US3546881A - Vapor turbine power plant - Google Patents

Description

Dec. 15, 1970 R. D. sowN VAPOR TURBINE POWER PLANT Filed July 29, 1968 Mm So 52; mm

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United States Patent 3,546,881 VAPOR TURBINE POWER PLANT Ralph D. Brown, Springfield, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed July 29, 1968, Ser. No. 748,463

Int. Cl. Flllk 7/16 U.S. CI. 60-73 10 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a turbine power plant utilizing pressurized condensible vapor, such as steam, as the motive fluid wherein during expansion some of the mot ve fluid forms objectionable condensate, so that the motive fluid becomes wet. An arrangement is provided for dividing the motive fluid into two streams after expansion in a turbine, namely a wet stream and a dry stream. The condensate is removed from the wet motive fluid after expansion in a first and higher pressure turbine by means splitting the exhaust into a first or outer outlet diverting a part of the motive fluid and condensate centrifuged by the turbine blades and a second or inner outlet for receiving the remaining and dryer portion of the motive fluid. The two outlets are connected to two inlets of a second and lower pressure turbine for further expansion. However, means is provided for removing the condensate from the motive fluid in the first outlet before delivery to the second turbine. In addition, the motive fluid in both outlets may be reheated to a superheated state before delivery to the second turbine, so that it may undergo additional expansion therein with the reduced possibility of forming additional condensate. The pressure of the motive fluid from the two outlets may be equalized by a suitable valve means responsive to the difference in pressure of the two fluid streams to insure that the flow of motive fluid delivered to the two inlets of the second turbine is substantially at the same pressure.

BACKGROUND OF THE INVENTION Steam turbine power plants are subject to blade erosion damage by condensate formed by the motive steam as it undergoes expansion and cooling to the saturated or wet steam state. Accordingly, many schemes have been proposed to intercept and remove the condensate from the wet stream during expansion, as for example between stages of expansion. Such schemes. while effective. involve losses in the same mass flow of steam remaining for motivating the turbine, since some steam is necessarily bled from the turbine with the condensate.

In view of the above, in plural unit turbine power plants including at least two units, wherein the steam undergoes partial expansion in the higher pressure turbine and is then diverted to the lower pressure turbine for further expansion, moisture separator and reheater devices have been employed between the outlet of the higher pressure turbine and the inlet of the lower pressure turbine to more effectively, collect and remove the moisture from the Wet steam and then to reheat the ensuing dryer steam to a superheated state before delivery to the second turbine. Such moisture separators and reheaters are usually combined in a single large vessel that, in operation, contains a huge mass of motive steam.

In the event of a loss in load on the turbine, the usual governing valves will trip in response to loss of load and/or overspeed, thereby interrupting the flow of high pressure steam to the higher pressure turbine. However, the large mass of steam entrapped in the separator/reheater vessel can continue to flow through the lower pres- 3,546,881 Patented Dec. 15, 1970 ice SUMMARY With the present invention, the condensate removal is effected by an annular structure associated with the outlet of the turbine and arranged to intercept a radially outer portion of the steam leaving the last stage of the turbine. This outer portion, due to the centrifuging action of the turbine blades is heavily laden with condensate or moisture, while the inner portion of steam is substantially free of condensate. The two portions are delivered from the turbine by separate conduits.

Since the inner portion is substantially free of condensate, it may be delivered to a second and lower pressure turbine without passage through a moisture separation device, with its attendant overspeed capabilities (as previously described). The outer portion is delivered to a moisture separator vessel before delivery in a dryer state to the second turbine. However, since the moisture separator is only required to accommodate a part of the steam exhausted from the first turbine it is considerably smaller in capacity than heretofore required and therefore its capability to overspeed the turbine in case of loss of load is considerably reduced.

The two portions of steam are preferably reheated to a superheated state before delivery to the second turbine to minimize the possibility of further condensate formation in the second turbine. One of the reheaters is preferably combined with the moisture separator, while the other reheater is contained in an individual vessel of considerably smaller volumetric capacity. Hence the capaccity of the two vessels is considerably smaller than that heretofore required, as for example with the Beldecos scheme.

