Drying apparatus and method

Abstract: Drying apparatus comprising a cylindrical drying vessel (4) the inner wall surface (2) of which constitutes a heat-transmitting surface, a heat-generating means (6) encircling the said vessel, and at least one rotary vane assembly (5) rotatably mounted in the vessel. The vane assembly has vane sections (5a) which leave between their circumferential edges and the said heat-transmitting surface an annular space (U) small enough to allow wet material to extend across it and contact the heat-transmitting surface without falling into said space. Each vane section extends obliquely upward in the direction opposite to the rotating direction, and the circumferential edge of each vane section extends through less than 360 degrees as viewed from above. All of the vane sections when rotating bear material on their upper surfaces to raise the material and enable it to be urged against the heat-transmitting surface under the influence of centrifugal force, thus causing it to continuously climb along the heat-transmitting surface for drying.

Description: This invention relates to a drying apparatus and a drying method. There are a variety of drying apparatuses for drying different water-containing materials such as fluid material, semi-fluid material or pulverized material. The present applicant has proposed a drying apparatus in Japanese Utility Model Application Laid-Open No. 3-19501. such apparatus comprises a cylindrical drying vessel to receive material to be dried, the inner wall surface of which vessel constitutes a heat-transmitting surface, a heat-generating means encircling the drying vessel to transmit heat to the heat-transmitting surface thereof, and a screw-like rotating vane assembly rotatably mounted in the drying vessel to form a conveyor for material to be dried. More specifically, a rotating axle stands up from the bottom of the drying vessel, and the rotating vane assembly is fixed to the rotating axle by a plurality of radial arms, which extend across a space for falling material carried in the drying vessel. After being carried up to the top of the drying vessel while having its water content removed, the dried material is allowed to fall down through the said space in the vessel. There is an annular space between the outer circumference of the vane and the inner wall surface of the drying vessel to allow the material to contact the heat-transmitting surface of the vessel, but without falling into such annular space. In operation, the material is spirally conveyed by the rotating vane assembly until it reaches the top of the drying vessel, is then allowed to fall, and is then again spirally raised to the top. On the way to the top the material is pushed against the heat-transmitting surface by centrifugal force, and this up-and-down cyclic motion is repeated until the material has been dried. This known drying apparatus, however, has the following defects: First, when drying a material of high viscosity, such sticky material is liable to adhere to the vane sections of the rotary vane assembly, and to the heat-transmitting surface, thus agglomerating between adjacent upper and lower vane sections to impede the continuous rising of the material to be dried. As a result the up-and-down cyclic motion is prevented, and unsatisfactory drying results. Second, the annular space between the outer circumference of the vane and the inner wall surface of the drying vessel extends upward in an elongate spiral form, and foreign substances in the material to be dried are liable to be caught somewhere in this elongate spiral gap, thereby preventing rotation of the vane assembly. Third, as the screw-like rotating vane assembly is fixed to the rotating axle by radial arms, these arms extend across the falling material space in the drying vessel. As a result, string-like or sheet-like materials, such as vinyl sheets, are likely to be caught by such radial arms when falling down, thereby preventing the smooth up-and-down cyclic movement of material in the drying vessel. Fourth, as a single spiral vane assembly is used to raise the material to be dried, only a limited amount of material can be conveyed for drying, compared with the material remaining at the bottom of the drying vessel, which is clearly inefficient. Fifth, the areas of the heat-transmitting surface facing the space between adjacent upper and lower vane sections are not wholly contacted by material which is urged against such areas by centrifugal force. In other words, the heat-transmitting surface is not fully used. Sixth, the rotating speed of the spiral vane assembly must be varied according to the kind of material being dried, because otherwise the cyclic up-and-down movement of the material in the drying vessel does not occur in such manner as to attain the best drying efficiency. It is, however, difficult to control the rotating speed of the spiral vane to attain the best drying efficiency. Viewed from one aspect the present invention provides a drying apparatus comprising a cylindrical drying vessel to receive material to be dried, the inner wall surface of which vessel constitutes a heat-transmitting surface, a heat-generating means encircling the cylindrical drying vessel to heat said