Crude oil refining relies on fractional distillation to separate crude oil into different commercial products, including gasoline, diesel, kerosene, lubricating oil, and heavy residual oil. For heavy crude components that cannot be separated through conventional atmospheric distillation, vacuum distillation becomes the essential secondary refining process in modern oil refineries.
By creating a low-pressure vacuum environment inside the distillation tower, refineries significantly reduce the boiling point of heavy hydrocarbons. This allows the separation of high-boiling fractions without thermal cracking or material degradation, ensuring high-purity petroleum products and maximizing crude oil utilization rate.
This guide explains the complete vacuum distillation process, core equipment configuration, vacuum pump functions, operational advantages, and professional optimization solutions for oil refineries.
1. What Is Vacuum Distillation in Petroleum Refining?
Vacuum distillation is a low-pressure thermal separation process designed for heavy crude oil fractions. At standard atmospheric pressure, heavy residual oil boils at extremely high temperatures above 350°C, which easily causes molecular cracking, carbonization, and product deterioration.
Vacuum distillation reduces the internal pressure of the distillation tower to 10–100 mbar absolute. Under negative pressure, heavy hydrocarbon boiling points drop sharply, enabling effective separation of lubricating oil fractions, wax oil, and residual oil at safe, controllable temperatures.
It is a mandatory process for high-efficiency crude oil deep processing and greatly improves the economic value of every barrel of crude oil.
2. Atmospheric Distillation vs Vacuum Distillation
To understand the importance of vacuum distillation, it is necessary to distinguish it from atmospheric distillation:
Atmospheric Distillation :
Operates under normal atmospheric pressure, used for separating light fractions such as gasoline, kerosene, and diesel. It cannot process heavy residual oil due to ultra-high boiling temperature limitations.
Vacuum Distillation :
Operates under deep vacuum negative pressure, specially used for heavy oil fraction separation. It avoids thermal cracking, protects product quality, and extracts high-value lubricant base oil and vacuum gas oil (VGO).
3. Full Vacuum Distillation Process Steps in Oil Refineries
1. Feed Preheating
The residual oil from atmospheric distillation is preheated through heating furnaces to reach the optimal temperature for vacuum separation, ensuring uniform vaporization after entering the tower.
2. Vacuum Tower Evacuation
Professional industrial vacuum pumps continuously evacuate the vacuum distillation tower, stabilizing the internal pressure within the designed low vacuum range and creating a negative pressure distillation environment.
3. Negative Pressure Fractional Separation
Preheated heavy oil enters the vacuum tower. Different hydrocarbon fractions vaporize at different boiling points under vacuum, realizing layered separation inside the tower.
4. Condensation & Collection
Vaporized fractions rise to the condensation section, cool down and liquefy. High-value products such as vacuum gas oil and lubricating fractions are collected separately.
5. Tail Gas Treatment & Pressure Stabilization
Vacuum systems continuously extract non-condensable tail gas to maintain stable tower pressure, preventing pressure fluctuation from affecting separation precision.
4. Core Equipment Used in Refinery Vacuum Distillation Units
A complete vacuum distillation unit consists of multiple core devices working together:
Vacuum Distillation Tower: The main equipment for fraction separation, designed to resist high temperature and negative pressure.
Heating Furnace: Preheats heavy residual oil to meet vacuum distillation temperature requirements.
Cooling & Condensing System: Cools vapor fractions into liquid petroleum products.
Vacuum Pump System: Provides stable negative pressure, the core power source of the entire process.
Tail Gas Recovery Device: Processes waste gas to meet environmental emission standards.
5. Role of Vacuum Pumps in Refinery Vacuum Distillation
Vacuum pumps are the heart of vacuum distillation units. The stability, pumping speed, and ultimate vacuum of the pump system directly determine distillation precision and product yield.
Core functions include:
Continuously evacuating air and non-condensable gas inside the tower to maintain stable negative pressure
Preventing pressure rise that causes increased boiling points and incomplete separation
Improving fraction separation accuracy and reducing product impurity rate
Supporting 24/7 continuous operation of refinery distillation units
6. Best Vacuum Pump Types for Oil Refinery Distillation Processes
Refinery vacuum distillation features water vapor, oil vapor, and corrosive tail gas, requiring vacuum equipment with strong vapor resistance and stable continuous operation.
