Method and system for fume purification in a salt bath heat treatment process for steel production

Abstract

The application discloses a salt bath heat treatment process fume and steam purification method and system for steel production, and belongs to the technical field of steel smelting environmental protection equipment, and comprises a fume absorption end, a fume purification end, a sedimentation reaction end and a PLC control end, is provided with the collection of fume and steam, a differential pressure self-adaptive type spray purification, sedimentation circulation of spray water, real-time monitoring and automatic adjustment of water, salt water separation, frequency conversion self-adaptive control, one-key start-stop interlocking control and blowdown control steps; the application realizes intelligent automatic control of the whole process from fume absorption, spray purification, sedimentation circulation to water quality adjustment through the cooperative optimization of system hardware and automatic control methods, solves the treatment problem of nitrate vaporization products in the special steel salt bath production process, and has the advantages of high purification efficiency, low operation energy consumption and high control precision.

Description

Technical Field

[0001] This invention relates to the field of environmental protection equipment technology in steel smelting, and in particular to a method for purifying flue gas in a salt bath heat treatment process for steel production, and also to a flue gas purification system for a salt bath heat treatment process for steel production capable of implementing the above method. Background Technology

[0002] With the increasing emphasis on national environmental protection, the demand for process improvements in special steel plants is growing. Salt bath heat treatment is a common process in the production of special steel. During salt bath heat treatment, the temperature inside the salt bath reaches approximately 550℃, containing molten nitrates (potassium nitrate + sodium nitrate). When the molten salt comes into contact with red-hot wire rods at approximately 900℃, a large amount of nitrate vaporization and thermal decomposition products are generated, forming aerosols in the air. This results in a large amount of white smoke in the workshop, seriously affecting the production environment and the health of workers.

[0003] The traditional approach is to directly extract the white smoke using dust collection equipment and release it into the upper atmosphere. This method has several problems: First, conventional dust collectors cannot effectively filter this type of vaporized gas containing nitrite, which can actually lead to a wider spread of pollutants; second, the flue gas has a high temperature, which ordinary filter bags cannot handle, requiring the use of high-temperature resistant filter bags, significantly increasing the cost of the equipment.

[0004] Existing technologies include several solutions for treating salt bath flue gas, such as devices that use water mist for cooling and dust suppression, and systems that collect smoke through closed cooling devices. However, these solutions have shortcomings in terms of flue gas purification efficiency, automation control level, and wastewater recycling. Therefore, there is an urgent need to develop a salt bath flue gas treatment system that can meet environmental emission requirements while effectively controlling equipment costs and operating conditions. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a flue gas purification method for salt bath heat treatment process of steel production that can solve the problem of nitrate vaporization products generated in the salt bath production process of special steel, achieve flue gas emission standards, and at the same time reduce equipment costs and operating energy consumption.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for purifying flue gas in a salt bath heat treatment process for steel production, comprising the following steps: SP1, Collection of flue gas and steam The vaporization and thermal decomposition products of nitrates generated in the salt bath tank are introduced into the spray fume tower through the flue gas dust collection hood by the salt bath induced draft fan, and at the same time, the water vapor at the end of the production line is introduced into the chimney through the steam dust collection hood by the steam induced draft fan, so as to achieve the separation treatment of flue gas and steam. SP2, Differential Pressure Adaptive Spray Purification The differential pressure data inside the spray tower is acquired in real time using the PLC control terminal. Based on the differential pressure data value, the corresponding number of circulating pumps are automatically matched and started to supply water spray into the spray tower, so that the water combines with the vaporization products of nitrate in the flue gas and flows to the bottom of the spray tower. SP3, sedimentation and circulation of spray water The water flowing to the bottom of the spray tower is sent to the primary settling tank through a pipeline, where it reacts with the chemicals sent to the primary settling tank. After sedimentation in the secondary settling tank, the supernatant is obtained and flows to the clear water tank. Each of the circulating pumps draws water from the clear water tank. SP4, Real-time monitoring and automatic adjustment of water usage The water quality parameters in the clear water tank are monitored in real time using a level gauge, pH meter, thermometer and conductivity meter, and each water quality parameter is fed back to the PLC control terminal. The PLC control terminal has preset monitoring standard values ​​corresponding to the above water quality parameters. When the liquid level detection value is lower than the corresponding monitoring standard value, automatic water replenishment is implemented under the control of the PLC control terminal; When the temperature detection value is higher than the corresponding monitoring standard value, under the control of the PLC control terminal, part of the water in the clear water tank will be discharged and automatic water replenishment will be started to regulate the temperature of the water in the clear water tank. When the pH value is lower or higher than the corresponding monitoring standard value, the agent is added under the control of the PLC control terminal for automatic neutralization and adjustment. When the conductivity reaches the corresponding monitoring standard value, the brine separation step is triggered; SP5, brine separation The conductivity of the water in the clear water tank is interlocked with the brine separation feed pump. When the conductivity reaches 0.5 S / cm or higher, If the pH value is equal to 7, the PLC control terminal directly controls the start of the brine separation feed pump to transport the brine from the clear water tank to the brine evaporator. If the pH value is greater than 7, under the control of the PLC control terminal, the agent is added to the clear water tank for automatic neutralization and adjustment, and then the brine separation water supply pump is started. SP6, Variable Frequency Adaptive Control The salt bath induced draft fan adopts frequency conversion control. The flow rate of the pipeline where the salt bath induced draft fan is located is obtained in real time by the PLC control terminal. The working frequency and damper opening of the salt bath induced draft fan are set according to the flow rate value. The frequency parameters and damper opening of the salt bath induced draft fan can be set, adjusted and displayed. SP7, One-button start / stop interlock control A one-button start mode is provided. When the one-button start is activated, two circulating pumps, one salt bath induced draft fan, and one flushing water pump will be started simultaneously, and the pipeline from the started flushing water pump to the spray fume tower and the pipeline from the spray fume tower to the primary sedimentation tank will be kept connected. SP8, Sewage Control The sewage pump is started via the PLC control terminal to discharge the sediment from the bottom of the primary sedimentation tank and the secondary sedimentation tank.

