US3312064A

US3312064A - Steam control apparatus

Info

Publication number: US3312064A
Application number: US444363A
Authority: US
Inventors: John D Dickinson; Lawrence K Koering
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1965-03-31
Filing date: 1965-03-31
Publication date: 1967-04-04
Anticipated expiration: 1984-04-04

Description

April 4, 1967 J. D. DICKINSON ETAL 3,312,064

STEAM CONTROL APPARATUS Filed March 31, 1965 INVENTORS John D. Dickinson and Lawrence K. Koering' United States Patent Ofitice 3,312,064 Patented Apr. 4, 1967 3,312,064 STEAM CONTROL APPARATUS John D. Dickinson, Springfield, Pa., and Lawrence K.

Koering, Elk Township, Ewan, N.J., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Mar. 31, 1965, Ser. No. 444,363 6 Claims. (Cl. 60-64) This invention relates to steam control apparatus, more particularly to apparatus for controlling and regulating the temperature of superheated steam by water injection, and has for an object to provide improved apparatus of this type.

In steam turbine power plants, gland structure encompassing the rotor shaft of a low pressure turbine expanding steam to a sub-atmospheric pressure is provided in the turbine housing to minimize leakage of atmospheric air past the shaft into the turbine exhaust area. In order to enhance the sealing characteristics of the gland structure, steam at a higher pressure than the internal steam pressure is introduced to the gland structure. The sealing steam may be taken from any suitable source. However, for economic reasons it is usually taken from a higher pressure and temperature region in the steam turbine cycle and cooled to the required temperature range by water spray before admission to the gland structure.

During operation, due to varying load on the power plant, the temperature of the gland supply steam may vary considerably, and if the temperature of the supply steam falls to a value below that required by the gland, or if an excess of water is injected into the steam line due to malfunction of the water injection control system, the

thermal shock on the turbine rotor shaft occasioned by the excessive cooling effect of the undesirably low temperature steam or slugs of water can cause warping of the turbine rotor shaft with attendant possibility of serious damage due to resulting vibration of the rotor and/ or blade rubbing.

Accordingly, it is an object of the invention to provide apparatus for regulating the temperature of steam to a steam turbine rotor gland structure by water injection and effective upon drop in temperature of the gland structure to a predetermined or unsafe value to automatically take corrective action and/ or initiate an alarm indicating such unsafe condition.

A further object is to provide apparatus of the foregoing type wherein the corrective action is effected by an emergency water valve structure in the event of malfunction of a primary water control valve and/or its as! sociated controls.

Another object is to provide apparatus for regulating the temperature of steam to a steam turbine rotor gland structure by Water injection and elfectiveupon rise in temperature of the gland structure to a predetermined or unsafe temperature to automatically take corrective action and/or initiate an alarm indicating such unsafe condition.

Briefly, in accordance with the invention, there is provided a primary valve for regulating the rate of water injection into a steam supply conduit for a turbine rotor gland structure in such a manner that the steam is cooled to a temperature range suitable for sealing the gland structure. This valve is controlled by a first thermostatic means responsive to temperature of the gland structure.

There is also provided a secondary valve for overriding the primary valve and effective to assume control of the water injection in the event of malfunction of the primary valve system causing a drop in temperature of the gland structure to a predetermined or unsafe value. The secondary valve is controlled by a second thermostatic means and is normally in the open or unblocking position but is movable to the closed or blocking position upon such drop in temperature.

The second thermostatic means is also effective to initiate an alarm upon rise in temperature to a predetermined or unsafe value, thereby alerting an attendant to such condition.

The above and the objects are effected by the invention as will be apparent from the following description and claims taken in connection with the accompanying drawings, forming a part of this application, in which:

The sole figure is a diagrammatic view illustrating a steam turbine gland structure equipped with sealing steam control apparatus in accordance with the invention.

Referring to the drawing in detail, there is shown a fragmentary portion of a steam turbine comprising a housing generally designated 10 having a circular aperture 11 provided therein through which a turbine rotor shaft 12 extends. The aperture 11 is considerably larger in diameter than that of the rotor shaft 12 and there is further provided a gland structure generally designated 14 which gland structure may be of any suitable and well known design or type. As well known in the art, the housing 10 defines an exhaust space 15 and, in operation, steam employed to motivate the rotor shaft 12 fills this space after expansion. The rotor shaft 12 is also only fragmentally shown, however, as well known in the art, it is provided with the usual turbine blades (not shown) for expanding and extracting energy from the steam to drive the rotor shaft 12 for power generation purposes. Since the steam pressure within the housing 10 is lower than that of the atmosphere externally of the housing, the gland structure 14 is employed to minimize or restrict the leakage of atmospheric air along the shaft 12 through the aperture 11 to the space 15, as well known in the art.

