EP0094825B1 - Convective drying - Google Patents
Convective drying Download PDFInfo
- Publication number
- EP0094825B1 EP0094825B1 EP83302767A EP83302767A EP0094825B1 EP 0094825 B1 EP0094825 B1 EP 0094825B1 EP 83302767 A EP83302767 A EP 83302767A EP 83302767 A EP83302767 A EP 83302767A EP 0094825 B1 EP0094825 B1 EP 0094825B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- radio frequency
- electrodes
- dryer
- heating power
- gas
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Images
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B13/00—Machines and apparatus for drying fabrics, fibres, yarns, or other materials in long lengths, with progressive movement
- F26B13/10—Arrangements for feeding, heating or supporting materials; Controlling movement, tension or position of materials
-
- 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
Definitions
- Such a dryer comprises a plurality of nozzles or jets for the heated air or gas and the material is passed between or below these jets or nozzles.
- the material may be a web, e.g. of fabric, which is passed between the jets or nozzles or it may be material, e.g. sheet material or pieces, which is carried on a belt or other carrier between or below the jets or nozzles.
- the radio frequency heating means heats the material internally so that heat transfer to the material occurs within the body of the material as well as on the surface thereof where the convective heating is effected.
Abstract
Description
- The invention relates to methods of and apparatus for convective drying of materials in which heated air or other gas is directed onto the material to be dried.
- Such a dryer comprises a plurality of nozzles or jets for the heated air or gas and the material is passed between or below these jets or nozzles. The material may be a web, e.g. of fabric, which is passed between the jets or nozzles or it may be material, e.g. sheet material or pieces, which is carried on a belt or other carrier between or below the jets or nozzles.
- EP-A-0009195 discloses a radio frequency drier for progressive drying of a paper web, in which nozzle chests are provided as the electrodes. Hot gases are emitted by the nozzles to support the web and to remove steam clouds which may occur in the radio frequency drying process.
- According to the present invention, there is provided a progressive dryer having a drying zone, means for continuously feeding material to be dried through the drying zone, a plurality of jets or nozzles in the drying zone for directing heated gas from a heater on to the material, the jets or nozzles being formed of electrically conductive material and constituting electrodes of radio frequency heating means to provide a radio frequency field in the drying zone, characterised in that the progressive drier is primarily a hot gas convective drier, the heating power input to the heater used to heat the gas forming a major part of the total heating power input supplied to both the heater and the radio frequency heating means.
- By this arrangement, the radio frequency heating means heats the material internally so that heat transfer to the material occurs within the body of the material as well as on the surface thereof where the convective heating is effected.
- The internal heating of the material causes moisture from the interior to move to the surface of the material, keeping this surface wet and so allowing higher air (or other gas) temperatures to be used than would be the case in the absence of radio frequency heating. Thus the overall drying efficiency is increased, resulting in increased drying speeds and reduced dryer length and may give improved material quality.
- The invention furthermore includes within its scope a method of drying, comprising continuously feeding a'material to be dried through a drying zone in which the material is simultaneously subjected to jets or streams of heated gas and to heating by a radio frequency field, characterised in that the heating power used to heat the gas forms a major 'part of the total heating power supplied to both the gas and generating the radio frequency field, so that the material is primarily dried by hot gas convection.
- The material to be dried would usually be electrically non-conductive and thus the radio frequency field would give dielectric heating. The frequency of operation may be chosen in accordance with known practice for dielectric heating.
- The radio frequency heating may be "stray field" heating in which the electrodes are all arranged beneath the material to be dried. Preferably however "through field" heating is effected using electrodes above the material co-operating with electrodes below the material. The electrodes in such an arrangement preferably are staggered, that is to say upper electrodes are arranged above spaces between lower electrodes.
- The major part of the total heat power input is applied to heating the air or other gas for the convective drying. Typically the amount of power input to the radio frequency heating is between 1/5th and 1/10th of the total energy input to the dryer.