[0007] The present invention also provides a flue gas purification system for a salt bath heat treatment process in steel production, comprising a flue gas absorption end, a flue gas purification end, a precipitation reaction end, and a PLC control end. The flue gas absorption end, the flue gas purification end, and the precipitation reaction end are respectively connected to the PLC control end, and the above-mentioned flue gas purification method for a salt bath heat treatment process in steel production is implemented under the control of the PLC control end.

[0008] As a preferred technical solution, the flue gas absorption end includes a flue gas dust collection hood and a steam dust collection hood located at the salt bath tank. The flue gas dust collection hood and the steam dust collection hood are respectively connected to the flue gas purification end through pipelines. A salt bath induced draft fan is connected to the pipeline between the flue gas dust collection hood and the flue gas purification end, and a steam induced draft fan is connected to the pipeline between the steam dust collection hood and the flue gas purification end. A flow meter is installed on the pipeline where the salt bath induced draft fan is located. The salt bath induced draft fan, the steam induced draft fan, and the flow meter are respectively connected to the PLC control terminal.

[0009] As a preferred technical solution, the flue gas purification end includes a spray flue tower. The inlet end of the spray flue tower is located at the bottom and is connected to the flue gas absorption end. The exhaust end of the spray flue tower is located at the top. The spray flue tower is provided with a packing layer and at least two spray layers from top to bottom. Two flushing water pumps and at least two circulating pumps are connected to the spray flue tower through water pipes. The flushing water pumps are arranged corresponding to the packing layer, and the circulating pumps are arranged one-to-one with the spray layers. The spray flue tower is also equipped with a differential pressure gauge for detecting the internal pressure difference. Each of the flushing water pumps, each of the circulating pumps, and the differential pressure gauge are respectively connected to the PLC control terminal.

[0010] As a preferred technical solution, the inlet end of each of the flushing water pumps is connected to a water tank, and the water tank is connected to the process water source.

[0011] As a preferred technical solution, the sedimentation reaction end includes a primary sedimentation tank, a secondary sedimentation tank, and a clear water tank arranged in sequence. The primary sedimentation tank is connected to the flue gas purification end. The primary sedimentation tank and the clear water tank are respectively connected to a dosing device. The clear water tank is connected to a brine evaporator through a pipeline and a brine separation feed pump. The supernatant in the brine evaporator is returned to the clear water tank through a return pump and a pipeline. Sewage pumps are installed at the bottom of the primary sedimentation tank and the secondary sedimentation tank through pipelines. Parameter detection devices are respectively installed on the clear water tank. The dosing device, the brine separation feed pump, the return pump, the sewage pump, and the parameter detection devices are respectively connected to the PLC control terminal.

