The Critical Role of Air Compressors in Chemical Production

In chemical production, air compressors are by no means merely auxiliary equipment used for “blowing” or “ventilation”; rather, they serve as a core power source and play a critical role in process reactions. Their key functions are primarily manifested in the following five aspects:

1. Providing Power for Instrumentation and Control Systems (The Most Common and Critical Function)

• Function: Supplying dry, clean, and pressure-stabilized “instrument air” to pneumatic control valves (regulating valves and shut-off valves), pneumatic actuators, and pneumatic instruments.
• Importance: Should the supply of compressed air be interrupted—or if it becomes contaminated with water or oil—thousands of pneumatic valves throughout the plant would instantly fail. This would lead to an unplanned plant shutdown and could even trigger serious safety accidents. Instrument air is often referred to as the “soft nervous system” of a chemical plant.

2. Supplying Oxidants or Feedstock Gases for Process Reactions

• Typical Processes:
  • Ammonia Synthesis: Air compressors provide high-pressure air, which reacts with carbon in a gasifier to produce semi-water gas (H₂ + CO).
  • Ethylene Oxide / Ethylene Glycol: Supplying high-purity oxygen or oxygen-enriched air to react with ethylene over a silver catalyst.
  • PTA (Purified Terephthalic Acid): Supplying air as an oxidant to oxidize paraxylene into crude terephthalic acid.
• Key Point: In these instances, the compressor is an integral part of the reaction system; its discharge volume and pressure stability directly impact the conversion rate and selectivity of the main reaction.

3. Enabling Pneumatic Conveying and Purging of Materials

• Pneumatic Conveying: Utilizing compressed air to transport powdery or granular materials—such as polypropylene, polyethylene powder, or urea granules—through enclosed pipelines. Compared to mechanical conveying systems, this method is cleaner, more flexible, and easier to automate.
• Purging and Displacement: Prior to plant startups, shutdowns, or maintenance operations, compressed air is used to purge residual flammable or toxic materials from pipelines. It is also used to displace the atmosphere within storage tanks or reactors to prevent the formation of explosive gas mixtures.

4. Providing Seal Gas and Buffer Gas for Critical Equipment

• Centrifugal Compressor Shaft Seals: In high-speed rotating centrifugal compressors (such as cracking gas compressors and synthesis gas compressors), a small quantity of high-pressure seal air is required to prevent the leakage of process gases (which often contain flammable and explosive components such as H₂, CH₄, and CO).
• Buffer Function: This serves to prevent lubricating oil from migrating into the process system and contaminating the product, while also preventing process gas from migrating into the lubrication system and causing oil degradation.

5. Drive Gas Recovery and Tail Gas Treatment Systems

• Gas Recovery: In polyolefin plants, for instance, air-driven ejectors or pneumatic pumps are used to recover hydrocarbons from flare gas, thereby minimizing material loss.
• Tail Gas Boosting: Low-pressure tail gases (such as desulfurized flue gas or drying bed regeneration gas) are boosted to a higher pressure before being fed into the fuel gas network or directed to a waste gas treatment system.

Special Emphasis: Specific Requirements for Air Compressors in Chemical Applications

Unlike standard air compressors, chemical production facilities predominantly utilize oil-free screw compressors or centrifugal compressors. These units are strictly paired with air drying systems (achieving a dew point of ≤ -40°C) and precision filtration systems (limiting oil content to ≤ 0.01 ppm). This strict requirement stems from the fact that the ingress of oil, moisture, or dust from the air into the reaction system can lead to catalyst poisoning, pipeline corrosion, or product non-compliance.