GB1588882A

GB1588882A - Apparatus and method for side stream purification of condensate in a steam cycle

Info

Publication number: GB1588882A
Application number: GB4376277A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-10-20
Filing date: 1977-10-20
Publication date: 1981-04-29

Description

(54) APPARATUS AND METHOD FOR SIDE STREAM PURIFICATION OF CONDENSATE IN A STEAM CYCLE (71) I, CHARLES WAYNE REED, a citizen of the United States of America, of 5174 Brookside Lane, Concord, California 94521, United States of America, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to condensate used in a steam cycle. More particularly, it relates to a method and apparatus for purification of the condensate. The term purification is used to cover removal, reduction or neutralisation of any undesired content in the condensate such as by demineralisation, filtration or sterilisation to kill germs, either singly or in combination.

Many conventional full flow condensate demineralisers in nuclear and other power plant cycles are located in a series flow arrangement in the feed water system downstream of the main condensate pump. This demineraliser equipment is, therefore, designed for the maximum system pressure, which is usually about 600-700 psi design, with normal operating pressures of about 500 psi. If the demineralisers in such a system are bypassed for operating purposes, the resulting reduction in the pressure against the condensate pump could upset the pumping system and thus decrease the power efficiency of the power plant even though throttling controls are used in the bypass operation. Demineralisers in such a series flow arrangement do not have recirculation capability and also do not provide the capacity required to handle demineraliser clean-up necessitated by either excessive condenser leakage or excessive mineral content in the water, thus requiring a plant shut-down in these instances.

A bypass water treating system designed for Cleveland Electric Illuminating Company for its Avon station, is reported in Electrical World, July 2, 1959, particularly at Pages 18, 26 and 31. This Avon installation is essentially designed for tube-to-tube sheet joint weepage. The Avon system contains several maior potential operating problems in common with conventional full- flow series demineralisers. In the Avon design, tube rupture is detected at the hot well pump. This is too late to prevent downstream contamination.

Further, in the Avon system, in the event of a tube rupture and a switch to the bypass system, the demineraliser pumps can no longer be bypassed but must be used in series with the condensate pump This then results in a series system with the demineraliser pump pumping through the suction of the hot well pumps and for practical purposes has the same drawbacks as the conventional series flow demineralisation arrangement.

According to the present invention, purification apparatus is incorporated in the condenser circuit upstream of the main condensate pump. If no demineralisation is required, the purification apparatus may be bypassed without affecting the pump system as the upstream bypass to the apparatus does not effect the discharge pressure from the condensate pump.

More specifically, the invention provides a condensate purification system for a power plant steam cycle, the system comprising a condenser for incorporation into a said cycle which defines first and second reservoirs for condensate contained therein, and means permitting flow of condensate from the first to the second reservoir; means spaced from the condenser for purifying condensate; first conduit means defining a fluid path from the first reservoir to the purifying means; and second and third conduit means defining fluid paths for returning purified condensate from the purifying means respectively to the first and second reservoirs. The second reservoir is normally the hot well of the condenser.

The system of the invention can operate with high mineral content condensate and provides additional benefits. It will be appreciated that the purification apparatus may be bypassed when desired for operating purposes without upsetting the pumping system. The system is also capable of handling excessive condenser leakage and condensate mineral content in a condenser that is part of a system utilising several condensers, all of which are connected to the purification apparatus. In this case the single leaking condenser alone can be serviced.

The invention also provides a method for removing impurities from condensate in a power plant steam cycle having a condenser which defines an upstream and a downstream reservoir for condensate contained therein,.

which method comprises: interrupting at least a part of the flow of fluid through the condenser from the upstream reservoir and withdrawing same from the condenser; separating impurities from the withdrawn fluid; and returning the purified fluid selectively to an or other of the reservoirs.

In normal operation, full condensate flow will be intercepted, purified and discharged to the condenser hot well ready for use in the steam cycle. However, if the mineral content or other factor in the purity of the condensate is still unsatisfactory after passing through the purification apparatus, the water can be recirculated through the apparatus until tolerable limits are achieved before the condensate is directed to the hot well and then to the concondensate pump thereby avoiding plant shut-down.

