US1723110A

US1723110A - Elastic-fluid turbine

Info

Publication number: US1723110A
Application number: US731240A
Authority: US
Inventors: Harrison L Wirt
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1924-08-11
Filing date: 1924-08-11
Publication date: 1929-08-06
Anticipated expiration: 1946-08-06

Description

H. L. WIRT ELASTIC FLUID TURBINE 2 Sheets-Sheet Filed Agg. l1, 1924 FLJ..

Inventor Harrison L .Wir-b,

H is Att own-ey Aug. 6, 1929.

Aug. 6, 1929. H. wlRT ELASTIG FLUID TURBINE Filed Aug. 1l, 1924 2 Sheets-Sheet 2 w w1.. vw

Inf P a H by A.

H i? Att orneyl Patented Aug. 6, 192.9.

UNITED STATES HARRISON L. WIRT, OF

SCHENECTADY, NEW YORK, .SSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF YORK.

ELASTIC-FLUID TRBINE.

Application filed August l1, 1924.

The present invention relates to elastic fluid turbines exhausting to a condenser or other exhaust means and especially to turiines of relatively large capacities operating condensing, that is, exhausting into a condenser.

With the best modern engineering practice it is possible to maintain in a condenser under ordinary operating conditions a vacuum of from 281/2 to 29 of mercury which correspond to absolute pressures ot l1/2 to l. of mercury, the main limiting feature being the temperature or' the cooling water available, and at present there appears to be little likelihood that this can be improved upon so that the possible condenser pressure seems fixed. The thing of importance in connection with a condensing turbine is not the absolute pressure in the condenser, however, but rather the absolute pressure just beyond the last row of buckets and it has been the practice to try to keep this pressure as near to the condenser pressure as possible. Furthermore, it has been recognized that if this pressure could be reduced below that existing in the condenser it would result in an increase in the eliiciency of the machine.

However, in the case ot large turbines, the volume of exhaust tluid to be handled in enormous and in ordinary. practice the pressure on the discharge side of the last row of buckets has been somewhat greater than the condenser pressure, the increase being represented by the drop in pressure required to convey the exhaust fluid from the last row of buckets through the exhaust hood to the condenser. In modern practice this drop in pressure is of the order of 0.05 mercury to 0.15 mercury.

Also, in a turbine, the elastic fluid leaves the last row of buckets with a certain velocity, this velocity being required in order for the elastic fluid to pass the last row of buckets, and the kinetic energy carried away by the elastic fluid stream by virtue of this 'velocity is termed usually the leaving loss. This kinetic energy is expressed by the formula Elyria Where E is the kinetic energy, M the mass, and V the velocity. Thus it will be seen that the leaving loss increases with the square ofthe velocity which means of course, that the velocity ot the elastic fluid leaving the last row of buckets should be kept as low Serial No. 731,240.

as possible. In order to pass a given quantity ot' elastic fluid through the last bucket row, the velocity required varies inversely in accordance with the total bucket area so that 't is readil f* seen that by increasing the bucket area, i. e., the length of the buckets and the diameter of the bucket ring, the velocity and hence the leaving losses are decreased. Howver, the permissible bucket ring diameters and bucket lengths are soon reached due to mechanical considerations so that with large machines the leaving loss may be considerabie, the leaving velocity being usually of the order of 700 ft. per second.

New, it is apparent that if. the energy represented by the leaving loss could be usefully employed it would result in a gain in the efticiency of the machine and it has been proposed repeatedly to utilize this energy to decrease the pressure on the discharge side of the last row of buckets by means of passing the exhaust elastic fluid through diusers or passages which would serve to convert a p0rtion of the velocity/ into pressure. By this means the kineticv energy of the exhaust fluid would be used to effect the flow of the exhaust fluid to the condenser so that it Would be possible to have a pressure on the discharge side of the last row of buckets which is lower than the condenser pressure. However, because of the enormous volumes of elastic fluid and the low pressure drop to be dealt with and the fact that the elastic fluid must be conveyed to a condenser opening, this problem is by no means a simple one, and, so far as I am aware, these proposed arrangements have failed to accomplish their intended purpose.

In this connection, it is pointed out that in' modern power plant practice, it is necessary to locate the driven machine, such as a generator tor example, directly adjacent to the low pressure end ot the turbine and in axial alignment with the turbine. This means, of course, that the condenser or condensers must be placed to one side ot or below the center line ot the turbine set.

