The present invention relates to apparatus for stabilising an agitator shaft. More particularly, it relates to apparatus for stabilising an agitator shaft which does not impede the removal of material from a vessel in which the stabilizing apparatus is located. Still more particularly, it relates to apparatus for stabilising an agitator shaft which includes a vortex breaker. In a further arrangement, it relates to a mixing vessei, such as a reactor, including the apparatus which stabilises the agitator shaft.

Various processes require constituents such as ingredients to be mixed. In some arrangements the constituents to be mixed are fluids or both fluids and solids. Generally, the constituents are mixed in a mixing vessel to form a desired mixture. In chemical processes the constituents to be mixed may be reactants and/or other constituents required for the reaction such as catalysts. These constituents may be mixed in the mixing vessei before being transferred to a reactor. Alternatively, the mixing may occur in the reactor such that mixing and reaction occur simultaneously. In this arrangement, what is removed from the mixing vessel will be the product of the reaction, optionally together with un reacted components. In many reactions, mixing of the reactants is required to ensure sufficient contact therebetween such that effective or improved reaction can take place. In one arrangement the reactants to be mixed will be liquids. In another arrangement, at least one liquid reactant will need to be mixed with a gaseous reactant. In addition one or more solids may be present with the liquid and/or gaseous reactants.

Whilst various mechanisms may be used to facilitate the mixing, mechanical mixers, which agitate the constituents, are conventionally used to provide the required level of mixing. These mechanical mixers may be powered by a drive unit such as an electric motor. The drive unit, which is generally located outside the mixing vessel, drives a rotatabie shaft to which impeller blades are attached. As the drive unit is operated, the rotatabie shaft is rotated which in turn rotates the impeller blades thereby facilitating mixing of the constituents in the mixing vessei.

In its simplest form the end of the rotatabie shaft remote from the drive unit is not attached and so is a free end. This arrangement is simple and hence has low manufacture costs. However, since the free end is unattached, the rotatable shaft can sway and/or vibrate during use which can result in incomplete mixing and may result in wear of the mixing apparatus particularly where the rotatable shaft is connected to the drive unit. This is particularly problematic in large mixing vessels where a longer rotatable shaft is required to achieve acceptable mixing.

With a view to addressing these problems, various designs to hold the free end of the rotatable shaft have been suggested. One such arrangement is a so-called 'steady bearing' assembly which is located in the mixing vessel such that it can receive the free end of the agitator shaft and thereby hold it steady as it rotates thereby preventing swaying and reducing or eliminating swaying.

Examples of steady bearings are described in US3149888 and US3489469. In this arrangement, the bearing is located outside of the mixing vessel and the rotatable shaft extends through the base of the mixing vessel before it is constrained in the steady bearing, in other arrangements, such as that described in US4660989, the steady bearing is located within the mixing vessel.

Generally the rotatable shaft will be located on the central axis of the mixing vessel to achieve optimum mixing. However, as the outlet of mixing vessels is typically located at the bottom-centre of the vessel, it is difficult to find a suitable location for the steady bearing. There is therefore a conflict between the need to locate an outlet at a bottom-centre of the mixing vessel and the requirement to locate the steady bearing at the bottom-centre of the vessel so as to ensure that the rotatable shaft is co-axial with the central axis of the vessel.

A proposed solution to this has been to mount the steady bearing at an elevated position within the mixing vessel such that both the outlet and the steady bearing can be aligned with the centre axis. Examples of steady bearings of this type are described in US2516918, US2657912, US2865615, US3443794, US3489469, US4932787, US5088832, US5568985, US5618107, US7378431 , and US7402023.

When the mixed components, or the product stream where the mixing vessel is a reactor, are withdrawn from the mixing vessel through an outlet located at the bottom of the mixing vessel, a vortex can form. Where a steady bearing is located at an elevated position above the outlet, the legs supporting the steady bearing in the elevated position and hence spaced from the bottom of the mixing vessel may themselves contribute to vortex creation.

The formation of a vortex is disadvantageous as it can result in gas being entrained in the liquid being removed from the mixing vessel. It can also lead to poor separation in downstream processes or excessive pressure drop. The presence of entrained gas can also cause cavitation in downstream pumps.

