Cryogenic Oxygen Nitrogen Plant For Refinery
Cryogenic air separation technology relies on low-temperature refrigeration and distillation to separate ambient air into high-purity oxygen, nitrogen, and rare gases. In refinery and petrochemical units, high-quality oxygen is used for oxy-fuel combustion and to enhance reaction efficiency, while nitrogen is essential for inerting, purging, and safeguarding sealed systems. Therefore, a well-designed cryogenic oxygen nitrogen plant for refinery can significantly improve a refinery's energy efficiency, operational stability, and overall plant safety.
Working Principles and Core Structure
Our cryogenic air separation unit is based on the classical low-temperature distillation process. The core workflow is as follows:
1. Air Compression and Purification
Ambient air first passes through an air filter to remove dust and mechanical impurities, and is then compressed to the required pressure by the main air compressor. The compressed air enters a molecular sieve purification system where moisture, carbon dioxide, and hydrocarbons are thoroughly removed. These impurities would otherwise freeze at cryogenic temperatures and block equipment, making purification essential for long-term stable operation of the plant.
2. Heat Exchange and Cooling
After purification, the air is routed into the main heat exchanger, where it exchanges heat counter-currently with returning low-temperature product streams (such as nitrogen and waste nitrogen). Through this process, the air is cooled to near its liquefaction temperature.
3. Cryogenic Distillation and Separation
The cooled air then enters the distillation column system. Inside the columns, separation is achieved by repeatedly applying partial vaporization and partial condensation, utilizing the differing boiling points of oxygen and nitrogen (at atmospheric pressure: oxygen −183 °C, nitrogen −196 °C). High-purity liquid oxygen is collected at the bottom of the column, while high-purity gaseous nitrogen is obtained at the top. A typical configuration includes a high-pressure column and a low-pressure column (often referred to as upper and lower columns) to ensure complete separation of oxygen and nitrogen.
4. Product Delivery and Pressurization
The separated oxygen and nitrogen streams are rewarmed to ambient temperature through the main heat exchanger and delivered as gaseous products. Depending on user requirements, nitrogen can be further pressurized by a nitrogen compressor. Oxygen can also be delivered as high-pressure gas through a liquid oxygen pump and vaporizer system.
Technical Parameters and Performance Range
(1) Oxygen / Nitrogen Purity and Flow Specifications
|
Product Gas |
Purity Range |
Typical Flow Rate (Nm³/h) |
|
Oxygen (O₂) |
90%–99.6% |
500 – 50,000 |
|
Nitrogen (N₂) |
99%–99.999% |
1,000 – 60,000 |
|
Liquid Oxygen (LOX) |
≥99.5% |
10 – 500 T/D |
|
Liquid Nitrogen (LIN) |
≥99.999% |
10 – 500 T/D |
(2) Operating Temperature and Pressure
|
Item |
Parameter |
|
Air inlet temperature to cold box |
−165 °C ~ −175 °C |
|
Temperature difference inside cold box |
≤ 3 °C |
|
Oxygen outlet pressure |
0.3–4.0 MPa (depending on configuration) |
|
Nitrogen outlet pressure |
0.6–4.0 MPa (configurable with nitrogen booster) |
(3) Energy Consumption Indicators
|
ASU Capacity |
Specific Energy Consumption (kWh/Nm³ O₂) |
|
Small ASU (≤3,000 Nm³/h) |
0.65–0.75 |
|
Medium ASU (5,000–15,000 Nm³/h) |
0.45–0.60 |
|
Large ASU (≥20,000 Nm³/h) |
0.38–0.48 |
Energy consumption depends on factors such as compressor efficiency, ambient temperature, liquid product recovery rate, and the level of process optimization.
(4) Equipment Modularization and Structural Features
- The cold box adopts an all-aluminum welded plate-fin heat exchanger structure.
- Molecular sieve purification system available in dual-tower, triple-tower, or bypass-switching configurations.
- Control system supports fully automated DCS / PLC operation.
- The entire equipment package can be modularized for easier transportation and installation in overseas refinery projects.
- LOX/LIN systems can be configured according to the refinery's liquid oxygen or liquid nitrogen demand.
Certification & Design Standards
The entire system can be designed and manufactured in accordance with international standards required by different regions:
- ISO 9001 - Quality Management System
- ISO 14001 (optional) - Environmental Management
- ISO 45001 - Occupational Health and Safety
- ASME Section VIII - Pressure vessel design & fabrication
- IEC electrical standards - Panels, wiring, protection
- CE compliance (for EU export)
Full material traceability, pressure test reports, welding records, and QA documentation
Why Refineries Choose Cryogenic ASUs
- Stable high-purity O₂/N₂ supply
- Low cost per Nm³ in long-term operation
- Higher efficiency for hydrotreating and reforming units
- Lower safety risk for tank farms and pipelines
- Robust performance even under load fluctuations
- Reduced dependence on delivered cylinders or liquid tanks
Shenger Gas goal is to help refinery owners build a reliable, energy-efficient, and sustainably operated oxygen-nitrogen supply system, ensuring that the cryogenic ASU becomes an integral part of the refinery's overall production and safety framework while delivering long-term engineering value to the project.
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