The gland structure 14 is of generally circular cross sectional shape. Accordingly, no cross sectional view thereof is shown or is thought to be required for comprehension. The gland structure 14- is provided with wall structure 14a defining a first space 16 and a second space 17 of generally annular shape and separated from each other by

annular wall structures

18, 19 and 20 jointly defining an axially extending opening 21 of slightly larger diameter than that of theshaft 12. The opening 21 is substantially restricted by a plurality of

labyrinth seal members

23, 24, 25 and 26 disposed in slightly radially spaced relation with the outer circumference of the shaft 12. Accordingly, it will be understood that leakage along the outer surface of the shaft 12 is substantially minimized but not absolutely prevented.

To prevent the flow of air from the atmosphere along the shaft 12 to the inside of the housing, there is pro vided a steam supply conduit 27 for admitting sealing steam into the space 16 at a sufliciently high pressure to oppose the atmospheric air pressure. The steam conduit 27 is provided with a suitable connecting ferrule 28 to provide a leakproof connection at the gland 14.

The gland walls 18, 19 and 21) are disposed in axially spaced relationship with each other. Hence, as the sealing steam flows into the space 16, it is free to move along the shaft 12 in two directions. More specifically, it is allowed to flow through the

labyrinth seal structures

24 and 23 into the housing and also along the shaft 12 beyond the seal structure 25 and thence into the space 17. The gland 14 is further provided with an outlet conduit 29 disposed in communication with the space 17. The conduit 29 is connected to a suitable region of lower pressure than that of the space 17 and the external atmosphere so that preferential flow of steam from the space 17 is established through the conduit 29 to the region of lower pressure. Accordingly, as well known in the art, the leakage of this sealing steam beyond the labyrinth seal 26 to the external atmosphere is prevented.

Steam for sealing the gland structure may be obtained from any suitable supply. However, for economic and expediency reasons it is usually provided from a region in the steam turbine cycle operating at a higher temperature and pressure value than that of the steam within the turbine housing 10. Accordingly, such steam is directed into the conduit 27, as indicated by the arrow 30, at a higher temperature value than required or desired, and is reduced to the required degree before admission to the gland space 16. More particularly, the temperature of the sea ing steam in the gland space 16 must be at a higher value than that of the steam within the turbine housing, thereby to minimize the possibility of condensation and consequent erosion of the turbine rotor 12 and

gland seals

23, 24, and as well as shock upon the rotor shaft 12 by sudden and localized chilling thereof with the possibility of warping. Hence, it is essential that the temperature of the sealing steam be maintained above a minimum safe value so that the formation of moisture or condensate in the gland structure 14 is prevented. It is also essential to insure that the temperature of the steam be maintained below a predetermined safe value to prevent overheating of the shaft 12.

In accordance with the invention, there is provided apparatus for reducing the temperature of the steam within an acceptable range including a minimum safe value and arnaximum safe value. This apparatus includes an injector or spray nozzle 32 disposed within the conduit 27 and connected to a suitable supply of water (not shown) by suitable conduits 33 and 34-. There is further provided a primary value structure '36 disposed in the conduit and arranged in a manner to control the rate of flow of water through the

conduits

34 and 33 to the injector 32, thereby to vary the amounts of liquid injected into the conduit 27 with attendant vaporization of the liquid and cooling of the steam to the desired degree in a manner which will hereinafter be more fully described.

As illustrated, the value 36 is of the pneumatically actuated diaphragm type and is spring biased to the open or unblocking position but is movable towards the closed or blocking position in response to the pressure of air admitted thereto. Hence, in the event of failure or malfunction, the valve will tend to move to the open position, thereby permitting the water to flow to the injector 32 at maximum rate.

There is provided a secondary valve structure 38 disposed downstream of the valve 36 in the conduit 33. This valve structure, as illustrated, is also of the same pneumatically operabe diaphragm type as valve 36, but is biased to the blocking position. Hence, in the event of failure of this valve, liquid to the injecting nozzle 32 would be interrupted, even though the valve 36 is in the fully open position. In normal operation, the secondary valve 38 is maintained in the open position by pneumatic fluid pressure acting thereon and directed thereto by a conduit 39.

