WO2023023729A1

WO2023023729A1 - System and method/process for drying products

Info

Publication number: WO2023023729A1
Application number: PCT/AU2022/050956
Authority: WO
Inventors: MD Imran Hossen KHAN; David Daniel Edward ATKINS; Azharul Karim
Original assignee: Agridry Dryers Pty Ltd
Priority date: 2021-08-24
Filing date: 2022-08-23
Publication date: 2023-03-02
Also published as: AU2021221544A1

Abstract

A system for drying a product, the system including: a drying chamber configured to house the product; one or more microwave (MW) sources configured to intermittently apply microwave energy to the product; at least one convection heat source configured to apply convective heat to the product; and an electronic controller configured to control the MW sources to intermittently apply the microwave energy, and to control the convection heat sources to apply the convective heat. The system may include a conveyor system for moving the product through the drying chamber at a selected (belt) speed, and the electronic controller may be configured to control the conveyor system. The conveyor system may have a drive unit that powers movement of a belt at the selected speed.

Description

SYSTEM AND METHOD/PROCESS FOR DRYING PRODUCTS

RELATED APPLICATION

[0001] The present application is related to Australian Patent Application No. 2021221544, the originally filed specification of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates to systems and methods or processes for drying, including drying bulk products. The bulk products may include nutraceuticals, meat, seafood, vegetables or vegetable portions (including leafy materials, legumes, and herbs), fruit or fruit portions, cereal grains (including wheat, rice, and coarse grains, e.g., barley, rye, maize, millet, oats, sorghum or triticale), mine/quarry products (e.g., sand, fracking sand, aggregate, blue metal, etc.), biomass (e.g., woodchips) and/or organic waste (e.g., sewerage).

BACKGROUND

[0003] Drying is a technique for food preservation. Traditionally, this involves convective drying, which is a highly energy-intensive process that may require long periods of time. Exposing food products to uncontrolled, hot air-drying environments for long periods of time can cause deterioration of the products' quality.

[0004] Microwave (MW) drying is capable of reducing the drying time required due to its volumetric heating characteristics. MW drying allows for a higher diffusion rate and pressure gradient in the drying sample to transport moisture from inside the material to be dried. However, non-uniformities in the electromagnetic field distribution in a MW

environment result in an uneven temperature distribution, giving rise to "hot spots" and "cold spots" which may affect the drying kinetics and quality of the dried product. For example, in the process of MW drying, the temperature of hot spots becomes extremely high, resulting in crust formation and in some cases burning or otherwise damaging the material. Non uniform temperature also causes variable local drying kinetics, resulting in uneven moisture distribution inside the material. This overheating and uneven drying can also affect the nutritional, sensory and/or physical quality of the dried product.

[0005] Furthermore, continuous use of MW energy may unnecessarily increase the energy consumption of the drying process.

[0006] Therefore, it is desired to address or ameliorate one or more disadvantages or limitations associated with the prior art, or to at least provide a useful alternative.

SUMMARY

[0007] Described herein is a system (100) for drying a product, the system (100) including: a drying chamber (102) configured to house the product; one or more microwave (MW) sources (106) configured to intermittently apply microwave energy to the product; at least one convection heat source (108) configured to apply convective heat to the product; and an electronic controller (110) configured to control the MW sources (106) to intermittently apply the microwave energy, and to control the convection heat sources (108) to apply the convective heat.

[0008] The system (100) may include a conveyor system (104) for moving the product through the drying chamber (102) at a selected (belt) speed, and the electronic controller

(110) may be configured to control the conveyor system (104). The conveyor system (104) may have a drive unit (604) that powers movement of a belt at the selected speed.

[0009] The drying chamber (102) may have a folded configuration.

[0010] Each of the MW sources (106) may have a power output of up to 1.5 kW, up to 2.5 kW, or up to 100 kW of radio-frequency (RF) energy. The MW sources (106) may include solid state MW generators or magnetrons. The MW sources (106) may be mounted on the chamber (102) in a configuration that provides substantial uniformity of an electromagnetic field inside at least a portion of the chamber (102), including pairs of the MW sources (106) on opposite sides of the drying chamber (102).