The pressure of the two steam flows to the second turblue is preferably balanced, such balancing being effected by a pressure responsive valve disposed to regulate one of the flows in response to the difference in pressure between the two flows.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a generally diagrammatic view of a con- FIG. 2 is a chart indicatin vapor flow along the turb their centrifuging effect.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, in FIG. 1 there is shown a steam turbine power plant 10 comprising a first and higher pressure axial flow turbine 11 and a second and lower pressure turbine 12 having their rotor shafts 13 and 14 connected in tandem and jointly driving a load, such as, for example, an electric generator (not shown).

The HP. turbine 11 is provided with an outer casing structure 15 and an inner ring structure 16 and 17 supported within the rotor casing 15 and supporting a plurality of rows of stationary vanes or blades 19. There is further provided a rotor structure 20 attached to the rotor shaft 13 and carrying a plurality of rows of rotatable blades 21 cooperatively associated with the vanes 19. As

g the moisture content of the me rotor blades occasioned by 'well known in the art, the rotor blades 21 are of airfoil shape and extend radially outwardly, while the vanes 19 are also of airfoil shape but extend radially inwardly across an annular motive steam passageway 23 defined jointly by the outer periphery of the rotor 20 and the inner surfaces of the blade rings 16 and 17.

Each row of vanes 19 precedes its associated row of rotor blades 21 and jointly therewith form a plurality of expansion stages for the motive steam including a first expansion stage 24 and a last expansion stage 25. Thus the turbine 11 may be termed a multistage, axial-flow turbine.

High pressure, high temperature steam from any suitable source is admitted to the turbine 11, through a suitable steam inlet 26 communicating with the first expansion stage 24.

The outer casing 15 further includes an end wall portion 28 defining an exhaust space 29 of toroidal, or at least annular, shape communicating with the last expansion stage and having an exhaust outlet 30. Within the exhaust space 29, there is provided a generally toroidal member 31 cooperating with the blade ring 17 to form a toroidal space 32 and having a marginal portion 33 or cusp extending into the motive steam passage 23 immediately downstream of the rotor blades 21 in the blades 21 in the last expansion stage 25. The cusp 33 is disposed in a substantially median position in the passageway and splits the passageway into an annular innermost passageway 35 and an annular outermost passage 36. The inner passage 35 is in direct communication with the outlet 29 via the exhaust space '25, while the outer passage 36 is in direct communication with a second outlet 38 via the space 32.

The LP. turbine 12 may be of any suitable type and is thus shown in elevational outline. In the example, the LP. turbine is of the central admission double opposedflow type having two centrally disposed steam inlets 40, 41 and a pair of oppositely disposed exhaust outlets 42 and 43. Typically, in operation, steam admitted to this turbine through the two inlets and 44 flows in opposite axial directions through two sets of bladed expansion stages (not shown) to motivate the rotor shaft, and then is exhausted through the outlets 42 and 43 to a region of low pressure for example, a steam condenser (not shown).

The outlet 30 of the HP. turbine 11 is connected to the inlet 40 of the LP. turbine by a conduit 46, while the outlet 38 is connected to the inlet 41 by a conduit 47. A reheater 48 including a shell structure 49 and a tubular heating element 50 is interposed in the conduit 46. Superheated steam from any suitable source (not shown) is directed through the heating element to reheat the steam as it passes therepast from the HP. turbine to the LP. turbine.

A combined moisture separator and reheater 52 is interposed in the conduit 47. The moisture separator/ reheater 52 includes a shell structure 53 divided into upper and lower chambers '54 and 55 by a demister element 56 and has a tubular heating element 57 in the upper chamber. superheated steam from any suitable source (not shown) is directed through the heating element 57. Combined moisture separator/reheaters of this type are well known in the art and are employed to remove the condensate from wet steam as it passes through the demister 56 and then to superheat the thus dryed steam to revaporize any residual moisture as it flows past the heating element 57. Condensate removed from the steam is removed from the lower chamber through a suitable outlet 58.

The steam flow through the conduits 46 and 47 may be balanced or equalized by a pressure responsive valve mechanism 60 disposed in the conduit 46 and movable in response to the differential in steam pressure in the two conduits, as determined by suitable pressure probes 61 and 62 disposed in the conduits 46 and 47, respectively. The ressure signals from the two pro es are delivered to a differential pressure responsive device 63 by suitable lines 64 and 65, and the resulting diiferential pressure is transmitted to the valve mechanism 60 by a suitable line 66.

