A tank with a double stirring system, primarily a curdling tank

Abstract: In tanks (2) consisting of two upright, mutually intersecting, circular cylindrical tank sections, each having a concentrically operating stirring system (6,8), the bottom portions (18,20) are shaped such that they are sloping to form respective concentric bottom grooves with downwardly pointed cross section, the lowermost portions (22) of which meet or overlap each other midway between the two shafts (6). Hereby is formed a lowermost groove system (22) shaped as the figure of eight and from which an effective emptying can be achieved through a single outlet (26).

Description: The present invention relates to a tank of the type specified in the introductory clause of claim 1, i.e. a tank often referred to as a "figure-eight tank". The two opposed stirring systems operate in synchronism and with such a mutual phase displacement between the stirring blades that these blades are alternately and freely movable through the container space portion that is common to both of the container sections, viz. in the overlapping area therebetween. It has been found that tanks of this type, i.e. with a cross section as a figure of eight and with two simply rotating stirring devices, are highly suitable for a desirable treatment of the mass of cheese coagulum which is produced in the tank, suspended in whey, where it is important that the coagulum grains be kept uniformly suspended in the whey, as they will otherwise sink down and choke the outlet. By the end of their stay in the tank the grains are to be pumped out together with the whey for delivery to a further processing equipment, and it is desirable that this delivery can take place as an even flow, without occurance of any concentration of the grains towards the end of the outflow from the container, as it may otherwise be difficult to achieve an effective emptying of the container. Also for this reason it is important that the stirring devices operate quite closely to the bottom surface. However, the final delivery from the bottom area gives rise to problems anyway. An effective final outflow is conditioned by the bottom areas underneath the stirring devices not being horizontally disposed, as they should slope downwardly towards the outlet, this most naturally being obtained by shaping the bottom areas conically, such that they form a downwardly narrowing well adjacent to each of the stirring shafts. The stirring blades may still operate immediately above the bottom surfaces, as they can be shaped with their lower edges extending outwardly and upwardly inclined corresponding to the bottom shape of the single container sections. Only it has to be accepted hereby that in the transition area between the two container sections a bottom elevation will occur. This elevation is a natural consequence of the intersection between the two conical bottom areas, and it makes no change in the fact that a very efficient final emptying of the two conical bottom areas is achievable. However, as known by the experts, the elevation gives rise to the drawback that it is required to make use of two mutually separated outlets from the tank, which can cause troubles, particularly towards the end of the emptying, where one bottom section may run dry before the other or even be found to be totally blocked by a compact mass of coagulum in the entire respective bottom area, this involving a considerable waste of coagulum. It should be briefly mentioned that in curdling tanks not only a stirring is to be effected, but also, at an intermediate phase, a cutting function which is achieved i.a. by reversing the direction of rotation of the stirring devices, whereby a stirring grating is changed into a cutting grating operating to cut the coagulated milk mass into coagulum pieces that deliver whey from the cut surfaces and thereby shrink considerably, viz. so as to form the said coagulum grains in the surrounding whey. Coagulum parts that are left uncut will in stead be converted into a crumbled mass, which can later on be difficult to separate from the whey, and it is extra important, therefore, that the stirring and cutting blades or gratings reach as far as possible towards the side and bottom faces of the tank. In this respect an entirely flat bottom is ideal, but such a bottom gives rise to special emptying problems, because a considerable tilting of the tank will be required for ensuring an efficient emptying through an outlet, and this is why other possibilities such as the first mentioned arrangement have been tried, though then with a required accept of other drawbacks. In EP-A-0,315,623, a tank is disclosed in which an outlet is arranged beneath each of the stirring shafts. The bottom, as usually, is arranged to slope downwardly from the side walls to the respective outlets, but the bottom between and just around the two outlets is kept horizontal and flat, and the outlets are arranged slightly excentrically relative to the axes of the stirring rotors. These in their turn are made with shafts which are held in bearings at the top only. Hereby there are no bottom bearings to cause disturbance in the outlet areas, and the stirring blades may sweep closely over the outlet holes. This may be operatively addvantageous, but the use of only top mounted rotors requires a very expensive construction, and besides, there will still exist a flat bottom portion which is difficult to empty, and still there is disclosed the two separate outlets. The ideal solution would be a fixed tank having downwardly narrowing bottom areas, at which an outlet is provided only at a single place, and it is just this, which