[0011] Each of the convection heat sources (108) may have a power input of up to 5 kW or up to 10 kW. Each convection heat source (108) may have an associated fan that moves hot air into the chamber. The electronic controller (110) may be configured to turn the convection heat sources (108) on and off and/or select their power output values/levels.

[0012] The drying chamber (102) may be partitioned into a plurality of sections by at least one partition. Each section may receive heated air from a respective one of the convection heat sources (108).

[0013] The conveyer system (104) may include a belt (602) including or made from a material that is MW safe such that it does not absorb or reflect MW radiation, and/or can withstand temperatures over 100 °C or over 140 °C.

[0014] The system (100) may include a user interface in communication with the controller ( 110), the user interface configured to allow a user to provide user input including one or more of the following: an initial moisture content, a final moisture content, a belt speed, and a drying temperature.

[0015] Further described herein is a method/process for drying a product, the method/process including:

housing the product in a drying chamber (102); an electronic controller (110): controlling one or more microwave (MW) sources (106) to intermittently apply MW energy to the product; and controlling at least one convection heat source (108) to apply convective heat to the product (either continuously or intermittently).

[0016] The method/process may include controlling a variable belt speed of a conveyer system (104) configured to move the product through the drying chamber (102).

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Some embodiments of the present invention are hereinafter described, by way of non-limiting example only, with reference to the accompanying drawings, in which: a. FIG. 1 is a schematic diagram of a system for drying a product; b. FIG. 2 is a perspective view of a first embodiment of the system; c. FIGs. 3A and 3B are top views of the first embodiment, where FIG. 3B shows a conveyer system; d. FIG. 4 is a side view of the first embodiment; e. FIG. 5 is a cross-sectional end-on view of the first embodiment; f. FIGs. 6A and 6B are perspective views of a drive unit and a return unit of a conveyer system of the system; g. FIGs. 7A and 7B are perspective views of a second embodiment of the system; h. FIG. 8 is a top view of the second embodiment;

i. FIG. 9 is a side view of the second embodiment; j. FIGs. 10A, 10B and 10C are three-dimensional (3D) graphs of an airflow distribution inside a drying chamber of the second embodiment; k. FIG. 11 is a 3D graph of a temperature distribution inside the drying chamber of the second embodiment; l. FIG. 12 is a 3D graph of an electromagnetic field distribution inside the drying chamber of the second embodiment; and m. FIGs. 13 to 17 are circuit diagrams of electrical circuitry of the system.

DETAILED DESCRIPTION

Overview

Non-uniformity caused by MW drying can be addressed by applying MW energy intermittently in combination with continuous and/or intermittent convective heat. This technique may be described as "intermittent MW convection drying" (IMCD). IMCD allows moisture inside a material to redistribute and dry the material with uniform moisture transport. This mechanism helps to improve the drying kinetics and thereby reduce any deleterious impacts to the material's quality.

System

[0018] Disclosed herein is a system 100 for drying a product.

[0019] The system 100 includes: a. a drying chamber 102 configured to house the product; b. one or more microwave (MW) sources 106 (e.g., eight) configured to intermittently apply microwave energy to the product;

c. at least one convection heat source 108 configured to apply convective heat to the product; d. a conveyor system (104) (with a variable speed) for moving the product through the drying chamber at a variable belt speed; and e. an electronic controller 110 configured to control the MW sources, the convection heat sources (on-off and power levels — to turn the convection heat sources on and off and/or select their power output values/levels) and the conveyer system.

[0020] A shown in FIG. 1, a system 100 for drying a product includes a drying chamber 102, a conveyer system 104, a plurality of MW sources 106, a plurality of convection heat sources 108 and an electronic controller 110.

[0021] The product is dried within the drying chamber 102. The chamber 102 is substantially enclosed. The chamber includes an entrance for the product to be dried to enter the chamber and an exit for the product to leave the chamber once dried. The chamber 102 can be include or be made from metal, such as stainless steel, mild steel, or galvanised iron; or another microwave resistive material.

