WO2013043044A1

WO2013043044A1 - Ultrasonic crystallizer and method for attracting particles from a liquid

Info

Publication number: WO2013043044A1
Application number: PCT/NL2012/050657
Authority: WO
Inventors: Hendrik Jannes CAPPON; Karel Jacob KEESMAN; Mateo Jozef Jaques Mayer
Original assignee: Stichting Wetsus Centre Of Excellence For Sustainable Water Technology
Priority date: 2011-09-19
Filing date: 2012-09-19
Publication date: 2013-03-28
Also published as: NL1039053C2

Abstract

The present invention relates to an ultrasonic crystallizer, and a system and method there for. The crystallizer according to the invention comprises: a liquid channel provided with an inlet and an outlet; one or more transducers capable of producing one or more waves to generate an attracting structure between the inlet and the outlet comprising a number of nodes and/or node regions resulting from the interfering waves for attracting and crystallizing particles from a liquid.

Description

Ultrasonic crystallizer and method for attracting particles from a liquid

The present invention relates to a crystallizer for crystallizing particles from a liquid.

Conventional crystallizers form salt crystals from a solution/liquid using cooling and/or evaporation to enable crystallisation of particles. The quality of the crystals in respect of size distribution and purity strongly depends on the interaction of the particles in the liquid. Conventional crystallizers often produce relatively inhomogeneous

crystals comprising a number of defects.

The present invention has for its object to provide a crystallizer that obviates or at least improves conventional crystallizers with the above problems.

This object is achieved with the ultrasonic crystallizer according to the present invention, the

crystallizer comprising:

a liquid channel provided with an inlet and an outlet; and

one or more transducers capable of producing one or more waves to generate an attracting structure between the inlet and the outlet comprising a number of nodes and/or node regions resulting from the interfering waves for attracting and crystallizing particles from a liquid.

The liquid channel of the separator may relate to a tube, pipe, conduit or reactor provided with an inlet and an outlet for receiving the liquid. In a presently preferred embodiment, the liquid relates to process water from chemical industry. Other liquids can also be supplied to the crystallizer according to the invention. In fact, the dimensions and/or specific configuration of the process including the channel can be designed upon characteristics of the entire process, including desired throughput, and liquid and particle characteristics. The liquid channel can be a cylindrical or rectangular channel with a liquid inlet and a liquid outlet. Other shapes for the channel would also be possible according to the invention.

By generating one or more interfering acoustic waves with one or more transducers it is possible to achieve a three-dimensional attracting structure of nodes and/or node regions. The nodes attract the particles that are present in the liquid. As a further effect, due to the use of acoustic waves, this structure of nodes improves the attracting of particles by increasing the apparent diffusion coefficient for the particles. As a result thereof, the concentration of these particles in this structure starts to increase. Preferably, the structure comprises substantially nodes and/or node regions. In use, the solid particles are captured in or at the nodes.

As a further effect the residence times, and in fact the residence time distributions, of the liquid itself and the particles start to differ. More specifically, the residence time difference is such that the particles to be crystallized and the crystals remain for a significant longer period of time in the channel. This increases the possibilities for concentrating, measuring and sampling, for example.

The structure of nodes is the result of the transducers being capable of producing acoustic waves that interfere with each other. Therefore, at least one

transducer needs to be provided. In case one transducer is provided at last one additional reflector is required to produce some nodes and/or node regions. Preferably, more reflectors and/or more than one transducer is provided to achieve a three-dimensional structure of nodes and node regions. Depending on the characteristics of the waves, the equipment and the particles, the particles can be "captured" in the nodes.

By capturing the particles they are separated from the liquid. The captured particles crystallize and the resulting crystals can be collected by periodically

switching off the transducers and allow the crystals to settle and be removed from the channel. Alternatively, or in combination therewith, crystals will settle in case they become too large of heavy to be kept in the node. Depending on flow characteristics the large or heavy particles will settle. In an alternative approach the separating structure with nodes is periodically switched off and flushed such that the crystals are separated from the liquid flow.

Preferably, the crystals that are produced in the

crystallizer according to the present invention are provided to a separate output.

