NFPA 8502


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We have a set of time for gas turbine purging which is 15 min prior the start of turbine to protect against gas leak. We want to reduce the time or skip it after a failed start.

When I had a look at the standard, it says boiler shall be purged before a cold start with the airflow higher than the %70 normal capacity. There seems no time limit for the purge set. Have you got any simliar application for reducing time set?

Phil Corso, PE


Time is not defined per se! However, see the definition of "Unit Purge" in NFPA 8502! The Purge-Time value is based on the purge-rate in percent of the unit's full-load mass flow and boiler enclosure volume. As an example, consider an oil or gas-fired boiler. A "minimum allowable" (italics mine) purge-time would be a flow of at least 25% of the full-load mass flow for (1) a period of at least 5 minutes or (2) five changes of the the boiler enclosure volume. Caution: make sure you have the boiler manufacturer's concurrance!!!

Regards, Phil Corso, PE ([email protected])