A bubble curtain model applied in chlorate electrolysis

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Current feeder Outlet electrolyte Inner vessel electrode HCl inlet pH electrode Figure 12: Top view of the inner vessel. The position of the pH electrode, anodes and cathodes, electrolyte outlet and HCl inlet are all located inside the inner vessel. The blue dots are the current feeders to the electrodes. All the different inlets and electrodes that enter the system from beneath are depicted in Figure 12. A maximum of five electrodes can be installed. Every electrode measures 3 by 5 cm. These electrodes are equally spaced, planar and vertically positioned. The anode was a Dimensionally Stable Anode (DSA electrode). It is used in all chlor-alkali and chlorate plants. It consists of a 10 μm electro catalytic coating of Ru x Ti 1−x O 2 . Under industrial conditions a steel cathode is used. In this experiment a titanium cathode is used in order to avoid corrosion. A rectifier is used to set the wanted magnitude of the current between the electrodes. The pH electrode (Mettler Toledo InPro®3100 UD/120/Pt1000) is applied from below which is quite unusual. This electrode also contains a Pt1000 temperature sensor. The pH electrode was calibrated with commercial 4.0 and 7.0 buffers at room temperature and is interconnected with the HCl pump. Whenever the pH rises, then HCl will be pumped through the HCl inlet to adjust it. Plastic curtains are placed around the rack beneath the system, there where the electrodes and HCl enters. This is done for safety reasons in case the HCl inlet gets loose. The thermostat bath is connected with spirals inside the outer vessel to keep the system at the desired temperature. The thermostat bath is not regulated by the temperature sensor in the pH electrode. To empty the reactor after usage another hose is installed through the bottom of the reactor. The pH electrode with temperature sensor, HCl pump and rectifier are connected to a computer where data are logged. 34
Above the electrolyte in the vessel there is a hose with air flow to dilute the hydrogen leaving the electrolyte. Hydrogen gas and air becomes an explosive mixture when the concentration of hydrogen exceeds 4%. On top of the vessel a suction cap is placed to remove the formed and already diluted hydrogen as an extra precaution. 2 H 2 + O 2 → 2 H 2 O (5.1) The following chemicals are used: -NaCl -NaClO 3 -HCl -Na 2 Cr 2 O 7 A brief risk analysis of these products can be found in the addendum. 5.2 Procedure The experiment is done by increasing the current since the electrode surface remains constant. First one liter of electrolyte is used during the experiment. Then it is repeated with two and three liters of electrolyte by adding one extra liter in the next trial. The amount of electrodes and their size can be changed in between two separated experiments. This means it might be possible to have a different current density for the same current. In the first attempts the warm water bath will maintain a temperature of 32℃. The consecutive steps in the experiment are: 1. The reactor is cleaned with water. 2. The thermostat bath is started. Check if the water volume is sufficient. 3. The ventilation suction is checked with a strip of paper. 4. If needed, the pH electrode is recalibrated with buffer 7 and 4 at room temperature. 5. The HCl valve is closed. 6. The bottom drainage function is checked with water. 7. The stipulated volume of chloride/chlorate electrolyte is prepared by dissolving the salts in hot, deionized water. Dichromate is added together with double the molar amount of sodium hydroxide to convert the dichromate to chromate. 8. Electrolyte is charged to the reactor and temperature equilibrium is awaited. 9. The inner vessel and the off gas suction hood are put in place. 10. The computer is started with pH settings according to plan. 11. A minimum through flow of 6 Nl/min air must continuously flush the headspace. To avoid explosive gas mixtures the maximum current for 6 Nlpm is 30 A. 10 Nlpm permits 50 A. 12. The HCl valve is opened. 35
Page 1 and 2: A bubble curtain model applied in c
Page 3 and 4: Acknowledgements Thank you Johan fo
Page 5 and 6: mR equivalent mR hydraulic Nomencla
Page 7 and 8: List of Figures FIGURE 1: THE SOLUB
Page 9 and 10: Chapter 1. Introduction Eka Chemica
Page 11 and 12: Chapter 3. Goal In chlorate electro
Page 13 and 14: Solubility diagram of sodium chlora
Page 15 and 16: Figure 2: Hydrogen solubility in a
Page 17 and 18: Equation (4.12) explains how the la
Page 19 and 20: transformation into the gaseous pha
Page 21 and 22: then be used as c H2 ,bulk. The ave
Page 23 and 24: 2) The next step is the drainage of
Page 25 and 26: Table 5: Reynolds and Eötvös numb
Page 27 and 28: 4.7 Gas voidage In this chapter, th
Page 29 and 30: 4.8 Conductivity and mass transfer
Page 31 and 32: T α z F absolute temperature charg
Page 33 and 34: The wall voidage is connected to th
Page 35 and 36: voltages are given for the model wi
Page 37 and 38: n H2 = PV 4 = 3 πd 1 2 3 4σ d1 +
Page 39 and 40: 4.11 Hydrogen Transport Newly produ
Page 41: Chapter 5. Experimental In the work
Page 45 and 46: 5.3 Results and discussion Table 10
Page 47 and 48: The cause of the early coalescence
Page 49 and 50: The experiments were made with elec
Page 51 and 52: Figure 15: This diagram divides bub
Page 53 and 54: Chapter 9. References [1] W. Bollen
Page 55: [30] L. Nylén, Influence of the el

A bubble curtain model applied in chlorate electrolysis

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