of the adjacent carriage when the carriages are in registration at predetermined positions on the tracks. The respective pathways are telescopically engageable.

There is further included a steam admission system located outside the pressure vessel, the steam admission system configured to supply steam into the pressure vessel at a steam flow rate that is sufficient in order for the porous load of material to reach the sufficient temperature within 15 minutes, while the steam admission system receives an external steam supply preferably at a predetermined pressure of between 120 kPa and 300 kPa. The steam admission system includes conduits connecting the external source of steam and the pressure vessel in a manner generally known in the art with at least one main steam inlet valve, the main steam inlet valve for controlling the flow of steam through a steam inlet port into the sterilizer vessel.

The invention is particularly targeted but not exclusively towards attaining higher energy efficiency by operating an oil palm fruit sterilizer using a lower steam temperature and pressure, and shorter sterilization time for a satisfactory sterilization treatment of the oil palm fruit bunches. The invention can be practised with conventional pressure vessels of any configuration and size treating porous loads placed in containers. The inventive method and arrangement can also be implemented as a retrofit in existing sterilizers.

The present invention provides a method and an arrangement for rapid and efficient removal of residual air from the pockets formed by the stacked fruit bunches in the interior space of fruit cage by inducing a flow of steam across the interior space of the fruit cage stacked with fruit bunches that sweeps the residual air out. For effective removal of residual air from the pockets the induced steam-air mixture flow across the interior space of the fruit cage has to attain a turbulent regime of fluid flow, which is effected by developing adequate pressure differential across the interior space of the fruit cage. This sweeping action facilitating the removal of the residual air from within the inner space of the fruit cage is induced when pressure in the pressure vessel rises following steam admission into the pressure vessel.

Most of the air in the interior between the outer walls of the sterilizer pressure vessel and the cages is advantageously dispersed by gravity displacement through the bottom primary air discharge ports when steam is first admitted into the pressure vessel and before the pressure rises appreciably. As the pressure in the sterilizer pressure vessel begins to rise above atmospheric pressure, the flow of steam across the interior space of the fruit cage stacked with fruit bunches begins to sweep the residual air out of the pockets. The rapid removal of residual air begins when the steam-air mixture flow attains turbulence. The surface temperature of the fruit bunches within the stacked fruit bunches in the cage rises rapidly thereafter closely following the temperature of steam in the internal interior of the vessel indicating efficient residual air dispersal from the interior of the fruit bunch stack in the cage. This air dispersal process continues until almost all the air is removed.

The sweep of steam across the fruit cage is induced when pressure differential is developed across the interior space of the fruit cage by means of a fluid connection with a first channel discharging a restricted flow of the sterilizing fluid through a first discharge port to the exterior. In practical implementation, the restricted flow of the sterilizing fluid to the exterior is controlled by external means to maintain the pressure differential to a design value of between about 1 00 Pa and 2000 Pa that is adequate to induce the required turbulent steam-air mixture sweep through the stacked fruit bunches across the fruit cage. A turbulent steam-air mixture sweep across the fruit cage for duration of about three to five minutes will disperse residual air to a desired level within the load of stacked fruit bunches in the fruit cages and thereafter the load of fruit bunches attaining rapid and more uniform surface temperature distribution within a range of 2 ^SC lower than the saturation steam temperature corresponding to the prevailing pressure in the interior of the pressure vessel. The rapid removal of residual air induces a saving in steam and thermal energy compared to the conventional practice of pressure pulsing the pressure vessel to achieve the same. Besides, where advantageous the invention can be practised with a reversal of steam flow where steam is admitted into the first channel from an exterior to induce steam flow across the interior space of the fruit cage from the first channel dispersing into the interior of the pressure vessel before the pressure in the interior begins to rise, during the residual air removal process.

Preferably, condensate collecting in the first channel is removed separately so that it does not interfere with removal of the air and other non-condensable gases through the first discharge port. A large quantity of condensate, and more notably oil and dirt contaminated condensate from the fruit mass wash into the first channel especially during the initial heating phase when the residual air removal process begins. The contaminated condensate is drained to the interior of the sterilizer pressure vessel by means of condensate seal legs positioned between the first or a second channel and the interior of the pressure vessel. The condensate drained from the.first or the second channel via the condensate seal legs is discharged out of the pressure vessel through the sterilizer condensate discharge ports.

The condensate seal legs advantageously provide a back up protection to limit the pressure differential should it rise uncontrolled. Limiting the pressure differential allows for a simpler economic sealing arrangement and design of first and second channels and avoids undue turbulence in the fruit bunches.

Where it is advantageous, condensate falling from the fruit cages and collecting in the first channel is segregated from the condensate precipitating from heating the mass of metal of the pressure vessel outer wall and fruit cage carriage collecting in the interior. The segregation may facilitate reuse of the clean condensate and oil separation from the contaminated condensate. An object of the present invention is to operate the sterilizer at reduced steam temperature and pressure near the effective sterilization temperature of the porous load under treatment whereby lower steam consumption and higher energy efficiency is achieved. An object of the present invention is to configure and operate the sterilizer using reduced external supply steam temperature and pressure consistent with the effective sterilization temperature for the porous load under treatment whereby improving mechanical power generation efficiency in an upstream back pressure steam engine supplying the steam to the sterilizer, the engine operating with a design operation point pressure for its exit pressure of the lower supply steam pressure.

Preferably, the sterilizer for treatment of oil palm fruit bunches is designed and configured to operate at a design operation point for the supply steam pressure between 1.2 bar (120 kPa) and less than 3.0 bar (300 kPa) and more preferable where the sterilizer is designed and configured to operate at a design operation point for the supply steam pressure between 1 .5 bar (150 kPa) and less than 2.5 bar (250 kPa). The present invention is configured to operate the sterilizer at a reduced steam pressure using external supply steam at a lower pressure to avoid sonic flows during steam admissions and releases to prevent excessive turbulence and noise levels. Discharging dry steam to atmospheric pressure from an upstream pressure lower than about 1.8 bar (180 kPa) avoids critical flow conditions in the sterilizer operation.

The present invention is also configured to operate the sterilizer on single peak sterilization that precludes the use of pressure pulsing the sterilizer to remove residual air, which otherwise is disturbing to a steady state upstream process where the supply steam comes from, like power generation by a back pressure steam engine.

In another aspect the present invention is to operate the sterilizer on single peak sterilization with a shorter batch cycle time than prior art and thereby achieve increased throughput capacity.

Yet in another aspect the present invention is to operate the sterilizer at a lower and more uniform temperature distribution throughout the bulk of the porous load under treatment that reduces the likelihood of thermal denaturing of the treated porous load and thereby improve product quality.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned attributes and other features and advantages of this invention and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: Figure 1 shows a prior art internal arrangement of a horizontal oil palm fruit sterilizer charged with fruit bunches stacked in cages and rolled into position on a pair of tracks inside the sterilizer. The diagram highlights the difficulty in air removal. Figure 2 shows in greater detail the cross sectional end view of a prior art arrangement of a carriage on a tracks carrying a fruit cage inside a sterilizer pressure vessel illustrating the carriage frame and wheels on a pair of tracks.

Figure 3 shows details of an internal arrangement of a horizontal oil palm fruit sterilizer with an inventive facility for expelling residual air from pockets internal to the fruit bunches stacked in cages by inducing a steam flow through the stacked fruit bunches (10) across the fruit cages (4). A lateral slidably engageable fluid connection (19) is employed to effect a fluid passage between an interior (8) and the exterior of the pressure vessel (40).

Figure 4 shows a preferred arrangement wherein condensate seal legs (18) are positioned between a second channel (16) and the interior (8) of the pressure vessel (40) to allow condensate from the second channel (16) to drain off to the interior (8c) of the pressure vessel (40), and facilitating discharge of only the gaseous and vapour content through the first discharge port (17) to the exterior of the pressure vessel (40).

