Abstract :
The paper outlines the trends in the design of large units of generating plant in the United States at the beginning of 1965. Unit sizes continue to rise, and supercritical steam conditions, with pressures around 3500lbf/in2 and temperatures in the 1000¿1050°F region, are now nearly always adopted for units of above 400 MW capacity. Great attention is paid by the makers of boilers and of turbines to secure higher availability, because it is now recognised that, as size increases, so does the difficulty of tracing faults which may arise in operation, and outage time means money. The trend to larger units is encouraged by lower overall costs per kilowatt, and users are attempting to reduce this still further by the adoption of 100% duty auxiliaries where possible, and careful layout of auxiliary plant. The mechanism of boiler-tube breakdowns is now more widely understood, and the tendency is to equip all high-pressure units with condensate polishing plant. More attention is being paid to the elimination from stack effluent of undesirable products of combustion. The position with regard to computer control of large units is now static, because of difficulties with early units and high prices of computer equipment. The tendency for manufacturers to increase boiler ratings is being resisted by users, particularly of coal-fired boilers. Much greater attention is being given to the supervision of shop and site welding techniques, in an attempt to avoid boiler outage during operation.
