Claims:We claim:
1. An internal bypass mechanism for feed water heater (200), the feed water heater comprising:
a channel (40) having an inlet (20) and an outlet (30) configured thereon;
a shell (12) attached to the channel(40) through tubesheet (11) at one end;
a tube sheet (11) fitted in between the shell (12) and the channel (40);
a plurality of tubes (10) secured inside the shell (12), the plurality of tubes (10) having open ends welded to the surface of the tube sheet (11);
a nozzle (13) configured on the shell (12), the nozzle allows steam therein;
characterized in that,
a pass partition plate (50) having a cover (80) configured with an orifice (100) mounted diagonally inside the channel (40), wherein the pass partition plate (50) divides the channel (40) into an inlet chamber (42) and an outlet chamber (44) for the feed water;
a manway (90) configured on the channel (40), the manway (90) facilitates installation of the cover (80);
wherein the feed water enters into the channel (40) through the inlet (20), circulates through the plurality of tubes (10), accumulates into outlet chamber (44) and releases through the fluid outlet (30), and the steam extracted from the steam turbine flows through the shell (12), while during tube (10) failures, by replacing the cover (80), a certain amount of feed water passes through the orifice (100) and remaining feed water passes through the plurality of tubes (10).
2. The internal bypass mechanism for feed water heater (200) as claimed in claim 1, wherein the shell (12) is cylindrical and the channel (40) is semispherical in shape.
3. The internal bypass mechanism for feed water heater (200) as claimed in claim 1, wherein the tubes (10) are U tubes.
4. The internal bypass mechanism for feed water heater (200) as claimed in claim 1, wherein the pass partition plate (50) cover (80) is configured with the orifice (100) at the center.
5. The internal bypass mechanism for feed water heater (200) as claimed in claim 1, wherein the orifice (100) configured at the cover (80) has any one of the shape selected from circular, square, rectangular, oblong and a combination of these shapes.
6. The internal bypass mechanism for feed water heater (200) as claimed in claim 1, wherein the cover (80) is fitted with a disk (110) having an aperture diameter matches with the orifice (100).
7. The internal bypass mechanism for feed water heater (200) as claimed in claim 1, the disc (110) is made of stainless steel or any other erosion resistant material.
8. The internal bypass mechanism for feed water heater (200) as claimed in claim 1, wherein the cover (80) is fitted over the pass partition plate (50) by means of methods selected from bolting, welding and similar method.
9. The internal bypass mechanism for feed water heater (200) as claimed in claim 1, wherein the disk (110) is fitted over the cover (80) by means of methods selected from bolting, welding and similar method.
10. The internal bypass mechanism for feed water heater (200) as claimed in claim 1, wherein a shaft mechanism (210) incorporated with a shaft (95), a bypass valve plate (96) and cylindrical hub (97) is mounted over the cover (80) with shaft projecting outside the channel (40).
Dated this on 16th day of December, 2019

Ragitha. K
(Agent for Applicant)
IN-PA/2832
, Description:Field of the invention:
The present invention relates to high pressure and low pressure feed water heaters and more particularly relates to an internal bypass mechanism for feed water heater.
Background of the invention:
The feed water heater is a component used in power plants to preheat the water before supplying to a steam generating boiler. This preheating of the feed water reduces plant operating costs and also helps to avoid thermal shock to the boiler metal when the feed water is introduced back into the steam cycle.The feed water heateris normally a “U” tube heat exchanger havinga plurality of tubes whose open ends are welded to a tubesheet. The feed water flows on tube side and steam extracted from steam turbine enters in the feed water heater through steam extraction nozzle. The input steam entering into the heater can be superheated or saturated and accordingly the feed water heater is provided with single zone, two zones or three zones.The extraction of steam from the turbine is uncontrolled and is governed by the process conditions on the feed water side and the geometry of the feed water heater.
The feed water heaters are generally arranged in either of two types, single train or double train. A feed water flow assembly for feed water heater in accordance with prior art is shown in Figure 1 and 2. The feed water heaters in single trainas shown in figure 1are arranged in single stream per power generating unit. Entire feed water / condensate flow is allowed to pass through High Pressure / Low Pressure (HP/LP) feed water heaters arranged in a single stream. Typically, there are two or three HP heaters per train and three or four LP heaters in a train. Arrangement is provided for the bypass of an individual feed water heater in a train. Bypass valves (60) completely isolate an individual feed water heater from heater train as such when required. These valves do not allow partial flow of feed water through feed water heater.