Figure 5 shows the reverse fluid flow situation where steam is being admitted into the first channel (15) from the exterior through the first discharge port (17) whereby air removal is stimulated by means of inducing a steam flow through the stack of fruit bunches (10) across the cages (4) into the interior (8) of the sterilizer during the residual air removal process. Figure 6 shows in greater detail the cross sectional end view of an arrangement of a fruit cage (4) on a carriage with wheels on a pair of tracks inside a sterilizer pressure vessel (40) with facility for dispelling residual air from pockets internal to the stack of fruit bunches (10) in cages (4) by inducing a steam flow across the interior of the cages (4). The carriage wheel arrangement, first channel (15) and second channel (16), slidably engageable fluid connection (19) and first discharge port (17) are illustrated in greater detail.

Figure 7 shows in greater detail the cross sectional end view with preferred condensate seal legs (18) positioned between the second channel (16) and the interior (8) that provides drainage means for condensate and limits the pressure differential across the interior of the cage (4) between the first channel (15) and the interior (8). Figure 8 shows in greater detail the cross sectional end view with greater detail of the first channel (15), second channel (16), slidably engageable fluid connection (19) and the first discharge port (17) with the preferred condensate seal legs (18) positioned between the second channel (16) and the interior (8c). The design static head legs, (hi ) that affects the condensate drainage and (h2) that affects the maximum operating pressure differential are indicated.

Figure 9 shows in greater detail the cross sectional side view of the lateral positions of the first discharge port (17) and condensate discharge port (7). Figure 10 shows in greater detail the cross sectional side view of an arrangement for removing the contaminated condensate collecting in the second channel (16) out of the pressure vessel (40) through a second discharge port (17a). Figure 1 1 shows a side elevation view of the first channel (15), second channel (16), first discharge port (17), the carriage frame (13) and the slidably engageable fluid connection (19) with the preferred condensate seal legs (18) positioned between the second channel (16) and the interior (8c).

Figure 12 shows a plan view of the fruit cage carriage first channel (15) aperture ( 61 ) aligned vertically with the aperture (162) on the second channel (16) forming a slidably engageable fluid connection ( 9). Figure 13 shows a plan view of an alternative arrangement of a single fruit cage carriage (13) with segmented first channel (15) with two apertures (161 ) abutting with the respective apertures (162) of the second channel (16) forming two slidably engageable fluid connections (19) per fruit cage (4). Figure 14 shows a plan view of slide shoe plate (21 ) under the first channel (15) attached to carriage frame (13) that engages with the resilient sealing gasket (20) on the second channel (16) to form the slidably engageable fluid connection (19).

Figure 15 shows a plan view of resilient sealing gasket insert (20) on the second channel (16) that engages with the shoe plate (21 ) under the first channel (15) attached to the carriage frame (13) to form slidably engageable fluid connection (19).

Figure 16 shows 3D geometric views of an arrangement of the first channel (15) attached to the carriage in the top view and the resilient sealing gasket insert (20) on the second channel in the bottom view that together form the slidably engageable fluid connection (19) when aligned in position.

Figure 17 shows the piping and valve arrangement to operate the sterilizer. Figure 18 illustrates the various stages of the sterilization process showing steam pressure in the pressure vessel with time as the sterilizer is placed into operation. Figure 19 shows an embodiment of the invention where axial telescoping slide fluid connection is employed to effect a fluid passage between an interior (8) and the exterior of the pressure vessel (40). A discharge duct (36) passes through the first channel (15) that is secured to the moving carriage. Figure 20 shows a side elevation view of the arrangement where the discharge duct (36) passes through the first channel (15) that is attached to the moving carriage (13).

Figure 21 shows details of detachably engageable fluid connections between the respective discharge ducts (36) of a plurality of carriages in tandem and with the first discharge port (17) forming the terminal discharge outlet to expel the residual air from the discharge duct (36) to the exterior. Detachably engageable fluid connections (22) by means of flexible hose joint (33, 34) and an alternative means of telescoping slide connector with O-ring seal to provide pathway between the respective discharge ducts (36) and between the discharge duct (36) and the exterior through the first discharge port (17) are shown.

Figure 22 shows an embodiment of the invention in a preferred arrangement wherein a pair of condensate seal legs (18) are located in the first channel (15) secured to the moving carriage frame (13) to allow drainage of condensate from the first channel (15) to the interior (8c) of the pressure vessel (40). A lateral slidably engageable fluid connection (19) is employed to effect fluid passage between an interior (8) and the exterior of the pressure vessel (40). A preferred embodiment of the present invention is detailed with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, material, relative positions and so forth of the constituent parts in the embodiments shall be interpreted as illustrative only and not as limitative of the scope of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The invention is directed towards a method and an apparatus to improve energy and time efficiency in the operation of a steam sterilizer used to treat porous loads placed in open containers and charged into pressure vessels.

In this description the term "effective sterilization temperature" refers to a temperature of minimum temperature-time relationship that must be maintained throughout all portions of a load mass to obtain effective sterilization. As the sterilization temperature decreases, time may be increased to obtain effective sterilization with the temperature having a minimum limiting value. For example, for sterilization of oil palm fruit bunches, the effective sterilization temperature is 1 10 ^fiC for an exposure time of about 65 minutes at the temperature. For an effective sterilization temperature at 100 ^eC, a longer exposure time of about 90 minutes is required. The temperature of 100 ⁸C is considered to be the lowest temperature for effective sterilization irrespective of any longer exposure duration. For sterilization of oil palm fruit bunches, the effective sterilization temperature-time relationship is determined by the desired percentage of unstripped bunches following sterilization. In this description the term "heat treatment" also means sterilization if the porous load of material is a load of oil palm fruit bunches. In this description the term "condensate seal leg" refers to a liquid seal leg for allowing liquid drained from the container to be drained to the interior of the pressure vessel without permitting gaseous and vapour content to bypass through.

In this description the term "steam engine" refers to a machine that performs mechanical work using steam as its working fluid through the agency of heat. It includes, steam turbines, reciprocating steam engines and rotary steam engines. In this description the term "pressurised steam" refers to steam at a pressure higher than one atmospheric pressure.

The pressure values described in the present specification refers to absolute pressure, where the atmospheric pressure is approximately one bar (100 kPa).

Elements which are not necessary to understand the invention, such as, for example, the doors of the sterilizer, the safety door mechanism, thermal insulation, the detail structural design of the cage and the carriage, the structural design of the first channel and detail design of the seals are not shown in the drawings.