heat-transmitting surface, and at least one rotary vane assembly rotatably mounted in the vessel to urge said material upwards therein, characterized in that the said rotary vane assembly has a plurality of vane sections whose circumferential edges are so spaced from the said heat-transmitting surface by annular spaces that the said material can extend across said spaces and contact the said heat-transmitting surface without falling through said spaces, each said vane section extending obliquely upward in the direction opposite to the rotating direction, and the said circumferential edge of each vane section extending through less than 360 degrees as viewed from above, whereby the vane sections when rotating bear said material on their upper surfaces to raise the material upwards and enable it to be urged against the said heat-transmitting surface under the influence of centrifugal force, thus causing the material to continuously climb along the heat-transmitting surface. The cylindrical drying vessel may have a central rotary axle upstanding from its floor, and such axle may have a plurality of said rotary screw-like vane assemblies at different levels, whereby all of such assemblies when rotating may raise a relatively large amount of material in turn, so that the material may be raised from the lowest to the highest level in the vessel while being urged against the heat-transmitting surface, thereby drying the material. In apparatus according to the invention a material to be dried is spirally raised and urged against the heat-transmitting surface of the drying vessel. Consequently, materials of high viscosity are not liable to adhere to the rotating vane sections and to the heat-transmitting surface. Even if such material does adhere thereto, it is forcibly raised along the whole area of the heat-transmitting surface and consequently does not agglomerate in localized fashion. Further, the outer circumference of each vane section extends through less than 360 degrees, and the annular space between the outer circumferences of the vane sections and the inner wall surface of the cylindrical drying vessel is continuous and small enough to prevent the catching therein of foreign substances in the material being dried. Third, there is no cyclic, up-and-down, movement of the material to be dried, and therefore there is no fear of catching string-like or sheet-like foreign substances when the material is falling to the bottom of the drying vessel. Fourth, a plurality of vane sections are used in raising the material to be dried, and therefore the ratio of the rising amount of material to the remaining material is increased, thus putting an increased amount of material in contact with the heat-transmitting surface, and accordingly increasing the drying efficiency. Fifth, the following rising material pushes the preceding rising material continuously upward, thereby spreading the rising material over the area of heat-transmitting surface so that the layer of material thus spread is of reduced thickness, thereby facilitating the transmittal of heat for efficient drying. Sixth, the rising material can be urged against the heat-transmitting surface with an increased force by increasing the rotating speed of the spiral vane assembly, thereby increasingly spreading the rising material over the heat-transmitting surface, to facilitate drying. Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Fig. 1 is a longitudinal vertical section of a single-stage drying apparatus having a single rotating vane assembly according to a first embodiment of the present invention; Fig. 2 is a plan view of a first type of rotating vane assembly having three spokes, as in the apparatus of Fig. 1; Fig. 3 is a side view of the assembly of Fig. 2; Fig. 4 is a view similar to Fig. 1, showing the apparatus in operation; Fig. 5 is an enlarged view of a part of the apparatus of Fig. 1, showing how wet material is dried; Fig. 6 is a plan view of a first type of rotating vane assembly having four spokes; Fig. 7 is a side view of the assembly of Fig. 6; Fig. 8 is a longitudinal vertical section of a multi-stage drying apparatus having a plurality of rotating vane assemblies at different levels according to a second embodiment of the present invention, showing the apparatus in operation; Fig. 9 is a perspective view of a single-stage drying apparatus according to a third embodiment of the invention, shown partly in section; Fig. 10 is a perspective view of a second type of rotating vane assembly having three spokes; Fig. 11 is a plan view of the assembly of Fig. 10; Fig. 12 is a view similar to Fig. 9, showing the apparatus in operation; Fig. 13 is a perspective view of a second type of rotating vane assembly having two spokes; Fig. 14 is a perspective view of a second type of rotating vane assembly having four spokes; Fig. 15 is a perspective view of a second type of rotating vane assembly having six spokes; Fig. 16 is a perspective view of a second type of rotating vane assembly having eight spokes; Fig. 17 is a perspective view of a single-stage drying apparatus according to a fourth embodiment, shown partly in section; Fig. 18 is a perspective view of a third type of vane assembly having three circular-arc vane sections; Fig. 19 is a