US1944520A

US1944520A - Steam turbine

Info

Publication number: US1944520A
Application number: US624822A
Authority: US
Inventors: Meyer Adolf
Original assignee: BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Germany; BBC Brown Boveri France SA
Priority date: 1930-12-30
Filing date: 1932-07-26
Publication date: 1934-01-23
Anticipated expiration: 1951-01-23

Description

Jan. 23, 1934. A. MEYER 1,944,520

STEAM TURBINE Filed July 26, 1932 Patented Jan. 23, 1934 UNITED STATES STEAlW TURBINE Adolf Meyer, Kusnacht, near Zurich, Switzerland, assignor to Alrtiengesellschaft Brown, Bcveri and Cie., Baden, Switzerland, a conseration of Switzerland Application July 26, 1932, Serial No. 624,822, and in Germany December 30, 1930 3 Claims. (0].. 253-69) This invention relates to steam turbines and more particularly to a steam turbine having one or more by-passes through which steam is bled. to the exhaust outlet.

In high power steam turbines utilizing high vacuum condensers, the great increase in volume of the steam by the time it has reached the end of its expansion causes difllculties to arise in the construction of such turbines. Inasmuch as the size of the rotors and blades is limited by admissable stresses, the steam in the later stages of expansion flows through them at a greater velocity than should be permitted for eflicient operation, resulting in considerable leaving losses.

Various expedients have been tried to diminish these losses and consequently increase the maximum power of a turbine having a given speed of revolution. Cfonstruc-tions have been used in which the steam passage is divided in its last stages by special annular partitions into separate passages having different rates of expansion. Such an arrangement is undesirable in that the guide and rotor blades usually must have different profiles on each side of the separating rings. Other constructions have been provided in which the steam has been divided into completely separate streams, each of which expands, performing work, to the condenser pressure. Such turbines form a separate class of high powered but correspondingly costly turbines. It has been found that the leaving losses can be reduced and the efficiency of a turbine correspondingly increased by by-passing a portion of the steam from in front of one or more of the later stages to the exhaust outlet.

The object of this invention is to reduce the leaving losses of a steam turbine.

Another object of this invention is to provide a steam turbine having a by-pass through which steam is bled from in front of one or more of the later stages directly to the exhaust outlet.

A further object of this invention is to bleed from ten to thirty per cent of the steam from before one or more of the later stages to the exhaust outlet.

These and other objects will be apparent from the following specification when taken with the accompanying drawing, in which Fig. 1 is a fragmentary sectional View of the outlet end of a turbine having one bleeding passage, and

Fig. 2 is a fragmentary sectional view of the outlet end of a turbine having two bleeding passages.

Figs. 3 and 4 are fragmentary detail views deal automatically with the greater drop.

showing alternative interchangeable forms of the invention; and

Fig. 5 is a fragmentary detail view showing an adjustable form of the invention.-

The low pressure turbine casing '1 is connected co 7 at 2 to the exhaustoutlet casing 3. The reversing blades 1 are attached to the turbine casing 1 and the rotor blades 5 are attached to the rotor 6. The last stage comprises the reversing blade '7 and the rotor blade 8 and is. separated (15- from the earlier stages by a space 9. Leading from the space 9 is a bleeding passage 10 which by-passes a portion of the steam from the earlier stages directly to the exhaust outlet.- The amount of steam which is icy-passed is controlled to; by the throttling passage 11, the size of which is regulated by the exchangeable ring 12.

Figs. 3 and 4 show two different forms of ring 12, whereby different sizes of throttling passages 11 are obtained. The rings 12 in Figs. 1, 3 and 4 are interchangeable.

In Fig. 5 ring 12 is adjustable longitudinally by means of inserts 13 of various thickness placed in oversize slot 13. In this manner also the size of throttling passage 11 may be varied.

Fig. 2 discloses a similar construction, but one which is adapted to bleed steam from before each of the last two stages instead of only the last stage, as shown in Fig. 1. In the modification shown, a single by-pass to the exhaust outlet is fed by two throttling passages, withdrawing steam from before the last two stages.

In ordinary constructional forms of steam turbines, the long blades of the last expansion stages normally operate with a non-uniform peripheral and steam velocity taken over their length. Consequently at the last expansion stage different pressures occur at diiferent diameters. In known constructions, these unequal pressures are counteracted by twisting the blades. In the turbine according to the present invention, a decrease in pressure occurs from the inside to the outside, namely, at a point Where a portion of the steam is removed for being throttled, which decrease is useful, since it diminishes the loss 100 due to throttling. However, the blades of the turbine adjacent to the bleeding passage are twisted in such a manner that a decrease in pressure from the inside to the outside is in sured. In general, it is not necessary that the 1G blades be twisted as much as in the standard turbine and at times it may not be necessary to have any twist at all. The greater peripheral speed of the outer portions of the blades will then The withdrawal of the steam by bleeding it to the exhaust outlet is not limited to the place of transition to the last stage. In many cases, it will be advantageous to withdraw the steam at several stages, for instance, as shown in Fig. 2. It has been found that best results are obtained by bleeding from ten to thirty per cent of the total steam, depending upon the degree of vacuum maintained in the condenser.

The drawing is'not intended to descriptively illustrate the details but is intended merely to diagrammatically illustrate the invention.

While on the surface, the above method may appear to be uneconomical, mathematical analysis has shown that the gain in output more than offsets the loss due to the reduced volume of steam.

I claim:

1. A condensing steam turbine adapted to handle large volumes of exhaust steam having in combination, a casing, a plurality of stages in said casing, an exhaust outlet, means including a by-pass leading from at least one of the intermediate stages direct to the exhaust outlet, for withdrawing steam from said intermediate stage, and means including an exchangeable throttling element in said by-pass for throttling the steam from the pressure of the stage from which it is withdrawn down to the exhaust pressure of the turbine.

2. A condensing steam turbine adapted to handle large volumes of exhaust steam having in combination, a casing, a plurality of stages in said casing, an exhaust outlet, means including a stationary, substantially unimpeded bypass leading from at least one intermediate stage direct to said exhaust outlet, and throttling means in said by-pass and including an adjustable throttling ring located adjacent the blades of the said intermediate stage.

3. A condensing steam turbine adapted to handle large volumes of exhaust steam having in combination, a casing, a plurality of stages in said casing, an exhaust outlet, means including a by-pass leading from at least one of the intermediate stages direct to the exhaust outlet, for withdrawing steam from said intermediate stage, and means including a throttling ring in said by-pass for throttling the steam from the pressure of the stage from which it. is withdrawn I of the turbine.

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