The transducers and/or reflectors are preferably provided at the side walls of the channel, or alternatively in side channels of the liquid channel. The frequency produced by the transducers in a presently preferred

embodiment is in the range of 20 kHz-100 MHz, more

preferably in the range of 1-10 MHz, and most preferably about 2 MHz. Preferably, a λ/2 or λ/4 resonator is applied to achieve the desired crystallization. It is noted that, optionally, dedicated internals can be implemented in the particle concentration volume to increase the effectivity of the particle concentration.

Preferably, a controller is provided for controlling the one or more transducers. The controller performs the switching on and off of the transducers.

Preferably, the controller also sets the parameters for the transducers including the frequencies and/of amplitudes of the waves. This opens op possibilities for capturing

particles of different sizes and/or different volumes at different nodes in the particles separating structure such that these different particles can be separated at the same time and/or with the same device. This improves the overall flexibility of the ultrasonic crystallizer for dealing with changes in the liquid.

The crystallizer according to the present invention captures the crystals in nodes and/or node regions such that they are suspended in the reaction mixture without introducing a high collision rate and/or shear rate near the crystal surface. As an affect thereof the produced crystals are relatively pure with a very low concentration of defects near the crystal surface.

Also, as mentioned, due to the application of acoustic waves in the solution the apparent diffusion coefficient of molecules in the liquid is increased. Due to the increase apparent diffusion coefficient mass transfer of the involved particles towards the crystal surface is enhanced. Therefore, the concentration of particles in or near to the nodes is significantly higher as compared to the concentration in other parts of the channel. In fact, in use, the channel comprises a heterogeneous system of solids in a liquid. This achieves a higher crystallisation rate such that the crystallisation can be performed more

efficiently.

As a further advantage the crystallizer according to the present invention enables the setting of the desired size of the crystals. Once the crystals that are formed in the nodes and/or node regions exceed a predefined size, the critical crystal size, they cannot be retained anymore in the nodes and/or node regions and will settle from the attracting structure and can eventually be removed from the crystallizer . This enables the production of a relatively narrow crystal size distribution. The actual size of the crystals that are produced can be manipulated by setting the characteristics of the waves that are produced by the transducers. For example, a controller can set the frequency and/or amplitude of the acoustic waves that are being used in the crystallizer according to the present invention.

An advantageous effect of the acoustic/ultrasonic crystallizer is that due to the use of acoustic waves fouling of the channel is prevented or at least minimised. This prevents or reduces cleaning requirements for the device according to the invention. In fact, cleaning the acoustically achieved attracting structure of nodes only requires switching on and off the transducers.

Also, the device according to the present invention can be implemented relatively easy online in an existing process. Also, the liquid flow is only affected in a minimal way by the acoustic waves without increasing flow resistance, for example. This prevents or reduces

destruction of fragile particles and/or aggregates. In addition, the invention can be applied in a continuous and/or semi-continuous and/or batch process, periodically or continuously. The crystallizer according to the invention can be a continuously operated stirred tank reactor (CSTR) , a plug flow reactor, or a fed batch reactor. The invention can advantageously be applied in pharmaceutical and chemical industry to improve the quality of the products, and also in water purification processes comprising the crystallization of inorganic salts, for example.

In a preferred embodiment according to the present invention one or more of the one or more transducers are placed at an angle to the longitudinal direction of the liquid channel. By placing some or all of the transducers at an angle to the longitudinal direction of the liquid channel the nodes and/or node regions and/or node lines of the attracting structure are also provided at an angle to this longitudinal direction. This has the advantage that the incoming liquid is, at least somewhere in the three- dimensional attracting structure, very close to a node. This improves the "capturing" of the particles in the nodes and thereby the efficiency the attracting structure. For

example, an angle is between 3 and 80°, preferably between 5 and 10° to achieve the aforementioned effect while

minimizing flow resistance.

In a further preferred embodiment according to the present invention the ultrasonic crystallizer comprises an output for removing crystals from the channel.

