Title of Invention

"A PRESSURE REDUCING AND DESUPERHEATING VALVE"

Abstract This invention relates to an improvement on a combined pressure reducing and desuperheating valve, used in steam turbine bypass applications in power plants. The valve includes concentric blind (straight) holes drilled in the spray nozzle body and each of such hole terminating with angular holes leading to spray. The top cover of valve is split into bonnet and spray nozzle body. Jetcage holes are distributed in such a way that the injection water does not impinge on valve seat. A water line connection to the bonnet is connected by sturdy flanged type. Gland flange and gland bush have been improved with spherical contact surfaces for self-aligning.
Full Text FIELD OF INVENTION
The present invention relates generally to a combined pressure reducing and desuperheating valve for steam turbine bypass application in power plants. In particular the invention relates to an improved pressure reducing and disuperheating valve used for steam turbine bypass application in power plants.
BACKGROUND OF THE lNVENTION
In power plants working on Rankine thermodynamic cycle using reheat and regeneration methodologies, the reheater of the boiler is fed with steam expanded and exhausted from the high pressure (HP) turbine. Whenever the HP turbine is not in operation, there will be no steam flow to the reheater. This situation is likely to occur during cold start-up or turbine trip. If there is no steam flow through the reheater, it will be necessary to shut down the boiler to safeguard reheater tubes form excessive metal temperature.
Alternately, steam flow through the reheater is necessary to protect the tubes from overheating. This is achieved by connecting the main steam line and the cold reheat line through a HP bypass system or turbine bypass (throttle) valve. Thus the combined pressure reducing and desuperheating valve has an application for bypassing steam turbine in power plants. Such applications are encountered for bypassing of steam through HP bypass system during cold startup, turbine trip-out, parallel operation, house load, sliding pressure, and hot/warm start-up operations.

