Working steam pressure: 0.9Mpa·A, cooling water temperature ≤32°C,pumping time ≤8min
In the steel smelting process, the high-efficiency and energy-saving multi-stage steam jet vacuum pump is used to vacuum the molten steel, which can effectively remove the gas in the molten steel, reduce the content of harmful elements such as sulfur, phosphorus, and hydrogen, and reduce the oxidation of active metals , Improve the yield of alloy, control the composition of steel effectively and conveniently, and greatly improve the quality and performance of steel. The steam jet vacuum pump designed and manufactured by our company for the vacuum treatment of molten steel usually consists of a five-stage or six-stage main pump, two or three-stage auxiliary pumps and four or six condensers.
The steam jet vacuum pump uses the gas dynamics principle of mutual conversion of static pressure energy and kinetic energy when fluid flows to form a vacuum. The pump has a certain pressure of water vapor. When the pumped gas passes through the nozzle, it will reach the speed of sound. When it reaches the diffuser of the nozzle, the static pressure energy is completely converted into kinetic energy, reaching supersonic speed. At the same time, a vacuum is formed at the nozzle outlet, and the pumped gas is drawn into the suction chamber under the effect of the pressure difference and the supersonic steam enters the venturi tube while mixing, and then exits from the venturi diffuser at subsonic speed. At the same time, the speed of the mixed gas gradually decreases, the pressure rises, and then it is discharged from the discharge port. If several jet pumps are connected in series and a condenser is added between the pump and the pump to condense the steam, a higher vacuum can be obtained. The whole steam jet vacuum pump is composed of several stages of pump body and condenser. The pump bodies at all levels are composed of nozzles, inlet chambers and diffusers. The nozzles can be single or multiple. The nozzles are generally made of stainless steel. Other parts such as the suction chamber and diffuser can be made of stainless steel, cast iron and carbon steel. And other materials.
1.Working steam and its dryness
Low steam pressure and pressure fluctuation will have a great impact on the capacity of vacuum pump, so the steam pressure should not be lower than the required working pressure, but the vacuum pump structure design has been finalized, too much increase in steam pressure will not increase the pumping capacity and vacuum degree.In addition, to ensure that the steam pressure supplied by the boiler is stable, it is best to use a boiler specifically to provide working steam to the steam jet pump, so that the steam pressure will not fluctuate, and the vacuum pump performance is stable.
The dryness of steam also has a great impact on the performance of the vacuum pump, in which the water content will cause vacuum fluctuations, and too much water will can’t even create a vacuum. The usual way is to install a separator to obtain working steam with a higher dryness, and at the same time to effectively heat the steam pipeline. In order to obtain the best working efficiency, the working steam provided for the jet vacuum pump should be superheated steam of 5℃~10℃. In particular, the five stage pump, the quality of the steam requirements are very high, containing trace water may cause the nozzle ice plug, resulting in the opening of the fifth stage ejector vacuum degree but decreased or no effect.
2.Requirements for circulating cooling water
Cooling water supply is insufficient, the condenser will heat up, the air flow sound becomes larger, the vacuum degree drops rapidly, and even the steam will return to the exhaust pipe. For tubular condenser, the water supply pressure should be guaranteed to be 0.2MPa, and the water supply should be slightly larger than the actual amount, so that the fluctuation of water will be relatively stable. In addition, in order to avoid the vacuum fluctuation caused by the unstable water supply, it is best to use a separate circulating water system to supply water to the condenser of the vacuum pump.
Cooling water temperature is too high, the vacuum pump capacity will decline, sometimes even can not vacuum, generally not more than 32℃. In addition, the higher the cooling water temperature, the more steam will be consumed.
The influence of cooling water quality on the capacity of vacuum pump is also a factor that cannot be ignored. If the water quality is poor and the hardness is high, the condenser will be fouled or even blocked, which seriously affects the heat exchange performance and makes the steam difficult to condense, thus affecting the vacuum degree.Therefore, it is necessary to ensure that the circulating cooling water is pure softened water.
3.The sealing requirements for vacuum pump system
When the vacuum pump is at its limit, little or no water is discharged from the first stage. Therefore, a large amount of water is discharged from the stage 1 pump, which can be considered a leak in the system.The usual reasons for air leakage are: gasket is not installed, installed wrong or damaged, bolts are not tightened, flange surface damage, weld has holes, joint (pressure gauge, vacuum gauge, etc.) is not installed.
The most common leak detection method is to fill the entire system with pressurized air and apply soapy water everywhere.If there is a leak, there will be bubbles at the leak point, and sometimes even the sound of the leak can be heard.
Check whether there is air leakage: the air tightness test of the vacuum system is carried out with 0.2Mpa compressed air, and the pressure drop of 24h is not more than 4.8%.
4. The nozzle requirements
Nozzle is an important component that affects the performance of vacuum pump. The existing problems are: nozzle installation error, installation distortion, blockage, damage, corrosion and leakage. No matter what preventive measures are taken, the blockage of nozzle is inevitable.On the one hand, due to the installation of steam pipe, the residual iron and welding slag in the pipe will block the nozzle; On the other hand, when the vacuum pump system is out of service, the steam pipe is easy to rust, and the rust spots fall off and block the nozzle during use.In general, the first and second level nozzle aperture is large, not easy to plug, the most easy to plug the third, four, five level of nozzle.Whether the nozzle is blocked can be confirmed by touching the temperature of the pump head and condenser.