WO2015144718A1

WO2015144718A1 - Improvements in or relating to flow channels

Info

Publication number: WO2015144718A1
Application number: PCT/EP2015/056279
Authority: WO
Inventors: Robert Ashe; Gary ECCLESON
Original assignee: Ashe Morris Ltd
Priority date: 2014-03-25
Filing date: 2015-03-24
Publication date: 2015-10-01
Also published as: GB201405281D0

Abstract

A flow channel (1) adaptable for process material flowing continuously into and out of the channel and a drive mechanism (3) is provided to rotate the flow channel (1) around the long axis in repeating arcs of 360° or less so as to promote mixing within the flow channel (1) and the flow channel is unbalanced by means of one or more counter weights (5) which accelerate the rotation of the flow channel as the counterweight or counterweights (5) approaches bottom dead centre position and decelerate the rotation of the flow channel as the counterweight or counterweights moves away from the bottom dead centre position provides energy savings and improved mixing of the process materials.

Description

IMPROVEMENTS IN OR RELATING TO FLOW CHANNELS

The present invention relates to flow channels which may be used for the continuous flow of material which is subject to change as it passes through the channel. The change may be physical or chemical and the invention is concerned with improving the homogeneity of the change during passage of the material through the channel combined with optimising the use of energy supplied to the flow channel to cause the change to take place. The channel containing the material is rotated backwards and forwards about its axis through an arc with a reciprocating motion as described in copending applications GB 1219476.7 and 1219479.1 .

Flow channels described here refer to systems used in the process industries such as but not limited to: foods, pharmaceuticals, fine chemicals, polymers, petrochemicals, minerals, biofuels, biosynthesis and enzyme processes. Flow channels may also be used in non- industrial applications where similar needs apply. In many cases flow channels are flow reactors but the term flow channel is used here as the scope of use is broader than reactor applications. The flow channel is used to bring about physical change, chemical change or separation of process material. Examples of unit operations include but are not limited to: temperature change, blending, reaction, polymerisation, extraction, crystallisation and precipitation. The flow channel described here applies to any of the above.

In a normal reciprocating movement such as a pendulum the speed of reciprocating movement decreases to zero as the pendulum reaches an end of the arc and increases under gravity as it reciprocates to the bottom dead centre position and then decreases again as it rises again to the other end of the arc. When a tubular reaction or mixing device is used in this way the decrease in speed, this can be compensated by extra power from the drive mechanism however, this is expensive and causes unacceptable stress on bearings and other mechanical aspects of the device. The present invention provides simple and low cost means to overcome these difficulties.

Efficient rotation in this document means that a high proportion of the kinetic energy used to rotate the mass of the flow channel through an arc in one direction is recovered and used to accelerate the mass of the flow channel through an arc in the opposite direction. Preferably the recovered energy will be greater than 50% and more preferably greater than 75% and more preferably greater than 85%. Inefficient rotation is undesirable and occurs when a high proportion of the energy is lost on impact at the end of the arc travel. The term process material used herein refers to a material capable of flow that undergoes change. This may be a liquid, immiscible liquids, gas, vapour, suspended solids, gels, super critical fluid or mixtures of these. The net flow direction of process material may be in a single direction in the long axis or counter current in the long axis. Orderly flow is preferred and in the case of counter current flow, the flow pattern of the respective bulk phases will also be substantially orderly.

The flow channel described here is for continuous processing and only a fraction of the total process material per cycle is present in the flow channel at any time. Flow channels are therefore smaller than equivalent batch vessels and operate under steady state conditions. The reduced size of the flow channel contributes to better heat transfer and mixing per unit volume. Steady state operation combined with smaller equipment contributes to lower capital cost, improved safety and improved energy efficiency. Depending on process type, improved heat transfer and mixing can also contribute to improved yield, better purity and lower utilisation of raw materials. Benefits vary according to process type and are well documented in literature.

The present invention relates to drive mechanisms which move the body of the flow channel or a structure on which the flow channel is mounted so as to generate mixing and to flow channels provided with such mechanisms. This allows mechanical stirrers within the flow channel to be moved without magnetic or shaft couplings to external drive shafts. It also permits mixing where there are no moving mechanical stirrers but materials of two different densities are present.

The invention therefore provides a tubular flow system comprising flow channel, preferably a tube with process material flowing therethrough capable of rotating about its axis through reciprocating arcs and a drive mechanism to cause such rotation wherein a weight is provided to accelerate the speed of rotation of the tube under gravity during the downward movement of the external surface of the tube.

