Oxygen Extraction Rate
Definition
The oxygen extraction rate is a key indicator used to evaluate the separation efficiency of air separation units. It is expressed as the ratio of total oxygen in the product oxygen to total oxygen in the feed air:
ψ=VO2⋅yO2/Vk⋅yk
| Symbol | Description |
|---|---|
| ψ | Oxygen extraction rate |
| VO2 | Oxygen production rate (m³/h) |
| yO2 | Oxygen volume fraction in product oxygen |
| Vk | Feed air flow rate (m³/h) |
| yk | Oxygen volume fraction in air (~20.9%) |
Key Findings
Primary Factor: When feed air flow and product oxygen purity are constant, the oxygen extraction rate mainly depends on the oxygen content in waste nitrogen.
Practical Example:
| Condition | Waste N₂ Oxygen Content | O₂ Production | Extraction Rate |
|---|---|---|---|
| Normal | 5.5% | 3200 m³/h | 84.2% |
| Degraded | 7.5% | 2982 m³/h | 71.8% |
A mere 2% increase in waste nitrogen oxygen content results in 218 m³/h reduction in oxygen production and a 12.4 percentage point drop in extraction rate.
Technological Progress:
Past: 80%–85%
Present: 90%–95%
State-of-the-art: up to ~99%
Engineering Significance
Reducing oxygen content in waste nitrogen is the most effective approach to increase oxygen production and improve extraction rate, directly impacting the economic performance of air separation units.