In operation, motive steam admitted to the HP. turbine 11 through the inlet 26 is directed through the expansion stages 24 to 25 of the turbine and during such expansion condensate is formed. The rotating rotor blades 21 centri fuge the liquid particles, i.e., they impart centrifugal energy to the condensate, causting the condensate to fly radially outwardly towards the tips of the rotor blades 21. Hence, the steam flow leaving the last stage 25 is heavily concentrated with moisture along the radially outer half of the rotor blades 21 and in a substantially dryer state along the radially inner half of the rotor blades 21.

The steam flow leaving the last rotating blade row is intercepted by the cusp 33 and split into two portions or streams, the moisture laden stream being directed into the toroidal chamber or space 32 and thence to the exhaust outlet 38, and the dryer steam being directed to the exhaust outlet 30.

The dryer steam flows from the exhaust outlet to the reheater 48 through the conduit 46 and is reheated to a superheated state before admission to the LP. turbine 12 through the inlet 40.

The moisture laden steam, on the other hand, flows through the conduit 47 to the moisture separator/reheater '52, wherein it is stripped of its condensate and reheated to a superheated state before admission to the LP. turbine through the inlet 41.

Accordingly, the quality of steam admitted to the LP. turbine, via the inlets 40 and 41 is substantially identical and is effective to motivate the turbine in an efiicient manner.

Also, since the pressure of the motive steam in the two conduits 46 and 47 is regulated by the pressure responsive valve mechanism- 60, the mass flow through the two inlets 40 and 41 is substantially equal, i.e., matched for optimum performance in the turbine.

Since the moisture separator/reheater 52 is required only to accommodate half of the steam flow from the HP. turbine 11, it is of considerably smaller volumetric capacity then heretofore required, with attendant reduction in cost of fabrication and, more importantly, less effective to overspeed the turbine 12 in case of loss of load on the turbines.

The radial position of the cusp 33 in the annular steam passage 23 is determined by analysis of the moisture content of the steam leaving the last rotating blade row 21. FIG. 2 is a chart in which the ordinate represents the Blade Radius, i.e., the radial length of the blades 21 in the last stage from base to tip, and the abscissa represents moisture content of the steam flow leaving the blades. It will be noted that the moisture content of the motive steam is quite low at the base of the blades and increases at a very slight rate to the median portion M of the blades to a value X. Above the median portion M, the moisture content increases at a very sharp rate towards the tip of the blades and reaches a maximum value Y at a point T adjacent the tip of the blades.

In view of the above, the cusp 33 is preferably positioned adjacent the median portion M of the rotor blades 21, thereby splitting the exhaust steam flow into substantially two equal portions-the dryer portion leaving the blades in the region extending from the base to the median portion M, and the heavily moisture concentrated portion leaving the blades in the region extending from the median portion M to the tip of the blades.

The residual moisture contained in the dryer steam portion is readily revaporized into superheated steam by the reheater 48.

It will now be seen that the invention provides a highly improved arrangement for dealing with the moisture forming problem in steam turbines and other condensible vapor turbines by first splitting the moisture laden steam.

leaving a first turbine into a relatively moisture free stream and a heavily moisture laden stream, and then removing the moisture from the moisture laden stream.

It will also now be seen that with the invention, the moisture separator is only required to handle about half of the exhaust steam from the first turbine and therefore provides many advantages as previously described.

Although only one embodiment of the invention has been shown, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof.

I claim:

1. In a power plant,

an axial flow turbine utilizing pressurized hot condensible vapor as the motive fluid, comprising casing structure defining a vapor inlet, a vapor outlet,

and an exhaust space,

a plurality of vapor expansion stages including a first expansion stage communicating with said inlet and a last stage communicating with said outlet by way of said exhaust space, whereby during flow of the motive fluid through said stages, with attendant expansion, condensate is formed,

each of said stages including an annular row of rotat able blades effective to centrifugally direct the condensate thus formed in radially outwardly direction,

said casing structure being formed in a manner to impart an annular shape to said exhaust space,

an annular deflector structure disposed in said exhaust space, said deflector being effective to intercept and prevent at least an outer portion of the vapor and the radially directed condensate from the rotatable blades in the last stage from flowing to said outlet, and permitting the remaining inner portion to flow through said outlet with a substantially reduced condensate content,

means including a second outlet for withdrawing the thus intercepted vapor and condensate portion from said casing structure,

a second turbine operable by pressurized condensible vapor at a lower pressure than the first ment ioned turbine,

said second turbine having vapor inlet means,

conduit means connecting the first outlet of the first turbine to said vapor inlet means of said second turbine and connecting said second outlet to said second turbine and effective to conduct the remaining vapor portion to said second turbine for further expansion, and

means for reheating the remaining inner vapor portion to a substantially dry stage before admission to the second turbine.

