Patent GB-825849-A (GB)
Title: Improvements relating to elastic fluid turbines
IPC: F01D25/14
Filed: 1956-02-28
Abstract: 825,849. Turbines. GENERAL ELECTRIC CO. Feb. 28, 1956 [March 1, 1955], No. 6182/56. Class 110 (3). [Also in Group XXVIII] A high-pressure high temperature steam turbine comprises an inner shell assembly composed of high temperature-resisting material through which the driving fluid passes, surrounded by an inner casing having relatively thick walls, a shield assembly arranged between the inner shell assembly and inner casing having walls to define with the outer surface of the inner shell assembly at least one thermal insulating space and with the inner surfaces of the inner casing a coolant flow path supplied with a coolant at a pressure above that of the driving fluid at the first stage of the inner shell assembly and passages communicating the coolant pressure to the thermal insulating space. An extremely high pressure turbine comprises a generally spherical outer casing 1, an intermediate inner casing assembly 2 and an inner high-pressure shell assembly 3a-3d. A shield assembly 3 is provided between the casing 2 and the shell assembly 3a-3d. The inner and outer casings and shell assembly are divided into lower and upper halves secured together by a row of bolts at a horizontal flange joint. The sections of the inner shell assembly 3a- 3d are attached to one another by annular hook arrangements having clearances between the radially facing faces of the hooks so as to allow adjacent sections to expand and contract radially without imposing excessive stresses on each other. The inner casing 2 is supported in the outer casing 1 by a casing portion 2a having a radial key 2b which engages a slot 9b in an insert 9a attached to the casing 1, by a radial key 10b which engages a groove 10a and by horizontal longitudinal flanges on the casing 2 which engages recesses on the casing 1. More than one key and slot arrangement may be provided at both ends of the casing 2 but when the horizontal flanges are provided only one at each end is necessary. The inner casing 2 is located at its right-hand end by ribs 2h, 2i defining a key-way which receives a key member 1r formed on the outer casing and may expand longitudinally to the left. The inlet conduit assembly 4 comprises a heavy outer conduit member 12, an intermediate spacer member 13 and a high temperature inner conduit 14. The member 12 is provided with a heavy flange 15 which is secured to the casing 1 by bolts 17 which act on the flange through a heavy ring member 17b. The upper end of the conduit 12 is welded at 12a to the main steam supply conduit 18. An inner terminal portion 18a of the conduit 18 is welded to the upper end of the inner high temperature conduit 14. The spacer member 13 has on its inner surface a plurality of axially spaced concentric ribs 19 which form a plurality of insulating dead steam spaces 19a to reduce the heat transfer from the conduit 14 and thus reduce the temperature gradient through the thin wall of this conduit. A helical rib 20 on the outer surface of the member 13 forms a helical flow passage for cooling steam supplied by a passage 15a formed by a thin-walled tube 21b spaced from the flange 15 to avoid the formation of a local cold spot. Some of this cooling steam passes upwards through the helical path 20a and has access to the spaces 19a by passing round the upper end of the spacer 13. The lower end of the conduit 12 is received in the boss portion 2c of the inner casing 2 by a multiple ring slip-joint 2d which may be of the construction shown in Specification 718,534. The lower end of the pipe 14 is enlarged at 24 to receive the inlet portion 25 of a nozzle box 26. The nozzle box is surrounded by a box member 28 spaced from the casing 2 to form a coolant flow passage 30. A thin shield member 31 forms an outer insulating " dead space," 31a and an inner substantially stagnant space 31b. At the lower end of the spacer 13 the cooling fluid flows from the passage 20a into the annular space 33b from whence it flows by way of passages 36 annular chamber 34a and passages 37 into the chamber 30. The coolant leaving the chamber 30 is directed by an annular shield 28d over the sealing support 29 and the upstream face of first stage bucket wheel 7a to the holes 7m. The fluid then flows over the downstream face of the wheel 7a and then leaks through the shaft packing 8a over the upstream face of the second stage bucket wheel 7b where the process described above is repeated. The wheels 7a...7d are provided with annular projections 7n which form close radial clearances with adjacent circumferential portions of the diaphragms to minimize leakage into the main working fluid stream. Coolant from the annular chamber 34a passes through a port 34d to a chamber 38 and thence by a passage 39 into a longitudinal passage 40. An orifice plate 38a determines the quantity and pressure of the coolant in the passage 40. The passage 40 is located adjacent the horizontal flange joint. Coolant from the left-hand end of passage 40 passes through passage 40c to cooling passages in the shield assembly 3. The shield assembly comprises a support casing portion 41 having a plurality of circumferential ribs 41o ... 41/, each of which have grooves to receive a pair of parallel radiation shield members 42a, 42b, 43a, 43b...47a, 47b. These shields define arcuate stagnant insulating spaces 42c, 43c...47c. Other substantially stagnant spaces 42d, 43d...47d are formed between the plates 42b, 43b...47b and the diaphragm sections 3d...3a. The cooling fluid flows into the outer arcuate passage 42e in which it flows circumferentially through 90 degrees. At this point it passes through ports in the rib 41a to the adjacent arcuate passage 43e in which it flows back to the horizontal flange joint. At this point it flows through ports in the rib 41b to the next arcuate passage 44e. The last pair of radiation shields 48a, 48b have ports 49 which pass the coolant to the chamber 34c whence it enters the working fluid path. The size of the orifice plate 38a is such that the pressure on the outer surfaces of the diaphragm sections 3a ... 3d will force these sections radially inward and so maintain the hooked edge portions in engagement. The ports 49 ensure that the stagnant spaces 42d, 43d ... 48d are maintained at the pressure of the coolant. Specification 655,235 also is referred to.