The feed water heaters in double trainas shown in figure 2are arranged in two streams per power generating unit. Typically, there are two or three high pressureheaters per train. Entire feed water / condensate flow is divided into two streams to pass through high feed water heaters arranged in two parallel trains. Arrangement is provided for the bypass of a complete train of feed water heaters. The bypass valves (70) isolate complete feed water heater train, as and when required.

Deficiencies or drawbacks of prior art
Forfeed water heatersarranged in a single train, in case of tube leaks / failures, the tubes are required to be plugged, which results in increase of the velocity of feed water flowing throughthe tubes. When the number of tubes plugged reaches a certain limit, the velocity of feed water in the tubes would exceed maximum velocity recommended by HEI (Heat Exchange Institute) Standards for closed feed water heaters and would result in erosion of tubes. To avoid erosion of tubes, when the number of tubes plugged in the feed water heater reaches the limiting value as explained above, the heater (200) needs to be bypassed from the train. Bypassing of a heater(200) would result in reduction in the plant performance and adversely affect the heat rateof the plant.
It would be obvious to those skilled in the art that bypass of an upstream feed water heater would result in the downstream feed water heater receiving feed water at a lower temperature than its design value. Since the extraction of steam from the turbine is uncontrolled, this would result in extraction of a substantially higher amount of steam from turbine in downstream feed water heater. In certain cases, the flow rate of extraction steam could be as high as two times that of the design flow rate. In case the downstream heater has not been designed for the condition with upstream heater being bypassed, there is high possibility of tubes in the downstream heater failing due to damage by flow-induced vibrations. The downstream feed water heater, if designed for this condition, will result into a larger size of heater with non-optimal design.
Forfeed water heatersarranged in a double train, in case of tube failures, tubes are required to be plugged, which results in an increase of the velocity of feed water in tubes. When the number of tubes plugged reaches a certain limit, the velocity of feed water in the tubes would exceed maximum velocity recommended by HEI Standards for closed feed water heaters and would result in erosion of tubes. To avoid erosion of tubes when the number of tubes plugged in the feed water heater reaches the limiting value as explained above, complete train needs to be bypassed. But, bypass of a complete train of heaters would result in significant reduction in the temperature (as much as 120 OC) of feed water at the inlet of the economizer section of the boiler and can cause failure of the economizer tubes due to thermal shock.
Accordingly, there exists a need to provide a bypassmechanism for feed water heatersthat wouldovercomethe above-mentioned drawbacks.
Objects of the invention:
An object of the present invention is to avoid bypass of a completefeed water heater of a single train or bypass of complete train of feed water heaters of a double train when the number of tubes plugged in the heater exceeds the limiting value.
Another object of the present invention is to increase plant efficiency by increasing the temperature of feed water at the inlet of the economizer section of the boiler.
Yet another object of the present invention is to prevent any failure of economizer tubes due to thermal shock.
Yet another objective of the invention is to prevent erosion of tubes of the feed water heater.
Yet another object of the present invention is to prevent damage in the downstream feed water heaters tubes due to increase in flow rate of extraction steam resulting from bypass of an upstream feed water heater.
Summary of the invention
Accordingly, the present invention provides amechanism to partially or completely bypass feed water in the feed water heater. The bypass mechanism of the feed water heater comprises a channel having a fluid inlet and a fluid outlet configured thereon, a shell, a plurality of tubes secured inside the shell, a tube sheet fitted in between the shell and the channel and a pass partition plate mounted inside the channel. The tube sheet has perforated surface where open ends of the plurality of tubes are welded thereon.The shell also comprises a nozzle to receive steam from a steam turbine and delivers into the shell. The pass partition plate divides the channel into an inlet chamber and an outlet chamber. Further the pass partition plate is configured with an opening at the centre that is sealed by a cover. The cover is detachably attached to the pass partition plate and can be replaced through a manway provided on the channel. During normal operation, the feed water enters into the channel through the inlet and circulates through the plurality of tubes, similarly the steam flows through the shell and transfers heat to the feed water inside the heat exchanger. The pass partition plate is closed by the cover, allowing no feed water flow directly from inlet chamber to the outlet chamber during normal operation. During tube failures, the pass partition plate is fitted with a cover having an orifice allowing certain amount of feed water through the orifice and remaining through the plurality of tubes.