Additional features of the system of the invention are that it can operate at low pressures, such at at about 50--100 psi, utilising the side stream condensate pump, and at relatively lower temperatures, up to 134"F because the water being treated is upstream of the hot well and has not yet been preheated in the condenser hot well where provision is made for such reheating. These features offer substantial cost reductions particularly in a demineralisation system and the resins required for it. Where a reheat zone is utilised in the condenser, the present invention provides condensate of lower temperature for contact with the demineralisation resins thereby extending resin life.

The invention will now be described by way of example and with reference to the accompanying drawings wherein: Figure 1 is a schematic steam cycle having a single condenser using a purification system according to the invention; and Figure 2 is a schematic view of part of a steam cycle having plural condensers connected for using a purification system according to the invention.

Figure 1 shows a steam cycle for a power plant in which the working fluid path includes a main condensate pump 10 in fluid communication with a series of low pressure feed water heaters 11 which flow to the main feed water pump 12. Main feed water pump 12 communicates with high pressure feed water heaters 13 from which the feed water is returned to steam boiler 14. Steam from boiler 14 operates turbine generator 15 from which the steam is flowed to main condenser 16. Main condenser 16 typically includes a hot well portion 17 at the downstream end of condenser 16. It will be understood that the above cycle is for illustration only and the present invention is equally applicable to the many possible variations and additions to a stream cycle.

The purification system includes a divider or horizontal baffle 18 defining an upstream portion 19 of condenser 16 and a downstream portion 20. Passageway 21 through divider 18 opens fluid communication between upstream portion 19 and downstream portion 20 of condenser 16. Horizontal baffle 18 includes weir 22 adjacent to passageway 21 to hold back a pool of condensate fluid on the upstream side of baffle 18 in a first reservoir 23.

There is further included a splash baffle 24 disposed over passageway 21 and weir 22 to prevent condensate from moving directly through passageway 21 and thereby avoiding residence in reservoir 23.

A bank of water purification apparatus, usually a bank of condensate demineralisers 25, is spaced from condenser 16. Pipe 26 is connected between reservoir 23 and demineralisers 25 and includes condensate pump 27 for causing fluid flow through pipe 26 and demineralisers 25. Pipe 28 receives demineralised condensate from demineralisers 25 and recirculates the same to reservoir 23 through pipe 29. Alternatively the demineralised condensate may be flowed through pipe 30 for communication with the downstream side of divider 18 and in communication with condensate 31 in hot well or second reservoir 17.

Valves 32, 33 and 34 are adapted to selectively open and close fluid flow through pipes 26, 29 and 30, respectively.

When the power plant is operating but no demineralisation of the condensate is required, valves 32 may be closed and pump 27 inactivated wherebv condensate in reservoir 23 will thus overflow weir 22 and pass directly to the condensate water 31 in hot well 17 completely bypassing the demineralisation system. When demineralisation is desired, valve 32 is opened and pump 27 is activated.

In a normal full flow demineralisation in which no recirculation is required, valve 33 is closed and valve 34 is opened whereby demineralised condensate is passed to the condensate in hot well 17.

In a start-up, emergency contamination situation, or when further demineralisation is required, valve 34 can be closed and valve 33 opened. Thus condensate from reservoir 23 flowing through pipe 26 and demineralisers 25 is recirculated through pipe 29 back to reservoir 23. Such recirculation may be continued until the contamination level in the fluid is at an acceptable level. In some designs of main condensers used in a steam cycle, there is provision for reheating the condensate either while it is in the hot well or, more usually, on its passage to the hot well 17. In such a unit the demineralised condensate returning to the main condenser in pipe 30 will be introduced into the main condenser at an appropriate location so that the condensate can pass through the reheating zone in the main condenser. For example, in the embodiment of Figure 1 pipe 30 would be located so that the condensate would enter the main condenser at a location above condensate water 31 so that the return flow would pass through the reheating zone before reaching condensate water 30.

In a typical installation, there may be three main condensers in the steam cycle receiving steam from three low pressure turbine elements of the main turbine. Where there is excessive leakage in one of the condensers, the side stream system of this invention permits the diversion of all of the water from the leaking condenser through the demineralisation system while permitting the two properly operating condensers to pass their condensate directly through the passageway in their baffles to their hot wells. Similar flexibility is available during start-up situations. Additional flexibility is available by adjusting valves 33 and 34 to recirculate a portion of the demineralised condensate while flowing a portion to hot well 17.