The length of a flow channel refers to the distance between the inlet and the outlet of the channel. Typically this will be two ends of a tube. This is also the long axis of the flow channel. This invention relates to systems where the preferred length of the flow channel is twice the diameter of the flow channel or greater. More preferably the flow channel length is 5 times the diameter of the channel or greater and more preferably 10 times the diameter or greater. The flow channel is normally a cylindrical tube although other profiles may be provided. Process material enters one end of the flow channel and emerges at the other end. In some systems, intermediate addition or take off points may also be used. Axial mixing refers to mixing which disperses fluid along the long axis of the flow channel. Radial mixing disperses fluid at 90° to the long axis of the flow channel. The preferred flow pattern provided by this invention is orderly flow whereby process material passes through the system in the same time order that it enters the flow channel. This requires a high ratio of radial to axial mixing.

A flow system may comprise of a single flow channel or multiple flow channels. Where multiple flow channels are used, these may be connected in parallel or series. Transfer pipes are used to transfer process material into (feed pipe) and out of (discharge pipe) the flow channel. The diameter of the transfer pipe is sized to ensure a superficial velocity which can maintain near plug flow conditions through the flow channel and where necessary, sufficient velocity for orderly transfer of materials of different densities. The required velocity will vary according to size and application but will preferably be in the range of 0.5 to 2 metres per second. A flow channel will have at least one feed pipe and at least one discharge pipe. Flow channels may have more than one feed pipe and some may have more than one discharge pipe. Some of the feed and discharge points may be at intermediate points along the flow channel. The transfer pipes must have sufficient flexibility to accommodate movement of the flow channel.

Flow channels are made in different materials and this invention applies to any material of construction. The drive mechanism described herein may be used for a single flow channel or multiple flow channels arranged in bundles which are rotated around their long axis. The flow channel or channels may be mounted on a mechanism to allow rotation around the long axis. For this different solutions can be used such as bearings, rollers, bushes or other mechanisms which permit rotational movement with the minimum of friction. The flow channel may be mounted directly on the rotating mechanism or on a frame which is mounted on the rotating mechanism.

A flow channel will have other components to meet the specific requirements of the process operation. By way of example, but not limited to, this may include internal stirrers, baffles, an external jacket for heating or cooling, instruments for measuring temperature, analytical instruments and intermediate sampling or addition points. Copending Patent Applications GB 1219476.7 and GB 1219479.1 describe flow channels which employ mechanical stirring whereby there is no direct or magnetic coupling between the external drive mechanism and the internal mechanical stirrers. The mechanical stirrers inside the channel may include fixed stirring elements (which can also be referred to as mixing baffles) and loose stirring elements mounted on an internal shaft or shafts. When the body of the flow channel rotates through an arc, the fixed stirring elements rotate with the body of the flow channel but the loose stirring elements resist the rotating action. This causes differential movement between the fixed and loose stirring elements. Where the loose stirring elements are unbalanced by a weight at one point, the degree of differential movement is enhanced. The present invention is applicable to flow channels described in GB 1219476.7 and GB 1219479.1. It also applies to systems where there are no internal moving mechanical stirrers but there are materials of at least two different densities within the channel and the rotational action of the flow channel body generates mixing by differential movement. In systems without moving stirring elements there may also be mixing baffles which rotate with the body of the flow channel.

When baffles are used the flow channel may have two types of radial baffle. Back mixing baffles are radial plates across the face of the flow channel which separate it into two or more stages. These have apertures at different radial distances across the face of the baffle to permit the passage of process material along the axis of the flow channel. These reduce or prevent back mixing between baffled stages. Flow path baffles are radial plates across the face of the channel which separates it into two or more stages. These have apertures near the centre or near the outer radius of the flow channel. Normally these alternate between having apertures near the centre and apertures near the outer radius of the flow channel. This creates an extended flow path through the flow channel. Baffles of this type as described in GB 1219476.7 and GB 1219479.1 may be used in the flow channels of this invention.

The invention is illustrated but in no way limited by reference to the accompanying drawings in which

Figure 1 is a cross section through a flow channel of the invention. Figure 2 shows a flow channel provided with a recoil device.

Figure 3 shows an alternate drive mechanism accordingly to the invention. Figure 1 shows a cross-section through the body of the flow channel (1 ). The internal elements of the flow channel are not shown. The body of the flow channel rotates around the long axis though an arc (shown as a dotted arrow) around the centre of rotation (2) describing a series of constantly repeating arcs. The rotating mechanism on which the flow channel is mounted is not shown. The preferred centre of rotation is the centre of the channel as shown but may also be offset from the centre. A drive mechanism (3) is used to drive the rotation of the flow channel. This is an active device using energy from an external source such as electricity, electro magnets, compressed air, hydraulic oil or other form of drive energy. In this example the drive mechanism is a piston. This pushes or pulls between a fixed surface independent of the flow channel and a drive surface (4) on the rotating flow channel during one phase of rotation. It is preferred that the drive mechanism is in physical contact with the drive surface for less than 90° of rotation and more preferably less than 45° of rotation. The system can be operated with a single drive mechanism, but opposing pairs of drive mechanisms as shown are preferred. Multiple drive mechanisms or pairs of drive mechanisms along the flow channel length may be used.