Brief description of the drawings:
The objects and advantages of the present invention will become apparent when the disclosure is read in conjunction with the following figures, wherein
Figure 1shows an arrangement of feed water heaters in single train in accordance with a prior art;
Figure 2 shows an arrangement of feed water heaters in double train in accordance with a prior art;
Figure 3 shows a schematic view of a three zone feed water heater, in accordance with present invention;
Figure 4 shows a cross sectional view of a channel along with pass partition plate where the bypass mechanism is placed for feed water heater in accordance with the present invention;
Figure 5 shows a schematic view of the pass partition plate of the feed water heater in accordance with the present invention;
Figure 6 shows a schematic view of the cover of the pass partition plate of the feed water heater in accordance with the present invention;
Figure 7a and 7b show a side view and top view of a stainless steel disk of the feed water heater in accordance with the present invention;
Figure 8 shows a cross sectional view of a channel with a shaft mechanism for feed water heater in accordance with the present invention.
Figure 8a shows a schematic of the shaft mechanism with fully open bypass valve plate for feed water heater in accordance with the present invention.
Figure 8b shows a schematic of the shaft mechanism with fully closed bypass valve plate for feed water heater in accordance with the present invention.
Detailed Description of the invention:
The foregoing objects of the invention are accomplished, and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiments.
The present invention provides a bypass mechanism for feed water heater by diverting the flow of feed water internally.The mechanism ensures full or partial bypass of feed water in an individual feed water heater without the requirement of any alterations in the existing feed water piping and addition of bypass valves.
The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures and in the table given below.
Table:
Components Name Component Number
Feed water heater tubes 10
Tube sheet 11
Shell 12
Shell inlet nozzle 13
Feed water inlet 20
Feed water outlet 30
Channel 40
Pass partition plate 50
Bypass valves 60,70
Cover 80
Manway 90
Shaft 95
Bypass valve plate 96
Cylinder hub 97
Orifice 100
Stainless Steel Disk 110
Economizer 170
De-aerator 180
Steam Turbine 190
Feed water heater 200
Shaft mechanism 210
Referring to the figures from 3 to 5, there is shownan internal bypass mechanism for feed water heater (200) in accordance with the present invention. The feed water heater (200) comprises a plurality of feed water heater tubes (10) (‘tubes (10)’ hereinafter), a shell (12), a channel (40) a tube sheet (11) and a pass partition plate (50).
The shell (12) is a hollow structure closed at one end. The shell contains tubes (10) fitted therein. The open end of the shell is fitted with the channel (40) through tube sheet (11). In a preferred embodiment, the shell is cylindrical and the channel (40) is semispherical in shape. The channel (40) is configured with an inlet (20) and an outlet (30) for the feed water to pass therethrough. The chamber inside the channel (40) receives fluid/feed water through the inlet (20) and release through the outlet (30). Preferably, the inlet (20) is a fluid inlet nozzle and the outlet (30) is a fluid outlet nozzle. The channel (40) is further configured with a manway (90) at its surface.
The tube sheet (11) is fitted in between the shell (12) and the channel (40) on either side. The tube sheet (11) is perforated plate where open ends of the tubes (10) can be fitted. The tubes (10) are mounted on the surface of the tube sheet (11) in such a way that they can receive the fluid/feed water from the channel (40). In the embodiment, the tubes (10) are U tubes and are welded to the tube sheet (11).
The shell (12) is further configured with a shell inlet nozzle (13) that extracts steam from a steam turbine and delivers therethrough.The steam entering into the shell (12) is either superheated or saturated. According to this, the feed water heater can be provided with single zone, two zones or three zones.
The pass partition plate (50) is equipped with a cover (80) and is fitted inside the channel (40).The pass partition plate (50) is open at the centre and is closed by the cover (80) attached thereon. In a specific embodiment, the pass partition plate (50) is bolted with the cover (80). The pass partition plate (50) and the cover (80) together divide the chamber inside the channel (40) into an inlet chamber (42) and an outlet chamber (44). The feed water received through the inlet (20) accumulates in the inlet chamber (42), flows through the tubes (10) and reaches to the outlet chamber (44). Finally, it goes out through the outlet (30) under normal conditions.
The cover (80) fitted on the pass partition plate (50) has varying designs. In a specific embodiment, the cover (80) having an orifice (100) at the center. This orifice allows a connection between the inlet and outlet chambers (42,44) and facilitates a partial or complete bypassing of the fluid/feed water from inlet chamber (42) through the orifice towards the outlet chamber (44) in case of tubes (10) plugging. The size of the orifice (100) is made according tothe number of tubes(10)plugged inside the shell (12).
The cover (80) is welded with a disk (110) thereon. In a specific embodiment, the disk (110) is a stainless steeldisk. The arrangement of cover (80) with the stainless steel disk (110) eliminates any erosion of the orifice (100) during bypassing of the fluid/feed water through the orifice (100). The cover (80) is installed through the manway (90) provided on the channel (40). In the specific embodiment, the process of installation of the cover (80) is manual.
