Drying apparatus

Abstract: A drying apparatus for removing moisture content from a substance (E) to be dried, comprises peripheral wall means (7) defining a working space for drying the substance, the peripheral wall means defining at least an inlet (12) for charging the substance to be dried, an outlet (15) for taking the dried substance therefrom and a drain. A rotary spiral blade assembly (4) disposed within the working space has a transporting surface (45) and is rotatable at a predetermined rotation speed sufficient for forcing the substance at the bottom of the working space to climb up the surface (45) toward the upper end of the rotary spiral blade assembly. Heating means associated with at least one of the peripheral wall means (7) and the rotary spiral blade assembly (4) heat a surface interfacing with the substance while the substance travels on the transporting surface (45) toward the upward end. The rotary spiral blade assembly defines a path for substance reaching the upper end thereof to fall down to the bottom and a baffle plate (M) located in opposition to the upper end of the rotary spiral blade assembly forces the substance reaching the upper end to fall down through this path.

Description: The present invention relates generally to a drying apparatus for removing moisture from substances in liquid state, fluid state or semi-fluid state. More specifically, the invention relates to a drying apparatus comprising the features as indicated in the preamble of claim 1. As is well known, there have been employed in various fields of industries various drying processes for drying and removing moisture from liquid state, fluid state, semi-fluid state, powder state or grain state substances. In the various sites, a variety of drying apparatus have been used. However, in the known technologies, drying apparatus having high efficiency is generally applicable only for specific application for a specific substances. In most case, such apparatus is not at all effective for the applications other than those specified. On the other hand, there has also been known general purpose drying apparatus which has wide range of applicability. However, such type of apparatus :is generally low in drying efficiency or requires complicated construction or facility which results in high cost. Namely, in the prior art, no drying apparatus may satisfy the requirement for high drying efficiency and wide applicable range. The commonly owned U.S. Patent No. 5074,057, issued on December 24, 1991 and Japanese Utility Model No. 1-79 430 propose a drying apparatus with a rotary spiral blade and having the features of the preamble of claim 1. The disclosed apparatus comprises a drying vessel to contain the moisture containing substance to be dried, the vessel having a heat conduction surface on its inner wall for transmitting heat to the substance, and circulating rotary means to put the substance in motion in the vessel, thereby increasing the efficiency with which the substance can be brought to the heat conduction surface. The circulating rotary means comprises a rotary shaft vertically extending ip the vessel in the direction of gravity, and a spiral blade integrally connected to and wound around the rotary shaft, the spiral blade having a flat upper surface, whereby rotation of the rotary shaft and hence the spiral blade may cause the substance to rise up in the direction of the gravity, and slide on the flat upper surface of the spiral blade until the so raised substances is allowed to fall down in the direction of the gravity through a falling space which is defined in the drying vessel, and until the substance has come in contact with the heat conduction surface. With the construction set forth above, the moisture containing substance is put in the drying vessel, and then the substance is located at the lower position, under the influence of gravity. The heat condition surface of the drying vessel is heated by heating means so that the heat is transferred to the moisture containing in the drying vessel. The spiral blade is made to rotate by rotating its axle. In the case where the spiral blade is hollow and heating medium is led into the inside of the spiral blade, the upper surface of the spiral blade will function as a heat conduction surface like the inner wall of the drying vessel. Although the foregoing prior proposed invention achieves capability of circulating the moisture containing substance at an increased speed and brings the substance into contact with the heat conduction surface of the drying apparatus at an increased efficiency and thus achieves both of high drying efficiency and wider range of application, there still remains room for improvement. Namely, in the prior proposed invention, the moisture containing substance is transported from the lower side of the drying vessel toward the upper side on the flat surface of the spiral blade, which serves as the heat conduction surface. The substance travelling along the flat surface