To minimise vapour entrainment in the liquid recovered from the bottom of the mixing vessel, a so-called 'vortex breaker' can be mounted directly on top of the outlet inside the vessel. These vortex breakers act to reduce some of the angular velocity of the liquid as it exits the drain.

One example of a vortex breaker is described in US8439071. The vortex breaker, which comprises a basket having cylindrical screen walls, fits over the vessel outlet. A flow modifier having vanes is located within the basket to break the radially directed flow. Other examples of vortex breakers are described in US4696741 , EP1309393, US8397751 and WO2013/096570.

Although in principle the raised steady bearings of the prior art can be used in combination with a vortex breaker, the resultant structure will suffer from various disadvantages and drawbacks. Since the support for the raised steady bearings themselves increase the vortex, their use exacerbates the problem particularly of gas entrainment which the vortex breaker has to try to minimise. This additional complication can mean that the vortex breaker is not able to effectively prevent the formation of the vortex and hence will not be able to minimise or prevent the formation of entrained gas.

Whilst the above-described steady bearing types and vortex breakers may have been satisfactory and may continue to be satisfactory in some situations, it is desirable to provide an improved arrangement which allows for both a steady bearing and a vortex breaker to be present but in a less complicated arrangement than might be envisaged using various combinations of known steady bearing types with known vortex breaker types. According to a first aspect of the present invention, there is provided an apparatus for stabilising an agitator shaft in a mixing vessel, said mixing vessel having an outlet located in a base thereof, said apparatus comprising:

a shaft-receiving bearing configured to receive an end of said agitator shaft; and

a support arrangement for supporting said shaft-receiving bearing and for spacing said shaft-receiving bearing from the outlet of the mixing vessel;

wherein said support arrangement comprises a vortex reducing formation.

Thus the apparatus of the present invention provides both a steady bearing for the agitator shaft and a vortex reducing formation. Thus the means for separating the bearing from the base of the mixing vessel provides a vortex reducing formation. Thus rather than the support increasing the likelihood of the formation of a vortex which is noted in the prior art, the support actually reduces and may even prevent vortex formation.

By providing the bearing and the vortex reducing formation as a single arrangement, the resultant apparatus is simple, elegant, mechanically stable and cheap to construct.

Since the apparatus of the present invention will reduce or even eliminate vortex formation, the amount of entrained gas in liquid exiting the vessel via the outlet will be reduced.

Any suitable vortex reducing formation may be used. In one arrangement, the vortex reducing formation is configured to reduce angular velocity of the exiting liquid. This may be achieved by the use of at least one vane. Generally a plurality of vanes will be used. These vanes may be arranged in any suitable configuration. In one arrangement the vanes may extend radially outwardly from a central axis of the apparatus to the tip of the vane. Two, three, four, five, six or more vanes may be used. Where a plurality of vanes is present they may be evenly spaced or the spacing between adjacent vanes may differ. in one arrangement, there are four substantially equally spaced vanes. In one alternative arrangement, there are six equally spaced vanes. It will be understood that the outlet may simply be an aperture in the base of the mixing vessel. However, in one arrangement, the base of the mixing vessel may be shaped to form a well-shaped outlet which extends outwardly from the base. In this arrangement, the vortex reducing formation may be configured to extend into the shaped outlet port.

The shaft-receiving bearing may be of any suitable configuration. Similarly the support arrangement may be of any suitable configuration. In one arrangement, it may be configured as a platform having three or four supporting legs.

The shaft-receiving bearing may be a separate component of the apparatus or it may be integrally formed with the support arrangement.

The support arrangement may further comprise a flange extending therefrom. The flange may define a circumferential rim extending laterally from said shaft- receiving bearing and said support arrangement. In use the flange assist in directing material to be removed from the mixing vessel to the outlet port. It may also minimise perturbation which may be caused at the outlet port interfering with the operation of the shaft-receiving bearing.

It will be understood that the apparatus of the first aspect of the present invention may be manufactured from any suitable material. The materials selected will depend on the use to which the mixing vessel is to be put. For example, where the mixing vessel is a reactor, the reaction conditions to which the apparatus will be exposed will determine the material to be selected. In one arrangement, metals will be used.

