In order to investigate the difference in thermal system between the back pressure extraction steam turbine(BEST) and the regular system

a complete system model was built with the EBSILON software

on the basis of design calcualtion of a supercritical 1 000 MW unit with double-reheat cycle. Moreover

the genetic algorithm and enumeration algorithm were applied to optimize the enthalpy rise distribution and reheat steam pressure

and the optimized results were compared between the two systems. The result shows that

the BEST system decreased the superheat degree of the extracted steam and weakened the influence of reheat cycle on the regenerative cycle

which made the enthalpy rise distribution more even.Due to changes of the system's cyclic property

part of the steam in the BEST system will not enter into the reheater

thus the optimized reheat pressure will be higher than that in the regular system.