WO1999036762A1

WO1999036762A1 - Method and means for measuring velocity and concentration of particles in a fluidized bed

Info

Publication number: WO1999036762A1
Application number: PCT/NO1999/000014
Authority: WO
Inventors: Davoud Tayebi; Hallvard F. Svendsen; Arne GRISLINGÅS; Thor Mejdell
Original assignee: Leiv Eriksson Nyfotek As
Priority date: 1998-01-15
Filing date: 1999-01-15
Publication date: 1999-07-22
Also published as: NO980191L; NO980191D0; AU2552199A

Abstract

Method for measuring the movements of particles and gas bubbles and the concentration of the gas bubbles in a gas-solid system, such as a fluidized bed particle system, thereby treating a selected amount of the particle mass with for example a reflecting material, to mix the marked amount into the rest of the particle mass, to register with a probe (1) having several receptors (4) each time a marked particle passes by the probe, to compute the received data to thereby calculate the direction of movement, the velocity, the frequency, etc., of the marked particles.

Description

Method and means for measuring velocity and concentration of particles in a fluidized bed

The present invention is related to a method and a means for measuring velocity and concentration of particles in a fluidized bed.

Solid particles are of great interest in the chemical process industry, pharmaceutical production, mineral processing, energy related processes, etc. In some cases the particles serve as catalysts for reacting gases and/or liquids. In other cases, they must be chemically converted and in some processes particles must undergo physical transformations.

Gas-solid systems such as fluidized bed reactors are used in many areas in the process industry, specially in the oil- and petrochemical industries. There are still many uncertainties in the design, operation and scale up of such reactors. For good design, proper contacting of phases is essential. In any case, one should be able to describe the real contacting pattern. Basic and detailed information about flow of both the solid phase and the gas phase is very important for understanding the physics and fundamental modelling of such systems. Amongst many variables, the specific parameters of interest for particle motion are the local distribution of particle velocities, size and concentration (i.e. mass or volume flux). Parameters characterizing bubbles are size, size distribution, shape, frequency of occurrence, and bubble rise velocity. Such information should be recorded spatially and over time to gain insight into the fundamental hydrodynamic properties of gas-solid systems. The increasing importance of the highly concentrated multiphase flow systems in combination with their complicated structures has led to numerous investigations on their hydrodynamics and has promoted the development of various measuring techniques. Also, any phenomenological model developed in this area require empirical data. The quality of these models therefore depends on the accuracy of measurement techniques used to produce these data.

Known methods for measuring separate the velocity of separate particles in a fluidized bed are connected with big uncertainties and are based partially on the particles being monodisperse. Such known methods for measuring the velocity of particles further concentrate on circulating fluidized beds or areas above fluidized bed having relatively small particle density, whereas there are few or no good possibility to register the velocity and the direction of the particles in a fluidized bed having relatively high particle density. Furthermore there are no safe method available for simultaneously measuring the movement of particles and gas bubbles. In this connection it is referred to DD 142 473, DD 142 606, DD 145 874, SE 465 337 and SE 502 148.

The main objective of the present invention is to develop a novel technique for simultaneous measurement of local movement of solids and bubble properties and solids volume fractions in multiphase flow systems such as gas-solid fluidized beds. Furthermore to develop a more general technique for application in other multiphase systems and environments than gas-solid systems at ambient temperature.

The method developed is based on fibre optics and tracer particles. This method enables simultaneous measurement of local particle velocity vectors, local solid volume fractions and local bubble properties, including bubble rise velocity, size, size distribution, appearance frequency and volume fractions. The optical probe developed is specially designed to operate in dense beds with particle concentration up to that of a fixed bed.

A particle present in the measuring volume in front of the probe is marked with a fluorescent dye. A light source illuminate the particles and the detecting fibres receive reflected light from uncoated particles and fluorescent light from the tracer particle. Using optical filters, the fluorescent light is separated out and together with a small fraction of background light from uncoated particles, is used to determine local flow properties. The method is independent of the physical properties of the uncoated solid or tracer particles such as size, distribution, density and shape. It is also independent of local solid concentrations from 0 to 60 vol . -% .