There is further provided an emergency valve structure 40 interposed in the conduit 39 for controlling the fluid flow to the valve structure 38. This valve structure 40, as illustrated, is of the electrically actuated type and is provided with a solenoid structure 41 for actuation. The valve structure 40 is provided with a venting port 42 for bleeding the air trapped in the conduit 39 to the atmosphere, as indicated by the arrow 43, through an outlet 44, and the valve is so designed that in normal operation (without energization) the venting port 42 is blocked and fluid from a conduit 45 is directed through the valve structure 40 to the conduit 39. Fluid (such as air) for actuating the valves 38 and 36 is admitted into the system from any suitable supply (not shown) by a conduit 46 having a filter F interposed therein and branching downstream therefrom into a branch conduit 47 leading to the valve structure 40 and a branch conduit 48 leading to the conduit 37 by way of a conduit 49 and a suitable variable air pressure controlling structure 50. The air supplied to the conduit 46 may vary in pressure within a wide range. Accordingly, there are provided pressure regulating valves 51 and 52 in the conduits 48 and 47, respectively to maintain the pressure of the air to the

valve structures

33 and 36 at constant prescribed operating pressure levels.

The pressure controller 50, as illustrated, is provided with a nozzle 53 interposed between the

conduits

49 and 37 and having a restricted outlet 54 disposed in close proximity to a Bourdon tube structure 55. As wellknown in the art, the controller 50 is effective to modify the pressure of the air elivered to the valve 36 by movement of the Bourdon tube 55 towards or away from the nozzle outlet 54, thereby varying the rate of bleeding of the air to the atmosphere.

Within the gland 14 there is provided a thermal sensing device 57, which, as illustrated, is of the vaporizable liquid filled bulb type, connected to the Bourdon tube 55 by a suitable capillary tube 58. In operation, as the sensing bulb 57 becomes heated, the vapor pressure formed therein is effective to distend the Bourdon tube 55 to a corresponding degree, thereby controlling the rate of bleed through the nozzle outlet 54 and the pressure acting on the valve 36, in a manner well known in the art.

In operation, as thus far described, the apparatus is effective to control the rate of water injection into the conduit 27 as follows. Assuming the steam turbine is of the low pressure type in which the temperature of the steam within the space 15 is normally maintained between 60 F. and 100 F., so that the average is about F., it is desired to maintain the temperature of the sealing steam admitted to the gland space 16 within a minimum and maximum safe range, for example 250 to 350 F. Accordingly, the thermal sensing bulb 57 is effective to sense the temperature of the steam in the space 16 and to regulate the Bourdon tube 55 in a manner to control the pressure of the air delivered through the conduit 37 to the primary valve 36, in such a manner that the primary valve structure 36 is effective to regulate the flow of liquid therethrough to the water injector 32 at the rate required to maintain the temperature of the sealing steam within this range. More particularly, should the value of the steam in the space 16 approach the maximum safe value of 350 F., the increased vapor pressure of the thermal sensing bulb 57 is effective to distend or flex the Bourdon tube away from the nozzle outlet 54, thereby bleeding more air to atmosphere and reducing the pres sure in the valve structure 36. The valve 36 is thus pef= mitted to move to a more open position thereby increas ing the rate of Water injection by the injectior 32, cooling; the steam flowing therepast to a greater degree, and there by reducing the temperature of the sealing steam in the space 16.

Conversely, should the temperature of the sealing steam in the space 16 approach the minimum safe value of 250 F., the reduced vapor pressure in the thermal sensing bulb 57 will permit the Bourdon tube 55 to contract, thereby restricting flow of the air through the outlet conduit 54 and building up the pressure of the fluid through the conduit 37 to the valve 36. Accordingly, the valve 36 is urged toward the closed or blocking position, thereby restricting the flow of the liquid therethrough to the injector 32 and permitting the temperature of the steam in the space 16 to rise.

During such operation, the air pressure in the conduit 47 and the valve 40 is effective to maintain the secondary valve 38 in the open position and permit the water to flow therepast under the control of the primary valve 36.

However, in the event of malfunction of the pressure controller 50 or the primary valve structure 36, for any reason, the valve 36 will be urged to the wide open position by its spring bias and thereby be ineflective to regu late the flow of water to the injector 32 as required.-

Should this happen, the rate of water injection may be so excessive that water droplets might be directed through the space 16 and the seals to the shaft structure 12 with attendant sudden thermal shock to the shaft structure and localized chilling causing bowing or warping thereof.

