Patent Grant
7914200
The present invention relates generally to apparatus and method for mixing liquids and, in particular, feedstock in the form of viscous liquids containing solid constituents, and pertains, more specifically, to directing the flow of such a feedstock to and from heat transfer surfaces within a vessel containing the feedstock in order to enhance heat transfer between the feedstock and the vessel, while attaining greater uniformity within a reduced mixing time.
Conventional mixing machines commonly employ mixing blades which confront and move across corresponding surfaces in a vessel within which a feedstock is contained while being mixed so as to facilitate the conduct of heat between the feedstock and these surfaces of the vessel. For example, in a typical mixing apparatus, a mixing blade constructed in the form of a helix is rotated within a vessel having a circular cylindrical side wall extending upwardly from a complementary circular bottom wall, the mixing blade being carried by a support structure having a horizontal support member which sweeps across the bottom wall and a vertical support member which sweeps across the side wall, while the feedstock is circulated within the vessel toward and away from the walls of the vessel by the helical mixing blade. The horizontal and vertical support members carry scrapers which engage corresponding walls of the vessel to scrape feedstock from the walls as the support members sweep past respective walls; however, the support members themselves play little or no part in moving the feedstock toward or away from the walls of the vessel to effect the desired heat transfer during a mixing operation.
The present invention provides a construction in which the support structure that carries the mixing blade works in concert with the mixing blade to attain better heat transfer between the feedstock and the walls of the vessel, with a concomitant increase in uniformity gained throughout the feedstock in less mixing time. As such, the present invention attains several objects and advantages, some of which are summarized as follows: Provides a mixing blade assembly in which a mixing blade support structure includes support members constructed to increase the effectiveness of the mixing blade assembly in mixing a batch of feedstock in a mixing vessel; facilitates heat transfer between a batch of feedstock and the walls of the vessel within which the feedstock is mixed, for attaining increased uniformity throughout the batch in less mixing time; reduces resistance to efficient circulation of feedstock within a batch of feedstock being mixed in a mixing vessel, with a concomitant reduction of energy needed to complete a mixing operation; provides a mixing blade assembly placed within a mixing vessel with an additional mixing mechanism, which mixing blade assembly is constructed to interact with the additional mixing mechanism to assist in circulating feedstock within the batch for increased effectiveness of both the mixing blade assembly and the additional mixing mechanism; attains a more uniform mixture within a batch of feedstock in less time and with the consumption of less energy; simplifies the maintenance of a mixing blade assembly for economical long-term operation; provides a rugged mixing blade assembly capable of exemplary performance over an extended service life.
The above objects and advantages, as well as further objects and advantages, are attained by the present invention which may be described briefly as a mixing apparatus for mixing constituents of a feedstock, the mixing apparatus comprising: a vessel including a heat transfer surface within the vessel for being engaged by the feedstock as the constituents of the feedstock are mixed within the vessel; a mixing blade assembly including a mixing blade and at least one mixing blade support member, the mixing blade assembly being adapted to move within the vessel to sweep the mixing blade and the mixing blade support member in a forward direction along a path of travel extending adjacent the heat transfer surface to circulate feedstock within the vessel; the mixing blade support member having a mixing surface confronting the heat transfer surface and spaced from the heat transfer surface to establish a passage between the mixing surface and the heat transfer surface, the mixing surface being configured to squeeze feedstock material passing through the passage, whereby the feedstock material squeezed within the passage will be subjected to mixing shear and to heat transfer between the squeezed feedstock and the heat transfer surface; and a scraper blade carried by the mixing blade support member in position to trail behind the mixing surface of the mixing blade support member and engage the heat transfer surface upon movement of the mixing blade support member along the path of travel so as to scrape from the heat transfer surface feedstock material squeezed between the mixing surface and the heat transfer surface and direct the squeezed feedstock material toward the mixing blade to be mixed with feedstock circulated by the mixing blade.
