Effect of rotation speed of electrode on the regeneration rate Figure 3 illustrates the effect of rotation speed of 138 Figure 2 Experimental process flow diagram I?power supply; 2?motor; 3?quid distributor; 4?cathode; 5?ceramic membrane; 6?gas distributor; 7?anode; 8?air steel container; 9?regenerated solution tank; 10?original decentralization solution tank; 11?pump is too high, the contact time between the collated iron elution and electrode is shortened, and the electrochemical oxidation reactions will be not complete, so the regeneration rate decreases slightly.
Moreover, it is well known that higher rotating speed will cause in industrial applications.In this experiment, the regeneration rate can reach a maximum value of 84.9% when rotation speed of electrode is equal to 180 rain-l, which is about 1.
6 times that achieves in the static electrode environment. The experiments demonstrate that the rotating electrode has significant advantages in improving the regeneration rate. Figure 3
Effect of rotation speed of electrode on the regeneration rate electrode on the regeneration rate at a voltage of 4 V, an inlet air flow rate of 2 MPH-1 and an inlet liquid flow rate of 80 Lo-l . A higher rotating speed of electrode is favorable to increase the regeneration rate, resulting in higher regeneration efficiency. At lower rotating speed, the air bubbles in solution and the bubbles created during electrochemical reactions can adhere easily to the electrode surface and reduce the electrode activity area, which will decrease the electrochemical oxidation efficiency.
With an increasing rotating speed, the bubbles can be timely detached from the electrode surface, and the thickness of diffusion layer decreases and the concentration difference can be eliminated rapidly. The increase of current density enhances the electrochemical regeneration effect. At the same time, the gas-liquid mixing degree and turbulence intensity will be enhanced to favor the mass transfer at a higher rotating speed, which can lead to the quick supplement of the dissolved oxygen consumed in the regeneration process.
Thus, the regeneration rate increases with increasing rotating speed. However, when the rotating speed of electrode 3. 2 Effect of voltage on the regeneration rate Figure 4 shows the influence of voltage on the regeneration rate at a rotation speed of electrode of 180 rain-l, an inlet air flow rate of 2 MPH-1 and an inlet liquid flow rate of 80 Lo-l . The regeneration rate increases as voltage increases due to that the current density increases rapidly at the initial stage with the increase of voltage, resulting in an increased electrochemical reaction driving force.
The increase of voltage is favorable to the regeneration rate in both of he rotating electrode and the static electrode environments. But the regeneration rate in the rotating electrode environment is higher than that in the static electrode environment at the same voltage due to that the rotating electrode can provide a great and rapid renewed surface of the electrode to strengthen the electrochemical oxidation process. When the voltage regeneration rate increases slowly probably due to that the current density and the electrochemical reaction driving force increases slowly.
Moreover, too high voltage easily leads to higher energy consumption and more side reactions. Thus, an appropriate voltage of 4 V is selected and the regeneration rate is 84. 8%. The new electrochemical reactor can be considered as the 139 strengthens the micro-mixing efficiency of the air and solution, resulting in excellent mixing and higher mass transfer rate. When inlet air flow rate increases to higher than 2 MPH-1, the regeneration rate increases slowly.
The reason may be that the residence time of air becomes shorter in solution and the gas-liquid mass transfer efficiency decreases with a too large inlet air flow rate. Therefore, an inlet air flow rate of 2 MPH-1 s appropriate and the regeneration rate is 84. 8%. The experiments indicate that the rotating electrode has significant influence on improving the regeneration efficiency of air oxidation. Figure 4 Effect of voltage on the regeneration rate rotating electrode; A static electrode traditional tank-type reactor on condition that the voltage is O V in the static electrode environment.
Under the optimum conditions, the regeneration rate of the new electrochemical reactor is increased from 45. 3% to 84. 8% compared with the traditional tank-type reactor. The experiments indicate that the rotating electrode can dramatically improve the efficiency of electrochemical oxidation. 3. 3 Effect of inlet air flow rate on the regeneration rate Figure 5 shows the effect of inlet air flow rate on the regeneration rate at a rotation speed of electrode of 180 rain-l, a voltage of 4 V and an inlet liquid flow rate of 80 Lo-l .
With increasing inlet air flow rate, the regeneration rate first increases rapidly and then changes slightly both in the rotating electrode and static electrode environments due to that the dissolved the rotating electrode environment, the regeneration rate is always higher than that achieved in the static electrode environment because the rotating electrode Figure 5 Effect of inlet air flow rate on the regeneration rate rotating electrode; A static electrode 3. Effect of inlet liquid flow rate on the regeneration rate Figure 6 illustrates the effect of inlet liquid flow rate on the regeneration rate at a rotation speed of electrode of 180 rain-l, a voltage of 4 V and an inlet air flow rate of 2 MPH-1. The regeneration rate first decreases slowly and then decreases rapidly with the increase of the inlet liquid flow rate in the rotating electrode environment, which shows the same trend as he case of the static electrode environment.
The smaller the inlet liquid flow rate is, the longer the residence time of liquid in the electrochemical reactor will be. Long residence time can benefit the regeneration of the collated iron decentralization solution because the gas-liquid contract time and the electrolysis time are one of the most important influence factors of the regeneration process. When inlet liquid flow rate is less than 80 Oh-I, the regeneration rate remains at over 84. 6%.
When inlet liquid flow rate continues to increase to higher than 80 Lo-l , the residence time of quid in the electrochemical reactor becomes shorter gradually, resulting in rapid decrease in the regeneration rate. Under the condition that the treatment capacity is bigger and the regeneration rate is higher, an optimum inlet liquid flow rate of 80 Lo-l is selected and the regeneration rate reaches 84. 6%, which is about 1. 6 times that in the static electrode environment.
The Figure 6 Effect of inlet liquid flow rate on the regeneration rate rotating electrode; A static electrode 140 experiments demonstrate that the rotating electrode has significant advantages in increasing the treatment opacity of regeneration process. A new type of electrochemical reactor with rotating cylindrical electrodes exhibits better regeneration performance for the collated iron decentralization solution than the traditional tank-type reactor due to its good electrochemical oxidation property and gas-liquid mass transfer performance.
The novel electrochemical reactor can not only provide a great and rapid renewed surface to accelerate the regeneration process of electrochemical oxidation, but also provide an excellent gas-liquid mixing environment to strengthen the regeneration recess of air oxidation, overcoming the poor mass transfer effect and the low oxidation regeneration efficiency in the traditional tank-type reactor. Under the optimum conditions, the regeneration rate of collated iron decentralization solution is increased from 45. 3% to 84. 8%.