A complete measuring assembly has been successfully designed, built and applied in a laboratory fluidized bed. With the method and the means according to the present invention a possibility is presented to provide detailed and accurate measurements from the movements of particles and gas bubbles in a fluidized bed, or a circulating fluidized bed. Local measurements are performed and any point in the reactor may be chosen, such as the most interesting places. The measurements as such are made without touching the particles thereby substantially avoiding any influence on the movement of the particles. Design and size of the probe is adapted to minimal influence of the probe on the particle flow.

The following local variables may be measured with the method according to the invention, the velocity of the particles, the direction of movement of the particles, the particle concentration and the particle mass flow as well as the velocity of the bubbles, appearance frequency, length (size) and possibly deformation. Tracing particles are use of the same type as the rest of the particles, e.g. having the same relation as to particle sizes in the particle mass, as well as the same distribution of particle size, the same shape and density as the rest of the particle mass. The bubble and particle frequency is a measure for how often a bubble or a tracing particle passes in front of the probe.

Even other types of tracing particles may be used than particles from the particle mass, such as particles having other shape, size or size distribution. It is also possible to use two or more particle types as tracing particles provided that their radiation properties are different.

With the method according to the invention furthermore two and three dimensional pictures may be provided of the flow in front of the probe. Further also the movement of the particles and the movement of the bubbles may be measured simultaneously.

Use of the method according to the invention is independent of the particle size, the variations of the particle size, the particle shape and the concentration and density of the particles. The method may be used in corrosive environments as well as in moisture environments and in pipe pressure and high temperature environments. The method also may be used in liquid- solid systems and gas-liquid-solid systems as well.

With the method and the means according to the present invention a possibility is provided to establish records on the velocity of the particles, their direction, e.g. their velocity vectors and their concentration as well as the frequency, velocity and length (size) of the bubbles and possibly the deformation in a gas-solid system such in a fluidized bed. This is achieved with the method and the means according to the invention as defined with the features stated in the claims.

The drawing discloses in figure 1 schematically an apparatus for performance of the method according to the invention, figure 2 discloses a front view of the tip of the probe, figure 3 discloses schematically a registration of the particle movement in relation to the receptors of the probe, figure 4 discloses a diagram for registrated data for the recording of the particle course V in figure 3 and figure 6 discloses a diagram of the bubbles in the particle mass.

According to the invention a given particle amount is chosen from the particle mass establishing the fluidized bed, in such a way that the treated amount of particles reflexed excitation light in a different way from the particles not treated. Before measurement the treated particles are mixed with the rest of the particle amount. The treatment may be for example colour impregnation with reflecting and/or fluorizant properties on single particles. The coating should be such that it does not influence the physical properties ( the dynamics ) of the treated particles in processes where the article later will participate.

After the treated particles being sufficiently mixed into the particle mass which is to create the fluidized bed, the fluidized bed is established and the measurements may be performed. The probe should be calibrated and the results may be used among others to estimate the outer limits of the probe measuring volume. In the present design, the probe measuring depth is 0.3-1.5 mm depending on the local solid concentration. The probe outer diameter is 2,5 mm. The choice of fluorescent dye impregnated tracer particles and proper optical filter combination should be based on light spectral analyses.

An apparatus is disclosed schematically in figure 1. Laser light is suitably treated before transmitted to a probe 1. The laser light is guided to the fluidized bed through optical fibres 3. Receptors 4 receives reflexes from the particles in the fluidized bed, whereby the reflexes from the treated particles have a different way of length, e.g. colour, than from the untreated particles. The signals received in the receptors 4 are treated and registered and may later, with appropriate computer treatment, used for calculation of the velocity of the particles perpendicularly to the probe 1, the direction of movement of the particles in relation to the probe 1 as well as registration of the local particle amount and the bubble characteristics in the fluidized bed.

The head 2 of the probe is arranged in an accurately defined position in relation to the moving direction of the fluidized bed in such a way that the single receptors 4 have an accurate and clearly defined position. The head 2 of the probe comprises an oriented bunch of optical fibres, for example as disclosed in figure 2, whereby some of the optical fibres 3 may emit laser light to eliminate particles. Uniformly distributed between these lights emitting optical fibres are receptors 4 arranged, receiving reflected light and registering this.

