1939: Turbines

Steam Turbines.

Looking backward over 1939, the important developments in steam-turbine construction and operation can be traced to three almost wholly unrelated events. First, if it had not been for the breathing spell in utility buying occasioned by the depression of 1932-35, research would not, in all probability, have advanced to a point where blade materials and casings could withstand steam at 900° F, or nearly red heat. Second, the post-depression spurt in power-plant construction found many old stations with good turbines and poor boilers, a condition requiring a new kind of turbine, designed for very high steam pressure (1,200-1,400 lb.) and to exhaust steam to existing turbines at moderate pressures (200-400 lb.). Third, the beginning of war in Europe made it necessary for power supply systems to extend their planning two years ahead, in order to order machines that take over a year to build and nearly another year to install.

The end of the year marked completion of at least two years operation for several of the newly designed superposed turbines, long enough to satisfy operators that the machines are workable and reliable. Steam from pulverized-coal-fired boilers strikes the blades of these turbines at 600 miles per hour, about the same speed that a bullet left the muzzle of the old Colt .45 revolver. Passing through the nozzles at this speed, the steam develops as much as 10,000 kilowatts in the first stage (two blade rows) of some of these turbines. Because they have to operate at practically red heat with 600-mile-an-hour steam weighing 1½ lbs. per cubic foot, much more rugged blade and root constructions are employed than in the turbines of only a few years ago.

Power stations employing modern high temperatures and pressures can generate a kilowatt hour for about 0.85 lb. of coal as compared to a country-wide average of 1.4 lb. This improvement would not be possible without years of fundamental research on the part of turbine manufacturers in development of stainless blade materials having high strength at elevated temperatures.

The war in Europe has had a pronounced and somewhat unexpected effect on turbine designs. Defense needs were immediately reviewed at the outbreak of hostilities in the light of what would happen either if the United States were drawn into the war or became the workshop of the belligerents. This survey found our power-producing capacity reasonably adequate for the present year, but insufficient in industrial centers, if loads grew rapidly in the next two years. New installations had been contemplated by many utilities for some time, so that the impulse of possible imminent need, combined with the desire to buy in advance of a rising market, released a flood of turbine orders the like of which has never before been seen. Almost a year's supply of new turbines was ordered within two months of the start of war.

This haste to place orders and the desire for the earliest possible shipping dates has resulted in specifications for known standard designs of turbines incorporating as little experimental and untried detail as practicable. In this respect the war will be found in later years to have crystallized turbine design at its present stage of advancement. Whether this standardization of design will be of ultimate benefit to the industry, or whether it will arrest major developments for several years, only future experience can indicate.

Gas Turbines.

An entirely new prime mover came into prominence in 1939. Electric power is now being made by direct combustion of oil or gas fuel within a turbine unit without the intermediate action of steam or any other heat-absorbing medium, and without the need for cooling water. While an experimental gas turbine has been in operation nearly two years, no technical information was published until this year.

The gas turbine, a conventional machine much like a steam turbine, has been the dream of inventors for over a century. Early designs, based on exploding charges of oil in separate chambers in rotation (Holzwarth) produced some useful power but at low efficiency and by complicated mechanism. Other designs failed to produce power at all. The recently developed unit (Brown-Boveri Co. Switzerland) not only is quite satisfactory as a prime mover but has reasonable efficiency even in its present early stage of development.

The gas turbine set, eleven of which are now on order or in operation, consists of four parts: (1) a five-stage turbine unit (2) an 18-20 stage axial-flow air compressor (3) a combustion chamber for oil firing, made of a 12-foot length of 24-in. pipe (4) an electric generator to convert the power output to the type and voltage of current desired.

Its operation is very simple. Air from atmosphere is compressed in the axial-flow compressor by rows of blades (having an air-foil cross section much like airplane propellors) to about 45 lb. per sq. in. gauge pressure. Part of this air is burned with oil in the combustion chamber under pressure; the remainder serves to cool the products of combustion to 1,000° F. The resulting mixture passes through the gas turbine wheels generating more than enough power to drive the compressor. The excess is available for electric output.

Minimum size for gas turbines for power generation is about 2,000 kw. net output. They will not compete with most Diesel engines, which are smaller in size. They are best suited for such applications as locomotive drive, power units for destroyers, and emergency standby plants where compactness, ruggedness and simplicity of construction are of prime importance. The first actual application, however, has been to the supply of compressed air to the Houdry Process of gasoline refining. In this process all the compressed air needs and some excess power are produced by waste refinery gas. See RAILROAD EQUIPMENT.

Hydroelectric Turbines.

Developments in hydro power have made each of the past three years a record period in one way or another. In 1939 water power activity continued much greater than normal.

Two more units of 115,000-h.p. capacity were put in service at Boulder Dam which now aggregates 975,000 h.p., the largest hydroelectric power plant in the world. (The largest steam power plant is in Brooklyn, N. Y. and is rated at 1,030,000 h.p.) When the two additional units now on order go into operation, Boulder Dam will have over 1,200,000 h.p. of capacity and will be the largest power-generating plant of any kind.

The largest hydro turbines so far constructed are two 150,000 h.p. units for Grand Coulee, now in the shops. These will go into operation in 1941.

The year was poor in water power because of general drought conditions. Only 34 per cent of the country's power for public use came from hydro in 1939 and compared with 38 per cent in 1938.

About 2,000,000 h.p. of new hydro turbines are now on order. By the end of 1942, these orders will raise the total above 20,000,000 h.p.