Magnesium electrolysis chlorine branch pipe integration system and control method

Abstract

The invention provides a magnesium electrolysis chlorine branch pipe integration system and a control method, the magnesium electrolysis chlorine branch pipe integration system comprises a magnesium electrolysis bath, a waste heat recovery box, an online dust removal module and an uninterrupted power switching system, the magnesium electrolysis bath is connected with the waste heat recovery box through a chlorine outlet header pipe, and the waste heat recovery box is used for recovering heat in high-temperature chlorine discharged by the magnesium electrolysis bath; the online dust removal module is arranged on the lower portion of the waste heat recovery box and used for removing a large amount of dust in chlorine and reducing the dust content of the chlorine, the waste heat recovery box is further connected with an equipment chlorine branch pipe, the equipment chlorine branch pipe is provided with a non-power-outage switching system, and the non-power-outage switching system comprises a main branch pipe and a standby branch pipe. The main branch pipe and the standby branch pipe are each provided with an electric blind plate valve assembly, the pressure difference delta P of the main branch pipe and the standby branch pipe is monitored in real time through a DCS, and opening and closing of the different electric blind plate valve assemblies are switched according to the pressure difference change.

Description

Technical Field

[0001] The present invention relates to the field of non-ferrous metal metallurgy, and particularly to an integrated device and method for waste heat recovery, on-line dust removal and power-off-free switching of a chlorine gas branch pipe of a magnesium electrolysis cell. Background Art

[0002] The electrolyte for magnesium electrolysis is composed of magnesium chloride, sodium chloride, calcium chloride and calcium fluoride. The chlorine gas discharged from the electrolysis cell contains electrolyte sublimates. For every 1 t of magnesium produced, about 11 kg of sublimates enter the chlorine gas. Generally, the chlorine gas comes out of the electrolysis cell, converges at the chlorine gas conveying main pipe through the chlorine gas branch pipes, and then enters the bag filter. After removing the sublimates, it is washed again by the chlorine gas spray tower and sent to the titanium chlorination process by the chlorine gas compressor. The bag filter is cleaned by reverse blowing with compressed air, and the bag filter is cleaned about once every half month. The removed sublimates are sent to the dissolution tank to be dissolved in water or neutralized with lime to become harmless substances and then sent to the waste residue yard.

[0003] In actual production, the temperature of the chlorine gas at the chlorine gas branch pipe is 340 - 420 °C, and it drops to 270 - 310 °C after entering the square box. The temperature at the inlet of the bag filter is 180 - 240 °C, and the temperature inside the bag filter is as high as 110 °C. With the increase in the chlorine gas production capacity of the electrolysis cell, the above temperatures still show an upward trend. When the temperature exceeds 120 °C, it is extremely easy to cause a fire accident inside the bag filter, which poses a great hidden danger to the stable operation of the chlorine gas treatment process.

[0004] The traditional magnesium electrolysis cell chlorine gas treatment system has the following defects:

[0005] First, the chlorine gas has a high dust content (>200 mg / Nm³), resulting in a large load on the subsequent purification system.

[0006] Second, the direct discharge of high-temperature chlorine gas (300 - 450 °C) causes energy waste.

[0007] Third, the switching of the branch pipes requires power-off operation, resulting in a 5 - 8% decrease in the current efficiency of the electrolysis cell. Summary of the Invention

[0008] In view of this, the present invention aims at the three core defects of the chlorine gas treatment system in the production process of magnesium electrolysis cells: 1. High chlorine gas dust content: The traditional system is not equipped with an on-line dust removal device, resulting in an excessive load on the subsequent purification equipment and easy blockage of pipelines; 2. Waste of high-temperature waste heat: The outlet temperature of chlorine gas reaches 300 - 450 °C, and the direct discharge causes energy waste; 3. Power-off required for branch pipe switching: Manual switching operation requires interrupting the power supply of the electrolysis cell, resulting in a decrease in current efficiency and potential safety hazards.