In addition, the invention includes a method for mixing feedstock within a vessel wherein the feedstock is moved along a heat transfer surface within the vessel as the feedstock is mixed within the vessel, the method comprising: providing a mixing blade assembly including a mixing blade and at least one mixing blade support member, the mixing blade support member having a mixing surface; confronting the mixing surface with the heat transfer surface and spacing the mixing surface from the heat transfer surface to establish a passage between the mixing surface and the heat transfer surface, the mixing surface being configured to squeeze feedstock material passed through the passage; moving the mixing blade assembly within the vessel to sweep the mixing blade and the mixing blade support member in a forward direction along a path of travel extending adjacent the heat transfer surface to circulate feedstock within the vessel and pass feedstock material through the passage to squeeze the feedstock material between the mixing surface and the heat transfer surface; placing a scraper blade on the mixing blade support member in position to trail behind the mixing surface of the mixing blade support member; and engaging the scraper blade with the heat transfer surface during movement of the mixing blade support member along the path of travel so as to scrape from the heat transfer surface feedstock material squeezed within the passage and direct the squeezed feedstock material toward the mixing blade, whereby feedstock material squeezed within the passage is subjected to mixing shear and heat transfer between the squeezed feedstock material and the heat transfer surface and then mixed with feedstock circulated by the mixing blade.
The invention will be understood more fully, while still further objects and advantages will become apparent, in the following detailed description of preferred embodiments of the invention illustrated in the accompanying drawing, in which:
Referring now to the drawing, and especially to
A mixing blade assembly 40 includes a helical mixing blade 42 and is mounted for rotation within vessel 12, about a central axis of rotation 44, to rotate mixing blade 42 in a direction R about the central axis of rotation 44 and effect mixing of a batch 46 of feedstock 48 placed within vessel 12. Mixing blade 42 is juxtaposed with vertical side wall 14 and, upon rotation about axis of rotation 44, in the direction R, effects mixing of the feedstock 48 while driving the feedstock 48 generally upwardly, in a direction from the bottom wall 16 toward the top end 18 of the side wall 14 to circulate the feedstock 48 within the vessel 12.
Mixing blade 42 is carried by a support structure 50 of the mixing blade assembly 40, the support structure 50 including a generally L-shaped frame 52 comprised of a vertical support member 54 and a horizontal support member 56. The mixing blade 42 is affixed, adjacent upper end 58 of the mixing blade 42, to the frame 52, adjacent upper portion 60 of vertical support member 54, and is affixed, adjacent lower end 62 of the mixing blade 42, to the frame 52, adjacent end 64 of horizontal support member 56, as by welding the mixing blade 42 to the frame 52 at each end 58 and 62 of mixing blade 42. The frame 52 is affixed, adjacent upper portion 60 of vertical support member 54, to a drive member 70 which, in turn, is coupled to a drive motor 72 for effecting rotation of the frame 52. An additional mixing mechanism is placed within vessel 12, and is shown in the form of a submersible media mill 80 located coaxial with mixing blade assembly 40 and mixing blade 42, the media mill 80 having an inlet at 82 and outlets at an apertured wall 84 and at an apertured bottom 86, as is known in media mills.
In the operation of mixing apparatus 10, mixing blade assembly 40 is rotated simultaneously with the operation of media mill 80, and feedstock 48 is circulated within vessel 12. Thus, feedstock 48 enters media mill 80 at inlet 82, as indicated by arrows A, is processed by the media mill 80 and exits through apertured wall 84 and bottom 86, directed generally toward the side wall 14, as indicated by arrows B, and toward the bottom wall 16 of the vessel 12, as indicated by arrows C. Helical mixing blade 42 moves the feedstock 48 upwardly, as indicated by arrows D, to once again enter the media mill 80 at inlet 82, again as indicated by arrows A.
