Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B3/00—Drying solid materials or objects by processes involving the application of heat
  • F26B3/32—Drying solid materials or objects by processes involving the application of heat by development of heat within the materials or objects to be dried, e.g. by fermentation or other microbiological action
  • F26B3/34—Drying solid materials or objects by processes involving the application of heat by development of heat within the materials or objects to be dried, e.g. by fermentation or other microbiological action by using electrical effects
  • F26B3/343—Drying solid materials or objects by processes involving the application of heat by development of heat within the materials or objects to be dried, e.g. by fermentation or other microbiological action by using electrical effects in combination with convection
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
  • F26B21/06—Controlling, e.g. regulating, parameters of gas supply
  • F26B21/08—Humidity
  • F26B21/086—Humidity by condensing the moisture in the drying medium, which may be recycled, e.g. using a heat pump cycle

Definitions

• This invention relates to a drying process which has particular applicability to, but is not restricted to, foodstuffs.
• Drying processes include evaporating liquids at rates varying from a few grams to many tonnes per hour from a single dryer. Drying temperatures for pharmaceutical, biological materials and foodstuffs may vary from 10° to 70° C depending on the process used. Dryers range in size from small cabinets to large towers.
• the materials dried may be in the form of thin solutions, suspensions, slurries, pastes, granular materials, bulk objects, fibres or sheets. Drying may be accomplished by convective heat transfer, by conduction from heated surfaces, by radiation, and by dielectric heating.
• This invention provides a drying process which has particular applicability to, but is not restricted to, foodstuffs which comprises the steps of:
• step (3) passing the warm dry air produced by step (2) to a heat reclaim coil wherein the temperature of the air is increased and the relative humidity decreased; (4) passing the hot dry air produced by step (3) over or through a product for a sufficient time to achieve the desired drying effect;
• step (4) venting the warm moist air produced by step (4) to the atmosphere.
• Figure 1 is a cross-sectional view of an apparatus used to carry the invention into effect
• Figure 2 is a diagrammatic view of a secondary heat exchanger and associated apparatus.
• Figure 3 is a frontal diagrammatic view of a rotating wheel heat exchanger forming part of the apparatus according to the invention.
• the ambient air used in step (1) may be warmed by heat-exchange in a secondary heat-exchanger with the warm moist air passed to step (5) .
• the result is warm ambient air with a high relative humidity.
• the primary heat exchanger is conveniently a rotary heat exchanger which is located adjacent a dehumidifier whereby warmed ambient air enters through one part of the primary heat exchanger rotary mechanism, in which it is cooled, passes through the dehumidifier, in which it loses moisture, and then to another part of the primary heat exchanger rotary mechanism, in which it gains heat.
• dehumidifiers were developed to provide continuous dry air.
• step (4) the product may be dried in bulk or in some broken-up or comminuted form.
• the product may be sampled from time to time to check whether sufficient drying has been achieved.
• a proportion of the warm moist air from step (4) may be passed to the primary heat exchanger to mix with incoming ambient air.
• the process according to the invention may be used to evaporate liquids at rates varying from 2 to 5 grams to 4 tonnes per hour, for example. Greater amounts of liquid can be removed depending on the load and the size of the apparatus.
• the drying temperature may vary from 10° to 70°C depending on the application.
• a typical power input in a process and apparatus according to the invention is from 10 to 120 kWh.
• incoming air is passed through the bottom of the rotary heat exchanger where its temperature is lowered sufficiently to enable it to be passed to an evaporator coil.
• This evaporator coil further lowers the temperature of the air to allow water to be removed.
• the resulting cold air is then returned to the top of the rotary heat exchanger where it is warmed to produce warm dry air.
• Heat may be reclaimed from the evaporator coil and passed to a reclaim coil.
• the warm dry air from the top of the rotary heat exchanger may be passed to the reclaim coil where it is heated to produce hot dry air which may then be used to dry the product.
• the product may be treated with electromagnetic waves which are adapted to bring moisture to the surface of the product.
