(19) TZZ Z_T

(11) EP 2 520 855 A1

(12) EUROPEAN PATENT APPLICATION published in accordance with Art. 153(4) EPC

(43) Date of publication: (51) Int Cl.: 07.11.2012 Bulletin 2012/45 F22D 11/00 (2006.01)

(21) Application number: 10840402.1 (86) International application number: PCT/CN2010/075272 (22) Date of filing: 20.07.2010 (87) International publication number: WO 2011/079613 (07.07.2011 Gazette 2011/27)

(84) Designated Contracting States: • CHEN, Renjie AL AT BE BG CH CY CZ DE DK EE ES FI FR GB Shanghai 200063 (CN) GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO • SHI, Gangye PL PT RO SE SI SK SM TR Shanghai 200063 (CN) • YE, Yongjian (30) Priority: 30.12.2009 CN 200910266839 Shanghai 200063 (CN) •LIN,Lei (71) Applicant: China Power Engineering Consulting Shanghai 200063 (CN) Group Corporation East China Electric Power Institute (74) Representative: Denjean, Eric Shanghai 200063 (CN) Cabinet Laurent & Charras "Le Contemporain" (72) Inventors: 50, Chemin de la Bruyère • SHEN, Songlin 69574 Dardilly Cedex (FR) Shanghai 200063 (CN)

(54) FEEDWATER AND DRAINAGE SYSTEM FOR MEDIUM PRESSURE HEATER IN POWER PLANT

(57) A feedwater and draining system for medium- pressure feedwater heater unit (300) comprising one or pressure heaters used in a power plant comprises a feed- more feedwater heaters is provided between the low- water piping (100) and a feedwater pump unit (200) pressure (203) and the high- pres- provided on the feedwater piping (100).The boiler feed- sure boiler feedwater pump (204).A generator set and a water pump unit (200) includes a low-pressure boiler power plant equipment comprising the feedwater and feedwater pump (203) and a high-pressure boiler feed- draining system for the medium- pressure heater are pro- water pump (204) provided along the upstream and the vided. The feedwater and draining system for the medi- downstream of the feedwater piping (100). A medium- um-pressure heater is low in cost, high in efficiency of thermodynamic system and more environment-friendly. EP 2 520 855 A1

