US20090134173A1

US20090134173A1 - Baffle System for a Vessel

Info

Publication number: US20090134173A1
Application number: US11/945,011
Authority: US
Inventors: Xiaoting Liang; Guy Wilkerson; John Minor; Albert P. Yundt, Jr.
Original assignee: Paul Mueller Co
Current assignee: Paul Mueller Co
Priority date: 2007-11-26
Filing date: 2007-11-26
Publication date: 2009-05-28

Abstract

A vessel has an annular upstanding wall and a bottom that together define an inner shell adapted to hold a vessel media. A baffle system is disposed in an interior of the inner shell and comprises a plurality of baffle portions each being generally an elongate planar member with a length edge and a width edge, and a tab projecting from the length edge. Each of the baffle portions is mounted to the upstanding wall at their respective tab with one of the baffle portion above the second baffle portion and a space therebetween.

Description

BACKGROUND OF THE INVENTION

The disclosed embodiments relate generally to a baffle system for a vessel, and, more particularly, the disclosed embodiments show a baffle system with improved ability to resist cracking from thermal fatigue.
Vessels are commonly used to mix various media in batch operations. When agitation is required in connection with the batch operation, baffles are commonly used in the vessel to promote the mixing of the media in the vessel. Generally, the baffles are arranged around an inner diameter of the vessel and baffle supports mount the baffle to a vertical wall of the vessel. The baffles generally run the full height of the vessel and the baffle supports position each baffle to be close to the vertical wall but with a gap therebetween to allow the vessel media to flow around the baffle.
Often batch operations require alternate heating and/or cooling of the vessel and the vessel media. To facilitate such heating or cooling steps, the vessel frequently includes a heat transfer jacket surrounding the vertical sidewalls and sometimes on the vessel bottom head. Hot or cold fluids flowing through this jacket then add or remove heat from the vessel and its contents.
Empty vessels used in food, beverage, cosmetic or pharmaceutical manufacturing are frequently sanitized or sterilized using steam. The vessel must then be cooled down before manufacturing operations may commence. During this cooldown period, coolant flowing through the jacket brings the vessel wall down in temperature much faster than the baffles. This difference occurs because the vessel wall directly contacts the cold fluid flowing through the jacket, while the baffle is cooled indirectly through the baffle supports and air in the vessel. As a result, the baffle supports experience high stresses caused by differential thermal expansion of the vessel wall compared to the baffles. The baffle supports are rigidly attached to both vessel wall and baffle, and so must bend in response to differential thermal expansion. Baffle supports on larger and taller vessels must handle a greater change in length between baffle and vessel wall, and therefore frequently experience problems with cracked baffle supports.
In addition to the loss of mechanical integrity of the baffle support, cracked baffle supports create cleaning problems for the vessel. Many applications in the food, beverage, cosmetic, and pharmaceutical industries require the inner shell of the vessel to be cleaned at the beginning of the batch. Cracks in the baffle supports often cannot be adequately cleaned using the vessel's clean-in-place (CIP) apparatus. This may place the vessel media at risk for contamination, and possibly scrap.

SUMMARY OF THE DISCLOSED EMBODIMENTS

The disclosure describes a baffle system that reduces the likelihood of cracking in baffle supports. One disclosed embodiment is a vessel with a generally cylindrical upstanding wall and a bottom spanning the wall. The wall and bottom define an inner shell adapted to hold a vessel media. A baffle system is disposed in an interior of the inner shell. The baffle system comprises a plurality of baffle portions, each being generally elongate planar members with a length edge and a width edge, and a tab projecting from the length edge. The preferred location for the tab is near the midpoint of the length edge. The plurality of baffle portions are secured to the upstanding wall by their respective tabs with the first baffle portion positioned above the second baffle portion with a space therebetween.
Another disclosed embodiment is a vessel with a cylindrical upstanding wall and a bottom spanning the wall to form an interior adapted to hold a vessel media. The vessel has a first baffle portion being a generally elongate planar member with a length edge and a width edge, and a first tab projecting from the length edge. The first tab secures the first baffle portion to the upstanding wall with the baffle portion length edge aligned generally parallel to and spaced from the upstanding wall. The vessel also has a second baffle portion being a generally elongate planar member with a length edge and a width edge, and a second tab projecting from the length edge. The second tab secures the second baffle portion to the upstanding wall with the length edge aligned generally parallel to and spaced from the upstanding wall. The second baffle portion is arranged below the first baffle portion with a space between the width edges of the first and second baffle portions.
Further features and advantages of the disclosed embodiments, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate various embodiments of the disclosure.

