Application of the hottest vacuum degassing furnac

2022-08-09
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Application of vacuum degassing furnace in electric furnace steelmaking

1. Preface

vacuum degassing treatment process, as a kind of refining outside the furnace, is widely used in the metallurgical industry. Its principle is to vacuum the vacuum chamber, degass the molten steel in the vacuum state, reduce the [h], [n] in the molten steel, and use the steel slag interface reaction for desulfurization treatment. In large-scale modern metallurgical production, VD ladle treatment has become the basic means of modern secondary metallurgy. At present, the typical steel types treated by VD in HANGGANG Changxing electric furnace steelmaking Co., Ltd. mainly include: hard wire steel (72A, 82B), bonded steel (40Cr, 20CrMnTi, 20CrMnMo, 35CrMo), spring steel (60Si2Mn), bearing steel (GCr15), cold pier steel (ml42crmo), etc

2. System overview

the 100tvd furnace of HANGGANG Changxing electric furnace steelmaking Co., Ltd. is designed and manufactured by VAI, and the supporting boiler is provided by standardkessc Duisburg. The system has a leading position in similar domestic products

as the main equipment of VD furnace, degassing system mainly includes electrical and mechanical solutions of degassing system, equipment and instrument detection system. The system consists of two tanks with diameter of Φ 5800mm, 5450mm high vacuum tank, vacuum cover system, vacuum funnel, temperature measurement and sampling system, double station double wire feeding system, argon blowing system and its lifting and moving trolley

3. System hardware

3.1 computer system

3.1.1 computer system composition

vacuum degassing furnace adopts two-level computer control of basic automation level and process control level. With the emergence of these new commercial packaging materials and utilization

the primary computer system adopts the basic automation level of electrical, instrument and computer control, which is composed of PLC (Siemens s Series) and upper computer (MMI). The main module of PLC is 6ES7 xkab0, the communication module is 6gk7 exxe0, the analog input module is 6ES7 kfab0, the analog output module is 6ES7 hdab0, the digital input module is 6ES7 blaa0, and the digital output module is 6ES7 blaa0. In addition, it also includes motor control center (MCC), boiler control system, wire feeder, capping control system and on-site primary detection elements. Human machine interface MMI adopts InTouch graphical interface software programming

the secondary computer system adopts the process control station and is connected with the electric furnace computer through Ethernet. The process control station adopts a multiprocessor host, the operating system is Windows NT, the network protocol is tcp/ip SINEC H1, and the basic software: Industrial Oracle, database, c/c++

3.1.2 main functions of the computer system

① basic automation level (Level 1):

· furnace cover operation control

· bottom blowing mixing control

· cooling water

· wire feeding control

· ferroalloy feeding control

· steam injection control

· water pump control of heat accumulator

· water treatment control

· equipment abnormal alarm and interlock

· degassing process screen display

· man machine dialogue interface

· molten steel splashing monitoring

· movable elbow station switching

· dust control

· alarm and event printing

② process control level (Level II):

· calculation of mathematical model of energy balance

· mathematical model calculation of molten steel temperature, composition and treatment time

· control of operation process, operation guidelines and accident records

· data detection of production process and storage of historical data

· ferroalloy charging calculation and treatment

· communication with electric furnace, continuous casting and laboratory control system

· production report printing

3.2 field detection instrument

in order to ensure the measurement accuracy, VD furnace basically adopts imported parts

· temperature measurement and oxygen determination instrument adopts Heraeus multi lab celox

· the hydrogen determination instrument adopts Heraeus multi lab hydras

· differential pressure transmitter adopts e+h deltabar s series

· electromagnetic flowmeter adopts e+h proline promag 50 series and prowirl 77 vortex series

4. Control principle and basic process

set relevant control parameters through the primary computer (MMI) screen. The relevant data is sent to the VD furnace PLC, boiler PLC and wire feeder PLC through SINEC H1 bus to control the relevant electrical operation. At the same time, the on-site primary instrument detection signal is collected as the basis of automatic control

