US2579027A

US2579027A - Overheat protection for steam reheaters

Info

Publication number: US2579027A
Application number: US87484A
Authority: US
Inventors: Paul R Walter; John W Thompson
Original assignee: Combustion Engineering Superheater Inc
Current assignee: Combustion Engineering Inc
Priority date: 1949-04-14
Filing date: 1949-04-14
Publication date: 1951-12-18
Anticipated expiration: 1968-12-18

Description

Dec. 18, 1 P. R. WALTER ETAL OVERHEAT PROTECTION FOR STEAM REHEATERS Filed April 14, 1949 2 SI'IEETSSI IEET l HEQTEB REA/77756 we #50 TEE 0072157 #54062 MRHEHTE'E INVENTORS Paul R. Walter BY John W. Thompson ATTORNEY Dec. 18, 1951 P. R. WALTER ETAL OVERHEAT PROTECTION FOR STEAM REHEATERS Filed April 14, 1949 2 SHEETSQ-SHEET 2 3 Fig. 2.

48 Fig.

Fig. 4.

.sx i l Stop Inlet 47b 47 r 4 \47 0 Hi Fig. 5.

INVENTORS Paul R. Walter BY John Thompson 04w ATTORNEY tures.

Patented Dec. 18, 1951 OVERHEAT PROTECTION FOR STEAM REHEATERS Paul R. Walter, East Orange, N. J., and John W.

Thompson, Weymouth Heights, Mass., assignors to Combustion Engineering-Superheater, Inc., a corporation of Delaware Application April 14, 1949, Serial No. 87,484

20 Claims.

This invention relates to means for protecting superheaters from damage by overheating and in particular for so protecting a superheater used for reheating the steam flowing between high and low pressure turbine elements.

The usual power generating station to which the invention may be applied comprises a steam generator which delivers steam to a multi-stage steam turbine. A superheater heats the steam flowing from the generator to the high pressure end of the turbine and a reheat superheater reheats the steam flowing from a high to a lower pressure stage of the turbine, or from a high pressure turbine to a low pressure turbine. Both the superheater and the reheater are usually associated with the steam generator and receive heat from the products of combustion of the fuel passing through the generator.

The steam turbines are provided with speed responsive governors which, when the speed of the turbine exceeds a predetermined amount, will cut off the supply of steam to the turbine. With the steam flow stopped in both the superheater and reheat superheater, the flow of the hot products of combustion over the superheaters will continue pending a stoppage of the fuel supply to the generator. Under these conditions both the superheater and the reheater may become destructively overheated unless means are provided to keep their metal temperatures approximately at their normal operating tempera- For this purpose safety valves have been placed in the superheater outlet which will be opened by the increased steam pressure resulting from the steam flow stoppage and their opening will reestablish a suflicient flow through the superheater to keep its metal temperature at a safe limit. The reheater, however, has received its steam only from the high pressure turbine stage and when the steam was cut off to the turbine, the steam flow through the reheater ceased.

Heretofore when the reheated steam temperatures were relatively low, the reheater was placed in a zone of the boiler furnace where the temperatures of the products of combustion were relatively low and there was only moderate danger of overheating the metal by the products of combustion in the event of steam flow stoppage. But in late power generating stations the reheated steam temperatures may be as much as about 1000-1050 deg. F. and the reheaters are placed in hot temperature gas zones so that in such present-day installations the danger of overheating the metal of the reheater does prevail to a degree clearly calling for protective measures. a

It is an object of this invention to provide novel means in a steam power station for protecting a reheat superheater from destructive overheating by maintaining a steam flow therethrough when the steam flow thereto from the steam turbine is interrupted.

Other objects and advantages will become apparent from the following description of an illustrative embodiment of the invention when taken in conjunction with the accompanying drawings wherein:

Figure l is a diagrammatic representation of a steam power generating station embodying one form of the invention, showing conduits and valves and controls therefor to direct steam flow through the reheat superheater upon interruption of steam flow through the high pressure steam turbine; and

Figures 2, 3, 4 and 5 are diagrams showing modifications of the controls utilized by the Figure 1 system.

The steam power station here represented comprises a steam generator generally designated as G having a furnace F and a steam and Water separating drum D. This generator G has located in the setting thereof a superheater in two sections Si and S2 and a reheater R, these elements 81-82 and R illustratively being organized with other parts of the generator as disclosed by copending application Serial No. 56,381 filed in name of John Van Brunt on October 25, 1948; but as the description hereof proceeds it will become apparent that power stations utilizing steam generators of other forms also may be benefited by the improvements of our invention.

In the arrangement shown, steam from the generator G flows through superheater SI, S2 thence serially through the stages of a high pressure steam turbine TI and thence through reheat superheater R and the stages of a low pressure steam turbine T2. C represents a condenser for the steam leaving T2. The condensate leaving condenser C is pumped by the usual means (not shown) back into the steam generator G. i

The products of combustion of the. fuel burned within the furnace F rise upwardly through the steam generator G in two parallel passes l and 2. An intermediate dampered pass 3 may be provided for by-passing some of the products of combustion from the furnace F around the other passes I and 2. Partitions 4 and 5 separate the bypass 3 from the passes l and 2 and the passes are bounded on their opposite sides by the front and rear walls 6 and l and the side walls 8 (of which there is but one shown, the other being opposite thereto) of the steam generator G which are substantial continuations of the furnace Walls below.

Adjacent the top of the generator G is a hori zontally inclined roof 9 and spaced therefrom a horizontally inclined partition 10 which connects to the top of bypass 3. The roof 9 and the partition is together with the side walls form passages which serve to conduct the gases from passes l and 2 separately to the generator outlet H. Dampers I2 and I3 are located adjacent the rear end of partition l8 and serve to control the proportionate flow of the products of conibustion through the passes l and 2. I

As the aforesaid Van Brunt application Serial No. 56,381 explains, the walls of the furnace F are preferably lined with steam generating tubes 14, the tubes of the front and rear walls inclining inwardly and upwardly toward the center of the furnace in open relation forming a cooling screen for the combustion products passing therethrough, thence pass upwardly adjacent the sides of partitions 4 and 5 and thence below partition IE to the steam and water drum D. By this arrang'ement the furnace wall tubes may serve as supports for partitions 4, 5 and Ill.

As here utilized the steam superheater of generator G is arranged in two sections Si and S2 and is located in major portion within pass I.