A steriliser operates by using a sterilizing agent such as steam under pressure. The sterilising effect comes from raising the temperature of the load charged into the sterilizer where the heat to raise the temperature of the material under sterilisation comes from the enthalpy of vaporization of the steam. Saturated steam is able to penetrate materials with cooler temperatures because once the steam contacts a cooler surface it immediately condenses to water imparting the enthalpy of vaporization, producing a concomitant large decrease in steam volume, for example a 1 ,100 fold decrease in volume on condensation at 1.5 bar (150 kPa) pressure. This creates negative pressure at the point of condensation and draws more steam into the area. Condensation continues so long as the temperature of the condensing surface is less than that of steam. These properties ensure rapid heating of surfaces and good penetration of heat into dense materials to treat the material under sterilization. The potential issues are air pockets that form a thermal insulation between the steam and the surface of the material, especially prevalent in porous loads. Condensed water wetting the surface may also impede steam imparting its enthalpy of evaporation efficiently. Any remnant diffused air present in the porous load will imparts a partial pressure and the resulting lower partial pressure of the steam in the air-steam mixture will render a lower temperature than that corresponding to the sterilization pressure in the interior (8). These issues are particularly eminent in porous loads placed in containers for sterilization and are addressed by the present invention. Superior energy and time efficiency of the sterilizer operation treating porous loads as described in these specifications are achieved by preconditioning the porous loads in the container with a flow of steam dispersing the pockets of air trapped in the porous load, which method is proficient, reliable and economic to withdraw the trapped air that currently inhibits the penetration of steam into the porous load. On substantially dispersing air and other non-condensable gases from the porous load of material, saturated steam is able to reach the interior of the whole porous load and condense on the porous load surfaces enabling the porous loads to attain a more uniform temperature distribution and rapid temperature rise throughout its bulk that closely follows the saturation steam temperature in the interior open space of the pressure vessel. Conversely, the efficient dispersal of air and other non-condensable gases enables employing steam in the interior open space of the pressure vessel at a temperature and pressure corresponding near to the effective sterilization temperature for the porous load. Where exit steam from a power generating back pressure steam engine is used as an external steam supply for the sterilization, there is a particular advantage in the upstream power generation efficiency by avoiding the use of any higher steam temperature and pressure other than that corresponding to the effective sterilization temperature for the treatment of porous load, the function of the higher steam conditions being merely to compensate for inefficient air removal. The more uniform temperature distribution and rapid temperature rise of the porous load permits a shorter period of time for effective sterilization thereby further reducing the thermal energy required per production throughput. The embodiments described herein are particularly targeted towards attaining higher energy and time efficiency in operating an oil palm fruit sterilizer where a plurality of carriages in tandem loaded with oil palm fruit bunches in open-top cages are rolled into a horizontally-laid cylindrical pressure vessel steriliser for treatment. The higher efficiencies are attained by using a lower pressure steam and shorter sterilization time for achieving a satisfactory sterilization treatment. However, the invention can be practiced with conventional pressure vessels of any configuration and size treating porous loads placed in open containers that inherently render the dispersal of pockets of air difficult. A sterilizer commonly used for treatment of oil palm and similar fruit bunches with steam under control conditions includes a horizontally-laid pressure vessel (40) having an inlet and outlet means for charging open-top cages loaded with fresh fruit bunches and for discharging the cages with treated fruit bunches. Such a sterilizer operation is illustrated, by way of example, to describe the invention.

It is known that the effective sterilization temperature for oil palm fresh fruit bunches is about 1 10 ^SC with an exposure time under this temperature for about 65 minutes, which time is to allow the heat to penetrate to the core of the fruit bunch. Saturated steam at about 1 10 ^SC temperature and 1 .5 bar (150 kPa) pressure as the sterilization agent is able to produce satisfactory treatment in a duration of 65 minutes if it gets in contact with the surface of the whole stack of the fruit bunches within the cages and charged into the sterilizer. However, residual air present in the pockets formed in the stacked fruit bunches in the cages after the conventional air removal methods prevent the steam from getting into contact intimately with the fruit bunch surfaces throughout the porous load.

The illustrated embodiment in Figure 3 provides a fluid passage for steam between an interior (8) and an exterior (yy) of the pressure vessel (40) through the load of the fruit bunches (10) across the fruit cage (4) effected by means including of a lateral engageable fluid connection between the movable and fixed components of the sterilizer.

A first channel (15) is provided with the movable carriage (13) to be in fluid communication with the interior of the fruit cage (4) via an opening in a wall of the first channel (15) and at least one opening (51 ) through the surface of the container (4) through which fluid can flow between the first channel (15) and the interior of the fruit cage (4). Conveniently the fluid communication is provided though the bottom floor surface (1 1 ) of the container (4) to facilitate discharge of condensate by gravity through the opening (51 ).

The first channel (15) engages in fluid communication with a second channel (16) that is installed inside the pressure vessel (40) when a first aperture (161 ) provided on a wall of the first channel (15) abuts a second aperture (162) provided on a wall of the second channel (16), forming an engageable fluid joint through which fluid can flow between the first channel (15) and the second channel (16) as the carriages are rolled into their positions inside the pressure vessel (40). The second channel (16) has fluid connection through at least one first discharge port (17) to the exterior of the pressure vessel (40). The arrangement provides a first fluid pathway (151 ) extending from the opening (51 ) through the surface of the container (4) to the interface at an engageable fluid joint on the movable carriage (13) and a second fluid pathway (152) extending from the interface at the engageable fluid joint to a first discharge port (17) to establish a fluid passage between the opening (51 ) through the surface of the container (4) and an exterior (yy) of the pressure vessel (40).

A pressure differential is established between the interior (8) and the opening (51 ) through the surface of the container (4) across the stack of the fruit bunches (10) in the container (4), when the first channel (15) is subjected to a pressure (P2) lower than the pressure (P1 ) prevailing in the interior (8) through the first channel (15) connecting to an external pressure. The pressure differential induces a flow of steam through the load of the fruit bunches (10) across the interior of the cages (4), thus dispelling residual air from the pockets within the stack of fruit bunches (10) in the cages (4). Where a reverse flow method is adopted the pressure (P2) at the first channel (15) is higher that the interior pressure (P1 ) as further described below. The first and second fluid pathways (151 , 152) will have effective flow area such as to generate sufficient fluid flow through the pathways (151 , 152) to establish the required pressure differential particularly when the pressure (P1 ) is small greater than atmospheric pressure.

At least one perforation (5) may be provided on the side walls of the cages (4) so that a more uniform flow distribution of steam is produced through the load of fruit bunches (10) across the fruit cage (4), dependent on the shape and dimension of the fruit cages (4), the nature of the stacking of the fruit bunches (10) in the cage and the size distribution of the fruit bunches. External steam is admitted into the pressure vessel (40) through one or more steam inlet ports (1 ) above the steam inlets baffle (2). When steam is initially admitted into the pressure vessel (40) that is sealed after being charged with fruit bunches (10) stacked into cages (4), most of the air present in the interior (8) is optionally vented by gravity downward displacement through bottom primary air discharge pipes (6). The primary air discharge pipes (6) are lateral pipes with perforations along the length of the pipes for venting air on either side of the cages and with at least one discharge outlet to the exterior of the pressure vessel (40). Condensate is discharged through condensate discharge port (7). Steam is admitted at low velocity during the initial air removal stage to limit any turbulence and allow buoyancy to lift the lighter steam upwards pushing the air downwards in the vessel (40). The difference in density between steam and air develops the buoyancy of steam to displace a stratified lower layer of air that is pushed out through the bottom primary air discharge pipes (6). As the air in the interior (8) is expelled out of the pressure vessel, the steam comes into contact and heats the mass of metal of the pressure vessel outer wall (3) and the fruit cage carriage. When the temperatures of the outer wall (3) and the fruit cage carriage approach the steam temperature in the interior (8), the pressure in the interior (8) begins to rise. As the pressure in the interior (8) rises, a pressure differential develops across the interior of the fruit cages (4) between the interior (8) and channel (15) that is open to the exterior at a lower pressure via the first discharge port (17) through which a restricted flow of fluid is passed out. The greater the rate of the restricted flow passing out through the first discharge port (17), the greater the pressure differential that develops. The pressure differential induces a sweep of steam through the stack of fruit bunches (10) across the interior space of the fruit cage (4) from the interior (8) to the first channel (15). For effective removal of residual air from the pockets the induced steam-air mixture flowing across the interior space of the fruit cage (4) has to attain a turbulent regime of fluid flow, which is effected by developing adequate pressure differential across the interior space of the fruit cage (4). In practical implementation, a pressure differential of about 100 Pa to 1000 Pa is adequate to induce the turbulent steam-air mixture sweep across the fruit cage (4). Preferably, a pressure differential of between 400 Pa to 1000 Pa is utilised for sterilization of oil palm fruit bunches. Residual air is swept off the pockets by the steam flow that continues as long as the first discharge port (17) is adequately discharging to the exterior. The flow of steam through the stacked fruit bunches (10) across the fruit cages (4) is maintained for a period of about three to five minutes after a turbulent steam-air sweep is induced or until substantial air is displaced from the stacked fruit bunches (10) in the interior space of fruit cage (4). During this period the bulk of stacked fruit bunches (10) in the fruit cages (4) would attain a rapid temperature rise and more uniform surface temperature distribution within a range of 2 ^SC lower than the saturation steam temperature corresponding to the prevailing pressure in the interior (8). The exuding fluid from the container consisting of air, other non- condensable gases, steam and entrained condensate from the interior of the stack of fruit bunches (10) is discharged through the at least one first discharge port (17) to the exterior. For more closely packed porous loads, deeper containers or for quicker air dispersal, a higher pressure differential of between about 1000 Pa and 2000 Pa is advantageously utilised.