after receiving the processing task and relevant data sent by the previous process, the main control personnel of VD furnace will start data processing and refining preparation. The vacuum furnace has 2 degassing tank positions and 1 vacuum cover car parking position. The vacuum cover car is parked between the two vacuum tanks. After the ladle is in place, manually connect the argon gas pipe, run the vacuum cover truck in place and lower the vacuum cover. Open the steam ejector according to the extraction speed and treatment steps of molten steel to be treated, and carry out vacuum treatment. In the vacuum state, the molten steel is stirred by blowing argon at the bottom of the ladle. A vacuum funnel is set on the vacuum cover. For steel grades that need fine adjustment of alloy, the necessary alloy is added through the vacuum funnel in the vacuum state of degassing process. Then temperature measurement and sampling are carried out under vacuum. After vacuum treatment, break the vacuum, raise the vacuum cover and return to the parking position, or move to another vacuum position. With the ladle open, continue argon blowing, soft stirring and wire feeding. After treatment, conduct final temperature measurement and sampling. At this time, the vacuum treatment of the next ladle of molten steel can be carried out at another tank position. In the process of molten steel treatment, the hydrogen and oxygen determination instrument can be used for rapid gas determination

vacuum pumping can select automatic mode, manual mode and standard mode for VD processing:

when selecting automatic mode, pumps at all levels need to start automatically according to the vacuum degree listed in Table 1: Under Table 1 automatic mode, pump start conditions at all levels

pump name e5ae4e4a start conditions atmospheric pressure ≤ 40kpa ≤ 40kpa

when the vacuum degree reaches 100mbar, select the standard mode "standard", at this time, the system automatically stops E5A, E4A vacuum pumps, Start E5 vacuum pump, E4 pump remains unchanged, and E3, E2 and E1 pumps automatically start according to the vacuum degree listed in Table 2: under the standard mode of Table 2, the starting conditions of pumps at all levels

pump name e3e2e1 starting range ≤ 10KPA ≤ 2KPa ≤ 0.8kpa

when selecting the manual mode, the vacuum pump system generally operates according to the standard mode "standard", gradually opens the check valve and turbid circulating water valve, and starts pumps at all levels according to the vacuum degree listed in Table 3: under the manual mode of Table 3, Starting conditions of pumps at all levels

pump name e5e4e3e2e1 starting range atmospheric pressure ≤ 40kpa ≤ 10KPA ≤ 2KPa ≤ 0.8kpa

5. Precautions in VD production process

① after the end of each furnace of VD, check the insulation layer at the center of the lower surface of the large tank cover. If it falls off seriously, report to the relevant departments in time and do not enter VD

② during vacuum pumping, the flow of Ar gas shall not exceed 400nl/min, and the pressure shall not exceed 0.5MPa (gauge pressure). Especially when the molten steel is full, so as to prevent the molten steel from sticking to the small furnace cover and the upper edge of the ladle, so that the tank cover cannot be lifted or the bricks in the ladle can be pulled off

③ when it is 20kpa~4kpa, pay close attention to the slag overflow. If it is found that the slag overflows, it should be broken in time. At the same time, the Ar gas flow can be appropriately increased to press the slag

④ in the high vacuum holding stage (67pa), the Ar gas flow can be appropriately increased and the exposed surface of molten steel can be expanded to accelerate degassing. At the same time, pay close attention to whether the temperature change at the bottom of the tank is abnormal

⑤ if it is found that the water level of the hot well water tank often gives an alarm, in the vacuum pumping state, the water level is more than 100% and cannot fall below 100% within 5 seconds. When the heat aging performance cannot fall below 100%, the vacuum must be broken immediately. After the steam valves at all levels are closed, the turbid circulating water should be stopped immediately to prevent the water level from being too high to break the hot water tank

⑥ after the end of VD of each furnace and the departure of the tank cover truck, it is necessary to timely check whether there is molten steel sticking between the ladle trunnion and the ladle support seat in the tank. If so, immediately command the crane to try to lift the ladle, and if necessary, deal with the cold steel, and then lift the ladle

6. Effect achieved after VD treatment

through VD furnace ladle treatment, the final molten steel [h] can reach less than 2ppm and [n] can reach less than 80ppm. After VD treatment, the income per ton of steel is more than 100 yuan

7. Conclusion

practice has proved that the operation of vacuum degassing furnace is very beneficial to adjust the product structure of the existing electric furnace steelmaking plant, expand the production varieties of 2 36000 KVA submerged arc furnaces, 2 sets of 50 ton medium frequency electric furnaces, and 1 set of 50 ton AOD refining furnace, further improve the product structure, expand the production varieties, further improve the product quality, and improve the business effect. (end)

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