Apparatus and method for measuring a gas volume fraction of an aerated fluid in a reactor

Abstract

A submersible system and method for measuring the gas volume fraction in an aerated fluid inside a reactor (1) wherein the aerated fluid comprises a gas dispersed in the form of bubbles in a fluid in the form of a solution, suspension, mixture of liquids or a combination thereof. The submersible system comprises: an open and pass-through gas exclusion device (20) of a variable cross section wherein the inlet opening whereby the fluid enters without gas bubbles towards the opened and through gas bubbles exclusion device (20) is greater than the outlet opening whereby the fluid exits without gas bubbles of the opened and through gas bubble exclusion device (20). The outlet opening abuts with an inlet pipe (23). A chamber (24) which can provide a sealed camera, can contain at least one flow meter to measure the gas-free fluid velocity when circulating between an inlet (27) and an outlet (28) of the chamber (24) or sealed camera The inlet (27) of the chamber (24) or sealed camera can be coupled to the inlet pipe (23). The outlet (28) of the chamber (24) or sealed camera can be coupled to an outlet pipe (26) of the liquid dispersion towards the reactor (1). A flow transmitter (29) connected to the flow meter, located inside or outside said chamber (24) or sealed camera, generates an outlet signal proportional to the bubbles-free fluid velocity through a gas bubble exclusion device and a calculation unit (30) which generates an output signal (31) proportional to the gas volume fraction in the aerated fluid.

Claims

1. A submersible system (19) for measuring a gas volume fraction in a aerated fluid inside a reactor (1) where the aerated fluid comprises a dispersed gas in the form of bubbles (3) in a fluid in a liquid form, a mixture of multiple liquids, a suspension of solids in a liquid, or a combination thereof, CHARACTERIZED in that said system comprises: an open and pass-through gas exclusion device (20) with a variable cross section, said open and pass-through gas exclusion device (20) defining an opening inlet and an outlet opening, whereby the fluid without gas bubbles enters the opening inlet, and exits through the outlet opening, said pass-through bubble exclusion device (20) has a diameter greater than the outlet opening wherein the outlet opening abuts with an inlet pipe (23); a flow meter-contain chamber (24) defining an inlet (27) and an outlet (28) and containing at least one flow meter that allows measuring velocity of the fluid without gas, when the fluid without gas is circulating between the inlet (27) and the outlet (28) of said flow meter-containing chamber (24), wherein said inlet (27) is coupled to said inlet pipe (23) and wherein said outlet (28) is coupled to an outlet pipe (26) for discharging the fluid without gas towards the reactor (1); a flow transmitter (29) connected to the flow meter, located inside or outside of said sealed camera (24), wherein said flow transmitter (29) generates an output signal proportional to the velocity of the fluid without gas through the gas exclusion device (20); and a processing unit (30) generating an output signal (31) proportional to a gas volume fraction in the aerated fluid.

2. The submersible system (19) for measuring the gas volume fraction in an aerated fluid, according to claim 1, CHARACTERIZED in that said open and pass-through gas exclusion device (20) comprises a cylindrical tube (21) of a constant straight diameter and a diameter reducing section (22) wherein the greatest diameter of the diameter reducing section (22) is equal to the diameter of the cylindrical tube (21) and the smallest diameter is equal to the diameter of the inlet pipe (23).

3. The submersible system (19) for measuring the gas volume fraction in an aerated fluid, according to claim 2, CHARACTERIZED in that said open and pass-through gas exclusion device (20) comprises only one diameter reducing section (22).

4. The submersible system (19) for measuring the gas volume fraction in an aerated fluid, according to claim 3, CHARACTERIZED in that said diameter reducing section (22) is an inverted cone.

5. The submersible system (19) for measuring the gas volume fraction in an aerated fluid according to claim 4, CHARACTERIZED in that said open and pass-through gas exclusion device (20) is vertically installed in the aerated fluid inside the reactor (1).

