An apparatus for use in a thermal power plant water vapor circuit associated with a steam generator and having a steam side and a water side, said apparatus being operable to reduce start-up and shutdown losses, to increase usable power from the plant and to improve control of the plant, said apparatus comprising pressure heat accumulator means connected to the steam side whereby start-up steam, shutdown steam and excess steam may be introduced to the pressure accumulator means, said apparatus being characterized by connection of the pressure heat accumulator means to the water side at a point after the water passes through feedwater preheater means, and by connection from the pressure heat accumulator means to a feedwater tank;
- with depressurizer means in circuit between the pressure heat accumulator means and the steam connection to the feedwater tank.