[0012] As a preferred technical solution, the dosing device includes a dosing tank, which is connected to the primary sedimentation tank and the clear water tank through pipelines. The dosing tank stores acidic and alkaline agents separately, and dosing solenoid valves are respectively installed on the two pipelines. The dosing solenoid valves are respectively connected to the PLC control terminal.

[0013] As a preferred technical solution, the parameter detection device includes a level gauge, a pH meter, a thermometer, and a conductivity meter, and the level gauge, the pH meter, the thermometer, and the conductivity meter are respectively connected to the PLC control terminal.

[0014] As a preferred technical solution, the primary sedimentation tank, the secondary sedimentation tank, and the clear water tank are an integrated structure, with adjacent tanks separated by a partition plate. The bottoms of the primary sedimentation tank and the secondary sedimentation tank are connected, and the tops of the secondary sedimentation tank and the clear water tank are connected. The bottoms of the primary sedimentation tank and the secondary sedimentation tank form a V-shaped pool area, and the dosing device is connected to the V-shaped pool area.

[0015] As an improvement to the above technical solution, the PLC control terminal includes a PLC controller, which is connected to a host computer via a twisted pair cable, and the PLC controller is also connected to a touch screen via a communication cable.

[0016] By adopting the above technical solution, the present invention has the following beneficial effects: Intelligent control. Utilizing a PLC controller, the system automatically adjusts the fan frequency, the number of circulating pumps started, and the dosage based on parameters such as differential pressure and pH value, achieving fully automated operation.

[0017] Energy saving and consumption reduction. Variable frequency control technology is adopted to dynamically adjust the operating frequency of the salt bath induced draft fan and the number of circulating pumps used according to the amount of flue gas generated, and to automatically adjust according to the actual pressure difference, thus avoiding energy waste.

[0018] Water resource recycling. Water is recycled through three-stage sedimentation of mixed water, reducing water consumption; it also allows for real-time monitoring of the water quality in the clear water tank, ensuring that the recycled water meets process requirements.

[0019] Costs are controllable. Replacing high-temperature resistant bag filters with water-based dust collection significantly reduces equipment costs and maintenance expenses. Attached Figure Description

[0020] The following figures are intended only to illustrate and explain the present invention and do not limit the scope of the invention. Wherein: Figure 1 This is a structural schematic diagram of an embodiment of the present invention; Figure 2 yes Figure 1 Enlarged structural diagram at point A; Figure 3 yes Figure 1 Enlarged structural diagram at point B; Figure 4 This is a structural schematic diagram of the primary sedimentation tank and related facilities according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the PLC control terminal in an embodiment of the present invention; Figure 6 This is a partial circuit diagram of an embodiment of the present invention; Figure 7 This is a partial control circuit diagram of the salt bath induced draft fan and circulating pump according to an embodiment of the present invention; Figure 8 This is a partial control circuit diagram of the sewage pump, flushing water pump, and brine separation water supply pump according to an embodiment of the present invention; Figure 9 This is a schematic diagram of part of the control circuit of the steam induced draft fan, reflux pump, etc. in an embodiment of the present invention; Figure 10 This is a schematic diagram of the input / output control circuit of the sewage pump, flushing water pump, and brine separation water supply pump in an embodiment of the present invention; Figure 11 This is a schematic diagram showing the connection of relevant detection facilities such as thermometers in an embodiment of the present invention; Figure 12 This is a schematic diagram showing the connection of relevant flow meters and other detection facilities in an embodiment of the present invention; Figure 13 This is a schematic diagram of the control connection of facilities such as the salt bath induced draft fan in an embodiment of the present invention; Figure 14 This is a diagram showing the content displayed on the touchscreen according to an embodiment of the present invention; In the diagram: 1-Flue gas dust collection hood; 2-Salt bath induced draft fan; 3-Spray flue; 4-Packing layer; 5-Spray layer; 6-Flushing water pump; 7-Circulation pump; 8-Differential pressure gauge; 9-Water tank; 10-Primary sedimentation tank; 11-Secondary sedimentation tank; 12-Clear water tank; 13-Brine separation water supply pump; 14-Brine evaporator; 15-Return pump; 16-Dosing tank; 17-Dosing solenoid valve; 18-Sewage pump; 19-PLC controller; 20-Frame base plate; 21-Host computer; 22-Touch screen. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the following detailed description, only certain exemplary embodiments of the invention are described by way of illustration. Undoubtedly, those skilled in the art will recognize that various modifications can be made to the described embodiments without departing from the spirit and scope of the invention. Therefore, the drawings and description are illustrative in nature and not intended to limit the scope of the claims.

