AU1643701A - Method and apparatus for heat treatment of particulate material - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "METHOD AND APPARATUS FOR HEAT TREATMENT OF PARTICULATE MATERIAL" The following statement is a full description of this invention, including the best method of performing it known to me: 1

TITLE

METHOD AND APPARATUS FOR HEAT TREATMENT OF PARTICULATE MATERIALS BACKGROUND OF THE INVENTION This invention is concerned with an apparatus and method for roasting coffee beans and for heat treatment of like particulate food or vegetable materials such as nuts and grains.

The invention is particularly, although not exclusively, concerned with a method and apparatus for roasting relatively small batches of coffee beans in a retail environment.

The most commonly employed apparatus for roasting coffee beans has been a rotatable drum roaster built to a large scale for commercial coffee manufacturers or on a smaller scale for boutique retail outlets.

15 Certain of such drum roasters have comprised a solid, externally heated drum which transferred heat energy to the coffee beans by convection through the drum wall. Other drum roasters •go* comprise a perforated drum surrounded by a jacket and wherein the beans are heated by a source of heated air introduced via the drum perforations.

The main problems associated with such drum roasters is the difficulty in obtaining even temperature distribution through a mass of coffee beans which leads to over-roasting of beans in direct contact 2 with the drum and under-roasting of others.

The prior art is replete with batch and continuous roasters which endeavour to obtain a greater degree of control of the roasting process to ensure even, controlled roasting within predetermined temperature limits and for a predetermined time period.

Generally, coffee roasters can be divided into two generic classes passive and dynamic. Although the description herein is limited to roasting of coffee beans it should be understood that the apparatus and method of the present invention is equally applicable to roasting or drying of all particulate organic materials such as foodstuffs of vegetable, animal and synthetic origin.

Passive roasters are those in which a static bed of coffee beans is subjected to heating by heated gas or air passing through the bed and/or infra red radiation from a heating element.

15 Examples of passive roasters are described in US Patent 4425720, US Patent 4455763, US Patent 4642906, German Patent ***Application No. DE 4405129-A (Derwent Accession No. 293670/39), European Patent Application EP 676148-A1 (Derwent Accession No. 95-345905/45), German Patent Application DE 3419251-A (Derwent Accession No. 85-304083/49) and Russian Patent Application SU 1660676-A1 (Derwent Accession No. 92- 174534/21). These passive roasters are generally small domestic appliances.

3 Dynamic roasters generally can be divided into mechanically agitated beds, drum roasters and fluidized bed roasters.

A mechanically agitated bed roaster is described in International Publication No. WO 96/38048 wherein particulate food material is mixed with a heated granular material to transfer heat into the particulate food product and thereafter separating the granular material from the food product.

Another mechanically agitated bed system is described in Australian Patent Application AU-A-63070/86 wherein coffee beans are subjected to a microwave irradiation in a horizontal tubular chamber having a helical screw conveyor to move the beans from an inlet to an outlet.

V A more complex apparatus is described in European Patent Application EP-137556-13 (Derwent Accession No. 85-094504/16) :15 wherein coffee beans are roasted while being advanced through at oooo°.

S•least six serially connected processing zones, each of which is supplied with roasting gas.

Drum roasting devices are ubiquitous in the prior art and are exemplified by German Patent Application DE 4100069-A (Derwent AN 92-235232/29), United States Patent 4737376, Italian Patent Application IT 1158395-B (Derwent AN 84-019339/04), Japanese a Patent Application J86031981-B (Derwent AN 85-253379/41), Spanish Patent Application ES 2013110-A (Derwent AN I '1 11, 4 4 158208/21), International Publication No. WO 96/35335, Australian Patent Application AU-A-26251/84 (Derwent AN 85-141247/24), International Publication No. WO 92/12643 and European Patent Application EP-366896-A (Derwent AN 90-140965/19).

Generally speaking, drum roasters are large scale devices used in commercial coffee roasting processes as a pre-cursor say, to manufacture of instant coffee powders.

While all of the above types of small scale domestic and large scale commercial coffee roasters are generally effective for their intended purpose, they are characterised in that it is not possible to obtain even, precise roasting on a consistent basis.

Fluidized bed roasters offer a greater degree of control and more evenness in a coffee roasting process.

