Chlor-alkali electrolysis cathode gas phase pressure and alkali concentration control system

Abstract

A control system for the cathode gas phase pressure and alkali concentration in chlor-alkali electrolysis includes a nitrogen replacement control unit: a nitrogen regulating valve, a nitrogen flow meter, and a nitrogen shut-off valve are sequentially installed on the pipeline; an alkali concentration regulating unit: a density transmitter and a pure water pipeline are installed on the outlet pipeline of the alkali circulation tank; and an alkali temperature control unit: used to cool the cathode liquid exiting the alkali circulation tank before it enters the electrolytic cell; the hydrogen inlet of the cathode liquid circulation tank is connected to the electrolytic cell, and the alkali inlet of the alkali circulation tank is connected to the electrolytic cell after passing through an alkali circulation pump and an alkali cooler. Compared with the prior art, this invention accurately maintains the set nitrogen flow rate, achieves automatic control, efficiently replaces hydrogen in the cathode system with nitrogen, and continuously maintains an inert atmosphere, reducing human error and accidents; it also controls the water addition in real time to ensure stable alkali concentration; and it cools the alkali solution temperature with circulating water before it enters the electrolytic cell, avoiding damage to the ion exchange membrane caused by temperature rise.

Description

Technical Field

[0001] This utility model relates to the field of chlor-alkali electrolysis chemical production technology, and in particular to a control system for the cathode gas phase pressure and alkali concentration of chlor-alkali electrolysis. Background Technology

[0002] In chlor-alkali electrolysis production, traditional nitrogen purging systems often rely on manual valve control, resulting in significant pressure fluctuations (above ±2 kPa) during the purging process. This poses a high risk of overpressure damage to the ion-exchange membrane or negative pressure intake of air, leading to explosive mixtures. Traditional nitrogen purging schemes fail to address the issue of precise pressure control and lack emergency interlock protection. Secondly, alkali concentration adjustment relies on manual sampling and detection, resulting in a response lag (typically 2-4 hours) and concentration deviations of ±3%, severely impacting electrolysis efficiency. Most existing technologies employ offline density meters, failing to achieve real-time closed-loop control. Furthermore, cathode liquid temperature control typically uses a single-stage cooling loop. During vigorous electrolysis, cooling lag leads to frequent alkali liquid temperature exceedances (>90℃), accelerating ion-exchange membrane aging. While some traditional cooling systems have increased heat exchange areas, they lack a coordinated mechanism with nitrogen purging and concentration control. More critically, existing units operate independently, and the DCS system lacks integrated design, failing to synchronously trigger nitrogen purging, concentration adjustment, and temperature control during emergency shutdowns, posing significant safety hazards. Utility Model Content

[0003] To address the aforementioned deficiencies in existing technologies, this utility model provides a control system for the cathode gas phase pressure and alkali concentration in chlor-alkali electrolysis, as follows:

[0004] The technical solution of this utility model is implemented as follows:

[0005] A control system for the cathode gas phase pressure and alkali concentration in chlor-alkali electrolysis includes:

[0006] Nitrogen replacement control unit: The nitrogen main pipe is connected to the gas phase inlet at the top of the cathode liquid circulation tank through a pipeline. A nitrogen regulating valve, a nitrogen flow meter and a nitrogen shut-off valve are installed on the pipeline in sequence. The nitrogen regulating valve, nitrogen flow meter and nitrogen shut-off valve are respectively connected to the DCS controller.

[0007] Alkali concentration adjustment unit: includes an alkali circulation tank, a density transmitter and a pure water pipeline are installed on the outlet pipe of the alkali circulation tank, and a flow regulating valve is connected in series on the pure water pipeline. The density transmitter (8) and the flow regulating valve are respectively connected to the DCS controller.

[0008] Alkali temperature control unit: The outlet of the alkali circulation tank is connected to the inlet of the alkali circulation pump through the alkali main pipe;

[0009] The outlet of the alkali circulation pump is connected to the alkali inlet of the alkali cooler via the alkali main pipe;

[0010] The alkali outlet of the alkali cooler is connected to the cathode inlet of the electrolytic cell via the alkali main pipe;

[0011] A temperature sensor is installed on the alkali outlet pipe of the alkali cooler.

