1. The ultimate vacuum of the water ring vacuum pump and the liquid ring vacuum pump is around 2000PA. To achieve a higher degree of vacuum, it is necessary to form a unit. For example, the probability of failure of the contact of the multi-stage Roots water ring vacuum unit is increased.
The oil-free dry variable-pitch screw vacuum pump can be pumped to 1PA (absolute pressure) under atmospheric pressure with a single pump. Its internal variable pitch has realized the function of vacuum unit.
2. The water ring vacuum pump, when the liquid ring vacuum pump is running for a long time, the water temperature rises slowly, which directly causes the vacuum degree of the water ring vacuum pump to drop. It is necessary to use frozen salt water to cool the water tank of the liquid ring vacuum pump, which promotes the use of the motor. Increased power increases energy consumption. Furthermore, if the low-boiling solvent that has been pumped out of the system but failed to condense enters the water body of the water ring vacuum pump, it will also fall under the vacuum of the water ring pump.
The oil-free dry variable-pitch screw vacuum pump can operate stably for a long time with a single pump, and is not affected by the water temperature and the extracted solvent. (The interior is basically self-cleaning)
3. There is no medium in the working chamber of the oil-free dry variable-pitch screw vacuum pump, and a clean vacuum can be obtained.
Therefore, a condenser under normal pressure can be installed at the exhaust end of the screw pump to further condense and recover the solvent that cannot be condensed under vacuum, so that the solvent recovery rate is greatly improved.
Take toluene as an example. Under the vacuum condition of 1mmHg, the condensation temperature of toluene is 0°C. If we want to condense toluene at the vacuum end, we must use a refrigerant below -15°C. Due to the small heat exchange temperature difference, a large condensation heat exchange area is required. In order to effectively condense and recover toluene, toluene is under normal pressure and the condensation temperature is 110 ℃. We only need to use circulating water and a small condensation heat exchange area to effectively condense and recover toluene. The solvent recovery rate can generally be increased to 96%. above.
For the water ring vacuum pump, because the uncondensed solvent is directly mixed into the water, the condensation recovery under normal pressure conditions cannot be performed, so the solvent recovery rate is low, and a large amount of waste water is generated. For low-boiling solvents, such as methanol, dichloromethane, etc., under vacuum conditions, the condensation temperature is very low, and it is difficult to condense with -15 ℃ cold brine, the recovery rate will be lower, and only most of the low-boiling solvents can enter the water Inside, waste water is produced.
4. The oil-free dry variable pitch screw vacuum pump only needs a small amount of circulating cooling water to flow around the pump cavity, and the operating cost is low.
The water vacuum pump keeps solvent entering the water tank, it is necessary to change the water in the water tank regularly or continuously to maintain the vacuum degree of the pump operation, and it needs to consume a lot of water. Operating costs are relatively large.
Although the equipment price of dry screw pump is higher than that of water jet pump or water ring pump, in terms of long-term operation and use, its cost is lower and it is more economical and environmentally friendly.
5. For the safety of chemical production and product quality, the oil-free dry variable-pitch screw vacuum pump also has its advantages. Many materials in the vacuum system we use often have to react with water, and even cause the danger of decomposition and explosion. The water ring vacuum pump has the risk of sudden stop of the pump and the water being sucked back into the vacuum system, which is likely to cause safety risks or affect product quality. Pollution; while the oil-free dry variable-pitch screw vacuum pump is water-free and oil-free, even if it sucks backwards, it will not cause danger or pollution, which is more beneficial to safety and quality assurance.
6. The flow parts of the dry screw vacuum pump can be nickel-plated or treated with various corrosion-resistant materials in the pump cavity, which can withstand the corrosion of most organic acid gas and inorganic acid gas. In the distillation system of extracting toluene and hydrochloric acid gas Has been successfully used in.
Because of the inconvenience of anti-corrosion treatment, water ring pumps generally cannot be used in acidic systems.