The described process of dispersing air stagnating within the interior space of fruit cage (4) is proficient, consistent and economical. As the air is removed from the air pockets the surface temperature of the fruit bunches stacked in the cage rises rapidly and more uniformly distributed across the stack following closely with the rising saturation temperature of steam prevailing in the interior (8), indicating efficient air dispersal from the interior of the fruit bunch stacked in the cage (4).

The efficient removal of air enables the use of lower pressure steam that in turn enables efficient use of steam for combined heat and power generation by an upstream back pressure steam engine. An increase in the throughput capacity of a sterilizer is also attained due to the shorter sterilization duration. The embodiments contemplated and disclosed herein narrows the range of temperature distribution in a porous load to be heat treated in a single-peak sterilisation to enable the use of a lower saturation steam temperature prevailing in the interior (8) compared to the prior art. The lowest saturation steam temperature in the interior (8) used in prior art method for satisfactory heat treatment of oil palm fruits is 134 ^aC at 3 bar pressure, which is 24 ^SC above the effective sterilization temperature of 1 10 ^SC. The present invention utilises a saturation steam temperature in the interior (8) of less than 10 ^SC above the predetermined effective sterilization temperature of the oil palm fruit bunches (10) is utilised for the heat treatment. Preferably, a saturation steam temperature in the interior (8) of less than 4 ^SC above the predetermined effective sterilization temperature of the oil palm fruit bunches (10) is utilised for the heat treatment. More preferably, a saturation steam temperature in the interior (8) of less than 2 ⁵C above the predetermined effective sterilization temperature of the oil palm fruit bunches (10) is utilised.

Preferably, condensate exuding from the interior of the container (4) is removed separately so as not to interfere with fluid flow in the first pathway (151 ) and the second pathway (152) and impede removal of the air and other non-condensable gases. A large quantity of condensate, and more notably oil and dirt contaminated condensate from the fruit mass wash into the first channel (15) especially during the initial heating phase when a flow of steam is established across the fruit cage (4). In another embodiment of the invention, the air initially present in the interior (8) is vented through the fruit bunches (10) in the cages via the first discharge port (17) to the exterior of the pressure vessel (40) precluding air evacuation through the bottom primary air discharge pipes (6) and without the use of perforation (5) on the fruit cage (4) side wall whereby air is deliberately retained in an interior (8b) between the outer wall (3) and the fruit cage wall. The use of a slightly raised grating (1 1 , Figure 7) particularly in this embodiment could promote a more uniform flow distribution of steam across the load of fruit bunches (10). The entrapped air in the interior (8b) provides thermal insulation between the outer wall (3) and the cage wall thereby reducing heat loss through heating the outer wall (3) and fruit cage carriage (13). A steam inlets baffle (2) configured to deflect inlet steam away from the pressure vessel outer wall (3) assists further in reducing heat loss. The condensate from the interior (8) is released through the condensate discharge port (7) and with a trap means to retain gaseous content. This arrangement requires removal of condensate from the second channel (16) via a second discharge port (17a, Figure 10) out of the sterilizer vessel (40).

Figure 4 shows a preferred arrangement wherein the condensate exuding from the interior of the container (4) is allowed to drain off from the second channel (16) to the interior (8c) by means of condensate seal legs (18) positioned between the second channel (16) and the interior (8c) of the pressure vessel (40). The gaseous and vapour content is discharged to the exterior via the discharge duct (37) in fluid connection with the first discharge ports (17). The condensate draining from second channel (16) to the interior (8c) via the condensate seal legs (18) is discharged out of the pressure vessel (40) through condensate discharge port (7). Where advantageous, in an embodiment as shown in Figure 5, the fluid flow is reversed wherein steam from an external source is admitted into the first channel (15) through the first discharge port (17) and a pressure differential is developed between first channel (15) and interior (8) to induce a steam flow across the stacked fruit bunches (10) in the cages (4) discharging into the interior (8) to effect residual air removal. The steam from an external source is admitted during the air removal process through the first discharge port (17) before or at the same time as steam is admitted into the interior (8) through the steam inlet port (1 ) and the resulting induced steam flow across the stacked fruit bunches (10) in the cages (4) continues until the pressure in the interior (8) begins to rise. The dispersed residual air from the interior (8) is released to the exterior through the bottom primary air discharge pipes (6).

Figures 6 and 7 show in greater detail the cross sectional end views of an arrangement of a fruit cage (4) on a carriage with wheels on a pair of tracks (14) inside a sterilizer pressure vessel (40) of the described embodiment.

Figure 6 shows an arrangement of a fruit cage (4) on a carriage (13) inside the pressure vessel (40) providing a lateral slidably engageable fluid connection (19) to effect fluid passage between the interior (8) and an exterior (yy) of the pressure vessel (40). The solid flat floor (1 1 ) of the fruit cage (4) is provided with an opening or perforations (51 ) through which fluid can flow between the interior of the fruit cage (4) and the first channel (15) to establish a fluid connection. The opening or perforations (51 ) through the cage floor (1 1 ) and the first channel (15) are so disposed to effect a more uniform flow distribution of steam through the stack of fruit bunches (10) across the interior of the fruit cage (4). Advantageously, the solid floor (1 1 ) base plate is provided with perforations (51 ) substantially on or adjacent the longitudinal centre line of the solid floor (1 1 ) to facilitate the more uniform flow distribution of fluid across the interior of the cage (4) through the first channel (15). The opening (51 ) may take the form of holes or elongated slots having an area adapted to flow therethrough of fluid including condensate so that the pressure difference across the opening (51 ) during the residual air removal process is preferably less than 200 Pa and more preferably less than 100 Pa. The pressure differential between the interior (8) and the opening or perforations (51 ) required to attain a turbulent regime of fluid flow across the interior space of the fruit cage (4) is influenced by the efficacy of condensate removal from the interior of the container (4) where a lower pressure differential is advantageous, and the design and dimensioning of the opening or perforations (51 ) has an effect on the outcome. Conveniently the fluid communication provided though the bottom floor surface of the cage (4) facilitates discharge of condensate by gravity through the perforations (51 ). The perforations (51 ) are so sized not to allow fruits or fruit bunches (10) to pass through but allow a copious flow of fluid including condensate. Conveniently, a slightly raised grating (12) above the solid flat floor (1 1 ) of the fruit cage (4) could provide a void for passage of fluid so as to enhance a more uniform flow distribution of steam across the load of fruit bunches (10). The fruit cage (4) is either secured to the carriage frame (13) as an integral part or removable. In the former, the first channel (15) is preferably attached to the fruit cage (4). Where the fruit cage (4) is removable from the carriage frame (13) the first channel (15) is preferably attached to the carriage frame (13) and a resilient sealing gasket insert (31 ) will provide fluid seal between the interior of the fruit cage (4) and the first channel (15) when the fruit cage (4) is placed on the carriage frame (13). The resilient sealing gasket insert (31 ) is compressed to deform and effect a sealing contact between the two mating surfaces providing a fluid connection to allow ingress and egress of the sterilising fluid between the interior of the fruit cage (4) and the first channel (15).

A first aperture (161 ) provided on a wall of the first channel (15) abuts a second aperture (162) provided on a wall of the second channel (16), forming a slidably engageable fluid joint (19) with an intermediate resilient sealing gasket insert (20) through which fluid can flow between the first channel (15) and the second channel (16) when the carriages are rolled into their predetermined positions on the tracks (14). The second channel (16) is in fluid connection through at least one first discharge port (17) to the exterior (yy) of the pressure vessel (40).