6. The submersible system (19) for measuring the gas volume fraction in an aerated fluid, according to claim 1, CHARACTERIZED in that said flow transmitter (29) is placed inside the reactor (1).

7. The submersible system (19) for measuring the gas volume fraction in an aerated fluid, according to claim 1, CHARACTERIZED in that said flow transmitter (29) is placed outside the reactor (1).

8. The submersible system (19)) for measuring the gas volume fraction in an aerated fluid, according to claim 1, CHARACTERIZED in that said flow meter-containing chamber (24) comprises a camera, and said flow meter and said transmitter (29) are part of a flow measurement means.

9. The submersible system (19) for measuring the gas volume fraction in an aerated fluid according to claim 1, CHARACTERIZED in that said processing unit (30) is selected from the group consisting of a computer; a programmable logic controller (PLC); a microprocessor; and a distributed control system (DCS).

Description

BRIEF DESCRIPTION OF FIGURES

(1) The accompanying figures are included to provide a better understanding of the invention; they are part of this specification and also illustrate one of the preferred embodiments of this invention.

(2) FIG. 1 shows a schematic view of an ore flotation machine wherein measurements techniques of the gas volume fraction which are described in the state of the art, are shown.

(3) FIG. 2 shows a schematic view of a submersible system for measuring the gas volume fraction dispersed in the form of bubbles in an aerated flow according to the present invention.

(4) FIG. 3 shows an exploded schematic view of a cylindrical tube of the gas exclusion device, according to the present invention.

(5) FIG. 4 shows a chart regarding the typical relationship between the measurement error of a magnetic flow meter and the magnitude of the measured flow velocity.

(6) FIG. 5 shows a chart regarding the relationship between the ascending velocity of air bubbles and its equivalent diameter.

(7) FIG. 6 shows a tube having minimum distance limitations between the flow sensor and the elements causing the energy loss.

(8) FIG. 7 shows in a schematic way, a design example of the apparatus according to the present invention.

(9) FIG. 8 shows a schematic view of a submersible sensor which is partially introduced in a tank containing a determined fluid which can be water, ore pulp or other fluid representing the characteristics of the fluid to be used in the final industrial application for determining the discharge coefficient model.

(10) FIG. 9 shows a chart with the experimental data showing the relationship between the discharge coefficient and the fluid velocity of the fluid, in this case, water.

(11) FIG. 10 shows a block diagram of the submersible system for measuring the gas volume fraction according to the present invention.

(12) FIG. 11 shows a chart with experimental data wherein it is possible to observe the direct relationship between the gas volume fraction and the velocity of a fluid.

DESCRIPTION OF THE INVENTION

(13) As illustrated in FIG. 2, a submersible sensor (19) providing a submersible system, is provided for measuring the gas volume fraction of an aerated flow in a reactor. The fluid (2) can be a liquid, a mixture of multiple liquids, a solid suspension in liquid or a combination thereof. An example of an aerated fluid is a multiphase mixture containing a finely ground solid suspension in water, thereby forming a ore pulp and gas in the form of bubbles as presently found in an ore flotation machines. To simplify the explanation of the present invention, the submersible sensor (19) will be described as a sensor for measuring the gas volume fraction in an aerated ore pulp, understanding that the submersible sensor can be used for measuring the gas volume fraction in any other aerated fluid when the gas is present in the form of bubbles. As will be now described in more detail, the submersible sensor measures the output speed of the pulp when flowing through a gas exclusion device for determining the gas volume fraction in the region where the apparatus is submerged.

