US1494850A - Back-pressure turbine and method of utilizing high-pressure steam in turbines - Google Patents

Description

May 20 1924.

1,494,850 F. L05 TURBINE AND UTILIZING HIGH sssuns s M ES Filed A '1 '2,

HOD OF BACK PRESSURE PR TURBIN u 2 5 Z 5 ///0 m/M J STAGE-S E5 Fatentecl May 2Q, 1924:.

FRANZ LGSEL, 0F BRUNN, CZECHQSLOVAKIA.

BACK-PRESSURE TURBINE AND METHOD OLE UTILIZING lFEIG'rH-PRESSURE STEAMZ ZN TUBBIILES.

Application filed April 7, 1923. Serial No. 630,661.

To all whom, it may concern:

lie it knovvn that l, FRANZ liiisnL. a citi zen of the Czechoslovakian Republic, and residing at .7 (,ilOCkQtIQ'HSSG, Brunn, Czecho- Slovakia, have invented certain new and use ful Ii'uprovements in Back-Pressure Turbines and Methods of Utilizing;- High-thes sure Steam in Turbines, of which the following is a specification.

My invention is an improved back pressure turbine and a novel method ot' utilizing high pressure steam for power purposes, which is availed of in my novel turbi e. The object of my invention is to increase the efliciency of such turbines, the most. marked increase being at tl'ie l'iighest pressure stage thereoi. By the praeticeof my invention, 1 am enabled to employ at very high elliciency much higher steam pressures and temperatures than have. heretofore been einployed for back pressure turbines, and atthe same time I may employ back pressure turbines at pressures heretofore employed and obtain a greatly increased etliciency.

It is a recognized fact that the high pressure parls of back pressure turbines have heretofore been far less eilicient than the high pressure cylinders of modern steam engines and that the methods and construetions employedhave been such that the very high pressures which can be most econom-- ically produced in large steam generators and utilized in reciprocating engines could not be practically used in turbines.

In the Parsons or reaction type of tur bine, in which approximately one-half of the pressure drops are in the rotor blades and therefore there is a substantial diti'erence of pressure 011 opposite sides oi each rotor blade, a {H1111 coi'istruction for the rotor was essential and relatively large clearances had to be provided. This type,

" because of the ditlerences in pressure at the opposite sides of the rotor blades, required many stages and steam velocities throughout-Which were relatively low, usually 150 meters to 350 meters per second. In this type of turbine when used for the higher pressures the velocities were greatest at the inlet end. This type oi turbine was reasonably ellicient for low pressures, but, the clearance losses were so large at. the higher pressures that it became usual to employ for back pressure turbines, turbines oi" the impulse type either with pressure stages, as in the llateau type, or with both velocity and pressure stages, as in the Curtis type.

This type of turbine could be, and has ordinarily been, constructed of the disc type because the pressure drops occur in the sta tionary diaphragms and there is only negligible difference of pressure on opposite sides of the rotor Wheels. Therefore, a considerable clearance could be allowed and the leakage loss became negligible. This type of turbines, however, has always been designed for relatively great heat, drops at each stage producing very high steam velocities and, correspondingly high peripheral velocities of the rotor Wheels. Moreover, the grez test heat drop occurred at the inlet to the turbine, andthe highest steam vel0city therefore occurred. in the very first stage oi the turbine. The great frictional and \vindage losses which result from these extremely high velocities caused a great loss of etliciency and set a limit to the pressures and temperatures which couldv be profitably utilized. in impulse turbines.

The universal practice of the art to employ such high velocities in impulse turbines has been based upon a misconception of the efficiency losses of steam flowing over impulse wheels. lVell. ltnovvn nozzle experiments by Jesse and Christlein (see for example their U. S. Patent No. 1,062,471) had been. accepted as proving that in all impulse turbines the maximum eiliciency \vas obtainable When the steam velocity at each stage considerably exceeds the critical velocity of about 4-50 meters per second from 10% to d liile these values have been depart ed from in the construction of impulse turbines, the velocities Ql'ljlplfiyttl lHUQ always been o'r' this order oi magnitude. in the lirst or highest pressure stage of back pres sure turbines the greatest heat drop occurred at the first stage and the liighest velocity, because variations from the supposed most etticient velocity in either direction, would decrease eliiciency, and, therefore it was preferable to increase the pressure and heat drop, and, therefore, the velocity rather than to decrease it in order to lessen the pressure that the glands must Withstand and the temperature upon the turbine parts.