Fluid flowing from the interior of the fruit cage (4) into the first channel (15) consisting of air, other non-condensable gases, steam and condensate is discharged through the second channel (16) via the first discharge port (17) to the exterior. Condensate from the interior (8) is discharged out of the pressure vessel (40) through the condensate discharge port (7).

The described embodiment of the invention illustrates an arrangement where a plurality of carriages in tandem carrying fruit cages (4) loaded with the porous load (10) are rolled into the sterilizer pressure vessel (40) on a pair of tracks (14). The carnages are aligned laterally by the tracks and positioned inside the pressure vessel before the sterilizer doors are closed. In such an arrangement of the oil palm fruit sterilizer, the engaging seal design is catered for lead carriages passing over several seal apertures before reaching their final positions. To facilitate this requirement a slidably engageable joint (19) design providing fluid connection between the interior of the movable cage (4) and the stationary second channel (16) is provided. The engageable joint (19) design will have simpler options where a single carriage with load for treatment is rolled into the sterilizer. For example, the tracks inside the sterilizer provided with sloped sections to a lower level to enable the carriage frame (13) to lower onto contact with the aperture (162) in the top wall of the second channel (16) forming the engageable fluid joint (19) with an intermediate resilient sealing gasket insert (20) when the cage (4) is rolled into position inside the sterilizer. Figure 7 shows an arrangement of the second channel (16) with preferred condensate seal legs (18). The condensate seal legs (18) facilitate the removal of condensate from the second channel (16) through the condensate seal legs (18) to the interior (8c) of the pressure vessel (40). A discharge duct (37) located above the liquid level in the second channel (16) facilitates discharging only the gaseous and vapour content to the exterior of the pressure vessel (40) via the first discharge port (17). The discharge duct (37) is an elongated duct with openings to allow flow of gaseous and vapour content into the duct. See Figure 9 for details. The condensate draining from second channel (16) via the condensate seal legs (18) is discharged out of the sterilizer vessel (40) through the condensate discharge port (7). The arrangement with the condensate seal legs (18) provides for an efficient removal of gases and vapours by keeping the condensate from interfering with the air removal conduits and valves. Any dirt sediment that accumulates in the second channel (16) is removed during regular maintenance. Advantageously, as shown in Figures 7 and 8, the pressure differential that develops between the first channel (15) and the interior (8) is limited by the condensate seal legs (18). The condensate collecting in the first channel (15) provides the liquid seal to the condensate seal legs (18) to maintain the pressure differential. At the beginning of the sterilizer operation cycle, the condensate seal legs (18) are filled with condensate from the previous operation.

Figure 8 shows greater details of a lateral slidably engageable fluid connection (19). The slidably engageable fluid connection (19) formed between a seal shoe plate (21 ) forming a periphery surface of a first open aperture (161 ) provided on a wall of the first channel (15) and a resilient sealing gasket insert (20) forming a periphery surface of a second open aperture (162) provided on a wall of the second channel (16). Conveniently, the seal shoe plate (21 ) may be provided on the wall of the second channel (16) and the resilient sealing gasket insert (20) provided on the wall of the first channel (15) the position being reversed. When the first aperture (161 ) aligns over the second aperture (162), the resilient sealing gasket insert (20) is compressed against the seal shoe plate (21 ) to deform and effect a sealing contact between the two mating surfaces providing a fluid tight slidably engageable fluid connection (19) to allow ingress and egress of the sterilising fluid between the first channel (15) and the second channel (16).

The resilient sealing gasket inserts (20, 31 ) are of any suitable material that has good compression set values and can withstand the maximum exposure temperature and resistant to the sterilising agent fluid and other contaminants, for example, steam, water and vegetable oil in the case of oil palm fruit sterilization. Among suitable materials for the resilient sealing gasket inserts (20, 31 ) are soft elastomeric materials like Nitrile (NBR), VMQ Silicone (VMQ) and CR Neoprene (CR). An elastomer with good compression set value will attempt to return to its relaxed position for many cycles of operation. The profile of the sealing gasket insert (20) and the matching profile for a groove holding the gasket insert in place can be of different suitable shapes or sizes to provide an efficient sealing joint forming the slidably engageable fluid connection (19). The insert Figure 8a shows an alternative profile. A sealing joint design that provides compression of about 25 % to the gasket is considered necessary to provide acceptable seal strength and a gasket deformation between 15 and 30 mm to take-up the dimensional tolerance of the carriage height from the tracks. Lateral movements are allowed by the inherent design feature of the sealing joint. The sealing gasket insert will be closed cell foam or solid or hollow or a combination of sections of suitable material. The sealing gasket insert can be extruded or spliced. The joint corners will be cut and vulcanised or spliced to provide an efficient fluid tight seal. The sliding surface of the seal shoe plate (21 ), preferably stainless steel, will be burnished to a highly smooth surface to reduce abrasion with the gasket. The sliding surface of the seal shoe plate (21 ) shall preferably be provided with shallow lubricant dimples. A means can be provided for brushing clean dirt and application of suitable lubricant to the surface of seal shoe plate (21 ) by means of an unattended applicator filled with suitable lubricant located either inside or outside the pressure vessel (40). A plurality of slidably engageable fluid connections (19) can be provided for each fruit cage (4) as shown in Figure 13, such number of slidably engageable fluid connections (19) depends on, for example, availability of sizes of sealing gasket inserts, ease of installation or maintenance and cost considerations.

The design of the second channel (16) can be adopted with different configurations. Where plurality of carriages in tandem carrying fruit cages (4) are rolled into the sterilizer, individual second channels (16) catering for each fruit cage (4) with its separate first discharge port (17) to the pressure vessel (40) exterior can be provided to isolate leaks in the slidably engageable fluid connection (19) of any fruit cage (4). Alternatively, one or more continuous second channel (16) with their respective separate first discharge port (17) can be provided to serve a plurality of carriages in tandem with cages rolled into the sterilizer, in which arrangement, a full set of cages must be positioned in the sterilizer to develop the pressure differential. However, in such an arrangement, leaks in one or more slidably engageable fluid connection (19) would cause to deteriorate the pressure differential in the whole system.

Figure 8 further illustrates the design static head legs (hi ) and (h2) of the condensate seal legs (18). These static heads are the differences in height between the respective surfaces of the liquid in the condensate seal legs (18) as indicated. An operating pressure differential between the second channel (16) and the interior (8) rising close to (hi ) will impede the flow of condensate through the condensate seal legs (18) and cause the condensate in the second channel (16) to rise, and further rise in operating pressure differential above (hi ) will cause condensate to overflow into the discharge duct (37). An operating pressure differential between the second channel (16) and the interior (8) rising to (h2) is the limiting value, above which pressure differential the condensate seal legs (18) will not sustain the sealing effect and steam from the interior (8) will pass through the condensate seal legs (18) to the second channel (16). Advantageously, limiting the operating pressure differential to (h2) allows for a simpler economic design for the first and second channels (15,16) together with sealing arrangements (19, 31 ) and avoids potential damage to the slidably engageable fluid connection (19) due to over pressure causing extrusion of the resilient sealing gasket insert (20). Further, undue turbulence in the fruit bunches (10) are avoided by maintaining the operating pressure differential small. In practical implementation, the condensate seal legs (18) are designed for operating the sterilizer at an operating pressure differential of between about 100 Pa and 1000 Pa (between 10 mm and 100 mm water gauge) that is adequate to induce a turbulent steam-air mixture sweep across the fruit cage. The operating pressure differential will be lower than (hi ) and is controlled by the restricted flow rate of fluid through the first discharge port (17). The design value of pressure differential leg (h2) is to provide an operating margin higher than (hi) before the condensate seal legs (18) break. The condensate seal legs (18) provides a back up protection to limit the pressure differential, in the event of the flow rate of fluid through the first discharge port (17) is inadvertently left unchecked.

Figure 9 shows in greater detail the cross sectional side view of the lateral positions of the discharge duct (37), first discharge port (17) and condensate discharge port (7).