[0022] The chamber 102 has a length, a width and a height. The length is the distance between the entrance of the chamber 102 and the exit of the chamber 102 between which the product is moved by the conveyer system 104. The length, width and height of the chamber 102 are selected based on a desired throughput of product to be dried (volume as a function of time). The chamber 102 of the system 100 as shown in FIGs. 2 to 5 can have a length of approximately 7.8 m, a width of approximately 0.45 m, and a height of approximately 0.25 m in order to dry 15 kg of product per hour. In the embodiment shown, the chamber 102 is raised off the ground by a frame of legs 202. In other implementations, depending on the volume and type of bulk product, the chamber 102 and the conveyor system 104 therein (including one or more of the belts arranged in series

and/or in parallel) can vary in length from around 5 meters to around 50 meters, e.g., being substantially 50 m in length.

[0023] The conveyer system 104 is configured to move the product through the drying chamber at a required speed, referred to herein as a "belt speed". The belt speed can be varied, by a drive unit 604 of the conveyer system 104, within a range of belt speeds, meaning that the belt speed is a variable belt speed. The conveyor system 104 may in an example run the belt with a speed of between 0.5 meters/minute and 5 m/min, e.g., around 1.2 or 1.3 m/min to dry a product comprising fruit or vegetable pieces. As shown in FIG. 6A, the conveyer system 104 includes a belt 602 upon which the product rests as it is moved through the drying chamber 102. The belt 602 extends along a base of the chamber 102 such that it can move the product along the length of the chamber 102 at the variable belt speed. The belt 602 extends from the entrance to the exit of the chamber 102. The belt 602 may extend to the outside of the entrance and/or the exit to allow the product to be loaded onto the belt 602 and removed from the belt 602 outside the chamber 102. The belt 602 includes or is made from a material that is MW safe such that it does not absorb or reflect MW radiation. The material of the belt 602 can also withstand temperatures over 100 °C or over 140 °C, such as between 130 °C and 160 °C, or between 140 °C and 160 °C. For example, the material of the belt 602 may be a commercially available low friction acetal resin material.

[0024] The conveyer system 104 includes the drive unit 604 that powers movement of the belt at the selected variable belt speed. The drive unit 604 may be located near the entrance of the chamber 102. The drive unit may be contained within a MW proof drive cover 606. As shown in FIG. 6B, the conveyer system includes a return unit 608 that returns the belt 602 to the drive unit 604. The return unit 608 may be located near the exit of the chamber 102. The return unit 608 may be contained in a MW proof return cover 610.

[0025] The MW sources 106 are configured to apply MW energy to the product housed in the chamber 102. Each of the MW sources 106 can be a solid-state MW generator.

Each MW generator can have a corresponding waveguide 402 to transmit produced microwaves into the chamber 102. Alternatively, each of the MW sources 106 can be a magnetron. The applied MW energy can have a frequency of approximately 2.45 GHz.

[0026] In particular, the MW sources 106 are configured to intermittently apply MW energy, i.e., in a non-continuous manner, to the product housed in the chamber 102. As discussed hereinbefore, application of intermittent MW power, rather than continuous MW power, to the product drying within the chamber 102 may reduce deterioration of the quality of the dried product (e.g., due to denaturing of enzymes contained in the product) and reduce the energy consumption required to dry the product. The intermittent application of MW energy is based on an intermittency ration between an active time of the MW sources 106 and the total time (an inactive time + active time) of the MW sources 106. The intermittency ratio may be between 1:3 and 1:5. An intermittency ratio of 1:3 may be achieved, for example, by repeatedly activating the MW sources 106 for 30 seconds and deactivating the sources 106 for 60 seconds while the product moves through the chamber 102. The intermittency ratio may be determined based at least in part on the kind of product to be dried. For example, where the product is apples, the intermittency ratio may be approximately 1:4. Where the product is papaya, the intermittency ratio may be approximately 1:3.

[0027] Each MW source 106 may have a variable output power such that the output power can be adjusted between a minimum output power (i.e., 0 kW) and a maximum output power, e.g., based on a particular kind of product to be dried. The maximum output power of each MW source 106 may be approximately 1.5 kW. In alternative implementations, the maximum output power of each MW source 106 may be 2.5 kW or 100 kW of radio-frequency (RF) energy.

[0028] The number of MW sources 106 may be based (at least in part) on the size of the drying chamber 102, such that the number of MW sources 106 increases proportionally with the size of the drying chamber 102.