Printed by Jouve, 75001 PARIS (FR) 1 EP 2 520 855 A1 2

Description is low in cost, high in , and more envi- ronment-friendly. Field of the invention Summary of the invention [0001] The invention relates to a feedwater and drain- 5 ing system for heaters, especially to a feedwater and [0006] The first object of the invention is to provide a draining system for heaters used in a power plant. feedwater and draining system for heaters used in a pow- er plant which is low in cost, high in thermal efficiency, Background of the invention and more environment-friendly. 10 [0007] The second object of the invention is to provide [0002] Nowadays, the environment protection and the a supercritical pressure generator set or an ultra-super- emission of the greenhouse gases have become a seri- critical pressure generator set which is low in cost, high ous concern, therefore, it is make much sense to save in thermal efficiency, and more environment-friendly. the energy in power generating industry [0008] The third object of the invention is to provide a [0003] Nowadays, in thermal power generation, the 15 power plant equipment which is low in cost, high in ther- after expansion is often used to heat feedwater in mal efficiency, and more environment-friendly. order to save energy. "Electrical Engineers Handbook" [0009] According to the first aspect of the invention, has disclosed a with feedwater thermal the invention provides a feedwater and draining system regeneration and its cycling equipment. It is constituted for medium-pressure heaters used in a power plant com- by boiler, steam turbine, condenser, feedwater pump and 20 prising a feedwater piping and a boiler feedwater pump extraction steam heater, wherein, the boiler is connected unit provided on the feedwater piping, to the steam turbine through super heating pipe, the con- wherein, denser, feedwater pump and extraction steam heater are connected to the boiler in consequence, the extraction - said feedwater pump unit includes a low-pressure steam heater is connected to the boiler through feedwa- 25 boiler feedwater pump and a high-pressure boiler ter pipe, and finally the extraction steam pipe from the feedwater pump provided along upstream to down- steam turbine is connected to the extraction steam heat- stream of the feedwater piping ; ers directly. For such regenerative cycle equipment, be- - a medium-pressure feedwater heater unit compris- cause the heat of the extraction steam of turbine is used ing one or more feedwater heaters is provided be- to heat feedwater, the loss of energy of the cycle de-30 tween said low-pressure boiler feedwater pump and crease, if the initial parameters are the same as the final said high-pressure boiler feedwater pump. parameters, the thermal efficiency is higher than that of the equipment without feedwater regenerative cycle. [0010] In one embodiment of the invention, the head [0004] Fig.1 shows the traditional configuration of of said low-pressure boiler feedwater pump amounts feedwater heaters of prior art power plant equipment. In 35 30-60 percent of total head which is the sum of the head the configuration, the feedwater piping 100 between de- ofthe low- pressureboiler feedwater pump andhigh- pres- aerator 1 and boiler 4 is provided with boiler feedwater sure boiler feedwater pump. pumps 200a , and feedwater heater unit 300a is provided [0011] In one embodiment of the invention, the head downstream of the boiler feedwater pumps 200a includ- of said low-pressure boiler feedwater pump (203) is 40 ing feedwater booster pump 201a and main feedwater 1200-2400 m H2O; preferably 1200-1800 m H2O. pump 202a.The feedwater heaters is very expensive, es- [0012] In one embodiment of the invention, the head pecially for the supercritical and higher pressure gener- of said high-pressure boiler feedwater pump is ator set, since the pressure at the outlet of the boiler 1600-2800 m H2O; preferably 2200-2800 m H2O. feedwater pumps 200a is high, and the pressure at feed- [0013] In one embodiment of the invention, the pres- water side of the feedwater heater unit 300a is high ac- 45 sure of water side of said feedwater heater unit (300) is cordingly. In addition, the drain water of steam side of in a range of 5~24MPa. g. the feedwater heaters of feedwater heater unit 300a [0014] In one embodiment of the invention, said feed- (which may be comprised of one or more feedwater heat- water heater unit (300) is comprised of 2-3 feedwater ers, for example, the first feedwater heater 301a, the sec- heaters in one row or 4-6 feedwater heaters in two rows. ond feedwater heater 302a, and the third feedwater heat- 50 [0015] In one embodiment of the invention, a drain self- er 303a, as shown in Fig.1) will flow automatically in a flowing pipe (205) is provided at the steam side of one stepwise manner, and finally reach at 1 or each feedwater heaters of said feedwater heater unit through drain self-flowing pipe 205a, since the pressure (300) . of feedwater downstream of feedwater heater unit 300 [0016] In one embodiment of the invention, a drain wa- is higher than upstream. The thermal efficiency of the 55 ter pump (206) is provided at the steam side of said feed- prior art configuration is relatively low. water heater unit (300). [0005] In a word, there is a need for a feedwater and [0017] In one embodiment of the invention, feedwater draining system for heaters used in a power plant which booster pump (201) is provided on the upstream of the

