Pre-operational Cleaning of Natural Gas Piping using Nitrogen

American Electric Power Dresden Plant 2x2x1 Natural Gas Combined Cycle

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Dresden Plant

550 MW natural gas fired combined cycle plantLocated near Dresden Ohio2x2x1 combined cycle, two (2) GE7FA combustion turbines, two (2) NEM HRSG’s, single GE D-11 Steam Turbine.COD early 2012

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Gas Blow Past Practice

Conventional practice for cleaning natural gas piping systems has been to admit the fuel gas into the piping system at the supply point, and vent the gas to atmosphere at the equipment athigh velocity, low pressure. Pipe cleanings (gas blow) are performed to scour and clear the gas lines of debris, scale, foreign objects and weld spatter.Gas lines are cleaned to the specification of the combustion turbine manufacturer, and verified with “targets” to assure the effectiveness of the cleaning process. 500,000 to 1,000,000 cf of natural gas may be released during the gas blow process, depending on the cleanliness of the gas pipingsystem.

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February 7, 2010 an explosion at the Kleen Energy Combined Cycle construction project killed 6 workers and injured 50 others

Pre-operational cleaning of the Natural Gas (NG) lines was in progress, which included venting of natural gas at high velocity from the gas piping systems.

CSB (Chemical Safety Board) investigation recommended the elimination of the use of NG for this process.

The State of CT passed regulations eliminating its use and sent letters to the other 49 states urging similar action.

Similar incident occurred on January 26, 2003 at Calpine’s Wolfskill Energy Center during the gas blow process.

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Nitrogen gas blow process used at the Dresden Plant

Both air and nitrogen gas were considered for the high velocity pipe cleaning process (gas blow)Nitrogen was the selected media for the following reasons:

Inert gas, free of Oxygen, bone dry, free of oil. Allows for a continuous blow process, without the use of large receiver tank.Vaporized on site, allowing large production of nitrogen gas and large flow rates.Nitrogen admitted at smaller diameter pipeline in each section, and blown in the direction of the larger pipeline sections for better control of debris at the discharge. This takes advantage of expansion of the nitrogen.Nitrogen gas delivered on a continuous basis from Praxair’s mobile positive displacement pump truck and high capacity fired vaporizer system.

Must manage the asphyxiation hazards associated with Nitrogen. Two pump and vaporizer trailers supplied by Praxair, each self contained and diesel powered. Capable of flow rates up to 660,000 scfh. (used in parallel). Liquid nitrogen provided by Praxair.

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Nitrogen gas blow process used at the Dresden Plant

Pipe cleanliness criteria specified by GE (GEK110483c)Cleaning Force Ratio (CFR) as recommended by the turbine manufacturer, and calculated by both AEP and Praxair. The CFR represents the momentum of the gas used to clean the piping with respect to the normal natural gas momentum design conditions.CFR is verified by the flow measurement from the Praxair equipment and by pressure measurement in the gas piping system. 11 separate blows were conducted over a 10 hour periodCleaning process continues until the plume at the pipe exit is clear and then cleanliness verified by insertion of polished metal targets into the outlet of the discharge during the last two cleaning operations, (know as the target blows)66,000 Lb liquid nitrogen consumed, ~950,000 cubic feet of gas discharged.

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Schematic of Natural Gas Piping systems Dresden Plant

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Bypass Piping Installed at Coalescing filters

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Vent stack and platform installed @ Gas yard for discharge of media and Target installation

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Praxair truck mounted diesel pump, vaporizer, and holding tank.

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Mobile Nitrogen PumperTrailer Mounted - Diesel Powered

LN2 Tank Triplex Pumps

Diesel Fired Vaporizer

Control Room

LN2 Tank provides storage to allow continuous pumping while switching tranports.Triplex Pumps driven by diesel engine pump LN2 to vaporizer which uses diesel

and air to vaporize the LN2 to gas.Control Room allows operator to adjust pump speed to control flow of Nitrogen and

Vaporizer to control Nitrogen temperature between -320 F and 600F

Diesel Engine (behind Vaporizer)

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Liquid Nitrogen Truck

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Targets used to establish cleaning effectiveness