of the spiral blade forms thin film contacting with the heat conduction surface for promoting heat transfer from the heat conduction surface to the substance. As set out above, in the construction set forth above, for obtaining a satisfactory level of removal of the moisture from the substance, it is necessary to smoothly shift the substance along the flat surface of the spiral blade. To achieve this, the substance approaching the upper end of the spiral blade needs to be effectively fallen down to repeat the heating cycles. The present invention is thus intended to provide an improvement for the dryer according to JP-U-1-79 430 so as to achieve smooth circulation of the moisture containing substances for achieving smooth travel of the substance and for assuring falling down of the substance reaching the top end of the spiral blade. According to the invention there is provided a drying apparatus for removing moisture content from a substance to be dried, comprising: a drying vessel to contain said substance; means for heating said substance within the vessel; and rotary spiral blade means for moving said substance within said vessel from a lower part to an upper part thereof; characterised in that it comprises baffle means provided in opposition to an upper end of said spiral blade said baffle means having a substantial extent in a direction perpendicular to the upper surface of said spiral blade so as to block passage of said substance past said baffle thereby forcing it off the upper end of said upper surface of the blade as the blade rotates past said baffle means. Preferably, the baffle means for forcing the substance off the upper end of the spiral blade comprises a baffle plate provided in opposition with the upper end of the spiral blade with a given angular relationship thereto. The baffle plate may be provided in direct contact with the inner wall of the drying vessel. In one embodiment, the heating means heats at least the peripheral wall means and the baffle plate is directly mounted on the peripheral wall means. In its preferred embodiments at least, the present invention provides an improved drying apparatus which can assure smooth circulation of a moisture containing substance and thereby enhance efficiency of drying the substance, and a drying apparatus having a spiral blade for transferring the substance upwardly, which ensures falling down of the substance reaching the end of the spiral blade. A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings. In the drawings: Fig. 1 is a longitudinal section of a preferred embodiment of a drying apparatus according to the present invention; Fig. 2 is a partial perspective view showing a relationship between a rotary spiral blade and a baffling plate employed in the preferred embodiment of the drying apparatus of Fig. 1; Fig. 3 is a partial perspective view showing the operation of the baffling plate for scraping down a substance to be dried at the top of the spiral blade; Fig. 4 is a diagrammatic illustrated side elevation showing dimensional relationship of the the baffling plate relative to the spiral blade; Fig. 5 is a diagrammatic illustrated plan view showing dimensional relationship of the baffling plate relative to the spiral blade; Fig. 6 is a diagrammatic illustrated enlarged partial section showing dimensional relationship of the baffling plate relative to the spiral blade; and Fig.7 is a fragmentary perspective view showing a modification of the preferred embodiment of the drying apparatus, in which three baffling plates are provided. Referring now to the drawings, particularly to Fig. 1 , a preferred embodiment of a drying apparatus 1 , according to the present invention, has an essentially cylindrical drying vessel 2 . The drying vessel 2 is supported by a plurality of legs 22 on a floor g so that the longitudinal axis thereof is oriented substantially in the vertical direction or the direction of gravity, A jacket 10 is arranged on the outer circumference of the drying vessel 2 . The jacket 10 defines a heating chamber 10a for introducing a heating medium, such as steam, or a heated fluid, thereinto for heating the side wall of the drying vessel 2 . In the preferred embodiment, steam is introduced into the heating chamber 10a from a boiler. The heat of the heating chamber 10a is thus transmitted to the side wall of the drying vessel 2 . Therefore, the inner wall surface of the drying vessel 2 serves as a heat conduction surface 7 . Although the shown embodiment is constructed to introduce the heating medium, such as steam, heating fluid or so forth into the heating chamber 10a defined between the outer periphery of the drying vessel 2 and the jacket 10, it can be replaced with various heating means appropriate for heating the side wall of the drying vessel. For example, the jacket may be replaced with an electric heater, a combustion type heater, induction type heater or so forth, for directly heating the side wall of the drying vessel. Furthermore, it