US2419681A

US2419681A - Circulating pump sealing system

Info

Publication number: US2419681A
Application number: US517608A
Authority: US
Inventors: Gartmann Hans
Original assignee: Laval Steam Turbine Co
Current assignee: De Laval Steam Turbine Co
Priority date: 1944-01-08
Filing date: 1944-01-08
Publication date: 1947-04-29
Anticipated expiration: 1964-04-29

Description

April 29, 1947. ||.l GARTMANN 2,419,681

CIRCULATFNG PUMP SEALING SYSTEM Filed Jan. 8, -1944 2 sheets-sheet 2 NS s Patented Apr. 29, 1947 star T OFFICE CIRCULATNG P SEG SYSTEM Application January 3, 1944, Seriali No. 51.7,@@55

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This invention relates to a sealing system for a pump and. in particular, to a system for sealing against boiler pressure a pump used for eiecting forced circulation through a boiler. l

The packing oi a centrifugal pump used for circulating purposes in eonnection'with a forcedcirculation boiler presents very substantial difficulties in view of the fact that the suctionl of the pump is subjected to the high boiler pressure, and corresponding high temperature, and conventional packing will not withstand such pressures and temperatures. It is the broad object of the pres` ent invention to provide a system in which effective packing against high boiler pressures may be secured. Specifically, this is accomplished by the use oi' a combined labyrinth and carbon seal with control of pressures to insure that th'ere is applied to the carbon seal no more pressure than this seal is capable of withstanding, the sealing member being steam. Since steam has a much larger specific volume than water at the same temperature, the use of steam, as lcompared with that of water, in the conventional breakdown seal, results in decreased weight flow through the labyrinth seal.

The foregoing broad object of the invention and more specific objects relating particularly to details of construction andoperation will become apparent from the following description read in conjunction with the accompanying drawings, in which:

Figure l is a diagrammatic illustration of a boiler circulating pump and auxiliary devices involved in a system constituting a preferred em.- bodiment of the invention;

Figure 2 is a vertical section through a circu lating pump provided in accordance with the invention; and

Figure 3 is a similar View of a somewhat dierent type of pump in which the packing is effected in a diiferent fashion.

Referring first to Figures 1 and 2, therev is indicated at 2 the drum ofa boiler with which a circulating pump 6 is associated, this pump being arranged to receive water from the boiler through the connection 4 and to discharge the water through twin outlets 8 and I0 communicating, respectively, with tube systems I2 and I4 of the boiler which are connected at I6 and I8, respectively,"with the boiler drum. The boiler itself forms `no part of the present invention, and it maybe of any of the usual types involving forced circulation.

Feed water for Athe boiler enters at 20 a boiler feed pump 22 of centrifugal multistage type which may be turbine driven, utilizing steam from the boiler. It will be assumed, for purposes of description, that this feedpump is of a six-stage type inasmuch as in the present instance, a connection is made to an intermediate stage establishing a desired pressure conditoin. The feed water from the pump 22 passes through a check valve 2611i the line 2S to an economizer 28, whence it enters the boiler drum at 3B.

Steam from the boiler drum 2 is provided through the line 32 connected to a superheater 34 from which the steam passes through the line 38 to the point o use. For purposes of discussion, some figures for a typical installation vmay be cited. The boiler, for example, may be designed tov deliver steam at 975 lbs. per square inch and a temperature of 543 F. Under these conditions, the boiler feed pump may deliver water at 1150 ibs. per square inch at a temperature of 232 F., receiving the feed water, for example, at 50 lbs. per square inch at about the same temperature. Under these same conditions, the circulating pump may provide a pressure increase of 35 lbs. per square inch so as to introduce the circulating water to the boiler tube systems at 1010 lbs. per square inch and 543 F.

A carbon, or other seal of conventional type may be provided to withstand pressures of th'e order of 300 lbs. per square inch, and the present invention is designed to secure a pressure on such seal limited to that amount.

, Referring, particularly, to Figure 2 showing the circulating pump 6 in detail, this pump comprises an inlet passage 38 to which the line 4 connects, the inlet passage serving to provide flow of water to the inlet eye 4u of the impeller 42 which discharges into the chamber 44 communicating withI the twin discharge passages 46. The impeller may be located, for example, about 8 ft. below the level of water in the boiler drum so that the suction pressure involves a static head of about 8 ft. in addition to the boiler drum pressure. If, as illustrated, the pump impeller is of the singlesuction over-hung type with the water flowing downwardly therein, there is provided a. selfventing arrangement similar to that common at .the present time for low submergence condensate pumps. Under such conditions, the pump will operate without noise or cavitation. The impeller is mounted on a Vertical shaft 48 driven through reduction gearing 50, 52 from a turbine (not shown). In order to balance some of the upward thrust caused by the action of the boiler .pressure on the area of the shaft at the packing. the lower wearing ring assembly 54 is made 3 of greater diameter than the upper wearing ring assembly 56.

Connections 56 and 60 to the steam line 32 provide steam saturated at boiler pressure to the chamber 62 through which passes the shaft 48.