[0029] The number and spacing of the MW sources 106 can be determined based (at least in part) on attenuation of the microwaves generated by the MW sources 106 and dispersed inside the chamber 102. The spacing of the MW sources 106 may be determined such that there is less than 10% power attenuation between each MW source 106, and/or such that the temperature of the air in the chamber 102 is constant along the chamber 102 to within +/- 1% "variability", or +/- 2%, or +/- 5%, or +/- 10%. A distance D between respective MW sources 106 can be determined based on the following empirical relationship between D and free space loss (as a decibel dB) dB = 201og₁₀(£>) + 201og₁₀( ) - 147.55, where D is the distance travelled by MW radiation from the MW source and /is the MW frequency (which may be 2.45 GHz, as described hereinbefore). Thus, the MW loss can be p • determined using the power loss over the distance D, i.e., dB = 101og(— — ), where P[_n is "out the "input power" at the MW source 106 and P_out is the "output power" at the distance D.

[0030] As shown in FIGs. 2 to 4, the system 100 can include six MW sources 106, although other numbers of MW sources 106 may be suitable depending on the size/configuration of the drying chamber 102. The total power level required from the MW sources 106 can be determined based on the geometry of the chamber 102 and the maximum amount of product to be dried in the chamber 102. The number and position of the of the MW sources 106 can be determined based on uniformity of the electromagnetic field inside the chamber 102 by modelling the electromagnetic field inside the chamber 102, i.e., to substantially maximize the uniformity of the electromagnetic field inside the chamber 102, e.g., such that the electromagnetic field, at least where is substantially overlaps a volume where the product does or is designed to he in the drying chamber 102, is constant along the length of the chamber 102 to within +/- 1% "variability", or +/- 2%, or +/- 5%, or +/- 10%. This may be achieved by computationally modelling the electromagnetic field inside the chamber for different configurations of the MW sources 106 using Maxwell’s equations, and iteratively adjusting the placements of the MW

sources 106 in the model until the selected variability is achieved in the computational model. The MW sources 106 mounted on the chamber 102 in a configuration that provides substantial uniformity of the electromagnetic field inside at least a portion of the chamber, e.g., within +/- 1%, or +/- 2%, or +/- 5%, or +/- 10% "variability". The configuration can include pairs of the MW sources 106 on opposite sides of the drying chamber 102, e.g., as shown in FIGs. 2 to 4.

[0031] Each of the MW source 106 can be mounted on one of a first side surfaces, a second side surface, atop surface or a bottom surface of the chamber 102. The first and second side surfaces are opposite outwardly facing sides extending the length of the chamber 102. Similarly, the top and bottom surfaces are opposite outwardly facing sides extending the length of the chamber 102. In the embodiment shown in FIGs. 2 to 5, two MW sources 106 are mounted on the first side surface and four MW sources 106 are mounted on the second side surface. The four MW sources 106 on the second side surface are evenly spaced along the second side surface. The two MW sources 106 on the first side surface are each located between mutually exclusive pairs of the MW sources 106 on the second side surface.

[0032] The at least one convection heat source 108 is configured to apply convective heat to the product housed in the chamber 102. As shown, the system 100 can include two convection heat sources 108, which are be configured to continuously and/or intermittently apply convection heat to the inside of the chamber 102. Heated air is transmitted from each of the convection heat sources 108 into the chamber 102 by a respective fan. The heated air moves from the heat sources 108 into the chamber 102 via input ducts 204. One or more output ducts 206 remove air from the chamber 102 that is substantially saturated with moisture and thus unable to further dry the product.

[0033] The power level of each convection heat source 108, i.e., controlling the temperature of the heated air transmitted from each convection heat source 108, can be variably controlled such that each convection heat source 108 is individually variable. The power level of each convection heat source 108 may be controlled based on a temperature

within the chamber (referred to herein as a "chamber temperature") measured by one or more temperature sensing modules located inside the chamber 102. The controller 110 may receive the chamber temperature from the temperature sensing modules and, based on the received temperature, adjust the power level of one or more of the convection heat sources 108.

[0034] Although system 100 is shown to include two convection heat sources, other numbers of convection heat sources may be suitable depending on the configuration of the drying chamber 102.

[0035] The system 100 can include one or more fans (not shown) configured for operation with one or more of the convection heat sources to move heated air into the chamber 102. The fans can each be variable speed fans.