may also possible to incorporate heating means, such as an electric heating,wire or an induction heating element within the side wall of the drying vessel for heating. In the shown embodiment, the jacket 10 is provided with a steam inlet 18 connected to a piping 17 connected to the boiler (not shown). The jacket 10 also has a drain outlet 21 for draining a condensed water in the heating chamber, which drain outlet 21 is connected to a drain piping 20 . An charge opening 12 is formed in the vicinity of the top end of the drying vessel 2 for charging liquid state, fluid state, semi-fluid state, powder state or grain state substances to be dried and have removed moisture therefrom. The charge opening 12 is openably closed by a closure lid 13 . Also, an outlet opening 15 is formed at the lower portion of the drying vessel 2 for taking out the dried product. A circulating means for circulating the moisture containing substance to be dried is provided within the interior space of the drying vessel 2 . In the preferred embodiment, the circulating means comprises a spiral blade assembly which is substantially the.same construction as that disclosed in the above-identified U. S. Patent No. 5074,057 , commonly owned. Namely, the spiral blade assembly includes a rotary shaft 3 extending vertically substantially along the longitudinal axis of the drying vessel 2 . A spiral blade 4 is rigidly mounted about the rotary shaft 3 for rotation therewith. The lower end of the rotary shaft 3 is received within a boss 24 via a thrust washer 25 . The upper end of the rotary shaft 3 extends through a through opening through a top end wall of the drying vessel 2 . At the outside of the drying vessel 2, the rotary shaft 3 is rotatably received through a bearing 28 for permitting free rotation in a direction indicated by an arrow R . For rotatingly driving the rotary shaft 3 , an electric motor 29 is employed. The motor 29 is rigidly secured on the drying vessel 2 via a mounting piece 30 . The motor 29 has an output shaft 31 , on which a drive gear (not clearly shown) is rigidly secured. The drive gear is coupled with a driven gear 32 rigidly secured on the rotary shaft 3 by means of a geared belt or cogged belt 33 for transmitting the output torque of the motor 29 . Therefore, the rotary shaft 3 carrying the spiral blade is rotatingly driven by the output torque of the motor 29 . It should be noted that the specific power train construction for the rotary shaft is mere example and can be of any appropriate construction depending upon the application. For instance, a reduction gear assembly or step-up gear assembly may be interposed between the motor and the rotary shaft, as required. Also, the electric motor may be replaced with any other driving power source, such as combustion type drive power source, steam type power source or so forth. In the shown embodiment, the rotary shaft 3 is formed into a hollow tubular construction. A siphon drain tube 34 is inserted through the interior space thereof. The siphon drain tube 34 is loosely received within a recess 37 formed in a siphon tube receptacle 36 . The lower end of the siphon drain tube 34 and the recess 37 of the siphon tube receptacle 36 are so dimensioned that the lower end of the siphon drain tube 34 may not contact with the inner periphery of the recess 37 . The upper portion of the siphon drain tube 34 extends through the upper narrower opening portion 39 of the rotary shaft 3 to upwardly project therefrom. To the upper end of the upper end portion of the rotary shaft 3 , a rotary connecting portion 41 of a locky joint 40 is connected. Also, the upper end of the siphon drain tube 34 is also connected to the locky joint 40 . Furthermore, the piping 17 connected to the boiler is connected to the locky joint 40 for introducing steam as a heating medium. In addition, the drain piping 20 is connected via a joint 42 . The steam introduced through the piping 17 is introduced into an annular space defined between the inner periphery of the rotary shaft 3 and the siphon drain tube 34 . The condensed water in the follow interior space of the rotary shaft 3 is drained through the siphon drain tube 34 and the drain piping 20 . It should be noted that although the shown embodiment is constructed to introduce the heating medium, such as steam, heating fluid or so forth into the interior space of the spiral blade, it can be replaced with various heating means appropriate for heating upper surface 45 of the spiral blade. For example, the lower part of the spiral blade may be replaced with an electric heater or so forth. Furthermore, it may also possible to incorporate heating means, such as an electric heating wire or an induction heating element within the member forming the upper surface 45 of the spiral blade. It should be noted that the locky joint 40 is rigidly secured to the drying vessel 2 by a mounting piece 55 . In the shown embodiment, the spiral blade 4 is formed into a hollow construction with essentially