[0022] like Figures 1 to 14 As shown, a flue gas purification system for salt bath heat treatment in steel production includes a flue gas absorption end, a flue gas purification end, a precipitation reaction end, and a PLC control end. The flue gas absorption end, the flue gas purification end, and the precipitation reaction end are respectively connected to the PLC control end. Under the control of the PLC control end, the flue gas purification method for salt bath heat treatment in steel production is implemented to separate nitrate vapors and thermal decomposition products in the flue gas generated by the contact between molten salt and red-hot wire rods in the salt bath. The purified flue gas is then discharged into the external atmosphere, thereby achieving environmentally friendly steel production.

[0023] The flue gas absorption end includes a flue gas dust collection hood 1 and a steam dust collection hood located at the salt bath tank. The flue gas dust collection hood 1 and the steam dust collection hood are respectively connected to the flue gas purification end through pipelines. A salt bath induced draft fan 2 is connected to the pipeline between the flue gas dust collection hood 1 and the flue gas purification end. A steam induced draft fan is connected to the pipeline between the steam dust collection hood and the flue gas purification end. A flow meter is installed on the pipeline where the salt bath induced draft fan 2 is located. The salt bath induced draft fan 2, the steam induced draft fan and the flow meter are respectively connected to the PLC control terminal. Because water is needed to cool special steel in the salt bath heat treatment process, a large amount of water vapor is generated, resulting in very low visibility in the workshop. Therefore, a steam exhaust fan is required to quickly send the water vapor into the chimney to achieve smoke and mist removal in the working environment. Simultaneously, the salt bath exhaust fan 2 will guide nitrate vapors and thermal decomposition products from the flue gas hood 1 to the flue gas purification end for purification. Since the flue gas hood 1 and the steam exhaust fan hood, as well as the salt bath exhaust fan 2 and the steam exhaust fan, are arranged in parallel in the diagram, they cannot be displayed. A simulation diagram displayed on the touchscreen 22 can be used for further understanding. The flow meter is used to detect the smoke flow rate to facilitate energy-saving control of the operation via the PLC control terminal.

[0024] The flue gas purification end includes a spray flue tower 3. The inlet end of the spray flue tower 3 is located at the bottom and is connected to the flue gas absorption end. The exhaust end of the spray flue tower 3 is located at the top. The spray flue tower 3 is provided with a packing layer 4 and at least two spray layers 5 from top to bottom. Two flushing water pumps 6 and at least two circulating pumps 7 are connected to the spray flue tower 3 through water pipes. The flushing water pumps 6 are arranged corresponding to the packing layer 4, and the circulating pumps 7 are arranged one-to-one with the spray layers 5. The spray flue tower 3 is also equipped with a differential pressure gauge 8 for detecting the internal pressure difference. Each of the flushing water pumps 6, each of the circulating pumps 7, and the differential pressure gauge 8 are respectively connected to the PLC control terminal.

[0025] In this embodiment, to ensure the cooling and purification effect of the flue gas, the spray layer 5 is configured with four layers, and correspondingly, four circulation pumps 7 are provided. As the flue gas travels upward from the bottom of the spray tower 3, it will pass through four sprays and sequentially be sprayed at the packing layer 4. The inlet of each flushing water pump 6 is connected to a water tank 9, which is connected to the process water source. It is used to supply water to the packing layer 4 through the flushing water pumps 6 to cool the flue gas, and water can be replenished to the sedimentation reaction end as needed by simultaneously turning on two of the flushing water pumps 6.

[0026] The sedimentation reaction end includes a primary sedimentation tank 10, a secondary sedimentation tank 11, and a clear water tank 12 arranged in sequence. The primary sedimentation tank 10 is connected to the flue gas purification end. The primary sedimentation tank 10, the secondary sedimentation tank 11, and the clear water tank 12 are an integral structure, with adjacent tanks separated by a partition plate. The bottom of the primary sedimentation tank 10 and the secondary sedimentation tank 11 are connected, and the top of the secondary sedimentation tank 11 and the clear water tank 12 are connected. When the mixed water containing nitrate vaporization products in the spray tower 3 flows into the primary sedimentation tank 10 through the pipe, it reacts with the reagents in the water to produce precipitation. The water containing the precipitate enters the secondary sedimentation tank 11 through the connection between the bottom of the primary sedimentation tank 10 and the secondary sedimentation tank 11 for sufficient sedimentation. The resulting supernatant enters the clear water tank 12 through the connection between the top of the secondary sedimentation tank 11 and the clear water tank 12. The water used by each spray layer 5 is drawn from the clear water tank 12 by the corresponding circulation pump 7, thereby realizing the recycling of water.

