1.(Liquid Ring Vacuum Pumps)

2.(Steam Jet Ejectors)

3. (Dry Vacuum Pumps，)

4. (Oil-Sealed Pumps，)

5.(Roots Booster Systems)

Detailed comparative analysis

 (Liquid Ring Vacuum Pumps)

This is the most conventional method in the chemical industry, where liquids (typically water or solvents) are used to form a liquid ring for gas compression.

The working principle is that the impeller rotates eccentrically, the liquid forms a liquid ring under the action of centrifugal force, and the chamber with periodic change of volume is formed between the blade and the liquid ring.

Advantages: • Isothermal compression: The compression process is nearly isothermal, ensuring high safety, making it particularly suitable for flammable and explosive gases.

o Strong tolerance: Insensitive to gases containing small amounts of dust or liquid droplets.

o Simple structure: easy to maintain and relatively low cost.

Drawbacks: • Limiting vacuum constraints: The system is constrained by the saturated vapor pressure of the working fluid (typically, the water ring can only reach approximately 33 hPa).

o High energy consumption: Significant liquid mixing losses result in low efficiency (typically 30%-50%).

o Environmental issues: generates substantial contaminated wastewater with high post-treatment costs.

2.2 Steam Jet Ejectors generate negative pressure by rapidly ejecting high-pressure steam through a nozzle.

Advantages: • No moving parts: extremely low failure rate and long service life.

o High air extraction capacity: Ideal for high-altitude tower tops and other high-flow applications.

o Corrosion-resistant: Can be made of graphite, ceramic, or stainless steel.

o Applicability: Capable of processing extremely contaminated gases.

Drawbacks: • High energy consumption: requires substantial amounts of high-grade steam.

o Environmental pressure: Direct contact with condensation generates substantial amounts of hard-to-treat chemical wastewater.

o High noise level: requires dedicated noise reduction measures.

2.3 (Dry Screw Vacuum Pumps) have emerged as a new favorite in the chemical industry in recent years. These pumps operate without oil or water in their chambers, utilizing a pair of screws that rotate synchronously at high speed in opposite directions to extract gas.

Advantages: • Clean vacuum: The pump chamber contains no medium, with recoverable medium (high solvent recovery rate) and no wastewater discharge.

High vacuum level: A single pump can achieve 1 Pa or even lower.

o Energy efficiency: Compared to water ring pumps and steam jet pumps, it has lower overall energy consumption.

Drawbacks: • High cost: The equipment requires substantial initial capital expenditure (CAPEX).

o Susceptible to viscous materials: If the process gas is prone to coking or polymerization, it may cause screw jamming (requires special coatings or cleaning processes).

o High exhaust temperature: requires cooling system.

2.4 (Roots Combinations) Roots pumps are typically not used as standalone units, but rather as boosters in series with the pre-stage pumps (water ring, screw, slide valve).

Function: Significantly increases pumping speed and enhances the system's ultimate vacuum level.

Common combination: Roots pump + water ring: This configuration overcomes the limitations of water ring pumps in achieving extreme vacuum, and is widely used in distillation and crystallization processes.

o Roots + screw: Enables fully dry high-vacuum systems with high pumping speeds.