(14) The submersible system (19) comprises an open and pass-through gas exclusion device (20) which comprises a tube which ends are opened, vertically installed in an aerated fluid, which cross section presents a reduction from its upper end towards its lower end. The reduction at the opening of the lower end of the gas exclusion device (20) prevents the bubbles (3) from freely entering inside said device, which produces a difference with respect to the apparent density of the aerated pulp outside of the gas exclusion device and that of the gas-free pulp inside the gas exclusion device (20), which generates a continuous descending flow of the pulp through the gas exclusion device exiting by the opening of the lower end, thus returning to the flotation machine (1), and which enters by the upper end of the gas exclusion device (20). This output flow from the gas exclusion device (20) by its lower end completes the bubbles exclusion. The upper section opening of the gas exclusion device (20) must be such that the fluid velocity at the entry of the gas exclusion device (Vp) must be lower than the velocity of the ascending bubbles (Vb) as illustrated in FIG. 3 to prevent these bubbles from being dragged towards the interior of the gas exclusion device (20). At the lower section of the gas exclusion device (20) a flow meter-containing chamber (24), can provide a sealed camera, containing a flow meter which measures, through a flow transmitter (29) the velocity of the pulp circulating by the sensor, is included. The flow metercontaining chamber or sealed camera can comprise a flow measurement means containing at least the flow meter which allows measuring the velocity of the gas-free fluid.

(15) A processing unit (30) determines the gas volume fraction in response to a signal generated by the transmitter (29) which is proportional to the velocity of the pulp.

(16) In an embodiment of the submersible system (19) the flow meter inside the flow meter-containing chamber or sealed camera and its corresponding transmitter (29) measure the pulp flow velocity descending in the lower section of a gas exclusion device (20) by means of a volumetric flow sensor, for instance, a magnetic flow meter which determines the velocity of a flow through the application of a magnetic field, which field lines are perpendicular to the flow direction and which generate an induced voltage which is measured through a pair of electrodes installed at opposite ends of the tube, thereby forming an imaginary orthogonal line both in the magnetic field direction and the flow direction and which is proportional to the velocity of the fluid according to the Faraday Law of Electromagnetic induction. The processing unit determines the gas volume fraction dispersed in the form of bubbles in the aerated pulp in response to the measurement of the descending flow velocity of the pulp.

(17) The open and pass-through gas exclusion device (20) can be formed by one or more different cross-sectional areas. In an preferred manner, the open and pass-through gas exclusion device (20) is formed by a cylindrical and straight tube (21) of a constant diameter, which is opened and through at its ends, which abuts with a diameter reducing section (22) also opened and through at its ends as for example, an inverted cone, wherein its greatest diameter is equal to the diameter of the cylindrical tube (21) which reduces up to a smaller diameter wherein it abuts with an inlet pipe (23).

(18) In a preferred manner, the open and pass-through exclusion device (20) could be formed only by one diameter reducing section (22) which can also be an inverted cone.

(19) The inlet pipe (23) is connected to the inlet (27) of a sealed camera (24) wherein a flow meter is located, which allows measuring the velocity of the pulp circulating through said inlet (27) and the outlet (28) of the sealed camera (24). The outlet (28) of the sealed camera (24) abuts with an outlet pipe (26) with which the ore pulp (2) returns to the flotation machine.

(20) The flow meter provides a sensor contained in the flow meter-containing chamber (24) or sealed camera and is adapted to be submerged and installed in the lower section of the open and pass-through exclusion device (20). The flow transmitter (29) which can be installed inside the flotation cell (1), or, in a remote way, for example, outside the flotation cell (1), generates an output signal proportional to the velocity of the pulp flowing through the flow meter located inside the sealed camera (24) which is processed by a processing unit (30) that generates an output signal (31) proportional to the gas volume fraction of the aerated fluid in the region wherein the submersible system (19) is submerged. The flow transmitter (29) is connected to the flow meter which can be located inside or outside said flow meter-containing chamber (24) or sealed camera.