Saturated steam leaving drum D passes through pipe [5 into superheater inlet header t6 and thence flows through the superheater in the direction'of the arrows to superheater outlet header IT. The first section St through which the steam flows comprises a multiplicity of sinuous coils arranged in parallel transversely of the gas flows through pass I. The outlets of said coils terminate ma desuperhe'ater' [8 which serves as the inlet header for superheater section 82 Superheater S2 comprises a'multiplicity of sinuous coils arranged in parallel transversely of the For supplying generated steam to the power station turbines, the outlet header ll of superheater Si and S2 is connected by pipe 21 to the inlet of high pressure turbine TI via

valves

22 and 23 later to bedescribe'd. The elxhaust fr'om turbine TI is connected by pipe 24 through check" valve 25 and desuperheater 26 to the inlet header 19 of reheater R. The outlet header 22 of reheater R'is connected by

pipes

27 and 28 to the inlet of low pressure turbine T2 through valve 29. The exhaustof turbine T2 is connected di- 7 'rectly into condenser C. A safety valve '30 is connected to outlet header ll of superheater S|-S2 and a safety valve 3! is connected into a continuation of pipe 2? beyond the connecting pipe 28 with respect to steam flow to turbine T2. Said pipe extension is provided beyond the safety valve 3| with a stop valve 32.'

In the illustrative arrangement here shown, the steam pipe I5 leading to the inlet header [6 of 'superheater Sl-SZ from the steam generator drum D is continued as pipe 33 through a shut on valve 34 thence through an automatically controlled valve 35 and into the pipe 24 leading from the exhaust or high pressure turbine Tl through desuperheater 26 to the inlet header IQ of reheater R. If desired a valved bypass connection 36 may be provided around the'valve 35 newly added in accordance with this inventionto permit passage (at proper times) of auxiliary cooling steam into the generators reheater R.- a

' maintained.

} Forming part of auxiliary steam supply facilities 'for the reheater R is a pipe connection 31 provided in pipe 33beyond valve 34 with respect to steam flow, pipe 31 being connected to a pipe 38 which is supplied with valves 33 and d0 either side of the connection. The pipe 38 connects the desuperheater I8 intermediate sections Si and S2 of the superheater to valve 39. A pipe at then connects to an associated valve so to supply steam from a niain in the boiler house at a lower pressure than that delivered by the steam generator G.

Looking now at turbines Tl and T2, steam deliver-ed from the steam generator G via superheater SI, S2 to the high pressure turbine TI passes through earlier mentioned conduit 21' and

valves

22 and 23. Valve 22 represents an automatic stop valve and is arranged to automatically close when the turbine exceeds a' predetermined maximum speed. Valve 23 represents the turbine governing or inlet valve or valves which controls the steam suppliedto the turbine and may be arranged to automatically close when the turbine exceeds a predetermined speed (usually lower than that at which valve 22 closes). The speedresponsive governor and associated means for automatically closing

valves

22 and 23 to stop the "flow of steam to the turbine 'Tl' may be conventional and henc'e'are not here shown in tail.

In one well known arrangement of such means full dethe named

valves

22 and 23 may be held open remain open. Arms 4'4 and M are adjustably attached to extend from stems 43 and 43' of valves'22 and 23 and move therewith. The extended ends of arms are provided with contacts andy45' which during normal operation of theturbine, are spaced from stationary con- But when the valve stem for "either

valve

22 or 23 drops to close the valve, the contacts 45 and ltla'ssociated therewith'engage and close a circuit here illustratively shown as facts '46 and 4B.

being'energized from conductors M and it! between which an electrical control potential is The earlier mentioned control tween a oo'oling stearn' source and reheater inlet [5) is provided with control means actuated by a solenoid '59, which when energized over either of the represented turbine valve switches t5-46 and ilt- 2$ acts to lift the stem of valve35 to open it and when deenergized' permits the valve to close again (under the action ofany suitable means such as a spring not shown).

Solenoid ts further may be connected with conductors t? and as so as to be energized by the potential appearing 'therebetween upon closure of a manually -operable switchfil, by means of which valve 35 may be manually opened if. de-

sired, as well as upon engag'einent of the contacts 4546 associated with either or the g'eiierator then to'maintain a steam flow through the reheater R.

"A so-called interceptvalve 29in pipe 28 ahead valve as (beof low pressure turbine T2, with respect to steam flow, is arranged to automatically close when turbine T2 exceeds a predetermined speed thereby throttling or stopping the flow of steam into that turbine. As such arrangement is conventional only symbolic representation thereof is here made.

The operation of our improved protecting facilities for reheater R will now be explained. Upon substantial closure of intercept valve 29, safety valve 3! opens and steam flowing through the reheater R and pipe 21 will then discharge through the safety valve to the atmosphere thereby protecting the reheater R against overheating by reason of stoppage (at valve 29) of steam flow into the low pressure turbine T2.

When either valves 22 or 23 (or both) close due to excess speed of high pressure turbine Tl, so as to cause

contacts

45, 43 to close, the solenoid 49 becomes energized (from conductors 4'|4|3) and thereby causes the valve 35 to open. With valve 34 open and valves 39 and 4D closed, steam (from generator drum D) will then flow from pipe 33 through the thus opened valve 35, into pipe 24, through desuperheater 26 and reheater R, pipe 21 and out through safety valve 3| into the atmosphere. Under these conditions check valve prevents steam from flowing back into the high pressure turbine TI.

The metal of reheater R will thereby be kept at a safe temperature due to the cooling by the steam flowing therethrough. In the absence of the automatically opening valve 35, the reheater R would be cut off from all steam flow from the high pressure turbine Tl when the

valves

22, 23

closed and. could be destructively overheated. Overheating would be due to its location in a relatively hot zone of combustion products from furnace F, which location is necessary to achieve the high steam temperatures now required.

Moreover, upon the aforesaid closure of

valves

22 or 23, the superheater SI-S2 is protected by the safety valve 30 "which will thereupon open and permit a flow of cooling steam through the superheater.

