Screw vacuum pump for solvent recovery

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These days, there are an increasing number of cases in the chemical industry where screw vacuum pumps are used for distillation or purification. This gives rise to the issue of recovering and reusing low-boiling-point substances: at the suction end of the screw pump, it is generally considered to be at normal temperature and under negative pressure. In this case, the vaporization of some low-boiling, volatile organic compounds is drawn away by the vacuum pump. At the discharge end of the screw pump, the temperature is usually around 100°C, at atmospheric pressure. These vaporized organic substances, once drawn out, are compressed into a liquid state, and this liquid gradually accumulates at the exhaust end. If the screw pump uses non-forced seals such as lip seals or expansion ring seals, the accumulated liquid can enter the front and rear gearboxes either due to 1、the rotation of the rotor, or 2、the failure of these lip seals or expansion ring seals when the pump stops operating. This contaminates the gear lubricant, thereby causing damage to the gears and bearings. (These two types of failure result from cumulative effects over time, and do not occur instantaneously.) To address this issue, it is necessary to replace non-mandatory sealing elements such as lip seals and expansion rings with mandatory sealing mechanisms, such as single-face mechanical seals. There is a vacuum pump factory in Yantai that, for screw vacuum pumps, replaces all the sealing points on the male and female rotors with single-face mechanical seals, using an external oil station to flush and cool the sealing surface. This structure differs from that of some vacuum pump manufacturers, who use methods such as lip seals, expansion rings, or combined seals as alternative non-mechanical sealing solutions at the suction side, while employing mechanical seals at the exhaust side. However, the mechanical seal at the exhaust end relies on the oil splashing disc inside the gearbox for lubrication, resulting in a high failure rate for this seal. Another advantage of using a full mechanical seal is that it allows cleaning solvents to be directly added to the pump. In situations where crystallization or coking occurs inside the screw, it is possible to operate the pump at a reduced speed via frequency conversion, while simultaneously adding cleaning solvents and keeping the rotor immersed in the solvent for cleaning purposes.