1. Liquid Ring Vacuum Pumps (Most Widely Used)
Liquid ring vacuum pumps are the mainstream choice for refinery vacuum distillation. They tolerate large amounts of water vapor and oil vapor without emulsification or damage. With explosion-proof and corrosion-resistant design, they fully adapt to flammable and explosive refinery working conditions.
2. Oil-Lubricated Rotary Vane Vacuum Pumps
Suitable for medium and small distillation units, providing high ultimate vacuum and stable pressure control for precise fraction separation.
3. Roots Vacuum Pump Combination Systems
Large-scale refinery vacuum distillation units adopt Roots + liquid ring composite systems to achieve higher pumping speed and deeper vacuum, improving overall distillation efficiency and output.
7. Key Benefits of Vacuum Distillation for Oil Refineries
Maximize Crude Oil Utilization: Recovers high-value heavy oil fractions that cannot be extracted by atmospheric distillation.
Avoid Thermal Cracking: Low-pressure low-temperature separation prevents hydrocarbon carbonization and product deterioration.
Improve Product Quality: Obtains high-purity lubricant base oil, vacuum gas oil and paraffin products.
Increase Refinery Economic Benefits: Greatly improves the yield of high-value petroleum products.
Stable & Safe Operation: Low-temperature processing reduces fire and explosion risks in refineries.
8. Common Operational Challenges & Solutions
1. Vacuum Pressure Instability
Caused by gas leakage or insufficient pumping speed. Solution: Upgrade high-stability vacuum pump systems and conduct regular tightness inspection for pipelines and towers.
2. Excessive Vapor Impurities Affecting Pump Life
Oil vapor and dust enter the vacuum system and cause wear. Solution: Install multi-stage gas-liquid separation and filtration devices to protect vacuum equipment.
3. Low Distillation Yield
Caused by insufficient vacuum degree. Solution: Optimize vacuum pump combination and adjust operating parameters according to load changes.
9. Maintenance Tips for Refinery Vacuum Distillation Systems
Monitor real-time vacuum pressure and pump operating status to avoid pressure fluctuation.
Regularly clean filter screens and separators to prevent vapor impurity accumulation and blockage.
Replace sealing parts and lubricants periodically to ensure system air tightness.
Inspect pipeline leakage points during regular refinery overhaul.
Adopt variable frequency control to reduce energy consumption under variable load conditions.
Conclusion
Vacuum distillation is the core deep-processing technology of modern oil refineries, enabling efficient separation of heavy crude oil fractions under low-pressure and low-temperature conditions. A stable and high-performance vacuum system determines distillation accuracy, product quality, and overall refinery economic benefits.
By selecting professional refinery-grade vacuum pumps and implementing standardized operation and maintenance, oil refineries can maximize crude oil utilization, improve high-value product yield, and achieve stable, safe, and energy-efficient long-term production.
FAQ
Q1: What is the purpose of vacuum distillation in oil refining?
A1: Vacuum distillation reduces the boiling point of heavy crude oil under negative pressure, separates high-value heavy fractions, and avoids thermal cracking to improve crude oil utilization and product quality.
Q2: Why can’t heavy oil be separated by atmospheric distillation?
A2: Heavy hydrocarbons have extremely high boiling points at atmospheric pressure. High-temperature heating will cause thermal cracking and carbonization, damaging product quality and causing equipment coking.
Q3: Which vacuum pump is best for oil refinery vacuum distillation?
A3: Liquid ring vacuum pumps are the most suitable for conventional refinery distillation due to excellent vapor resistance and explosion-proof performance. Large units use Roots combined vacuum systems.
Q4: How does vacuum degree affect distillation efficiency?
A4: Higher and more stable vacuum lowers boiling points further, improves fraction separation precision, reduces impurities, and increases the yield of high-quality petroleum products.