[0036] The chamber 102 can be partitioned into a plurality of sections by at least one partition to minimise air flow between the sections. In particular, as shown in FIG. 3B, the chamber 102 of system 100 can be split into two sections 102a, 102b by a single partition 302. Although the chamber is partitioned into two sections, the partition 302 is configured such that the product on the belt is able to be moved through the entire length of the chamber 102 by the conveyer system 104. In this sense, the partition 302 does not divide the chamber into discrete sections. Convective heat is introduced into a first end of each section 102a, 102b by respective input ducts 204 such that the heated air moves in the same direction as the belt. Air (and moisture) is removed from a second end of each section 102a, 102b by respective output ducts 206. The input ducts 204 may receive heated air from a single convection heater or from different (e.g., respective) convection heaters.

[0037] Each partition can be made of metal. Each partition can be made of the same material as the chamber 102.

[0038] Dividing the chamber 102 into sections 102a and 102b facilitates "multi-stage drying", which may increase the energy efficiency of the system 100. The multiple sections 102a, 102b allow air that is saturated with moisture (and thus unable to extract more moisture from the product) to be removed from the chamber 102 and replaced with fresh heated air. Multi-stage drying allows different patterns of intermittent MW energy can be applied in different sections of the chamber 102, e.g., based on the average expected moisture content of the product in each respective section. Multi-stage drying also allows the convection heat sources 108 to provide convective heat of differing temperatures to each section of the chamber 102. For example, the final section (adjacent to the exit of the chamber 102) may receive convective heat at a lower temperature compared to one or more other sections so that the final dried product is not at an undesirably high temperature when it exits the chamber 102.

[0039] A number of sections into which the chamber 102 is divided may be determined by computational modelling of air flow inside the chamber, such as by computational fluid dynamics (CFD).

[0040] The electronic controller 110 may be a programmable logic controller (PLC). The controller 110 is configured to automatically control the activation, deactivation and power level of each of the MW sources 106 and the convection heat sources 108 such that the controller 110 can cause the system to perform intermittent microwave convective drying on products housed within the chamber 102. The controller 110 also controls the conveyer system 104 and the fans associated with the convection heat sources 108.

[0041] As shown in FIGs. 7A to 9, the chamber 102 can have a folded configuration such as a "U" shape, i.e., consisting of three substantially rectangular sections sequentially joined at right angles to form a continuous chamber with a left section and a right section that are parallel, connected by a rear section. The folded configuration may reduce an overall footprint of the system 100 such that it is easier to store and/or transport. In the embodiment shown, the chamber 102 has a total length of 7.8 m. Each of a left and a right side of the chamber 102 has a length of approximately 2.72 m. The chamber has a width

of approximately 0.45 m (i.e., the width of each section). A back side of the chamber 102, which is associated with the rear section and joins the left and the right sides, has a width of approximately 1.45 m. The chamber 102 has a height (i.e., from a bottom surface to a top surface of the chamber 102) of approximately 0.25 m.

[0042] The U-shaped chamber 102 reduces the effective length of the system 600 to approximately half the length of an equivalent "unfolded" system (e.g., as shown in FIGs.

2 to 5), which may make it more suitable for construction and storage in certain spaces. As shown in FIGs. 10A to 10C, the U-shaped chamber 102 may achieve a substantially uniform air velocity and reduce the prevalence of "dead zones" associated with minimal air flow. Furthermore, as shown in FIGs. 11 and 12, respectively, the U-shaped chamber 102 may achieve a substantially uniform temperature distribution and electromagnetic field based on the placement of the MW sources 106 and convection heat sources 108 discussed hereinbelow.

[0043] The embodiment shown includes eight MW sources 106. The locations on the chamber where the MW sources are mounted 106 are selected to increase the uniformity of the microwave field distribution within the chamber 102. Six of the MW sources 106 are mounted on the first side surface of the chamber 102, while the other two MW sources 106 are located on the second side surface of the chamber 102. Each of the left section and the right section has two of the MW sources 106 mounted on the first side surface and one MW source 106 mounted on the second side surface.

[0044] In the embodiment shown, the chamber 102 is divided into two sections by partition 702 located at a midway point along the length of the rear section. The system 100 includes two convection heat sources 108 (shown as a single unit) each associated with a respective fan (not shown). The convection heat sources 108 provide heated air to each section of the chamber 102 via the input ducts 204. Air is removed from each section of the chamber 102 via a respective one of the output ducts 206.

