When is a fuel gas compressor required on gas turbines?

A fuel gas compressor is required on gas turbines when the gas supply pressure is less than the compressor's last stage pressure. This scenario is critical because gas turbines operate optimally within specific pressure ranges. If the incoming gas pressure is inadequate, the compressor cannot maintain the necessary pressure levels for efficient combustion in the turbine.

This situation ensures that the fuel gas is delivered at the appropriate pressure to the combustion system, allowing for complete combustion, stable operation, and efficient turbine performance. Additionally, having sufficient gas pressure is essential for ensuring that the fuel mixes well with air and burns effectively within the combustor, which influences overall efficiency and emissions.

In contrast, situations described in the other options may affect system performance or efficiency but do not specifically pinpoint the need for a compressor to address low gas supply pressure directly. For instance, complexity in the gas system could lead to pressure drops but doesn't inherently necessitate a compressor unless it results in inadequate inlet pressure. Similarly, significant pressure drops across combustors or multiple gas nozzles can impact performance but won't necessarily require a compressor if the upstream pressure is still adequate.