According to a second aspect of the present invention there is provided mixing apparatus comprising:

a mixing vessel comprising an in let port and an outlet port;

an rotatable agitator shaft extending into the mixing vessel;

an impeller attached to the rotatable agitator shaft; and

apparatus for stabilising the agitator shaft according to the above first aspect, said apparatus being located within the mixing vessel and secured to an internal surface thereof such that said stabilising apparatus is located over the outlet port and the rotatabie agitator shaft is received in the shaft-receiving bearing.

The mixing vessel may be a reactor.

The apparatus for stabilising the agitator shaft may be of any suitable size. In one arrangement, the distance between a tip of a first vane and a tip of a second vane is from about 1.5 to about 3 times, optionally about 2 to about 2.5 times, the width of the outlet port. Where the outlet port is of circular cross section, the distance will be about 1.5 to about 3 times, optionally about 2 to about 2.5 times, the diameter of the outlet port.

The apparatus may be of any suitable height. In one arrangement, the stabilising apparatus may be of a size that the shaft-receiving bearing is spaced from the outlet port by a distance of from about 1.5 to about 2.5 times, optionally about twice, the width of the outlet port. Where the outlet port is of circular cross section, the distance is of from about 1.5 to about 2.5 times, optionally about twice, the diameter of the outlet port.

In one alternative arrangement, the height of the apparatus of the first aspect of the present invention will be of the order of from about 1 to about twice, optionally about 1.5 times, the width of the outlet port. Where the outlet port is of circular cross section, the height will be of the order of from about 1 to about twice, optionally about 1.5 times, the diameter of the outlet port.

Where the flange is present in the apparatus of the first aspect of the present invention, it may be of any suitable size. In one arrangement, it extends beyond the tip of the vanes by a distance which is about a quarter to about three quarters, optionally about half, the width of the outlet port. Where the outlet port is of circular cross section, the distance will be about a quarter to about three quarters, optionally about half, of the outlet port. In one arrangement, the flange may be formed by a disc which has a diameter substantially equivalent to three times the width of the outlet port. Where the outlet port is of circular cross section, the diameter of the flange will be from about twice to about four times, optionally about three times, the diameter of the outlet port. In one arrangement of the present invention, the vortex reducing formation extends at least partially into the outlet port. In one arrangement, it extends into the outlet port by a distance which is about one quarter to about three quarters, optionally about half, the width of the outlet port. Where the outlet port is of circular cross section, it extends into the outlet port by a distance which is about one quarter to about three quarters, optionally about half, the diameter of the outlet port.

In one alternative arrangement, a portion of the vortex reducing formation which is over the outlet port terminates at a distance above the outlet port by an amount which is about one quarter to about three quarters, optionally about half, the width of the outlet port. Where the outlet port is of circular cross section, terminates at a distance above the outlet port by an amount which is about one quarter to about three quarters, optionally about half, the diameter of the outlet port.

It will however be understood that the vortex reducing formation may terminate at any suitable position which allows the desired reduction and preferably elimination of vortex formation to be achieved.

Where the mixing vessel is a reactor which is for use in a gas liquid reaction, the mixing vessel will include means for introducing the gas to the reactor. In one arrangement, the mixing vessel will include a gas feed conduit. The gas feed conduit may be connected to a gas dispersion sparger. In one arrangement, the sparger, may comprise a gas dispersion ring. The gas dispersion ring will generally be arranged such that it encircles the apparatus of the first aspect of the present invention. The gas dispersion ring may be spaced from the apparatus of the above first aspect by a distance which is about three to about five times, optionally about four times, the width of the outlet port. Where the outlet port is of circular cross section, the distance will be which is about three to about five times, optionally about four times, the diameter of the outlet port.

The mixing vessel of the present invention may additionally include a barrier plate which is located on a bottom surface of the mixing vessel surrounding the outlet port. In one arrangement, the barrier plate may be of circular configuration, in use, the barrier piate minimises gas from the gas dispersion ring flowing to the outlet port.

The barrier plate may be of any suitable size. In one arrangement, it has a height of from about one quarter to about three quarters, optionally, about one half, the width of the outlet port. Where the outlet port is of circular cross section, the barrier plate has a height of from about one quarter to about three quarters, optionally, about one half, the width of the outlet port.

