- With the rapid development of the production process of ion exchange membrane caustic soda, a new type of membrane electrode distance electrolytic cell has been applied in ion exchange membrane electrolysis devices, providing strong technical support for further reducing the energy consumption of ion exchange membrane caustic soda products. The membrane electrode distance electrolytic cell mainly shortens the distance between the membrane and the electrode network by improving the shape of the anode side electrode network. Due to the fact that the ion film of the membrane electrode distance electrolytic cell is attached to the anode and cathode, and the cathode mesh is relatively rough, higher requirements are put forward for the stable operation of the pressure and pressure difference between the anode and cathode chambers. If the pressure or pressure difference is unstable, it may cause mechanical damage to the ion membrane, usually due to pinholes, bubbles, delamination, or “smiling face” shaped tears on the ion membrane. Slight damage to the ion membrane and short duration can affect its performance, leading to a decrease in current efficiency; If the ion membrane is severely damaged, the alkaline solution migrates from the cathode side to the anode side, corroding the anode mesh and the anode back plate of the unit tank. If the leakage point appears around the center radiation of the unit cell back plate, if not detected in a timely manner, the anode liquid will quickly corrode the cathode half shell, which may cause an explosion accident caused by the mixture of hydrogen and chlorine gas in the cathode and anode electrolysis chamber. Therefore, the process control of chlorine gas, hydrogen pressure, and chlorine hydrogen pressure difference is particularly important in the production process.
- Analysis of the reasons for the fluctuation of hydrogen chloride pressure difference2.1 The discharge valve is installed on both sides in front of the electrolytic cell, and the ambient temperature of the electrolytic cell is not less than 36 ℃ throughout the year; Therefore, if the pressure relief valve is exposed to high temperature for a long time, the electronic module in the pressure relief valve positioner is prone to aging, burning, and other faults.2.2 The frequency of use of pressure relief valves is relatively low, and long-term inactivity can lead to jamming; So during operation, there may be situations such as jamming, inability to open or close.2.3 The discharge valve is an accident on-off valve. Sudden rupture of the gas source pipe, loosening of the instrument line, and other faults can cause the pressure relief valve to open instantly, leading to instantaneous fluctuations in the pressure difference between chlorine and hydrogen.The above are the main reasons for the sudden opening, jamming, and inaccurate positioning of the pressure relief valve.
- Limitations of the pressure relief valve itselfIn order to meet the process requirements and quickly relieve pressure in case of accidents, the relief valve is a butterfly valve, and the limitations of the butterfly valve itself lead to excessive pressure relief during operation, resulting in fluctuations in the pressure difference between chlorine and hydrogen. Although the nitrogen filling valve at the end of the tank can be manually opened to replenish pressure during operation, it is still unable to maintain the balance of the chlorine and hydrogen pressure difference.
- Based on the analysis of the reasons for the fluctuation of chlorine and hydrogen pressure difference during the single groove cutting system, and through continuous practical exploration and demonstration by the team, the following two points are summarized.(1) On the premise of not changing the process, the operator is required to open and close the pressure relief valve by observing the pressure on the cathode and anode sides. The experimental data is analyzed, and it is found that the pressure on the cathode and anode sides will not change until the opening of the pressure relief valve is between 20% and 25%. Therefore, it is possible to continue to slowly open during this process, while observing the actual opening of the relief valve on site. If the opening of the valve on site is consistent with the opening of the operation screen, close the relief valve to 0% and repeat it three times to ensure that the relief valve can operate normally. When the opening of the pressure relief valve is greater than 25%, the pressure may drop or fluctuate at any time. Therefore, during the operation, the pressure relief valve should pause every 2% opening to observe the pressure changes on the positive and negative sides. If there is a fluctuation, the nitrogen filling valve at the end of the tank should be opened for pressure replenishment. When the opening of the negative and positive pressure relief valve reaches 65%~70%, the gas phase of the negative and positive system is basically relieved, and the pressure relief valve can be operated significantly until the pressure of the negative and positive system is 0 and the opening of the pressure relief valve is 100%.(2) Technological transformation was carried out on the process pipeline, and a DN25 bypass pipeline control was added to the relief valve pipeline (see Figure 1 for details). The DN25 control valve was moved to the front of the electrolytic tank, and the operator manually relieved the pressure based on the data from the chlorine hydrogen pressure display cabinet in front of the electrolytic tank, which can avoid the problem of pressure relief valve failure. After all the pressure of chlorine and hydrogen has been relieved, open the relief valves 3 and 4, close the manual valves 5 and 6, open the automatic control valve for the feeding of the anode and cathode, and the electrolytic cell can circulate normally. This can greatly reduce the fluctuation of chlorine and hydrogen pressure.
Pressure relief bypass technology transformation
1. -Anode discharge main pipe，2-Cathode discharge main pipe，
3- Anode pressure relief valve 4. Cathode manifold valve，
5,6- DN25 Manual relief valve added to the bypass pipeline