Usually, feedstock 48 consists of a viscous liquid which contains solid constituents and tends to accumulate along the side wall 14 and the bottom wall 16 of vessel 12, at the respective heat transfer surfaces 25 and 29. In order to facilitate the transfer of heat between the feedstock 48 and the heat transfer surfaces 25 and 29 of walls 14 and 16 of vessel 12, mixing blade assembly 40 is provided with scrapers which engage the walls 14 and 16, as the mixing blade assembly 40 is rotated, to scrape accumulated feedstock from the heat transfer surfaces 25 and 29 of the walls 14 and 16 and maintain contact between the circulating feedstock 48 and the heat transfer surfaces 25 and 29 of the walls 14 and 16. Thus, as seen somewhat diagrammatically in
In a like manner, as seen somewhat diagrammatically in
Turning now to
A mixing blade assembly 140 includes a helical mixing blade 142 and is mounted for rotation within vessel 112, about a central axis of rotation 144, to rotate mixing blade 142 in a direction RR about the central axis of rotation 144 and effect mixing of a batch 146 of feedstock 148 placed within vessel 12. Mixing blade 142 is juxtaposed with side wall 114 and, upon rotation about axis of rotation 144, in the direction RR, effects mixing of the feedstock 148 while driving the feedstock 148 generally upwardly, in a direction from the bottom wall 116 toward the top end 118 of the side wall 114, to circulate the feedstock 148 within the vessel 112.
Mixing blade 142 is carried by a support structure 150 of the mixing blade assembly 140, the support structure 150 including a generally L-shaped frame 152 comprised of a vertical support member 154 and a horizontal support member 156. The mixing blade 142 is affixed, adjacent upper end 158 of the mixing blade 142, to the frame 152, adjacent upper portion 160 of vertical support member 154, and is affixed, adjacent lower end 162 of the mixing blade 142, to the frame 152, adjacent end 164 of horizontal support member 156, as by welding the mixing blade 142 to the frame 152 at each end 158 and 162 of mixing blade 142. The frame 152 is rotated about axis of rotation 144 in a manner similar to that described above in connection with the rotation of frame 52 of mixing blade assembly 40. As before, an additional mixing mechanism is placed within vessel 112, and is shown in the form of a submersible media mill 180 located coaxial with mixing blade assembly 140 and mixing blade 142, the media mill 180 having an inlet at 182 and outlets at an apertured wall 184 and at an apertured bottom 186, as is known in media mills.
In the operation of mixing apparatus 110, mixing blade assembly 140 is rotated simultaneously with the operation of media mill 180, and feedstock 148 is circulated within vessel 112. Thus, feedstock 148 enters media mill 180 at inlet 182, as indicated by arrows AA, is processed by the media mill 180, and exits through apertured wall 184, directed generally toward the side wall 114, as indicated by arrows BB, and exits through bottom 186, directed toward the bottom wall 116 of the vessel 112, as indicated by arrows CC. Helical mixing blade 142 moves the feedstock 148 generally upwardly, as indicated by arrows DD, to once again enter the media mill 180 at inlet 182, again as indicated by arrows AA.
As set forth above, usually feedstock 148 consists of a viscous liquid which contains solid constituents and tends to accumulate along the side wall 114 and the bottom wall 116 of vessel 112. As before, in order to assist in the transfer of heat between the feedstock 148 and the respective heat transfer surfaces 125 and 129 of walls 114 and 116 of vessel 112, mixing blade assembly 140 is provided with scrapers which engage the heat transfer surfaces 125 and 129 of walls 114 and 116, as the mixing blade assembly 140 is rotated, to scrape accumulated feedstock from the walls 114 and 116 and maintain contact between the circulating feedstock 148 and the heat transfer surfaces 125 and 129 of walls 114 and 116. Thus, as seen somewhat diagrammatically in
Scraper blade 190 is mounted upon a bracket 196 carried by horizontal support member 156, the bracket 196 extending rearwardly to space the scraper blade 190 from trailing face 194 in a rearward direction, relative to the direction of rotation RR of the mixing blade assembly 140. With scraper blade 190 engaged with the heat transfer surface 129 of the bottom wall 116 at an angle θ, and apex δ of the horizontal support member 156 spaced a short distance from the bottom wall 116, feedstock material M adjacent bottom wall 116 passes through an entrance portion 197 of passage 188 where the passage 188 contracts along leading face 192 and, by virtue of angle α, is urged into a narrow constriction, shown in the form of a throat T at an intermediate portion of passage 188 where the feedstock material M is squeezed between the apex δ and the bottom wall 116, forcing the feedstock material M against the bottom wall 116, thereby generating additional shear within the feedstock material M.