By providing a separate outlet for the crystals that are captured in the nodes of the attracting structure the crystals can be removed from the channel separately. This can be achieved by periodically switching off the transducers such that the particles can be removed from the structure. Alternatively, or in combination therewith, crystals that are captured in the nodes that become too large will drop out of the nodes and may settle in the channel, for example due to gravity.

In a further preferred embodiment according to the present invention the device further comprises

electromagnetic generating means, wherein the liquid channel comprises a first conductor and a second conductor that is placed at a distance from the first conductor such that the distance defines the attracting structure acting as a fluid containing transmission line.

By filling the volume of the attracting structure with a liquid this liquid volume defines a liquid containing transmission line. The liquid acts as dielectricum between the conductors. The characteristics of this liquid in the particle concentration volume depends, amongst other things, on the dielectric constant of the liquid. This constant is influenced by the presence of small solid particles,

bacteria and also dissolved components. This influence can be determined by comparing the supplied broad radio

frequency spectrum to the particle concentration volume with the outgoing signal, for example, preferably as a function of time.

In this embodiment the particle concentration volume acts as an antenna filter that can be used to

characterise properties of the liquid by measuring the response by a receiver or input signal from a transmitter. In a presently preferred embodiment of the invention, the dielectric permittivity of the liquid can be deduced from the measured response. This correlates to specific contents, like contaminations and presence of bacteria in the liquid thereby enabling online measurement of a liquid to determine its contents. This measurement can be applied in

applications including monitoring of water quality, physical separation processes, and pharmaceutical and chemical reactions in process industry. Also, the sensor with this antenna filter will be able to detect aggregates of

molecules, such as primary crystals, that can be useful to monitor and control crystallisation and scaling processes, for example. This results in an effective and efficient manner to measure such liquid. From the response it is possible to detect the type of components in the liquid and/or the concentration thereof.

With the coax-filter according to one of the preferred embodiment of the invention homogeneously

distributed particles over the liquid within the channel results in an effective dielectric permittivity of the particle suspension that hardly changes as function of the length coordinate of the channel. As a result thereof, the properties and/or volume fraction of particles within the coax-sensor can be determined from the resonant frequency of the coaxial stub or particle concentration volume.

In a presently preferred embodiment the first conductor is provided as a co-axial cable with a solid metal or tubing. This first conductor is surrounded by the second conductor comprising a metal tubing. Preferably, this second conductor is part of the wall of the liquid channel.

In this preferred embodiment a combination of a particle concentrator and a sensor is achieved. This enables an on-line detection of bacteria in drinking water, for example.

Optionally, the antenna filter is an open line quarter wavelength co-axial antenna filter. Preferably, the antenna filter comprises an open end. Such antenna filter behaves like a series resident circuit. To improve the sensitivity of the antenna filter the inner and/or outer conductors can be insulated. Also, the antenna filter can be a flow-through filter to prevent the requirement for the taking of samples of the liquid. In a presently preferred embodiment the input signal by a transmitter comprises a frequency in the range of 20 MHz to 2 GHz providing good results on the detection of components and concentrations thereof in the liquid. In fact, in this preferred embodiment a so-called coax sensor with integrated particle

concentration device is obtained. The particle concentrator can be switched off easily by switching off the transducers, in order to flush the particle concentration volume, for example. Preferably, the diameter of the optional side channels that are connected to the liquid channel is sufficiently small to avoid undesired interaction of the side channel with the electromagnetic waves fed to the antenna filter.

The ultrasonic crystallizer can also be applied as a catalyst reactor or bioreactor. For a catalyst reactor and bioreactor the relevant particles are attracted towards the nodes and/or node regions similarly as described for the crystallizer such that reactions take place at a higher rate. The same effects and advantages apply as described for the crystallizer. This improves the overall efficiency of the reactions taking place in the catalyst reactor or bioreactor .

In addition, for the catalyst reactor an additional advantage is the applicability of the invention to catalyst particles with a mechanically limited stability without requiring a carrier. In case the reaction product is a solid the reaction conditions in the nodes can be chosen such that the reaction products are not captured in the nodes. This will make the reaction products leave the attracting structure while the catalyst remains suspended in the structure. Therefore, a separation step between catalyst and reaction product can already be achieved integrally in the attracting structure without requiring additional steps.

