Theme: Modeling & Simulation, P - 107
Hydrodynamic Performance of Prototype Static-Mixer Based Pulsed Column M. Balamurugan, U. Kamachi Mudali and Shekhar Kumar* Process Design & Equipment Section Reprocessing Research and Development Division, Reprocessing Group, Indira Gandhi Centre for Atomic Research Centre, Kalpakkam – 603102 *Corresponding Author, e-mail:
[email protected] Key words: Pulse Column, Hold up in Pulse Column, Static mixer, reprocessing application Abstract Sieve-plate pulsed column was a very mature and conventionally used contactor in nuclear reprocessing industry. Sieve plate pulsed columns have its own limitation of inability to handle suspended solids and hold-up is lower as compared to pulsed disk and doughnut column. The Miniature SMPC pulse column has been developed to handle the suspended solids without any choking and hold-up experiments have been conducted. Miniature SMPC pulse column made up of Ko-Flow static mixer (Material-SS 316, No of static element – 12, height of the column – 255mm and diameter of the column – 16mm). For demonstration, hold-up experiments have been conducted at different throughput and different Af (product of Amplitude and frequency, also called pulsation velocity) at constant A/O ratio of unity with 0.01N HNO3 (Aqueous phase) and 30% TBP (organic phase) system. Aqueous phase was continuous and organic phase is dispersed. From experiments it has found that hold up inside the column was found to be highly dependent on Af. Upper limit of holdup was found to be approx. 32% as compared for the 20% for the conventional liquid pulsed columns. Introduction One of the major equipment available for solvent extraction unit operation is pulse column. Early stages pulsation is created by moving the internals inside the pulse column. Now pulsation inside the column is created by moving the liquid up and down inside the column by external force (by compressed air or by reciprocating pump). There are different types of pulse column available in the market, they are sieve plate, disc and doughnut, rotating disc, etc,. In reprocessing application Sieve Plate pulse column is widely used due to five to six decades of operating experience and also it is well matured compare to all other pulse columns. Here new type of miniature Static mixer based pulse column was developed for reprocessing application in which, it can handle the solid particle without any choking problem.
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Mass transfer performance of the pulse column is mainly depends upon the holdup (surface area available for mass transfer). Hold up inside the column depends upon the operating conditions; they are total throughput, O/A ratio, and pulsation velocity. Pulsation velocity is mainly depends upon the amplitude and frequency inside the column. Holdup inside the static mixer based miniature pulse column was studied in non-mass transfer operating condition at different total throughput and with different pulsation velocity (Af). Experimental Work Description of the setup Experimental setup consist miniature pulse column with two feed pumps and two tanks (one is aqueous tank and another one is organic tank) The miniature static mixer pulse column is made up of in-line static mixer from M/S Ko-Flow Corp. (Material-SS 316, No of static element – 12, height of the column – 255mm and diameter of the column – 16mm). Internals inside the column consists 12 elements each element is made up of two half shaped elliptical plate placed across each other. Pulsation inside the column is created by external pulsing unit, connected in-between pulsing limb in pulse column and compressed air line. Pulsation unit contains two solenoid valves with timer and vacuum line with pressure regulator to control frequency and amplitude respectively. The schematic diagram of the experimental setup is as shown in Fig.1 and photographic view is shown in Fig 2.
Fig. 1 Schematic of setup for non-mass transfer holdup experiments.
Fig. 2 photographic view of miniature static mixer based pulse column.