Fluidized bed roasters are exemplified in German Patent No.

4028111, German Patent Application DD-255079-A (Derwent AN 88- 228392/33), German Patent Application DE 3437432-A (Derwent AN 86-252630/39, German Patent Application DE 3609612-A, German Patent No. 3116723, United States Patent 4698916, United States S• Patent 4494314, European Patent Application EP 55462-A (Derwent *o* AN 82-57614 E/28) and United States Patent 5230281.

Other types of fluid bed roasters have a means for transferring particulate material from one zone or compartment to another during the roasting process. Such apparatus is described in Russian Patent Application SU 1824155-A1 (Derwent AN 94-356497/44), United States Patent 4444553, United States Patent US 4169164, British Patent Application GB 2054345-A (Derwent AN 81-12303D/08) and German Patent Application DD-160209-A (Derwent AN 83- 759220/37).

The above described fluidized bed roasters are generally applicable to large scale commercial coffee roasting and thus lack precise and consistent roasting within and between batches.

Of recent times there has been a proliferation of cafes and specialised coffee shops selling exotic coffee blends at premium prices. Customers may try various blends by consuming an individual brew and then order, say, 0.5 kg of a particular blend as roasted/ground beans for home consumption. With the premium prices being charged, customers expect to be able to obtain freshly 15 roasted coffee of consistent high quality.

S* Medium sized fluid bed batch roasters suitable for coffee shops to produce quality roasted beans have, of recent times entered the market place. These roasters are characterised by a relatively *compact size and sophisticated control mechanisms to provide ooo.

consistent roasting temperatures and cycle times. These roasters also include a means to separate husks detached during the roasting process.

One such roaster is described in Japanese Patent Application 6 JP 93020063-B (Derwent AN 92-077320/10). This apparatus comprises a vertical tube with a perforated frusto-conical floor through which heated air is introduced under pressure. Located just above the floor on the vertical axis of the tubular roasting chamber is a concentrically positioned tube with an outwardly divergent mouth facing the floor. Coffee beans are directed up the concentrically positioned tube and are recirculated within a generally toroidal volume between the inner and outer tubes.

Another similar such roaster is described in United States Patent 4489506. In this apparatus a fluidized bed is created in a tubular roasting chamber with an inner coaxial tube through which heated air is directly downwardly from a plenum chamber. Heated air enters the roasting chamber adjacent the base thereof and moves the :beans through a toroidal path without entering the inner tube and 15 then the spent heated air exits the roasting chamber via apertures.

Yet another such apparatus described in International ~Publication No. WO 9006-694-A comprises a downwardly convergent hopper with a restricted outlet port at its lower end and an open mouth or inlet port at its upper end. The outlet port leads via a throat to a duct having a source of pressurized heated air upstream of the throat. The duct follows a curvilinear path with an upper opening adjacent the mouth of the hopper. A guide plate positioned above the duct upper opening guides coffee beans issuing from the duct through a smooth 1800 angle to enter the top of the hopper.

Strictly speaking, this is not a fluidized bed apparatus but rather a fluid transport system wherein coffee beans are roasted during the fluid transport phase in the duct whilst being circulated from the bottom of the hopper to the top of the hopper.

Again, whilst generally effective for their intended purpose, the ability to precisely control the roasting process is limited in each case.

While the apparatus of JP 93020063-B and United States Patent each describe a fluidized bed having a toroidal volume the distribution of the beans during the roasting phase is strictly random and can give rise to differences in the rate of transfer of heat from the heated gas to coffee beans such that true homogeneity within a batch is difficult to achieve even with strictly controlled roasting cycle times. This may be due to differences in velocity distribution within 15 the toroidal volume.

The apparatus of WO 9006-694 A is considered to give rise to uneven roasting within a batch due to the manner of movement of the coffee beans from the top to the bottom of the hopper. Due to frictional engagement between the beans at the outer extremities of the hopper and the significant difference between the path lengths of beans located on the one hand on the central axis of the hopper and, on the other hand, the outer extremities of the hopper as they progress from top to bottom, some beans in the batch are directed up 8 the roasting duct more frequently than others.