plan view of the vane assembly of Fig.18; Fig. 20 is a view similar to Fig. 17, showing the apparatus in operation; Fig. 21 is a perspective view of a third type of rotating vane assembly having two circular-arc vane sections; Fig. 22 is a perspective view of a third type of rotating vane assembly having four circular-arc vane sections; Fig. 23 is a perspective view of a single-stage drying apparatus according to a fifth embodiment, shown partly in section; Fig. 24 is a perspective view of a third type of rotating vane assembly having eight circular-arc vane sections; Fig.25 is a perspective view of a third type of rotating vane assembly having six circular-arc vane sections; Fig. 26 is a perspective view of a multi-stage drying apparatus according to a fifth embodiment of the invention, shown partly in section; and Fig. 27 is a perspective view of a multi-stage drying apparatus according to a sixth embodiment, shown partly in section. Figs. 1 to 5 show a drying apparatus 1 according to a first embodiment of the present invention. It comprises a cylindrical drying vessel 4 to receive material 3 to be dried, the inner wall surface of which vessel constitutes a heat-transmitting surface 2, a heat-generating jacket 6 encircling the vessel 4 to transmit heat to the surface 2, and a screw-like rotating vane assembly 5 rotatably mounted to the bottom of the vessel 4. The vessel 4 has a material feeding pipe 13 fixed to its cylindrical wall at a level close to the bottom of the vessel, and a material discharging pipe 15 fixed to its cylindrical wall at a level close to its ceiling. The material feeding pipe 13 has a spiral conveyor 14 therein for feeding a controllable amount of material to be dried into the lower part 4a of the drying vessel 4, while the material discharging pipe 15 has a spiral conveyor 16 therein for removing the raised and dried material from the upper part 4b of the vessel, and delivering it to a storage means (not shown). The heat-generating jacket 6 communicates with an associated steam-generating boiler via an upper inlet 11 and a lower outlet 12. As shown in Fig. 1, the screw-like rotating vane assembly 5 is rotatably mounted to the bottom 4a of the hollow cylinder 4, and its axle 5b is connected to an electric motor 17. The vane assembly 5 has a plurality of vane sections 5a, three in this particular example. All of the vane sections 5a have a similar shape, extending obliquely in the direction opposite to the rotating direction R, and leaving an annular space U between their outer circumferential edges 10a and the inner wall surface 2 of the hollow cylinder 4, which annular space U is small enough to prevent the material 3 from falling through it. Each vane section has a flat surface 80 on its upper side. As best seen from Fig. 2, each vane section 5a extends less than 360 degrees. Specifically, the circular-arc length from one end 18 to the other end 19 of the vane section forms an angle which is less than 360 degrees with respect to the center of rotation. The lower end 18 of the vane section 5a functions as a scraper 20. An alternative form of heat-generating means could comprise an encircling jacket filled with a heat-transmitting medium, and an electric heater attached to the jacket, so that heat generated by the electric heater is transmitted to the heat-transmitting surface 2 of the hollow cylinder via the heat-transmitting medium. Still another alternative would be an electric heater directly encircling the drying vessel. In operation, first the screw conveyor 14 is rotated to drive the material to be dried into the hollow cylinder 4, and at the same time, the electric motor 17 is started, to rotate the spiral vane assembly 5. Also, the steam generated by the boiler is directed to the encircling jacket 6 to heat the heat-transmitting surface 2 of the hollow cylinder 4. The vane sections 5a of the rotating vane assembly 5 scrape material up and move it upwards along their inclined vane surfaces 80, causing it to move from the scraping end 18 to the top end 19 of each vane section. While the material is thus being raised it is urged against the heat-transmitting surface 2 of the hollow cylinder 4 under the influence of the centrifugal force P. As may be seen from Fig. 4, one side of the rising material mass 3 is pushed against the heat-transmitting surface 2 of the hollow cylinder 4 on one side, and the other side of the rising material mass 3 is exposed to the inner atmosphere A of the hollow cylinder 4 for evaporation to occur. The material which contacts the heat-transmitting surface 2 is deprived of water by evaporation, and the so partly dried material moves toward the evaporation surface F, thus changing the position of the wet material. The partly dried material thus coming to the evaporation surface F is exposed to the hot environment A for evaporation. As the material moves towards the evaporation surface F the following material pushes the preceding material upwards, while climbing up the heat-transmitting surface 2. As the vane assembly rotates, material exiting the top end 19 of each vane section 5, and thus about to fall, contacts the material exiting from the following vane section, thus causing a turbulent flow. In this turbulence zone, material is