[0045] The power requirements of the system 100 (i.e., the MW sources 106 and the convection heat sources 108) can be determined based on one or more of the following: a drying capacity (volume of product to be dried), an anticipated initial moisture content (of the product before drying), an anticipated final moisture content (of the product after drying), the belt speed of the belt 602, an ambient temperature, a relative humidity, and a drying temperature. For example, the power requirements of the system 100 as shown in FIGs. 7A to 9 can be determined based on a drying capacity of 15 kg of product with an initial moisture content of about 80% (common for many fruits and vegetables), a final moisture content of about 5%, an ambient temperature of approximately 15 °C, a relative humidity of approximately 70%, a drying temperature of between 40-60 °C with an air speed of between 0.5 m/second and 3 m/second - in which case the power requirements for the system 100 may be approximately 13 kW.

[0046] A power ratio between the proportion of the power requirements of the system to be derived from the MW sources 106, and the proportion to be derived from the convection heater 108, can be determined based on one or more of the following: dielectric properties of the product to be dried, one or more desired properties of the dried product, a desired speed of the drying process. An example of a desired property of the dried product is minimal denaturing of enzymes contained in the dried product (e.g., for dried fruits or vegetables to be used in nutraceutical products), in which case the proportion of power derived from the MW sources 106 may be reduced. Another example of a desired property of the dried product is maximal denaturing of enzymes contained in the dried product, in which case the proportion of power derived from the MW sources 106 may be increased. In different implementations, the power ratio may be between 1 : 9 and 9: 1. For many products, a ratio between 1: 1 and 7:3 may be most effective. In some implementations the power ratio may be most effective at 3:2 to balance between energy utilization, quality of the dried product and drying time. In certain implementations, it may be desirable for the power requirements to be solely derived from the convection heat source 108, e.g., if the product will be seriously damaged if exposed to MW radiation; accordingly, the controller

110 may be configured to turn off the MW sources 106 when selected for such bulk products.

[0047] In the example discussed above, where the power requirements for the system 100 are approximately 13 kW, if 60% of the power is to be derived from the MW sources 106 (i.e., for a 3:2 power ratio), then the power to be derived from the MW sources 106 can be met by eight MW sources 106, each with a capacity of at least 1 kW. To improve the safety of the system the MW sources 106 may have maximum power capabilities above 1 kW. For example, each of the MW sources 106 can have a variable power capacity between 0 and 1.5 kW. In alternatives, each of the MW sources 106 may have a variable power capacity between 0 and 2.5 kW, or 0 and 100 kW.

[0048] To allow the convective air temperature inside the chamber 102 to reach 60 °C, the two convection heat sources 108 may each require power of approximately 5 kW. In alternatives, each convection heat source 108 may require up to 5 kW, or up to 10 kW.

[0049] The maximum power requirements of the system 100 may be determined based at least in part on a maximum capacity of the system 100 including a maximum drying capacity and a maximum initial moisture content (and associated dielectric properties) of any product to be dried using the system 100.

[0050] As shown in FIGs. 13 and 14, the controller 110 may be a PLC that is connected to the MW sources 106, convection heat sources 108, the fans associated with the convection heat sources 108 and the conveyer system 104 via electrical circuitry. The system 100 can include a user interface such as a touch screen in communication with the controller 110. The user interface is configured to allow a user to provide input including one or more of the following, which can be used by the controller 110 to automatically control the MW source power, convection heater power and/or belt speed: the anticipated initial moisture content, the anticipated final moisture content, the belt speed, the ambient temperature, the drying temperature.

[0051] As shown in FIGs. 15 and 16, the system 100 can include the one or more temperature sensing modules for monitoring and measuring the chamber temperature. Each temperature sensing module can include a thermocouple connected to a temperature controller.

[0052] As shown in FIG. 17, the conveyer system includes a belt motor that is controlled by a variable frequency drive (VFD) module that includes an inverter that drives the motor (e.g., a three phase belt motor), and an external potentiometer.