The embodiment of Figure 2 illustrates the manner of interconnecting the plurality of main condensers with a single demineralisation system. Thus, main condensers 100 and 101 are connected with condensate pumps 102 and 103, respectively, which form part of a steam cycle as illustrated in Figure 1. Usually three main condensers will be employed in such a system, although the same principle would apply to any number of main condensers desired. The condensate pump from each main condenser, such as pump 102, would normally discharge to low pressure feed water heaters (not shown) and the output from all such heaters consolidated for flow through the remainder of the system as shown in Figure 1.

With respect to the purification of the condensate in the main condensers, a bank of demineralisers is shown at 104. Condenser 100 is connected to demineralisers 104 and condensate is pumped through polisher or condensate pump 105. The condensate in main condenser 101 is similarly connected and is pumped to demineralisers 104 through condensate pump 106. In an excessive leakage situation as mentioned above, valves such as valve 107 are closed on all properly functioning main condensers. Assuming a contamination problem in main condenser 100, valve 108 is opened and the condensate in main condenser 100 is pumped through the entire demineralisation bank 104. The condensate may be recirculated until contamination is reduced to an acceptable level by closing valves 109-109e and opening valves 110 110e. Conversely, the condensate can be passed to the hot well of main condenser 100 when recirculation is to be terminated or if only a single pass through the demineralisation bank 104 is desired.

Special features of the system to be noted include the ability of detecting contamination an early stage before the contamination proceeds downstream. Contamination may be detected while the condensate is in reservoir 23 on the upstream side of baffle 18. If detected, the condensate may be recirculated through pipe 26, demineralisers 25, and pipes 28 and 29 until the contamination is sufficiently reduced. It should be further noted that at no time is demineraliser condensate pump 27 used in series with main condensate pump 10. Consequently, condensate pump 27 can be designed for 100 psi or lower operation.

WHAT I CLAIM IS: 1. A condensate purification system for a power plant steam cycle, the system comprising a condenser for incorporation into a said cycle which defines first and second reservoirs for condensate contained therein, and means permitting flow of condensate from the first to the second reservoir; means spaced from the condenser for purifying condensate; first conduit means defining a fluid path from the first reservoir to the purifying means; and second and third conduit means defining fluid paths for returning purified condensate from the purifying means respectively to the first and second reservoirs.

2. A system according to Claim 1 wherein the second reservoir is a hot well.

3. A system according to Claim 1 or Claim 2 including valves means in each of the first, second and third conduit means for selectively permitting and precluding fluid flow through the respective conduit means. 4. A system according to any preceding Claim including means for ensuring that a preselected volume of condensate is retained in the first reservoir before flow thereof is permitted to the second reservoir.

5. A system according to Claim 4 wherein said means comprises a weir defining a boundary of the first reservoir, the second reservoir being located to receive condensate from the weir.

6. A system according to any preceding Claim including a plurality of said condensers connected to said purifying means and valves associated with the respective first, second and third conduit means for selectively connecting one or more of the condensers to the purifying means.

7. A condensate purification system for a power plant steam cycle substantially as described herein with reference to and as illustrated in Figure 1 or Figure 2 of the accompanying drawings.

8. A power plant steam cycle including a condensate purification system according to any preceding Claim.

9. A method for removing impurities from

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Claims

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be introduced into the main condenser at an appropriate location so that the condensate can pass through the reheating zone in the main condenser. For example, in the embodiment of Figure 1 pipe 30 would be located so that the condensate would enter the main condenser at a location above condensate water 31 so that the return flow would pass through the reheating zone before reaching condensate water 30.

In a typical installation, there may be three main condensers in the steam cycle receiving steam from three low pressure turbine elements of the main turbine. Where there is excessive leakage in one of the condensers, the side stream system of this invention permits the diversion of all of the water from the leaking condenser through the demineralisation system while permitting the two properly operating condensers to pass their condensate directly through the passageway in their baffles to their hot wells. Similar flexibility is available during start-up situations. Additional flexibility is available by adjusting valves 33 and 34 to recirculate a portion of the demineralised condensate while flowing a portion to hot well 17.