Moreover, as the velocity of the beans varies significantly across the cross section of the hopper, the residence time and thus contact time between beans in the hopper varies dramatically.

SUMMARY OF THE INVENTION According to one aspect of the invention, there is provided an apparatus for roasting particulate material, said apparatus comprising:an upright cylindrical housing; an inner tubular member mounted coaxially within said cylindrical housing to form an annular space between an inner wall of said housing and an outer wall of said tubular member, said tubular oo*o member having an inlet at one end adjacent a lower end of said 15 housing and an outlet at an opposite end intermediate opposite ends S• of said housing; a gas permeable perforated floor extending from an inner surface of said housing about and spaced from the inlet of said tubular member, said perforated floor including an aperture aligned o*o.

with the inlet of the tubular member; a first gas inlet in fluid communication with said annular space via said perforated floor; a second gas inlet in fluid communication with the inlet of said tubular member via said aperture in said perforated floor; and a gas outlet port located in an upper region of said housing.

Preferably said housing is formed from a heat resistant transparent glass material.

Suitably said perforated floor comprises a free area of greater than Preferably said perforated floor comprises a free area of greater than The perforated floor may comprise apertures having a dimension of 2mm or less.

Suitably a deflector is spaced above the outlet of the tubular member to deflect upwardly directed particulate material downwardly into said annular space.

*":One or more baffles may be provided in the upper portion of 15 the housing to prevent egress of gas entrained particulate material.

If required a separating means, in fluid communication with *".said gas outlet port, may be provided to extract entrained particulate material from gases issuing from said outlet port.

Preferably said housing includes an access port in an upper region thereof for introduction of particulate material.

If required, said access port may be associated with a hopper for particulate material.

The housing may include a discharge port adjacent a lower end thereof for discharge of treated particulate material.

Suitably the first gas inlet is adapted in use to meter a source of heated pressurized gas into said housing at a predetermined velocity and/or volumetric flow rate.

Preferably the first gas inlet includes a gas metering valve.

The second gas inlet is adapted in use to meter a source of heated pressurized gas into said tubular member at a predetermined velocity and/or volumetric flow rate.

Preferably the second gas inlet includes a gas metering valve.

If required, the apparatus may include temperature measurement means to measure the temperature of particulate material in the annular space between the inner wall of the housing and the tubular member.

**oo Suitably the temperature measurement means comprises a 15 thermoresponsive probe extending into the annular space via an aperture in said housing.

***According to another aspect of the invention there is provided a method for heat treatment of particulate material said method comprising the steps of:pneumatically conveying, by a first meterable source of heated pressurized gas, particulate material upwardly through a tubular member located concentrically within a cylindrical housing; collecting said particulate material in an annular space between 11 said tubular member and an inner wall of said housing; directing, via a perforated floor located adjacent a lower region of said housing, a second meterable source of heated pressurized gas into said annular space to heat a bed of particulate material accumulated therein as said bed moves downwardly under the influence of gravity to provide a supply of particulate material to an inlet of said tubular member for pneumatic conveyance therewithin by said first meterable source of heated pressurized gas.

Suitably said second meterable source of heated pressurized gas is introduced into said annular space at a velocity and/or volumetric flow rate sufficient to maximise gas flow through the bed of particulate material without fluidizing the bed of particulate material.

Preferably the velocity of the second source of gas is metered 15 to a velocity less than the minimum fluidization velocity of the a particulate material.

,The method according to the invention is preferably applied to roasting or dehydration of particulate organic materials such as foodstuffs of animal, vegetable or synthetic origin.

Most preferably the method is applicable to the roasting of coffee beans.

The method may include the further step of de-husking coffee beans by impact against a deflection device located above the outlet

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12 of the tubular member.

BRIEF DESCRIPTION OF DRAWINGS In order that the invention may be more readily understood and put into practical effect, a preferred embodiment of the invention will now be described with reference to the accompanying drawings in which:- FIG 1 shows schematically a cross-sectional side elevation of a coffee roasting apparatus.

FIG 2 shows the operation of the apparatus of FIG 1.

DETAILED DESCRIPTION OF THE DRAWINGS In FIG 1, the coffee roasting apparatus 1 comprises an upright cylindrical housing 2 having an inner tubular member 3 located coaxially therewithin for slidable movement by guides 4.