If the steam for supplying the reheater R through valve is taken directly from the drum D, its pressure may be too high for reheater R. To suitably reduce the pressure in the reheater, valve 35 and/or pipe 33 for conducting the steam to it from pipe l5, may be made small so as to incur a suitable pressure drop therethrough; or an orifice resistance may be inserted in pipe 33 ahead of valve 35 with respect to steam flow. When steam is supplied to pipe 33 either from desuperheater I8 via pipe 38 or from a boiler room pipe main via pipe 4| at lower than boiler pressure, the above mentioned resistance may be unnecessary. With such steam supply, valve 34 is closed. Check

valves

62, 65 may be provided to prevent high pressure steam from drum D entering desuperheater l8 and boiler room header 4| and to prevent steam from desuperheater |8 entering boiler room header 4|.

Obviously means other than the electrical solenoid 49 here disclosed may be employed to open valve 35 when

valves

22, 23 close; one example of such other means including employment of the fluid means mentioned above for closing

valves

22, 23, to simultaneously act on a diaphragm or piston within a cylinder (not shown) mounted on stem 53 of valve 35 to open said valve.

Should valve 32 be selected of a type similar to valve 35, similar means may be employed to simultaneously and automatically open valve 32.

than the high pressure turbine T2.

For example, control meansactuated by a solenoid 49' may be arranged to operate valve 32 and be connected (as through a manually closable switch 63) into the circuit Of

conductors

41, 48 with the solenoid 49 arranged in parallel with the solenoid 49. as shown. With such an arrangement (andwhen switch 63 is closed) the safety valve 3| need not be depended upon to open since venting of the steam leaving reheater outlet 2|! via pipe 2! can then be efiected through valve 32. i In some installations it may be desirable to delay the opening of valve 35 so as to establish a predetermined period of time before the reheater R receives steam from a source other To accomplish such delayed opening of valve 35, Figure 2 shows a delay-introducing switch 52 provided in the circuit, to thesolenoid 49 of valve 35. In the illustrative form represented switch 52 is normally held open by a compression spring 52; but at proper times is delayedly actuated to the closed position by a solenoid 53 through an armature 54, which armature extends from the switch contact bar through the solenoid to a piston in a cylinder 55. The cylinder head above the piston is provided with a needle valve 56 to therewith control the rate of influx of a fluid into the cylinder and thereby the rate of downward movement of the piston and the time delay in closing switch 52.

As above indicated, switch 52 is normally open. Upon closure of contacts 45-46' of the turbines inlet valve 23 in Figure 1 (designated as IV in Figure 2), current flows from control line 41 through conductor 41b, 41c, solenoid 53, and conductor 48a to control line 48. The solenoid being energized acts to close switch 52 but is delayed in doing so for a predetermined time by the slow moving piston in cylinder 55. Upon such delayed closure of switch 52 the control current flows from conductor 41b through conductors 41d and 416, solenoid 49 and conductor 48b to line 48. Reheater steam admission valve 35 is now opened by the thus energized solenoid, to assure continued passage of cooling steam through the steam generators reheater R.

But, closure of

contacts

45, 46 of the turbines stop valve 22 (designated as SV in Figure 2) acts upon protecting valve 35 without any such delay. Such closure establishes a current flow from line 41 through conductors 4111, 41c, solenoid 49 and conductor 48b to line 48, and the valve 35 thus opens instantly in response to closure of the turbines stop valve IV.

Other generally similar control arrangements are shown in Figures 3, 4 and 5 in each of which diagrams the circuits, switches and solenoids that are the same as those of Figure 2 carry the same designations as appear in Figure 2. Such common parts include the contacts connected to actuate delayed-action switch 52 and valveopening solenoid 49, and the operation of these elements is the same as that described above for the operation of the same elements in Figure 2.

Each of Figures 3, 4 and 5 further includes provision for opening reheater venting valve 32 simultaneous with the opening of reheater steam admission valve 35. In each of said diagrams conductors 41 and 480 are provided to carry current from conductor 41b through solenoid 49' to line 48. Upon closure of contacts 45,. 46 of the turbines inlet valve IV (valve 23 in Figure 1). reheater venting valve 32 will be instantly opened. by solenoid 49". l

In Figure 4; a-switch 51 is interposed --ii1 :coii-'- ductor 41 to' interrupt the current flow to solenoid 6'91" and cause: the consequent closing of valve 32; Switch ET is mounted on stem 58 of pressure responsive means 59-; Means 59; here shown as a sylph'on bellows; connectedby a pipe- 6 into the reheater steam conduits (a's via outlet: header 20-) so as to. be responsive to the steam pressurewithin the reheater R. The contacts of switch 1 5-1 I are normallv closed at a positives ressure in the: bellows 59; .andiimayr be: adjusted to openlatgionexample;atmospheric pres:- sure for: under; Consequently% when therreheater pressure falls to: orr belo'W- atmospheric, valve- 3i!v is by solenoid 49! (then deenergized)r permitted to :close: and preventzain flow-i into: the: steam pip-- ingithrough valvei3-2.

7 Further! considering: Figure/14'; a: check-waive 61 mar berp'rovided; in? pipe: 251 (Figure 1). beyond the valve 32; .with: respect to steam flow; which will act: toprevent a back fiowof air into pipe 25ft: through'walve 3324.. With such check'valve 6| it: mayr'nota. be" necessary: to utilize the pressure responsive switch 512 (of'. Figure: 4).- which closes valveiekuporillossof pressure:

taneously; with. the opening of: valv'et 35-" by the circuits; shown l in Figure 51 whichlmay' be substitute diin Eigures 3fa1ld 4. In-Figured; the st'op valverswitch; SV; is; provided with a second set-of contacts y, 45ws-4tizg: contact? 45111 being connected to: line; M and contact 48a: tof conductor 41b; Upon closinglcontacts' flat-46a current will flow through. conductorsi 412i; 417; l solenoid 4'9 and conducton'tfioto lineL-ABpthereby instantaneously openin valveu32a,

Sili czrnum'erous' changes may be: made; in the above deseribediorganizations andfdiiierent. embodiments-Inf thezinventi onimay be made-without departin Ifro-mi the spiritand scope: thereof; it that all matter containea in the abovetd'escriptionlmfshowniint 'e accompa-nyingdrawingstshall be' interpreted as illustrative and not} in a limitingsense.-

