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1.Current situation of blast furnace hot blast stove system
High air temperature is an important technical feature and development direction of modern blast furnace ironmaking. Increasing air temperature can effectively reduce fuel consumption and improve the efficiency of blast furnace energy utilization. A customer company owns two 5500m3blast furnace, each blast furnace is equipped with four BSK top burning hot stoves with a design air temperature of 1300 ° C.
1.1Problems in hot blast stove system
The hot blast system (hot blast stove body and pipe system) generally has the problem of high-temperature point cracking, and the frequency increases and the degree increases. The design specification of hot air system requires that the temperature of hot air stove body is less than 150 ° C, and the temperature of hot air duct is less than 200 ° C. However, there are many high-temperature points in the hot blast stove body and hot blast pipe, such as 2# stove. The average detection temperature of the embedded thermocouple (16 points) in the hot blast stove body is 128 ° C, of which the temperature of 5 points is > 150 ° C. Statistics show that the hot blast furnace shell cracked 57 times in 2014, 30 times in 2015 and 58 times in 2016, and the cracking parts are mainly concentrated in 14-16 zones. After the bellows of the hot air system was put into operation, high temperature points (the design temperature is less than 200 ° C) and cracks occurred successively. As shown in Figure 1.
1.2Limitations of manual inspection
The blast furnace hot blast stove (shell and piping) belongs to the ultra-high temperature area (internal hot blast temperature 1400 ° C), and the weak points crack to varying degrees under high temperature, which has great potential safety hazards. The blast furnace hot air system has no prediction or feedback measures and means, and only relies on routine manual inspection every 2h. There are two problems in manual patrol inspection: ① due to the limitation of site and time, there are great limitations and contingencies. The inspection route is affected by the platform, the distribution of high temperature points and the uncertainty of inspection time, so the status of hot blast stove shell cannot be monitored comprehensively and all-weather; ② The cracking of the furnace shell is sudden, and the safety of the inspectors cannot be guaranteed, so there are great potential safety hazards. In order not to affect the normal production and operation of blast furnace hot blast stove, the primary task is to comprehensively, in detail and in real time monitor the unsafe factors of the existing hot blast system, and process the monitoring data information, so as to control the hot blast system within the safe operation range.
2.Development of infrared imaging monitoring system for hot blast stove
2.1Infrared imaging system of hot blast stove
The infrared imaging monitoring system of the hot air system is equipped with 15 temperature monitoring points, including 9 temperature monitoring points of the hot air furnace shell and 6 hot air piping monitoring points. Considering the cost, after site investigation, it is proposed to set five fixed thermal imager temperature measurement points and another mobile temperature measurement point. The monitoring pictures of each infrared thermal imager are transmitted to the monitoring computer in real time through optical fiber. The computer displays the picture online, establishes a database at the same time, automatically analyzes and processes the data of monitoring points, draws the temperature change curve of each region, and gives the temperature change rate of each region and the alarm of abnormal points. As shown in Figure 2.
2.2Principle of infrared imaging system for hot blast stove
According to the principle that the infrared intensity is different under different temperatures of the object, the infrared thermal imager uses the infrared detector and optical imaging objective lens to receive the infrared radiation energy distribution pattern of the measured object and reflect it on the photosensitive element of the infrared detector, so as to obtain the infrared thermal image. This kind of thermal image corresponds to the thermal distribution field on the surface of the object, and the temperature distribution in different areas of the measured object is obtained by conversion. The data measured by the infrared thermal imager is transmitted to the computer system. The computer software integrates, analyzes and processes the data, obtains useful information, and presents it to the operator through a simple and clear interface. Using infrared imaging equipment to complete the test work has the advantages of all-weather and wide coverage. Figure 3 shows the infrared imaging monitoring diagram of hot blast stove.
2.3Development of infrared imaging system for hot blast stove
Main objective: to develop infrared imaging monitoring technology for blast furnace hot air system. Main research contents: ① hardware and network architecture scheme and implementation; ② Program code writing and software system development.
The functions to be realized or satisfied by the infrared imaging technology of the hot air system: ① monitoring function, the monitoring range of the hot air system in the suspicious area, continuous monitoring in time sequence, and reliable trend and high accuracy in the monitoring results of the surface temperature; ② For the alarm function after reaching a certain temperature, according to the design specifications, the hot air duct ＜ 200 ° C, the hot air stove body 150 ° C, according to the degree close to the temperature, carry out warning or alarm, and give the location of the warning area (accuracy 0.5m); ③ For parts or areas that exceed the design specifications, in addition to the above temperature monitoring data, video data information for a period of time can be recorded and played back; ④ The system should have strong compatibility and redevelopment. The research and development of infrared imaging technology is applied to practical production to ensure the safe and stable operation of large blast furnace hot air system.
