US1896508A - Method and apparatus for the preheating and maintaining at operating temperature the cylinders of steam or gas turbines - Google Patents

Description

E. BROWN- Feb. 7, 1933.

2 Sheets-Sheet l F/IZ REHEATING AND MAINTAINING AT OPERATING Filed NOV. 24, 1928.

"'11 Ill TEMPERATURE THE CYLINDERS 0F STEAM 0R GAS TURBINES METHOD AND APPARATUS FOR THE P Feb. 7, 1933. 5 BROWN 7 METHOD AND APPARATUS FOR THE PREHEATING AND MAINTAINING AT OPERATING TEMPERATURE THE CYLINDERS OF STEAM 0R GAS TURBINES Filed Nov. 24, 1928 2 Sheets-Sheet 2 Patented Feb. 7, 1933 UNITED STATES:

nnro snow, or BADEN, swrrzn n-LAnn, ASSIGNOR TO Axrrn'nensnnnsonerr BROWN BOVERI & CIE, OF BADEN, SWITZERLAN LAND METHOD AND APPARATUS FOR THE PREHEATING. AND MAINTAINING AT OPERATING nA JOINT-STOCK COMPA1\TY or SWITZER- TEMPERATURE THE CYLINDERS O.F STEAM 0R GAS TURBINES Application filed November 24, 1928, Serial No,

This invention relates to steam turbines and especially to-means for enabling such turbines to beput into operation in a shorter time than hitherto possible.

It is well known that the various sections of steam and gas turbines do not heat and cool uniformly when being put into and out of operation and that during such periods of unequal heating and cooling, the cylinders and shafts are subjected to objectionable stresses with resulting distortion. If, therefore, a turbine is placed into operation during the periods of such stresses and distortions, the turbine will be subjected to excessive vibration with consequent damage unless structural allowances, such as excessive running clearances, are made. Otherwise, the turbine must be preheated at a Very slow rate to approximately the operating temperature which may require several hours for large turbines and for turbines operating at particularly high temperatures or at high pressures.

Moreover, the admission of steam at the rate, or in the amount, necessary for the operation of the turbine will, in consequence of the high heat transfer due to condensation on the contact surfaces, create heat stresses in the several portions of the turbine which may greatly exceed the elastic limits of the materials used, and may produce permanent distortion with resulting cracked casings and other parts, stretched flange bolts and leakage at the various joints between the several portions.

The method hitherto used for preheating, and maintaining in a hot state, of the various sections of the turbine to be protected against the dangers of distortion and stressing beyond the elastic limit when rapidly placed in operation, by providing a continuous flow of steam therethrough or thereabout, is inadequate as preparation for rapid placing in operation, as, in spite of the costly expenditure of steam, the degree of heating attained and maintained is limited by the temperature of saturation or condensation corresponding to the low pressure of the steam flowing through the sections to be heated. r

The disadvantages and difficulties above set 321,749, and in Germany November as, 1927.

forth in'starting a turbine are overcome by Q the present inventiomof whichitis an object to maintain a turbine in'heated condition for the purpose of facilitating starting thereof without the expenditure oftlarge quantities of heat. i I I A further object of theinvention is to .maintain a turbine in aheated condition by heating from the interior or from the exterior thereof or by a combination of heating from both the interior and exterior thereof. 7 y

A further object of the invention is to maintain the surfaces ofnthe turbine to be .brought in contact with the operating medium at a temperature substantially equal to or higher than that corresponding to the temperature of condensation of said. medium.

, Another object of the invention'isto supply heat for maintaining a turbine ina. heated condition,'between the casin g and the lagging thereof. I

A further object of the invention is to ,provide a combination of steam and electric heating means which maybe used separately or in combination for maintaining a turbine in a heated condition to facilitate quick starting thereof. v I j Another object of the invention is to provide means for securing diiferent temperature zones during the maintenance of a tur-i bine in a heated condition which zones are similar to those occurring during operation.

Other objects and advantages will be apparent to those skilled in the art. from the following description in connection with the drawings accompanying and forming part. of this specification.

In the drawings: a Fig. l is a partial sectional view of the. casing wall of a turbineincased in lagging;

Fig, 2 is a cross-sectional View of a turbine embodying the invention, taken mately on a central line; Fig. 3 is a view showing a turbine in elevation and the lagging thereon in section Fig. 4 is a view partially in section and parj ppro tially in elevation of aturbine' showing one -material. Any" other suitable arrangement '30 arranged to illustrate a plurality of embodiments of the invention in such a manner as will enable ready comprehension by those skilled in the art.

Referring to the drawings by characters of v reference, 10 indicates a casing of a turbine cylinder which comprises a pluralityv of removable sections to facilitate manufacture, assembly and inspection of thevarious portions of the device enclosed therein. The casing portions 10 have'flanges 11' formed integral therewith to provide for the aligning and j oining-of the'several casing portionsby means including bolts 12 passing through the fiangesll. 'Conductance of heat to the bolts may be increased by providing the flanges with passageways as shown. The turbine is shown as entirelysurrounded by a lagging 13 formed of materials having a low coefficient of heat conductivity and comprising an inner and an outer shell separated by insulating may; however, be employed.