Figure 10 shows in greater detail the cross sectional side view of an arrangement for removing the condensate collecting in the second channel (16) out of the sterilizer vessel (40) through a second discharge port (17a). Where it is advantageous condensate falling from the fruit cages (4) and collecting in the second channel (16) will be segregated from the condensate precipitated from heating the mass of metal of the pressure vessel (40) outer wall (3) and the fruit cage carriage (13) collecting in the interior (8c). A second discharge port (17a) is provided to discharge the contaminated condensate collecting in the second channel (16) out of the pressure vessel (40) maintaining the first discharge port (17) for the gaseous content discharge. In such an arrangement, the condensate seal legs (18) may be retained to limit the pressure differential. The condensate discharge port (7) discharges the clean condensate collecting in the. interior (8c). The segregation may facilitate reuse of the clean condensate and oil separation from the contaminated condensate.

Figures 1 1 , 12, 13, 14, 15 and 16 are presented to illustrate the described embodiment of the invention.

Figure 17 shows the piping and valve arrangement to operate the sterilizer. A main steam inlet valve (23) and an auxiliary steam inlet valve (24) control the flow of external steam supply through the steam inlet ports (1 ) into the pressure vessel (40) above the steam inlets baffle (2). The auxiliary steam valve that has a smaller bore serves to admit steam at low flow rate during the initial heating and de-aeration stage when the steam consumption is the highest to limit the velocity and moderate turbulence and thereby allowing the buoyancy of steam to push the air in the vessel (40) downwards. The steam inlet baffle (2) distributes the inlet steam more uniformly over the length of the sterilizer. The steam admission system, including the steam inlet ports (1 ), steam inlet baffle (2), main steam inlet valve (23) and the auxiliary steam inlet valve (24) are configured and sized for the higher specific volume of the steam inherent of the reduced steam pressure of sterilizer operation and the reduced pressure of an external steam supply to limit pressure drops and flow velocities. The steam admission system will allow the required steam flow rate into the sterilizer to attain the desired pressure-time profile of operation as shown in Figure 18 with an external steam supply pressure to the steam admission system maintained preferably at a predetermined design value between 120 kPa and less than 300 kPa such that the duration between steam admission at point (a) and attaining operating pressure at point (d) in Figure 18 will be less than 15 minutes. More preferably, the external steam supply pressure to the steam admission system is maintained at a predetermined design value between 150 kPa and less than 250 kPa. The conduits to convey the required amount of external supply steam at the predetermined design steam pressures to the pressure vessel (40) are preferably sized such that the velocity of flow does not exceed 40 m/s to prevent excessive erosion and noise levels. An increased number of steam inlet ports (1 ), main steam inlet valve (23) and the auxiliary steam inlet valve (24) could be employed to achieve an economic configuration. The steam inlet baffle (2) is configured to admitted steam at low velocity during the initial air removal stage to limit any turbulence and facilitate initial gravity downward displacement of air in the vessel (40). An exhaust steam valve (25) releases the steam from the pressure vessel (40) to the exterior at the end of the sterilization cycle. A primary air discharge valve (28) releases air and other non- condensable gases through the primary air discharge ports (6) from the interior (8) of the pressure vessel (40) to the exterior. Condensate discharge valve (29) releases the large quantity of condensate precipitated during initial heating and collecting in the interior (8) through the condensate discharge ports (7) rapidly to prevent flooding of the pressure vessel (40). A condensate discharge by-pass valve (26) is a continuous bleed valve that is open substantially throughout the sterilization cycle where an orifice could be fitted as an alternative to valve (26) to provide a continuous condensate bleed. The condensate discharge by-pass valve (26) is sized to bleed condensate from the pressure vessel (40) at the sterilizer operating pressure. A first air discharge valve (30) capable of selectively providing fluid communication between the first discharge port (17) and an exterior connected to the valve (30) is provided as an external means of throttling and venting the fluid flow. The first air discharge valve (30) releases air and other non-condensable gases from the second channel (16) through the first discharge ports (17) to an exterior during the de- aeration stage when the pressure in the pressure vessel (40) is low. The first air discharge valve (30) and associated discharge piping from the first discharge port (17) are sized to discharge fluid consisting of air, other non-condensable gases and steam at a rate sufficient to develop an operating pressure differential adjustable between about 100 Pa and 1000 Pa across the first channel (15, Figure 3) and interior (8, Figure 3) when the sterilizer pressure attains a small pressure rise, about 1 .2 bar (120 kPa) in the interior (8) during operation. Development of the required differential pressure differential is advantageously delayed until a small pressure rise is attained to offer an economic sizing of fluid pathways (151 , 152) and the external means of flow control. The operating pressure differential between the first channel (15, Figure 3) and the interior (8, Figure 3) during sterilizer operation under steam pressure is verified by a differential pressure gauge measuring the pressure differential between the first discharge port (17) at pressure tap offs external to the sterilizer pressure vessel (40) and a tap off for pressure in the interior (8). Making a tapping off external to the sterilizer pressure vessel (40) for the differential pressure measurement reduces the number of apertures to the pressure vessel (40). A first air discharge by-pass valve (27) is a continuous bleed valve that is open substantially throughout the sterilization cycle where an orifice could be fitted as an alternative to valve (27) to provide the continuous bleed of air and other non-condensable gases, steam and entrained condensate from the second channel (16). The first air discharge by-pass valve (27) is sized to prevent condensate accumulation in the discharge piping connecting the first discharge port (17) when the first air discharge valve (30) is closed during the sterilizer operation. Figure 18 illustrates the various stages of the sterilization process with the method and apparatus disclosed herein showing steam pressure in the interior (8) with time as the sterilizer is placed into operation. It is a single peak sterilization process to attain a sterilisation temperature of 1 10 ^SC. Referring to Figure 17, the required number of carriages in tandem carrying the fruit cages (4) stacked with oil palm fruit bunches (10) are rolled on the pair of tracks (14) into the open sterilizer and positioned for correct alignment of the first aperture (161 ) with the second aperture (162) to form the slidably engageable fluid connection (19) as afore described. The sterilizer door is then closed followed by closure of the exhaust steam valve (25). The primary air discharge valve (28), condensate discharge valve (29) and first air discharge valve (30) are opened to the exterior. The condensate discharge by-pass valve (26) and the first air discharge by-pass valve (27) remain open. The auxiliary steam inlet valve (24) is then opened to admit external steam supply into the pressure vessel (40) to begin the sterilization operation. The air, other non- condensable gases and condensate begin to discharge from the pressure vessel (40) starting at point (a).