We claim: 1

1. In a system comprising asteam-generator having a steam superheater and a ste-am reheater disposed; therein t'oab'sorh heat from the combustiongases thereof, stearn' turbine apparatus including a highpressurestage connected to receive high pressure steam fromthe outlet of' said superheater and arranged i to disch'arge that steam at -reduced pressure Y into the. inlet of said reheater; said turbine apparatusfurther meme:

ring a low pressure stage connected to receive said reduced pres-sure steam as discharged from the outlet of said reheater, a valve in the supply connection from the superheater outlet to the prctecti said reheater. against overheating by said combustion gases in" the event. of: a closure;

of said high pressure turbine supply'v'alveand 8 consequentstoppage"ofrnow'throughitheireheater of. said: discharge steam? from the big-hi pressure turbine outlet, said: protectinglmeans comprising asve'nting valve establishing connection fromlthe reheater outlet totheatmosphere and. organized to:- be closed as long. as: said reduced pressure steam flows from the high pressure turbineioutlet through the reheater into the low pressure turhineinlet; and means rendered: effective-upon clo'sure of saidhigh'ipressure turbine supply valve for then openingisaid. venting valve allowing the." high pressure steam contained in the: reheater to gradually escape through saidventing valve and ex pand within the reheater thereby coolin'gflthe reheater by absorptionof heat there from.

2. In as system comprising a steam generator having a steam' superheater and a steam' reheater dispos'ed therein-to absorb heat from the combustion: gases thereof; steam turbine apparatus including a highpressure stage connected to receive highlpressnresteam from the outlet-of said superheater and arrangedto discharge that steam: at reduced'pressure intothe inlet of-said reheater, said turbine apparatus further" includirigi a low pressure stage connected. toreceive said: reduced pressure steam as discharged from the outlet of said rehe'ater', valve in the 1 supply connection from: the: superheater outlet to the high pressure" turbine inlet? arranged normally to be at least partially: open; and: means respon sive to. turbine speed foreffecting closure of that valve and resultant" cut ofii of the higl'r pressure turbine: steam. supply when said" speed reaches a given? value; the combination of means? for rotecting saidi reheater against. overheating: by said eombusticn gasesin the event of a: closure of said high? pressure turbine supply: valve and consequent'stoppage of iiowl'through' the reheater of saidi discharge steam from" the? high pressure turbine outiet; said protecting means'comprising a= source of steam other than the I aforesaid? tur= bin'e outlet discharge, a norma1ly.="closed shutoff valve establishing 'connection'ilfrorn said other steam source to the reheater inlet,'. a: venting valve establishing connection from the reheater outlet to the atmosphere and organized to 'be closed as long as said reduced: pressure steam flows from the high' pressure turbine outlet through the reheater into the low. pressure turbine inlet; means rendered: effective upon closure of said highpressure turbine supply valve for then opening said normally closed shut -off 'v'al-ve whereby then tosupply steamfrom said other: source to the reheater inlet,and means efiecti-ve upon" admissionthrough said' shuton valveof said other" source steanr into: the reheater inlet for then opening said venting valve thereby a1- lovving" that: other-source steam" to pass as a coolant-through the reheat'er for escape to at mosphere by way of 'the reheater "outlet and the venting" valve.

33 In a' system comprisin'g-a steam generator having a steam superheater and a steam' reheat'er disposed therein to absorb heat fromthe cornbustion gases thereof; steam turbine apparatus including" ahigh pressure stag'econnected to receive high pressure steam from'the outlet of saidsuperheater anda'rranged to discharge'tliat steam at reduced pressure into the inlet o'f"sa'id reh'eater; said"turbine apparatusjfurther includ ing a. low pressure stage connected to receive saidu'educed pressure steam as. dischargedtfrom theoutle'tof saidireheateria valvein'the' supply connection from" the supenieater outlt""to the 9 high pressure turbine inlet arranged normally to be at least partially open, and means responsive to turbine speed for efiecting closure of that valve and resultant cut off of the high pressure turbine steam supply when said speed reaches a given value, the combination of means for protecting said reheater against overheating by said combustion gases in the event of a closure of said high pressure turbine supply valve and consequent stoppage of flow through the reheater of the said discharge steam from the high pressure turbine outlet, said protecting means comprising a source of steam other than the aforesaid turbine outlet discharge and having a pressure higher than that of said discharge, a norvalve being set to stay closed as long as the pressure within the reheater is at or below the aforesaid reduced value had by the steam normally entering the reheater from said high pressure turbine outlet and to open when the pressure within the reheater rises to or above that had by steam from said other steam source, and means rendered effective upon closure of said high pressure turbine supply valve for then opening said normally closed shut-off valve whereby then to supply into the reheater inlet steam from said other source which steampasses as a coolant through the reheater and thence to atmosphere by way of said relief valve now opened by the pressure of that steam.

4. In a system comprising-a steam generator having a steam superheater and a steam reheater disposed therein to absorb heat from the combustion gases thereof, steam turbine apparatus including a high pressure stage connected to receive high pressure steam from the outlet of said superheater and arranged to discharge that steam at reduced pressure into the inlet of said reheater, said turbine apparatus further including a low pressure stage connected to receive said reduced pressure steam as discharged from the outlet of said reheater, a valve in the supply connection from the superheater outlet to the high pressure turbine inlet arranged normally to be at least partially open, and means responsive to turbine speed for effecting closure of that valve and resultant cut off of the high pressure turbine steam supply when said speed reaches a given value, the combination of means for protecting said reheater against overheating by said combustion gases in the event of a closure of said high pressure turbine supply valve and consequent stoppage of flow through the reheater of said discharge steam from the high pressure turbine outlet, said protecting means comprising a source of steam other than the aforesaid turbine outlet discharge, a normally closed shut-01f valve establishing connection from said other steam source to the reheater inlet, a venting valve establishing connection from the reheater outlet to the atmosphere and organized to be closed as long as said reduced pressure steam flows from the high pressure turbine outlet through the reheater into the low pressure turbine inlet, means rendered effective upon closure of said high pressure turbine supply valve for then opening said normally closed shut-off valve whereby then to supply steam from said other source to the reheater inlet, check valve means in the discharge connection from the high pressure turbine outlet to the reheater inlet '7 effective to prevent said thus supplied other source steam from reversely flowing into that outlet in by pass relation to the reheater, and means effective upon admission through said shut-off valve of said other source steam into the reheater inlet for then opening said venting valve thereby allowing that other source steam to pass as a coolant through the reheater for escape to atmosphere by way of the reheater outlet and the venting valve.