The rotating assembly which carries the flow channel (1 ) is unbalanced by one or more counter weights (5). The counter weights may be mounted directly on the flow channel or on a structure which carries the flow channel. The counterweight accelerates the rotation of the flow channel (1 ) as it approaches bottom dead centre and decelerates the rotation as it moves away from bottom dead centre. This conserves energy of rotation. The weight and distance of the counterweight from the centre of rotation varies according to need. A heavy counterweight (5) close to the centre of rotation gives a compact system. A light counter weight (5) with a large offset from the centre of rotation has the benefit of lower mass but requires a higher clearance from the base.

Different drive mechanisms may be used such as, such as pistons, rollers, gears, rotating arms, chain drives, belts, electro magnets or other such mechanisms. The drive mechanism operates intermittently and therefore power must be applied to this device at the correct point of rotation. It is preferable to apply power at the start of the rotating arc (by pushing) although it can be at the end of the rotating arc (by pulling) or a combination of both. Activation of the drive mechanism can be at fixed time intervals however the preferred method is to use a switch device such as proximity sensors, light sensors, pressure sensors or other such mechanisms to initiate activation. The duration of activation can be with a timed delay or a second switch device. The duration of activation and force on the drive element will depend on many variables and many solutions may be used according to need. Figure 2 shows a recoil device (6) which in this example is a spring. This accumulates energy as it is compressed between the drive surface and a fixed surface. Other mechanisms may be used such as repelling magnets, pistons (containing compressible gas) or anything which can accumulate energy during compression and use this to accelerate the rotation of the flow channel on the next cycle. This is disclosed in GB 1219476.7 and GB 1219479.1. Recoil devices that operate in arcs are simpler to engineer if the compression distances are short. The preferred recoil device will therefore have a working travel length of 200 mm or less and more preferably 100 mm or less and even more preferably 50 mm or less. Short recoil devices however have limited capabilities to decelerate large masses effectively. Pairs of recoil devices as shown are preferred to single recoil devices and multiple pairs of recoil devices along the length of the flow channel can be used.

The recoil device decelerates the rotation of the flow channel at the end of an arc and accelerates the rotation of the flow channel at the start of the next rotating arc. It is preferred that the recoil device (6) does not remain in physical contact with the drive surface (4) for the fully cycle of the arc. It is preferred that the maximum angle of travel during which the recoil device remains in contact with the drive surface is 90° or less and more preferably 45° or less. The drive mechanism and the recoil mechanism can be combined into a single device. An example of this is a compressed air cylinder where the cylinder piston is in a mid-position and is forced back against a closed volume of air before more compressed air is used to drive the piston forward. A similar arrangement can be achieved by other means. The counterbalance method of accelerating and decelerating the rotation of the flow channel has the advantage that it is simple to engineer so that it operates over the full cycle of the rotating arc. For optimum efficiency however such a method relies on gravity to arrest rotation. This implies one speed of rotation for a given configuration. In many cases, faster speeds will be required. Recoil devices can decelerate rotation efficiently in a shorter distance than using the counter balance alone. Where greater speed or multiple speeds of rotation are required it is preferred that the counter balance method and recoil device are used in combination.

The drive mechanisms (3), counter weights (5) and recoil devices (6) are collectively referred to here as the drive elements. It is preferred that the drive elements are located between the ends of the flow channel so as to give good access to the ends of the flow channel. This means that the drive elements are mounted at a radius from the centre of rotation which of necessity has to be equal to or greater than the outer diameter of the flow channel assembly at the point where the drive elements are located. The flow channel assembly will include the flow channel and where applicable, the heating/cooling jacket, insulation, cladding or any other elements.

The angle of contact and point of contact between drive mechanism (3) and the drive surface (4) tends change as the flow channel rotates. Figure 3 shows a roller (7) mounted on the drive mechanism. This is preferred so as to improve rotating efficiency and to reduce wear. A similar arrangement can be used for the recoil mechanism.

The drive mechanism (3) and recoil mechanism (6) can be mounted on the flow channel or on a fixed surface. Thus the drive surfaces (4) will be mounted on the flow channel or on a fixed surface as appropriate. Separate drive surfaces (4) can also be used for the drive mechanism and recoil mechanism respectively. The position of these respective elements can also be varied so as to alter the arc of rotation.