[0027] The primary sedimentation tank 10 and the clear water tank 12 are respectively connected to the dosing device. The clear water tank 12 is connected to the brine evaporator 14 through a pipeline and a brine separation water supply pump 13. A fully automatic self-cleaning filter is also connected in series on the pipeline between the two. The supernatant in the brine evaporator 14 is sent back to the clear water tank 12 through a return pump 15 and a pipeline. Parameter detection devices are respectively installed on the clear water tank 12. The dosing device, the brine separation water supply pump 13, the return pump 15 and the parameter detection devices are respectively connected to the PLC control terminal.

[0028] Based on the detection data from the differential pressure gauge 8, the PLC control terminal automatically selects and controls the start of an appropriate number of circulating pumps 7 to achieve both sufficient water use to combine the vaporization products of nitrate in the flue gas and water conservation. The parameter detection devices include level gauges, thermometers, pH meters, conductivity meters, and other measuring instruments, each with corresponding preset reference values ​​on the PLC control terminal, facilitating automated control of water replenishment, chemical dosing, and cooling. For example, when the liquid level in the clear water tank 12 is too low, the PLC control terminal will control both flushing water pumps 6 to start simultaneously, increasing the water consumption to achieve automatic water replenishment through the water tank 9; when the temperature is too high, the PLC control terminal will control the brine separation water supply pump 13 to start, discharging the water in the clear water tank 12 to the brine evaporator 14 for cooling. At this time, the two flushing water pumps 6 start simultaneously to achieve rapid cooling through water replenishment; when the pH of the water in the clear water tank 12 is too high, the PLC control terminal will control the dosing device to start, adding chemicals to the primary sedimentation tank 10 and the clear water tank 12 to neutralize the pH value of the water, making it neutral, etc.

[0029] The dosing device includes a dosing tank 16, which stores acidic and alkaline chemicals separately. Dosing solenoid valves 17 are installed on the two pipelines respectively, and each solenoid valve 17 is connected to the PLC control terminal. The parameter detection device includes a level gauge, a pH meter, a thermometer, and a conductivity meter. The level gauge, pH meter, thermometer, and conductivity meter are connected online to the PLC control terminal. The PLC control terminal automatically controls the opening and closing of the dosing solenoid valves 17 based on the detected values ​​to ensure the water quality in the clear water tank 12, thereby ensuring the flue gas purification effect.

[0030] A sewage pump 18 is installed at the bottom of the primary sedimentation tank 10 and the secondary sedimentation tank 11 via pipelines. The sewage pump 18 is connected to the PLC control terminal. The bottom of the primary sedimentation tank 10 and the secondary sedimentation tank 11 forms a V-shaped pool area, and the dosing device is connected to the V-shaped pool area. After long-term sedimentation, sediment will form in the primary sedimentation tank 10 and the secondary sedimentation tank 11 and collect in the V-shaped pool area. The sewage pump 18 can be activated by the PLC control terminal to discharge the sediment, thereby ensuring the sedimentation effect of the primary sedimentation tank 10 and the secondary sedimentation tank 11.

[0031] The PLC control terminal includes a PLC controller 19, which is mounted and fixed via a frame base plate 20. The PLC controller 19 uses an S7-300 PLC and includes a power module, CPU module, CP module, DI module, DI / DO module, AI module, and AO module. The PLC controller 19 is connected to a host computer 21 via a twisted-pair cable and also to a touchscreen 22 via a communication cable. All field device signals are connected to the input module of the PLC controller 19. After data processing and analysis by the CPU module, control signals are generated and output by the output module of the PLC controller 19 to the flue gas absorption end, flue gas purification end, and sedimentation reaction end, achieving fully automatic system operation. The touchscreen 22 displays a simulation diagram of the system and related statuses and allows for manual control. Data can also be transmitted to the remote host computer 21 for multi-point remote monitoring.

[0032] like Figures 1 to 4 The pipeline of this system is also equipped with various valves, flow meters, thermometers, observation instruments and other conventional components to achieve automatic control. The names of each measuring instrument are shown in Table 1, and the functions of each measuring instrument are shown in Table 2.