[0009] To achieve the above object, the technical solution of the present invention is realized as follows:

[0010] A magnesium electrolysis chlorine gas branch pipe integrated system, comprising a magnesium electrolysis cell, a waste heat recovery tank, an on-line dust removal module and a power-off-free switching system. The magnesium electrolysis cell is connected to the waste heat recovery tank through a main chlorine gas outlet pipe. The waste heat recovery tank is used to recover the heat in the high-temperature chlorine gas discharged from the electrolysis cell. The on-line dust removal module is arranged at the lower part of the waste heat recovery tank to remove a large amount of dust inside the chlorine gas and reduce its dust content rate. An equipment chlorine gas branch pipe is also connected to the waste heat recovery tank, and a power-off-free switching system is arranged on the equipment chlorine gas branch pipe. The power-off-free switching system includes a main branch pipe and a standby branch pipe. Electric blind valve assemblies are arranged on both the main branch pipe and the standby branch pipe. The differential pressure ΔP between the main branch pipe and the standby branch pipe is monitored in real time through a DCS system, and the opening and closing of different electric blind valve assemblies are switched according to the change of the differential pressure.

[0011] Further, a plurality of heat exchange coiled pipes arranged in a serpentine shape are arranged inside the box body of the waste heat recovery tank.

[0012] Further, annular fins are uniformly welded on the outer wall of the heat exchange pipe.

[0013] Further, the heat exchange medium is introduced into the heat exchange coiled pipe. The heat exchange medium inlet of the heat exchange coiled pipe is arranged at the lower part, and the heat exchange medium outlet is arranged at the upper part. The medium after heat exchange through the heat exchange coiled pipe is in a high-temperature liquid phase or gas phase.

[0014] Further, a partition plate is arranged inside the waste heat recovery tank. The partition plate is arranged vertically and divides the space inside the waste heat recovery tank into two parts.

[0015] Further, the on-line dust removal module adopts a dust cleaning spiral mechanism, and the dust cleaning spiral mechanism is horizontally arranged at the bottom of the waste heat recovery tank.

[0016] Further, the on-line dust removal module further includes a dust collection system.

[0017] Further, the valve body of the electric blind valve adopts a fluororubber sealing ring + nickel-based alloy valve plate, with a temperature resistance ≥ 200 °C and a leakage rate < 0.1%; the valve actuator is integrated with a position sensor, and the opening and closing response time ≤ 15 seconds.

[0018] A control method for a magnesium electrolysis chlorine gas branch pipe integrated system, using the above-mentioned magnesium electrolysis chlorine gas branch pipe integrated system, the control valve method includes:

[0019] The differential pressure ΔP between the main branch pipe and the standby branch pipe is detected in real time through a DCS system;

[0020] Judge whether the differential pressure ΔP exceeds a preset threshold;

[0021] When the differential pressure ΔP exceeds the preset threshold, judge that the pipeline is blocked or the resistance is abnormal, and the DCS system sends an over-standard instruction;

[0022] Open the spare branch blind plate valve. After confirmation of its proper position, close the original branch blind plate valve.

[0023] Furthermore, after the DCS system sends an out-of-specification instruction, the blind plate valve of the spare branch is opened within a preset time. After confirming that the blind plate valve of the spare branch is opened in place, close the original branch blind plate valve.

[0024] Compared with the prior art, the magnesium electrolysis chlorine branch integrated system of the present invention has the following advantages:

[0025] 1) Functional integration. The three functions of dust removal, waste heat recovery, and branch switching are integrated into a single device.

[0026] 2) Zero-shutdown switching. Based on the intelligent control logic of the DCS, the switching time is shortened to within 20 seconds.

[0027] 3) Efficient heat utilization. The annular fin design enables the heat transfer efficiency to be increased by more than 3 times compared with the traditional smooth tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic process flow diagram of the system described in the embodiment of the present invention.

[0029] Description of the reference numerals:

[0030] 1 - magnesium electrolysis cell, 1.1 - chlorine outlet pipe of the electrolysis cell, 1.2 - first pressure gauge, 1.3 - first thermometer; 2 - waste heat recovery box, 2.1 - ash cleaning screw mechanism, 2.2 - detachable ash hopper, 2.3 - heat exchange coil, 2.4 - pure water water pump, 2.5 - second pressure gauge, 2.6 - second thermometer, 2.7 - partition board; 3 - equipment chlorine branch, 3.1 - electric blind plate valve; 4 - chlorine main pipe; 5 - waste heat steam DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention is made with reference to the accompanying drawings.

