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[pklavinsJ]

We are modifying an existing oil battery/gas processing facility to handle surface production from a gas/oil/water field. Due to changes to the field production, the asset team would like to handle significantly more water production. This would require increased capacity to send water from the inlet separator to the produced water tanks and thus require either a larger level control valve or parallel level control valves. 

 

If we increase the level control valve size, the gas blowby case for the downstream atmospheric produced water tanks increases beyond the capacity of the existing emergency pressure relief valves. To handle that failure mode, we would need to make costly modifications to these existing produced water tanks to increase the relief capacity of these tanks (or install a costly HIPPS/SIL-3 rated system).

 

An alternative option that we are exploring would be to install a parallel level control valve. This would be controlled from a separate level bridle with a different type of level transmitter with a higher setpoint. At what point would you consider these two parallel level control valves independent from each other (for failure mode analysis) and thus keep the blowby gas flow rate limited to just one of the control valves failing open? Do you consider favorable action of the other level controller/level control valve to close if the liquid level drops creating gas blowby?  

 

I'm not confident that this alternative design will survive a HAZOP analysis and I am trying to eliminate this option early in the project.