5. In a system comprising a steamgenerator having a steam superheater and a steam reheater disposed therein to absorb heat from the combustion gases thereof, steam turbine apparatus including a high pressure stage connected to receive high pressure steam from the outlet of said superheater and arranged to discharge that steam at reduced pressure into the inlet of said reheater, said turbine apparatus further including a low pressure ste ge connected to receive said reduced pressure steam as discharged from the outlet of said reheater, a valve in the supply connection from the superheater outlet to the high pressure turbine inlet arranged normally to be at least partially open, and means responsive to turbine speed for effecting closure of that valve and resultant cut oif of the high'pressure turbine steam supply when said speed reaches a given value, the combination of means for protecting said reheater against overheating by said combustion gases in the event of a closure of said high pressure turbine supply valve and consequent stoppage of flow through the reheater of the said discharge steam from the high pressure turbine'outlet, said protecting means com prising a source of steam other than the aforesaid turbine outlet discharge and having a pressure higher than that of said discharge, a normally closed shut-off valve establishing connection from said other steam source to the reheater inlet, a relief valve establishing connection from the reheater outlet to the atmosphere, said relief valve being set to stay closed as long as the pressure within the reheater is at or below the aforesaid reduced value had by the steam normally entering the reheater from said high pressure turbine outlet and to open when the pressure within the reheater rises toor above that had by steam from said other steam source, means rendered effective upon closure of said high pressure turbine supply valve for then opening said normally closed shut-off valve whereby then to supply into the reheater inlet'steam from said other source which steam passes as a coolant through the reheater and thence to atmosphere by way of said relief valvenow opened by the pressure of that steam, and a check valve in the discharge connection from the high pressure turbine outlet to the reheater inlet effective to prevent said thus supplied other source steam from reversely flowing into that outlet in'by pass relation to the" reheater.

6. In a system'comprising a steam generator having a steam superheater and a steam reheater disposed therein to absorb heat from the combustion gases thereof, steam turbine apparatus including a high pressure stage connected. to receive high pressuresteam from the outlet of said superheater and arranged to discharge that steam at reduced pressure into the inlet of said reheater, said turbine aparatus further including a low pressure stage connected to re ceive said reduced pressure steam as discharged from the outlet of said reheater, a valve in the s pply connection from, the superheater outlet to the high pressure turbine inlet arranged normally to beat'least partiallyopen, and means responsive to turbine speed for effecting closure 'of that valve and resultant cut off of the high pressure turbine steam supply when said speed reaches agiven value, the combination'of-means for protecting said reheater against overheating by said'combustiongases in the event of a closure of said high pressure turbine supply valve and consequent stoppage of flow through the reheater of said discharge steam from the high pressure turbine outlet, said protecting 'means "comprising a source of steam other than the aforesaid turbine outlet discharge, anormally closed shut-off valve establishing connection from said other steam source to the reheater inlet, a normally closed venting valve establishing connection from thereheater outlet to the atmosphere, means rendered effective upon closure of said high pressure turbine supply valve" for then opening'both-said shut-off valve and said venting valve wherebythen to admit into the reheater inlet steam from said other source which steampasses as a coolant through the redisposed therein to :absorb heat from. the combustion gases thereof, steam turbine apparatus including a high pressure stage connected to re- -ceive high pressure steam from the outlet of said superheater and arranged to discharge that steamat reduced pressure into the inlet of said reheater, said turbine apparatus further including a low pressure stage connected to receive said reduced pressure steam as discharged from the :outlet of said reheater, and inlet valve in the supply connection from the superheater-outlet to the high pressure turbine inlet arranged normallyto be at leastpartially open, a normally open stopvalve also disposed 'in'said supply conpressure turbine outlet-to the reheater inlet effective topreventsaid thus suppliedother source steam from reversely flowing into that outlet in bypass relation'tothe reheater, and means-effective upon admission through said shut-off,

valve of said othersource steam into the reheater inlet for then opening said venting'valve thereby allowing that other source steam-to pass as a coolant through, the reheater-and escape to atmosphere byway ofthe reheater outlet and the venting valve.

-8. In a system comprising asteam generator having a steam superheater and asteam'reheater disposedtherein'to absorb heatfrom'the combus tion gases thereof, steam turbine aparatus including ahigh'pressure stage connected to receive high pressure steamiromthe outlet of saidsuperheaterand arrangedto discharge that steam at nection in series with said inlet valve, and means responsive to turbine speed for effecting closure of said :inlet valve when said speed reaches a (first given value and for further efiecting closure of said stop valve when said speed reaches .asecond :given value, the combination of means for protecting said reheater against overheat-- ing by said combustion gases in the event of a reheater inlet, a venting valve establishing conmotion from the reheater outlet to the atmosphere-and organized to .be closed as long as said reduced pressure steamiflows from the high pressure iturbine outlet through the reheater into the low pressure turbine xinlet, control means for saidnormally closed shut-on valve organized to effect a delayed opening of that valve upon closure of said turbine inlet valve and to effect a more-prompt opening .of the shut-off valve upon closure of said turbine stop valve whereby in either event steam from said other source will be supplied to the reheater inlet, check valve means in the'discharge connection from the h j l reduced pressure into the inlet of said reheater, said turbine apparatus further including a low pressure stage connected to receivesaidireduoed when said sp-eed reaches a secondgiven value, the

combination of "means for protecting said reheat er against overheatingby said combustion gases in the'even't of a closure'of either of -said "turbine inletandstop valves, said protecting 'm'eanscom prising a source of steam other than the aforesaid discharge from the "high pressure "turbine outlet, anormally closed shut-offvalveestablishing connection from said othersteam source to the reheaterinlet, a normally closed venting Valve establishing connection from the reheater out let was atmosphere, control means for said new mally closed shut-off valve organized to effect a delayed opening of that valve upon closure of said turbine inlet valve and to effect .a more prompt'opening of'theshut-oif valve upon closure? of said turbine stop valve whereby in either event steam from said other source will be suppliedjto the reheater inlet, check valve means in the discharge connection from the high pressure turbine outlet to the reheater inlet elTective to prevent the thus supplied other source steam from reversely flowing into that outlet in by pass relation to "the reheater,.and means further eiiective upon closure of said turbine inlet valvefor then opening said venting valve thereby allowing the saidother source steam supplied as aforesaid to the reheater inlet to pass as a coolant through the reheater and escape .to atmosphereby way of the reheater outlet and the venting valve.