[0032] A chlorine branch pipe system integrating waste heat recovery, on-line dust removal and power-off-free switching functions, specifically including a magnesium electrolytic cell 1, a waste heat recovery box 2, an on-line dust removal module and a power-off-free switching system 3. Among them, the magnesium electrolytic cell 1 is connected to the waste heat recovery box 2 through a chlorine outlet main pipe 1.1. The waste heat recovery box 2 is used to recover the heat in the high-temperature chlorine gas discharged from the electrolytic cell. The on-line dust removal module is arranged at the lower part of the waste heat recovery box 2 to remove a large amount of dust inside the chlorine gas and reduce its dust content rate. An equipment chlorine branch pipe 3 is also connected to the waste heat recovery box 2. The equipment chlorine branch pipe 3 is provided with a power-off-free switching system. The power-off-free switching system includes a main branch pipe and a standby branch pipe. Electric blind valve assemblies 3.1 are arranged on both the main branch pipe and the standby branch pipe. The differential pressure (ΔP) between the main branch pipe and the standby branch pipe is monitored in real time through the DCS system, and the opening and closing of different electric blind valve assemblies are switched according to the change of the differential pressure.

[0033] When ΔP is greater than the preset value, it is determined that the pipeline is blocked or the resistance is abnormal; the switching program is automatically triggered; during the switching period, the current fluctuation is controlled within ±1%, ensuring the stability of the electrolysis process.

[0034] Among them, the structure of the waste heat recovery box 2 is set as a square box, which is welded to the end of the chlorine outlet main pipe of the electrolytic cell and is made of high-temperature-resistant and corrosion-resistant Hastelloy (HastelloyC276), with dimensions of length × width × height = 2.5m × 1.2m × 1.8m. A multi-layer serpentine heat exchange coil 2.3 is arranged inside the box body of the waste heat recovery box 2. The specification of a single heat exchange tube is Φ50mm × 3mm (outer diameter × wall thickness), and the material is carbon steel.

[0035] To ensure the heat exchange efficiency, a heat exchange enhancement design is carried out: annular fins are evenly welded on the outer wall of each heat exchange tube, the fin height is 15mm, the spacing is 12mm, and the finning ratio ≥8, significantly increasing the heat exchange area.

[0036] In this embodiment, the heat exchange medium is introduced into the heat exchange coil 2.3. The heat exchange medium inlet of the heat exchange coil 2.3 is arranged at the lower part, and the heat exchange medium outlet is arranged at the upper part. The medium after heat exchange through the heat exchange coil 2.3 is high-temperature liquid phase or gas phase. Preferably, the heat exchange medium can be pure water. The heat exchange medium after passing through the heat exchange coil 2.3 absorbs the heat in the chlorine gas and is converted into waste heat steam. For example, softened water is introduced into the heat exchange tube through a pure water water pump 2.4, the flow rate is controlled at 1.5~2.0m / s, the inlet water temperature ≤40°C, and the outlet water temperature is raised to 90~100°C; the waste heat is transported to the heating system of the electrolysis workshop or used for liquid chlorine gasification through a circulation pump, and the heat recovery efficiency ≥65%.

[0037] A partition plate 2.7 is arranged in the waste heat recovery box 2. The partition plate 2.7 is arranged vertically, dividing the space in the waste heat recovery box into two parts, increasing the flow path of chlorine gas in the waste heat recovery box 2, increasing its contact time with the heat exchange coil 2.3, and thus improving the heat exchange effect.

[0038] The on-line dust removal module adopts a dust cleaning spiral mechanism. Among them, the dust cleaning spiral mechanism 2.1 is horizontally arranged at the bottom of the waste heat recovery box 2. The spiral shaft adopts a hollow shaft structure (Φ80mm), with continuous spiral blades with a pitch of 60mm welded on the surface. The blade thickness is 5mm, and the material is Hastelloy; it is driven by an explosion-proof reduction motor, with an adjustable speed range of 25r / min and a power of 1.2kW to achieve continuous dust cleaning. The spiral pushing direction is perpendicular to the chlorine gas flow direction to avoid gas flow interference.

[0039] In addition, the on-line dust removal module also includes a dust collection system. Specifically, a conical ash hopper is arranged at the bottom of the square box, with an inclination angle ≥60° to prevent ash accumulation; a double-layer flap valve is equipped at the outlet of the ash hopper, which is alternately sealed by gravity to ensure that the system maintains a negative pressure during ash discharge and zero leakage of chlorine gas. A detachable ash hopper 2.2 is also arranged below the ash hopper for facilitating the treatment of the collected dust.