` From this chamber 62, flow of steam takes place both upwardly and downwardly. In flowing downwardly, it passes through the labyrinthine packing 63 to the chamber 64 which is connected through the passage B6 to the chamber 68 of a regulating valve involving a valve member 10A adapted to permit the bleeding of steam from the chamber 68 into the chamber 12 which is connected through the line 14 to the fourth stage of the six-stage boiler, feed pump as indicated at 16.-

In such fourth stage, for example, the pressure is about 785 lbs. per square inch. The connection to such an intermediate pressure point permits the pressure drop between the chambers 68 and 12.

from the chamber 62 to the region 64, there is` insurance against the possibility that any water from the pump will pass upwardly through the packing 18 into the chamber 80, so that the steam passing into the line 82 can contain only the small amount of moisture which may result from the expansion through the labyrinthine packing 18. By reason of the submergence of the impeller, the pressure at the suction is greater than the steam pressure bythe amount of submergence which, for example, may amount to about 21/2 lbs. per square inch. Since the pressure in connection 66 is maintained by the regulating valve below the pressure at the impeller eye, lwater will flow upwardly through the labyrinthine packing 65 into the chamber 64 to pass with the steam through the regulating valve.

The carbon packing indicated at 84 can withstand the pressure in the chamber 80. A connection 86 leads ofi the leakage of steam to a sump.

Cooling water for the lower bearing may be provided from the boiler feed pump through the connection 88'.

To insure the proper pressure in the line 66 at, for example, 965 lbs. per square inch, the regulating valve 10 is controlled by connection to a diaphragm 92 in a housing 94. The lower side of the diaphragm is exposed through the line 90 to steam which is at boiler pressure. The upper side of the` diaphragm is subjected to the pressure vin the chamber 68. A spring 95, adjustable through the medium of a screw 98, exerts the proper differential pressure on the diaphragm 92 so that in the example given, the pressure in 68 is always 10 lbs. per square inch less than the boiler pressure. A In this fashion, the pressure in the chamber 64 is maintained to insure a proper slow rate of flow both downwardly from the chamber -62 and upwardly from 4. wise being used in a system such as that shown in Figure 1. In this case, the pump |00 comprises the impeller |02 receivingwater at boiler pressure through the passage |04 and discharging it into the chamber |06 connected through one or more passages |01 to the tube systems of the boiler. Above the impeller is the chamber I|0 which is maintainedat a. pressure slightly lbelow the suction pressure by the provision of an auxiliary impeller |08 at the back of the regular pump impeller but slightly larger in diameter. Since this auxiliary impeller is of larger diameter and discharges into the same 'chamber |06 as' the impeller |02, it will beevident that this dif-- ference in pressure is secured. A connection ||2 -chamber I I6 downwardly through the packing ||8 to meet `the cooling water in ||0, whereby it is condensed so that the impeller |08 will handle water only to insure that it maintains the differential in pressure which is required.

Steam from the chamber I |6 may flow upwardly through the labyrinthine packing |20 to the chamber |22 where, as in the preceding modification, the pressure may be about 300 lbs. per square inch, capable of being withstood by the carbon packing |26 and of supplying auxiliaries through the connection |24. The steam drain outlet |28 may lead to a sump.

It will be clear from the above that loss of water at the high temperature and pressure of the boiler is either completely prevented or minimized to a negligible degree by the arrangements in accordance with the invention, this being effected by the use of a relatively small amount of steam usable for the driving of auxiliaries, while the pressure on carbon or similar packing is maintained within a limit which it is capable of withstanding. `It will be obvious that various changes in thel details of the invention may be made without departing from its scope as defined in the following claims.

What I claim and desire to protect by Letters Patent is:

1. In a forced-circulation boiler system, a'boiler, a centrifugal impeller, means connecting said impeller to the boiler for forced ,circulation of liquid through the boiler, a shaft mounting said impeller, packing for the shaft, said packing being of a type liable to damage at'boiler pressure, means providing a chamber about the shaft, means yconnecting said chamber to the vapor space oi' said boiler, means restricting iiow along the shaft between said-chamber and said packing thereby to reduce the pressure of vapor reaching the packing to a safe value substantially below that in said chamber, a second chamber about the shaft on the side of the first chamber opposite said packing, means for maintaining in the second chamber a pressure below both the pressure in the first chamber and the suction pressure of the impeller, and means for restricting ow along the shaft from the rst chamber to the second chamber, said arrangement preventing passage of liquid from the impeller to the first chamber.

2. In a forced-circulation boiler system, a

amasar boiler, a centrifugal impeller, means connecting said impeller to the boiler for forced circulation of liquid through the boiler, a shaft mounting said impeller, packing for the shaft, said packing being of a type liable to damage at boiler pressure, means providing a chamber about the shaft, means connecting said chamber to the vapor space of said boiler, means restricting flow along the shaft between said chamber and said packing thereby to reduce the pressure of vapor reaching the packing to a safe value substantially below that in said chamber, a second chamber about the shaft on the side of the iirst chamber opposite said packing, means for maintaining in the second chamber a pressure below both the' pressure in the first chamber and .the suction pressure of the impeller, said last mentioned means comprising a device for maintaining in the second chamber a pressure at a predetermined differential -below the boiler pressure, and means for restricting iiow along the shaft from the iirst chamber to the second chamber, said arrangement preventing passage of liquid from the impeller to the first chamber.

