Patent GB-1130767-A (GB)
Title: A method of controlling steam temperatures in steam turbine power plant cycles having one or more interstage reheats
Inventor: KNIZIA KLAUS
IPC: F01K7/24
Filed: 1966-12-09
Abstract: 1,130,767. Steam turbine power plant. L. & C. STEINMULLER G.m.b.H. Dec.9, 1966, No.55284/66. Headings F1Q and F1T. A method of controlling the temperatures of reheat steam in a steam turbine power plant comprises producing secondary steam in a secondary steam generator by abstracting superheat from bled steam and controllably introducing the secondary steam into the interstage reheaters to increase the volumetric steam flow therethrough. The plant includes Fig. 1, a main steam generator 1, high (H.P.) and low (L.P.) pressure main turbines 2, 21, secondary turbine 17, reheater 11, and secondary steam generators 4, 13. Super-heated steam tapped at 3 from the H.P. turbine 2 flows through the steam generator 4 and in giving up its super-heat, before being condensed in a feedwater heater 5, generates secondary steam from feedwater flowing through line 66 and taken from the feedwater pump 15. Secondary steam is also generated by steam tapped at 12 from the L.P. turbine 21 giving up heat to feedwater flowing through the generator 13. Both streams of secondary steam combine in line 61 to flow to the secondary turbine 17. Some secondary steam is tapped off from turbine 17 through line 19, under the control of valve 20, to mix in line 8 with the main steam flow from H.P. turbine 2 to the reheater 11, thus reducing the temperature of the mainsteam upstream of the reheater, increasing the volumetric flow therethrough and thereby reducing the temperature of the reheated steam entering the L.P. turbine 21. A small quantity of main steam flowing from H.P. turbine 2 towards L.P. turbine 21 is tapped adjacent a check valve 7 to flow to a feedwater heater 10. If the degree of reheat in the reheater 11 is too low, then the steam flow through the reheater can be reduced by tapping steam from the reheater inlet line 8 through a line 58 and a valve 59 to a low pressure stage of secondary turbine 17. The temperature of the reheated steam thus rises since the flow is reduced with an unchanged heat supply. The exhaust steam from turbine 17 flows through line 18 to the feedwater reservoir 14. In a modified plant, Fig.3, two reheaters 11, 35 and two secondary turbines 17, 45 are provided. In this case the secondary steam raised in secondary generators 13, 37 can be optionally introduced into the main steam generator 1 through a valve 38, or fed through a valve 39 to the first secondary turbine 17. In the latter case, the expanded steam from turbine 17 flows through check and control valves 41, 42 to mix at 43 in the first reheater 11 with the main steam flow to thus cool the reheated steam flowing to turbine 21. The steam from turbine 17 may alternatively flow through a valve 44 to join the secondary steam from secondary generators 4, 36 flowing to the additional secondary turbine 45. Steam can be tapped through valve 46 from turbine 45 to control the reheat in second reheater 35. In a further modification Fig. 2 (not shown), the plant has a single secondary turbine (23) supplied with secondary steam at different pressures from secondary generators (4, 24, 29), higher and lower pressure tappings (31, 33) from the turbine controlling the flow in higher and lower pressure reheaters (11,35), respectively.