- The jets or nozzles for the heated gas may be arranged, in the known way, to form an air flotation device to support the material to be dried. Such an arrangement may conveniently be used for the drying of webs of material.
- For materials which have to be carried through the dryer on a belt, it is convenient to provide jets or nozzles both above and below the belt, these jets or nozzles being arranged to form electrodes of a "through field" radio frequency heating system. Such an arrangement may conveniently be applied to the drying of sheet materials such as insulation board and plaster board and to other products such as pulp or fibre mouldings.
- In the following description of one embodiment of the invention, reference will be made to the accompanying drawing which illustrates diagrammatically in side elevation a dryer for web material.
- Referring to the drawing, the material to be dried is shown diagrammatically as a web 10 of electrically non-conductive material which is moved through the dryer in the direction of the arrow A. Above the web is a plurality of spaced
nozzle boxes 11 each constituting an electrode and each having one or more nozzles 12 for directing heated air onto the web. Similarly, below the web, there arenozzle boxes 13, these nozzle boxes constituting electrodes and having nozzles 14 to direct heated air onto the web. - Electrically' the
nozzle boxes 11 are connected as shown at 15 in parallel to oneoutput terminal 16 of aradio frequency generator 17. Thenozzle boxes 13 are connected electrically in parallel as shown at 18 to thesecond terminal 19 of the radio frequency generator. The various nozzles are fed from anair heater 20 in which the heat may be generated from any convenient fuel source for example, gas, oil, steam banks or electrical resistance heaters. - The resonant frequency of the output circuit of the radio frequency heater may be made controllable, as is well known in radio frequency heating, e.g. by the use of adjustable capacitors or inductors in the radio frequency circuit.
- The positional arrangement of the electrodes in which the
upper electrodes 11 are staggered with respect to thelower electrodes 13, provides a "through field" radio frequency heating system which permits relatively thick materials to be processed without substantial differential heating occurring. The ratio of the vertical spacing between the upper and lower electrodes (as shown at a in the figure) to the horizontal spacing (as shown at b in the figure) is chosen to suit the particular material -being dried, this ratio being chosen in accordance with the thickness of the material, the loss factor and the vapour diffusion characteristics through the material, as well as to give optimum web stability and convective heat transfer. The radio frequency heating heats the material internally and so tends to drive moisture towards the surface of the material thereby keeping the surface of the material wet. This allows the drying to take place at a much higher air temperature than would be possible if there was no radio frequency heating and hence gives an improved drying efficiency and increased drying speeds. - The major part of the energy input to the system is into the air heaters. The amount of energy provided by the radio frequency heating is typically between 1/5th and 1/10th of the total energy input to the dryer.
- Although in the embodiment illustrated, the electrodes and nozzles are spaced along the length of the web to be dried, they may additionally or alternatively be spaced across the width of the web.