Where the barrier plate forms a circle, the diameter of the circle will be about a quarter to about three quarters, optionally about a half, of the width of the outlet port. Where the outlet port is of circular cross section, the diameter of the circle will be about a quarter to about three quarters, optionally about a half, of the width of the outlet port.

The present invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a schematic view of a mixing apparatus for mixing fluids, comprising an apparatus according to the first aspect of the present invention;

Figure 2 is an enlarged side view of a lower region of the mixing apparatus illustrated in Figure 1 ;

Figure 3 is an enlarged perspective view of the apparatus of Figure 2;

Figure 4 is an enlarged schematic side view of one arrangement the votex reducing formation;

Figure 5 is a schematic view from below of an apparatus according to the present invention in an optional arrangement;

Figure 6 is a schematic bottom plan view from below of one alternative vortex reducing formation;

Figure 7 is an enlarged schematic view from the side of a further alternative vortex reducing formation; Figure 8 is an enlarged schematic view from the side of a stili further alternative vortex reducing formation; and

Figure 9 is an enlarged schematic side view of apparatus according to the present invention additionally including a gas feed conduit and bubble diverting means.

In particular, the present invention will be described in an arrangement in which the mixing vessel is a reactor. In particular the invention will be described with reference to a reactor for use in the hydroformyiation of an alkene to form an aldehyde in which the aikene is contacted with carbon monoxide and hydrogen. A catalyst will generally be present.

As illustrated in Figure 1 , the reactor 10 comprises a reactor shell 12 having a top wall 14, a side wail 16 and a bottom wall 18. Top wail 14, side wall 16 and bottom wall 18 define a chamber 20 for containing a liquid which in the hydroformyiation reaction wili be the alkene. The reactor shell 12 may be of any cross-sectionai configuration, but generally it will be substantially cylindrical.

The reactor 10 includes an agitator which when operated mixes the reactants. A drive unit 22 such as, for example, an electric motor, mounted outside the reactor shell 12, is coupled to an agitator shaft 24, which extends into the chamber 20. When operated, drive unit 22 causes the agitator shaft 24 to rotate which in turn drives the impeller 26. The impeller 26 will general comprise a plurality of biades.

The distal end of the agitator shaft 24 engages stabilising apparatus 28. The stabilising apparatus 28 comprises a shaft-receiving bearing 30. The shaft- receiving bearing 30 permits the agitator shaft 24 to be rotatable about its longitudinal axis 31 , whilst inhibiting vibration and/or sway of the agitator shaft 24. The shaft-receiving bearing 30 may be of any suitable configuration provided that this function is achieved.

The stabilising apparatus 28 also comprises a support 32 extending downwardly from the underside of the shaft-receiving bearing 30. The support 32 may be separate from the shaft-receiving bearing 30 or may be formed integrally therewith. The support 32 supports and spaces the shaft-receiving bearing 30 from an outlet port 34 of the reactor shell 12. The stabilising apparatus 28 is suitably affixed to the bottom wall 18 of the reactor shell 12 via the support 32. The support 32 is configured such that it permits fluid flow from the chamber 20 via the outlet port 34. As the stabilising apparatus 28 is fixed by any suitable means to the bottom wai! 18 of the reactor shell 12, the support 32 provides a steady base for the shaft-receiving bearing 30.

The support arrangement 32 comprises a flow modifying formation, illustrated in detail in figures 2 to 8, which modifies the flow of fluid prior to exiting said mixing vessel 12 via said outlet port 34. Thus the flow modifying formation is a vortex breaker.

Fluid outlet paths 36, denoted by arrows, from the mixing chamber 20 to the outlet port 34 are defined by spaces beneath the support arrangement 32 and around the flow modifying formation of the support arrangement 32. The flow modifying formation of the support arrangement 32 is configured to influence fluid in these fluid outlet paths 36 to reduce angular velocity of fluid in the fluid outlet paths 36. Since this reduces or inhibits vortex formation it will reduce or inhibit the entrainment of gas in the fluid in the fluid outlet paths 36.

In operation, the liquid alkene 38 is introduced to the mixing chamber 20 via feed conduit 40.