The bioreactor relates to a biomass reactor with bacteria with the attracting structure made selective for a specific type of micro-organism, for example. In addition, as the forming of a biofilm is suppressed and micro^¬ organisms are suspended as single cells or small aggregates this enhances the conversion rate that can be achieved per gram of biomass.

The present invention also relates to a system for crystallizing particles from a liquid, the system comprising an ultrasonic crystallizer as described above. Such system provides the same effects and

advantages as those described with reference to the

crystallizer .

The system comprises a second or further ultrasonic crystallizer in one of the preferred embodiments thereof. Such further crystallizer can be placed in series and/or parallel. When provided in parallel the overall capacity of the system is increased while the dimensions of the ultrasonic crystallizer can be maintained to effective values. When the crystallizers are placed in series, a further crystallization can be performed such that a

purified water flow remains.

In a preferred embodiment according to the present invention the ultrasonic crystallizer is provided at an angle.

By providing the ultrasonic crystallizer at an angle the solids that are captured in nodes will settle more easily and can be removed more effectively from the reactor. For example, this angle is between 5 and 20° between the longitudinal direction of the liquid channel and a vertical direction. The crystals settle due to gravity, for example when the transducers are switched off. The system is

preferably provided with a controller for controlling one or more transducers. The controller sets the amplitude and/or frequency of the waves to generate the separating structure. Preferably, the controller receives information about the liquid from sensors that are located upstream and/or

downstream the attracting structure. These sensors may involve acoustic measurements, light scattering

measurements, light reflection measurements, conductivity measurements, pH measurements, temperature measurements, impedance measurements and/or dielectric measurements, for example . Besides the advantage that no physical membranes are required costs associated with downtime for cleaning purposes are reduced significantly as cleaning the acoustic separating structures of nodes requires switching on and off the transducers. Also, the crystallizer according to the present invention can be implemented relatively easy on-line in an existing process. Furthermore, the liquid flow is only affected in a minimal way by the acoustic waves without substantially increasing flow resistance, for example.

The invention further also relates to a method for attracting particles from a liquid, the method comprising:

providing the liquid particles to a liquid channel with an inlet and an outlet;

providing an attracting structure comprising nodes and node regions with one or more transducers that produce interfering waves; and

attracting particles from the liquid in the nodes and/or node regions to crystallize and/or catalyze the particles from the liquid.

Such method provides the same effects and advantages as those described with reference to the

crystallizer and/or the system.

In the (bio ) chemical process industry and the water purification industry most chemical and biochemical reactions are heterogeneous reactions such as

crystallisation reactions, biochemical conversions, by micro-organisms and catalytic conversions in fluids by the use of a solid catalyst. Important aspects in these

reactions are the specific surface area that defines the efficiency of the catalyst and the mass transfer of

reactants and/or reaction products from and to the location where the reaction takes place. Due to the application of ultrasonic waves the apparent diffusion coefficient increases such that one of the important aspects defining the rate of the reactions taking place at the nodes and/or node regions of the

attracting structure according to the invention is

increased .

According to the method the particles are captured in the node lines of the separating structure that is achieved by interfering waves generated by one or more transducers. The transducers are configured such that the separating structure in use comprises substantially parallel channels of liquid and particles. Preferably, the particles are immobilised in the node lines. By applying the

transducers and the acoustic waves the apparent diffusion coefficient for the particles increases such that the particles move to the node lines.

To minimise the forces that are applied to the particles and the liquid the liquid is preferably provided in a substantially laminar flow.

The frequency and/or amplitude of one or more generated waves are set and/or adjusted by a controller in a presently preferred embodiment according to the present invention. This increases the flexibility of the method. Preferably, the controller receives information about the liquid from one or more sensors measuring the liquid as mentioned before. Optionally, a further crystallizer, catalyst reactor and/or bioreactor can be provided in series and/or parallel, as was already mentioned.

Further advantages, features and details of the invention are elucidated on basis of preferred embodiments thereof wherein reference is made to the accompanying drawings wherein: Figure 1A shows a schematic overview of components from the ultrasonic crystallizer according to the present invention;

Figure IB shows an attracting structure according to the present invention;

Figure 2 shows a system according to the invention; and

Figure 3 shows a system with multiple

crystallizers according to the system.