FIG. 1 illustrates a vessel as disclosed herein with its front section cut away to show the internals of the vessel including an inner shell, an agitator, and the improved baffle system;

FIG. 2 illustrates a partial cut away view of the outer jacket, inner shell and baffle system;

FIG. 3 illustrates an outer edge view of the baffle system of FIG. 2; and

FIG. 4 illustrates a detail view of a baffle portion of the baffle system of FIG. 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to the accompanying drawings in which like reference numbers indicate like elements, FIG. 1 indicates a bioreactor vessel 20 employing the baffle system with increased resistance to cracking. The vessel 20 comprises a heat transfer jacket 22 that surrounds an inner shell 24. Both the heat transfer jacket 22 and inner shell 24 may be formed from a corrosion resistant material like stainless steel. The vessel 20 may also have a layer of insulation or be covered by lagging 26 to better control temperature in the vessel. Flow channels 28 are formed between the heat transfer jacket 22 and the inner shell 24 for containing a heat transfer fluid for controlling the temperature of the vessel. For instance, the vessel may comprise a “dimpled jacket,” in which the heat transfer jacket 22 is stamped into a three dimensional quilted shape with holes at the bottom of each embossment that are in turn then plug-welded to the inner shell to form “dimples,” thereby allowing the heat transfer fluid to flow around the “dimples” between the inner shell and jacket (see for instance U.S. Pat. No. 4,305,456). Alternatively, the vessel may comprise an “inflated jacket,” in which the heat transfer jacket comprises a relatively thin material that is spot welded to the inner shell, such that under high pressure (e.g., 500 psi to 3000 psi), the heat transfer jacket permanently bulges outward between the spot welds, thereby allowing the heat transfer fluid to flow around the spot welds between the inner shell and heat transfer jacket. Alternatively, the vessel may comprise a “half-pipe jacket”, in which a coil with “c” cross-section is welded to the outside of the inner shell to form a heat transfer jacket comprising a coil-like channel that surrounds the inner shell and contains the heat transfer fluid. In each case, the flow channels contain the heat transfer fluid, which is most often steam, water, or a glycol solution and may be introduced into the flow channels from an inlet nozzle 30 or 66, circulated through the flow channels around the exterior of the inner shell, and discharged from the flow channels through an outlet nozzle 32. A pump (not shown) may circulate the heat transfer fluid through the flow channels and through a heat exchanger (not shown) that regulates the temperature of the heat transfer fluid.
The vessel has a top head 34 with an access opening 36 that extends over the top of the vessel. The vessel includes a mechanism to remove the agitator for service. This may comprise a removable head, or the access opening 36 on the top head 34 may be sized large enough to pass the agitator impeller blades. Removable heads are typically used on smaller vessels, and access openings on larger ones. A vessel with an access opening is shown in FIG. 1. The heat transfer jacket 22 frequently extends on the bottom head. There is a continuous seal weld to the vessel sidewall at the upper and lower edges 42,44 of the heat transfer jacket 22. The vessel may be supported by either legs (not shown) or mounting lugs 38.
The inner shell 24 comprises a cylindrically shaped upstanding wall 50 with bottom 52 that spans across the upstanding wall. As shown in the drawings, the bottom 52 frequently has a dish shape, although the bottom may alternatively be conical, flat or hemispherical. The upstanding wall 50, top 34, and bottom 52 define an interior 54 adapted to hold the vessel media. A baffle system 60 is arranged vertically on the upstanding wall extending the height of the wall. A nozzle 68 may admit clean steam through the vessel top 34 into the interior of the inner shell to assist in sterilization of the vessel. An agitator 70 extends through the vessel bottom 52 into the inner shell interior for mixing the vessel media. The agitator may alternatively be mounted on the access opening with a longer shaft so the impellers end up in the same location shown. A mixture of pressurized gases such as nitrogen, process air and carbon dioxide may be introduced into the interior of the inner vessel through a nozzle 71 opposite a vent 72. Sparge gases may be introduced through the lower side wall to sparge wands 73 located beneath the bottom impeller of the agitator. The reactor vessel may also be provided with a rupture disk 74 to relieve over pressure of the vessel.
