Patent Application
20090134173
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.
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.
The accompanying drawings, which are incorporated in and form a part of the specification, illustrate various embodiments of the disclosure.
Referring to the accompanying drawings in which like reference numbers indicate like elements,
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
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.
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.