Tubular member 3 is open at both ends with an inlet 5 and 15 outlet 6. Supported above outlet 6 is a deflector 8, the purpose of which will be described later.

Deflector 8 is connected to a conical closure plug 9 by a connecting rod 10. Closure plug 9 is shown in a normally closed position to seal an aperture 11 in the base of a hopper 12 for green unroasted coffee beans. The upper end of plug 9 is connected via a further connecting rod 13 to a double acting pneumatic cylinder 14 for selective movement of plug 9 between a closed position as shown and an open position to introduce a charge of green coffee beans for 13 roasting. The upper end of tubular member 3 is also coupled to deflector 8 by the brackets 3a such that when plug 9 is opened to introduce a fresh batch of beans, tube 3 moves downwardly to close gap 43 to prevent beans entering cylindrical throat 21. Gap 43 is reopened when plug 9 seals aperture 11 in the hopper 12. Cylinder 14 is supported within hopper 12 by brackets 15 and a conical cover 16 prevents accumulation of coffee beans on the upper surface of the cylinder mount.

Frusto-conical baffles 17 are located about connecting rod to collect any gas entrained coffee beans and by reducing their velocity, enable them to fall back down the housing near the inner wall thereof.

A thermocouple 18 extends through the wall of housing 2 to measure the temperature of coffee beans in that region.

Adjacent the inlet 5 of tubular member 3 is a perforated frustoconical floor 19 with a central aperture 20 opening into a cylindrical throat 21 which in turn extends into a base chamber 22 in housing 2.

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A flap valve 23 actuated by a pneumatic cylinder 24 selectively opens or closes flap valve 23.

A first air duct 25 is in fluid communication with the annular space between housing 2 and tubular member 3 via perforated floor 19. A second air duct 26 is in fluid communication with the interior of tubular member 3 via chamber 22 and cylindrical throat 21. Each 4' 14 of air ducts 25, 26 has a flow regulating valve 27, 28 respectively.

Air ducts 25, 26 are coupled to a common conduit 29 which receives a source of pressurized air from blower 30 via a three way pneumatic valve 31. Valve 31 is capable of directing pressurized air via a high efficiency electric heater 32 to conduit 29 or it may allow a full or partial by-pass of heater 32 via by-pass conduit 33 having a flow regulating valve 34.

Adjacent the upper end of housing 2 is a spent gas outlet coupled to a cyclone separator 36 to collect husks or the like entrained in the air flow through housing 2. Air is exhausted from separator 36 via an outlet port 37.

At the lower end of separator 36 is a flap valve 38 actuable by a pneumatic cylinder 39.

o Situated below flap valves 23, 38 are roasted coffee bean and o15 separated husk hoppers 40, 41 respectively.

The operation of the apparatus will now be described with reference to FIG 2 in which like reference numerals are used for like 8 0 features.

Initially a charge of green coffee beans is introduced from hopper 12 into housing 2 by actuating cylinder 14 to open plug 9 and thereafter closing plug 9 to seal hopper aperture 11. By virtue of baffles 17 and deflector 8, the charge of beans is directed into the annular region between the tubular member 3 and the wall of housing 2.

With blower 30 and heater 32 actuated, a flow of heated air is directed via duct 25 through perforated floor 19 and into the mass of beans 42. At the same time, heated air is directed via duct 26 into chamber 22 and through cylindrical throat 21 into tubular member 3.

Respective gas flows through the annular space and tubular member 3 are adjusted by flow regulating valves 27, 28.

The gas flow entering tubular member 3 is adjusted to achieve pneumatic transport of beans through tubular member 3 as the beans flow, under the influence of gravity, into the restricted gap 43 between inlet 5 and aperture 20 in perforated floor 19. Beans entrained in the gas flow in tubular member 3 impact against deflector 8 and are returned to the annular space. In the event that a as 06B@ bean by-passes deflector 8, it contacts baffles 17 whereby its *:so :.ae 15 velocity is reduced sufficiently to drop back into the annular space.

eggs °°°Any husk material dislodged from beans as they impact on deflector 8 are entrained in the spent gas flow path which is connected to the cyclone separator 36 to separate the husks for later discharge into hopper 41.