In the embodiment, the orifice (100) is circular in shape. In alternative embodiments, the shape of orifice (100) is selected from square, rectangular, oblong or combination of these shapes. The number and dimension of the orifice (100) are determined by the number of tubes (10) plugged inside the feed water heater (200). Reasonable variations and modifications will become apparent to those skilled in the art as shown in Figure 5 and Figure 6 but not limited to these can be made from this invention without departing from the spirit and scope thereof.
In another alternative embodiment, the orifice (100) is covered with a cylindrical hub (97) and a bypass valve (96) assembly. The bypass valve plate (96) is connected with a shaft mechanism (210) having a shaft (95) projecting out of the channel (40). The opening of orifice (100) can be controlled via the shaft mechanism (210) from outside. The shaft (95) can be rotated from outside to open the bypass valve plate (96) as per the process requirement and avoiding the manual intervention of placing the cover (80) with required size of orifice (100) according to the number of tubes (10) plugged. Hence the pass partition plate (50) can be fully open or fully closed based on the plugging of the tubes (10).
Again referring to the figures from 3 to 8, an operation of the bypass mechanism for feed water heater (200) in accordance with the present invention is described. The operation is described in conjunction with the diagrams.
The fluid/feed water enters into the channel (40) through the fluid inlet (20) and is collected in the inlet chamber (42). During normal operations with no plugging of tubes (10), this fluid/feed water flows through the tubes (10), and outlet chamber (44) and releases through the fluid outlet (30). In this state, the pass partition plate (50) is completely closed by the cover (80) and will not allow bypass of feed water to happen directly from inlet chamber (42) to outlet chamber (44). But during tube failures, by replacing cover (80) with a orifice fitted on the pass partition plate (50), a certain amount of feed water is bypassed through the pass partition plate (50), from the inlet chamber to outlet chamber (42,44). Thus, by incorporating the cover (80) having orifice (100) of different dimensions, the flow can be controlledby allowing certain amount of feed water through the orifice and remaining through the plurality of tubes.
The bypass mechanism (200) eliminates the need of complete isolation of feed water heaters (200) during failures in tubes (10). The internal bypass is provided in the upstream heaters to limit erosion of the tubes (10) where the number of tubes (10) plugged reaches a certain limit. The internal bypass is also provided in the downstream feed water heaters to limit extraction of steam in the heater (160) and thereby reducing the possibility of flow-induced vibrations.
Experimental Analysis:Computational fluid dynamics (CFD) analysis are carried out to ensure that the high velocity flow stream coming out of orifice (100)will not cause any damage to the internals. A higher fluid/feed water temperature can be achieved with the feed water heater (200) as the feed water heater is partially bypassed and some part of water flows through tubes (10).The size of the orifice provided on the cover (80) is decided by the pressure drop equalization for internal bypass flow through orifice and remaining flow through tubes (10).
Advantages of the invention
a) The feed water heater (200) internal bypass mechanism ensures partial bypass of individual feed water heater in case of excessive tubes (10) plugging without change in the existing feed water piping and addition of bypass valves.
b) The mechanism of the feed water heater (200) can also be useful to facilitate complete or partial bypass of those feed water heaters having no provision for individual heater bypass. This can be done without changing in the existing feed water piping and addition of bypass valves.
c) The bypass mechanism in the feed water heater (200) limits the erosion of the feed water tubes (10) when the number of tubes (10) plugged reaches a certain limit.
d) The bypass mechanism in the feed water heater (200) also limits the extraction of steam in the downstream heaters and thereby reduces possibility of flow induced vibrations.
e) The bypass mechanism in the feed water heater (200) allows varying flow rates of the feed water from inlet to outlet chamber by simply replacing the cover (80) of varying orifice (100) sizes.
f) The installation of the cover (80) can be executed easilyby accessing the location through the manway(90) in a very short time, thereby avoiding long shutdowns andassociated production losses.
g) The manual or automated process of changing the bypass opening size in the mechanism facilitates bypassing of the feed water as per the requirement.
h) The cover (80) with various sizes of orifice (100) can be kept ready in the power plant and can be easily replaced in case of failures in tubes (10).
i) The shaft mechanism (210) incorporated with the cylindrical hub (97) and the bypass valve plate (96), that can be regulated externally by using the shaft (95) in the pass partition plate (50) as per the number of tubes (10) plugged. This eliminates the manual intervention of replacing the cover (80) with correct size of orifice according to the changes made in the tubes or plugging of tubes.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the scope of the present invention.