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Wet Fuel Gas System problem from missing Dehydration Equipment

asked Aug 4, 2016 in Engineering by Normandy (21,040 points)
There will be a problem if dehydration equipment is taken out for services or totally removed from the offshore platform.

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answered Aug 4, 2016 by Normandy (21,040 points)

The fuel gas to the generator will no longer has a low -400F dew point. As a result, expansion of the quantity of gas across the regulator will result in freezing of water and/or hydrate formation.

There are few options available to address this problem. They are:

  • Heat the gas prior to expansion to avoid subsequent freezing and line sweating.
  • Inject methanol into the gas prior to expansion to suppress solids formation.
  • Install electric tracing on the fuel gas line near the regulator to prevent line sweating.

Heating the gas may be accomplished in a number of ways:

  1. Exchange the generator exhaust gas against the fuel gas. Two units are required.
  2. Partially reduce the pressure of the fuel gas across a new regulator - lowering the fuel gas temperature, then exchange produced gas against cool fuel gas to raise its temperature above its dew point. This option introduces additional operational complications into the system.
  3. Install a conventional line heater - a gas-fired water bath heater.
  4. Use generator jacket - water to heat the gas.

All above 4 options require a back up inhibitor injection system for start-up.

The cheapest and recommended option is to use a methanol system on the fuel gas line with electric tracing. This is the lowest cost alternative and is easiest to operate.

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