Whenever turbine trips, the steam suppfy to turbine is totally cut off from the main steam line. A controlled quantity of the high pressure and high temperature steam is passed through HP bypass system, where the pressure of the steam is reduced by throttling and temperature of the steam is conditioned by spraying and mixing of warm water. The comparatively cold steam at lower pressure and lower temperature is passed through reheat to prevent any overheating of the reheater coils. After the turbine trip outs are over, HP bypass system can be closed and the high pressure and high temperature steam in the main steam line can be made available at appropriate temperature and pressure for quick restart of the turbine.
US Patent 4,278,619 of July 14 1981 provides a steam throttle valve with thin walled water supply duct.
The cooling water discharge to the valve for desuperheating purpose is through the thin walled hollow member, which is located between the valve cage and cover (spindle guide) with injection ducts for directing cooling water into the flow chamber. The ducts are formed in the top cover. A number of holes are drilled on the cage which makes the flow passage for water to enter the valve. At the point of water injection, the space available is very less and hence improper mixing of water with steam takes place.
Top enclosure and steam guide of the valve is a single member named as cover. In case of erosion / damage of ducts, the cover is to be replaced with a new one.
The spray water connection to the valve is done by bolting of flange with the cover. This flange is further welded with spray water piping. In case of threads failure in cover due to frequent tightening / loosening of flange bolts, the top cover is to be replaced with a new one.
Cage of the valve is having multi holes drilled on the circumference uniformly. These holes are equidistant holes, which extend to the bottom of the cage (i.e., there are holes at the vicinity of valve seat). With this construction, there is possibility of water impinging over valve seat.
Top flange and stem guide at cover (top end) is a single member named as gland bush. This gland bush is inserted over the gland packing. Bolts are inserted through top flange to the cover and tightened to avoid leakage through gland. In case of uneven seating of gland bush over the gland packing, the tightening forces will not be uniform and hence possibility of gland leaks.
US Patent 4,66,833January 4,1983 discloses a throttle valve with ducts In the form of grooves in the flange.
The cooling water discharge to the valve for desuperheating purpose is through a contact surface and a plurality of ducts that are formed between the cage and top cover (spindle guide). A number of semi cylindrical holes are formed on the cage. Outer edges of these holes are covered by top cover, thus forming passages for supply of water to the valve. The drilling of semi cylindrical holes in cage is a difficult process in manufacturing. Here also at the point of water injection, the space available is very less resulting in improper mixing of water with steam.
Top enclosure and steam guide of the valve is a single member named as cover. In case of erosion / damage of ducts, the cover is to be replaced with a new one.
The spray water connection to the valve is done by bolting of flange with the cover. This flange is further welded with spray water piping. In case of threads failure in cover due to frequent tightening / loosening of flange bolts, the top cover is to be replaced with a new one. Other problems like replacement of the composite top cover, water impinging over valve seat and uneven seating of gland bush over gland packing resulting in gland leaks are also encountered in the throttle valve of US Patent 4,366,833.
SUMMARY OF THE INVENTION
The main object of the present invention therefore, is to provide a combined pressure reducing and desuperheating valve using a simple process of manufacture having sufficient space at the point of water injection in the middle portion of the jet cage for thorough mixing of steam and water.
Another object of the present invention is to provide a combined pressure reducing and desuperheating valve with reduced maintenance cost in replacing the top cover.
One more object of the present invention is to provide a combined pressure reducing and desuperheating valve where there is no possibility of water impinging over the valve seat.
In a preferred embodiment of the present invention, the water spray is arranged in the middle portion of the jet cage which is voluminous thus allowing through and effective mixing of steam and water. Concentric blind (straight) holes are drilled in the spray nozzle body for connecting spray water passage into the valve down stream.
In order to prevent direct impingement of cold water on valve seat, the blind holes are terminated at the end with the angular holes. An added advantage of the angular holes is that they further improve the mixing of steam and water in the middle portion of the jet cage.
In an advantageous refinement of the invention, for reducing the maintenance cost of replacement of the top cover, it is split into two parts, one forming the bonnet of the valve and the other the spray nozzle body. The bonnet serves as the top cover and the spray nozzle body for supplying spray water and as a stem guide. In case of erosion of the holes only the spray nozzle body need to be replaced without having to replace the entire top cover.
In another advantageous refinement of the present invention, the cost of replacing the spray water flange is reduced by welding the spray water flange with the bonnet, which connects the spray water piping with fastening of a mating flange. In case of threads failure in spray water flange, due to frequent tightening / loosening of flange bolts, the spray water flange alone can be replaced without replacing the entire cover.
A further advantageous feature of the present invention is to ensure that no
uncooled steam can escape near the valve seat. Also it is desirable to ensure atomization and quicker evaporation inside valve downstream side. This can be achieved by redistributing the holes in the jet cage in such a way that the injection water does not impinge on valve seat and there are no holes at the vicinity of the valve seat. This ensures that no uncooled steam can escape near the valve seat. This is provided to improve atomization and quicker evaporation.
Another advantageous refinement of the present invention is providing self-alignment between gland bush and gland flange and to provide a spherical mating surface between the gland flange and gland bush. This is, achieved by splitting the top flange into gland flange and gland bush and providing spherical mating at the gland flange and gland bush. The gland flange is fastened to the bonnet with the help of hexagonal bolts. Since there are spherical mating surfaces on the gland flange and gland bush, self-aligning takes places, which eliminates uneven tightening of bolts. With this self-aligning of the gland flange and gland bush, gland leaks are eliminated.
Thus the present invention provides a pressure reducing and desuperheating valve comprising a jet cage with a plurality of holes provided around its circumference for passage of pressure reduced and temperature reduced steam, a valve top cover arranged over said jet cage a valve stem seating on valve seat for controlling the pressure and flow of steam and a spray water flange for supplying water through a plurality of holes for reducing the temperature of steam by mixing water with steam in the space inside said jet cage characterized in that said space inside said jet cage is arranged as a
voluminous space in the middle portion of said jet cage sufficient for thorough
mixing of steam with sprayed water and said plurality of concentrio holes drilled
and distributed in a spray nozzle body and provided with angular holes such that
the injection of concreting holes drilled and distributed in a spray nozzle body
and provided with angular holes such that the injection of cold water does not
impinge on said valve seat.
These and other advantageous features of the present invention will be apparent from the description that follows which should be read in conjunction with the accompanying drawing where
Figure 1 shows an elevational cross -sectional view of the valve according to the present invention.
DETAILED DESCRIPTION
Figure 1 is cross-sectional elevation of a combined pressure reducing and desuperheating valve of the present invention. The valve is provided with a jet cage 15 having a plurality of jet cage holes 16.
Water is sprayed in a voluminous space 5 is arranged in the middle portion of the jet cage 15 through a plurality of blind or straight holes 12 drilled in spray nozzle body 14. Steam enters the space 5 through steam passages 4 or grooves 4 formed on valve stem 3 and the opening between valve seat 2 welded on to valve body and valve stem 3.
Steam which when passed through these grooves or passages 4 get throttled to the downstream side of the valve.
This allows through mixing of steam and water in the voluminous space 5.
The other end of stem 3 is having threads to connect with the actuator piston rod, via a coupling. This stem 3 is guided at valve seat 2, spray nozzle body 14, guide bush 18 and gland bush 20.
The blind holes 12 can be terminated with angular holes 13 so that direct impingement of cold water from the spray on seat 2 can be prevented.
In a preferred embodiment of the present invention the valve top cover is split into two parts. A bonnet 7 serving as the valve cover and a spray nozzle body 14, as mentioned earlier serves to supply spray water, in addition to acting as the guide for valve stem 3. In case of erosion of holes 12 in the spray nozzle body 14, the spray nozzle body can be replaced without the necessity to replace the entire valve top cover.
In another preferred embodiment of the invention a spray water flange 6, which connects the spray water piping with fastening of a mating flange, is welded on to the bonnet 7. In case of failure of threads due to frequent tightening / loosening of flange bolts, only the spray water flange 6 need to be replaced and not the entire cover.
Jet cage 15 and spray nozzle body 14 is fastened to bonnet 7 by studs and nuts.
Bonnet 7 is having spray water passage 9, which is horizontal and passage 10, which is vertical. These passages are connected to an annulus 11 of spray nozzle body 14. This annulus 11 is connected by many concentric blind-drilled holes 12. Each drilled hole 12 is opened by small angular drill hole 13.
Bonnet flange 6 is welded to bonnet 7, matching passages 8 and 9. Gland bush 20 with gland flange 21 compress the packing 19, thereby arresting the leakage through gland. Gland flange 21 is fastened to bonnet 7 by hexagonal bolts 22, which provide enough compression force.
A brief description now follows for the operation of the valve. As shown in Fig.l, the valve is in closed position. Valve stem 3 ensures leak tightness against valve seat 2 by actuator force. Steam force always tries to open the valve. Whenever the stem 3 moves up, steam throttles through many grooves 4 in the stem 3. At space 5, pressure of steam is less due to throttling effect.
For reducing the temperature, spray water is sprayed through many holes 13. Spray water enters through the spaces 8, 9,10 and 11 and sprayed into space 5 through the holes 12 and 13 in the spray nozzle body 14. Since the size of holes 13 is smaller than size of holes 12, jet action is created and the spray water is sprayed as fine particles. This reduces the temperature of the stem.
Pressure and temperature reduced steam leaves the space 5 through many small holes 16 of the jet cage 15 and reaches the space 17 of downstream side, thus bypassing the steam from main steam line pipe to cold reheat line pipe.
The foregoing description illustrates the preferred embodiments of the present invention. It is to be understood that modifications / additions can be made by one skilled in the art without departing from the spirit and scope of the invention.