The gas flow rate entering the annular space in housing 2 is adjusted so that the velocity is just below the fluidization velocity of the beans accumulated in the annular space. By maintaining the gas velocity at or just below the transition to a fluidized bed state, the w 16 mass flow of the beans through the annular space is maximised with significantly friction losses on the surfaces of the tubular member and housing wall which otherwise would give rise to a flow rate gradient across the mass of beans. At the same time, reduced friction losses in the bed of beans permits a greater volumetric gas flow through the annular space to maximise heat exchange between the heated incoming gas flowing countercurrent to the bed of beans.

Using an air flow rate of 2.5 3.0 cubic metres/minute at, say, a pressure of 600-800mm water gauge and a heater capacity of kW, the temperature of the air entering housing 2 reaches a steady state temperature of between 2500C and 3000C within one minute.

The roasting process commences when the beads reach a temperature of 1600C to 1800C after which an exothermic reaction accelerates the rate of temperature increase in the bed. During roasting, the volume of the beans increases by about 80-100%.

The apparatus in use will be found to be very efficient in batch times as the coefficient of thermal transfer to the beads as they are S° pneumatically transported up the tubular member is very high.

Moreover, the even volumetric flow of the beans through the annular 20 space countercurrent to the heating gas flow permits a uniform heat transfer from the outer surface of the beans to the interior thereof.

When the thermocouple 18 detects that the mass of beans has reached a predetermined temperature value, control circuitry (not

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17 shown) deactivates heater 32 and activates by-pass valve 31 to direct a flow of cool air through the apparatus. The movement of the coffee beans in housing 2 is the same during the cooling cycle as in the roasting cycle.

When the mass of coffee beans is lowered to a predetermined temperature value, the control circuitry deactivates blower 30 at which point pneumatic transport in the tubular member and the fluidic support of the beans in the annular space collapses whereby the beans drop down into chamber 22.

Flap valves 23 and 38 are actuated to discharge the roasted beans and husk debris into respective hoppers 40, 41 and thereafter the entire batch process is repeated as required.

°Oo It readily will be apparent to a person skilled in the art that an 6% o apparatus of the type described above may be easily sealed up for large scale commercial processing of green coffee beans with operational parameters set for prolonged periods to deal with large volumes of the same type of coffee beans. Such a commercial scale apparatus may accommodate batches of 1000kg or even higher.

It equally will be apparent that the apparatus may be adapted 20 for small "one-off" batches of say 0.5 to 5.0 kg for single customer orders in a coffee shop or the like. Predetermined roasting parameters for a variety of coffee types or blends may be stored in memory to facilitate instant programming of control circuitry.

18 Similarly, data relating to specific customer blend/roast preferences may also be stored to provide precise, reproducible results for even the most discerning afficionados of coffee.

In other embodiments of the invention, temperature monitoring devices may be provided in the upper region of housing 2 to monitor changes arising from differing moisture contents of beans.

A temperature monitoring device may be coupled with valves 31 and/or 34 to change or modify roasting air temperatures and, if required, a spent gas analyser may be employed to monitor gaseous by-products of the roasting process for even greater process control.

Apart from the advantage of ease of scalability from small capacity to large commercial roasters, the present invention also S°offers other significant advantage over the prior art.

In operation the apparatus does not develop "hot spots" which 15 could be contacted by beans nor does it allow for "hot spots" to "'°:°develop within the bed of beans in the annular space or for that matter in individual beans as they progress through the tubular member 3 due to the even temperature distribution throughout the apparatus Accordingly, the risk of bean spoilage or the possibility of 20 generating carcinogenic decomposition residues in the beans is substantially reduced.

Yet another advantage in the present invention is the ease of maintenance. The absence of "hot spot" surfaces does not permit 19 the build up of decomposition residues over time and in fact the motion of the beans gives a self cleaning effect within the housing.

The absence of pockets or corners or surfaces which could accumulate bean fragments or husks also simplifies cleaning particularly as decomposition residues arising from static material is avoided.

