In the degassing process of molten steel, the selection of vacuum pump should be considered comprehensively, such as space requirements, energy medium supply, emergency plan, cleaning and maintenance shutdown, necessary auxiliary equipment, and the cost required to meet the requirements of discharge and safety standards. There are many types of water ring vacuum pump. According to different classification modes, it can be divided into several parts. In addition, water ring vacuum pump has been applied in vacuum technology for a long time, such as ladle degassing, steel flow degassing, vacuum circulation degassing, etc. This paper mainly describes how to choose the right equipment in the process of the application of the first water ring vacuum pump in the degassing process of molten steel.
The application of water ring vacuum pump in the degassing process of molten steel has made great progress in the past 10 years, but it is mainly limited to below 150 t furnace capacity; the work of extending to a larger furnace capacity is in progress. Because of the steam source, the steam jet vacuum pump is mainly used for the large furnace capacity of 150-350 t in the United steel plant. In addition to investment and operation cost considerations, all types of vacuum processes and equipment can use any type of modern vacuum pump system without restriction, and both systems can meet all metallurgical requirements.
According to different structures, water ring vacuum pump can be divided into the following categories:
Single stage single effect water ring vacuum pump: single stage means that there is only one centrifugal impeller, and single effect means that every revolution of the centrifugal impeller, suction and exhaust are carried out once respectively. The limiting vacuum of this kind of pump is higher, but its efficiency and efficiency are lower.
Single stage double effect water ring vacuum pump: single stage means that there is only one centrifugal impeller, and double effect means that every revolution of the centrifugal impeller, suction and exhaust are carried out twice. Under the same pump efficiency standard, the double effect water ring vacuum pump greatly reduces the specification and the net weight compared with the single effect water ring vacuum pump. Because the symmetry of the working cavity is distributed on both sides of the pump rim, the load of the efficiency on the motor rotor is improved. This kind of pump has great efficiency and high efficiency, but the limiting vacuum is low.
Bipolar water ring vacuum pump: most of the bipolar water ring vacuum pumps are single function pumps connected in series. In essence, the centrifugal impeller of two single-stage single effect water ring vacuum pumps is connected by a journal. Its main feature is that it still has great pump efficiency under high vacuum, and the working condition is stable.
Compared with other kinds of mechanical equipment, water ring vacuum pump has the following advantages:
The structure is simple, the production and manufacturing precision is not high, and it is very easy to produce and process. The practical operation is simple and the maintenance is convenient.
Compact structure, pump and motor direct connection, high speed. With a smaller construction specification, a large amount of exhaust gas can be obtained.
There is no friction surface of metal material in the pump cavity, so it is not necessary to carry out moistening in the pump. The sealing between the rotating part and the fixing card can be performed immediately by the exhaust valve.
The temperature change of the whole process of reducing gas in the pump cavity is not big, which can be considered as isothermal reduction, so it can pump out inflammable and explosive gas.
Because there is no exhaust valve and friction surface, the gas with floating dust, condensable gas and water gas compound can be removed.
water ring vacuum pump key points for selection:
1. The definition of the type of water ring vacuum pump
The type of water ring vacuum pump depends on the material pumped, the air supply required in the work, vacuum degree or exhaust working pressure.
2. There are two points that must be paid attention to after the water ring vacuum pump works normally:
(1) As far as possible, the vacuum degree of the selected vacuum pump shall be specified to operate in the high efficiency section, that is, in the area where the vacuum degree required by the critical value or the exhaust working pressure required by the critical value is required, so as to ensure that the vacuum pump can operate normally in accordance with the necessary standards and regulations. It should be prevented from operating around the scope of larger vacuum degree or larger exhaust working pressure of vacuum pump.
In this area, not only the high efficiency is very low, but also the work is very unstable, which is very easy to cause vibration and noise. As for the vacuum pump with high vacuum degree, when it operates in this area, it will continue to produce cavitation, which is caused by noise and vibration in the vacuum pump. Excessive cavitation will cause damage to pump casing, centrifugal impeller and other parts, so that the vacuum pump can not work normally.
It can be seen that when the vacuum degree or gas working pressure required by the vacuum pump is not high, it can be selected preferentially in the single-stage pump. If the vacuum degree or exhaust working pressure is specified as high, the single-stage pump can not be considered generally, or the specified pump still has a large amount of air supply under the condition of high vacuum degree, that is to say, the specified characteristic curve is relatively flat when the vacuum degree is high, and the secondary pump can be used. If the vacuum degree is above – 710mmhg, the compass water ring vacuum generator set can be used as the vacuum pumping equipment.
(2) . select the vacuum pump properly according to the amount of pumping and air supply required by the system software
When comparing the application of water ring vacuum pump in the degassing process of molten steel, only the total cost should be considered, including the cost that must be paid to meet the requirements of emission limits and safety standards and the pressure in the reaction tank. In addition, the type and use of dedusting systems should be reconsidered as they can significantly reduce costs by reducing the number of cleanups, saving water, reducing sludge treatment, and reducing the system’s design air extraction capacity.