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The experimental work consists: (i) Hold-up measurement in non mass transfer region for 0.01N HNO3 and 30% TBP system at different pulsation velocity for 50, 100 and 150 ml/min throughput conditions. (ii) Hold-up measurement in non mass transfer region for 0.01N HNO3 and 30% TBP system at different total throughputs with constant pulsation velocity (approx. 2.9 cm/sec). Holdup measurement In these holdup experiments, samples are collected in-between bottom settler and below column internals (bottom sample point). Mixture of organic and aqueous solution was collected into measuring cylinder and kept for 2-3 minutes for settling. After settling, volume of organic and aqueous was noted and holdup is calculated by using below formula. xd =
Vd VC + Vd
(1)
Where xd = holdup Vd = Dispersed phase volume (ml) Vc = Continuous phase volume (ml) In all experiments, continuous phase is 0.01N HNO3 (aqueous) and dispersed phase is 30% TBP in NPH (organic). Results and discussions:Holdup with respect to different pulsation velocity at constant throughput:Pulsation velocity: Pulsation velocity (Af) is the function of amplitude (A) and frequency (f). It’s directly measures the energy input to the pulse column. Pulsation velocity is increased then energy input to the pulse column will increase and holdup also will increase. In this work, how holdup is increasing with respect to pulsation velocity is analyzed and discussed below for different constant throughput conditions At total throughput of 50 ml/min In this experiment, total flow rate of aqueous and organic was maintained at 50 ml/min with O/A ratio of 1. Organic holdup (dispersed phase) was measured with respect to different pulsation velocity and it is shown in fig 3. Results shows holdup is increasing with increase in the pulsation velocity.
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At total throughput of 100 ml/min In this experiment, total flow rate of aqueous and organic was maintained at 100 ml/min with O/A ratio of 1. Organic holdup (dispersed phase) was measured with respect to different pulsation velocity and it is shown in fig 4. Results shows holdup is increasing with increase in the pulsation velocity At total throughput of 150 ml/min In this experiment, total flow rate of aqueous and organic was maintained 150 ml/min with O/A ratio of 1. Organic holdup (dispersed phase) was measured with respect to different pulsation velocity and it is shown in fig 5. Results shows holdup is increasing with increase in the pulsation velocity Correlation for holdup xd with respect to pulsation velocity (Af) was developed for different throughput conditions and it is shown below For 50ml/min xd = 0.0007 + 0.0131(A𝑓) + 0.001(A𝑓)2
(2)
xd = 0.0482 + 0.0007(A𝑓) + 0.0039(A𝑓)2
(3)
xd = 0.042 e0.327(A𝑓)
(4)
For 100ml/min
For 150ml/min
Where A = Amplitude (cm) f = frequency (sec-1) Af = pulsation velocity (cm/sec)
Fig 3: holdup vs pulsation velocity at constant throughput (50ml/min)
Fig 4: holdup vs pulsation velocity at constant throughput (100ml/min) 4
Holdup with respect to different total throughput at constant pulsation velocity (Af ~ 2.9 cm/sec):Here holdup is measured at different throughput by keeping the pulsation velocity is constant. Results shows holdup increases linearly with respect to the total throughput at A/O ratio =1 and it is shown in fig 6. Correlation for holdup xd with respect to throughput was developed for constant pulsation velocity (Af = 2.9 cm/sec) and it is shown below xd = 0.0035 + 0.0008q
(5)
Where q = total throughput (ml/min)
Fig 5: holdup vs pulsation velocity at constant throughput (150ml/min)
Fig 6 holdup vs total throughput at constant pulsation velocity
Conclusions Holdup experiments result shows that holdup is increases with increasing in pulsing velocity but it various according to the total throughput. For lower throughput holdup is high at higher pulsation velocity (xd around 0.2 at Af ~ 9 cm/sec at total throughput of 50ml/min) and at higher throughput holdup is high at much lesser pulsation velocity (xd around 0.32 at Af ~ 6 cm/sec at total throughput of 150ml/min). Similarly holdup is increasing linearly with respect to total throughput at constant pulsation velocity. From results it has found that holdup inside the column was found to be highly dependent on Af and also total throughput. Upper limit of holdup was found to be approx. 0.32 as compared to the 0.2 for the conventional sieve plate pulse column. It has concluded that, miniature SMPC column should be operated at higher total throughput and higher pulsation velocity to achieve good mass transfer inside the column. 5
Nomenclature xd = Holdup (fraction) f = frequency (sec -1) q = Flow rate or throughput (ml/min) A = Amplitude (cm) Vd = Dispersed phase volume (ml) Vc = Continuous phase volume (ml)
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