semi-circular cross section. The spiral blade 4 is oriented so that the upper plane 45 is formed with the flat plane extending diametrically in the semi-circular cross section of the hollow spiral blade 4 . The spiral blade 4 is rigidly supported on the rotary shaft 3 by a plurality of supporting arms 43 extending substantially in radial direction. The outer periphery of the spiral blade 4 is positioned in the vicinity of the inner periphery of the drying vessel with maintaining the possible minimum clearance necessary for permitting the spiral blade 4 to rotate without conflicting with the inner periphery of the drying vessel 2 . On the other hand, inner periphery of the spiral blade 4 defines an annular space A between the outer periphery of the rotary shaft 3 . The annular space defined between the inner periphery of the spiral blade 4 and the outer periphery of the rotary shaft 3 serves as a path for allowing the substance to fall down to the bottom of the drying vessel. The supporting arms 43 are of hollow construction. The inner ends of the interior spaces of the supporting arms 43 communicate with the interior space of the rotary shaft 3 . The outer ends of the interior spaces of the supporting arms 43 communicate with the interior space of the spiral blade 4 . Therefore, the steam introduced into the interior space of the rotary shaft 3 is introduced into the interior space of the spiral blade 4 for heating. Therefore, the flat upper surface 45 of the spiral blade 4 may serve as a heat conduction surface for transmitting the heat to the moisture containing substance traveling upwardly thereon. It should be noted that although the shown embodiment is constructed to introduce the heating medium, such as heat steam, heating fluid or so forth. into the interior space of the spiral blade, it can be replaced with various heating means appropriate for heating upper surface 45 of the spiral blade. For example, the lower part of the spiral blade may be replaced with an electric heater or so forth. Furthermore, it may also possible to incorporate heating means, such as an electric heating wire or an induction heating element within the member forming the upper surface 45 of the spiral blade. Furthermore, although the shown embodiment is constructed to establish steam communication through all of the supporting arms, it may be possible to establish steam communication between the interior space of the rotary shaft and the interior space of the spiral blade through only limited number of supporting arms. In addition to the construction set forth above, the shown embodiment of the drying apparatus is provided with baffle plates M in order to achieve smooth circulation of the substances to be dried. As seen, the baffle plates M extend from the upper end portion of heat conduction surface 7 of the side wall of the drying vessel 2 with the lower edges thereof in close proximity to the uppermost end of flat upper surface 45 of the spiral blade 4 with a possible minimum clearance S . The number of the baffle plates M is not limited and can be of any number depending upon application and necessity. For instance, in the example of Fig.1 , a pair of baffle plates M are arranged in radially symmetric positions. On the other hand, in the examples of Figs. 3 ∼ 5 , only one baffle plate M is provided, and in the example of Fig. 7 , three baffle plates M are arranged with a regular angular interval. The configuration of the baffle plate can be selected in any way and not limited to the shown rectangular configuration. The clearance S to be provided between the lower end L and the uppermost end of the upper surface 45 of the spiral blade 4 can be selected in a range between 0.01 mm to 50 mm depending upon the kind, nature, grain or particle size of the substance to be dried. The installation angle of the baffle plate M is not limited to vertical as illustrated and can be oblique relative to the vertical plane. In the later case, the obliquity or inclination angle of the baffle plate may be selected depending upon the kind, nature, grain or particle size of the substance to be dried. Also, the orientation of the baffle plate M is not limited to the radial direction as illustrated, but can be of various angle as shown by T in Fig. 5. In operation, the rotary shift 3 carrying the blade 4 is driven to rotate by the motor 29. The spiral blade 4 is thus rotated in the direction R at a predetermined rotation speed. Then, due to static inertia moment, the substance to be dried rides on the upper surface 45 of the spiral blade 4. Then, centrifugal force and the static inertia moment act on the substance to force the substance to slidingly climb up along the upper surface 45 of the spiral blade 4 at a speed lower than the rotation speed of the spiral blade 4. During upward travel, the substance is spread into a thin film form to maximize the interface area interfacing with the heated upper surface 45 serving as the heat conduction surface. Also, due to