Combined cycle have been used in large power generation equipment since the 90’s using industrial gas turbines followed by a heat recovery steam generator and steam turbine to give very high efficiency power plant usually fired by Natural gas.
Using a similar approach, Bluebox has developed a combined cycle approach using hot air turbines followed by an organic Rankine cycle that can achieve efficiencies as high as 27.5% for plant in the 2MWe class (much smaller than steam turbine systems).