9. In a steam power generating station, a steam generator, a high pressure stage .of asteam turbine and alow pressure stage,ia steam superheater and a steam reheater associated with the steam generator, a first conduit for conveying steam from the steam generator to the inlet of the superheater, a second conduit connecting the=su-- perheater outlet with the high pressure stage.-

steam turbine inlet, a turbine steam admission valve in said second conduit, means responsive: to turbine speed for eifecting automatic closure of that valve when said speed reaches a predetermined value, a third conduit connecting the high pressure stage turbine outlet with the inlet of the:

reheater and a check valve in said conduit to prevent reverse flow of steam therethrough, a fourth conduit connecting the reheater outlet with the low pressure stage turbine inlet, a relief valve in said fourth conduit for at proper times venting steam therefrom to the atmosphere, a fifth conduit interconnecting a source of reheater cooling steam with the reheater inlet through said third conduit, a normally closed shut-off valve in said fifth conduit, and means rendered effective upon closure of said turbine admission valve for then opening said shut-off valve whereby upon interruption of the steam flow to the high pressure stage of the turbine by said turbine valve closure the aforesaid shut-off valve in the fifth conduit will open and admit steam from said reheater cooling source into the reheater inlet and thereby cause that steamto pass as a coolant through the reheater and out to the atmosphere through the relief valve in the fourth conduit.

' 10.111 a steam power generating station, a steam generator, a high pressure stage of a steam turbine and a low pressure stage, a steam superheater having low and high temperature 1 sections and a desuperheater therebetween with respect to steam fiow and a steam reheater all associated with the steam generator, a first conduit for conveying steam from the steam generator to the inlet of the superheater, conduits interconnecting the desuperheater with the superheater sections, a second conduit connecting the superheater outlet with the high pressure stage steam turbine inlet, a. turbine steam admission valve in said second conduit, means responsive to turbine speed for effecting automatic closure of that valve when said speed reaches a predetermined value, a third conduit connecting the high pressure stage turbine outletwith the inlet of the reheater and a check valve in said conduit to prevent reverse flow of steam therethrough, a fourth conduit connecting the reheater outlet with the low pressure stage turbine inlet, a relief valve in said fourth conduit for at proper times venting steam therefrom to the atmosphere, a fifth conduit interconnecting the desuperheater with the reheater inlet through said third conduit, a normally closed shut-off valve in said fifth conduit, and means rendered effective upon closure of said turbine admission valve for then opening said shut off valve whereby upon interruption of the steam flow to the high pressure stage of the turbine by said turbine valve closure the aforesaid shut off valve in the fifth conduit will open and admit steam from the said desuperheater into the reheater inlet and thereby cause that steam to pass as a coolant through the reheater and out to the atmosphere through the relief valve in the fourth conduit.

11. In a steam power generating station, a steam generator, a high pressure stage of a steam turbine and a low pressure stage, a steam superheater and a steam reheater associated with the steam generator, a boiler room steam main for supplying steam at lower pressure than does the steam generator, a first conduit for conveying steam from the steam generator to the inlet of the superheater, a, second conduit connecting the superheater outlet with the high pressure stage steam turbine inlet, a turbine steam admission valve in said second conduit, means responsive to turbine speed for effecting automatic closure of that valve when said speed reaches a predetermined value, a third conduit connecting the high pressure stage turbine out- 14 let with the inlet of the reheater and a check valve in said conduit to prevent reverse flow of steam therethrough, a fourth conduit connecting the reheater outlet with the low pressure stage turbine inlet, a relief valve in said fourth conduit for at proper times venting steam therefrom to the atmosphere, a fifth conduit interconnecting said boiler room steam main with the reheater inlet through said third conduit, a

normally closed shut-off valve in said fifth con duit, and means rendered effective upon closure of said turbine admission valve for then opening said shut-off valve whereby upon interruption of the steam flow to the high pressure stage of the turbine by said turbine valve closure the aforesaid shut-off valve in the fifth conduit will open and admit steam from the said boiler room steam main into the reheater inlet and thereby cause that steam to pass as a coolant through the reheater and out to the atmosphere through the relief valve in the fourth conduit.

12. In a steam power generating station, a steam generator, a high pressure steam turbine, a low pressure steam turbine, a steam superheater and a steam reheater associated with the steam generator, a first conduit for conveying steam from the steam generator to the inlet of the superheater, a second conduit connecting the superheater outlet with the high pressure steam turbine inlet, a turbine steam admission valve in said second conduit, means responsive to turbine speed for effecting automatic closure of that valve when said speed reaches a predetermined value, a third conduit connecting the high pressure steamturbine outlet with the inlet of the reheater and a check valve in said conduit to prevent reverse flow of steam therethrough, a fourth conduit connecting the reheater outlet with the low pressure steam turbine inlet, a relief valve in said fourth conduit for at proper times venting steam therefrom to the atmosphere, a fifth conduit interconnecting said first conduit leading from the steam generator with said third conduit leading to the reheater inlet, a normally closed shutoff valve in said fifth conduit, and means rendered effective upon closure of said turbine admission valve for then opening said shut-off valve whereby upon the interruption of steam flow to the high pressure steam turbine by said turbine valve closure the aforesaid shut-off valve in the fifth conduit will open and admit steam from the steam generator into the reheater inlet and thereby cause that steam to pass as a coolant through the reheater and out to the atmosphere through said relief valve in the fourth conduit.

13. In a steam power generating station, a steam generator, a high pressure stage of a steam turbine and a low pressure stage, a steam superheater and a steam reheater associated with the steam generator, a first conduit for conveying steam from the steam generator to the inlet of the superheater, a second conduit connecting the superheater outlet with the high pressure stage steam turbine inlet, a turbine steam admission valve in said second conduit, means responsive to turbine speed for effecting automatic closure of that valve when said speed reaches a predetermined value, a third conduit connecting the high pressure stage turbine outlet with the inlet of the reheater and a check valve in said conduit to prevent reverse flow of steam therethrough, a fourth conduit connecting the reheater outlet with low pressure stage turbine inlet, a normally closed venting valve V in said fourth conduit-forat proper times releasing steam from the reheater outlet to the atmosphere, a ififth conduit connecting a source of reheater cooling steam'with the reheater inlet through said third conduit, a normally closed shut-off valve in said fifth conduit, and means rendered effective upon closure of said turbine admission valvefor then opening both said venting valve and said shut-off valve whereby upon interruption of the steam flow to the high pres sure turbine by said turbine valve closure the aforesaid shut-off valve in the fifth conduit will open andiadmitrsteam from said reheater cooling source intothereheater inlet and thereby cause that stream :to :pass as a coolant through the reheater and out to the atmosphere through the venting valve in the fourth conduit.

