There isnt any "trade off". If you need a vent, then you must design to code. If you rate says it must be 50m heigh, then it must be 50m high. But usually the height is associated to ensure that thermal radiation is acceptable at ground level. An alternative is to fence off the area beneath the vent and only allow entry when the plant is shut in and depressurized. Then you could allow a higher thermal radiation within the fence and have the max. allowable radiation at the fence.

Best regaards, Morten

It is rather basic, but make absolutely sure you are looking up the right references for this exact installation. A natural gas compressor station on a natural gas transfer point of a pipeline usually does not have a hot flare at all. Vent pipes are far, far shorter on natural gas end-points in a GT power plant, but are installed for cold venting (no flares!) the turbine and NG control piping on emergency shutdown.

API controls the safety and venting and pressure systems inside a refinery or plant. Are you assuming its restrictions and requirements are also controlling the NG piping inside the refinery boundary by default?