(21) The open and pass-through gas exclusion device (20), in order to resist adverse working conditions during an extended period of time, preferably is manufactured from a material resistant to corrosion and abrasion, for example, a plastic or ceramic material (PTFE, PVDF or derivatives thereof). At the lower section of the open and pass-through gas exclusion device (20) is installed the flow meter providing a sensor inside the flow meter-containing chamber (24) or sealed camera which can be installed by means of flanges fixed by means of bolts and nuts, screwed or in a similar way. The flow meter providing a sensor protected inside the flow meter-containing chamber or sealed camera is electrically connected to the flow transmitter (29) which generates an output signal proportional to the velocity of the pulp passing through a sensor located inside the flow meter-containing chamber (24) or sealed camera.

(22) The flow meter providing the sensor or sensor element contained inside the sealed camera (24) is adapted to be submerged in a suspension, for example, by means of the encapsulation of the electronic components of the sensor in a mechanical way or by means of chemical additive providing it with IP 68 properties.

(23) The flow transmitter (29) is preferably installed outside the aerated flow, for example, outside the flotation machine and is electrically connected to the flow meter providing the sensor inside the flow meter-containing chamber (24) or sealed camera by means of a cable, which is canalized through a conduct that protects it from external conditions.

(24) The processing unit (30) receives an output signal proportional to the velocity of the pulp passing by the flow meter providing the sensor located inside the flow meter-continuing chamber (24) or sealed camera (24) and calculates the gas volume fraction dispersed in the form of bubbles (3) in the ore pulp (2). The processing unit (30) can be implemented in any electronic device with processing capacity such as a computer, a PLC (Programmable Logic Controller), a DCS (Distributed Control System), a microprocessor or the like.

(25) According to the present invention, the flow meter inside the flow meter-containing chamber (24) or sealed camera measures the velocity of the pulp to determine the gas volume fraction by means of the following equation (3), which is obtained when applying the energy-conservation principle to the fluid passing through a flow meter inside the sealed camera (24) installed at the lower section of a gas exclusion device (20).

(26) $\begin{array}{cc}{\mathrm{.Math.}}_g=\frac{1}{2\mathrm{gL}}.Math.{\left(\frac{v}{C_d}\right)}^2.Math.\left[1-{\left(\frac{d}{D}\right)}^4\right]& \left(3\right)\end{array}$

(27) wherein .sub.g. Gas volume fraction in the aerated fluid L: Total length of the apparatus according to the present invention v: Fluid velocity through the gas exclusion device measured at the lower section thereof C.sub.d: Discharge coefficient d: Lower end diameter of the gas exclusion device D: Upper end diameter of the gas exclusion device (D>d) g: Acceleration of gravity

(28) The discharge coefficient (C.sub.d) represents the quotient between the flow real velocity measured by the flow meter located inside the sealed camera (24) and the theoretical velocity that would result if the flow did not experiment any energy loss when flowing through the apparatus proposed in this invention as defined in the book titled Applied Fluid Mechanics (2006) by Mott for a fluid flowing through a Venturi tube. According to the present invention, the discharge coefficient can be expressed as:

(29) $\begin{array}{cc}{C}_d=\sqrt{\frac{1-{\left(\frac{d}{D}\right)}^4}{1-{\left(\frac{d}{D}\right)}^4+K}}& \left(4\right)\end{array}$

(30) wherein D and d are the diameters of outlet and inlet openings of the gas bubble exclusion device (20) respectively and K is the total resistance coefficient regarding the passing of the fluid. Parameter K is a function of the geometry of the gas exclusion device, the type of the flow meter, the surface roughness whereby the fluid flows and Reynolds (Re) Number of the fluid. Once the geometry and the material of gas exclusion device as well as the type of flow meter are completely determined, the total resistant coefficient (K) is mainly a function of the velocity of the pulp in the lower section of the gas exclusion device, that is, K=(v). A preferred mathematical function, but not the only one, to relate the fluid velocity of the lower end of the gas exclusion device and the resistance coefficient is:
K=a.Math.v.sup.bc(5)

(31) wherein a, b and c are real values to be experimentally determined or this can be done means of a flow dynamic simulation.

(32) In this way, the discharge coefficient is a function of the velocity of the pulp (v) exiting through the lower section of the gas exclusion device (20) and the outlet and inlet diameter ratio (d/D) thereof.