[0053] As shown in FIG. 14, the system 100 may include one or more relative humidity and temperature (RHT) sensors attached in mutually different positions of the drying chamber 102, including at the inlet and the outlet of the drying chamber 102, to monitor the drying air quality by continuously observing the change of relative humidity and temperature of drying air over the drying processes. The RHT sensors are configured to measure the relative humidity (RH) of the drying air. If the RHT sensors determine that the air has high RH (which means a low drying capacity of the air), the electronic controller can be configured to increase the incoming air temperature and/or the air velocity such that the RH is reduced into a predefined desirable range or level.

[0054] As shown in FIG. 13, the system 100 may include a plurality of micro fans, which are small fans that are configured and attached to cool the microwave magnetrons.

[0055] The system 100 described herein may include a commercially available dryer that relies on convection heat only. For example, a commercially available grain roaster dryer such as a conveyor Max includes a drying chamber 102, at least one convection heat source 108 and a conveyer system 104. The commercially available dryer may be adapted by fitting multiple MW sources 106 to the drying chamber 102 and configuring a controller 110 to control the MW sources 106, the convection heat source 108 and the conveyer system 104, as described hereinbefore.

Method/Process

[0056] Disclosed herein is a method/process for drying a product.

The method/process includes: a. housing the product in the drying chamber 102; and b. the electronic controller 110: i. controlling the one or more MW sources 106 to intermittently apply microwave energy to the product; ii. controlling the at least one convection heat source 108 to apply convective heat to the product (either continuously or intermittently); and iii. controlling the variable belt speed of the conveyer system 104 configured to move the product through the drying chamber.

[0057] The product is housed in the chamber 102 by resting on the belt 602 of the conveyer system 104, as the belt moves the product through the chamber 102, e.g., from the entrance to the exit.

[0058] The convective heat may be applied to the product continuously or intermittently.

[0059] In accordance with the method/process, the intermittent microwave energy and the convective heat may be applied to the product housed in the drying chamber 102 simultaneously. Simultaneous application of intermittent MW energy in combination with convective drying allows moisture inside the product to redistribute so that the product can be dried with uniform moisture transport. This may mitigate any damage done to the product that could reduce its quality.

[0060] The controller 110 may control the convection heat source 108 to maintain a drying temperature inside the chamber 102. The drying temperature may be maintained by the controller 110 receiving a chamber temperature from one or more temperature sensing modules located inside the chamber 102, and adjusting the power level of the convection heat source 108 based on the chamber temperature.

Implementations

[0061] The systems and methods/processes described herein may be implemented to dry a variety of different products. For edible products, the conveyor system 104 includes a food-safe surface for bearing the bulk product, e.g., nutraceuticals, meat, seafood, vegetables or vegetable portions (including leafy materials, legumes, and herbs), fruit or fruit portions, cereal gains (including wheat, rice, and coarse grains, e.g., barley, rye, maize, millet, oats, sorghum ortriticale). Examples of the system 100 may be configured for drying: a. wood chips; b. fruit; or c. vegetables.

[0062] The system 100 may be coupled/connected to an input/front end or to an output/back end of a commercially available convection drying system, e.g., a roaster. Thus the method/process can include convection drying the product before and/or after drying the product in the system 100. The coupling/connection to the convection drying system can include aligning a conveyor of the convection drying system with the conveyor system 104, and/or connecting/sealing a drying chamber of the convection drying system with the drying chamber 102.

[0063] One or more of following benefits may be realised in accordance with implementations of the systems and methods/processes described herein:

a. damage to the quality of the dried product may be minimised; b. the drying process may be energy efficient, as the microwave energy is applied in pulses rather than continuously and because the IMCD process may require a shorter amount of time; c. the drying time may be reduced by more than 70% by comparison to traditional convective drying; and d. the method/process and system are scalable and may be easily scaled up and down based on the desired implementation.

[0064] An agricultural example of the system 100 may be configured to have a drying capacity of substantially 500 kg/hr, including drying the product from substantially 90% moisture level to substantially 5% moisture level. The drying power is provided by MW sources combined with the convection heat source: the MW sources may provide substantially 50% to 70%, e.g., 60% of the drying power, and the convection heat source may provide the rest of the drying power (e.g., 40%). The agricultural example may generate substantially 200 kW from its MW sources and substantially 135 kW from its convection source. The agricultural example may include: a. substantially 210 magnetrons (of power level substantially 1 kW each); b. substantially 210 microwave power supplies forthe 210 magnetrons; c. substantially 210 rectangular coupled waveguides for the 210 magnetrons; d. a central cooling tower; e. a control board; f. a PLC system;

g. a convection heat source including a heater (e.g., with a diesel or gas burner) and a blower (with a fan); h. one set of a conveyor belt and its driving accessories; i. a product entrance section for one end of the conveyor belt set, and a product exit section for the other end of the conveyor belt set; and j . MW leakage protective materials.

