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.

1940: Turbines

Steam Turbines.

Of outstanding interest in 1940 was the large number of steam turbine capacity ready for service, being built, and on order. About 1,500,000 kw. of steam turbine went into service during the year; almost 2,000,000 more were in the shops at the year's end for 1941; and orders placed for 1942 indicate that the 1941 record will be exceeded if manufacturers can devote shop capacity to building turbines. These figures are exclusive of a large number of marine turbines, both warship and cargo craft, concerning which information cannot be published.

This situation has resulted in the use of previous designs for many of the new turbine units in order to avoid engineering delays. Fortunately designs of the past few years have been tried and tested in service, and the units now building are efficient and dependable.

Interesting research is being conducted at the Schuylkill station of the Philadelphia Electric Co. by the Westinghouse Co. on high-frequency resonant vibration of turbine blades exposed to 1,200-lb., 900°-F. steam. An experimental two-row turbine delivering 10,000 kw. is equipped with an optical system through its shaft which permits inspection of the actual movement of the blade tip while the unit is in operation under load. A water brake of special design can absorb as much as 15,000 h.p., enabling tests at varying speed. Long-time tests will be run on a 10,000 kw. generator connected to the utility system. The series of tests is expected to explain some of the several recent blade failures and lead to improved design against fatigue failure.

Industrial turbines now are provided with greatly improved governing units and control valves. Steam can be extracted or admitted at two process pressures in addition to the high pressure admission to the throttle, all under control of the one governor which maintains constant pressure at both extraction points as well as desired load on the machine. Governors of both mechanical and hydraulic design have been proven adequate.

Hydrogen cooling of large generators has become standard practice. It has been found that increased ratings may be secured for short periods by raising hydrogen pressure within enclosed generator casings to about 9 lbs. per sq. in., as compared to normal pressures of a few ounces. Purity of hydrogen must be kept well over 99 per cent to assure that an explosive mixture will not exist; and automatic control equipment and alarms have proved to be satisfactory in service.

A turbine is now being built by the General Electric Co. to generate 22,000 kw. from steam at 2,400-lb. pressure. This unit will start operation in the Twin Branch station of the American Gas & Electric Co. about June 1941. One smaller turbine is now running in a chemical industries plant at about this same high pressure.

Gas Turbines.

Continuous-combustion gas turbines, in which oil fuel is burned directly, have proved practical, safe and reasonably efficient, in oil refineries, so far their only application. The gas-turbine unit is made up of an axial-flow compressor which compresses air to about 50 lbs. gage pressure; a combustion chamber operating under pressure with a continuous oil flame; and a six-row turbine to utilize the energy of the hot exhaust gas. About three-quarters of the output of the turbine is required by the compressor, the remainder being available as electrical energy or as compressed air. In oil refineries, gas turbines supply large amounts of compressed air to catalytic processes such as the Houdry process for producing high test gasoline.

Twelve such units, ranging from 500 to 1,200 kw. net output (2,700 to 5.300 kw. turbine output) have run for from one to four years. Larger units are now under construction. They are entirely successful and practical as now used. Further application to locomotive and marine power are under investigation but no units are actually being constructed for these purposes.

Single-row high-speed (20,000-rpm.) gas turbines are being employed as superchargers for high-altitude gasoline airplane engines. Exhaust gases at 1,600°-1,800° F. drive the gas turbine to supply power to a centrifugal compressor. One design has hollow blades of intricate shape provided with a stream of cooling air to permit withstanding the red-heat gases.

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.