The embodiment of Figure 2 illustrates the manner of interconnecting the plurality of main condensers with a single demineralisation system. Thus, main condensers 100 and 101 are connected with condensate pumps 102 and 103, respectively, which form part of a steam cycle as illustrated in Figure 1. Usually three main condensers will be employed in such a system, although the same principle would apply to any number of main condensers desired. The condensate pump from each main condenser, such as pump 102, would normally discharge to low pressure feed water heaters (not shown) and the output from all such heaters consolidated for flow through the remainder of the system as shown in Figure 1.

With respect to the purification of the condensate in the main condensers, a bank of demineralisers is shown at 104. Condenser 100 is connected to demineralisers 104 and condensate is pumped through polisher or condensate pump 105. The condensate in main condenser 101 is similarly connected and is pumped to demineralisers 104 through condensate pump 106. In an excessive leakage situation as mentioned above, valves such as valve 107 are closed on all properly functioning main condensers. Assuming a contamination problem in main condenser 100, valve

108 is opened and the condensate in main condenser 100 is pumped through the entire demineralisation bank 104. The condensate may be recirculated until contamination is reduced to an acceptable level by closing valves 109-109e and opening valves 110 110e. Conversely, the condensate can be passed to the hot well of main condenser 100 when recirculation is to be terminated or if only a single pass through the demineralisation bank 104 is desired.

Special features of the system to be noted include the ability of detecting contamination an early stage before the contamination proceeds downstream. Contamination may be detected while the condensate is in reservoir 23 on the upstream side of baffle 18. If detected, the condensate may be recirculated through pipe 26, demineralisers 25, and pipes 28 and 29 until the contamination is sufficiently reduced. It should be further noted that at no time is demineraliser condensate pump 27 used in series with main condensate pump 10. Consequently, condensate pump 27 can be designed for 100 psi or lower operation.

WHAT I CLAIM IS: 1. A condensate purification system for a power plant steam cycle, the system comprising a condenser for incorporation into a said cycle which defines first and second reservoirs for condensate contained therein, and means permitting flow of condensate from the first to the second reservoir; means spaced from the condenser for purifying condensate; first conduit means defining a fluid path from the first reservoir to the purifying means; and second and third conduit means defining fluid paths for returning purified condensate from the purifying means respectively to the first and second reservoirs.
2. A system according to Claim 1 wherein the second reservoir is a hot well.
3. A system according to Claim 1 or Claim 2 including valves means in each of the first, second and third conduit means for selectively permitting and precluding fluid flow through the respective conduit means.
4. A system according to any preceding Claim including means for ensuring that a preselected volume of condensate is retained in the first reservoir before flow thereof is permitted to the second reservoir.
5. A system according to Claim 4 wherein said means comprises a weir defining a boundary of the first reservoir, the second reservoir being located to receive condensate from the weir.
6. A system according to any preceding Claim including a plurality of said condensers connected to said purifying means and valves associated with the respective first, second and third conduit means for selectively connecting one or more of the condensers to the purifying means.
7. A condensate purification system for a power plant steam cycle substantially as described herein with reference to and as illustrated in Figure 1 or Figure 2 of the accompanying drawings.
8. A power plant steam cycle including a condensate purification system according to any preceding Claim.
9. A method for removing impurities from

condensate in a power plant steam cycle having a condenser which defines an upstream and a downstream reservoir for condensate contained therein, which method comprises: interrupting at least a part of the flow of fluid through the condenser from the upstream reservoir and withdrawing same from the condenser; separating impurities from the withdrawn fluid; and returning the purified fluid selectively to one or other of the reservoirs.
10. A method according to Claim 9 wherein the withdrawn fluid is returned to the upstream reservoir, thereby permitting recirculation of the fluid.
11. A method according to Claim 9 or Claim 10 wherein the withdrawn fluid is returned to the downstream reservoir of the condenser for further passage through the cycle.
12. A method according to Claim 11 wherein the downstream reservoir is a hot well
13. A method according to any of Claims 9 to 12 wherein substantially the entire flow of fluid through the condenser is interrupted.
14. A method of removing impurities from condensate in a power plant steam cycle, according to Claim 1 and substantially as herein described.