(33) $\begin{array}{cc}{C}_d\left(v\right)=\sqrt{\frac{1-{\left(\frac{d}{D}\right)}^4}{1-{\left(\frac{d}{D}\right)}^4+\left(a.Math.v^{-b}+c\right)}}& \left(6\right)\end{array}$

(34) For the experimental determination of the parameters a, b and c in the discharge coefficient model preferably an adaption of the set-up proposed in the Engineering Master Thesis at the McGill University in Canada, titled Design of a gas holdup sensor for flotation diagnosis (1998), by Franklin Corts-Lpez, is used. FIG. 8 illustrates an application of said set-up in the determination of the discharge coefficient model according to the present invention.

(35) In the set-up, the submersible sensor is partially introduced in a tank containing a determined fluid, this can be water, ore pulp or other fluid representing approximately the characteristics of the fluid to be used in the final application. By means of a pump and a valve (39) a recirculation fluid flow is regulated from the tank towards the upper opening of the gas exclusion device (20) which produces, in a stationary status, a difference between the fluid level inside the submersible sensor and the fluid level in the tank (H) as illustrated in FIG. 8. The real velocity (40) of the fluid is provided by means of the flow meter inside the flow meter-containing chamber (24) or sealed camera and its corresponding transmitter (29). The theoretical or ideal velocity, that is, under the assumption that there are no energy losses, can be calculated when applying the Bernoulli equation to the fluid through the sensor proposed according to the present invention.

(36) $\begin{array}{cc}{v}_{\mathrm{ideal}}=\sqrt{\frac{2.Math.g.Math.H}{1-{\left(\frac{d}{D}\right)}^4}}& \left(7\right)\end{array}$

(37) In this way, the discharge coefficient can be calculated as the quotient between the velocity of the flow determined by means of the flow meter inside of the flow meter-containing chamber (24) or sealed camera and its corresponding transmitter (29) and the theoretical velocity calculated by means of the equation (7). This procedure is repeated by modifying the recirculation flow and storing the flow velocity data and the corresponding height difference H, thus generated. FIG. 9 shows the typical relationship between the discharge coefficient and the velocity of the fluid. Parameters a,b and c which are determined by means of the minimization of the sum of the squared differences between the experimentally determined discharge coefficient and the value provided by the model shown in FIG. 9 turned out to be for this particular case a=0.794, b=0.715 and c=0.

(38) In order to facilitate the process of measuring the fluid velocity without gas bubbles, for instance, the ore pulp (2) and determining the gas volume fraction dispersed in the form of bubbles (3), in such a way that said volumetric fraction can be used for monitoring and controlling the process inside a flotation machine, the system is provided with a processing unit (30) which block diagram is shown in FIG. 10. The processing unit (30) receives the information of the fluid velocity from the transmitter (29) and provides as an output signal (37) the gas volume fraction value, .sub.g. Said processing unity (30) has stored the geometrical parameters of the gas exclusion device in a memory (34) and it is also provided with a processor (35) which calculates the discharge coefficient C.sub.d considering the velocity of the flow provided by the transmitter (29), the diameter reducing ratio (d/D) and parameters experimentally determined or by means of a computer simulation. The flow velocity value provided to the processing unit (30) by the transmitter (29), the geometrical parameter values of the gas exclusion device stored in the memory (34) and the discharge coefficient C.sub.d provided by the first processor (35) go in confluence up to a second processor (36) which calculates the gas volume fraction .sub.g, and provides it as an output signal (37) for monitoring the process, or, to perform corrections as for example, injecting a greater quantity of air, or incorporating more chemical reagents such as frothers with which is possible to implement an automatic control system for flotation machines.

(39) Example of the design calculation with the design conditions of the exclusion device.

(40) Conditions of the Design

(41) 1) The measurement range of the gas volume fraction in a flotation machine normally varies between 5% and 30%.