accelerated to move at an increased speed towards the heat-transmitting surface 2, thus causing the material to be positively urged against the surface 2 and thereby expediting drying of the material. The turbulence effect can be increased by increasing the number of vane sections 5a and the speed of rotation of the vane assembly 5. Dried material is removed from the hollow cylinder 4 by the spiral conveyor 16, for storage. Material to be dried may be fed to the hollow cylinder 4 either intermittently or continuously. Figs. 6 and 7 show an alternative form of rotating vane assembly having four radial arms and four vane sections 5a. Each vane section is circular-arcuate in shape, similar to the vane section in Figs. 2 and 3. Fig. 8 shows a multi-stage drying apparatus having a plurality of vane assemblies 5 fixed to its axle 21 at different levels. Each vane assembly 5 has two radial arms and two vane sections 5a. In operation of the apparatus of Fig. 8, steam 7 is supplied to the jacket 6 via the steam inlet 11, and leaves via the steam outlet 12. Electric motor 17 rotates vertical axle 21 in the direction indicated by arrow R. The lowest rotating vane assembly scrapes up material 3 from the bottom 4a of the hollow cylinder 4, having been introduced by the spiral conveyor 14, and the material so scraped up is urged against the heat-transmitting surface 2 of the hollow cylinder 4, climbing therealong until the intermediate rotating vane assembly in turn picks up the rising material 3. Similarly the material so picked up is urged against the heat-transmitting surface 2, climbing therealong until the highest rotating vane assembly in turn picks up the rising material which is again urged against the surface 2, climbing therealong up to the level 4b at which the outlet conduit opens from the cylinder. The dried material is then conveyed by the spiral conveyor 16 to storage. Figs. 9 to 12 show another single-stage drying apparatus according to the invention, which is different from the apparatus of Figs. 1 to 5 in that it has an elongate vertical axle 21 and a broken wheel-like vane assembly 5. Specifically, axle 21 extends from the bottom 4a to the ceiling 4b of the hollow cylinder 4. As best seen from Fig. 10, the vane assembly 5 comprises a center disk 9A having an aperture 8 therein, three radial arms 9Ba, 9Bb and 9Bc each integrally connected at one end to the circumference of the center disk 40, and three circular-arc vane sections 10a each integrally connected at one end to a respective radial arm. As seen from Figs. 9 and 10, each circular-arc vane section 5a extends obliquely upward. The vertical elongate axle 21 passes through the aperture 8 of the ring 9A, and the inner circumference 9e of the aperture 8 is connected to the outer circumference of the axle 21. Referring to Fig. 13, another vane assembly 5 comprises a center disk 40 having an aperture 8 therein, two radial arms 9Ba and 9Bb each integrally connected at one end to the circumference of the ring 9A, and two circular-arc vane sections 10a each integrally connected at one end to a respective radial arm. As seen from the drawing, each circular-arc vane section 5aA or 5aB extends obliquely upward. Figs. 14, 15 and 16 show similar vane assemblies having four, six and eight radial arms 9B and circular-arc vane sections 5a respectively. Such a vane assembly 5 may have as many radial arms and vane sections as required. Referring to Figs. 17 to 20, still another single-stage drying apparatus is shown as having a circular vane assembly which comprises a circular support 30 having three circular-arc vane sections 5aA, 5aB and 5aC integrally connected to its circumference 9d as indicated at 18. Fig. 21 shows a similar circular vane assembly 5, which comprises a circular support 40 having two circular-arc vane sections 5a integrally connected to its circumference 9d as indicated at 18. Figs. 22, 24 and 25 show similar vane assemblies 5 having four, eight and six circular-arc vane sections respectively. Referring to Fig. 23, still another single-stage drying apparatus is shown, incorporating a circular vane assembly having eight circular-arc vane sections. Fig. 26 shows a two-stage drying apparatus which uses a circular vane assembly at a lower level and a broken wheel-like vane assembly at an upper level. The broken wheel-like vane assembly has two radial spokes 22 and an annular vaned member integrally connected thereto. The spokes 22 extend radially a distance H from the vertical axle 21, and the annular vaned member has eight circular-arc vane sections 80. The circular vane assembly has eight circular-arc vane sections 80, also. In operation these vane assemblies are rotated and material to be dried is spirally raised from the lower to the upper vane assembly while being urged against the heat-transmitting surface 2 of the hollow cylinder 4. Finally, Fig. 27 shows a five-stage drying apparatus uses a circular vane assembly at a lower level and four broken wheel-like vane assemblies at higher levels. Each vane assembly has eight vane sections. In operation these vane assemblies are rotated and material to be dried is spirally raised up from stage to stage while being urged against the heat-transmitting surface 2 of the hollow cylinder 4.