DATED this Twenty-Second day of January 2001 DZEMAL E. HADZISMAJLOVIC By His Patent Attorneys FISHER ADAMS KELLY *e *o

Claims (17)

1. An apparatus for roasting particulate material, said apparatus comprising:- an upright cylindrical housing; an inner tubular member mounted coaxially within said cylindrical housing to form an annular space between an inner wall of said housing and an outer wall of said tubular member, said tubular member having an inlet at one end adjacent a lower end of said housing and an outlet at an opposite end intermediate opposite ends of said housing; a gas permeable perforated floor extending from an inner surface of said housing about and spaced from the inlet of said tubular member, said perforated floor including an aperture aligned with the inlet of the tubular member; a first gas inlet in fluid communication with said annular space via said perforated floor; a second gas inlet in fluid communication with the inlet of said tubular member via said aperture in said perforated floor; and a gas outlet port located in an upper region of said housing. 20 2. The apparatus of claim 1 wherein said housing is formed from a heat resistant transparent glass material.

3. The apparatus of claim 1 or claim 2 wherein said perforated floor comprises a free area of greater than 21

4. The apparatus of claim 1 or claim 2 wherein said perforated floor comprises a free area of greater than The apparatus of any one of claims 1 to 4 wherein said perforated floor comprises apertures having a dimension of 2mm or less.

6. The apparatus of any one of claims 1 to 5 wherein a deflector is spaced above the outlet of the tubular member.

7. The apparatus of any one of claims 1 to 6 wherein at least one baffle is provided in the upper portion of the housing.

8. The apparatus of any one of claims 1 to 7 wherein a separating means is in fluid communication with said gas outlet port and is provided to extract entrained particulate material from gases issuing from said gas outlet port. S9. The apparatus of any one of claim 1 to 8 wherein said housing includes an access port in an upper region thereof for introduction of particulate material. The apparatus of claim 9 wherein said access port is associated with a hopper for particulate material.

11. The apparatus of any one of claims 1 to 10 wherein said housing includes a discharge port adjacent a lower end thereof for discharge 20 of treated particulate material.

12. The apparatus of any one of claims 1 to 11 wherein said first gas inlet is adapted in use to meter a source of heated pressurized gas into said housing at a predetermined velocity and/or volumetric flow rate.

13. The apparatus of any one of claims 1 to 12 wherein said first gas inlet includes a gas metering valve.

14. The apparatus of any one of claims 1 to 13 wherein said second gas inlet is adapted in use to meter a source of heated pressurized gas into said tubular member at a predetermined velocity and/or volumetric flow rate. The apparatus of any one of claims 1 to 14 wherein the second gas inlet includes a gas metering valve.

16. The apparatus of any one of claims 1 to 15 wherein the apparatus includes temperature measurement means to measure the temperature of particulate material in the annular space between the *o°°o inner wall of the housing and the tubular member. ~17. The apparatus of claim 16 wherein the temperature measurement means comprises a thermoresponsive probe extending into the S* annular space via an aperture in said housing.

18. A method for heat treatment of particulate material said method comprising the steps of:- pneumatically conveying, by a first meterable source of heated 20 pressurized gas, particulate material upwardly through a tubular member located concentrically within a cylindrical housing; collecting said particulate material in an annular space between said tubular member and an inner wall of said housing; A 23 directing, via a perforated floor located adjacent a lower region of said housing, a second meterable source of heated pressurized gas into said annular space to heat a bed of particulate material accumulated therein as said bed moves downwardly under the influence of gravity to provide a supply of particulate material to an inlet of said tubular member for pneumatic conveyance therewithin by said first meterable source of heated pressurized gas.

19. The method of claim 18 wherein said second meterable source of heated pressurized gas is introduced into said annular space at a velocity and/or volumetric flow rate sufficient to maximise gas flow through the bed of particulate material without fluidizing the bed of particulate material.

20. The method of claim 18 or 19 wherein the velocity of the second source of gas is metered to a velocity less than the minimum o.- e fluidization velocity of the particulate material.

21. The method of any one of claims 18 to 20 wherein the method is applied to roasting or dehydration of particulate organic materials S"such as foodstuffs of animal, vegetable or synthetic origin.

22. The method of any one of claims 18 to 21 wherein the method is 20 applicable to the roasting of coffee beans.

23. The method of claim 23 wherein the method includes the further step of de-husking coffee beans by impact against a deflection device located above the outlet of the tubular member.