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.