(42) 2) The minimum diameter at the lower end of the gas exclusion device must be of at least 1 inch (25 mm) in order to prevent the sensor of the design from clogging in case of existing elements alien to the process.

(43) 3) The minimum velocity of the fluid at the lower end of the gas exclusion device must be greater than 0.7 m/s (which is a value that guarantees a good accuracy on the part of the flow meter according to what is shown in reference (32) of FIG. 4).

(44) 4) The maximum velocity at the upper end of the gas exclusion device must be lower than 3 cm/s, which guarantees that bubbles of a diameter greater to approximately 0.3 mm, will not be dragged towards the interior of the gas exclusion device as a result of the circulating flow, as shown in reference (33) in the FIG. 5.

(45) 5) The minimum closest distance between the flow meter inlet and the restriction regarding the flow passing upstream must be at least 5 times the diameter of the nominal pipe of the flow meter element in order to guarantee that the fluid is completely developed at the measurement point as shown in FIG. 6.

(46) 6) The minimum closest distance between the flow meter outlet and the restriction regarding the flow passing downstream must be at least 3 times the diameter of the nominal pipe of the flow meter element in order to guarantee that the fluid is completely developed at the measurement point as shown in FIG. 6.

(47) According to the aforementioned, an example of calculation can be carried out in the following way:

(48) An electromagnetic flow meter Siemens TRANSMAG2 911/E of a nominal diameter of 25 mm, which satisfies the design condition 2) will be considered. This flow meter has a length of 270 mm as shown in FIG. 7.

(49) In order to satisfy the design condition 5), the distance between the cone and the flow meter inlet, located inside the flow meter-containing chamber (24) or sealed camera is selected equal to 6 times the diameter of the pipe, that is, 625 mm=150 mm.

(50) In order to satisfy the design condition 6), the distance between the flow meter outlet and the discharge is selected equal to 80 mm (3, 2 times the nominal diameter of the pipe).

(51) The length of the sensor containing gas can be calculated from the minimum velocity condition (0.7 m/s) which is obtained when the gas volume fraction is minimum (5%). Considering an average initial discharge coefficient equal to 0.7 and isolating the total length L of equation 3, it is obtained: L1000 [mm]

(52) Considering the dimensions already found, then the length of the upper inverted cone of the gas exclusion device results to be of 500 mm as shown in FIG. 7.

(53) It is necessary to confirm that the design condition 4 is satisfied for the selected dimensions, that is, that the inlet fluid velocity at the upper end of the gas exclusion device is lower than 3 cm/s for the maximum value of the gas volume fraction desired to be measured (30%). The outlet value of the fluid velocity v.sub.2 in the tube (23) for the selected conditions, obtained using the equation 3 is of 1.70 m/s.

(54) The velocity at the upper end can be calculated by means of the continuity equation, that is:
v.sub.1.Math.A.sub.1=v.sub.2.Math.A.sub.2

(55) Wherein v.sub.1 y v.sub.2 is the fluid velocity at the upper and lower end respectively and A.sub.1 and A.sub.2 is the cross section of the gas exclusion device at the upper and lower end respectively:

(56) $v_1=v_2.Math.{\left(\frac{d}{D}\right)}^2<0.03\left[m\text{/}s\right]$

(57) If the upper diameter of the gas exclusion device equal to 200 mm is selected, then it is obtained:

(58) $v_1=1,7.Math.{\left(\frac{25}{200}\right)}^2=0.0265<0.03\left[m\text{/}s\right]$
which satisfies the design criterion 4.

(59) With the previously mentioned results, a design example of the exclusion device is the one shown in FIG. 7.