The receptors 4 being uniformly distributed between the emitting fibres 3 may for example have a composition as disclosed in figure 2 with an orientated bunch of optical fibres where the distance between the seven receptors 4 is equal and all receptors 4 are surrounded by the same number of light emitting fibres 3. This leads to an optimal and symmetric lightening of the area in front of the receptors. The position of the single receptors 4 in relation to the probe head 2 and as well in relation to the moving direction of the fluidized bed, is fixed and known. To protect the ends of the fibres against wearing from the particles it is suitable with a transparent and wear resistant plate in front of the ends of the fibres. With the transparent plate or window, the probe is prolonged in such a way that blind sounds in front of the receptors will be covered. The equipment used for the measurements is disclosed schematically in figure 1. Light is emitted from a laser source 5, guided through a band pass filter 6 to a coordination table 7 with high accuracy also being used for focusing of the laser beam to the ends 3 of the omitting fibres in the head 2 of the probe 1 .

Signals received by each of the receptors 4 are transmitted through an optical filter 8 to a light detector diode 10 to an amplifier 9. In this case for example seven receptors are used, seven optical fibres (separately), seven separate light detectors and seven separate amplifiers are used. The amplifier 9 comprises a control function 11. The singles are guided further through and A/D converter 12 to a data computer 13 to register and compute the data. By means of the registration data for the single receptors 4, diagrams may be provided corresponding with figure 4 as data from every single receptor 4 is treated separately.

From the diagram in figure 4 can be read that a treated particle has moved corresponding to figure 3 and the diagrams in figure 4. The velocity of the particle in the direction of the curve corresponds with the distance between the maximum values of the succeeding two curves. The figures 6, 1 and 3 refer to the receptors having corresponding figures in figure 3. From the course of the curve in figure 4 is obvious that a tracing particle had a movement corresponding to IV in figure 3.

The lower part of the diagram on figure 6 discloses measurements of the other receptors 4, e.g. measurements of reflexes from not treated particles. The intensity of the these signals is used for calculation of the local particle concentration in front of the probe head.

As the marked as the total particle mass is known, the particle concentration can be calculated based on the tracing particles registered as it is assumed there exists a substantially uniform distribution after the mixing operation. in this way two calculation methods for the particle concentration is achieved.

Figure 5 discloses registered data for a tracing particle V in figure 3. This is achieved based on the mutual positions of the single curves in relation to each other, as well as to their shape and size.

Figure 6 discloses a diagram with curves corresponding to the preceding figures, but where it is obvious that bubbles in the particle mass are registered.

Local bubble characteristics, such as the bubble rise velocity, the bubble appearance frequency, the size and the volume fraction, are calculated based on the background singles from untreated particles. The rise velocity of the bubbles are calculated based on measured time difference between signals from different detectors. The diameter of the bubbles is calculated based on the measured bubble endurance and rising velocity. The appearance frequency of the bubbles is calculated based on the number of measured bubbles per time unit. The volume fraction of the bubbles is calculated from the time in a bubble divided on o the time measured.

A software program for simultaneous treatment of signals from all detectors has been developed. Local particle velocity vectors are measured based on signals from the passing tracer particle by various detectors and geometrical s configuration of the optical fibres in the probe. Local bubble properties and local solid concentrations are determined based on background signals from uncoated particles in the same time series.

The probe can be employed for simultaneous measurement o of following variables in gas-solid systems with local solid concentrations from 0 to 60 vol.-%. Local particle velocity vectors based on signals from the passing tracer particle, local solid concentrations by using an empirical calibration function, and local bubble properties. 5 Local bubble properties such as bubble rise velocity are based on measured time delays. Bubble equivalent diameter is based on measured duration time and rise velocity. Bubble appearance frequency is measured from the number of successfully measured bubbles per time unit. Bubble volume fractions is 0 measured from the time in bubbles divided by total measuring time.