is aimed at and achieved by the present invention. The invention is based on the consideration that a downwardly narrowing bottom configuration should not necessarily result in a single pointed structure, but in stead and with almost the same effect in a roundgoing groove which, when horizontally disposed, can be provided with an outlet just somewhere along the length thereof; by the final emptying a small amount of material will then be able to collect along the bottom of the groove, but in a groove of pointed cross section this amount will be very small. In this manner it is possible to provide for a spacing between the outlet area and the respective middle points of the container sections, viz. such a considerable spacing that the two container sections can meet or overlap each other in the said transition area, whereby an interjoined system of bottom grooves in the two sections may be obtained in a common level, and this entire system may very well be emptied through but a single outlet. Accordingly, the invention is characterized by the features stated in the characterizing clause of claim 1. It will even amount to a constructional advantage that the outlet opening may thus be arranged spaced from the stirring shafts, as it will not then be necessary to provide for any combination of an outlet opening and a shaft bearing. Further advantages will be connected with the invention, as apparent from the following. In the following the invention will be described in more detail with reference to the drawing, in which:- Fig. 1 is a perspective view of a tank which can represent both the prior art and the invention, Fig. 2 is a top view thereof, Fig. 3 is a side view of a known tank bottom, Fig. 4 is a corresponding view of the tank bottom according to an embodiment of the invention, and Fig 5 is a perspective view of the bottom area of a tank according to the invention. Figs. 1 and 2 show a tank2 consisting of two circular cylindrical tank sections that are built together in such a manner that they are open towards each other through a chord plane 4. In each of the sections there is mounted a stirring device comprising a central shaft 6 and a agitator and cutter blade 8, which project radially from the shaft 6, the blades 8 here being shown only schematically as a number of agitator wings. For each of the said sections this blade 8 extends outwardly very closely to the inside of the surrounding tank plate, and the tank sections are joined with such mutual locations that during their rotation each of the stirring blades will be moved past the opposite shaft 6 in a short distance therefrom, this being most clearly seen in Fig 2, such that the stirring blade in one section may agitate the tank contents located immediately at the center line of the opposite section, where the agitation effect would otherwise be very low. Usually the two tank sections, as illustrated in Fig. 3, are shaped with downwardly pointed, conical bottom portions 10 in which, at the lower end of the shafts, there are provided respective outlet openings 12; in the meeting area between these two bottom portions an elevation 14 will occur which necessitates the use of two mutually separated outlet openings 12, and as mentioned above this implies certain drawbacks. It will be noticed that the lower end of the stirring wing 8 has to be outwardly and upwardly inclined in such a manner that in order for it to sweep along bottom portion 10 it must have the outer portion of its lower edge 16 located at a height such that the wing gets no possibility to closely sweep the bottom area adjacent to the lower end of the shaft 6 in the opposite tank section. Moreover, it can be problematic to arrange a lower rotation bearing for the shaft 6 in just the same area in which an outlet opening 12 should be provided. According to the invention the tank bottom is produced with a profilation as shown in Fig. 4. The areas between the shafts 6 and the respective outer tank sides are subdivided in an inner or central area 18, in which the bottom is conically upstanding, and an outer edge area 20, in which the bottom is inwardly and downwardly sloping, such that about each of the shafts 6 a circular, groove shaped bottom area 22 will be shaped midway between the center and the surrounding tank side plate. In the transition area between the two tank sections these areas will be coinciding, as shown in Fig. 4, and when an outlet stub 24 is provided in or under this groove area it will be possible to drain off liquid and coagulum through this sole stub from the groove areas 22 in both of the opposed tank sections. As shown in Fig. 4 the stirring blades 8 can be shaped such that their lower edges closely follow the contour of the associated bottom portions, whereby they will each, at their outer end, sweep closely past the opposite stirring shaft also along the entire lower portion thereof, which, per se, is an important advantage over the system according to Fig. 3. It is true that the stirring blade of each of the shafts extends entirely down to the lower end of the shaft, but in the vicinity of the shaft the stirring effect will be weak, so it is extra important, therefore, that this area be periodically passed or swept by the outer end of the stirring blade of the opposite shaft. In the known tanks it can amount to a problem that just in the critical areas immediately above the outlet openings there will be no efficient agitation, and it will be appreciated that this problem is eliminated by the invention. In the illustrated tank according to the invention the lower edge of the stirring blade of each shaft 6 will follow the bottom contour in the