US2529880A

US2529880A - Turboexpander

Info

Publication number: US2529880A
Application number: US81461A
Authority: US
Inventors: Arthur W Mcclure
Original assignee: Elliott Co
Current assignee: Elliott Co
Priority date: 1949-03-15
Filing date: 1949-03-15
Publication date: 1950-11-14
Anticipated expiration: 1967-11-14

Description

Nov. 14, 1950 A. w. MCCLURE TLiRBOEXPANDER Filed March 15, 1949 M x; r rap/v5 Y5.

Patented Nov. 14, 1950 TURBOEXPANDER Arthur W. McClure, Jeannette, Pa., assignor to Elliott Company, Jeannette, Pa., a corporation of Pennsylvania Application March 15, 1949, Serial No. 81,461

3 Claims.

This invention relates to turbo-expanders which are used to reduce the temperature of gases through expansion at temperatures below ambient.

As high pressure gas is expanded in a turboexpander to a lower pressure and temperature, some of the gas escapes along the rotating shaft of the expander wheel to the atmosphere. To make up this loss, make-up gas must be taken at a much higher temperature level, so there is a considerable B. t. u. loss. It therefore is highly desirable to reduce the leakage to atmosphere as much as possible.

It is among the objects of this invention to provide a turbo-expander for low temperature gases which diverts back into the expander casing some of the gas attempting to leak out along the shaft, in which this diversion is accomplished entirely within the expander itself, and in which there is no necessity .for an insulated external diversion conduit that must pass through insulation surrounding the turbo-expander.

In accordance with this invention, the turboexpander casing has front and rear walls connected by an encircling side wall forming a toroidal chamber provided with an inlet for cold high pressure gas. The front wall of the easing has a central outlet opening in it, and the rear wall also has a central opening. A shaft is rotatably mounted in the rear opening and extends forward into the casing. Inside the casing a bladed expander wheel is rigidly mounted on the shaft for receiving gas from the toroidal chamber and delivering it to the casing outlet at a lower pressure and temperature. Connected to the rear wall of the casing is a sealwhich encircles the shaft to reduce leakage of the gas from the casing rearwardly along the shaft. The shaft is provided with one or more radial passages between the ends of the seal. The inner end of these passages are connected by an axial passage extending forward through the shaft into the casing. A large proportion of the gas which starts to leak out of the casing between the shaft and seal is led through these passages back into the casing where it mixes with the gas that has passed through the expander wheel. Preferably, the gas expanded through the wheel flows across the outlet of the axial passage in such a direction as to create a slight aspirating effect at that point.

The preferred embodiment of the invention is illustrated in the accompanying drawing, in which the single figure is a fragmentary longitudinal section through a turbo-expander.

Referring to the drawing, the turbo-expander has the usual casing formed from a front wall I spaced from a rear wall 2 by a toroidal side wall 3 that encircles the outer edges of the other two walls. The side Wall forms a chamher 4 extending around the casing and having z an inlet 5 at any convenient location. The annular space that connects this chamber with the space between the front and rear walls of the casing generally contains a nozzle ring 6 provided with a plurality of radial ports I.

The rear wall of the casing is provided with a central opening 8 through which a rotatable shaft 9 extends. The front end of the shaft projects a short distance into the casing to support the usual bladed expander wheel I0 having a peripheral intake and an axial outlet. A nosepiece or retaining nut II is screwed on the front end of the shaft to lock the wheel in place.

The front wall of the casing is provided with a central opening l2 having substantially the same diameter as the outlet of the wheel. Bolted to the front of the casing is a diffuser l3 which, with the casing, is surrounded by thermal insulation H.

The shaft is supported behind the casing by means of a bearing 16 mounted in a support I! to which the casing is bolted. Between this hearing and the expander wheel the shaft is.

encircled by a sealing ring l8 that is bolted to the casing. The inside of this ring may be provided with a plurality of annular teeth l9 which substantially engage the shaft. Although these teeth or their equivalent materially reduce the leakage of gas outwardly along the shaft, as compared to an unsealed shaft, they obviously cannot stop it entirely.

It is a feature of this invention that the gas leakage past the shaft seal to atmosphere is reduced materially more than is possible with the seal alone. Accordingly, the portion of the shaft encircled by the seal is provided with an annular groove 2| around it, and one or more, preferably four, passages 22 are drilled from this groove radially toward the axis of the shaft. The inner ends of these passages are connected by alarger axial passage 23 extending forward through the shaft and the retaining nut l l. Thus, the groove around the shaft is in direct communication through these passages and the expander wheel with the casing outlet l2 and the diffuser. The seal may be provided with an annular groove 24 registering with the one in the shaft. These grooves are shown at approximately the center of the seal, but they may be in other locations. However, it is better that the grooves be nearer the front or inner end of the seal than its rear end, because it means that there will be a longer sealing area between the grooves and the outer end of the seal.

