1941: Turbines

During the year 1941 more steam turbines were built than in any previous year, nearly 3,000,000 kw. for utilities and industrial power plants and about the same amount more for marine service. New construction of land turbines of all types, including nearly 1,000,000 kw. of hydro units increased the nation's power generating capacity about 8 per cent.

The industry has concentrated on standard types which can utilize engineering and design already developed — so contributing to speed of construction and early delivery. More units of 25,000-kw. size have been ordered and built than of any other size. Pressure at 800 lb. and steam temperature of 900° F. have been most popular. Three quarters of this year's turbines will operate at 3,600 r.p.m., whereas the standard speed of ten years ago was 1,800 r.p.m. This indicates a definite trend to smaller high-speed units that require less steel and building space.

Several new ideas have been proposed and a few others confirmed as satisfactory by practice and test:

Hydrogen cooling of generators has become accepted practice during the year because of universal reports of satisfactory operation and complete safety of this explosive gas when confined within a pressure-tight casing. Hydrogen cooling improves generator efficiency between  and  per cent at little extra cost. The first central station started operating at 2,400 lb. pressure. A few European installations of small size have previously operated above this pressure level and one American industrial plant generates steam at above 2,000 lb. The new 2,400-lb. station, located at Mishawaka, Ind., now holds the world's efficiency record for conversion of the energy of coal to electricity by steam at about 10,200 Btu per kilowatt hour.

Three mercury boiler-turbine units are now in regular normal operation at heat rates effectively below 10,000 Btu per kwhr. The latest design mercury boiler at Kearny, N.J., has eliminated many of the troubles which characterized early years of operation. Welded throughout, the new boiler has much of its heating surface filled with mercury 'fog,' a mixture of mercury and mercury vapor that is mostly all vapor. Mercury turbines seem to have practically no operating troubles but the boilers have suffered from corrosion due to the introduction of oxygen at the condenser. Treatment of the mercury with titanium, zirconium and magnesium in pure metallic form has overcome most of the difficulties.

The first new forced-circulation boiler is nearing completion at Somerset, Mass. This unit will make steam at 1,800-lb. pressure. Instead of relying on the natural circulation effect of steam and water in the boiler tubes, a circulating pump forces the water through the circuit at high velocity ensuring that the tubes will have adequate water at all times to keep them from burning out. These pumps, of which there are three per boiler, pump only against 50-lb. pressure but their casings must stand full boiler pressure of 1,800 lb. They are therefore of very heavy and unusual construction. The boiler itself is entirely welded.

There have been no important changes in the details of turbine design. New machines for pressures above 1,600 lb. continue to be built with a double shell. An intermediate space between the two casings carries a pressure of about 400 lb. so that the inner section need be strong enough for only the difference between 1,600 and 400 lb. Inner-shell bolts can therefore be smaller and avoid serious temperature stress.

Turbine manufacturers have this year developed a practice of rating machines at more than nominal load for emergency purposes. In some cases this is accomplished by carrying a hydrogen pressure of several pounds instead of a few ounces in the generator. The higher pressure affords increased cooling of the generator coils and thus allows greater loads on the same machine types.