Agitator shaft 24 is driven by drive unit 22 to rotate, as denoted by arrow 42, around its longitudinal axis 31. Rotation of agitator shaft 24 causes the impeller 26 to rotate within the mixing chamber 20 such that mixing occurs.

Reaction product is recovered from the mixing chamber 20 via outlet port 34. As the fluid travels toward the bottom of the mixing chamber 20 it maintains a component of angular velocity due to the influence of the impeller 26. The product stream proceeds with this angular velocity component down and around the shaft- receiving bearing 30 following the fluid outlet paths 36. The product stream then encounters the flow modifying formation of the support arrangement 32. This serves to break up the fluid flow and reduce the angular velocity component of the fluid mixture. As the angular velocity component of the product stream is reduced, the major component of the flow is a downward velocity component such that further flow of the product stream is generally in a downward direction toward the outlet port 34 from where it is passed to downstream processing or to a storage vessel as appropriate.

An enlarged side view of a lower region of the mixing apparatus in which the stabilising apparatus 28 is illustrated in more detail is illustrated in Figure 2. The flow modifying formation of the support arrangement 32 comprises a plurality of vanes. In the embodiment illustrated in Figure 2, the support arrangement comprises four vanes, only three of which can be seen, which extend radially from a centra! axis of the support arrangement 32. First vane 44 extends from the central axis in a first direction and terminates at first vane tip 46 at a point remote from the central axis. Second vane 48 extends from the central axis in a second direction opposite to the first direction and terminates at second vane tip 50 at a point remote from the central axis. Third vane 52 extends from the centra! axis in a third direction transverse to the first and second directions and terminates at third vane tip 54 at a point remote from the central axis. A fourth vane is not illustrated in Figure 2 but can be seen in Figure 6. Fourth vane 56 extends from the centra! axis in a fourth direction opposite to the third direction and transverse to the first and second directions, and terminates at fourth vane tip 58.

Portions of the lower edges of each of the vanes, denoted generally by reference numeral 60 in Figure 2, terminate at a level below the lowest level of the bottom wail 18 of the mixing vessel 12. That is, portions of each of vanes 44, 48, 52 and 56 extend downwardly into the outlet port 34.

A flange 62 extends from the stabilising apparatus 28 around a circumference of the stabilising apparatus 28. The flange 62 extends from a location between the shaft-receiving bearing 30 and the support arrangement 32. The flange 62 assists in directing the outflowing product stream to the outlet.

Figure 3 is a perspective view of the features described above in relation to Figure 2. Features illustrated in Figure 3 which are common to those illustrated in Figures 1 and 2 are denoted using like reference numerals. Some reference numerals are omitted from Figure 3 for clarity. Figure 4 illustrates an enlarged schematic side view of the support arrangement 32 in which various dimensions are denoted by reference letters D, H, S, T, and W where:

D is the diameter of an outlet port 34 of circular cross-section;

H is the distance between a point in a same horizontal plane as the lowest level of the bottom wail 18 of the mixing vessel 12 and a top of the support arrangement 32;

S is the distance by which flange 62 extends beyond the tips of the plates of the support arrangement 32;

T is the distance between the point in a same horizontal plane as the lowest level of the bottom wall 18 of the mixing vessel 12 and the lower edges 60 of each of the plates. Thus it describes the distance that the lower edges 60 are above or be!ow the mouth of the outlet port 34; and

W is the distance between the tips of oppositely extending plates of the support arrangement 32.

The dimensions can have the following relationships:

W=2D;

H=D;

T=D/2;

S=D/2.

However, these dimensions are indicative only and can be varied as deemed suitable to enable the flow required, and provide sufficient mechanical strength in the support arrangement 32 such that the shaft-receiving bearing 30 can be mounted thereon.

Figure 5 illustrates a bottom plan view of support arrangement 32. The first 44, second 48, third 52, and fourth 56 plates extend radially outward from central axis 31 and are arranged in a cross configuration. That is, first vane 44 extends in a direction opposite to second vane 48 such that first vane tip 46 is located on an opposite side of the central axis to the second vane tip 50. Third 52 and fourth vanes 56 extend in directions transverse to those of the first 44 and second vanes 48. Further, third vane 52 extends in a direction opposite to fourth vane 56 such that third vane tip 54 is located on an opposite side of the central axis to the fourth vane tip 58. Thus the vanes are equally spaced and the angle between adjacent vanes is substantially 90°.

