Conventional vacuum pump degassing relies on large steam injection vacuum systems, which are expensive because of increased fuel costs and wastewater treatment costs. The latest vacuum degassing station equipped with modular dry vacuum pump system can ensure the stability, reliability and environmental protection of molten steel, which has great economic benefits. 1 Vacuum degassing overview Vacuum degassing of steel is carried out by vacuuming molten steel with inert gas such as argon under vacuum to remove harmful gas inclusions (especially hydrogen and nitrogen) and other trace elements (metals and non-metals) from molten steel. Realize the refining of steel. Vacuum degassing of molten steel removes most of the solid non-metallic (eg, oxide) inclusions that affect the quality of the final steel product because these inclusions affect the mechanical properties of the product and its suitability for hot working and other processing conditions. The use of suitable liquid mold flux also facilitates the removal of sulfide from the molten steel. The use of vacuum degassing (VD) for secondary refining can optimize the performance of the steel efficiently and effectively, meet specific product performance requirements, and increase product added value. The VD process maintains the molten steel in an “optimal†vacuum environment for approximately 20 minutes, typically at a vacuum of 0.67 mbar. At the same time, the inert argon gas is introduced into the molten steel to stir the molten steel. Hydrogen diffuses from the turbulent molten steel into the argon bubble. The vacuum degree is kept at a proper level to maximize the bubble size while keeping the argon consumption within a reasonable range and ensuring that the gas mixture is rapidly discharged from the slag. Nitrogen is removed in a similar way but with low efficiency, so the nitrogen content in molten steel is usually maintained at a high level. The high temperature of molten steel means that light metal and non-metallic inclusions evaporate from the surface of the molten steel and promote the removal of lead, zinc, manganese and copper. These substances evaporate together with argon and flow into the evacuation system and condense out of the degassing tank. Generates fine dust, which must be filtered out to prevent overloading the vacuum pump. Vacuum in the degassing tank also enhances the interaction between the molten steel and the slag layer and promotes the chemical removal of sulfide from the molten steel. The interaction of the molten steel with the slag layer, the argon stirring rate and the degassing time are also key parameters for the removal of non-metallic inclusions. These parameters together with argon stirring, molten steel turbulence and vacuum during the whole process of VD treatment ensure that the molten steel is homogenized, the temperature is uniform, and the high-efficiency turbulent contact with the covering slag leads to the high efficiency of the vacuum degassing and refining process. , to obtain high cleanliness of molten steel and optimal steel composition. 2 Comparison of mechanical and steam degassing Optimal VD processing efficiency requires a stable and reliable vacuum environment in VD cans at a low cost. Historically, vacuum was used with steam-driven injection systems. Many modern steel degassing plants now use dry mechanical vacuum. Suction system. The calculated combined flow rate of the above gases can be used to determine the nominal suction flow rate rating. Under typical operating parameters, when the VD treats one ton of molten steel, a vacuum of 0.67 mbar requires approximately 1259 m3/h of pump flow. This corresponds to an equivalent mass flow of 1.0 kg/h (air temperature 20°C) at this pressure. Recent studies on large-scale systems (above 100 tons) using mechanical vacuum suction systems have shown that the quality of the molten steel is very good, and in some cases the residual hydrogen content in the steel is as low as 0.5 ppm. Whereas typical steam injection systems generally require higher flow rates, at 0.67 mbar, tons of steel require mass flow of up to 2.4 kg/h (air temperature 20°C), which is generally considered to be a high value for the selected parameters because of the need Considering the change in steam quality, and the fouling of industrial dust between the two cleanings of the system, the effect of steam injection is reduced. 3 Advantages of Dry Vacuum Pump Systems The custom-designed mechanical vacuum system designed for each workshop in the early days is not flexible, inefficient, costly and relatively complex. The modular three-stage dry vacuum pumping system developed today is optimized for degassing, power consumption, and power consumption reduction. It also facilitates quick installation and rapid use. The latest modular system is a fully integrated three-stage pump system that is mounted on a mobile gantry and optimized for VD and VOD (vacuum blown oxygen decarburization) processes. The first-stage pump used in the modular degassing system is a reciprocating pre-vacuum pump with a nominal displacement of 36,000 m3/h. With the cooperation of the 2-stage and 3-stage (main) pumps, the 1 stage pump provides 78% The peak volumetric efficiency, at approximately 0.67 mbar, is typically 28300 m3/h. Recently, a reciprocating pump with a displacement of 40000 m3/h was used in the first stage, which can further increase the net module suction rate, and the flow rate reached about 30,800 m3/h per module at 0.67 mbar. The nominal displacement of the 2-stage pump in the modular system is 8640m3/h, which provides a high compression rate at moderate vacuum. Dry-running "main" vacuum pumps are the latest generation of IDX's large, double-headed adjustable screw pumps, which have become the international standard for dry vacuum degassing. The pump provides a relatively gradual “compensated†suction rate after the 2 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 pumping rates as required. This is achieved by integrating the pump control system directly into the shop floor control system and using the pump motor in the electronic variable frequency drive control module. The use of an electronic drive also increases the pumping efficiency, achieves optimal use of energy, and allows the pump to operate in the most efficient manner. The modular vacuum system configures the drive for highly reproducible operation. 5 Reduce costs One of the main advantages of the modular three-stage mechanical vacuum pump system compared to the steam injection vacuum system is the realization of operating cost savings. In many old VD plants, the increase in steam costs driving the steam injection system has become a key factor. As fuel costs continue to climb, the stable supply of fuel has become a hot issue in some parts of the world. In a typical VD plant, the cost of steam consumption may account for more than 50% of the total pumping system operating costs. In addition, the costs of water supply, condensate, and sewage treatment must also be considered. The cost of electricity required to operate an equivalent mechanical vacuum pump system is only 5% of the steam generation cost. The initial investment cost of the modular dry mechanical pumping system may exceed the cost of purchasing a new steam boiler and injection device, but if the existing equipment such as a sewage treatment plant needs upgrading to treat the injector-generated sewage, the steam injection vacuum The total cost of the system may be comparable to a dry suction system. In this case, the operating cost savings provided by dry suction systems can quickly realize the recovery of investment costs, making it a viable solution. More vacuum pump information is available at China Vacuum Pump Trading Network (/).
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