• Suitable electromagnetic waves are those of microwave or radiofrequency. Infra-red waves may be used but are less preferred.
• the invention is particularly effective in controlling bacterial growth. It is thought that one reason for the effectiveness of this control is the rapid change of temperature in the airflow which interferes with the metabolism of bacteria.
• ambient air at, for example 20°C may be hated to, for example, 40°C in an external heat exchanger. It may then be cooled to, for example, 15°C in the bottom of a rotary heat exchanger and to, for example, 10°C in the evaporator coil. This cold air may then be heated to, for example, 50°C in the top of the rotary heat exchanger. The heated air may then be further heated to, for example, 70°C in a reclaim coil before being passed to the product to be dried.
• an external heat- exchanger This heat-exchanger cools the air from, for example, 50°C to, for example, 25°C before it is vented to the atmosphere.
• numeral 11 indicates an air-intake duct which leads downwardly to a rotary heat exchanger 12 located at one end of the structure 10.
• Rotary heat exchanger 12 is divided into a bottom portion 12A and a top portion 12B. Warmed ambient air passes down through inlet duct 11 and is mixed with a proportion of warm moisture-laden air coming off the product Heat is extracted from the mixture in bottom portion 12A of the rotary heat exchanger and passed to upper portion 12B.
• Cooled air passes to evaporating coil 13 where water is removed.
• Evaporating coil 13 is located near the bottom of an ancillary chamber 14.
• the further cooled air is reflected from the rear of ancillary chamber 14, passes above evaporating coil 13 and then through upper portion 12B of rotary heat exchanger 12.
• the heated air is then passed upwards, directed by baffle 15, to a horizontal, upper duct 15 A located at the top of structure 10.
• a first fan 16 is located in horizontal upper duct 15 A. Heated air is forced by first fan 16 through reclaim coil 17 and second fan 18. The now hot air is passed down through a vertical duct 18A located at an end of structure 10 distal from heat exchanger 12.
• the hot air is passed from vertical duct 18A into an internal housing 19 in which is located an upper conveyor 20, conveying from right to left as viewed in the drawing. Part of the air-stream is forced into housing 19 by means of a bottom-mounted, third fan 18B.
• Hot moisture-laden air is then passed to a downwardly sloping duct 22 and an upper intemal duct 23.
• Sloping duct 22 conducts part of the warm moisture-laden air to lower portion 12A of the rotary heat exchanger 12.
• Intemal duct 23 leads the remaining part of the warm moisture-laden air, through first filter 23A, to an exit duct 24.
• heating equipment such as microwave apparatus may be located on the structure of internal duct 23.
• Numeral 25 refers to a heat control bypass linked to reclaim coil 17 and located outside external structure 10. The purpose of this integer is to dump excess heat from reclaim coil 17 to the atmosphere.
• an external heat exchanger 30 is supplied with warm moisture-laden air from exit duct 24 passing through second filter 31. The cooled air is returned to atmosphere through first exhaust fan 32. Incoming ambient air passes to heat exchanger
• numerals 12, 12A and 12B refer to the same integers discussed above.
• Numeral 40 refers to a barrier between lower portion 12A and upper portion 12B of the rotary heat exchanger 12.
• Numerals 41 and 42 indicate the arrows showing the direction of flow of warm ambient air to lower portion 12A.
• Numeral 43 indicates the direction of flow of hot air from upper portion 12B.
• numeral 44 indicates the direction of rotation of the wheel constituting the essential operative part of the rotary heat exchanger 12.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Microbiology (AREA)
• Health & Medical Sciences (AREA)
• Biomedical Technology (AREA)
• Biotechnology (AREA)
• Molecular Biology (AREA)
• Drying Of Solid Materials (AREA)

Applications Claiming Priority (3)

Publications (2)

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Citations (3)

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• 1994
  • 1994-05-31 AU AUPM6017A patent/AUPM601794A0/en not_active Abandoned
• 1995
  • 1995-05-31 NZ NZ285997A patent/NZ285997A/en unknown
  • 1995-05-31 CN CN95190677A patent/CN1130938A/zh active Pending
  • 1995-05-31 EP EP95919940A patent/EP0711394A4/de not_active Withdrawn
  • 1995-05-31 WO PCT/AU1995/000324 patent/WO1995033169A1/en not_active Application Discontinuation
  • 1995-05-31 BR BR9505498A patent/BR9505498A/pt not_active Application Discontinuation

Patent Citations (3)

Non-Patent Citations (1)

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