[0012] The circulating water inlet of the alkali cooler is connected to a temperature regulating valve via a pipe, and the circulating water outlet is connected to the return water network.

[0013] The temperature sensor and temperature regulating valve are respectively connected to the DCS controller.

[0014] The hydrogen inlet of the cathode liquid circulation tank is connected to the electrolytic cell, the hydrogen outlet of the cathode liquid circulation tank is connected to the hydrochloric acid station, and the alkali inlet of the alkali circulation tank is connected to the electrolytic cell after passing through the alkali circulation pump and alkali cooler.

[0015] Preferably, it also includes an alkaline solution high-level tank level stabilization unit, which is installed on the alkaline solution pipeline between the alkaline solution cooler and the electrolytic cell. The alkaline solution high-level tank level stabilization unit includes an alkaline solution high-level tank, on which a level sensor is installed, and the level sensor is connected to a DCS controller.

[0016] Preferably, the nitrogen replacement control unit further includes a pressure controller, whose input end is connected to a pressure sensor installed in the pipeline via a cable, and whose output end is connected to a nitrogen regulating valve via a cable, forming an independent pressure closed-loop control branch.

[0017] Preferably, the DCS controller has a built-in interlocking module that automatically opens the nitrogen shut-off valve and nitrogen regulating valve after receiving an emergency stop signal, and controls the nitrogen flow rate to ≥50 Nm / h.

[0018] Preferably, in the alkaline solution temperature control unit, a flow meter and a flow regulating valve are provided on the circulating water circuit, both of which are electrically connected to the DCS controller to form a secondary control circuit.

[0019] Preferably, the cathode liquid circulation tank and the alkali liquid circulation tank are integrated devices, with the cathode liquid circulation tank located above the alkali liquid circulation tank, and an alkali liquid drainage hole provided between the cathode liquid circulation tank and the alkali liquid circulation tank.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The chlor-alkali electrolysis cathode gas phase pressure and alkali concentration control system of this utility model uses a pressure controller, flow meter, regulating valve and protection shut-off valve to form a closed-loop control circuit, accurately maintain the set nitrogen flow rate, realize automatic control, improve the safety and reliability of the device, efficiently replace hydrogen in the cathode system with nitrogen, and continuously maintain an inert atmosphere, reducing human error and accidents.

[0022] Equipped with a high-precision density transmitter and flow meter, along with an automatic control valve, the system's alkali concentration is monitored in real time. The water supply to the cathode system is adjusted based on the alkali concentration to ensure stability.

[0023] The alkaline solution is cooled by circulating water before entering the electrolytic cell to prevent the temperature from rising and damaging the ion membrane. At the same time, the boiling of the alkaline solution due to high temperature will affect the electrolysis efficiency.

[0024] This invention achieves triple safety closed-loop control through pipeline connection and control logic integration. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the system principle of the chlor-alkali electrolysis cathode gas phase pressure and alkali concentration control system of this utility model.

[0026] In the diagram: 1. Nitrogen main pipe, 2. Cathode liquid circulation tank, 3. Nitrogen regulating valve, 4. Nitrogen flow meter, 5. Nitrogen shut-off valve, 6. DCS controller, 7. Alkali circulation tank, 8. Density transmitter, 9. Pure water pipeline, 10. Flow regulating valve, 11. Alkali circulation pump, 12. Alkali cooler, 13. Flow meter, 14. Temperature sensor, 15. Temperature regulating valve, 16. Alkali high-level tank, 17. Liquid level sensor, 18. Pressure controller, 19. Pressure sensor. Detailed Implementation

[0027] The present invention will now be described clearly and completely with reference to the accompanying drawings of the embodiments thereof.