The object of my invention is to provide an improved arrangement tor accomplishing the above referred to result and for a consideration of what I believe to be novel and my invention, attention is directed to the accompanying description and the claims appended thereto. y

In the drawing, Fig. l is a top plan view, partly in section, or" a turbine structure emeffi@ bodying my invention; Fig. 2 is a side view of the exhaust hood; Fig. 3 is a perspective view of the construction shown in Fig. 1, and Figs. et and 5 are transverse, sectional views taken on lines l1- 4 and 5 5, respectively, of Fig. 1.

Referring to the drawing, 5 indicates the last row of buckets of an elastic fluid turbine which turbine may be of any suitable type. In the present instance it is shown as being of the impulse type and as comprising a shaft 6 upon which are mounted bucket wheels 7 which rotate in stages formed by nozzle diaphragms 8. Diaphragme 8 are arranged in the turbine shell 9. The bearing for shaft 6 at the low pressure end of the machine is indicated at 10 and the low pressure packing at 11. Only the low pressure end of the turbine is shown in the drawing. It will be understood that the particular structure indicated is only by way of example and is to be taken as typical of any suitable turbine structure to which my invention may be applied.

I have discovered that I can effect a conversion of velocity of the exhaust fluid into Y pressure by providing an exhaust housing which comprises first an annular expanding passageway having' an admission end of a radial width between walls, i. e., a difference between the inner and outer radii, equal substantially to the length of the buckets of the last bucket row and a length throughout at least the major portion of its circumference equal to at least twice the length of the buckets of the last bucket row followed by a plurality of branches which change gradually from curved -or semi-annular passageways to approximately circular or rectangular passageways before reaching the condenserasuch change taking place very gradually with a continual increase in cross-sectionall area and without changing substantially the direction of the fluid flow until the greater portion ofv the diffusion has taken place. To accomplish this result, I have found that for the usual leaving velocities found in present day turbine v` `design, an exhaust passage length equal to at leas-t twice the diameter of the last stage wheel is required and that the area should increase until the final area perpendicular to theMelastic yfluid flow isof anorder two or 4.tlneegtimtesas, large as the annular admission areaaPreferably, the annular expanding passhould Ihave a length throughout its entire circumferential area equal2 to at least twice the last rowl bucket length. I'Iowever, for practical reasons, itis difficult sometimes to ,accomplishthis result.Y `For rthis reason, at 1ereforeI iin-d., it necessary insome instances in carryingout my invention, todepart sgme- 1 what from this desirable condition. Some dc- .partura however., `does not affect to an appreciable extent thev results obtained. v y The admission end of the annular expandin-gpassageway should have yawidth so as to Hconfine.;butnot.obstruct the elastic fluid discharge immediately after it leaves the blades and such passageway should extend in a direction so that while gradually expanding it does not change the direction of flow of the annular fluid stream. Furthermore, the branches into which the annular passageway merges should diverge gradually so as to direct the stream of fluid gradually away from the center line of the turbine at low velocity. In this connection, the diversion of these branches should establish a curvature so gradual that the angle between successive cords drawn parallel to the direction of flow `and equal in length to the length of the last row of moving buckets shall not exceed 12.

Referring now to the drawing, 12 indicates the annular expanding passageway of the exhaust hood which, after extending a distance equal to about two bucket lengths throughout at least the major portion of its circumference, divides into two branches 13 and 14- which terminate in openings 15 and 16. Openings 15 and 16 are connected directly to the openings 17 and 18 of suitable condensers indicated at 19 and 20 in Fig. 1.

In order to obtain discharge openings from the branches 13and 14 of sufficient area for distributing the elastic fluid tothe condensers without going to unduly long branches, I preferably cut the branches off at an angle as is best illustrated in Fig. 1, and I then provide stationary buckets or guide blades 21 for turning the elastic fluid and directing it into the condensers. Preferably theseblades 21 are shaped so as to provide an expanding crosssection and thereby secure some additional diffusion while turning the elastic fluid. The condenser tubes are indicated at 19a and as will be seen from Fig. 1 of the drawing, by the arrangement illustrated the rows of tubes extend at an angle with the center' line of the passageway through which the exhaust fluid flows. By this arrangement it will be seen that the exhaust fluid is fed to the condenser at an angle and the result is obtained that an area of flow to the tubes is obtained which area is greater than the area of the passageway.-