An alternative configuration is illustrated in Figure 6. In this arrangement, the support arrangement 32 comprises six vanes arranged in a star configuration. The first vane 64, second vane 66, third vane 68, fourth vane 70, fifth vane 72, and sixth vane 74 extend radially outward from central axis 31.

First vane 64 extends in a direction opposite to second vane 66. Third 68 and fourth vanes 70 extend in different directions to those of the first 64 and second vanes 66. Further, third vane 68 extends in a direction opposite to that of fourth vane 70. Yet further, fifth 72 and sixth vanes 74 extend in different directions to those of the first 64, second 66, third 68 and fourth vanes 70. Fifth vane 72 extends in a direction opposite to that of sixth vane 74. Thus the vanes are equally spaced and the ang!e between adjacent vanes is substantially 60°.

One alternative arrangement of the support arrangement is illustrated in Figure 7, there is illustrated an optional arrangement of the support arrangement 32 of the stabilising apparatus 28. In this optional arrangement, the level at which lower edges 60 of the plates terminate is above the lowest level of the bottom wall 18 of the mixing vessel 12. This corresponds to a point above a mouth of the outlet port 34.

A still further arrangement of the support arrangement 32 of the stabilising apparatus 28 is illustrated in Figure 8. In this optional arrangement, the level at which lower edges 60 of the plates terminate is at a point in a same horizontal plane as the lowest level of the bottom wall 18 of the mixing vessel 12. This corresponds to an entrance to the outlet port 34.

Where the reactor is to be used to for the reaction of a gas with a liquid, such as in the hydroformylation reaction, the reactor 10 will include means for introducing the gas. The means can be located in any suitable position. One arrangement is illustrated in Figure 9. In this arrangement, a gas feed conduit 76 allows gas to be supplied to a gas dispersion ring 78. Thus in the hydroformylation reaction, the hydrogen and carbon monoxide are supplied through this gas dispersion ring and so can bubble through the alkane. Gas dispersion ring 78 comprises a generally toroidal conduit, which is located so that it encircles the agitator shaft 24. Generally, the centre of the torus will be coincident with a point on the longitudinal axis of agitator shaft 24. Gas dispersion ring 78 comprises pores or perforations in wails of the conduit to permit gas from the gas feed conduit 76 to be introduced to the mixing chamber.

As illustrated in Figure 9, in one arrangement, the reactor may additionally comprise plate 80 which extends upwardly from bottom wail 18 of reactor shell 12. In one arrangement, the plate 80 comprises a cylindrical plate which is located so that an axis thereof is coaxial with the iongitudinai axis of the agitator shaft and so that it encircles the stabilising apparatus.

Plate 80 acts to reduce and preferably prevent gas bubbles in the fluid mixture from reaching the flow modifying formation of the support arrangement 32, thereby further reducing gas entrainment in the product stream recovered from the reactor

10.

In Figure 9, a number of dimensions are denoted by reference letters A, F, and G, where:

A is the height of plate 80, i.e. a distance which plate 80 extends upwards from bottom wall 18;

F is a diameter of the cylinder which forms plate 80; and

G is the height of the gas dispersion ring 78 above a point in a same horizontal plane as the top of the support arrangement 32.

The dimensions can have the following relationships:

G = 4D to 6D;

F = 0.5D to 3D;

A = 0.5D to 1.5D.

The cross-sectional diameter of the gas dispersion ring 78 is typically the same diameter as that of the gas feed conduit 76. However, these dimensions are indicative on!y and can be varied as deemed suitable to enable the flow required, varied for different mixing processes, and/or varied for different fluids to be mixed.

Whilst the plate 80 will generally present where a gas dispersion ring 76 is used, it may be omitted. Similarly it may be present in arrangements where a gas dispersion ring is not used.

It will be understood that the reactor described may be used for carrying out other reactions.

All references made to orientation (e.g. top, bottom, above, below, etc.) are made for the purposes of describing relative spatial arrangements of the features of the apparatus, and are not intended to be limiting in any sense.