[0040] At the outlet end of the chlorine gas branch pipe 3 of the equipment, a main branch pipe and a standby branch pipe are connected. The main branch pipe and the standby branch pipe are respectively connected to a system chlorine gas main pipe. Electric blind plate valves 3.1 are arranged on both the main branch pipe and the standby branch pipe, and the opening and closing of the blind plate valves are controlled by an intelligent control program. The valve body of the electric blind plate valve 3.1 adopts a fluororubber sealing ring + nickel-based alloy valve plate, with a temperature resistance ≥200°C and a leakage rate <0.1%; the valve actuator is integrated with a position sensor, and the opening and closing response time ≤15 seconds, which can be remotely / automatically controlled.

[0041] In this embodiment, a first pressure gauge 1.2 and a first thermometer 1.3 are arranged on the chlorine gas outlet pipe 1.1 of the electrolytic cell, which are respectively used to detect the temperature and pressure of the chlorine gas in the chlorine gas outlet pipe 1.1. A second pressure gauge 2.5 and a second thermometer 2.6 are arranged on the waste heat recovery box 2 to detect the temperature and pressure in the waste heat recovery box 2 for facilitating timely control.

[0042] As one of the embodiments of the present invention, a control method using the above system is also provided, which specifically includes the following steps:

[0043] The differential pressure ΔP between the main branch pipe and the standby branch pipe is detected in real time through the DCS system;

[0044] Judge whether the differential pressure ΔP exceeds the preset threshold;

[0045] When the differential pressure ΔP exceeds the preset threshold, judge that the pipeline is blocked or the resistance is abnormal, and the DCS system sends an over-standard instruction;

[0046] Open the spare branch blind plate valve. After confirmation, close the original branch blind plate valve.

[0047] During the switching process of different branch blind plate valves, the electrolytic cell does not need to be powered off, and the current fluctuation during the switching period is controlled within ±1%, ensuring the stability of the electrolysis process.

[0048] Furthermore, after the DCS system sends an over-standard instruction, the blind plate valve of the spare branch is opened within a preset time. After confirming that the blind plate valve of the spare branch is opened in place, the original branch blind plate valve is closed. The preset time is set to 10 - 20 s. Preferably, the pre-examination time is set to 15 s.

[0049] Through the collaborative design of the waste heat recovery box, the spiral dust cleaning mechanism and the electric blind plate valve, the present invention realizes for the first time: First, functional integration. The three functions of dust removal, waste heat recovery, and branch switching are integrated into a single device. Second, zero-shutdown switching. Based on the intelligent control logic of the DCS, the switching time is shortened to within 20 seconds. Third, efficient heat utilization. The annular fin design increases the heat transfer efficiency by more than 3 times compared with the traditional smooth tube. Specifically:

[0050] Waste heat recovery stage: After the high-temperature chlorine gas (300 - 450 °C) enters the box, it comes into full contact with the finned heat exchange tubes, and the temperature drops below 150 °C; the chlorine gas flow rate is reduced to 0.5 - 1.0 m / s, promoting the natural settlement of dust.

[0051] Online dust removal stage: The settled dust (mainly MgCl2, NaCl, CaCl2, etc.) is pushed by the dust cleaning spiral to the ash hopper, and the ash discharge amount per hour ≤ 20 kg. The dust content of the purified chlorine gas < 50 mg / Nm³, reducing the subsequent treatment load.

[0052] Branch switching stage: When it is detected that the pressure difference of the main branch exceeds the standard, the DCS system sends an instruction, and the blind plate valve of the spare branch is opened within 15 seconds; the original branch blind plate valve is closed synchronously, and the current of the electrolytic cell remains continuous during the switching process without production interruption.

[0053] The beneficial effects obtained thereby are:

[0054] First, in terms of energy conservation and consumption reduction. Each electrolytic cell recovers waste heat ≥ 1.2 MW per year, which is equivalent to saving 150 tons of standard coal per year; avoiding the power loss caused by shutdown switching, saving 1.2 million kWh per year.

[0055] Second, in terms of high-efficiency dust removal. The dust content of the chlorine gas is reduced by more than 75% (from 200 mg / Nm³ to 50 mg / Nm³), extending the service life of subsequent equipment.

[0056] Third, in terms of labor intensity. The dust cleaning spiral operates continuously without manual intervention, and the maintenance cost is reduced by 40%.