Medium pressure gas which fills the space between the expander wheel and the casing will leak out along the shaft between the shaft and seal. However, a large amount of this outwardly leaking gas will not reach the outer end of the seal because it will be diverted by the radial passages 22 into the axial passage 23, by which it will be led back into the lower pressure region in the casing where the gas leaves the expander wheel. Of course, this returned leakage gas. having by-passed the blades of the expander wheel without doing any work, will not be at as low a temperature as the gas which turns the wheel, but it still will be at a very much lower temperature than would be the gas that otherwise would have to enter the system to make up for this leakage gas if it had escaped to the atmosphere. Consequently, the overall efllciency of the turbo-expander is increased materially.

To take a specific example, where air is being cooled, air in the toroidal chamber at 95 pounds per square inch absolute and a temperature of --166 F. was expanded to a pressure of 49 p. s. i. a. in passing through the nozzles. then had a temperature of 218 F. Some of this air was distributed in the clearance spaces between the revolving wheel and the casing. The rest of this air passed through the expander wheel in which it was expanded to 21 p. s. i. a. and to a temperature of -252 F. It will be seen that the air between the wheel and the casing would be that which would leak out through the seal and which would have to be replaced by atmospheric air at a temperature of perhaps 70 F. or higher. By reason of this invention it was found that the leakage to atmosphere was reduced more than 40%, thus reducing by about 34% the leakage B. t. u. loss based on using 70 F. atmospheric air for replacing the air that leaked out to atmosphere.

In order to cause the leakage gas to flow inward through the radial passages 22 and then out through the front end of the shaft, the pres sure at the inlets of the radial passages needs to be only slightly higher than the pressure at the casing outlet. It therefore will be seen that the pressure drop between the groove 24 and the outer end of the sealing ring also will be very small, and that most of the pressure drop in the seal will occur between its inner end and the annular rooves 2| and :24 around the shaft. Consequently, the leakage of gas from those grooves outwardly along the shaft to the atmosphere will be greatly reduced. By forming the retaining nut II with a forward taper, across which gas passing through the wheel will flow, a slight aspirating effect will be produced by that gas at,

the outlet of the axial passage 23 through the shaft and nut.

According to the provisions of the patent statutes, I- have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims. the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. A low temperature turbo-expander comprising a casing having front and rear walls connected by an encircling side wall forming a toroidal chamber provided with an inlet forcold high pressure gas, the front wall of the casing having a central outlet opening therein, the rear wall of the casing having a central opening therein, a bearing mounted behind said rear wall opening, a shaft rotatably mounted in said bearing and extending forward through said rear opening into the casing, a bladed expander wheel rigidly mounted on the shaft in the casing for receiving gas from said chamber and deliverin i it to said outlet at a lower pressure and temperature, and a seal connected to said rear wall in front of said bearing and encircling the shaft to reduce leakage of gas from the casing rearwardly along the shaft toward said bearing, the shaft being provided with at least one radial passage extending inward from a point between the ends of said seal and also being provided with 'an axial passage connecting the inner end of the radial passage with said outlet, whereby a large proportion of said gas leakage along the shaft is led through said passages to the casing outlet.

2. A low temperature turbo-expander comprising a casing having front and rear walls connected by an encircling side wall forming a toroidal chamber provided with an inlet for cold high pressure gas, the front wall of the casing having a central outlet opening therein, the rear wall of the casing having a central opening therein, a bearing mounted behind said rear wall opening, a shaft rotatably mounted in said bearing and extending forward through said rear opening into the casing, a bladed expander wheel rigidly mounted on the shaft in the casing for receiving gas from said chamber and delivering it to said outlet at a lower pressure and temperature, and a seal connected to said rear wall in front of said bearing and encircling the shaft to reduce leakage of gas from the casing rearwardly along the shaft toward said bearing, the shaft having an annular groove around it between the ends of said seal, the shaft being provided with radial passages extending inward from said groove and also being provided with an axial passage connecting the inner ends of the radial passages with said outlet, whereby a large proportion of said gas leakage along the shaft is led through said passages to the casing outlet.

3. A turbo-expander comprising a casing having front and rear walls connected by an encircling side wall forming a toroidal chamber provided with an inlet for cold high pressure gas, the front wall of the casing having a central outlet opening therein, the rear wall of the casing having a central opening therein, an overhung shaft rotatably mounted in said rear opening and extending forward into the casing, a

bladed expander wheel rigidly mounted on the shaft in the casing for receiving gas from said chamber and delivering it to said outlet at a lower pressure and temperature, a forwardly tapered retaining member mounted on the front end of the shaft for holding said wheel thereon, and a seal connected to said rear wall and encircling the shaft to reduce leakage of gas from the casing rearwardly along the shaft, the shaft being provided with radial passages extending inward from points between the ends of said seal, and said retaining member and shaft being provided with an axial passage connecting the inner ends of the radial passages with said outlet.

ARTHUR W. McCLURE.

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

UNITED STATES PATENTS Number Name Date 1,328,286 McClave Jan. 20, 1920 1,750,818 Sauveur Mar. 18, 1930 2,165,994 Zerkowitz a.. July 11, 1939 2,280,585 Kapitza Apr. 21, 1942 2,442,489 Frei June 1. 1948