The pressure in the interior (8) begins to rise at point (b) indicating that temperatures of the mass of metal of the pressure vessel (40) outer wall (3) and the fruit cage carriage (13) have reached close to the saturation steam temperature in the interior (8). Most of the air in the interior (8) is dispersed by gravity downward displacement through the bottom primary air discharge ports (6) at point (b). As the pressure in the interior (8) rises beyond point (b), a pressure differential develops across the fruit cages (4) between the interior (8) and the first channel (15) that is open to an exterior via the first discharge port (17) and first air discharge valve (30) passing out fluid to the exterior. The pressure differential between first channel (15) and the interior (8) varying as the pressure in the interior (8) rises is adjustable by throttling and venting the fluid flow between the first channel (15) and the exterior b means of the first air discharge valve (30), however, in practice the first air discharge valve (30) may be kept full open when the pressure is rising in the sterilization process. The pressure differential induces a flow of steam through the stack of fruit bunches (10) across the interior space of the fruit cage (4) from the interior (8) to the first channel (15) sweeping off pockets of air. Point (c) indicates that sufficient pressure differential is developed between the interior (8) and the first channel (16) to induce a turbulent steam-air sweep through the interior space of the fruit cage (4). Point (c) can be verified by the differential pressure gauge described above. However, in practice point (c) is established by the small pressure rise in the vessel (40), about 1 .2 bar (120 kPa), at which point the primary air discharge valve (28) and condensate discharge valve (29) are closed. Alternatively, the point (c) is established by the temperature of the condensate at the condensate discharge port (7) or second discharge port (1 a), say about 103 ⁵C. The fluid flow through the first air discharge valve (30) is continued thereafter for duration of about three to five minutes until point (g) to substantially disperse residual air out of the fruit cages (4). The first air discharge valve (30) is then closed and the main steam inlet valve (23) is gradually opened to admit steam into the pressure vessel (40). Most of the residual air in the interior space of the fruit cage (4) with stack of fruit bunches (10) will be dispersed at point (g). Alternatively air detection means for fluid discharging from the first air discharge port (17) can be used to verify point (g). Efficient air dispersal is objectively verified by the desired percentage of unstripped fruit bunches following sterilization. Beyond point (g) a more uniform surface temperature distribution is attained within the load of fruit bunches (10) closely following the saturation steam temperature corresponding to the prevailing pressure in the interior (8). Condensate discharge by-pass valve (26) remains open substantially throughout the sterilization cycle providing a continuous bleed of the condensate. Similarly, the first air discharge by-pass valve (27) preferably remains open substantially throughout the sterilization cycle providing a continuous bleed of any residual air and other non- condensable gases, steam and entrained condensate through the first channel (15). The purpose of providing a continuous bleed is to prevent condensate accumulation in the discharge piping when the first air discharge valve (30) is closed during the sterilizer operation. The first air discharge by-pass valve (27) when suitably sized could be used to subject the fruit bunches (10) in the cages to a flow of steam passing between the interior (8) and the first channel (15) sweeping off any residual pockets of air when the sterilizer is operating at high pressure beyond point (g) if necessary.

The pressure in the interior (8) is raised until it reaches a steam pressure corresponding to a saturation steam temperature that maintains a minimum temperature within the range of temperature distribution in a porous load that meets the predetermined effective sterilization temperature at point (d), when the auxiliary steam inlet valve (24) is closed and the opening of the main steam inlet valve (23) may be regulated to maintain the pressure in the interior (8).

At point (e), the main steam inlet valve (23) is closed followed by opening the condensate discharge valve (29) and the exhaust steam valve (25) to depressurize the pressure vessel (40). At point (f) when pressure in the vessel (40) is confirmed to be atmospheric, the vessel (40) door is opened to remove the cages with treated fruit bunches. The interval between point (d) and (e) is considered the exposure time for the effective sterilization temperature. Figures 19, 20 and 21 show an embodiment of the invention where axial fluid connection (22) is employed to effect a fluid passage between an interior (8) and the exterior of the pressure vessel (40). A perforated axial discharge duct (36) through the first channel (15) provides the fluid passage with the exterior.

Figure 19 shows the cross sectional end views of an arrangement disposing a first channel (15) and a discharge duct (36) attached to the moving carriage frame (13). A resilient sealing gasket insert (31 ) establishes a fluid connection between the interior of the cages (4) through an opening or perforations in the solid flat floor (1 1 ) of the fruit cage (4) and an opening on the wall of the first channel (15), when the fruit cage (4) is placed on the carriage frame (13). The discharge duct (36) open at its ends is provided protruding through the first channel (15) at the end wall of the first channel (15) with a fluid tight joint to effect a fluid passage to the exterior of the pressure vessel (40). The arrangement provides a first fluid pathway (151 ) extending from the opening (51 ) through the surface of the container (4), via orifice (32), discharge duct (36) to a first aperture (161 , Figure 20) at an axial fluid connection (22) (Figure 21 ) on the movable carriage (13), and a second fluid pathway (152) extending from a second aperture (162, Figure 21 ) at the axial fluid connection (22) to a first discharge port (17) to establish a fluid passage between the opening (51 ) through the surface of the container (4) and an exterior (yy) of the pressure vessel (40). Fluid passage between the first channel (15) and discharge duct (36) is through orifice (32) provided on the discharge duct (36) within and along the length of the first channel (15). The Figure 19 further shows an arrangement of the first channel (15) with preferred condensate seal legs (18) where the condensate from the first channel (15) is drained to the interior (8c) of the sterilizer vessel (40). The orifice (32) on the discharge duct (36) is located above the liquid level in the first channel (15) to allow unimpeded flow of gaseous and vapour content through the fluid path.

The design of the discharge duct (36) and the orifice (32) will provide sufficient pressure differential between the first channel (15) and the interior (8) of the sterilizer pressure vessel (40). The cross section area of the discharge duct (36) is influenced by the number of cages (4) in tandem. The pressure drop along the length of the discharge duct (36) will be kept low to provide sufficient pressure differential at all fruit cages (4). It is contemplated that the discharge duct (36) will have an internal cross sectional area of about 0.04 square meters.

Figure 20 shows a side elevation view of the arrangement with the first channel (15) and a discharge duct (36) attached to the moving carriage (13). The discharge duct (36) extends across the end walls of the first channel (15) protruding through the end walls with fluid tight joints at the interfaces to cater for a plurality of carriages in tandem. The discharge duct (36) terminates in the first aperture (161 ) in the proximal end and a third aperture (163) in the distal end to provide fluid passage between a trail carriage (13) and the exterior of the pressure vessel (40) via a lead carriage (13) through the lead carriage discharge duct (36). The extent of orifice (32) provided on the discharge duct (36) within and along the length of the first channel (15) to provide fluid passage between the interior (8) of the pressure vessel (40) to the exterior through the discharge duct (36) is shown.

Figure 21 illustrates an arrangement for a plurality of carriages in tandem carrying the porous load (10) rolled into the sterilizer on a pair of tracks. In such an arrangement of the oil palm fruit sterilizer, the cages are linked together is an array of full set to fill the sterilizer. This practice enables a convenient flexible hose connection (33) means to provide an axial detachably engageable fluid connection (22) between the carriages (13) as shown.

Figure 21 illustrates two means of providing the axial detachably engageable fluid connection (22), one by means of flexible hose and hose clip (33, 34) and the other a telescoping connector with O-ring seal joint (35). The telescoping connector compensates for heave and offset of the carriages in tandem and renders it a preferred detachably engageable fluid connection (22). The movement is achieved through the stroking movement of the inner and outer barrel of the telescoping connector with the resilient O-ring seal. The telescoping connector design will provide to take-up lateral misalignment due to dimensional tolerance between the carriage and the track in addition to dimensional tolerance of the carriage height from the tracks. The detachably engageable telescoping connector will be more preferred for the terminal discharge connection at the proximal end to the first discharge port (17) that goes through the outer wall (3) of the pressure vessel (40) to effect a fluid connection between the first discharge duct (36) and the exterior of the pressure vessel (40). The third aperture (163) at distal end of a lead carriage discharge duct (36) connects to the first aperture (161 ) at proximal end of a trail carriage discharge duct (36) through a telescoping connector providing fluid passage between adjacent carriages in tandem. Fluid connection between the discharge duct (36) and the first discharge port (17) to the exterior of the pressure vessel (40) is shown indicating the locations of first and second apertures (161 ,162).

Where advantageous, comparable to that shown in Figure 5, the flow is reversed wherein steam from an external source is admitted into the first channel (15) through the first discharge port (17) via the discharge duct (36) and a pressure differential is developed between first channel (15) and interior (8) of the sterilizer vessel (40) to induce a steam flow through the stack of fruit bunches (10) across the interior of the cages (4) into the interior (8) of the sterilizer to effect residual air removal.

Figure 22 shows an embodiment of the invention in a preferred arrangement wherein a pair of condensate seal legs (18) are located in the first channel (15) disposed in the moving carriage (13) to allow drainage of condensate from the first channel (15) to the interior (8c) of the pressure vessel (40). The gaseous and vapour content flows between the first channel (15) and an aperture (161 ) through the discharge duct (36). A lateral slidably engageable fluid connection (19) is employed to effect fluid passage between the first channel (15) and the second channel (16). This arrangement precludes removal of condensate from the first channel (15) via a second discharge port (17a, Figure 10) out of the sterilizer vessel (40).