[0065] In another example, the system 100 may include substantially 60 magnetrons.

Interpretation

[0066] The FIGs. included herewith show aspects of non-limiting representative embodiments in accordance with the present disclosure, and particular structural elements shown in the FIGs. may not be shown to scale or precisely to scale relative to each other. The depiction of a given element or consideration or use of a particular element number in a particular FIG. or a reference thereto in corresponding descriptive material can encompass the same, an equivalent, an analogous, categorically analogous, or similar element or element number identified in another FIG. or descriptive material associated therewith. The presence of "/" in a FIG. or text herein is understood to mean "and/or" unless otherwise indicated, i.e., "A/B" is understood to mean "A" or "B" or "A and B". The recitation of a particular numerical value or value range herein is understood to include or be a recitation of an approximate numerical value or value range, for instance, within +/- 20%, +/- 15%, +/- 10%, +/- 5%, +/- 2.5%, +/- 2%, +/- 1%, +/- 0.5%, or +/- 0%. The term "essentially all" or "substantially" can indicate a percentage greater than or equal to 50%, 60%, 70%, 80%, or 90%, for instance, 92.5%, 95%, 97.5%, 99%, or 100%.

[0067] Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention.

[0068] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0069] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

- 22 - CLAIMS:

1. A system for drying a product, the system including: a drying chamber configured to house the product; one or more microwave (MW) sources configured to intermittently apply microwave energy to the product; at least one convection heat source configured to apply convective heat to the product; an electronic controller configured to control the MW sources to intermittently apply the microwave energy, and to control the convection heat sources to apply the convective heat; and a conveyor system for moving the product through the drying chamber at a selected speed, wherein the electronic controller is configured to control the conveyor system.

2. The system of claim 1, wherein the conveyor system has a drive unit that powers movement of a belt at the selected speed.

3. The system of claim 1 or 2, wherein the drying chamber has a folded configuration.

4. The system of any one of claims 1 to 3, wherein each of the MW sources has a power output of up to 1.5 kW, up to 2.5 kW, or up to 300 kW of radio-frequency (RF) energy.

5. The system of any one of claims 1 to 4, wherein the MW sources include solid state MW generators or magnetrons.

6. The system of any one of claims 1 to 5, wherein the MW sources are mounted on the chamber in a configuration that provides substantial uniformity of an electromagnetic field inside at least a portion of the chamber, including pairs of the MW sources on opposite sides of the drying chamber.

7. The system of any one of claims 1 to 6, wherein each of convection heat sources may have a power output of up to 5 kW or up to 10 kW of thermal power.

8. The system of any one of claims 1 to 7, wherein each convection heat source has an associated fan that moves hot air into the chamber.

9. The system of any one of claims 1 to 8, wherein the electronic controller is configured to turn the convection heat sources on and off and/or select their power output values/levels.

10. The system of any one of claims 1 to 9, wherein the drying chamber is partitioned into a plurality of sections by at least one partition.

11. The system of claim 10, wherein each section receives heated air from a respective one of the convection heat sources.

12. The system of any one of claims 1 to 11, wherein the conveyer system include a belt including or made from a material that is MW safe such that it does not absorb or reflect MW radiation, and/or can withstand temperatures over 100 °C or over 140 °C.

13. The system of any one of claims 1 to 12, including a user interface in communication with the controller, the user interface configured to allow a user to provide user input including one or more of the following: an initial moisture content, a final moisture content, a belt speed, and a drying temperature.

14. A process for drying a product, the process including: housing the product in a drying chamber; and an electronic controller: controlling one or more microwave (MW) sources to intermittently apply MW energy to the product; controlling at least one convection heat source to apply convective heat to the product; and

controlling a variable belt speed of a conveyer system configured to move the product through the drying chamber.