I Thelagging 13 is spaced from the turbine casing 10 to' provide an intervening space in which a plurality of heating coils or pipes 15 are located and which are preferably ar-' ranged closely adjacent the turbine casing. The rate of heat conduction to the several portions of the turbine casing may be increased by providing the casing with fins or projections as at which will increase the surface areas of the turbine in contact with the heating means. 7

An electric heating coil 16 is shown as secured near the interior surface of the lagging 13. It will be apparent that the spacing of the turns of the steamheating coil 15 and the electric heating coil 16 may be increased or decreased to provide for different heating zones adjacent the different portions of the turbine casing. The heating coil 16 will be supplied from a suitable source of electricf current controlled by any of the usual suitable means. Instead of spacingthe lagging 13 from the turbine, the casing 10 of the turbine may be coated with a material of low heat conductivity as of 62 applied directly thereto and, when so applied, the heating coils 15 may be imbedded therein, preferably closely adjacent the turbine casing. WVhen the electric heating coil 16 is employed, it will, preferably, be imbedded in the surface of the lagging asshown in Fig. 1 and in contacting or closely adjacent relation to the turbine caslng.

The thermal action produced by maintaining'theturbine in a 'heated condition will be static devices.

may be placed in the conductor 19 immedireadily understood by reference to lines 17 and 18 of Fig. 7, indicating the heat gradient in the structure. Considering the contacting surfaces'of the flanges .11 as one of two coordinate axes and a line perpendicular to the flange surfaces as the other, the line 17 represents the heat gradient or the rate of heat conduction when a turbine is started fromrest without being maintained in a heated condition. Line 18 represents the heat "gradient when a turbine is started in a heated condition. The steepness ofline 17 i s caused by high heat conduction due to condensation of steam on the casing. As soon as a condition of thermal equilibrium is reached, the heat gradient conforms to line 18, and a comparison of the lines shows'that all danger of creatingheat stresses is eliminated by maintaining the turbine in heated condition.

' in addition to the heat supplied by the heating coils 15 and 16, the space between the ycasing 10 of the turbine and the-lagging 13 maybe supplied with heated gases circuiated therethrough. When such addition is made, a tubular conductor 19' is-connected with the lagging 13 inc, suitable gas-tight manner. The conductor 19 is'in communication with a fan 21 which is joined to a heat exchanger QQWlllCll is connected, ina suitable manneig'to aninlet through the lagging 13 into the space between the lagging and the turbine casing 10. The fan 21 exhausts the space within the lagging 13 thereby forcing a circulation of fluid through the heat exchanger 22'and through the space within the lagging 13 surrounding theturbine. A heating medium is'supplied to the heat exchanger through an inlet 26, from a suitable source which may, for instance, be high pressure steam. If electric heating 1S utilized, the several heating elements may be connected in any of the known circuits for obtaining the desired temperature differences. After pass through theheat exchanger, the heating medium isdischarged therefrom through an outlet 27. During the preheating period or while the. operating temperature is being maintained, the turbine rotor should be turned, preferably slowly, by any suitable device to secure even heating of the several portions of the structure.

The quantity of heat required for proper maintenance of the turbine in heated condition may be regulated, either manually, in

response to theindications'of thermometric devices located in 'diiferent parts of the device, or automatically by means of thermo- For example, a thermostat 28 ately ahead of the fluidinlet to thefan 21, and the thermostat may be connected, by a system of levers 30,'to a throttling valve 31,

which permits the temperatureof the heating fluid passing through the space between the lagging and the turbine casing to be automatically controlled by control of the amount of heating fluid passing throu-gh'the pansion of the elements thereof will take place in direct ratio to the amount of heat supplied. ()ne end of the turbine being fixed at 32, it is necessary that the turbine expand in a dircction'awa-y from the point of attach ment 32 and the lug 33, resting upon a foundation or base member at one end of the turbine',' opposite to the fixed'point of attachment 32, permits expansion in that direction. In this way the heat supplied is directly dependentbn thetemperature of the casing which serves as a thermostat.

Y A pin extending outwardly from the turbine casing portions 10 into the space be tween the turbine casing and the lagging 13 and connected by the system of levers 36 with valve member 37 arrangedto vary the size of the opening through the lagging for the tubular'connection 23-to the heat exchanger 22, provides for variation in'the quantity of heatingfluids surrounding the turbine casing.- Any suitable means such as '38 may be connected to an extension of the lever system'36 to open and close the circuit to the heating element 16. It will be seen, therefore, that the expansion of the turbine under the influence of heat, may be utilized to govern 1 a suitable amount of steam may be allowedto circulate throughout the interior of the turbine casing, thereby assistingin maintaining the same 1n a properly heated conditlon.