[0028] like Figure 1 As shown, a control system for the cathode gas phase pressure and alkali concentration of chlor-alkali electrolysis includes:

[0029] Nitrogen replacement control unit: The nitrogen main pipe 1 is connected to the gas phase inlet at the top of the cathode liquid circulation tank 2 through a pipeline. The pipeline is sequentially equipped with a nitrogen regulating valve 3, a nitrogen flow meter 4 and a nitrogen shut-off valve 5. The nitrogen regulating valve 3, nitrogen flow meter 4 and nitrogen shut-off valve 5 are respectively connected to the DCS controller 6.

[0030] The alkali concentration adjustment unit includes an alkali circulation tank 7. A density transmitter 8 and a pure water pipeline 9 are installed on the outlet pipe of the alkali circulation tank 7. A flow regulating valve 10 and a flow meter 13 are connected in series on the pure water pipeline 9. The density transmitter 8, flow regulating valve 10, and flow meter 13 are connected to a DCS controller 6. As the alkali circulates in the alkali circulation tank 7, the alkali concentration gradually increases. For effective circulation, the concentration of the cathode liquid entering the electrolytic cell needs to be reduced. A high-precision density transmitter 8 and pure water pipeline 9 are used to monitor the system's alkali concentration in real time. The water supply to the cathode system is adjusted in real time according to the alkali concentration to ensure a stable alkali concentration.

[0031] Alkali temperature control unit: The outlet of alkali circulation tank 7 is connected to the inlet of alkali circulation pump 11 through alkali main pipe;

[0032] The outlet of the alkali circulation pump 11 is connected to the alkali inlet of the alkali cooler 12 through the alkali main pipe;

[0033] The alkali outlet of the alkali cooler 12 is connected to the cathode inlet of the electrolytic cell via the alkali main pipe;

[0034] A temperature sensor 14 is installed on the alkali outlet pipe of the alkali cooler 12;

[0035] The circulating water inlet of the alkali cooler 12 is connected to the temperature regulating valve 15 via a pipe, and the circulating water outlet is connected to the return water network.

[0036] Temperature sensor 14 and temperature regulating valve 15 are respectively connected to DCS controller 6.

[0037] Furthermore, after the alkali solution enters the electrolytic cell, an electrochemical reaction occurs, and the temperature of the alkali solution gradually increases. Therefore, a cathode liquid heat exchanger is provided to cool the temperature of the alkali solution with circulating water before it enters the electrolytic cell, so as to avoid damage to the ion membrane caused by the temperature rise. At the same time, the boiling of the alkali solution due to high temperature will affect the electrolysis efficiency.

[0038] The hydrogen inlet of the cathode liquid circulation tank 2 is connected to the electrolytic cell, and the hydrogen outlet of the cathode liquid circulation tank 2 is connected to the hydrochloric acid station. The alkali inlet of the alkali circulation tank 7 is connected to the electrolytic cell after passing through the alkali circulation pump 11 and the alkali cooler 12.

[0039] The system also includes an alkaline solution high-level tank level stabilization unit, which is installed on the alkaline solution pipeline between the alkaline solution cooler 12 and the electrolytic cell. The alkaline solution high-level tank level stabilization unit includes an alkaline solution high-level tank 16, on which a level sensor 17 is installed, and the level sensor 17 is connected to a DCS controller 6.

[0040] The nitrogen replacement control unit also includes a pressure controller 18, whose input end is connected to a pressure sensor 19 installed in the pipeline via a cable, and whose output end is connected to a nitrogen regulating valve 3 via a cable, forming an independent pressure closed-loop control branch. This is to effectively control the nitrogen replacement and positive pressure of the chlor-alkali electrolysis cathode system, ensuring a slight positive pressure is maintained during the replacement process to avoid overpressure damage to the ion membrane and related instruments. A closed-loop control circuit is constructed using the pressure sensor 19, nitrogen regulating valve 3, nitrogen flow meter 4, and nitrogen shut-off valve 5. Precisely maintaining the set nitrogen flow rate allows for the regulation of the pressure in the cathode liquid circulation tank 2, monitoring the nitrogen flow rate, and ensuring that hydrogen is replaced in the system during shutdown, maintenance, or abnormal conditions, preventing the formation of explosive mixtures. This achieves automatic control, improves the safety and reliability of the device, efficiently replaces hydrogen in the cathode system with nitrogen, and continuously maintains an inert atmosphere, reducing human error and accidents.