Vith the above described arrangement, I have foundthatI am enabled to obtain conversion of'veloeity ofY the exhaustelastic fluid yinto pressure wit-hentat the Sametime increasingthe overall length of the machine or interfering withthelocation 'of the driven'inachine up close tothe low pres-sure end of the turbine. In ,e ,Order to vprovide accessibilityy vto -the lowy pressure bearing itis sometimes ,nec-

essary at the top'v of. therannularmportion of the exhaust housingvtoinake it somewhat shorter than ,twowbueket lengths and this is true linthe,construction illustrated. injfzhe drawinv. However, havingthe annular porton somewhat shorter lattliis-peint doesnot .affectmaterially the `results obtained.l 3v l As statedabovait is tberustomiamlin'faifll from a practical standpoint, it is necessary to place the machine driven by the turbine, a generator for example, directly adjacent to the low pressure end of the turbine, thus making necessary the positionino' of the condenser to one side of or below the 'turbine and hence in conveying the exhaust elastic fluid from the turbine to the condenser it is necessary to change its direction of flow. In exhaust hoods heretofore proposed for accomplishing conversion of velocity of the exhaust fluid into pressure, it has been attempted to effect rsuch conversion while at the same time changing the direction of iow of the exhaust elastic fluid. By exhaustive tests which I have made, I have demonstrated that the desired result cannot be accomplished in this manner. As illustrative of the gain to be made by my improved exhaust hood, the following numerical example is given. Assume the case of an average steam turbine of present day design, and operating with a condenser pressure of 1 inch of mercury. In such a turbine with an exhaust hood of usual known construction, the drop in pressure interposed by the exhaust hood is of the order of 0.1 inch of mercury, making the pressure on the discharge side of the last row of blades of the order of 1.1 inches of mercury. With my iinproved exhaust hood I am enabled un der siniilar operating conditions to maintain a pressure of the order of 0.825 inches of mercury on the discharge side ofthe last row of blades thus effecting a gain of the order of 0.275 inches of mercury. In large condensing turbines running under the assumed conditions a change of l inch mercury in the condenser pressure represents a change of the order of 6% in the water rate. In other words, in such machines the vacuum correction is of the order of 6% per inch of mercury. Under these conditions, therefore, a gain in vacuum of 0.27 5 inches of mercury on the discharge side of the last blade row would represent a reduction in water rate of about 1.65 per cent.

Or viewed from another aspect, my improved exhaust hood permits of increasing the capacity of a turbine having buckets in its last row of a given length, from 25% to 40% without suffering an increase in the net leaving losses over what they would be with ordinary known types of exhaust hoods. This is because of the fact that the recovery of a part of the residual velocity loss by means of the exhaust hood makes it possible to run with a leaving loss of higher value and still maintain the same economy as before.

Referring now to the structure of the exhaust hood, I preferably form each branch in two sections by dividing them verticali as indicated at 22 thereby providing inner portions 23 and outer portions 24. The inner portions ofthe two branches are formed integral with each other, being connected by the annular wall 12 and are split horizontally as is indicated at 25. ThisI enables the inner upper halves of the exhaust housing to be removed for inspection purposes without disturbing the condenser connections.

In accordance with the provisions of the patentstatutes, I have described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, butl I dcsire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

lVhat I claim as new and desire to secure by Letters Patent of the United is l. The combination with an elastic liui d turbine, of an exhaust hood therefor comprising an annular diverging portion hav' difference between the inner and outer radii at its admission end equal to substantially the length of the buckets of the last wheel and a length throughout at least the major portion of its circumference equal to substantially twice the length of such buckets, and a plurality of branches into which said annular portion merges, said branches divcrgin gradually from the center line of the turbine and acquiring in a distance equal to about two last stage wheel diameters an arca equal to at least twice the annularI admission arca.

2. The combination with an elastic fluid turbine, of an exhaust hood therefor comprising an annular diverging portion having a difference between the inner and outer radii at its admission end equal to substantially the length of the buckets of the last wheel an-fl a length throughout at least the major portion of its circumference equal to substantially twice the length of such buckets, a plurality of branches into which said annular portion merges, said branches curving` away and outward from the tips of the buckets of the last stage wheel with a curvature so gradual that the angle between successive cords drawn parallel to the direction of flow and equal in length to the length of the 'buckets of the last stage wheel shall not exceed l2".

