Some Operating Experiences with High-Pressure Steam Power Plant

Between the years 1938 and 1944 the Northmet Power Company placed in commission four high-pressure steam power plant installations comprising 50 and 60 megawatt units at Brimsdown “A” and “B” Power Stations respectively, operating on the 1,900 lb. per sq. in., 930 deg. F. reheat cycle, and two 32 megawatt non-reheating units at Willesden Power Station, operating at 1,300 lb. per sq. in. and 950 deg. F.

These cycles were selected for the respective sites from considerations of coal cost and of circulating water make-up facilities, both stations relying upon rail-borne coal supplies and operating with cooling towers. The capacity and design of the plant were largely determined by the available space, existing buildings being utilized to accommodate most of the new machines and auxiliaries.

The pressure and temperature conditions involved consideration of creep characteristics in selecting suitable alloy steels for the pressure parts, and their mechanical properties were closely investigated before contracts were placed. Welding was extensively employed in boiler and pipework construction, and preliminary tests and subsequent radiographic examination presented many interesting problems.

Early performance figures promised the achievement of the thermal efficiency to be expected from the cycles, and subsequent experience shows that, as indicated by theoretical considerations, the 1,300 lb. per sq. in. cycle is capable of equal or greater economy than the higher pressure with the reheating arrangements.

Certain difficulties in operation have been encountered—not all inherently associated with high-pressure working. The paper gives an account of these difficulties and of the steps taken to surmount them.

In the light of these operating experiences, the future of high-pressure steam power generation is discussed with comments on features which are considered essential to a successful design of plant. The initial ventures are felt to have been justified by results and by the contribution made to mechanical engineering in general. The present and future urgent need for coal for international barter calls for the fuller development of the use of high-pressure cycles, and experience to date warrants a continued advance toward their more general application.