mechanical - steam turbine power plant design.pdf

TM 5-811-6 CHAPTER 3 STEAM TURBINE POWER PLANT DESIGN Section 1. TYPICAL PLANTS AND CYCLES 3-1. Introduction a. Definition. The cycle of a steam power plant is the group of interconnected major - ponents selected for optimum thermodynamic char- acteristics, including pressure, temperatures and ca- pacities, and integrated into a practical arrange- ment to serve the electrical (and sometimes by-prod- uct steam) requirements of a particular project. Se- lection of the optimum cycle depends upon plant size, cost of money, fuel costs, non-fuel operating costs, and maintenance costs. b. Steam conditions. Typical cycles for the prob- able size and type of steam power plants at Army es- tablishments will be supplied by superheated steam generated at pressures and temperatures between 600 psig (at 750 to 850°F) and 1450 psig (at 850 to 950o F). Reheat is never offered for turbine genera- tors of less than 50 MW and, hence, is not applicable in this manual. c. Steam turbine prime steam tur- bine prime mover, for rated capacity limits of 5000 kW to 30,000 kW, will be a multi-stage, multi-valve unit, either back pressure or condensing. Smaller turbines, especially under 1000 kW rated capacity, may be single stage units because of lower first cost and simplicity. Single stage turbines, either back pressure or condensing, are not equipped with ex- traction openings. d. Back pressure turbines. Back pressure turbine units usually exhaust at pressures between 250 psig and 15 psig with one or two controlled or uncon- trolled extractions. However, there is a significant price difference between controlled and uncontrolled extraction turbines, the former being more expen- sive. Controlled extraction is normally applied where the bleed steam is exported to process or dis- trict heat users. e. Condensing units ex- haust at pressures between 1 inch of mercury abso- lute (Hga) and 5 inches Hga, with up to two con- trolled, or up to five uncontrolled, extr