Advantages of the Present Invention

(60) The present invention comprises the differentiating and advantageous characteristics with respect to the current technologies. 1. It allows an on-line and real time measurement of the gas volume fraction. 2. The gas volume fraction measurement is not affected by the presence of other disperse phases such as solid particles or liquid drops. 3. The accuracy only depends on the measurement of a variable, the pulp velocity circulating through a tube using a non-invasive technique (for example, a magnetic flow meter). Measured velocities with this kind of instrument present an error rate lower than 0.5%. 4. The measurement is precise since the error propagation when calculating the volumetric fraction is minimum when based only on one measurement. 5. Once installed in the process, the device does not require to be re-calibrated. 6. It provides a wide measurement range of the gas volume fraction in pulps, which includes the range observed in the flotation process (5% up to 30% approximately). 7. The measurement provides an average of the gas content (hold-up) in the whole volume of the flotation machine comprised between the depths defined by the upper and lower ends of the device and is not limited to the radial position in which the device is installed.

BIBLIOGRAPHICAL REFERENCES

(61) Corts-Lpez, F. Design of a gas holdup sensor for flotation diagnosis. Thesis of Master of Engineering, McGill University, 1998. Finch, J. A, & Dobby, G. S. Column Flotation. Pergamon Press, pp. 10, 1990, ISBN: 0-08-040186-4. Finch, J. A., Xiao, J., Hardie, C., Gomez, C. O. Gas dispersion properties: bubble surface area flux and gas holdup. Minerals Engineering, Vol. 13, No. 4, pp. 365-372, 2000. Finch, J. A., Gelinas, S., Moyo, P. A frother-related research at McGill University. Minerals Engineering, 19, pp. 726-733, 2006. Gomez, C. O., Corts-Lpez, F. & Finch, J. A. Industrial testing of a gas holdup sensor for flotation systems. Minerals Engineering, Vol. 16, Issue 6, pp. 493-501, 2003. Gorain, B. K., Franzidis, J.-P. & Manlapig, E. V. Studies on impeller type, impeller speed and air flow rate in an industrial scale flotation cell. Part 2: effect on gas holdup. Minerals Engineering, Vol. 8, No. 12, pp. 1557-1570, 1995. Gorain, B. K., Napier-Moon, T. J., Franzidis, J.-P., Manlapig, E. V. Studies on impeller type, impeller speed and air flow rate in an industrial scale flotation cell. Part 5: Validation of k-Sb relationship and effect of froth depth. Minerals Engineering, Vol. 11, No. 7, pp. 615-626, 1998. Harbort, G. J. & Schwarz, S. Characterization measurements in industrial flotation cells. Chapter 5 Flotation Plant Optimisation, C. J. Greet (Ed), AusIMM 2010, pp. 95-106, ISBN 978-92-522-47. Jin, H., Han, Y., Yang, S., He, G. Electrical resistance tomography coupled with differential pressure measurements to determine phase hold-ups in gas-liquid-solid outer loop bubble column. Flow Measurements and Instrumentation, 21, pp. 228-232, 2010. Lopez-Saucedo, F., Uribe-Salas, A., Prez-Garibay, R. & Magallanes-Hernandez, L. Gas dispersion in column flotation and its effect on recovery and grade, Canadian Metallurgical Quarterly, Vol. 51, No. 2, pp. 111-117, 2012. Mott, R. L. Applied Fluid Mechanics. 6th Edition, Pearson Prentice Hall, 2006, pp. 478, ISBN: 0-13-197643-5. Patel, A. K. & Thorat, B. Gamma ray tomographyAn experimental analysis of fractional gas hold-up in bubble columns. Chemical Engineering Science, Vol. 137, Issue 2, pp. 376-385, 2008. Sanwani, E., Zhu, Y., Franzidis, J.-P. Manlapig, E. V., & Wu, J. Comparison of gas holdup distribution in a flotation cell using capturing and conductivity techniques. Minerals Engineering, Vol. 19, Issue 13, pp. 1362-1372, 2006. Schweitzer, J-M., Bayle, J., Gauthier, T. Local gas hold-up measurements in fluidized bed and slurry bubble columns. Chemical Engineering Science, 56, pp. 1103-1110, 2001.