Document zojDQ1wp5QODp95VMd86ynBv6

Got turbine lower* plant heot rote ot oil turWno-eondenser pressures Gas turbine improves Overall plant performance ot all load mognltudes temperature. Use of.i "minimum" open cycle hookup permits the unit to be simple In design, lightweight and in expensive. Normal rating ol the unit .will be 3500 kw based on ombient temperature o( 80 F and an altitude o( 1500 -ft. The turbine, direct conncotcd to the compressor, runs ot 6700 rpm. A pre cision helical gear couples the turbine to a conventional 4000-kw 3600-rpm generator and exciter, see Fig. 18. The OG4E 'Co requested the oversize gen erator. Atmospheric air enters the com pressor to be raised to about 87 psia at full load. The high-pressure air then enters six cylindrical combustors whero burning luel raises the temperature to that required for the load. With the essentially constant air flow, turbine inlet temperature will vary directly with load. Hot high-pressure gas then ex pands through the turbine. ' Since the net power equals'the differ ence of gas-turbine output end power required to drivo the compressor, and power needed to drive the compressor remains constant, efficiency falls off os load reduces. The unit design, as far as gas turbina and compressor are con cerned, U identical with the one which has been on test at the General Electrio plant, Schenectady, New York, for eome time, (see Powta, May 1948, pp 95, 98, and August, 1947, pp 68-70). Fig. 19 shows a cross section of the unit. Compressor. The axial-flow compres sor baa IS stages, for a compression ratio of about 6:1. The built-up rotor has separate wheels held concentric by fits near the center with through bolls holding the wheels together. This per mits complete freedom of selection ol materials for each stage. For example,, in the low-temperature section, the first six stages, a light aluminum alloy Is M ISM) Simple-Cyele got turbine unit develops 3500 kw ot 1400- let, 15-stoge compressor, 6 combustion chambers. 2-stoge lmF turbine-inlet temperature. Ceft to right: compressor in- pulse gos turbine, exhaust hood. Unit runs ot stoody 6700 rpm each split on the horizontal centerline, bolted together. This cpmtructjon . illows easy disassembly without sacri ficing the casing's strength to resist dis(.tortioa under transient conditions. As in the rotor, the low-temperature section . 0f the casing is aluminum and the high' temperature end is of steel. Fig. 13. . Combustors. Six combustors. aYe equally spaced around the body of the unit between turbine and, compressor. Fig. 22 shows the elements of one com bustor. Because of the high operating 'temperature it is reasonable to expect that the metallic inner liners will be the highest single maintenance item, . hence this design permits easy and inex pensive replacement of the .linen, if ; neeesjary. The Inner liners, about 35 in. long ind 10 in. dia, aro of stoinless material and outer casings of carbon |teel. . To mix the combustion products ade. quaicly and avoid possibilities of local .hot spots, the inner liner permits, air to enter through annular slita between the various sections as well as through '.dial holes and louvers.- The design excellent combustion over s wide f*age without sacrificing stability or 'ignition characteristics. J*U 'k testa in Schenectady are made on Bunker C and diesel oils, ru* installation will use natural gas " I* 1* Ml that no fundamental t * cm* wW be involved with gas as ""Nwd to oil, but to be sure, tests . now being conducted using com.'honors fire,| with natural gas. jbustion starts by mentis of spark ties i two of the six combus- i>the * cr0M ^re tubes Ignite v;0yuryM*n'n combustors. Aircraft . Te this arrangement for fimiVe,aVnd lt prove* reliflhle and Mon i, a in a gas-fired boiier.com- continuous process after the start. OWE*. Sspt.mber 1948 Torbina. The two-stage gas turbine steel while the inner pieces are of stain- achieves compactness and simplicity and lesa. These rings are bolted to the eas keeps the first-stage bucket temperature ing of low-carbon steel. The ring-obr as' low as feasible. With an inlet posite the second stage is welded to six temperature ol 1400 F. the first-stage struts inside the exhaust hood and sup buckets operate at 1160 F, not much ports the low-pressure turbine bearing. higher than the buckets In some high- Air Cooling. Air from an intermedi temperature steam turbines. ate stage of the compressor cools vari Tho turbine rotor consists of two . ous parts of tho turbine. It reaches the wheels, each integral with its own shaft. wheels by being bled Into the space be The two shafts bolted together form the tween the wheel and Its adjoining dia complete rotor, Fig. 15. Each wheel is phragm wall.Pipes also carry ex made up of two parts, tho rim of Mgh- tracted air through the nozzle partitions temperature stainless material'and the across the gas path to the packing., A center portion of low-alloy high-strength small fan on the turbine sbalt Sucks air steel suitable for 700 F, Fig. 11. Weld through axial holes in the casing ring ing the stainless rim to the wheel allows to cool the exhaust easing. Cooling using the proper materiel for each sec air olso passes through hollow tubes tion of the rotor. This composite con over the struts in the exhaust casing, struction has proven wholly successful' thus keeping them from coming In con In airplane jet units. In addition, the tact with the hot exhaust gas and mini forging and quality control problems, mizing, any distortion that might be are materially reduced. caused by uneven temperatures.' The The considerable step-up in height of exhaust hood Is of ordinary steel with buckets between the two stages keeps insulating -lagging. the leaving losses to a low value. Auxiliaries. Normal turbine acces The first-stage nozzles. Fig. 14, of the sories are supplied with the unit and In welded type, ore not split on the hori addition many protective, features aro zontal center line as is common in steam included. An accessory gear box turbines. The partitions are welded to mounted on tho front end of the-unit an outer ring and come through closely drives n tachometer, ovenpeed gover fitted holes in an inner ring. These two nor, lubrieaiing-oil pump and fuel regu rings welded to two additional rings lator. form the completed diaphragm. This The speed governor is electro-hydrau construction permits freo expansion lic, similar to tli6se used for some steam radially and maintains concentricity turbines and diesel engines. A perma without tho uso of pins or keys. nent-magnet clectric-tachomter-gener- The second-stage nozzles use the same ator gives the speed indication which is construction except that the partitions transmitted hydraulically to the fuel are welded to the inner ring alto and the regulator. The latter varies the gas assembly'is split on the horizontal centerline. The casing is made up of circular supply to the combustors in terms of. load requirements. In addition to the speed regulating equipment the gover rings opposite each wheel with L- nor has an over-riding control to limit shaped pieces bolted at tho inside diam the'exhoust temperature. eter to form the gas path and surface An auxiliary 400-cycle- motor-gener- opposite which the blade tips run, Fig. alor set provides power (or operating 19. The rings are of ordinary carbon the motor control. A conventional over- (523) 69