-mission of steam to the interior of the turhim: to assist in maintaining the turbine at operating temperature is illustrated in Fig. at, wherein the turbine casing 10 is provided with an annular passageway ll within the lagged space, which passageway encloses ports 64 spaced about the periphery of the turbine so that steam introduced into the interior of the turbine casing may pass there from into the space enclosed by the lagging 13. A fan 21 which exhausts the heating mcdium from the interior of the turbine casing through the ports in the annular passageway 41, may be utilized to force the heating medium through the exchanger 22 and discharg the same therefrom into the tube 23 from which it again passes through the turbine. In addition to heating the turbine, the tube 23 may be so connected with the main steam supply valve 42 as to maintain the valve 42 in a heated condition and thus further facilitate rapid starting of the turbine. v

The invention may also be applied to a multi-cylinder turbine as shown in Fig. 5. The heat exchanger may also be an electrical device which is supplied from asuitable source of energy rather than the steam heated heating exchanger above described.

Whenthe invention is applied to a multi cylinder turbine the discharge tube 23 may be connected to the conduit 42 joining the intermediate and low pressure cylinders 45 and 46 respectively and to a high pressure cylind'er 47 connected with the exhaust end of the intermediate cylinder 45, whereby the heating medium is permitted to flow through the high pressure cylinder 47 from which it is returned through the heat exchanger '22, andth'e cycle is repeated- It will be understood that the auxiliary heating circuit is provided with valves 48, 50 and 51, by means of which the same may be en 751F013, disconnected from the turbine, 'or

which will permitvariation 1n the direction offlow of the heating medium so thatthe low pressure cylinder 46 may be cut off from the heating circuit and may be maintained unof the turbine. Any desired temperature and velocity of gases may be obtained by adjust ment of the valves and the speed of the fan.

Automatic regulation of the heat supplied to the heat exchanger may be obtained by enclosing a thermostatic member 52 within the walls of the turbine casing which member may, preferably, be of such character that the heating thereof will produce longitudinal expansion and thus control the action of a relay 55 through the medium of the con nected lever system which relay in turn controls a device 56 to regulate the admission of. heating fluid to the heat exchanger '22. it will be apparent that the heat exchanger may be supplied with steam from any suit- One means ror accomplishlng partial a-d able source or that the same may be equipped with an electric heating element such as is shown in Figs. 5and 6,

It has been found that the invention may be so satisfactorily applied to turbine instal lations that the samemay be utilized as a reserve power machine capable of instantaneous operation on demand,rather than requiring a period of several hoursfor an imperfect preheatin operation before being capable of operation. I p a It should be clearly understood that the invention has nothing inc-ommon with the welllrnown drying of turbines and the accompanying condensers, but deals with means for quicklystarting a turbine from rest. The temperature ranges for the'two operations are entirely different and are brought about by difie-rent means. In the invention, the 1 heating fluid is of such temperature that the turbine structure is preheated to'and mainpreventing stresses and distortions in said turbine comprising an inclosure' of low heat conductivity forming a chamber about the casing, a heat exchanger in communication with the chamber, means for circulating a heating medium through the said heat exchanger, means for controlling the supply of heating medium by the external surface temperature of the turbine, and means for circulating a fluid heated by said heat exchanger through the chamber surrounding said turbine, to maintain the turbine during periods of non-operation at a temperature substantially equal to or higher than the temperature of condensation of the operating medium.

2. In an elastic-fluid turbine'system comprising a turbine having a casing, means for preventing distortions and vibration in said turbinecomprising a. heat insulating inclosing member forming a heat retaining chamber surrounding the casing, a heat exchanger means in communication with the chamber, means for supplying a heating medium to said heat exchanger, a fan in communication with said heat exchanger and with the chamher for circulating a fluid to be heated there- 7 through, and means for controlling the rate of supply of said heating medium by the temperature of the circulated fluid, to maintain the turbine during'periods of nonoperation at a temperature substantially equal to or higher than the temperature of condensation of the operating medium. I

3. In an elastic-fluid turbine system, means for preventing stresses and distortions in a turbine during non-operating periods there- .of including an enclosure of low heat conductivity forming a chamber about the turbine, a heat exchanger in communication with the chamber, means for c1rculat1ng a heating medium through said heat exchanger,

,means for controlling the supply ofheating medium in response to the external surface temperature of the turbine, and means for circulating a fluid heated by said heat exchanger through the chamber about said turbine.

e. In an elastic-fluid turbine system, means for preventing stresses in the turbine struc ture comprising a heat insulated enclosing ber about said turbine for circulating a heat ini fluid therethrough, and means for controlling the rate of supply of'said heating medium in response to the temperature of the circulated fluid.

5. In the art of operation of steam turbine apparatus wherein it is required that said apparatus be placed from a state of non-operation into a state of operation substantially instantaneously, and that the state of opera tion into which said apparatus is placed substantially instantaneously be at any degree of load for which said apparatusis designed; the method for such purpose which comprises maintaining the temperatures throughout the high-pressure end of the turbine structure at least substantially as high, during the nonoperating state, as the temperatures ofcondensation of the full-load working steam, and in such manner that the temperature gradients in the turbine structure, formedin the substantially instantaneous transition from the non-operating state to the full-load operating state, are maintained within the range of substantially instantaneous temperature change-to which'thematerials of the turbine structure can be subjected and still remain Within the range of permissible strain below their elastic limits.

In testimony whereof I have hereunto subscribed my name this 27th day of October ERIC BROWN.

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