blade position, in which the blade points directly against the opposite shaft, as illustrated in Fig. 4. The outer half of the lower edge of the blade here extends outwardly and upwardly along the generator of the opposite bottom cone 18 which is directed towards the middle of the bottom. During its rotation to and from this position the same lower edge portion will not extend down to the bottom in the sweeping areas located between the said middle position and the places, where the two bottom sections meet with each other. Thus, in these areas each of the stirring blades will not sweep closely above the bottom portion of the opposite section, but these bottom portions are swept by their own associated stirring blade, and the areas are located substantially spaced from their associated shafts 6, such that the blades are here moved with a substantial speed and thus also with a resulting good agitation effect. Thus, it cannot be said that the problems have just been moved to somewhere else, where they would be just as difficult. The entire outflow area 22 will be subjected to a quite efficient agitation. By comparing Figs. 3 and 4 it will be readily appreciated that the building height of the tank bottom will be substantially smaller in connection with the invention than according to Fig. 3. Particularly from Fig. 5 it will be clear that the grooves 22 of both of the tank sections will exhibit a common area adjacent to the middle outlet 24. The groove system will be shaped as a figure eight, which is horizontally disposed, when the bottom is generally horizontally disposed. The groove system will be widely emptied even if the outlet is placed at some other place, e.g. at one end of the system. Optionally the bottom may be slightly downwardly inclined towards such a place, whereby the final emptying will be promoted, but even when the bottom is generally horizontal the emptying takes place quite effectively, and afterwards it is easy to clean the tank by flushing out the small amount of coagulum that is left in the groove system. From a constructive point of view it is highly advantageous that it is possible to provide fixed rotation bearings for the shafts 6 at the top portions of the respective central bottom cone portions, without this in any way influencing the outflow conditions, this being an important deviation from the tank according to Fig. 3. With a chosen inclination of the bottom portions the shaping of the tank bottom will be accurately geometrically determined if based on the condition that the stirring blades shall sweep closely past the respective opposite stirring shafts 6, but if this condition is slackened, then the design may be modified, e.g. resulting in a broader width of the common groove system 22. The cone angles of the inner and outer bottom cones, respectively, should not necessarily be identical. A further possibility would be to combine more than two tank sections, as one or more sections could be added both lengthwise and crosswise. It should be remarked that that the new design of the tank bottom presents noticeable advantages also in such cases where two bottom outlets may be tolerated. Hereby the opposed two groove systems should not necessarily communicate with each other.

Claims: A tank with a double stirring system, primarily a curdling tank, shaped as a vertically oriented container (2) comprising two mutually intersecting, circular container sections, each of said circular container sections including a stirring device having a vertical drive shaft (6) for rotation of at least one partly open stirring blade (8) radially projecting from said drive shaft (6), said stirring blade (8) extending from the drive shaft (6) substantially to a side wall of the respective circular container section and extending substantially from a top of each of the circular container sections to the bottom portion thereof, the bottom portion including closeable outlet means (24) located at a lower area of the bottom of the cylindrical container sections, said bottom of each container section being downwardly inclined from said side walls towards said lower area, characterized in that said lower bottom area of each container section is arranged as a ring-shaped area (18,20) around the drive shaft (6), the ring-shaped area (18,20) having a groove (22) concentric to the drive shaft (6), the bottom being downwardly inclined towards this groove (22) both inwardly (20) from the outer side wall and outwardly (18) from the area adjacent the drive shaft (16), these circular grooves (22) of the respective opposed container sections meeting each other between the drive shafts (6) of these sections. A tank according to claim 1, in which the stirring blades (8) on the two shafts (6) are radially projecting almost as far as the distance between the shafts (6), such that they each will sweep closely past the opposite shaft, characterized in that the lower edges (26) of the stirring blades extend corresponding to the shape of the groove profile (20, 22, 18) in such a manner that the outer and lower blade portions will sweep closely past the lowermost portions of the respective opposite shafts (6). A tank according to claim 1, characterized in that the circular bottom grooves (22) have a radius equal to the half of the distance between the opposed shafts (6). A tank according to claim 1, characterized in that the closeable outlet means are arranged as a single outlet stub (24) at a meeting area between the two grooves (22).

Inventors: CHRISTENSEN JENS ERIK, CHRISTENSEN, JENS ERIK
Applicants: APV PASILAC AS, APV PASILAC A/S
Application year: 1991
Main classification: A01J25
IPC codes: A01J25