2. The structure recited in claim 1, and further including means for equalizing the pressure of the vapor in the outer and the remaining inner portions before delivery to the second turbine.

3. The structure recited in claim 1, and further including means responsive to the vapor pressure in the outer and the remaining inner portions, and

means including a valve operable in response to said pressure responsive means for equalizing the pressure of the vapor in the outer and the remaining inner portions before delivery to the two respective inlets of the second turbine.

4. The structure recited in claim 1, and further including means for removing condensate from the vapor in the outer portion only before admission of the vapor to the second turbine.

5. In a power plant,

an axial flow turbine utilizing pressurized hot condensible vapor as the motive fluid, comprising casing structure defining a vapor inlet, a vapor outlet,

and an exhaust space,

a plurality of vapor expansion stages including a first expansion stage communicating with said inlet and a last stage communicating with said outlet by way of said exhaust space, whereby during flow of the motive fluid through said stages, with attendant eX pansion, condensate is formed,

each of said stages including an innular row of rotatable blades eflective to centrifugally direct the condensate thus formed in radially outwardly direction,

said casing structure being formed in a manner to impart an annular shape to said exhaust space,

an annular deflector structure disposed in said exhaust space, said deflector being effective to intercept and prevent at least an outer portion of the vapor and the radially directed condensate from the rotatable blades in the last stage from flowing to said outlet, and permitting the remaining inner portion to flow through said outlet with a substantially reduced condensate content,

means including a second outlet for withdrawing the thus intercepted vapor and condensate portion from said casing structure,

a second turbine operable by pressurized condensible vapor at a lower pressure than the first mentioned turbine,

said second turbine having vapor inlet means,

conduit means connecting the first outlet of the first turbine to said vapor inlet means of said second turbine and connecting said second outlet to said second turbine and effective to conduct the remaining vapor portion to said second turbine for further expansion,

said vapor inlet means including a first and a second vapor inlet,

conduit means providing a fluid communication between the Withdrawing means and said second inlet, and

means for removing the major portion of the condensate from the vapor in the outer portion before admission of the vapor to said second turbine.

6. The structure recited in claim 5, and further including means for reheating the outer portion after removal of the condensate.

7. In a power plant,

a first turbine utilizing pressurized hot condensible vapor as the motive fluid,

said first turbine having a casing structure defining a vapor inlet and a first vapor outlet,

a plurality of vapor expansion stages, whereby during flow of the motive fluid through said stages, with attendant expansion, condensate is formed,

means for directing the condensate thus formed in radially outwardly direction,

means for intercepting at least a first portion of the vapor and the radially directed condensate after expansion in said stages to a lower pressure,

means including a second outlet for removing said first portion from said first turbine,

means for directing the remaining portion of said vapor through said first outlet after expansion in all of said stages to said lower pressure,

a second turbine utilizing hot condensible vapor at said lower pressure as the motive fluid,

said second turbine having at least two vapor inlets,

one of said vapor inlets being in fluid receiving communication with said first vapor outlet and the other of said vapor inlets being in fluid receiving communication with said second vapor outlet, and

means for removing the condensate from the vapor in said first portion before delivery of the vapor to said second turbine.

8. The structure recited in claim 7, and further including means for equalizing the pressure of the vapor in the first and remaining portions before delivery to the second turbine. 9. The structure recited in claim 7, and further including means for reheating the vapor in the first and second portions before delivery to the second turbine. 10. The structure recited in claim 8, wherein the equalizing means includes means responsive to the vapor pressure in the first and the remaining portions; and means including a valve for controlling the vapor floW in response to said pressure responsive means.

References Cited UNITED STATES PATENTS 1,834,452 12/1931 Frey et al 25376 3,149,470 9/1964 Herzog 60-64 3,289,408 12/1966 Silvestri 25376X 3,360,939 1/1968 Beldecos M 60-73 3,400,911 9/1968 Kojima 6064X FOREIGN PATENTS 39,729 12/1936 Netherlands 25376 CARROLL B. DORITY, JR., Primary Examiner US. Cl. X.R. 4l5l2l, 168

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