A liquid channel 2 (figure 1A) is provided with inlet 4 and outlet 6. It is noted that figure 1A is one of the many embodiments possible with the technology according to the present invention. Other configurations according to the invention are also possible, for example by providing additional transducers, side channels etc. In the

illustrated embodiment channel 2 is a cylindrical or

rectangular liquid channel. Other shapes of this first channel 2 are also possible according to the invention. In fact, a large number of other geometrical shapes of the liquid channel would be feasible according to the invention.

In the illustrated embodiment the optional liquid side channels 8, 10 are provided with first and second acoustic wave generating means or transducers 12, 14, respectively. In the illustrated embodiment two sets of transducers are being provided generating two separating structures in series.

Transducer 12 provides signal 16 that has the shape of a sinusoid with amplitude 18 and period 20.

Transducer 14 provides signal 22, which is a similar

sinusoid with amplitude 24 and period 26. Due to wave interference between the two waves/signals 16, 22, a

standing wave with nodes 28 or node regions 30 is achieved. It is noted that in the illustrated embodiment transducer 14 can be replaced by a reflector. Also, additional transducers 12, 14 can be provided to enlarge the separating structure in channel 2. In a second separating structure signals 22, 23 can be provided with different amplitudes and/or

frequencies.

Nodes 28 (figure IB) attract particles 32 that are present in liquid 34. In the illustrated embodiment this results in a number of nodes and/or node regions 30. This effectively results in an attracting structure where

crystals can be formed, catalyst reactions and/or biomass conversions can be performed.

System 36 (figure 2) comprises a liquid supply 38 and a pump 4 for supplying liquid 34 to channel 2. In the illustrated embodiment sensor 42 measures one or more properties of water 34 such as temperature, amount and/or type of particles 32, and dielectrical constant.

Furthermore, in the illustrated embodiment channel 2 is provided with two sets of transducers 12, 14. At the end of channel 2 sensor 44 also measures one or more properties of the liquid. Optionally, sensor 46 provides a measurement signal 48 towards the attracting structure in channel 2.

In an alternative embodiment sensor 44 is a coax- sensor comprising a co-axial cable with a solid metal or tubing that is insulated and acts a conductor. Around the cable and at a distance is provided a metal tubing that acts as another conductor. The distance defines a volume between conductors that in use is at least partially filled by a fluid to be measured acting as transmission line. In

addition, the sensor comprises a transmitter that is

connected to a receiver through the transmission line. From the response of the receiver, the dielectric permittivity of the fluid can be determined. This dielectric permittivity is correlated to one or more specific components, and

preferably also the concentrations thereof can be detected.

The sensing principle of at least one of the sensors 42, 44 for sensing the liquid properties for the liquid in channel 2 is preferably based upon at least one of the following sensing techniques: acoustic measurements, light scattering measurements, light reflection

measurements, conductivity measurements, pH measurements, temperature measurements, impedance measurements, dielectric measurements. In case temperature measurements are applied, these measurements preferably comprise temperature

measurement using infrared technology and/or PTC s and/or NTC's and/or PtlOO sensing elements preferably sensing elements preferably placed in liquid channel 2 and/or connected to the inner wall and/or outer wall of channel 2.

Signals 50, 52 produced by sensor 42, 44 are fed to controller 54, such as a microprocessor, preferably to a micro controller, preferably by the use of an analogue-to- digital converter. Controller 54 is provided with software for controlling the transducers 12, 14. Controller 54 provides transducers 12, 14 with control signals 56.

The liquid is provided to system output 58.

Optionally, output 60 collects the crystals that have exceeded the maximum crystal size for nodes 28 and/or node regions 30.

In the illustrated embodiment liquid channel 2 is provided under an angle with the horizontal plane, for example 5-80°, preferably about 20°. Due to gravity the crystals that are formed and grown in the nodes 28 and/or node regions 30 will settle that can be collected by output 60.