[0041] The DCS controller has a built-in interlocking module. After receiving an emergency stop signal, it automatically opens the nitrogen shut-off valve 5 and the nitrogen regulating valve 3, and controls the nitrogen flow rate to ≥50 Nm / h.

[0042] In the alkaline solution temperature control unit, a flow meter 19 and a flow regulating valve 10 are provided on the circulating water circuit, both of which are electrically connected to the DCS controller 6 to form a secondary control circuit.

[0043] The cathode liquid circulation tank 2 and the alkali liquid circulation tank 7 are integrated devices. The cathode liquid circulation tank 2 is located above the alkali liquid circulation tank 7. An alkali liquid drainage hole is provided between the cathode liquid circulation tank 2 and the alkali liquid circulation tank 7. Since both hydrogen and alkali liquid come from the electrolytic cell, the hydrogen entering the cathode liquid circulation tank 2 will be mixed with alkali liquid. The alkali liquid accumulates in the cathode liquid circulation tank 2 and can enter the lower cathode liquid circulation tank 2, ensuring that the replaced hydrogen has a high purity.

[0044] Working process: After the interlocking system achieves an emergency shutdown, the nitrogen regulating valve and nitrogen shut-off valve entering the cathode liquid circulation tank automatically open, sending nitrogen from the nitrogen main pipe into the cathode liquid circulation tank. The nitrogen flow rate and pressure are controlled by the nitrogen regulating valve 3 to ensure positive pressure in the cathode liquid circulation tank. The nitrogen flow meter 4 monitors the real-time nitrogen flow rate. After the system's emergency shutdown, nitrogen enters the cathode liquid circulation tank 2 through the nitrogen shut-off valve 5. The nitrogen flow rate needs to be controlled above 50 Nm3 / h. The nitrogen flow rate should be large enough to ensure effective mixing and replacement efficiency. In the initial stage of replacement, a large amount of nitrogen rushes in, and the pressure may rise rapidly. By installing the nitrogen regulating valve 3 and nitrogen flow meter 4, remote control is possible. If the pressure is too low, air may be sucked in during the replacement process, causing an accident. After the system replacement is completed, the pressure in the cathode liquid circulation tank 2 is reduced by adjusting the nitrogen regulating valve 3.

[0045] The cathode liquid alkali solution from the electrolytic cell enters the alkali solution circulation tank 7, and then passes through the alkali solution circulation pump 11. A portion of the alkali solution is sent to the outside for sale via the liquid level regulating automatic control valve 20. A temperature sensor 14 and a temperature alarm 21 are installed on the pipeline to the outside sale area to analyze the alkali solution concentration. Another portion of the alkali solution is sent to the alkali solution cooler 12, where it is cooled by circulating water. The temperature sensor 14 detects the alkali solution temperature, forming a control loop with the circulating water flow regulating valve. This ensures that the alkali solution enters the electrolytic cell at a qualified temperature. Additionally, a liquid level stabilization unit for an alkali solution high-level tank is installed on the main alkali solution pipeline to form a control loop, controlling the liquid level and stabilizing the pressure of the alkali solution entering the electrolytic cell, thus preventing fluctuations in the flow rate into the electrolytic cell.

[0046] Based on the structure and working process of this utility model, the chlor-alkali electrolysis cathode gas phase pressure and alkali concentration control system of this utility model, through the use of a pressure controller, flow meter, regulating valve, and protective shut-off valve to form a closed-loop control circuit, accurately maintains the set nitrogen flow rate, achieves automatic control, improves the safety and reliability of the device, efficiently replaces hydrogen in the cathode system with nitrogen, and continuously maintains an inert atmosphere, reducing human error and accidents; equipped with a high-precision density transmitter flow meter, flow meter, and automatic control valve, it monitors the alkali concentration of the system in real time. The water addition to the cathode system is adjusted in real time according to the alkali concentration to ensure stable alkali concentration; the alkali temperature is cooled by circulating water before entering the electrolytic cell to avoid damage to the ion exchange membrane caused by temperature rise, and to prevent the alkali from boiling due to high temperature, which would affect electrolysis efficiency; this utility model achieves triple safety closed-loop control through pipeline connection method and integrated control logic.