[0033] Table 1 Table 2 The salt bath exhaust fan 2 of this system adopts frequency conversion control, which can be automatically adjusted and controlled by the PLC controller 19 according to the air volume, air pressure and the amount of salt spray generated on site. The set frequency can be set, adjusted and displayed on the touch screen 22.

[0034] This embodiment utilizes the above-described system to implement a method for purifying flue gas from a salt bath heat treatment process used in steel production, comprising the following steps: SP1, Collection of flue gas and steam The nitrate vaporization products and thermal decomposition products generated in the salt bath tank are introduced into the spray tower 3 through the flue gas dust collection hood 1 by the salt bath induced draft fan 2. At the same time, the water vapor at the back end of the production line is introduced into the chimney through the steam dust collection hood by the steam induced draft fan, thereby achieving demisting of the working environment and completing the separation treatment of flue gas and steam.

[0035] SP2, Differential Pressure Adaptive Spray Purification By connecting the PLC control terminal to the differential pressure gauge 8, the differential pressure data inside the spray flue gas tower 3 is acquired in real time. Based on the differential pressure data value, the corresponding number (1-4 units) of circulating pumps 7 are automatically matched and started to supply water spray into the spray flue gas tower 3, so that the water combines with the vaporization products of nitrate in the flue gas and flows to the bottom of the spray flue gas tower 3.

[0036] SP3, sedimentation and circulation of spray water The water flowing to the bottom of the spray tower 3 is sent to the primary settling tank 10 through a pipeline, where it reacts with the chemicals sent to the primary settling tank 10. After sedimentation in the secondary settling tank 11, the supernatant is obtained and flows to the clear water tank 12. Each of the circulating pumps 7 draws water from the clear water tank 12 to realize water recycling, thereby reducing water consumption and achieving energy-saving operation.

[0037] SP4, Real-time monitoring and automatic adjustment of water usage The water quality parameters in the clear water tank 12 are monitored in real time using a level gauge, pH meter, thermometer and conductivity meter, and each water quality parameter is fed back to the PLC control terminal. The PLC control terminal has preset monitoring standard values ​​corresponding to the above water quality parameters, so that appropriate strategies can be adopted according to specific situations.

[0038] Specifically, when the liquid level detection value is lower than the corresponding monitoring standard value, automatic water replenishment is implemented under the control of the PLC control terminal. During water replenishment, the flushing water pump 6 draws water from the water tank 9 and sends the replenished water into the spray flue tower 3 to cool and purify the flue gas inside. Finally, the water is collected into the primary sedimentation tank 10, which is equivalent to increasing the water consumption to make full use of water resources.

[0039] When the temperature detection value exceeds the corresponding monitoring standard value, under the control of the PLC control terminal, part of the water in the clear water tank 12 is discharged, and automatic water replenishment is initiated to regulate the temperature of the water in the clear water tank 12. The discharge of water from the clear water tank 12 can be achieved by setting up a water pump and a water storage tank. The water in the water storage tank can also be used as a water source for replenishment, further avoiding the waste of water resources.

[0040] When the pH value is lower or higher than the corresponding monitoring standard value, the agent is added under the control of the PLC control terminal for automatic neutralization and adjustment.

[0041] When the conductivity reaches the corresponding monitoring standard value, the brine separation step is triggered.

[0042] SP5, brine separation The conductivity of the water in the clear water tank 12 is interlocked with the brine separation water supply pump 13. When the conductivity reaches 0.5s / cm or higher, if the pH value is equal to 7, the PLC control terminal directly controls the start of the brine separation water supply pump 13 to transport the brine from the clear water tank 12 to the brine evaporator 14. If the pH value is greater than 7, under the control of the PLC control terminal, an acidic agent such as dilute nitric acid is added to the clear water tank 12 for automatic neutralization and adjustment, and then the brine separation water supply pump 13 is started.

[0043] SP6, Variable Frequency Adaptive Control The salt bath induced draft fan 2 adopts frequency conversion control. The flow rate of the pipeline where the salt bath induced draft fan 2 is located is acquired in real time using a PLC control terminal. Based on this flow rate, the operating frequency and damper opening of the salt bath induced draft fan 2 are set. Furthermore, the frequency parameters and damper opening of the salt bath induced draft fan 2 can be set, adjusted, and displayed via the touch screen 22. Specifically, as shown... Figure 14 As shown.

