Traditional vacuum degassing relies on large-scale steam jet vacuum system, which is expensive due to the increase of fuel cost and wastewater treatment cost. The latest vacuum degassing station equipped with modular dry vacuum pump system can ensure the stable and reliable quality of molten steel, protect the environment and have significant economic benefits.
1. Vacuum degassing overview
Degassing of steel by dry vacuum pump is to blow molten steel properly under vacuum with argon and other inert gases to remove harmful gas inclusions (especially hydrogen and nitrogen) and other trace elements (metal and non-metal) in molten steel, so as to realize steel refining. Most of the solid non-metallic (such as oxide) inclusions that affect the quality of the final steel products can be removed by vacuum degassing, because these inclusions affect the mechanical properties of the products and the suitability of the products under hot working and other processing conditions. It is also advantageous to remove sulfide from molten steel by using suitable liquid flux.
The secondary refining by vacuum degassing (VD) can effectively optimize the properties of steel, meet the specific requirements of product properties and increase the added value of products.
The VD process keeps the molten steel in the “optimal” vacuum environment for about 20 minutes, and the vacuum degree is usually 0.67 mbar. Meanwhile, inert argon is circulated into the steel water to stir the molten steel, and hydrogen diffuses from the turbulent molten steel into the argon bubble. The vacuum degree is kept moderate, which can make the bubble size the largest, and make the argon consumption in a reasonable range, and ensure the gas mixture is discharged from the slag quickly Go. A similar way is used to remove nitrogen, but the efficiency is low, so the nitrogen content in molten steel is usually maintained at a high level.
2. Comparison of mechanical degassing and steam degassing
The optimal VD treatment efficiency needs to create a stable and reliable vacuum environment in VD tank in a low-cost way. Historically, steam driven injection system was used to achieve vacuum, while many modern steel degassing workshops now use dry mechanical vacuum suction system.
The calculated comprehensive flow rate of the above gases can be used to determine the nominal suction flow rating. Under typical operating parameters, when VD processes one ton of molten steel, the pump flow rate is about 1259m3 / h under the vacuum degree of 0.67mbar, which is equivalent to the equivalent mass flow rate of 1.0kg/h (air temperature of 20 ℃) under this pressure.
3. Dry vacuum pump system advantages
The early customized mechanical vacuum system designed for each workshop does not have flexibility, low efficiency, high cost and relatively complex. Now the modular three-stage dry vacuum pumping system is optimized in degassing treatment, power consumption and power consumption reduction, and it is also convenient for rapid installation and use. The latest modular system is a fully integrated three-stage pump system, which is installed on a mobile bench to optimize the VD and VOD processes.
The nominal displacement of the two-stage pump in the module system is 8640m3 / h, which can provide high compression rate under medium vacuum. The “main” vacuum pump in dry operation is the latest generation of IDX large, double head adjustable screw pump, which has become the international standard for dry vacuum degassing. The pump provides a relatively gentle “compensated” suction rate after the second stage pump, with a nominal displacement of 1000m3 / h or 1300m3 / h.
4. Dry vacuum pump system operation
The operator can usually control the system and change all the suction rates according to the needs, which is realized by integrating the pump control system directly into the workshop control system and using the pump motor in the electronic frequency conversion drive control module. The use of electronic drive also improves the efficiency of suction, realizes the optimal use of energy consumption, and makes the pump work in the most effective way. The modular vacuum system is equipped with the driver to achieve highly reproducible operation effect.
5. Reduce costs
Compared with the steam jet vacuum system, one of the main advantages of the modular three-stage mechanical vacuum pump system is to realize the saving of operation cost.
In many old VD plants, the increase of steam cost of driving steam injection and suction system has become a key factor. With the rising cost of fuel, the stable supply of fuel has become a hot issue in some regions of the world. In a typical VD plant, the cost of steam consumption may account for more than 50% of the total operating cost of the suction system. In addition, the cost of water supply, condensate and sewage treatment should be considered. The electric cost of running an equivalent mechanical vacuum pump system only accounts for 5% of the steam cost.
The initial investment cost of modular dry mechanical suction system may exceed the cost of purchasing a new steam boiler and jet device. However, if the existing equipment such as sewage treatment plant needs to be upgraded to deal with the sewage generated by the jet, the assembly required by the steam jet vacuum system may be equivalent to the dry suction system. In this case, the operation cost savings provided by the dry-type suction system can quickly realize the recovery of investment cost, making it a practical scheme.