"14. In a steam power generating station, a steam generator, a high pressure steam turbine, a low pressure steam turbine, a steam superheater and a steam reheater associated with the steam generator, a first conduit for conveying steam :from the steam generator to the inlet of the superheater, a-second conduit connecting the superheater outletwith the high pressure steam turbine inlet, a-stop valve and an inlet valve for said high pressure steam turbine in said second conduit, :motor means for each of said valves organized to cause automatic closure of those'respective valves in response to predeterminedrelative:speeds-ofsaid high pressure steam turbine, :a third conduit connecting the high pressure steam turbine outlet with the inlet of the reheater and a check valve in said conduit :to prevent reverse fiow of steam therethrough, a fourth conduit connecting the reheater outlet with the low pressure steam turbine inlet, a relief valve in said-fourth conduit for at proper times venting steam from the reheater outlet to the atmospheres fifth conduit interconnecting the' tl'iird conduit to a source of reheatericooling steam, a normally closed :shut-ofi valve in said .fifth conduit having :a solenoid for opening said valve, :a switch responsive to the position'of the aforesaid turbine stop valve and a switch responsive tolthe position of the aforesaid turbine inlet valve, each switch being constructed and arranged to close with 'theclosing of its respective turbine valve, and conductors connecting the switches in parallel and said shut-off valve solenoid in series with'the'switches into an electric control circuit whereby upon the interruption of steam flow to the high pressure steam turbine by the closing either of said stop or inlet valves the aforesaid shut-off valve in the fifth conduit will be opened'to admitsteam from the reheater cooling source into the reheater inlet and thereby cause that steam to pass-as a coolant through the reheater andout-to theatrncsphere through the relief valve in the fourth conduit.

15. In a steam power generating station, a steam generator, a high pressure steam turbine, a low pressure steam turbine, a steam superheater and a steam reheater associated with the steam generator, a first conduit, for

conveying steam from the steam generator to the inlet of the superheater, a second conduit connecting the superheater outlet with the high pressure steam turbine inlet, a turbine steam admission valve in .said second conduit, means responsive to turbine speed for effecting automatic closure of that valve when said speed reaches a predetermined Value, a third conduit valve in said conduit to prevent reverse flow of steam therethrough, a fourth conduit con .necting the reheater outlet with the low pressure steam turbine inlet, a relief valve in said fourth conduit for at proper times venting steam from the reheater outlet to the atmosphere, a fifth conduit interconnecting the third conduit to a source of reheater cooling steam, a normally closed shut-off valve in said fifth conduit having a solenoid for opening said valve, a switch responsive to the position of the aforesaid steam admission valve for the high pressure turbineconstructed and arranged to close with the closing of that valve, conductors connecting said switch and said shut-off valve solenoid in series with an electrical control circuit whereby upon the interruption of steam flow to the high pressure steam turbine by closure of said turbine valve the aforesaid shut-01f valve in the fifth conduit will be opened to admit steam from the reheater cooling source into the reheater inlet and thereby cause that steam to pass as a coolant through the reheater and out to the atmosphere througli said relief valve in the fourth conduit, and a manually operable switch effective when closed to short circuit said first mentioned switch to thereby energizeand optionally open said solenoid controlled cut off valve independently of said first mentioned switch.

16. In a steam power generating station, a steam generator, a high pressure stage of a steam turbine and a low pressure stage, a steam superheater and a steam reheater associated with the steam generator, a first conduit for conveying steam from the steam generator to the inlet of the superheater, a second conduit connecting the superheater outlet with the high pressure stage steam turbine inlet, a turbine steam admission valve in said second conduit, means responsive to turbine speed for eifecting automatic closure of that valve when said speed reaches a predetermined value, a third conduit connecting the high pressure stage turbine outlet with the inlet of the reheater and a check valve in said conduit to prevent reverse flow of steam therethrough, a fourth conduit connect ing the reheater outlet with the low pressure stage turbine inlet, a relief valve in said fourth conduit for at proper times venting steam from the reheater outlet to the atmosphere, a fifth conduit connecting the third conduit to a source of reheater cooling steam, a normally closed shut-off valve in said fifth conduit, motor means organized to open said shut oif valve and having associated therewith response-delay means which retard each valve openin for a predetermined period, and means rendered effective upon closure of said turbine admission valve for then activating said motor means whereby upon interruption of the steam now to the high pressure turbine by said turbine valve closure the aforesaid shut-off valve in the fifth conduit will open after a predetermined period and then admit steam from the reheater cooling source into the reheater inlet for passage as a coolant through the reheater and out to the atmosphere through said, relief valve in the fourth conduit.

17. In a steam power generating station, a

steam generator, a high pressure stage of a pressure stage steam turbine inlet, a stop valve and an inlet valve for said turbine in said second conduit, motor means for each of said valves organized to cause automatic closure of those respective valves in response to predetermined speeds of said turbine, a third conduit connecting the high pressure stage turbine outlet with the inlet of the reheater and a check valve in said conduit to prevent reverse flow of steam therethrough, a fourth conduit connecting the reheater outlet with the low pressure stage turbine inlet, a relief valve in said fourth conduit for at proper times venting steam from the reheater outlet to the atmosphere, a fifth conduit connecting the third conduit to a source of re heater cooling steam, a normally closed shut-on valve in said fifth conduit having a solenoid for opening aid valve, switches respectively responsive to the positions of said turbine stop and inlet valves in the second conduit, circuit means including a source of energy and conductors interconnecting the switches with the aforesaid shut-off valve solenoid and with the energy source for causing the respective closing of said stop and inlet valves to establish individual paths of current flow to said solenoid, a normally open switch in the conductor interconnecting said inlet valve switch with the shut-off valve solenoid, a closing solenoid for said switch energized over said inlet valve switch, and means retarding the closure of the solenoid operated switch for a predetermined period whereby upon interruption of the steam flow to the high pressure turbine by the closure of said inlet valve the aforesaid shut-off valve in the fifth conduit will open after a predetermined period while upon interruption of the steam flow by the turbine stop valve saidshut-off valve will open immediately, in either of which events the thus opened shut-off valve will admit steam from said reheater cooling source into the reheater inlet for passage as a coolant through the reheater and out to the atmosphere through the relief valve in the fourth conduit.