Accordingly, there is further provided a second thermal sensing device 60 disposed in the space 16 and etfective to sense the temperature of the steam therein. As illustrated, the thermal sensing device 60 is of the ditferential expansion type and includes a tubular shell structure 61 having an elongated rod 62 disposed therein. The shell structure 61 is rigidly fastened to the gland structure 14 in any suitable manner and the free end of the rod 62 extends into abutment with a switch lever 63 provided in an electrical control device 64. The lever 63 is fulcrumed at 65 intermediate its two ends and is provided with three sets of electrical contacts 66, 67 and 68 movable into and out of abutment with

stationary mating contacts

69, 70 and 71. The stationary contacts 70 and 71 are disposed above the lever 63, while the stationary contact 69 is disposed below the lever 63. The lever 63 is biased into abutment with the elongated rod 62 by a suitable spring 72 and in normal operation (within the minimum and maximum safe temperatures) the movable contacts are disposed in spaced relation with the stationary contacts, as illustrated.

The shell structure 61 has a greater thermal expansion coefiicient than that of the rod 62, so that with a rise in temperature of the space 16 the rod 62 will move in upward direction, thereby permitting the lever 63 to rotate clockwise while, when the temperature within the space 16 falls the rod 62 will move downwardly and is eifective to rotate the lever 63 in the opposite direction or towards the stationary contacts 70 and 71. The thermal sensing device 60 and the electrical control 64 are so arranged and calibrated that upon rise in temperature of the steam in the space 16 to above the safe value of 350 F., the contact 66 is moved into abutment with the contact 69 and conversely, when the value of the steam in the space 16 falls to the minimum safe value of 250 F. the contacts 67 and 68 are moved into abutment with the stationary contacts 70 and 71.

The solenoid 41 of the emergency valve 40 and electrical alarm devices 74 and 75 are interconnected in electrical circuitry which is energized from any suitable electrical supply, as indicated by the conductors '76 and 77, and controlled by the control device 64. The movable contacts 67 and 68, as well as the stationary contact 69, are connected in parallel to the conductor 77, and the solenoid 41 is interconnected between the stationary contact 71 and the conductor '76 by a pair of

suitable conductors

78 and 79. The electrical alarm 75 for example, a lamp, is connected to the stationary contact 70 and to the conductor 76 by suitable conductors 80 and 81. Hence, it will be seen that the lamp 75 and the solenoid 41 are disposed in parallel with each other and arranged in such a manner that when the switch lever 63 is rotated in counterclockwise direction by the thermal sensing rod 62 in response to a reduction in steam temperature in the space 16, circuits are established jointly through the solenoid 41 and the lamp 75. During such conditions, the solenoid is energized to actuate the emergency valve 40 to the air blocking position, thereby interrupting the flow of air from the conduit 47 to the valve 38 andpermittmg the air trapped in the valve 38 and the conduit 39 to be vented to the atmosphere through the outlet 44. S multaneously therewith, the lamp 75 is energized to provide a visual warning of such an event.

It will also now be seen that when the switch lever 63 is rotated in the clockwise direction by the elongated rod 62 in response to a steam temperature within the space 16 of above 350 F., the movable contact 66 is moved into abutment with the stationary contact 69, thereby interrupting the circuit through the solenoid 41 and the lamp 75, and establishing a circuit through the alarm device 74, for example, a bell, to provide an audible warning of such event.

More specifically, in the event of failure of the primary system and movement of the primary control valve 36 to the Wide open position with attendant greatly increased flow of water injection into the steam conduit 27, as previously described, the temperature of the resulting steam in the space 16 may rapidly fall below the minimum safe value of 250 F. This condition is sensed by the thermal sensing device 60, with attendant establishment of the circuit through the solenoid 41 to effect movement of the valve 38 to the water flow blocking position, thereby interrupting flow of the water to the injector 32, and initiation of a visible alarm to the operator of such a state or condition, by energization of the lamp 75.

In the event that, for any reason, the emergency valve structure 40 should fail to operate as required, the valve 38 may move to the blocking position, thereby interrupting the flow of water to the injector 32 with attendant rise in temperature of the sealing steam in the space 16. Should such an event occur, the thermal sensing device 68 is effective to move the switch lever 63 in clockwise direction thereby establishing a circuit. through the alarm 'bell 74 to provide a warning to the operator of such a condition.

In such an event it might be necessary to shut down the apparatus or take any other steps that are necessary to remedy the situation.