FIGS. 2 and 3 show further detail of an embodiment of the baffle system 60. The baffle system comprises three baffle portions 84 extending the length of the upstanding wall of the inner shell. While three baffle portions are shown in the drawings, it should be appreciated that any number of baffle portions may be used, preferably using the design criteria described below. Preferably, the length of the baffle portions and the number of baffle portions used are varied in accordance with the size of the vessel, length of the upstanding wall and strength of the vessel wall and baffle support materials of construction. For vessels made from austenitic stainless steels type 304L or 316L, the maximum baffle portion length is preferably between 40 inches and 42 inches, with each baffle portion being approximately the same length. Thus, in a vessel having a 126 inch high upstanding wall, three baffle portions approximately 41½ inches long may be used. However, shorter baffle portion lengths may be used if the length better accommodates the vessel height. Higher strength vessel materials of construction, such as duplex stainless steel 2205, allow longer length baffle portions. Additionally, the number of baffle sets spaced about the inner shell may be varied in accordance with the size of the vessel. Three or four sets are most common, but one or two sets of baffles may be used on a vessel having a relatively small diameter and low power input from the agitator. As shown in FIGS. 2 and 3, each of the baffle portions has the same length such that each baffle portion extends along the upstanding wall an equal amount with the three baffles portions together covering the entire length of the upstanding wall. As shown in FIGS. 2 and 3, the baffle portions are arranged above each other in a line so that the three baffle portions form a generally vertical plane projecting from the upstanding wall into the interior of the inner shell. The baffle portions may also be placed above one another in a staggered pattern around the vessel's circumference instead of in the vertical plane shown in the drawing figures. In such a staggered pattern, the baffle portion width edges are not aligned, and additional steps must be taken during CIP to assure that all baffles surfaces are completely wetted. The baffle portions are arranged adjacent to each other with a small gap 85 between adjacent portions. Generally speaking, a ⅛ to ¼ inch gap is preferred. The gap allows for thermal expansion, so one baffle portion does not touch another during empty vessel heating or cooling. It also allows the cleaning solutions to cascade from one baffle portion to the one beneath it, as well as vessel media to flow through and around the adjacent baffle portions with little adverse effect on agitation of the vessel media.
FIG. 4 shows greater detail of a typical baffle portion 84 of the baffle system. The baffle portion 84 is an elongate planar member, preferably generally rectangular in shape, with a length edge 86 and width edge 88. Preferably, a generally rectangularly shaped tab 90 preferably projects from about or at a midpoint of a length edge 86. The length of the tab may correspond to ¼ to ⅓ of the baffle portion length. Preferably, the tab 90 is positioned on or near the midpoint of the baffle portion length edge to reduce stresses caused by fluid forces during agitation. Preferably, the baffle portion and the tab are monolithically formed from the same piece of material. The tab may be directly welded to the upstanding vessel wall, and preferably, the weld is ground to a relatively smooth surface finish (such as 15 to 25 microinch Ra or lower). For instance, the tab may be formed with an abutment surface 92 along its distal edge that is secured to the upstanding wall 50. The abutment surface 92 may be conditioned as needed for welding. The tab may be rectangular as shown, or arc or yoke shaped, with its two outside corners welded to the upstanding wall and a center portion of the tab being relieved. The tab may also project from the baffle portion at a location other than the midpoint of the length edge. Generally speaking, the tab 90 holds the baffle portion away from the upstanding wall 50 with a gap 96 between ⅙ to about ⅓ of the baffle's width. Preferably, the length edge 86 is generally parallel to the upstanding wall 50. The gap 96 allows the vessel media to flow around the baffle portion 84 during agitation, thereby preventing the formation of dead spots or stagnated zones. Fillets 98 are placed in the corners of the tab 90 and the baffle portion 84 to reduce stress created by agitation of the vessel media and stress from any temperature gradient across the tab created during the switchover between heating and cooling of the vessel. Corners 100 formed by the baffle portion length edges 86 and width edges 88 are rounded to promote the even flow of clean-in-place fluids around the baffle portion 84. Creating rounded outer edges 102 and rounded corners 100 and fillets 98 allows clean-in-place fluids to gravity flow from the exposed faces of the topmost baffle portion to the exposed faces of the next adjacent bottom baffle portion.
The general principles of the baffle system described above may be applied to a vessel comprising a 20,000 liter bioreactor having an inner shell approximately 14 feet high with a diameter of 9 feet. Four sets of baffles may be provided equiangularly spaced about the circumference of the inner shell with each set comprising four baffle portions extending along the vertical wall of the inner shell. Each baffle portion may be approximately 41 inches long, 9 inches wide, and ⅜ inches thick. The tab of each baffle portion may be 10 inches long and the vertical gap between adjacent sections may be ⅛ to ½ of an inch with ⅛ to ¼ of an inch being preferred. The baffle and tabs may be formed monolithically from 316L stainless steel. The tabs may have a 3/16 inch groove at the abutment surface and be welded to the upstanding wall with an ¼ inch fillet weld. This particular configuration has been found to improve crack resistance for the baffle system when the vessel is subjected to a heat transfer fluid temperature of 2° C. and an initial vessel temperature of 125° C.
The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.

