Gas Release Near Turbine Exhaust

[nashc0]

We had a situation last week where natural gas was released from a sensing line just a few feet away from a turbine exhaust stack. Luckily, the leak was detected and the plant evacuated with no significant damage. As for assessing future risk, there is a worry that if the wind had been blowing in the direction of the exhaust stack (which it normally does), the gas could have ignited. It seems to me like there ought to be an industry standard or best practice regarding location of the exhaust stacks relative to process piping, tubing, etc. Can anyone point me in the right direction? I understand that these things should have been taken into consideration when the equipment was designed, but I operate in a country where unfortunately these things seem to slip through the cracks on occasion.

The worst-case scenario has the flow of natural gas (MW 17.2) at around 5 mmscfd. It is estimated that the line leaked for 5 - 10 minutes before it was isolated. The exhaust temperature is normally in the 400 - 600°C range, and the skin of the exhaust stack is normally in the 275 - 300° range. According to the MSDS, this temperature is below the auto-ignition temperature of methane, which is 537°C.

Thanks for your help...
Clayton

 

[nicovdven]

A dispersion model (as used in emission calculations)could be used to calculate concentration levels under varying circumstances to determine "safe" distances or heights. Explosion and exposure (& sometimes odor) limits should be incorporated into the model to arrive at the "safe" exhaust position.

 

[JLSeagull]

Many offshore platforms use natural gas for starting gas turbine engines with the start gas vented at about the elevation of the turbine exhaust. I may be able to find someting on the start gas volumetric flow for GE LM2500's. My recollection is that the inlet line size is about 3 NPS and pressure is about 200 psig. The start gas is vented to the atmosphere for a minute or more while firing the turbine.

 

[dcasto]

There are API and other recommended practices for hazardous locations (RP500). Adequate ventilation and inpections are a requirment since you cannot always remove all sources of gas in an engine room.

A look at all your piping and tubing to see if it is protected from damage, minimal mechanical connects, and routing that keeps lines protected.