3. In a forced-circulation boiler system, a boiler, a centrifugal impeller, means connecting said impeller to the boiler for forced circulation of liquid through the boiler, a shaft mounting said impeller, packing for the shaft, said packing being of a type liable to damage at boiler pressure,

means providing a chamber about the shaft,

means connecting said chamber to thev vapor space of said boiler, means restricting flow along the shaft between said chamber and said packing thereby to reduce the pressure o f vapor reaching the packing to a safe Value substantially be` low that in said chamber, a second chamber about the shaft on the side oi the firstv chamber oppo, site said packing, means for maintaining in the second chamber a pressure below both the pressure in the first chamber and the suction pressure of the impeller, a multiple stage boiler feed pump, said last mentioned means comprising means controlling connections between the second chamber and an intermediate stage of the feed pump to control flow of fluid between the second chamber and the feed pump to maintain said required pressure, and means for restricting ow along the shaft from the first chamber to the second chamber, said arrangement preventing passage of liquid from the impeller to the first chamber.

4. In a forced-circulation boiler system, a boiler, a centrifugal impeller, means connecting said impeller to the boiler for forced circulation of liquid through the boiler, a shaft mounting said impeller, packing for the shaft, said packing being of a type liable to damage at boiler pressure, means providing a chamber about the shaft, means connecting said chamber to the vapor space of said boiler, means restricting flow along the shaft between said chamber and said packing thereby to reduce the pressure of vapor reaching the packing to a safe value substantially below that in said chamber, a second chamber about the shaft on the sideof the rst chamber opposite said packing, means for maintaining in the second chamber a pressure below both the pressure in the first chamber and the suction pressure of the impeller, a multiple stage boiler feed pump, said last mentioned means comprising means controlling connections between the secmined dierential below boiler' pressure, and means for restricting fiow along the shaft from the first chamber to the second chamber, said arrangement preventing passage of liquid from the impeller to the first chamber. V

5. In a forced-circulation boiler system, a boiler, a centrifugal impeller, means connecting said impeller to the boiler for forced circulation of liquid through the boiler, a shaft'mounting said impeller, packing for the shaft, said packing being of a type liable to damage kat boiler pressure, means providing a chamber about the shaft, means connecting said chamber to the vapor space of said boiler, means restricting flow along the shaft between said chamber and said packing thereby to reduce the pressure of vapor reaching' the packing to a safe value substantially below that in said chamber, a second chamber about the shaft on the side of the rst chamber opposite said packing, means for maintaining in the second chamber a. pressure below both the pressure in the rst chamber and the suction pressure of the impeller, said last mentioned means comprising an auxiliary impeller, and means for restricting flow along the shaft from the rst chamber to the second chamber, said arrangement preventing passage of liquid from the impeller to the first chamber.

6. In a forced-circulation boiler system, a boiler, a centrifugal impeller, means connecting said impeller to the boiler for forced circulation of liquid through the boiler, a shaft mounting said impeller, packing for the shaft, said packing being of a type liable to damage at boiler pressure, means providing a chamber about the shaft, means connecting said chamber to the vapor space of said bollen, means restricting ow along the shaft between said chamber and said packing thereby to reduce the pressure of vapor reaching the packing to a safe Value substantially below that in said chamber, a second chamber about the shaft on the side of the rst chamber-opposite said packing, means for maintaining in the second chamber a pressure below both the pressure in the rst chamber and the suction pressure of the impeller, said last mentioned means comprising an auxiliary impeller receiving iiuid from the second chamber and discharging into the same region as vthe main impeller, and means for restricting flow along the shaft from the iirst chamber to the second chamber, said arrangey ment preventing passage of liquid from the imond chamber and an intermediate stage of the peller to the rst chamber.

7. In `a forced-circulation boiler system, a boiler, a centrifugal impeller, means connecting said impeller to the boiler for forced circulation of liquid through the boiler, a shaft mounting said impeller, packing for the shaft, said packing being of a type liable to damage' at'boiler pressure, means providing a chamber about the' shaft, means connecting said chamber to the vapor space of said boiler, means restricting flow along the shaft between said chamber and said packing thereby to reduce the pressure of Vapor reaching the packing to a safe value substantially below that in said chamber, a second chamber about the shaft on the side of the first chamber opposite said packing, means for maintaining in the second chamber a pressure below both the pressure in the rst chamber and the suction pressure of the impeller, said last mentioned means comprising an auxiliary impeller receiving fluid from the second chamber and discharging into the same region as the main impeller, means for directing relatively cool feed water lventing passage of liquid from the impeller to the first chamber.

, HANS GARTMANN.

REFERENCES The following references are of record in the lo le of this patent:

Number UNITED STATES PATENTS Name Date Spilimann e- Jan. 27, 1942 Vorkauf Aug, 15, 1939 Verkauf Aug, 15, 1939 Zwilling Aug. 22, 1939 Beyer Jan. 1, 1935 Karassik Jan. 29, 1946