b'Zy own experiments conducted under conditions that alce intoconsideration the practical conditions of the flow of steam over the blades and through the other parts of a turbine have developed the fact that there is a quite different and a much lower zone of steam velocities at which a substantially greater etliciency can be obtained than in' the zone heretofore supposed to be the best. This zone is that which is ordinarily referred to by engineers in my own country as Rohrreibungszone, which translated literally means pipe friction zone, and as tech nically used means a velocity which gives rise to frictional losses of the order of magnitude of those acceptable in pipe lines, such pipe friction zone velocities in a turbine with its very smooth passages being understood to be higher than ordinarily accepted in pipes with their rough surfaces, but in a completely different zone from that of the velocities of ordinary impulse turbines. In order to give precise information to enable turbines to be best constructed in accordance with my invention, I would say that 1 ascertained by my experiments that the maximum etliciency is obtainable when the steam velocities relative to the blade surfaces is about 100 meters per second, this eliiciency falling ofl' as the relative velocity is reduced from about this ligure and as it is increased. The eliieiency begins to decrease very sharply at'a relative velocity of about I40 meters per second. At a considerably higher velocity the eliicien'cy again begins to increase, in accordance with the rule laid down by Jesse and Christlein, but never reaches the high etlicicncy that I make use of in the lower or pipe friction zone.

As there is in practically all impulse turbines a small reaction effect. the relative velocity cannot be the same at all parts of the blade surface. and therefore. to take the fullest advantage of my invention, the relative velocity at no part of the blade surface should be higher than 1H) meters per second. This necessarily means in any practical construction that the absolute velocity of the steam entering each stage of the turbine will also he of a different and lower order of magnitude than any velocities heretofore employed in impulse turbines.

in the drawings zn-conipanying this specilication Fig. l is a cross-section through one-half of a back pressure turbine embodying the principle of my invention. Fig. 2 on the same scale as Fig. 1 illustrates a similar section of that part of a prior art turbine of the same. type designed to utilize the same pressure and ten'iperature drop as would be utilized by the entire turbine of Fig. 1.

Fig. 3 is a diagram illustrating the coinparalive pressuredrops in the turbine of Fig. 1 and the lirst stage of the turbine of Fig. 2.

Fig. 4 is a diagram illustrating the compalison of-the absolute and relative veloci ties of the turbine of Fig. 1 and the first stage of the turbine of Fig. 2.

My invention consists essentially in the application to back pressure impulse turbines including particularly the first stage thereof of the discovery I have made that the relative steanr velocities" in turbines T reach their highest efficiency in a low velocity zone far below the high zone heretofore thought to be the most efficient. A back pressure turbine constructed in accordance with my invention and utilizing the method thereof has, therefore, only such small heat and pressure drop from the inletto the highest stage and from each stage to the next as will cause a substantially uniform low pipe friction zone velocity throughout, preferably a relative velocity at all parts of the blades not exceeding 140 meters per second. \Vhile this both as a matter of method and as a matter of structure, is, as above pointed out, a reversal of 55 present engineering principles, yet a turbine built in accordance with my invention and adapted to utilize iny method differs from the present existing impulse turbines of the disk type in no essential feature except those that are dimensional or matters of degree, and, therefore, the drawings illustrating the embodiments of my invention do so by comparing my turbines with the nearest known prior turbi-ne. .95

Fig. 1 illustrates a turbine adapted for an inlet pressure of 300 lbs. the exit pressure of-this turbine being 140 lbs. The turbine is preferably not constructed for a lower exit pressure. although it could be, because it is preferable to utilize this high pressure in a second similarly designed turbine rather than to utilize the lower pressure in a longer turbine. 1 represents the shaft. of the rotor and 2 the casing of the turbine; 3 is the inlet nozzle and 4 the guide passages in the diaphragms 5 supported from the. rotor asing; 6 represents the rotor wheels carried bvthe shaft and 7 the passages through the blading carried by the wheel.

In Fig. 2 is shown that part of a standard prior impulse turbine of the pressure coniponnded type. the type that I employ which would utilizcjhe pressure drop from 300 lbs. to 1-10 lbs. t'he'rotor shaft being designated as 1, the casing as 2", the inlet nozzle as 3, a rotor wheel as (3. a diaphragm as 5 and the passage therethrough as 4. Additional rotor wheels and diaphragms are not shown in this figure because in such a prior turbine the entire pressure drop from. 300 lbs. to 14-0 lbs. corresponding to the pressure drop in the multi-stage back pressure turbine of Fig. 1 occurs at the first stage. Most existing impulse turbines for such large inlet pressure have a considerably greater pressure drop in the first stage than at the one just specified.