3. The combination with a horizontal elastic fluid turbine, and two vertical condenser-s located on opposite sides of t ie center line of the turbine, of an exhaust hood for conveying exhaust elastic iiuid from the turbine to the condensers, said exhaust hood conngrising first an annular divergingvportion having a length throughout at leastthe maj or portion of its circumference equal to approximately twice the length of the buckets of the last stage wheel followed by two branches which gradually increase in area and diverge from the center line of the turbine until they reach the condensers.

4. The combination with a horizontal elastic fluid turbine, and two vertical condensers located on opposite sides of the center line of the turbine and provided with openings which face toward such center line, of an exhausthood for conveying exhaust elastic fluid from the turbine to the eondensers, said exhaust hood comprising first an annular portion which incieases gradually in area in the direction ot flow through it followed by two branches which gradually increase in area to where they oin the condenser openings.

5. The combination with a horizontal elastic fluid turbine and two vertical condensers located on opposite sides of the center line of the turbine and provided with openings which face toward such center line` of an exhaust hood for conveying exhaust elastic fluid from the turbine vto the condensers, said exhaust hood comprising first an annular portion which increases gradually in area in the direction of How through it followed by two branches which gradually increase in area to where they join the condenser openings, and turning and diffusion blades set in the plane of discharge of the branches, the entrance edges of such blades facing approximately in the direction of the flow of exhaust elastic fluid and the discharge of such blades being normal to the planes of the condenser openings.

6. The combination with a horizontal elastic fluid turbine and vertical condensei's on either side of the center line of the turbine, of an exhaust hood therefore comprising an annular diverging port-ion and plurality of branches which lead to said vertical condensers, said exhaust hood being split horizontally for about half its length at which point it is split vertically.

7. The combination with an elastic fluid turbine, ol an exhaust hood therefore comprising a passageway leading to a condenser, the direction of flow in the passageway being different from the direct-ion of flow into the condenser, and a series of blades along the plane of intersection ot' the two directions of flow, said blades being shaped so as to turn the flow in the new direction and increase the cross-sectional area of flow.

8. The combination with an elastic fluid turbine and a condenser means, ot an exhaust hood structure for conveying exhaust elastic fluid from the turbine to the con-denser means,

said exhaust hood structure comprising first alportion'of gradually-increasiiig area which extends in the direction vof flow ot exhaust elastic fluid frompthe turbine fora distance of theorder of at least two times the length hand thisl 9th day'ot' August,192e.r

of the buckets ofthe last'buclxet row and through which the exhaust elastic fluid flows without change in direction, -followed by a portion ot gradually-increasing area wherein the direction of flow of the exhaust elastic fluid is changed and directed to the condenser means.

9. rl`he combination with an elastic fluid turbine and a condenser means located to one side ot the center line ot' the turbine, of an exhaust hood for conveying` exhaust elastic fluid from the turbine to the condenser means, said exhaust hood comprising first an annular portion ot gradually-increasing area which extends in the direction of flow of the exhaust elastic fluid followed by a plurality of branches which diverge gradually and serve to direct the exhaust elastic fluid to the condenser means, and bearing means for the turbine located in the space between said branches and within said annular portion.

l0. The combination with a 'horizontal elastic fluid turbine and two vertical `condensers located on opposite sides of the center line of the turbine and provided with openings which face toward said center line, ot' an exhaust hood for conveying exhaust elastic fluid from the turbine to the condensers, said ed'iaust hood comprising first an annular poA lon which increases gradually in area in the direction of flow through it followed by two branches which gradually increase in a ea to where they join the condenser openings, and bearing means tor the turbine located in the space between said branches and within said annular portion.

ll. rlhe combination with a horizontal elastic fluid turbine and two condensers located on opposite sides of the center line of the turbine and provided with openings, of an exhaust hood for conveying exhaust elastic fluid from the turbine to the condensers, said exhaust hood comprising lirst an annuular portion which increases gradually in area in the direction ot flow through it followed by two branches which gradually increase in area to where they joi-n the condenser openings, and bearing means foi-the yturbine located@ in f the?` space In witness whereof, .I haVehereuntoy set `tiny n 'between said branches and :withinsaid annular p ortioin v j