Concentration of the emulsion phase is based on local solid concentrations and bubble volume fractions.

The probe can be applied in most gas-solid systems 5 regardless of the local particle size, the size distribution and shape as well as in high pressure systems, high temperature systems, liquid-solid systems, liquid-gas systems, gas-liquid-solid systems, slurry reactors, systems with various particle types for simultaneous measurement of each particle phase and also as a control/inspection sensor in the above mentioned systems.

Appropriate tracer particles with i.e. fluorescent colour should be prepared for each case. In this connection the choice of fluorescent dye is important. A complete, robust and user friendly program for determination of the desired variables furthermore is of importance for practical use preferably combined with an algorithm for determination of particle velocity vectors in 3-D. Using a three dimentional registration of the particle movements of can register not only the movements of the particles in a plane perpendicularly to the probe, but also in a three dimentional system of co-ordinates.

For determination of particle velocity vectors in high temperature environments, the main challenge is the choice of proper tracer particles. These particles should be chosen based on other radiation properties than fluorescent light.

Claims

P a t e n t C l a i m s

1. Method for measuring the movements of particles and gas bubbles and the concentration of the gas bubbles in a gas- solid system, such as a fluidized bed particle system, CHARACTERIZED IN treating a selected amount of the particle mass with for example a reflecting material, to mix the marked amount o into the rest of the particle mass, to register with a probe (1) having several receptor (4) each tim a marked particle passes by the probe, to compute the received data to thereby calculate the direction of movement, the velocity, the frequency etc of the marked particles. s

2. Probe for measuring the movement of particles in a gas-solid system, such as a fluidized bed with particle, CHARACTERIZED IN said probe comprising a bunch of optical fibres being arranged substantially perpendicular to the direction of movement of the particles, a minority of the fibres being adapted o to be used as receptors ( 4 ) and the rest of the fibres ( 3 ) being adapted to be used for emission of light, the mutual position of the different receptors (4) and the outer surface of the probe being accurately registered, the probe during use thereby always being arranged in exactly the same position in relation to the 5 direction of movement in the fluidized bed.

3. Probe for measuring the movement of particles in a gas-solid system, such as a high temperature fluidized bed with particle, CHARACTERIZED IN said probe comprising a bunch of optical fibres being arranged substantially perpendicular to the o direction of movement of the particles, at least some of the fibres being adapted to be used as receptors (4) for registration of light from a limited figure of the particle mass being specially treated to radiate light of another frequency than the rest of the particles, the mutual position of the different 5 receptors ( 4 ) and the outer surface of the probe being accurately registered, the probe during use thereby always being arranged in exactly the same position in relation to the direction of movement in the fluidized bed.

4. Probe according to claims 2-3, CHARACTERIZED IN a wear resistant, transparent plate, such as sapphire having an approximate thickness of 0.5 mm being arranged abutting the ends of the fibres in the fibre bunch.

5. Method for measuring the movements of particles and gas bubbles and the concentration of the gas bubbles in a gas- solid system, such as a fluidized bed particle system, using the method and the probe according to the preceding claims, CHARACTERIZED IN guiding excitation light from a light source ( 5 ) through emitting fibres ( 3 ) to a probe ( 1 ) for accurate radiation into the fluidized particle system, to receive reflected laser light with the receptors (4) in the probe and to transfer the reflected laser light through at least one filter ( 8 ) , a light detector (10), an amplifier (9) and a control device (11) to a computer ( 13 ) thereby to calculate the movements and the concentration of the local particles and gas bubbled.

6. Means for measuring the movements of particles and gas bubbles and the concentration of the particles in a gas-solid system, such as a fluidized particle bed system, with a method and a probe as defined in claims 1-3, CHARACTERIZED IN the means comprising a source ( 5 ) for emitting excitation light through an emitting fibre ( 3 ) to a probe for directional radiation in the fluidized particle system, the probe thereby comprising receptors ( 4 ) for receipt of reflected laser light and transmittal through a filter (8) and a light detector (10) to an amplifier (9), the amplified signals thereafter being transferred to a data computer (13) for further treatment.