the centrifugal force induced by high speed rotation of the spiral blade, the substance is also forced outwardly to form an interfacing layer with the inner periphery of the drying vessel 2 which also serves as the heat conduction surface. This provides additional interface area between the substance and the heat conduction surfaces for promoting removal of moisture from the substance by effective heat transmission. Since the outer periphery of the spiral blade 4 is placed in opposition to the inner periphery of the drying vessel with a minimum clearance W, e.g. 0.01 mm to 20 mm which is selected depending upon the kind, nature, grain or particle size of the substance to be dried, the substance may not fall down from the outer periphery of the spiral blade 4. When the substance E reaches to the position in the vicinity of the upper end P of the upper surface 45, as shown in Fig.3 . the substance E initially contacts on one surface H of the baffle M. Then, part of the substance E is scraped off and falls down through the clearance A . The remaining substance E passes through the clearance S between the upper surface 45 of the spiral blade 4 and the lower edge L of the baffle M to reach the upper end P . Since the climbing up speed of the substance E on the upper surface 45 of the spiral blade 4 is lower than the rotation speed of the spiral blade 4 , the substance E may accumulate at the upper end P . However, by further rotation of the spiral blade 4, the substance E accumulated at the upper end P contacts with the surface H of the baffle plate M and is scraped off to fall down co the bottom of the drying vessel 2 . With the shown construction, since upward travel of the substance contacting with the heat conduction surfaces will not be blocked by accumulation of the substance on the spiral plate, the substance can be smoothly circulated. By this, substantial improvement in the moisture removing efficiency can be achieved. As set forth above, the present invention achieves substantial and.useful improvement in the drying apparatus employing the rotary spiral blade, with simply construction. Also, since the construction of the baffle plate is very simple, the improvement proposed by the present invention can be easily applied to any existing apparatus without requiring substantial increase of the cost for facility. While the present invention has been discussed in detail in terms of a preferred embodiment of the invention, the invention can be implemented in various fashion with incorporating various modification, addition, omission.

Claims: A drying apparatus for removing moisture content from a substance to be dried, comprising: a drying vessel (2) to contain said substance; means for heating said substance within the vessel; and rotary spiral blade means (4) for moving said substance within said vessel from a lower part to an upper part thereof; characterised in that it comprises baffle means (M) provided in opposition to an upper end of said spiral blade (4) said baffle means having a substantial extent in a direction perpendicular to the upper surface (45) of said spiral blade (4) so as to block passage of said substance past said baffle thereby forcing it off the upper end of said upper surface of the blade as the blade rotates past said baffle means. Apparatus as claimed in claim 1 wherein said baffle means (M) is a plate. Apparatus as claimed in claim 1 or 2 wherein said baffle means (M) extends substantially vertically. Apparatus as claimed in claim 1 or 2 wherein said baffle means (M) extends at an angle to the vertical. Apparatus as claimed in any preceding claim wherein said baffle means (M) extends substantially radially of said vessel (2). Apparatus as claimed in any of claims 1 to 4 wherein said baffle means (M) extends at an angle to a radius of said vessel (2). Apparatus as claimed in any preceding claim wherein said baffle means (M) is provided in direct contact with the inner wall (7) of said vessel. Apparatus as claimed in any preceding claim comprising means for heating the upper surface (45) of said blade (4), said blade being hollow. Apparatus as claimed in claim 8 wherein said spiral blade (4) is hollow so as to permit heating medium to flow inside the blade. Apparatus as claimed in any preceding claim wherein the upper surface (45) of said blade (4) is substantially perpendicular to the axis of said vessel. Apparatus as claimed in any preceding claim wherein the upper surface (45) of said blade (4) is flat. Apparatus as claimed in any preceding claim wherein the inner wall (7) of said vessel (2) has a heat conduction surface to transmit heat to said substance. Apparatus as claimed in any preceding claim wherein the rotary blade (4) is concentric with the vessel (2) and its outer edge is positioned close to the inner wall (7) of the vessel.

Inventors: KANAI MASAO, KANAI, MASAO
Applicants: KANAI MASAO, KANAI, MASAO
Application year: 1992
Main classification: F26B11
IPC codes: F26B25, F26B17, B01F7, F26B11