The low efficiency of thermal power plants is evident from second law of thermodynamics and as such it is not practical to convert heat energy to mechanical energy without temperature difference. The wider the temperature difference from the upper heat sink and the lower heat sink, the greater the energy converted and hence the resultant loss of heat to the surrounding. The obvious solution to the low efficiency of steam plants lies in the recovery of heat from flue gases before it is discharged. For gas turbine power plants, the regeneration of the hot exhaust gases is important and can be used to raise steam in conventional steam plants as you aptly described in CCGT plants. Your post is always a joy to read. Thanks for the good job.