GB1135766A - Improvements in or relating to steam turbines - Google Patents

Abstract

1,135,766. Steam turbines. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. March 28, 1966 [April 2, 1965 (3)], Nos. 14190/65, 14194/65 and 14195/65. Heading F1T. A steam turbine cylinder comprises a number of successive expansion stages through which the driving steam flows, an outer casing protected internally from contact with hot steam from the driving steam flow up to an intermediate stage, and means situated after that stage for collecting steam from the driving steam flow and circulating the collected steam to the inside of the outer casing for cooling the casing, this means being arranged to collect the steam in such manner as to convert at least part of the velocity head of the collected driving steam into a pressure head as a result of impact, which pressure head prevents undesired leakage of hot steam to the casing via a leakage path from the driving steam flow at or close to the intermediate stage. The casing 5, Fig.2A, of an H.P. steam turbine cylinder is formed as a one-piece casting or forging having an integral inlet branch 47 with a wall 47A sufficiently thick to withstand the reduced working pressure obtaining immediately downstream of the second stage. Steam at the full inlet pressure and temperature passes through a much thinner inner wall 47B of the branch 47 to an annular nozzle box 34. The inner wall 47B is clamped at its outer end to the outer wall 47A and a sleeve 93 is secured to its inner end. To allow for thermal expansion, the outer end of the sleeve 93 slidably engages the inner wall 47B, and the inner ends of the inner wall and sleeve slidably engage packing rings 95, 97 carried by the nozzle box 34. Steam at the reduced pressure and temperature obtaining immediately downstream of the second-stage rotor blading 57 is collected in a slot 125 in each of a series of spokes 123, the impact converting some of the velocity head into pressure head to increase the pressure of the collected steam. The collected steam passes via radial passages 127 to anannular chamber 129 and thence around the nozzle box 34 to the annular space 99 between the outer wall 47A and the sleeve 93, whence it flows through holes 101 at about the mid-length of the sleeve into the annular space 103 between the sleeve and the inner wall 47B. From the inner end of the space 103, the steam flows via an annular chamber 105 and ducts (107, 109), Fig. 2B (not shown), to a point of lower pressure. The flow of steam through the annular spaces 99, 103 cools the outer wall 47A so that its inner end is held at about the temperature of the casing 5. The transition between this temperature and the inlet temperature to which the outer end of the outer wall 47A is subjected occurs over a cylindrical part of the outer wall of uniform cross-section so that no undue thermal stress occurs.