US2613504A

US2613504A - Compound turbine power plant with intercept valve

Info

Publication number: US2613504A
Application number: US229992A
Authority: US
Inventors: Glenn B Warren
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1951-06-05
Filing date: 1951-06-05
Publication date: 1952-10-14
Anticipated expiration: 1969-10-14

Description

G. B. WARREN Oct. 14, 1952 ,COMPOUND TURBINE POWER PLANT WITH INTERCEPT VALVE Filed June 5, 1951 GIF/14679470@ Inventor:

mud he ..n er l Bft HA n@ @H G Patented Oct. 14, 1952 n UNITED STATE coMrouNn TUBBINE POWERPLAN'I* Wi'rii INTERCEPT VALVE f I A* I'(ilemi. Warren,v Schenectady, N'. Y., assigner to General Electric Company, a. corporation yci' New York Application .June s, 1951, 'sria1nu.*2`2'9, e92 l g rIhis invention-relates to 'elastic fluid turbines, particularly to vcompound steam turbine plants having in series a rst high pressure turbine Isection, areheater forincreasing the vtemperature of the motive fluid, a second high pressure turbine section, and one or 'more lower pressure turbines exhausting into a condenser.

In elastic fluid turbine plants of the type' described, the control problem is complicated by the fact that thevariousjturbine sections maybe connectedl by steam conduits of diameters `on the order Vof 18 inches `and from 50 to 300 feet in length, The flow of motive `iluid is primarily controlled by suitableregulatlng valve vmeansat the inlet to the first high pressure section. To prevent unsafe overspeed conditions, one or more emergency stop valves vare arranged to be actuated by suitable speed responsive devices, vas will be vwell understood by those skilled in the art. However, with such powerplants it has been found that an additional valve is required in` or# der to prevent overspeeding of thelower Ypressurev turbine sections bythe action of the very substantial amount of steam stored in the high pressure turbine casing-s, rehe'at boiler, and the long conduits connecting them. vThis vadditional valve is known as anintercept valve, and previous practice has 4been to locate it between `the 'reheater and the` next lower pressure'l turbine element to whichthe reheater supplies steam. Or dinarily, this intercept valve is located 'immediately adjacent `the entrance to such lower pressure turbine.

2 claims... (ci. cci-eroi i Asinitiai steam conditions `have risen to ythe neighborhood of 2400 pounds per squarefinch gage pressure and 1100i F. 'temperature and with high resuperheat temperatures, ,the previously used intercept valve `arrangements have been found inadequate to prevent overspeeding and costly to build because of the vspecial materials required by the hightemperatures to which the intercept valve is subjected. The present invention relates to-{amnovel `arrangement which greatly enhances the efficacy of the intercept valve in preventing such' overspeeding, and should reduce the cost of the valve, as compared with the previously used `practice of placing the intercept valve between turbineand'reheater.

Accordingly, the object'of 'this invention is to provide an improved compound turbine vplane characterized by 'a novelv location for 'the vintercept valve to produce lmore effective 'speed control` action` when theload'o'n the "plant is -suddently disconnectedand the' speed of the 'turbine-'- generator increases.`

Other objects and advantageswill become apparent from the following description taken in connection with the Aaccomrianying drawing in which the single iigure represents vdiagnrarrirnatically a compound turbine plane having anintercept valve arranged lin accordance with the invention. v

Generally stated, the invention is practiced by arranging the reheater in series between two high pressure turbine sections and locating the interuv cept valve at the inlet to the intermediate .prese sure turbine so that at' lea-stone high pressure turbine section is interposed in series between the reheater and the'intercept valve.- v

Referring now more particularly to the drawing, vthe invention is shown vapplied to a compound turbine plant including 'a two-section high pressure turbine indicated-generally at l, and, on a separate shaft, anA intermediate pressure turbine 2 anda low pressure turbine v(l, exhaust ing into a condenser ll.

Steam is generated in the boiler 5 and a superheater 6, which may lsupply motive iluid -at pressures as high as 2400flb. per sq.- in. and temperatures in the neighbor-hood of 1100 F. The flow of motive fluid to the inlet l -oi the first high pressure turbine element la is regulated by vsuitable' valve means in a steam control chest indicated generally at 8. Aswill be understood by those skilled in the art, the chest 8 may have a number of separate poppet' or other type valves, each controlling the viiow of steam to one of several' steam inlets similar 'to that designated l. The details of this governing valve mechanism are not material to an understand-ing of the present invention and are therefore not described in more detail.