WE CLAIM:
1. A pressure reducing and desuperheating valve comprising
a jet cage with a plurality of holes provided around its circumference for passage of pressure reduced and temperature reduced steam; a valve top cover arranged over said jet cage; a valve stem seating on valve seat for controlling the pressure and flow of steam;
a spray water flange for supplying water through a plurality of holes for reducing the temperature of steam by mixing water with steam in the space inside said jet cage; characterized in that said space (5) inside said jet cage (15) is arranged as a voluminous space in the middle portion of said jet cage (15) sufficient for thorough mixing of steam with sprayed water and said plurality of concentric holes (12) drilled and distributed in a spray nozzle body (14) and provided with angular holes (13) such that the injection of cold water does not impinge on said valve seat (2).
2. The valve as claimed in claim 1, wherein said valve top cover is
split into two parts, a first part forming a bonnet (7) as a top
cover of the valve and a second part forming a spray nozzle
body (14) for supplying spray water.
3. The valve as claimed in claims 1 or 2, wherein said spray nozzle
body (14) also serves as a guide for said valve stem (3) through
of top flange (21).
4. The valve as claimed in preceding claims, wherein said spray water flange (6) is welded on to said bonnet (7), such that in case of failure only spray nozzle body (14) need to be replaced.
5. The valve as claimed in preceding claims, wherein the top flange for the valve stem (3) is split into a gland flange (21) and gland bush (20) with spherical mating surfaces (23) for making said gland flange and said gland bush self-aligning.
6. The valve as claimed in preceding claims, wherein said angular holes (13) are smaller in size than said straight holes (12), thus creating a jet action for effectively reducing the temperature of steam.
7. A pressure reducing and desuperheating valve substantially as herein described and illustrated in the accompanying drawing.

Documents:

70-del-2003-abstract.pdf

70-del-2003-claims.pdf

70-del-2003-complete specification (granted).pdf

70-del-2003-correspondence-others.pdf

70-del-2003-correspondence-po.pdf

70-del-2003-description (complete).pdf

70-del-2003-drawings.pdf

70-del-2003-form-1.pdf

70-del-2003-form-19.pdf

70-del-2003-form-2.pdf

70-del-2003-form-3.pdf

70-del-2003-form-4.pdf

70-del-2003-form-5.pdf

70-del-2003-gpa.pdf


Patent Number 243954
Indian Patent Application Number 70/DEL/2003
PG Journal Number 47/2010
Publication Date 19-Nov-2010
Grant Date 11-Nov-2010
Date of Filing 28-Jan-2003
Name of Patentee BHARAT HEAVY ELECTRICALS LIMITED
Applicant Address SIRI FORT, NEW DELHI-110 049,INDIA
Inventors:
# Inventor's Name Inventor's Address
1 DAKSHINAMURTHY KRISHNAMURTHY BHARAT HEAVY ELECTRICLA LTD. BHEL HOUSE, SIRI FORT NEW DELHI-110049 INDIA
2 PERIASAMY LOGANATHAN C/O BHARAT HEAVY ELECTRICALS LIMITED, BHEL HOUSE, SIRI FORT, NEW DELHI-110 049,INDIA
3 NATARAJAN RAJASEKAR C/O BHARAT HEAVY ELECTRICALS LIMITED, BHEL HOUSE, SIRI FORT, NEW DELHI-110 049,INDIA
PCT International Classification Number F16K31/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA