Issues with the instrument air storage tank
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To ensure the requirements for instrument air in the event of an accident, during design, how long should the amount of gas stored in the instrument air tank be sufficient to supply instrument air at the minimum pressure during such an accident?
Is an accident referred to as an air compressor incident where it cannot operate properly? If a compressor failure prevents the supply of compressed gas, the pressure in the instrument air storage tank will drop immediately. The size of the tank can generally be estimated based on the diameter of its outlet pipe; an airflow rate of around 15 minutes is sufficient to take into consideration.
I wonder if there are clear requirements in the specifications?
Not necessarily; if it has a backup air compressor, it will take at most 5 to 10 minutes, thereby reducing the size of the air buffer tank
Storage tanks are generally designed and used based on one-third of the air compressor’s gas production rate per hour.
The SH3020-2001 Standard for Design of Gas Supply for Petrochemical Instruments specifies that 4.4.2 The maintenance time t should be determined based on the production scale, the complexity of the process flow, and the level of design for safety interlock automatic protection. If there are no special requirements, the value can be obtained within 15–30 minutes; in special cases, the duration time t is determined by the design.