The gas and pipework characteristics are -
Biogas - 60% CH4, 40% CO2, traces of NOX, SOX & HCL
Temperature at source is 36C and cools to 6C in winter and 20C in summer because gas passes through a condensate trap and so im assuming the gas will pass through and emerge at same temperature as the water across the seasons.
The pressure at source is about 20 mbar and ideally the same at consumption.
The pipework is 100m total length has 2 90 degree bends, the diameter changes after each bend it goes from 200mm to 300mm to 250mm.  Theres a condensate trap at the end of the final leg of pipe.  The whole pipeline falls consistently at 2 degrees.  There are 2 gate and 2 butterfly valves on the system.  Theres 1 gas flow meter and 2 gas pressure switches on the system.  The pressure switches dont protrude into the pipeline they have their own 2" take off legs but the gas flow meter is an endress & hauser t mass and im not sure how it fits into the pipe.
We don't normally measure biogas water content, but you are correct, it is important.   The gas starts is journey from the headspace of the digester to the boiler, engine or gas store at digester temperature  37 -56 degrees C typically. As it has been stripped out of the water phase it is assumed to be at 100% relative humidity and condensing.   The gas will continue in this condition until it either gets burned in the engine after a dewatering / gas cooling stage or it sits in the gas bag overnight and the water is removed.   Dry gas is so rare in biogas systems that we ignore the possiblity and assume condensing gas is always present.  The only exception is if the above mentioned gas drying stage is inserted upstream of the engine to protect it and this might be checked periodically to ensure the drying process is working.

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