'In order to prevent dangerous -overspeed conditio'ns,v an emergency stop valve 9 isl interposed between the superheater 6 and the govern-ing valve '8. It will of course be appreciated that this valve is intended to be lclosed automatically by a suitable over-'speed governor (not-shown). Such emergency overspeed governor arrangements are well-'known Vin the art, one `such being disclosed in United States Patent 2,524,552, issued October 3, 19'50 on lan application of L. B. Wales et al. and assigned 'to the saine assignee'as the present application. l

As will bereadily appreciated by those skilled in the turbine art,"high temperature high preslsure motive fluid is supplied from the superheater G'through conduit I l through the normally open' stop valve l9 to the controlvalve chest 8. From the valve chest, motive fluid iio'ws to the 3 high pressure inlet 1 of the ilrst turbine section la. The motive fluid iiows to the left through the iirst high pressure turbine section la, as indicated by the arrows, and by way of a conduit |2 to a reheater indicated generally at I3. The reheater raises the steam temperature from about 750 F. to approximately its initial value, in the neighborhood of 1100 F. From the reheater, the motive iluid passes through a conduit I4 containing a strainer |5 to the inlet I6 of the second high pressure turbine section Ib. From inlet I6, the motive fluid ows to the right as indicated by the arrows in the drawing through the second high pressure sectionJb, which of course has a plurality of bucket-wheels, only two of which are shown at I8 as being forged integral with the turbine rotor I9. The second high pressure section Ib may have in the neighborhood of four bucket-wheels, while the first high pressure section la may have about ten stages. After passing through bothhigh pressure sections Ia, Ib, the motive fluid passes through conduit 20, having at this point a temperature on the order of 925 F. and a pressure on the order .of 280 1b. per sq. in. f

As will be understood by those familiar with large capacity compound turbine plants, the conduit 20 may be of very substantial length, perhaps as much as 150 feet-,and of a diameter on the order of 18 inches. In'accordance with the invention, the intercept valveI 2| is located atthe inlet to the intermediate pressure turbine 2, as contrasted with the prior practice of providing such a valve at the inlet I6 to the high pressure turbine Ib. The intercept valve 2| has a suitable motor, indicated at 22, interconnected with the "pre-emergency governor"` 26 for causing the valve to close automatically when the pre-emergency governor is tripped by a preselected rise in speed of the generator 24. The governors and 26 are arranged to effectv simultaneous closing of valves 8 and 2| respectively.

From the intermediate pressure turbine 2, motive fluid flows through the cross-over pipe 23 tothe double-flow low pressure turbine 3. Spent steam from the low pressure turbine is exhausted into the condenser 4.

As will be seen from the drawing, the intermediate pressure turbine 2 and low pressure turbine 3 are coupled together to drive a suitable load, represented by an electric generator at 24. Similarly, the rotor |9 of the high pressure turbine I is arranged to drive a suitable generator 25.

The high pressure turbine I is described in more detail in my application, Serial No. 62,678, led November 30, 1948, abandoned and published in the Oiilcial Gazette of May 23, 1950.

It will now be apparent from theabove description of this plant that, if the intercept valve 2| were located at the inlet I6 to the high pressure section turbine lb, then, upon simultaneous closing of the intercept valve 2|, stop valve 9, and governing valve 8, the very substantial quantity of high pressure steam contained in the casing Ib and long conduit 20 would tend to cause overspeeding ci the intermediate pressure turbine 2. However, with the intercept valve 2| located as shown in the drawing, this motive fluid is trapped between the control valve 8 and the intercept valve 2|. This has a triple eiect in preventing overspeeding of the turbines.

In the first place, there is a smaller quantity of high pressure motive iiuid left free to expand through the lower pressure turbines 2, 3. That is, only the comparativelysmall amount of steamin rotor.

the intermediate pressure turbine 2 and the crossover pipe 23 will expand through the low pressure turbine 3. The resulting energy delivered to the low pressure turbine rotor will not be suicient to produce excessive overspeed. As soon as the intercept valve 2| closes, the iiow of motive iiuid through -the comparatively long interconnectingconduit and through the high pressure turbine is stopped, so that there is no further delivery of energy to the high pressure turbine In the second place, the number of turbine stages through which the trapped steam is ing effect on the high pressure turbine rotor I9.