3.Application of infrared imaging monitoring system for hot blast stove
3.1Architecture of infrared imaging monitoring system for hot blast stove
According to the layout and internal equipment connection of 4 hot blast furnaces of 1# blast furnace, in order to realize the temperature measurement monitoring coverage of the hot blast furnace shell (14-16 belts) and hot blast pipe system (hot blast branch pipe and hot blast main pipe), five fixed thermal imager temperature measurement points and one mobile temperature measurement point are set after field investigation. As shown in Figure 4, probe 1 is under the viaduct of the blast furnace control room; Probe 2 is on the top platform of blast furnace gas bag dedusting system; Probe 3 is at the east end of the East-West Center Line on the hot blast stove frame; Probe 4 is at the center point of the East-West Center Line on the hot blast stove frame; Probe 5 is at the west end of the East-West Center Line on the hot blast stove frame.
Each point thermal imager is equipped with an automatic rotating PTZ, in which probe 1 and probe 2 are supported PTZ, and probe 3, probe 4 and probe 5 are suspended PTZ. Through the rotation of each PTZ, the thermal imager can realize the regular scanning or fixed-point monitoring of all monitoring target areas. According to the monitoring results of each fixed point, the setting point of the mobile infrared thermal imager sets the mobile infrared thermal imager at a short distance for continuous monitoring when the most dangerous area is blocked by pipes or equipment around and cannot be directly monitored by the fixed probe.
The monitoring picture of infrared thermal imager is transmitted to the monitoring computer in real time through optical fiber. The computer displays each picture online, establishes a database at the same time, automatically analyzes and processes the data of the monitored points, draws the temperature change curve of each area, and gives the alarm of the temperature change rate and abnormal points of each area.
3.2Problems and solutions in the application of infrared imaging monitoring system
(1) The infrared radiation emission characteristic of the material itself is the key to the accurate temperature measurement of the hot blast stove shell by the thermal imager. In the previous hot blast stove test, it was found that the temperature measured by the thermal imager in different areas of the same equipment was different at the same temperature. The reason for analysis is that the emissivity of different surface materials of the equipment is different, and the infrared radiation energy is different. When the temperature of the whole monitoring object is converted with a fixed emissivity, a large error will occur.
Solution: ① investigate the infrared emissivity of different materials (base metal steel plate, weld material, antirust paint, etc.) on the surface of hot blast stove shell; ② The contact surface thermometer is used to measure the surface temperature of representative areas of different materials, and the infrared emissivity of different material areas is determined by comparing with the temperature measurement of infrared thermal imager; ③ The monitoring area of each measuring point is set with different infrared emissivity to obtain the accurate thermal imaging monitoring temperature of the area; ④ Regularly use the contact surface thermometer for local inspection and correction to ensure the long-term accuracy of the temperature measurement results of the infrared thermal imager.
(2) Setting of measuring points of infrared thermal imager. Each blast furnace has 4 hot blast stoves, which are arranged in a staggered rectangle. The on-site investigation found that, except for the relatively open and unobstructed north side, there are many devices around the other three sides, so it is difficult to find a fully covered installation point of the infrared thermal imager. The equipment area for close monitoring is limited. In addition, the internal pipelines and valves of the four hot blast stoves are densely covered, and there is no directional installation point that can cover all the monitoring areas.
Solution: realize full coverage monitoring in all areas by setting multiple measurement points and adopting the method of rotating pan tilt. The scanning frequency of the automatic rotating pan tilt to the monitoring area also fully meets the monitoring requirements. For the partially sheltered area, by comparing the temperature changes in the surrounding monitoring area and directly measuring with the surface thermometer, if it is considered to be a dangerous area, a movable infrared thermal imager is set for online monitoring.
(3) Data analysis and processing. The multi-point infrared thermal imaging thermometer set in the system will generate massive data in real time, and the change of hot blast stove shell state is a relatively slow and continuous process. Therefore, the computer system is required to screen and compare massive data, obtain the required parameters and change process of key parts, and accurately predict the change trend and possible risks.
Solution: according to the monitored hot blast stove shell area, establish the corresponding database. Develop temperature data to ensure the accuracy and representativeness of monitoring data and processing results.
4.Epilogue
The infrared imaging monitoring system of blast furnace hot blast stove is based on the principle that the infrared thermal imager is based on the different intensity of infrared radiation under different temperatures of the object, and uses the infrared detector and optical imaging objective lens to receive the infrared radiation energy distribution pattern of the measured object and reflect it on the optical sensor of the infrared detector, so as to obtain the infrared thermal image, which corresponds to the thermal distribution field on the surface of the object, The temperature distribution in different areas of the measured object is obtained by conversion. The data measured by the infrared thermal imager is transmitted to the computer system. The computer software integrates, analyzes and processes the data, obtains useful information, and presents it to the operator through a simple interface. The infrared imaging monitoring system can monitor and analyze data changes, prevent and alarm the cracking of the hot blast stove shell and hot blast pipe. It is suitable for the hot blast stove system of iron making blast furnace, realize real-time monitoring and data analysis, replace the inspectors in the dangerous area of the hot blast stove, eliminate potential safety hazards, and ensure safe production.
