Application of Liquid Ring Vacuum Pumps in Ethylene Glycol Evaporation
1. Process Background and Physical-Property Basis
Ethylene glycol is widely used in polyester (PET), antifreeze, resins, pharmaceutical intermediates, and fine chemicals. During production, recovery, and downstream treatment, evaporation or refining units are often required to remove water, low-boiling organic compounds, solvents, by-products, and trace impurities. These operations increase EG concentration and reduce the load on subsequent distillation or polishing units.
From a thermodynamic perspective, EG has a normal boiling point of approximately 197 °C and is therefore a high-boiling oxygenated organic compound. If atmospheric evaporation is used directly, the process requires a higher heat duty and may increase the residence time of the material in the high-temperature region, raising the risk of color formation, polymerization, or the generation of thermally induced impurities. Industrial systems therefore commonly establish a vacuum environment to lower the liquid-phase boiling temperature and allow evaporation to proceed under milder thermal conditions.
2. Vacuum-Evaporation Mechanism and Process Value
The essential mechanism of vacuum evaporation is the reduction of total pressure in the evaporator, allowing the liquid to reach vapor-liquid equilibrium at a temperature below its normal boiling point. In practice, the boiling temperature is jointly affected by mixture composition, evaporation pressure, impurity level, heat-transfer driving force, and condenser capacity. Consequently, engineering design should determine the target vacuum level through vapor-liquid equilibrium data, material balance, and energy balance rather than treating a specific pressure interval as a fixed boiling-point condition.
In EG evaporation, reduced-pressure operation provides the following process benefits:
It lowers the evaporation temperature and reduces the influence of thermal history on product color, purity, and stability.
It improves the effective heat-transfer driving force and increases evaporation rate and unit capacity under the same heating conditions.
It reduces the load on downstream distillation or deep-removal units, supporting overall energy optimization.
It creates a more controllable pressure boundary for condensation and recovery of volatile solvents, water vapor, and light components.
3. Function of the Vacuum System in EG Evaporation
Establishing and maintaining the target operating pressure. The vacuum system removes gas from the evaporator and connected piping so that system pressure reaches the process set point, thereby lowering the boiling temperature of the EG-containing mixture.
Continuously removing non-condensable gases. During operation, air and small quantities of volatile gases may enter through leakage, material entrainment, or side reactions. If these gases are not removed promptly, condenser performance is weakened, vacuum level declines, and evaporation capacity decreases.
Stabilizing evaporation load and product concentration. Vacuum fluctuations cause variations in boiling temperature, vaporization rate, and concentration endpoint, directly affecting product concentration, steam consumption, and downstream separation load.
Coordinating condensation and exhaust-gas treatment. The vacuum pump, pre-condenser, gas-liquid separator, and tail-gas treatment unit collectively determine condensable-component recovery, working-fluid contamination, and emission compliance.
4. Applicability of Liquid Ring Vacuum Pumps
A liquid ring vacuum pump uses a liquid as the working medium. An eccentrically mounted impeller drives the liquid ring to form periodic volume changes, enabling gas suction, compression, and discharge. This pump type is well suited to wet gases, entrained droplets, and a certain quantity of condensable vapor, making it common in evaporation, distillation, crystallization, filtration, and condenser air-removal applications.
In EG evaporation systems, the main advantages of liquid ring vacuum pumps include:
Strong wet-gas tolerance, allowing the pump to handle mixtures containing water vapor, EG vapor, and small amounts of entrained liquid.
Flexible working-fluid selection. Depending on material compatibility, contamination control, and recovery requirements, water, EG, or another compatible liquid may be selected.
Stable operation and relatively simple construction, suitable for continuous production with steady gas-removal demand.
High tolerance to short-term system disturbances and limited liquid carryover, providing good engineering adaptability.
However, the ultimate pressure achievable by a liquid ring pump is strongly influenced by working-fluid temperature, working-fluid vapor pressure, and the sealing-liquid circulation mode. When an EG evaporation unit requires a lower operating pressure, higher pumping speed, or more stable deep vacuum, it is often necessary to use a Roots booster, a pre-condenser, or a multi-stage vacuum package.
5. FORYOU Vacuum-System Recommendations
Considering the high wet load, significant condensable content, and stringent vacuum-stability requirements of EG evaporation, FORYOU can select and design the vacuum system based on material composition, target pressure, throughput, condensation temperature, leakage rate, and emission requirements. Common configurations include Roots-liquid ring vacuum packages and Roots-dry screw vacuum packages.
5.1 Roots-Liquid Ring Vacuum Package
A Roots vacuum pump is typically used as a booster and combined in series with a liquid ring vacuum pump. The Roots pump provides high pumping speed in the medium-to-low pressure range, while the liquid ring pump functions as the backing pump for compression, discharge, and wet-gas handling. This configuration is suitable for stable evaporation loads, high water content, and operating conditions that prioritize wet-gas tolerance and reliability.
Vacuum stability: the Roots pump increases effective system pumping speed, helping reduce pressure fluctuation and improve evaporation-temperature control.
Production efficiency: when the backing pump is correctly matched, the Roots pump can increase the overall gas-handling capacity of the vacuum system and improve evaporator throughput.
Engineering adaptability: the liquid ring pump performs well with wet gases and limited liquid carryover, which are common in EG evaporation service.
5.2 Roots-Dry Screw Vacuum Package
When the unit places greater emphasis on product purity, solvent recovery, tail-gas cleanliness, or lower operating pressure, a combination of Roots pump and dry screw vacuum pump may be considered. Because the gas path of a dry screw pump does not involve working liquid, it can reduce working-fluid contamination and secondary separation requirements, while also facilitating integration with condensers, gas-liquid separators, and tail-gas treatment equipment.
Lower-pressure capability: dry screw pumps can operate stably over a broad pressure range, although actual attainable pressure must be verified against upstream condensation, leakage, and gas load.
Improved EG purity: an oil-free and working-liquid-free gas path helps reduce cross-contamination risk, making the package suitable for high-purity EG or line-upgrade projects.
Organic-solvent recovery: pre-condensation or interstage condensation can recover vaporized organic solvents and reduce emissions and material loss.
Operating-cost optimization: with proper condensation, variable-frequency control, and exhaust-gas treatment, material loss and maintenance burden can be reduced; project economics should be confirmed by material-balance and energy-consumption calculations.
6. Conclusion
The core function of an EG evaporation vacuum system is not merely to “create vacuum”; rather, it is to establish a stable pressure boundary, effectively remove non-condensable gases, and coordinate condensation recovery so that low-temperature evaporation, product-quality control, and energy optimization can be achieved simultaneously. Owing to its wet-gas tolerance, operating stability, and strong process adaptability, the liquid ring vacuum pump offers high engineering value in conventional EG concentration and recovery. Where lower pressure, greater product cleanliness, or solvent recovery is required, a Roots-dry screw vacuum package can be used as an upgraded configuration.
During solution design, FORYOU can provide customized selection based on site-specific material composition, throughput, vacuum target, condensation conditions, and operating-cost objectives. By properly matching Roots pumps, liquid ring pumps, dry screw pumps, condensers, and exhaust-gas treatment units, the system can improve evaporation efficiency, reduce steam consumption, minimize material loss, and support continuous, stable, and efficient EG-plant operation.