[0044] SP7, One-button start / stop interlock control A one-button start mode is provided. When starting with one button, two circulating pumps 7, one salt bath induced draft fan 2, and one flushing water pump 6 will be started simultaneously. The pipeline from the started flushing water pump 6 to the spray flue 3 and the pipeline from the spray flue 3 to the primary sedimentation tank 10 will be kept connected. The above is the basic operation start. After starting, the PLC control terminal will automatically adjust according to the specific detection values ​​so that the entire system can reach the optimal operating state that balances treatment quality and energy consumption.

[0045] SP8, Sewage Control The sewage pump 18 is started by the PLC control terminal to discharge the sediment at the bottom of the primary sedimentation tank 10 and the secondary sedimentation tank 11. The amount of sediment accumulation is unstable due to changes in the production plan, so this step can be manually controlled and started as needed.

[0046] This invention uses the PLC control terminal to integrate multi-dimensional data such as differential pressure, pH value, conductivity, temperature, and liquid level for coordinated judgment and automatic control. It has high control accuracy and rapid response. Combined with the frequency conversion regulation of the salt bath induced draft fan 2 and the automatic selection of the number of circulating pumps 7, it ensures that the purification requirements can be met with the lowest energy consumption under different production loads.

[0047] The description of this invention is given for illustrative and descriptive purposes only and is not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A method for purifying flue gas in a salt bath heat treatment process for steel production, characterized in that: Includes the following steps, SP1, Collection of flue gas and steam The vaporization and thermal decomposition products of nitrates generated in the salt bath tank are introduced into the spray fume tower through the flue gas dust collection hood by the salt bath induced draft fan, and at the same time, the water vapor at the end of the production line is introduced into the chimney through the steam dust collection hood by the steam induced draft fan, so as to achieve the separation treatment of flue gas and steam. SP2, Differential Pressure Adaptive Spray Purification The differential pressure data inside the spray tower is acquired in real time using the PLC control terminal. Based on the differential pressure data value, the corresponding number of circulating pumps are automatically matched and started to supply water spray into the spray tower, so that the water combines with the vaporization products of nitrate in the flue gas and flows to the bottom of the spray tower. SP3, sedimentation and circulation of spray water The water flowing to the bottom of the spray tower is sent to the primary settling tank through a pipeline, where it reacts with the chemicals sent to the primary settling tank. After sedimentation in the secondary settling tank, the supernatant is obtained and flows to the clear water tank. Each of the circulating pumps draws water from the clear water tank. SP4, Real-time monitoring and automatic adjustment of water usage The water quality parameters in the clear water tank are monitored in real time using a level gauge, pH meter, thermometer and conductivity meter, and each water quality parameter is fed back to the PLC control terminal. The PLC control terminal has preset monitoring standard values ​​corresponding to the above water quality parameters. When the liquid level detection value is lower than the corresponding monitoring standard value, automatic water replenishment is implemented under the control of the PLC control terminal; When the temperature detection value is higher than the corresponding monitoring standard value, under the control of the PLC control terminal, part of the water in the clear water tank will be discharged and automatic water replenishment will be started to regulate the temperature of the water in the clear water tank. When the pH value is lower or higher than the corresponding monitoring standard value, the agent is added under the control of the PLC control terminal for automatic neutralization and adjustment. When the conductivity reaches the corresponding monitoring standard value, the brine separation step is triggered; SP5, brine separation The conductivity of the water in the clear water tank is interlocked with the brine separation feed pump. When the conductivity reaches 0.5 S / cm or higher, If the pH value is equal to 7, the PLC control terminal directly controls the start of the brine separation feed pump to transport the brine from the clear water tank to the brine evaporator. If the pH value is greater than 7, under the control of the PLC control terminal, the agent is added to the clear water tank for automatic neutralization and adjustment, and then the brine separation water supply pump is started. SP6, Variable Frequency Adaptive Control The salt bath induced draft fan adopts frequency conversion control. The flow rate of the pipeline where the salt bath induced draft fan is located is obtained in real time by the PLC control terminal. The working frequency and damper opening of the salt bath induced draft fan are set according to the flow rate value. The frequency parameters and damper opening of the salt bath induced draft fan can be set, adjusted and displayed. SP7, One-button start / stop interlock control A one-button start mode is provided. When the one-button start is activated, two circulating pumps, one salt bath induced draft fan, and one flushing water pump will be started simultaneously, and the pipeline from the started flushing water pump to the spray fume tower and the pipeline from the spray fume tower to the primary sedimentation tank will be kept connected. SP8, Sewage Control The sewage pump is started via the PLC control terminal to discharge the sediment from the bottom of the primary sedimentation tank and the secondary sedimentation tank.