Mixing has a number of functions including: blending, enhanced heat transfer, enhanced mass transfer, phase dispersion and good orderly flow (good mixing reduces back mixing by eliminating poorly mixed zones). The rotation speed of the flow channel is varied to suit different mixing requirements.

For processes with low mixing requirements the counterbalance method alone can be used. These will be for processes with reaction times of 30 minutes or longer. Where higher mixing energy is required, higher average rotational speeds are used. The length of arc described by the rotation of the flow channel is:

L =□ x D x Y/360

Where L = the distance travelled (m)

□ = ratio of circumference to diameter of a circle

D = the inside diameter of the flow channel (m)

Y = the angle of rotation (degrees)

The average radial speed (U) that the single point on the internal diameter of a circular flow channel is:

U = L/t

Where U = average radial velocity (m/s)

L = length of arc (m)

t = time to travel through arc (s) Where high mixing performance is required, the preferred value of U is >0.1 m/s and more preferably >0.2 m/s and more preferably >0.4 m/s and more preferably >0.8 m/s and more preferably >1.2 m/s. The flow capacity of a flow channel is determined by throughput (litres per hour) x residence time (hours). Given that the preferred length to diameter ratio described previously, this means that the diameter and length of the flow channel will vary according to need. Flow channels may have a diameter of less than 10 mm or up to 1 metre in diameter or more. The preferred size however will be in the diameter range of 50 mm to 300 mm.

Repeating arcs rather than a continuous rotation of the flow channel is preferred for two reasons. Firstly, a high ratio of radial to axial mixing is desirable and this is easier to achieve with repeating arcs since continuous rotation can promote axial currents. Secondly, the use of rotating arcs allows electrical wires, instrument wires, feed and discharge pipes and heat transfer fluid pipes or any other connecting parts to be connected between fixed objects and the moving flow channel without the use of rotating joints. These connections are made flexible to move with the flow channel arc.

The flow channel can rotate through any arc between 1 ° and 360°. Rotating arcs of between 45° and 180° are preferred.

The system of this invention is for use as a flow mixer and/or reactor for continuous processing. Examples of reactions include chemical synthesis, crystallisation, polymerisation, bio reactions, cell growth and precipitation.

The system of this invention is for use as a flow extractor for continuous processing. Extraction may be co-current or counter current and involves two immiscible fluids of different densities.

Claims

1 . A flow channel adaptable for process material flowing continuously into and out of the channel and comprising the channel and a drive mechanism is provided whereby the flow channel rotates around the long axis in repeating arcs of 360° or less so as to promote mixing within the flow channel and that the rotating flow channel is unbalanced by means of one or more counter weights which serve to accelerate the rotation of the flow channel as the counterweight or counterweights approaches bottom dead centre position and decelerate the rotation of the flow channel as the counterweight or counterweights moves away from the bottom dead centre position.

2. A flow channel according to Claim 1 provided with at least one feed pipe and one discharge pipe.

3. A flow channel according to Claim 1 or Claim 2 which uses one or more recoil devices in addition to the counter weight.

4. A flow channel according to any of the preceding claims wherein the maximum angle of travel during which the drive mechanism remains in contact with the drive surface is 45°.

5. A flow channel according to any of the preceding claims wherein the drive mechanism uses a roller in contact with the drive surface.

6. A flow channel according to any of Claims 3 to 5 wherein the maximum angle of travel during which the recoil device remains in contact with the drive surface is 45° or less.

7. A flow channel according to any of any of the preceding claims wherein average radial speed (U) of rotation is greater than 0.2 metres per second.

8. A flow channel according to any of the preceding claims wherein the angle of rotation of the flow channel is between 45° and 180°.

9. A flow channel according to any of the preceding claims provided with back mixing baffles within the flow channel.

10. A flow channel according to any of the preceding claims provided with flow path baffles.

1 1 . A flow channel according to any of the preceding claims provided with one or more internal fixed stirring elements mounted on an internal shaft or shafts and where there is no mechanical or magnetic link to an external drive mechanism.

12. A flow channel according to any of the preceding claims provided with one or more internal loose stirring elements mounted on an internal shaft.

13. A flow channel according to Claim 1 1 or 12 to which the loose and fixed elements are mounted on the same shaft or shafts.

14. A flow channel according to any of the preceding claims which contains materials of two or more different densities whereby the rotation of the flow channel in arcs generates internal mixing of the material.

15. A flow channel according to any of the preceding claims which is a flow reactor.

16. A flow channel according to any of Claims 1 to 14 which is a flow extractor.