Claims: A drying apparatus comprising a cylindrical drying vessel (4) to receive material (3) to be dried, the inner wall surface of which vessel constitutes a heat-transmitting surface (2), a heat-generating means (6) encircling the cylindrical drying vessel to heat said heat-transmitting surface, and at least one rotary vane assembly (5) rotatably mounted in the vessel to urge said material upwards therein, characterized in that the said rotary vane assembly has a plurality of vane sections (5a) whose circumferential edges are so spaced from the said heat-transmitting surface by annular spaces (U) that the said material can extend across said spaces and contact the said heat-transmitting surface without falling through said spaces, each said vane section extending obliquely upward in the direction opposite to the rotating direction, and the said circumferential edge of each vane section extending through less than 360 degrees as viewed from above, whereby the vane sections when rotating bear said material on their upper surfaces to raise the material upwards and enable it to be urged against the said heat-transmitting surface under the influence of centrifugal force, thus causing the material to continuously climb along the heat-transmitting surface. A drying apparatus according to claim 1, wherein the said vessel (4) has a central rotary axle (21) upstanding from its floor, said axle having a plurality of said rotary vane assemblies (5) mounted at different levels thereon, whereby all of said rotary vane assemblies may raise the material in turn so that the material may be raised from the lowest to the highest level in the vessel. A drying apparatus according to claim 1, wherein the said vessel (4) has a central rotary axle (21) upstanding from its floor, said axle being adapted to be driven by an associated motor (17), and the said rotating vane assembly (5) having a central part (40) with an opening (8) therein securely receiving said axle, a plurality of circumferential vane sections (5a), and connecting means (30) integrally connecting said central part to one end (18) of each said vane section. A drying apparatus according to claim 3, wherein said central part of the said rotary vane assembly (5) comprises a relatively small disk (9A) having an opening (8) therein securely receiving the said axle (21), and a plurality of radial arms (9B) each extending radially from said disk and integrally connected to respective ends (18) of said vane section 5a. A drying apparatus according to claim 3, wherein said central part of said rotary vane assembly (5) comprises a relatively large disk (9C) having an opening (8) therein securely receiving the said axle (21), one end of each said circumferential vane section (5a) being integrally connected to the outer circumference (9d) of said disk. A drying apparatus according to claim 1, wherein the said vessel (4) has a central rotary axle (21) upstanding from its floor, and the said rotary vane assembly (5) comprises an annular member (31), and a plurality of radial arms (22) each extending a radial distance (H) to integrally connect the inner circumference (31B) of the said annular member to the said axle. A drying method in which material (3) to be dried is urged against a heat-transmitting surface (2) of a drying vessel (4) under the influence of centrifugal force, thereby drying the material, characterized in that it comprises the steps of: spiralling raising the said material from the bottom to the top level of said vessel; enabling the spiralling material to be urged against the said heat-transmitting surface under the influence of centrifugal force, thereby removing liquid content from the material; allowing the so liquid-deprived material to mix with material which is still wet while allowing the spiralling material to move toward an evaporating interface (F) surrounding the central region of the said vessel; and allowing the following spiralling material to push the preceding spiralling material continuously upwardly along the said heat-transmitting surface.

Inventors: KANAI MASAO, KANAI, MASAO
Applicants: KANAI MASAO, KANAI, MASAO
Application year: 1995
Main classification: F26B17
IPC codes: F26B11, F26B17