Abstract
The purpose of this project was to evaluate the effectiveness of a hybrid inert gas/water mist fire suppression system on aero-derivative style gas turbines. A utility company and its fire protection engineer provided the opportunity to test the system on an operating unit under load, enabling the research team to assess system efficacy in real-world scenarios. The utility company established the test criteria; testing would be deemed successful if the system could cool the turbine skin to less than 380°F within 10 minutes. 380°F represents the auto ignition temperature of lube oil and turbine fuel plus a safety factor, as determined by the company. The 10-minute timeframe was established to match the performance of the existing CO2 extinguishing system.
A series of tests were devised to demonstrate the suppression system's effectiveness for cooling. The tests involved operating a Pratt and Whitney FT4 aero-derivative turbine generator off and on the power grid at full speed/base load and allowing the unit to cool naturally, as well as on the grid and allowing the system to discharge. Systematic changes in water flow and installation parameters were used to find optimal results. Temperatures were recorded at the compressor section, combustion section front, combustion section rear, hot turbine section, exhaust diffuser and in the enclosure.
Testing demonstrated that the hybrid fire suppression system is capable of quickly cooling the turbine skin to below 380°F—within 33 seconds, in fact—without damaging the turbine. The test results show successful cooling with the emitters installed overhead and aimed toward the hot section of the turbine. Results indicate that the hybrid fire suppression system adequately protects aero-derivative turbines under normal operating conditions. The testing offers a proof point that the system is not damaging to equipment, overcoming historic objections to the use of water mist style systems.