Figs. 1 and 2 are drawn to the same climensiona-l scale in order that the difference in principle and the resulting difference in details of construction may be best observed. Because the low, or pipe friction zone. ve-

locity, is employed throughoutmyturbine "much less and therefore the diameter of the the rotor or height of rotor blading can be much The difference in this respect is reduced. I illustrated in Figs. 1 and 2. For the same reason the shaft diameter may be much reduced. wherefore the gland diameter is likewise reduced and the glands are capable of withstanding the higher pressure. As the entire pressure drop of the tnrbineof Fig. 1 is found in the first stage of the turbine of Fig. 2. it is obvious that the inlet nozzle as shown in Fig. 2 is as large as the exit nozzle of the turbine of Fig. 1 and that the inlet nozzle of Fig. 1 is very much smaller while the passages through the various diaphragms of Fig. 1 progressively increase but are all smaller than the inlet of the turbine of Fig. 2. As there is in Fig. 2 a pressure on opposite sides of the diaphragiu 5" equal to the sum of the differences of pressures on the opposite sides of the numerous diaphragii'is of Fig. 1, the diapliragms of Fig. 1 can all be made lighter and thinner than those of Fig. 2-. as indicated in these figures. The fundamental difference between the new turbine of Fig. 1 and the nearest existing turbine the first stage of which is shown in Fig. 2 is further shown by comparing the Figs. 3 and 4. In Fig. 3 the line 8 shows the pressure changes from 300 pounds to 140 pounds in the turbine of Fig. 1. The line 9 shows same drop in the single first stage of the turbine of Fig. 2. Similarly in Fig. 4 the comparative velocities are illustrated. The lines It) show the velocities developed in the guide blades or guide nozzles of the turbine of Fig. 1. while the horizontal lines '10 show the substantially relative uniform velocities in the rotating blades. Similarly, the. line 11 illustrates the high velocity through the inlet nozzle of the turbine of Fig. 2. while the line 11 shows the relative velocity in the rotor blades of the first stage. It is to be understood thatin the turbines taking the full u. e of e well known .losse and (bristleui nciple,

higher velocities than those show lll Figure 4 would appear. and the pressure drop would be greater than shown in Fig. 3.

The general design of Fig. 1 can well be used for very much higher pressures, the

.tive throughout the turbine.

number of stages varying according to the total pressure and heat drop for which the back pressure turbine is desired, but whatever the inlet pressure. the low zone relavelocity is substantially uniform Having thus described my invention, what I. claim, and desire to protect by Letters Patent, is:

1. A back )ressurc steam turbine-of the impulse type f aiid guide passagesproportioned throughout to cause asubstantially uniform relative yelocity of the steam at all stages, including thehighest stage, such velocity being in the low velocity zone where the losses are those corresponding to pipe friction losses as conti'adistiiigiiislied from the high velocity zone heretofore recognized as the turbine efficiency zone.

therein and provided with an inlet to its highest stage so small that the pressure and temperature therein are nearly those of the steam applied to the inlet, thus causing a velocity so low as to increase the efficiency above those of like tiirbincsemploying known velocities of over 450 meters per second.

3. A high pressure turbine having back pressure and provided with many stages with an impulse wheel for each. the inlet and guide passages each giving sufficiently small drops of pressure that a low zone of steam velocity where efficiency is high is found in every stage in contradistinction to therecognized high velocity efficiency zone for. turbines. v

4. A high pressure steam turbine having a backpressnre provided with many stages and impulsiwheels therein, the inlet passages and the guide passages each giving sufficiently small drops of pressure that a low zone steam velocity where efficiency is high is found incvery stage in contradistinction to the known efliciency zone above 450 iiielers per second.

The method of utilizing high pressure steam for power purposes in turbines of the impulse. type which consists in reducing the iaving sufficiently many stages pressure and temperature drop of such steam by a plurality of drops each such as to produce a substantially uniform relative velocity in a low zone of steam velocity Where .cflicicncy is high as contradist-ingiiished from the known high velocity efiicieney zone, the steam after passing through all Stlltl stages still having a high pressure and temperature.

7. The. method of utilizing high pressure steam in bQUflC-IH'OSSIUQ impulse turbines which consists in first reducing the pressure and temperature of the steam in such small degree as to produce a dense stream of a velocity in a low zone where its thermodynamic etticieucy is relatively high as contradistinguished from velocities in or above the known high velocity efficiency zone causing this low velocity stream to act upon the lilatling of an impulse Wheel of a turbine, then reducing the pressure and tem wrature by similar small but progressively increasing tlrops such that saitl low zone velocity shall he maintained at each stage, and causing the steam after each such drop to act upon another impulse wheel of the turbine, wherehy hat-kn'esstire impulse turbines may be tlesignetl of increased efiiciency as contrasted with any efliciency obtainable in the high velocity zone of over 450 meters.

In testimony whereof l have signed my name to this specification.

FRANZ LosEL.

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