Since 1990, liquid ring vacuum pump was gradually used in domestic ketene consumption. At the initial stage of operation, due to the defects of process and the lack of understanding of liquid ring vacuum pump by consumer technicians, the explosion accident of liquid ring vacuum pump occurred in relevant manufacturers. The successful application of liquid ring vacuum pump in ethylene ketone consumption has experienced about three stages.
The first stage is the selection of circulating medium for liquid ring vacuum pump. Since ethylene ketone will generate acetic acid immediately when meeting with water, water and other substances that react with vinyl ketone or acetic acid, anhydride and diketene can not be used as circulating medium. Kerosene is initially used as circulating liquid. Due to the problem of saturated vapor pressure of kerosene, the pump can only operate in a low vacuum state, and the consumption efficiency is reduced After many other experiments, it is concluded that transformer oil as circulating fluid not only solves the problem of vacuum, but also avoids the reaction with ketene and other substances. At present, more than 95% of domestic ketene manufacturers still use transformer oil.
The second stage is the choice of liquid ring vacuum pump. There are two kinds of liquid ring vacuum pump: single-stage liquid ring vacuum pump and double-stage liquid ring vacuum pump. The use of single-stage liquid ring vacuum pump has low energy consumption and heat generation, but its vacuum degree is low, which can not meet the process requirements. Therefore, the double-stage liquid ring vacuum pump is widely used in ethylene ketone consumption.
The third stage is the separation of the liquid produced after the circulating liquid and the gas are compressed. The gas pumped by the liquid ring vacuum pump still needs to stop tightening in the cavity. As the tightening process of the liquid ring vacuum pump is isothermal, there will be no ketene coking after the contraction. However, due to the vivid nature of the ketene gas, it is easy to self polymerize to produce diketene, and a small amount of vinegar will be mixed in the gas Acid gas, so a small amount of substances such as diketene and acetic anhydride will be produced during tightening. Since the solubility of ketene gas in diketene and acetic anhydride is large and it is easy to self polymerize after dissolution, the liquid produced effectively is particularly important in consumption.
The advantages of liquid ring vacuum pump in ketene production are as follows
1. The liquid ring vacuum pump can operate continuously for a long time. Because the transformer oil is used as the circulating medium, the transformer oil can not only produce oil ring to form vacuum, but also can lubricate the pump body. Therefore, the liquid ring vacuum pump not only solves the problem that the dry vacuum pump needs regular maintenance, but also can operate without fault for a long time due to its few vulnerable parts;
2. The liquid ring vacuum pump is an isothermal compression process. Due to the extremely unstable properties of ketene, the waste of materials is greatly reduced. Both reciprocating pump and slide valve vacuum pump will produce a lot of diketene, acetic anhydride and other substances due to the rise of gas temperature during compression, and a lot of Coke will be produced when the temperature is too high;
3. It is safer to use liquid ring vacuum pump in production. It is decided by the working principle of liquid ring vacuum pump. It will not cause cylinder flushing or cylinder leakage as often as reciprocating vacuum pump, which greatly avoids the risk of cooling brine entering into the system, and greatly reduces the sudden vacuum drop and even ketene leakage caused by sudden failure of vacuum pump;
4. The use of liquid ring vacuum pump is more environmentally friendly, low noise, less pollution, no need for regular maintenance, reducing the discharge of ketene.
At present, most liquid ring vacuum pump manufacturers use the density difference between circulating liquid and produced liquid to stop standing and layering. At present, liquid ring vacuum pump has been very successful and widely used in ketene consumption. It has made great contribution to the stability and safety consumption of ketene.