As the feedstock material M passes through throat T and then through an exit portion 198 of passage 188 where the passage 188 expands along the trailing face 194, a pressure drop occurs within the feedstock material M, by virtue of angle β. Thus, the leading face 192 and the trailing face 194 establish portions 197 and 198 of passage 188 which, in combination with the intermediate portion of passage 188 at narrow throat T, act in concert to create additional shear in feedstock material M for enhanced mixing. At the same time, the trailing scraper blade 190, spaced rearwardly from trailing face 194, directs the flow of feedstock material M toward the helical mixing blade 142, allowing the mixing blade 142 to pick up the feedstock material M and move mixed feedstock 148 toward the top end 118 of side wall 114, enabling the scraped feedstock material M to be moved in an orderly and predictable manner, rendering the mixed feedstock 148 more uniform and enhancing heat transfer between the feedstock 148 and the heat transfer surface 129 provided by bottom wall 116.
Further, whereas the flow pattern followed in mixing apparatus 10, wherein the direction of flow of scraped feedstock material S, as indicated by arrow F in
In a like manner, as seen somewhat diagrammatically in
Scraper blade 200 is mounted upon a bracket 206 carried by vertical support member 154, the bracket 206 extending rearwardly to space the scraper blade 200 from trailing face 204 in a rearward direction, relative to the direction of rotation RR of the mixing blade assembly 140. With scraper blade 200 engaged with heat transfer surface 125 of the side wall 114 at an angle θθ, and apex 66 of the vertical support member 154 spaced a short distance from the side wall 114, feedstock material MM adjacent side wall 114 passes through an entrance portion 210 of passage 205 where the passage 205 contracts along leading face 202 and, by virtue of angle αα, is urged into a narrow constriction, shown in the form of a throat TT at an intermediate portion of passage 205 where the feedstock material MM is squeezed between the apex 66 and the side wall 114, forcing the feedstock material MM against the side wall 114, thereby generating additional shear within the feedstock material MM.
As the feedstock material MM passes out of throat TT and along an exit portion 212 of passage 205, where the passage 205 expands along the trailing face 204, a pressure drop occurs within the feedstock material MM, by virtue of angle ββ. Thus, the leading face 202 and the trailing face 204 establish portions 210 and 212 of passage 205 which, in combination with the intermediate portion of passage 205 at narrow throat TT, act in concert to create additional shear in feedstock material MM for enhanced mixing. At the same time, the trailing scraper blade 200, spaced rearwardly from trailing face 204, directs the feedstock material MM toward the helical mixing blade 142, allowing the mixing blade 142 to pick up the feedstock material MM and move the feedstock material MM toward the top end 118 of side wall 114, enabling the scraped feedstock material MM to be moved in an orderly and predictable manner, rendering the mixed feedstock 148 more uniform and enhancing heat transfer between the feedstock 148 and the heat transfer surface 125 provided by the side wall 114.
Scraper blades 200 and 190 preferably are constructed of a flexible material enabling the scraper blades 200 and 190 to conform closely to the respective side and bottom walls 114 and 116 for effective scraping of feedstock material M and MM to accomplish the objectives of the present invention.
It will be seen that the present invention attains all of the objects and advantages summarized above, namely: Provides a mixing blade assembly in which a mixing blade support structure includes support members constructed to increase the effectiveness of the mixing blade assembly in mixing a batch of feedstock in a mixing vessel; facilitates heat transfer between a batch of feedstock and the walls of the vessel within which the feedstock is mixed, for attaining increased uniformity throughout the batch in less mixing time; reduces resistance to efficient circulation of feedstock within a batch of feedstock being mixed in a mixing vessel, with a concomitant reduction of energy needed to complete a mixing operation; provides a mixing blade assembly placed within a mixing vessel with an additional mixing mechanism, which mixing blade assembly is constructed to interact with the additional mixing mechanism to assist in circulating feedstock within the batch for increased effectiveness of both the mixing blade assembly and the additional mixing mechanism; attains a more uniform mixture within a batch of feedstock in less time and with the consumption of less energy; simplifies the maintenance of a mixing blade assembly for economical long-term operation; provides a rugged mixing blade assembly capable of exemplary performance over an extended service life.
It is to be understood that the above detailed description of preferred embodiments of the invention is provided by way of example only. Various details of design, construction and procedure may be modified without departing from the true spirit and scope of the invention, as set forth in the appended claims.
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