This will be apparent from the fact that, as soon as the intercept valve 2| closes, the pressure throughout the conduit 20, low pressure turbine Ib, and high pressure turbine la becomes equalized at al pressure on the order of 500 to 600 lbs. per sq. in. This steam is sufficiently dense that rotation, of the high pressure bucket-wheels I1,

- I8, etc. in this uid produces a very substantial `braking eiect, which ,may be equivalent to a braking load on the order of 800 to 900 horsepower.

Thus', by reducing the volume of trapped steam, reducing the number of turbine stages through which this trappedsteam is free to expand when the intercept valve closes, and by reason of the above-described hydraulic braking action, the problem of preventing overspeed when the stop valve and .intercept valve are tripped is greatly simpIiiied.

` vAnother important advantage of this intercept valve' arrangement lies in the fact that the temperatures to which the valve is subjected are only on the order of 900 F., whereas it would have to withstand temperatures continuously on the orderof 1100 F. and pressures of 500 poundsA per square inch if located in accordance with prior art practice at the inlet to the high pressure section lb. This. is a matter of substantial importance, as it makes possible the use of. much lower cost and more readily available alloys, amatter of signicance in the light of the fact that the intercept'valve may be on the order of 40" to 50" in diameter and may weigh in the neighborhood of 15,000 pounds.

While the invention has been speciiically described herein as applied to a compound turbine having rotors arranged on two mechanically independent shafts, it will be appreciated by those skilled in the art that the invention may `also Ibeapplied .to plants in .which all the turbine'elements arelona common shaft. Such an arrangement maybe readily visualized by assuming that the generator 24 in the drawing is relocated to coincide with generator 25. In such a case,y the pre-emergencyoverspeed governor 26 .isrelocated near the speed governor |0, and. is arranged, as described above, to effect'closingV of the 'intercept'valve 2| in synchronism with the stop valve 9 and throttle valve 8.

It will be apparent to those skilled in the art that many other'changes might be made. For instance, .the intercept valve might conceivably be located at. the inlet to the low pressure turbine 3, so as to still further reduce the volume of trapped steam and the temperatures at which th'e'valvehas to operate. At the same time, this would mean that steam trapped in the intermediate pressure turbine 2 would produce the above-described hydraulic braking effect on the low pressure turbine rotor. This might be carried one step further by locating the intercept valve at the exit of the low pressure turbine 3; although this probably would not be feasible in most cases because of the tremendous size of the valve which would be required to handle the volume flow at that point. The entrance to the intermediate pressure turbine 2, as illustrated in the drawing, appears to be the best compromise between utilizing a valve of reasonable size, but yet attaining the advantages described above.

It is of course intended that the appended claims shall cover all such modifications and changes as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a turbine powerplant having a vapor generator supplying motive fluid to a first high turbine section, a reheater for increasing the temperature of motive fluid received from the rst high pressure section and delivering it to a second high pressure turbine section, and a comparatively long cross-over conduit supplying motive fluid from the second high pressure turbine section to the inlet of an intermediate pressure turbine, the combination of a high pressure turbine control valve located between the vapor generator and the high pressure turbine, an intercept valve located in said cross-over conduit adjacent the entrance to the intermediate pressure turbine, and governing means for simultaneously closing said control valve and intercept valve whereby, upon closing of said valves, the motive fluid trapped in the high pressure turbine and cross-over conduit are prevented from expanding through the intermediate pressure turbine and the high pressure uid remaining in the high pressure turbine exerts a braking effect on the high pressure turbine rotor.

2. In a compound turbine powerplant having a vapor generator supplying motive uid to a rst high pressure turbine section, a reheater for increasing the temperature of motive iiuid received from the rst high pressure section and delivering it to a second high pressure turbine section, and a comparatively long cross-over conduit supplying motive iiuid from the second high pressure section to the inlet of a lower pressure turbine section, the combination of a control valve located between the vapor generator and the first high pressure section, an intercept valve located in said cross-over conduit at the entrance to said lower pressure section, and speed responsive means for simule taneously closing said valves, whereby elastic fluid trapped in the high pressure turbine and cross-over conduit upstream from the intercept valve is prevented from expanding through the lower pressure turbine, and the high pressure uid remaining between said valves exerts a hydraulic braking effect on the high pressure turbine rotor.

GLENN B. W'ARREN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,759,452 Hartmann et al May 20, 1930 1,774,974 Hilgers et al. Sept. 2, 1930 1,920,781 Caughey Aug. 1, 1933 2,504,640 Bryant Apr. 18, 1950