If desired, the conduit 34 may be provided with a pair of suitable normally open manually operated valves 82 and 83 and a bypass line 84 having a normally closed manually operated valve 85 may be provided to circumvent the primary valve 36. During an emergency where in the valve 36 fails in the open position and the valve 38 fails in the open position, the flow of water to the injector 32 may be regulated by either the valve 82 or 83, as required. However, in the event that it is desired to repair the valve 36 while maintaining the sealing steam and gland structure in operation, the two valves 82 and 83 may be rotated to the blocking position and the water injection may then be controlled manually by regulation of the valve 85 in the bypass line 84.

Although only one embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without de parting from the spirit thereof.

We claim as our invention:

1. Apparatus for regulating the temperature of steam for sealing a steam turbine gland structure, comprising means including a conduit connected to said gland structure,

means for admitting steam to said conduit at a temperature higher than required by said gland structure, means for injecting water into said conduit to cool said steam,

primary means including a primary thermostatically controlled valve for regulating the rate of water in jection in a manner to cool the steam to a predeter mined range of temperature including a maximum safe temperature and a minimum safe temperature, and

secondary means including a secondary thermostaticab ly controlled valve for interrupting the water injection in the event that the steam temperature falls below said minimum safe temperature.

2. The structure recited in claim 1 and further includ means responsive to a temperature exceeding the maximum safe temperature for initiating an alarm.

3. The structure recited in claim 1, and further including primary thermal sensing means for controlling the primary valve,

secondary thermal sensing means for controlling the secondary valve, and

means actuated by said secondary thermal sensing means for initiating an alarm signal indicative of a steam temperature exceeding the maximum safe temperature.

4. Apparatus for regulating the temperature of steam for sealing a turbine gland structure, comprising means including a first conduit for delivering steam to said gland structure;

means for admitting steam to said first conduit at a temperature higher than required by said gland structure;

means including a second conduit for injecting water into said first conduit to cool said steam;

a primary system for controlling the rate of water injection in a manner to cool the steam to a predetermined range of temperature including a maximum safe temperature and a minimum safe temperature;

said primary system including a first valve disposed in said second conduit;

means including first thermal sensing means for detecting the temperature of said gland structure and effective to control the degree of opening of said first valve;

a secondary system for overriding said first system in the event of malfunction of the latter;

said secondary system including a normally open second valve disposed in said second conduit; and

means including a second thermal sensing means for detecting the temperature of said gland structure and effective to actuate said second valve to the closed position, when the temperature of the gland structure falls below the minimum safe temperature, thereby interrupting injection of Water.

5. The structure recited in claim 4, and further including means providing an alarm signal, and

means actuated by the second thermal sensing means to actuated said alarm means when the temperature of the gland structure exceeds the maximum safe temperature.

6. The structure recited in claim 4, in which the first and second valves are actuated by pressurized fluid, and further including third conduit means for delivering pressurized fluid to the second valve,

said second valve is normally maintained in the open position by the pressurized fluid, and

a solenoid valve disposed in said third conduit and electrically actuable from a fluid conducting position to a fluid blocking position when the temperature of the gland structure falls below the minimum safe temperature.

No references cited.

MARTIN P. SCHWADRON, Primary Examiner.

ROBERT R. BUNEVICH, Examiner.

Claims

1. APPARATUS FOR REGULATING THE TEMPERATURE OF STEAM FOR SEALING A STEAM TURBINE GLAND STRUCTURE, COMPRISING MEANS INCLUDING A CONDUIT CONNECTED TO SAID GLAND STRUCTURE, MEANS FOR ADMITTING STEAM TO SAID CONDUIT AT A TEMPERATURE HIGHER THAN REQUIRED BY SAID GLAND STRUCTURE, MEANS FOR INJECTING WATER INTO SAID CONDUIT TO COOL SAID STEAM, PRIMARY MEANS INCLUDING A PRIMARY THERMOSTATICALLY CONTROLLED VALVE FOR REGULATING THE RATE OF WATER INJECTION IN A MANNER TO COOL THE STEAM TO A PREDETERMINED RANGE OF TEMPERATURE INCLUDING A MAXIMUM SAFE TEMPERATURE AND A MINIMUM SAFE TEMPERATURE, AND SECONDARY MEANS INCLUDING A SECONDARY THERMOSTATICALLY CONTROLLED VALVE FOR INTERRUPTING THE WATER INJECTION IN THE EVENT THAT THE STEAM TEMPERATURE FALLS BELOW SAID MINIMUM SAFE TEMPERATURE.