2. A flue gas purification system for salt bath heat treatment processes in steel production, characterized in that: The method includes a flue gas absorption end, a flue gas purification end, a precipitation reaction end, and a PLC control end. The flue gas absorption end, the flue gas purification end, and the precipitation reaction end are respectively connected to the PLC control end. Under the control of the PLC control end, the flue gas purification method for salt bath heat treatment process in steel production as described in claim 1 is implemented.

3. The flue gas purification system for salt bath heat treatment process in steel production as described in claim 2, characterized in that: The flue gas absorption end includes a flue gas dust collection hood and a steam dust collection hood located at the salt bath tank. The flue gas dust collection hood and the steam dust collection hood are respectively connected to the flue gas purification end through pipelines. A salt bath induced draft fan is connected to the pipeline between the flue gas dust collection hood and the flue gas purification end. A steam induced draft fan is connected to the pipeline between the steam dust collection hood and the flue gas purification end. A flow meter is installed on the pipeline where the salt bath induced draft fan is located. The salt bath induced draft fan, the steam induced draft fan, and the flow meter are respectively connected to the PLC control terminal.

4. The flue gas purification system for salt bath heat treatment process in steel production as described in claim 2, characterized in that: The flue gas purification end includes a spray flue tower. The inlet of the spray flue tower is located at the bottom and is connected to the flue gas absorption end. The exhaust end of the spray flue tower is located at the top. The spray flue tower has a packing layer and at least two spray layers arranged sequentially from top to bottom. Two flushing water pumps and at least two circulating pumps are connected to the spray flue tower through water pipes. The flushing water pumps are arranged corresponding to the packing layer, and the circulating pumps are arranged one-to-one with the spray layers. The spray flue tower is also equipped with a differential pressure gauge for detecting the internal pressure difference. Each of the flushing water pumps, each of the circulating pumps, and the differential pressure gauge are respectively connected to the PLC control terminal.

5. The flue gas purification system for salt bath heat treatment process in steel production as described in claim 3, characterized in that: The inlet of each of the flushing water pumps is connected to a water tank, which is connected to the process water source.

6. The flue gas purification system for salt bath heat treatment process in steel production as described in claim 2, characterized in that: The sedimentation reaction end includes a primary sedimentation tank, a secondary sedimentation tank, and a clear water tank connected in sequence. The primary sedimentation tank is connected to the flue gas purification end. The primary sedimentation tank and the clear water tank are respectively connected to a dosing device. The clear water tank is connected to a brine evaporator through a pipeline and a brine separation feed pump. The supernatant in the brine evaporator is returned to the clear water tank through a return pump and a pipeline. Sewage pumps are installed at the bottom of the primary sedimentation tank and the secondary sedimentation tank through pipelines. Parameter detection devices are installed on the clear water tank. The dosing device, the brine separation feed pump, the return pump, the sewage pump, and the parameter detection devices are respectively connected to the PLC control terminal.

7. The flue gas purification system for salt bath heat treatment process in steel production as described in claim 6, characterized in that: The dosing device includes a dosing tank, which is connected to the primary sedimentation tank and the clear water tank via pipelines. The dosing tank contains acidic and alkaline chemicals in isolation, and dosing solenoid valves are installed on the two pipelines respectively. The dosing solenoid valves are connected to the PLC control terminal.

8. The flue gas purification system for salt bath heat treatment process in steel production as described in claim 6, characterized in that: The parameter detection device includes a level gauge, a pH meter, a thermometer, and a conductivity meter, and the level gauge, the pH meter, the thermometer, and the conductivity meter are respectively connected to the PLC control terminal.

9. The flue gas purification system for salt bath heat treatment process in steel production as described in claim 6, characterized in that: The primary sedimentation tank, the secondary sedimentation tank, and the clear water tank are an integrated structure, with adjacent tanks separated by a partition plate. The bottoms of the primary sedimentation tank and the secondary sedimentation tank are connected, and the tops of the secondary sedimentation tank and the clear water tank are connected. The bottoms of the primary sedimentation tank and the secondary sedimentation tank form a V-shaped pool area, and the dosing device is connected to the V-shaped pool area.

10. The flue gas purification system for salt bath heat treatment process in steel production as described in claim 2, characterized in that: The PLC control terminal includes a PLC controller, which is connected to a host computer via a twisted pair cable. The PLC controller is also connected to a touch screen via a communication cable.

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