The invention as described herein provides cost savings with the use of related plant equipment configured for a lower design pressure.

While the present invention has been described as having a preferred design, it can be further modified within the scope of this disclosure. This application is therefore intended to cover any variations, uses or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come with a known or customer practice in the art to which this invention pertains.

While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of examples only. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the invention herein. Accordingly it is intended that the invention be limited only by the scope of the appended claims.

Claims

A method to heat treat a porous load of material (10) in a pressure vessel (40) including the steps of:

a. Transporting at least one open topped container (4) containing the porous load of material (10) into the horizontally positioned cylindrical pressure vessel (40), the container (4) mounted on a carriage on tracks within the pressure vessel (40),

b. sealing the pressure vessel (40),

c. admitting steam into interior (8) of pressure vessel (40) whilst releasing air from the pressure vessel (40), and

d. raising a temperature of the porous load of material (10) until it reaches a sufficient temperature and maintained thereafter for a time interval sufficient so that the porous load of material (10) is substantially heat treated,

characterised in that step (d) includes inducing a flow of steam through the porous load of material (10) across interior of the container (4) between the interior (8) and an exterior of the pressure vessel (40) by maintaining a pressure differential across the container (4), the pressure differential is between a first pressure (P1 ) prevailing in the interior (8) and a second pressure (P2) prevailing in a first fluid pathway (151 ) at perforation (51 ) wherein the second pressure (P2) is varied by inducing a fluid flow between the first fluid pathway (151 ) and the exterior, thereby substantially dispelling residual air from within the porous load of material (10).

2. A method to heat treat a porous load of material (10) in a pressure vessel (40) according to claim 1 , wherein the flow of steam through the porous load of material (10) is substantially turbulent and wherein the pressure differential is between 100 Pa and 2000 Pa.

3. A method to heat treat a porous load of material (10) in a pressure vessel (40) according to claim 2, wherein the pressure differential is between 400 Pa and 1000 Pa.

4. A method to heat treat a porous load of material (10) in a pressure vessel (40) according to claim 2, wherein the residual air from within the porous load of material (10) is substantially dispelled in a period of time between 3 and 5 minutes when turbulent flow is maintained.

5. A method to heat treat a porous load of material (10) in a pressure vessel (40) according to any of claims 1 to 4, wherein the pressure differential comprises the first pressure (P1 ) having a higher pressure than the second pressure (P2), so that fluid flows from the interior (8) to the first pathway (151 ).

6. A method to heat treat a porous load of material (10) in a pressure vessel (40) according to any of claims 1 to 4, wherein the pressure differential comprises the first pressure (P1 ) having a lower pressure than the second pressure (P2), so that fluid flows from the first pathway (151 ) to the interior (8).

7. A method to heat treat a porous load of material (10) in a pressure vessel (40) according to any of the preceding claims, wherein the fluid flow between the first fluid pathway (151 ) and an exterior is induced by throttling and venting the fluid flow.

8. A method to heat treat a porous load of material (10) in a pressure vessel (40) according to any of the preceding claims, further including draining condensate discharging from the interior of the container (4) into the interior (8c) via at least one condensate seal leg (18) in fluid communication between the condensate stream discharging from the interior of the container (4) and the interior (8c).

A method to heat treat a porous load of material (10) in a pressure vessel (40) according to any of the preceding claims, further includes discharging the condensate from the interior of the container (4) via at least one second discharge port (17a) to the exterior of the pressure vessel (40) and separately discharging the condensate from the interior (8c) via at least one condensate discharge port (7) to the exterior of the pressure vessel (40).

10. A method to heat treat a porous load of material (10) in a pressure vessel (40) according to any of the preceding claims, wherein the porous load of material (10) is plant produce.

1 1 . A method to heat treat a porous load of material (10) in a pressure vessel (40) according to claim 10, wherein the plant produce is oil palm fruit bunches.

12. A method to heat treat a porous load of material (10) in a pressure vessel (40) according to claim 1 1 , wherein saturation steam temperature corresponding to the pressure in the interior (8) is less than 10 ^SC above the predetermined sterilization temperature of the porous load of material (10).

13. A method to heat treat a porous load of material (10) in a pressure vessel (40) according to claim 12, wherein saturation steam temperature corresponding to the pressure in the interior (8) is not more than 2 ^SC above the predetermined sterilization temperature of the porous load of material (10).

14. A sterilizer operable with pressurised steam for heat treatment of a porous load of material (10) comprising a horizontally positioned cylindrical pressure vessel (40) with at least one steam inlet port (1 ) and at least one open topped container (4) mounted on a carriage (13) transportable along a pair of tracks (14) mounted within the pressure vessel (40),

characterised in that the sterilizer further includes a first fluid pathway (151 ) mounted on the carriage (13) and extending from the surface perforation (51 ) to at least one first aperture (161 ) to be in fluid connection with a second fluid pathway (152) and wherein the second fluid pathway (152) secured to the pressure vessel (40) extending from at least one second aperture (162) to at least one first discharge port (17) to be in fluid connection with the exterior (yy) of the pressure vessel (40)..

15. A sterilizer operable with pressurised steam for heat treatment of a porous load of material (10) according to claim 14, wherein the fluid connection between the first fluid pathway (151 ) and the second fluid pathway (152) is effected via an engageable connection (19) formed by way of a resilient sealing gasket (20) between peripheral lips surrounding the first and second apertures (161 , 162) when the carriage (13) is in registration at predetermined position on the tracks.

16. A sterilizer operable with pressurised steam for heat treatment of a porous load of material (10) according to claim 14, wherein the fluid connection between the first fluid pathway (151 ) of a carriage (13) and the second fluid pathway (152) secured to the pressure vessel (40) is effected via an axially engageable connection (22) between conduit ends forming the first and second apertures (161 , 162) and wherein the fluid connection between adjacent carnages in tandem is effected via the axially engageable connection (22) between conduit end forming the first apertures (161 ) and the conduit end forming a third aperture (163) of the adjacent carriage when the carriage (13) is in registration at predetermined position on the tracks..

17. A sterilizer operable with pressurised steam for heat treatment of a porous load of material (10) according to claim 16, wherein the axially engageable fluid connection (22) between the adjacent pathways is through a telescoping connector.

18. A sterilizer operable with pressurised steam for heat treatment of a porous load of material (10) according to claim 14, wherein the container (4) includes a solid base plate (11 ) with perforations (51 ) on or adjacent the longitudinal centre line of the solid base plate (1 1 ) to facilitate the flow of fluid through the perforations (51 ) substantially between the perforations (51 ) and the first pathway (151 ).

19. A sterilizer operable with pressurised steam for heat treatment of a porous load of material (10) according to claim 14, further including at least one condensate seal leg (18) in fluid communication between the first pathway (151 ) or the second pathway (152) and the interior (8c), wherein the at least one condensate seal leg (18) provides drainage for the condensate discharging from the container (4) to drain into the interior (8c).

20. A sterilizer operable with pressurised steam for heat treatment of a porous load of material (10) according to claim 19, wherein the condensate seal leg (18) limits the pressure differential between a first pressure (P1 ) prevailing in the interior (8) and a second pressure (P2) prevailing at the perforations (51 ).

21 . A sterilizer operable with pressurised steam for heat treatment of a porous load of material (10) according to any of claims 14 to 20, further includes at least one second discharge port (17a) that forms a fluid passage between the second channel (16) and the exterior, for discharging any condensate from the second channel (16) into the exterior of the pressure vessel (40).

22. A sterilizer operable with pressurised steam for heat treatment of a porous load of material (10) according to any of the preceding claims, wherein the porous load of material (10) is a plant produce.

23. A sterilizer operable with pressurised steam for heat treatment of a porous load of material (10) according to claim 22 wherein the plant produce is oil palm fruit bunches.