What is the backup supply if the instrument air compressors fail to provide enough pressure?

The backup supply when instrument air compressors fail is nitrogen. In many refinery processes, nitrogen is used as a backup source for instrument air systems because it can provide a stable and non-reactive supply of pressure. Unlike compressed air, which may contain moisture and oil, nitrogen is an inert gas that does not react with other substances in the refinery, making it ideal for maintaining the integrity of sensitive instrumentation.

Additionally, nitrogen is often used to ensure the reliability of pneumatic controls, particularly in environments where air quality cannot be guaranteed. Using nitrogen also helps prevent contamination and maintains operational safety, especially in processes where the presence of moisture or other contaminants could lead to equipment malfunction or damage.

Other options like hydrogen and steam are not used in place of instrument air due to their reactivity and potential hazards. Hydrogen is flammable and poses safety risks, while steam may not provide the consistent pressure and dryness required for instrumentation. Consequently, nitrogen stands out as the most appropriate and safest backup supply for instrument air compressors in refinery operations.