Claims

1. A chlor-alkali electrolysis cathode gas phase pressure and caustic concentration control system, characterized by, include: Nitrogen replacement control unit: The nitrogen main pipe is connected to the gas phase inlet at the top of the cathode liquid circulation tank through a pipeline. A nitrogen regulating valve, a nitrogen flow meter and a nitrogen shut-off valve are installed on the pipeline in sequence. The nitrogen regulating valve, nitrogen flow meter and nitrogen shut-off valve are respectively connected to the DCS controller. Alkali concentration adjustment unit: includes an alkali circulation tank, a density transmitter and a pure water pipeline are installed on the outlet pipe of the alkali circulation tank, and a flow regulating valve is connected in series on the pure water pipeline. The density transmitter (8) and the flow regulating valve are respectively connected to the DCS controller. Alkali temperature control unit: The outlet of the alkali circulation tank is connected to the inlet of the alkali circulation pump through the alkali main pipe; The outlet of the alkali circulation pump is connected to the alkali inlet of the alkali cooler via the alkali main pipe; The alkali outlet of the alkali cooler is connected to the cathode inlet of the electrolytic cell via the alkali main pipe; A temperature sensor is installed on the alkali outlet pipe of the alkali cooler. The circulating water inlet of the alkali cooler is connected to a temperature regulating valve via a pipe, and the circulating water outlet is connected to the return water network. The temperature sensor and temperature regulating valve are respectively connected to the DCS controller. The hydrogen inlet of the cathode liquid circulation tank is connected to the electrolytic cell, the hydrogen outlet of the cathode liquid circulation tank is connected to the hydrochloric acid station, and the alkali inlet of the alkali circulation tank is connected to the electrolytic cell after passing through the alkali circulation pump and alkali cooler.

2. The chlor-alkali electrolysis cathode gas phase pressure and alkali concentration control system as described in claim 1, characterized in that, It also includes an alkaline solution high-level tank level stabilization unit, which is installed on the alkaline solution pipeline between the alkaline solution cooler and the electrolytic cell. The alkaline solution high-level tank level stabilization unit includes an alkaline solution high-level tank, on which a level sensor is installed, and the level sensor is connected to a DCS controller.

3. The chlor-alkali electrolysis cathode gas phase pressure and alkali concentration control system as described in claim 2, characterized in that, The nitrogen replacement control unit also includes a pressure controller, whose input end is connected to a pressure sensor installed in the pipeline via a cable, and whose output end is connected to a nitrogen regulating valve via a cable, forming an independent pressure closed-loop control branch.

4. The chlor-alkali electrolysis cathode gas phase pressure and alkali concentration control system as described in claim 1, characterized in that, The DCS controller has a built-in interlocking module. After receiving an emergency stop signal, it automatically opens the nitrogen shut-off valve and the nitrogen regulating valve, and controls the nitrogen flow rate to ≥50 Nm / h.

5. The chlor-alkali electrolysis cathode gas phase pressure and alkali concentration control system as described in claim 1, characterized in that, In the alkaline solution temperature control unit, a flow meter and a flow regulating valve are installed on the circulating water circuit, both of which are electrically connected to the DCS controller to form a secondary control circuit.

6. The chlor-alkali electrolysis cathode gas phase pressure and alkali concentration control system as described in claim 1, characterized in that, The cathode liquid circulation tank and the alkali liquid circulation tank are integrated into one unit. The cathode liquid circulation tank is located above the alkali liquid circulation tank, and an alkali liquid drainage hole is provided between the cathode liquid circulation tank and the alkali liquid circulation tank.

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