[0057] Fourth, in terms of safety. The electric blind valve features a two-way sealing design with a leakage rate lower than the industry standard (<0.1%); the system switching process is fully automated to eliminate the risk of human operation errors.

[0058] Fifth, process compatibility. It can be directly adapted to the transformation of existing magnesium electrolyzers without changing the original chlorine treatment process; it is applicable to metallurgical scenarios with highly corrosive gaseous by-products such as titanium and sodium.

[0059] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined by the claims.

Claims

1. An integrated system for magnesium electrolysis chlorine gas branch pipes, characterized in that, It includes a magnesium electrolysis cell, a waste heat recovery box, an on-line dust removal module and a power-off-free switching system. The magnesium electrolysis cell is connected to the waste heat recovery box through a main chlorine outlet pipe. The waste heat recovery box is used to recover the heat in the high-temperature chlorine gas discharged from the electrolysis cell. The on-line dust removal module is arranged at the lower part of the waste heat recovery box to remove a large amount of dust inside the chlorine gas and reduce its dust content rate. An equipment chlorine gas branch pipe is also connected to the waste heat recovery box, and a power-off-free switching system is arranged on the equipment chlorine gas branch pipe. The power-off-free switching system includes a main branch pipe and a standby branch pipe. Electric blind valve assemblies are arranged on both the main branch pipe and the standby branch pipe. The differential pressure ΔP between the main branch pipe and the standby branch pipe is monitored in real time through the DCS system, and the opening and closing of different electric blind valve assemblies are switched according to the change of the differential pressure.

2. The integrated system of magnesium electrolysis chlorine gas branch pipes according to claim 1, characterized in that, A multi-layer serpentine heat exchange coil is arranged inside the box body of the waste heat recovery box.

3. The integrated magnesium electrolysis chlorine gas branch pipe system according to claim 2, characterized in that Annular fins are evenly welded on the outer wall of the heat exchange tube.

4. The integrated magnesium electrolysis chlorine gas branch pipe system according to claim 2, wherein, A heat exchange medium is introduced into the heat exchange coil. The heat exchange medium inlet of the heat exchange coil is arranged at the lower part, and the heat exchange medium outlet is arranged at the upper part. The medium after heat exchange through the heat exchange coil is in a high-temperature liquid phase or gas phase.

5. The integrated magnesium electrolysis chlorine gas branch pipe system according to claim 1, characterized in that, A partition plate is arranged in the waste heat recovery box. The partition plate is arranged vertically and divides the space in the waste heat recovery box into two parts.

6. The integrated magnesium electrolysis chlorine gas branch pipe system according to claim 1, characterized in that, The on-line dust removal module adopts a dust cleaning spiral mechanism, and the dust cleaning spiral mechanism is horizontally arranged at the bottom of the waste heat recovery box.

7. The integrated system of magnesium electrolysis chlorine gas branch pipes according to claim 1 or 6, characterized in that The on-line dust removal module also includes a dust collection system.

8. The integrated magnesium electrolysis chlorine gas branch pipe system according to claim 1, characterized in that, The valve body of the electric blind valve adopts a fluororubber sealing ring + nickel-based alloy valve plate, with a temperature resistance of ≥200 °C and a leakage rate of <0.1%; the valve actuator is integrated with a position sensor, and the opening and closing response time is ≤15 seconds.

9. A control method for an integrated system of magnesium electrolysis chlorine gas branch pipes, characterized in that, Using the integrated system of the magnesium electrolysis chlorine gas branch pipe described in any one of claims 1 to 8, the control valve method includes: Real-time detecting the differential pressure ΔP between the main branch pipe and the standby branch pipe through the DCS system; Judging whether the differential pressure ΔP exceeds a preset threshold; When the differential pressure ΔP exceeds the preset threshold, judging that the pipeline is blocked or the resistance is abnormal, and the DCS system sends an over-standard instruction; Opening the blind valve of the standby branch pipe, and closing the blind valve of the original branch pipe after confirmation.

10. The control method of the integrated system for magnesium electrolysis chlorine gas branch pipes according to claim 9, characterized in that, After the DCS system sends an over-standard instruction, the blind valve of the standby branch pipe is opened within a preset time. After confirming that the blind valve of the standby branch pipe is opened in place, the blind valve of the original branch pipe is closed.

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