The solvent recovery vacuum pump is applied to the deep processing of food, milk, wine, beverage and plant (Medicine), including the recovery of organic matters in the process of reactor exhalation and vacuum pump desolvation;
For solvent recovery, the main characteristics of screw vacuum pump, liquid ring vacuum pump or roots liquid ring vacuum unit are compared as follows:
Solvent recovery method:
The screw vacuum pump uses a condenser installed on the exhaust side to condensate the solvent gas pumped.
The working fluid of the liquid ring vacuum pump is pumped by the medium, and the heat exchanger is installed in the circulating pipe of the working fluid to make the working fluid work in a reasonable temperature range. Because of the isothermal compression characteristic of the liquid ring vacuum pump, the solvent is mostly changed from gas to liquid phase when the pump is compressed.
Because the screw vacuum pump needs to be compressed, it will rush into nitrogen and other gases to cool the pump cavity, so a lot of non condensable gas will be discharged at its exhaust port, resulting in a lot of solvent loss, the liquid ring vacuum pump does not need to be filled with non condensable gas, so the solvent recovery rate is higher than the screw vacuum pump.
The screw vacuum pump is a dry vacuum pump, the gas temperature after compression is higher, and the exhaust temperature of the screw vacuum pump with equal pitch can reach 150 ~ 200 ℃; the liquid ring vacuum pump adopts the working fluid with lower temperature, which is similar to the isothermal compression characteristics, and the exhaust temperature can be controlled at 40 ℃. If there is cold water at the working site, the exhaust temperature can be lower.
So in terms of safety, liquid ring vacuum pump is good.
At present, because most of the screw vacuum pumps are designed with equal pitch, which is equivalent to a number of Roots pumps with the same flow rate used in series, there is no theoretical internal compression process in the screw vacuum pump, so its energy consumption is large.
Although the efficiency of liquid ring vacuum pump is low (it needs to lose energy when swinging the liquid ring), because of the design of its flexible exhaust port, it can automatically adjust the exhaust port according to different compression ratio, so it has internal compression characteristics.
In most applications, the energy loss of liquid ring vacuum pump is lower than that of screw vacuum pump.
For example, when the liquid ring vacuum pump is used in series with roots vacuum pump as a unit, the interstage compression ratio can be flexibly configured according to the system pressure, so the roots liquid ring vacuum unit is more energy-saving than the single screw vacuum pump in the high vacuum area
At present, the main material of screw vacuum pump is cast iron + nickel phosphorus or cast iron + plating + PTFE. Because stainless steel is difficult to process, so screw vacuum pump is seldom made of stainless steel (the price of stainless steel screw vacuum pump is high). At present, the coating technology is not perfect in China, and it still needs a long time to verify in various applications. Once the coating of screw vacuum pump is damaged, it will be damaged quickly in the corrosion situation.
Liquid ring vacuum pump can be made into various stainless steel materials to resist various corrosive media.
The corrosion resistance of liquid ring vacuum pump is better than that of screw vacuum pump.
The liquid ring vacuum pump has been widely used in the process of recovering various solvents such as methanol, ethanol, toluene, xylene, acetone, DMF, etc. for example, when the design and selection of materials are correct, the liquid ring vacuum pump is very stable with low failure rate.
Screw vacuum pump has advantages in recovery of acetone, dichloromethane, tetrahydrofuran and other low boiling point solvents, but when the extracted gas is corrosive, the inhaled gas contains dust, and the extracted gas is easy to deposit carbon, screw vacuum pump is prone to failure and high maintenance rate.
Because the screw processing of screw vacuum pump is more complex, the price of screw vacuum pump is higher than that of stainless steel liquid ring pump.
To sum up, screw vacuum pump is suitable for recovery of acetone, dichloromethane, tetrahydrofuran and other low boiling solvents, and has high requirements for use and maintenance. For methanol, ethanol, xylene and other solvents, liquid ring vacuum pump or roots liquid ring vacuum pump unit can meet the use requirements, and has high reliability.