18. In a steam power generating station, a steam generator, a high pressure stage of a steam turbine and a low pressure stage, a steam superheater and a steam reheater associated with the steam generator, a first conduit for conveying steam from the steam generator to the inlet of the superheater, a second conduit connecting the superheater outlet with the high pressure stage steam turbine inlet, a turbine inlet valve in said second conduit, means responsive to turbine speed for effecting automatic closure of that valve when said speed reaches a predetermined value, a third conduit connecting the high pressure stage turbine outlet with the inlet of the reheater and a check valve in said conduit to prevent reverse flow of steam therethrough, a fourth conduit connecting the reheater outlet with the low pressure stage turbine inlet, a normally closed venting valve in said fourth conduit for at proper times releasing steam from the reheater outlet to the atmosphere, a solenoid for opening said venting valve, a fifth conduit connecting a source of reheater cooling steam with the reheater inlet through said third conduit, a normally closed shut-off valve in said fifth conduit, a solenoid for opening said shut-off valve, a switch responsive to the position of the aforesaid turbine inlet valve, circuit means including conductors interconnecting said switch with said shut-off valve solenoid and said venting valve solenoid and with a source of energy where-- by closure of said inlet valve will cause said switch to establish individual paths of current flow to said two solenoids and thereby open the shut-off and venting valves, a normally open switch in the conductor interconnecting said inlet valve switch with the shut-off valve solenoid, a closing solenoid for said switch energized over said inlet valve switch, and means retarding the closure of the solenoid operated switch for a predetermined period whereby upon interruption of the steam flow to the high pressure turbine by the closure of said inlet valve the aforesaid venting valve in the fourth conduit will immediately open while the aforesaid shut-off valve in the fifth conduit will open after a predetermined period, whereupon the thus opened shut-off valve will admit steam from said reheater cooling source in the reheater inlet for passage as a coolant through the reheater and out to the atmosphere by way of the opened venting valve.

19. In a steam power generating station, a steam generator, a high pressure stage of a steam turbine and a low pressure stage, a steam superheater and a steam reheater associated with the steam generator, a first conduit for conveying steam from the steam generator to the inlet of the superheater, a second conduit connecting the superheater outlet with the high pressure stage steam turbine inlet, a turbine inlet valve in said second conduit, means responsive to turbine speed for effecting automatic closure of that valve when said speed reaches a predetermined value, a third conduit connecting the high pressure stage turbine outlet with the inlet of the reheater and a check valve in said conduit to prevent reverse fiow of steam therethrough, a fourth conduit connecting the reheater outlet with the low pressure stage turbine inlet, a normally closed venting valve in said fourth conduit for at proper times releasing steam from the reheater outlet to the atmosphere, a solenoid for opening said venting valve, a fifth conduit connecting a source of reheater cooling steam with the reheater inlet through said third conduit, a normally closed shut-off valve in said fifth conduit, a solenoid for opening said shut-off valve, a switch responsive to the position of the aforesaid turbine inlet valve, circuit means including conductors interconnecting said switch with said shut-off valve solenoid and said venting valve solenoid and with a source of energy whereby closure of said inlet valve will cause said switch to establish individual paths of current flow to said two solenoids and thereby open the shutoff and venting valves, so that upon interruption of the steam flow to the high pressure turbine by the closure of said inlet valve said shut-off valve in the fourth conduit and said venting valve in the fifth conduit will both open and cause steam from said reheater cooling source to be admitted into the reheater inlet for passage as a coolant through the reheater and out to the atmosphere by way of the venting, valve, a pressure respon sive switch in the conductor interconnecting said inlet valve switch with the venting valve solenoid, and means responsive to the pressure in said reheater to open said pressure responsive switch when the said pressure reduces to about atmospheric and thereby close said venting valve when need for holding same open no longer exists.

20. In a steam power generating station, a steam generator, a high pressure stage of a steam turbine and a low pressure stage, a steam superheater and a steam reheater associated with the steam generator, a first conduit for conveying steam from the steam generator to the inlet of the superheater, a second con'dut connecting the superheater outlet with the high pressure stage steam turbine inlet, a stop valve and an inlet valve for said turbine in said second conduit, motor means for each of said valves organized to cause automatic closure of those respective valves in response to predetermined speeds of said turbine, a third conduit connecting the high pressure stage turbine outlet with the inlet of the reheater and a check valve in said conduit to prevent reverse flow of steam therethrough, a fourth conduit connecting the'reheater outlet with the low pressure stage turbine inlet, a normally closed venting valve in said fourth conduit for at proper times releasing steam from the reheater outlet to the atmosphere, a solenoid for opening said venting valve, a fifth conduit connecting a source of reheater cooling steam with the reheater inlet through said third conduit, a normally closed shut-off valve in said fifth conduit, a solenoid for opening said shut-off valve, switches respectively responsive to the positions of said turbine stop and inlet valves in the second conduit, circuit means including a source of en'- ergy and conductors connecting both the venting valve solenoid and the shut-off valve solenoid to that source through said inlet valve switch and said shut-off valve solenoid further to that source through said stop valve switch, said stop valve switch havingtwo branches one of which 20 is connected in parallel with the inlet valve switch, a solenoid operated switch in the conductor interconnecting said inlet valve .switch with the shut-off valve solenoid and means retarding the closure of the solenoid operated switch fora predetermined period whereby upon interruption of the steam flow to the high pressure turbine by the'closure of said inlet valve the aforesaid venting valve in the fourth conduit will immediately open while the aforesaid shut-off valve in the fifth conduit will open after a predetermined period, while upon interruption of steam flow to th turbine by the stop valve both the venting and shut-off valves will immediately open, in either of which events the thus opened shut-01f valve will admit steam from said reheater cooling source into the reheater inlet for passage as a coolant through the reheater and out to the atmosphere by way of the thus opened venting valve.

PAUL R; WALTER.

JOHN W. THOMPSON.

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

FOREIGN PATENTS Number Country Date 244,773 Great Britain Sept. 30, 1926 416,091 Great Britain Sept. 10, 1-934