For performing a crystallisation, a catalyst reaction and/or a biomass conversion a liquid with the relevant particles is provided to channel 2. Transducers 12, 14 are activated by controller 56 such that an attracting structure has been formed in channel 2. The relevant

particles 32 from liquid 32 move towards nodes 28 and/or node regions 30. In and/or near the nodes 28 and/or node regions 30 crystallisation, reactions and/or conversions take place.

In a possible embodiment, system configuration 62 (figure 3) comprises a first crystallizer 64. A second crystallizer 66 and a third crystallizer 68 are put in series. A liquid 70 is provided to the first crystallizer 64. The output 72 of the first crystallizer 64 is fed to the second crystallizer 66. In a similar way output 74 of the second crystallizer 66 is provided to a third crystallizer 68. The resulting output 76 relates to water from which particles 34 have been removed and that optionally can be treated further. The outputs 78, 80, 82 from the individual crystallizers 64, 66, 68 can be treated further or

optionally fed back in process 62. Configuration 62 enables crystallizing at different conditions for each individual crystallizer 64, 66, 68. As an example, it would be possible to have a first phase in crystallizer 64 with transducers being controlled in about 50 kHz to form relatively small crystals. In the second crystallizer 66 the transducers can be controlled at about 500 kHz to form a second size of crystals. The third crystallizer 68 can be controlled at about 2 MHz to produce a third size of crystals. This improves the overall crystallization operation as the crystal size distribution can be controlled more

effectively. Instead of crystallizers also catalyst reactors and/or bioreactors can be applied in configuration 62.

An experiment was performed with system 36 for biomass particles with a size of about 0.1 mm. By switching on transducers 12, 14 it appears that these particles can be captured at nodes 28 and/or node regions 30. In a further experiment the frequency was maintained while the size of particles 34 was increased. Without manipulating the

frequency these particles could not be captured. This illustrates the interaction between particle size and frequency .

The present invention is by no means limited to the above described embodiments thereof. The rights sought are defined by the following claims within the scope of which many modifications can be envisaged.

Claims

Ultrasonic crystallizer, comprising:

a liquid channel provided with an inlet and an outlet; and

one or more transducers capable of producing one or more waves to generate an attracting structure between the inlet and the outlet comprising a number of nodes and/or node regions resulting from the interfering waves for attracting and

crystallizing particles from a liquid.

Ultrasonic crystallizer according to claim 1, wherein one or more of the one or more transducers are placed at an angle to the longitudinal direction of the liquid channel .

Ultrasonic crystallizer according to claim 1 or 2, the liquid channel further comprising an output for

crystals .

Ultrasonic crystallizer according to claim 1, 2 or 3, further comprising electromagnetic generating means, wherein the liquid channel comprises a first conductor and a second conductor that is placed at a distance from the first conductor such that the distance defines the attracting structure acting as a fluid containing transmission line.

System for crystallizing particles from a liquid, comprising an ultrasonic crystallizer according to any of the foregoing claims.

6. System according to claim 5, further comprising a second ultrasonic crystallizer that is placed in series .

7. System according to claim 5 or 6, wherein a further

ultrasonic separator is placed in parallel.

8. System according to claims 5, 6 or 7, wherein the

ultrasonic separator is provided at an angle.

9. Method for attracting particles from a liquid,

comprising :

providing the liquid particles to a liquid channel with an inlet and an outlet;

10. Method according to claim 9, wherein the crystals

and/or catalysts are immobilized in the node lines.

11. Method according to claim 10, wherein the crystals grow in the nodes and/or node regions up to a critical crystal size and settle down from the nodes and/or node regions .

12. Method according to claim 9, 10 or 11, wherein the

transducers are configured such that the apparent diffusion coefficient for the particles increases.

13. Method according to any of the claims 9-12, wherein the liquid is provided to the attracting structure in a substantially laminar flow.

14. Method according to any of the claims 9-13, further comprising the step of adjusting the frequency and/or amplitude of one or more of the generated waves by a controller .

15. Method according to claim 14, wherein the controller receives information about the liquid from a sensor measuring the liquid.

16. Method according to the foregoing claims 9-15, further comprising the step of providing a second crystallizer in series and/or parallel.