Claims (8)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT83302767T ATE35454T1 (en) | 1982-05-17 | 1983-05-16 | CONVECTION DRYING. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB08214289A GB2123537B (en) | 1982-05-17 | 1982-05-17 | Convective drying |
GB8214289 | 1982-05-17 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0094825A2 EP0094825A2 (en) | 1983-11-23 |
EP0094825A3 EP0094825A3 (en) | 1985-01-16 |
EP0094825B1 true EP0094825B1 (en) | 1988-06-29 |
Family
ID=10530398
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP83302767A Expired EP0094825B1 (en) | 1982-05-17 | 1983-05-16 | Convective drying |
Country Status (10)
Country | Link |
---|---|
EP (1) | EP0094825B1 (en) |
JP (1) | JPS5932777A (en) |
AT (1) | ATE35454T1 (en) |
AU (1) | AU565203B2 (en) |
CA (1) | CA1241537A (en) |
DE (1) | DE3377227D1 (en) |
FI (1) | FI831711L (en) |
GB (1) | GB2123537B (en) |
NO (1) | NO831748L (en) |
ZA (1) | ZA833515B (en) |
Families Citing this family (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2159613A (en) * | 1984-05-31 | 1985-12-04 | Stocker Electronics Company | Timber drying |
DE3515600C1 (en) * | 1985-04-30 | 1986-10-09 | Bayerische Motoren Werke AG, 8000 München | Blow tunnel for drying painted workpieces |
US4638571A (en) * | 1986-04-02 | 1987-01-27 | Cook William A | Radio frequency nozzle bar dryer |
GB8628138D0 (en) * | 1986-11-25 | 1986-12-31 | Greenbank Eng Co Ltd | Suction drying apparatus |
GB8629882D0 (en) * | 1986-12-15 | 1987-01-28 | Greenbank Eng Co Ltd | Convective drying apparatus |
US5659972A (en) * | 1995-10-06 | 1997-08-26 | Avery Dennison Corporation | Apparatus and method for drying or curing web materials and coatings |
Family Cites Families (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB620956A (en) * | 1947-02-04 | 1949-04-01 | P R T Lab Ltd | Improvements in or relating to heating and drying by radio frequency currents |
GB914546A (en) * | 1959-08-20 | 1963-01-02 | Basf Ag | Apparatus for the thermal treatment and/or reaction of materials in a high-frequencyfield |
GB1236374A (en) * | 1967-07-17 | 1971-06-23 | Sericol Group Ltd | Improvements in the drying of sheet or web material |
FR2089900A5 (en) * | 1970-04-23 | 1972-01-07 | Menschner Johanne Textil | |
GB1424431A (en) * | 1973-03-19 | 1976-02-11 | Kanebo Ltd | Process and apparatus for drying porous material |
GB1486415A (en) * | 1974-09-16 | 1977-09-21 | Wira & Mather | Method and means for drying objects of or containing textile fibres |
GB1556296A (en) * | 1978-02-10 | 1979-11-21 | Magnetronics Ltd | Apparatus for electromagnetic irradiation of a material web |
DE2841371B1 (en) * | 1978-09-22 | 1980-02-14 | Siemens Ag | Device for guiding a web, in particular a paper web |
-
1982
- 1982-05-17 GB GB08214289A patent/GB2123537B/en not_active Expired
-
1983
- 1983-05-16 FI FI831711A patent/FI831711L/en not_active Application Discontinuation
- 1983-05-16 EP EP83302767A patent/EP0094825B1/en not_active Expired
- 1983-05-16 CA CA000428244A patent/CA1241537A/en not_active Expired
- 1983-05-16 AU AU14580/83A patent/AU565203B2/en not_active Ceased
- 1983-05-16 NO NO831748A patent/NO831748L/en unknown
- 1983-05-16 AT AT83302767T patent/ATE35454T1/en not_active IP Right Cessation
- 1983-05-16 DE DE8383302767T patent/DE3377227D1/en not_active Expired
- 1983-05-17 JP JP58086497A patent/JPS5932777A/en active Pending
- 1983-05-17 ZA ZA833515A patent/ZA833515B/en unknown
Also Published As
Publication number | Publication date |
---|---|
EP0094825A3 (en) | 1985-01-16 |
AU1458083A (en) | 1983-11-24 |
EP0094825A2 (en) | 1983-11-23 |
CA1241537A (en) | 1988-09-06 |
DE3377227D1 (en) | 1988-08-04 |
ZA833515B (en) | 1984-01-25 |
GB2123537A (en) | 1984-02-01 |
GB2123537B (en) | 1985-10-02 |
AU565203B2 (en) | 1987-09-10 |
NO831748L (en) | 1983-11-18 |
FI831711L (en) | 1983-11-18 |
FI831711A0 (en) | 1983-05-16 |
ATE35454T1 (en) | 1988-07-15 |
JPS5932777A (en) | 1984-02-22 |
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