What would QC-500 be used on though, two of these could power a 055 replacement(ie. next generation CG/large DDG) while one of these could power a general-purpose destroyer like the speculated 9000-ton class destroyer
So, I assume next gen general DDG would still go with 2 smaller gas turbines which really only leaves next generation CG/large DDG, modified 076 and hypothetical conventional carrier.
There are the
CGT-30M, CGT-40M and QC400 marine gas turbine engines with smaller power outputs than the QC500 (and also CGT-50M in the future) that can be used for propelling and/or powering general-purpose DDG-sized warships.
For instance, the Arleigh Burke DDGs have 4x LM2500s with an individual propulsion power output of ~19.57 MW (under USN SD conditions), meaning a combined propulsion power output of ~78.28 MW in COGAG configuration.
On a hypothetical/future general-purpose DDG in the PLAN with similar size and displacement as the Arleigh Burke DDG, the same propulsion power output demand can be met with 2x CGT-30Ms or 2x CGT-40Ms, supplemented by several 4-6 MW diesel/diesel-electric engines in CODAG/CODLAG or CODOG/CODLOG configurations.
although I'm not sure how good of an idea it is to power your ship with a single large turbine as if you lose that you *don't* have anything left.
There are plenty of FFGs which feature only one gas turbine engine per boat. The Mogami, Constellation and FREMM-classes of FFGs are prime examples.
Of course, this sole high-power gas turbine engine are working
in addition to several diesel (or diesel-electric) engines onboard these types of warships in CODAG/CODLAG or CODOG/CODLOG configurations.
The sole gas turbine engine is used mainly during high-speed dashes, whereas the diesel (or diesel-electric) engines are used for low-speed cruising (which is often the majority portion of most journeys at sea). That means in case the sole gas turbine engine is rendered inoperable, the warship can still rely on its onboard diesel/diesel-electric engines to return to base.