Claims

1. A vessel comprising:

a generally cylindrical upstanding wall and a bottom spanning the wall, the wall and bottom defining an inner shell adapted to hold a vessel media; and

a baffle system in an interior of the inner shell comprising a plurality of baffle portions each being an elongate planar member with a length edge and a width edge, and a tab projecting from the length edge, the plurality of baffle portions being secured to the upstanding wall solely by their respective tabs with one of the plurality of baffle portions positioned above another of the plurality of baffle portions with a space therebetween.

2. The vessel of claim 1, wherein the plurality of baffle portions are aligned to form a generally vertically planar baffle.

3. The vessel of claim 1, wherein the width edges of each of the baffle portions are aligned.

4. The vessel of claim 1, further comprising fillets between the tab and the respective baffle portion.

5. The vessel of claim 1, wherein the tab and the respective baffle portion are monolithically formed.

6. The vessel of claim 1, wherein the length and width edges of the baffle portion are formed with edges that are rounded.

7. The vessel of claim 1, wherein the tab is welded to the upstanding wall.

8. The vessel of claim 1, wherein the tab and the respective baffle portion have the same thickness.

9. The vessel of claim 1, wherein the baffle portions and the upstanding wall are made from the same material.

10. The vessel of claim 1, wherein each of the baffle portions are the same length.

11. The vessel of claim 1, wherein each of the baffle portion is generally rectangular in shape.

12. The vessel of claim 1, wherein the tab is arranged about or at a midpoint of the respective baffle portion.

13. A vessel comprising:

a cylindrical upstanding wall and a bottom spanning the wall to form an interior adapted to hold a vessel media;

a first baffle portion being a generally elongate planar member with a length edge and a width edge, and a tab projecting from the length edge, the tab solely securing the first baffle portion to the upstanding wall with the baffle portion length edge aligned generally parallel to and spaced from the upstanding wall; and

a second baffle portion being a generally elongate planar member with a length edge and a width edge, and a tab projecting from the length edge, the tab solely securing the second baffle portion to the upstanding wall with the length edge aligned generally parallel to and spaced from the upstanding wall;

wherein the second baffle portion is arranged below the first baffle portion with a space between the width edges of the first and second baffle portions.

14. The vessel of claim 13, wherein the first and second baffle portions are aligned to form a generally planar baffle.

15. The vessel of claim 13, wherein the width edges of the first and second baffle portions are aligned.

16. The vessel of claim 13, further comprising fillets in the corners of each tab and baffle portion.

17. The vessel of claim 13, wherein the tab and respective baffle portion are monolithically formed.

18. The vessel of claim 13, wherein the length and width edges of each baffle portion form edges that are rounded.

19. The vessel of claim 13, wherein the tab and respective baffle portion have the same thickness.

20. The vessel of claim 13, wherein the first and second baffle portions are the same length.

21. The vessel of claim 13, wherein the first and second baffle portions and the upstanding wall are made from the same material.

22. The vessel of claim 13, wherein each of the tabs is generally rectangularly shaped.

23. The vessel of claim 22, wherein each of the tabs has an abutment surface extending along its length spaced from the length edge of the respective baffle portion, and each baffle portion is mounted to the upstanding wall at the tab abutment surface.