2 3 EP 2 520 855 A1 4 low-pressure boiler feedwater pump (203) of said boiler pressure boiler feedwater pump; and the medium-pres- feedwater pump(200). sure heater unit includes drain water pipe and drain water [0018] he second aspect of the invention, a supercrit- pump. In the system, the pressure of the feedwater from ical pressure generator set or an ultra- supercritical pres- deaerator is increased firstly by the low-pressure boiler sure generator set including a feedwater and draining 5 feedwater pump along the feedwater piping, then the system for medium-pressure heaters used in a power feedwater enters the medium-pressure heater, after plant according to the invention is provided. heating by the medium-pressure heater, the pressure of [0019] he third aspect of the invention, a power plant the feedwater is further increased by high- pressure boiler equipment which includes a feedwater and draining sys- feedwater pump, and finally, the feedwater flows into boil- tem for medium-pressure heaters used in a power plant 10 er. The steam used to heat the feedwater by the medium- according to the invention is provided. pressure heater condenses into drain water which then [0020] The advantages of the invention are: flows back to the deaerator or the feedwater system [0021] On one hand, compared with the prior art high- through a drain water pipe and a drain water pump. pressure heater and feedwater system, the cost of the [0025] The concepts of the invention are as follows: medium-pressure heater and feedwater system is lower ; 15 [0026] The invention is based on the theory of thermal on the other hand, compared with the prior art drain self- cycle: the boiler feedwater pumps which located in front flowing system, it is easy to provide a drain water pump of feedwater heaters are separated into low-pressure in the draining system of the a medium- pressure heater, boiler feedwater pump(s) and high-pressure boiler feed- therefore, it possesses higher thermal efficiency and is water pump(s), the low-pressure boiler feedwater pump more environment-friendly. 20 is arranged in front of feedwater heaters, and the high- pressure boiler feedwater pump is arranged behind feed- Brief description of the drawings water heaters, and the total head of the boiler feedwater pumps is reassigned (the total head remains almost the [0022] same as the head of a conventional configuration). The 25 head of the low-pressure boiler feedwater pump in front Figure 1 is a prior art high- pressure heater feedwater of the feedwater heaters both satisfies the requirement and draining system. for undercooling behind feedwater heaters and net pos- Figure 2 is a medium- pressure heater feedwater and itive suction head (NPSH) of high-pressure boiler feed- draining system of an embodiment of the invention. water pump behind feedwater heaters as well. The head Figure 3 is a medium- pressure heater feedwater and 30 of high-pressure boiler feedwater pump satisfies the re- draining system of an embodiment of the invention. quirement for feedwater of the boiler. In the configuration, Figure 4 is a medium- pressure heater feedwater and the feedwater heaters are provided behind the low- pres- draining system of another embodiment of the inven- sure boiler feedwater pump and in front of the high- pres- tion. sure boiler feedwater pump, the pressure of water side Figure 5 is a medium- pressure heater feedwater and 35 of feedwater heaters is relatively low, which leads to a draining system of another embodiment of the inven- lower cost of the feedwater heaters, and the cost of piping tion. is relatively low due to the pressure of feedwater piping Figure 6 is medium-pressure heater feedwater and (including pipes, , etc) in front of and behind the draining system of another embodiment of the inven- feedwater heaters is lower. Thus, the overall cost could tion. 40 be lowered. [0027] Since the pressure of the feedwater behind the The best mode for carrying out the invention medium-pressure heater is relatively low, it is easy to match drain water pump(s) to conduct the drain water of [0023] After widely and deeply study, the inventors the heaters into the feedwater behind the heaters, which found a new configuration of feedwater heaters through 45 improves the efficiency of thermal system of the turbine improving the process of preparation. The configuration as compare with the system in which the drain water flows lowers the cost and improves the efficiency of the thermal automatically in a stepwise manner. system, and great economic and social benefits can be [0028] The explanations of terms used in the invention attained by simple technical means. The invention is are as follows: completed based on the new configuration. 50 [0029] As used herein, "feedwater" means the water [0024] The invention provides a feedwater and drain- fed to boiler. ing system for medium- pressure heaters used in a power [0030] As used herein, "medium-pressure heater" plan. The system includes: a feedwater piping; a feed- means a heat exchanging apparatus for heating the feed- water pump unit provided on the feedwater piping, the water using steam, wherein the pressure of the feedwater feedwater pump unit comprising a low-pressure boiler 55 lies between the high pressure at the outlet of the boiler feedwater pump and a high-pressure boiler feedwater feedwater pump set and the low pressure at the inlet of pump; a medium-pressure heater unit provided between the boiler feedwater pump set. "medium-pressure heat- the low-pressure boiler feedwater pump and the high- er" is known to the person skilled in the art, and the pres-

3 5 EP 2 520 855 A1 6 sure of the medium-pressure heater can be chosen ac- Medium-pressure feedwater heater unit cording to engineering handbooks of the art. [0031] As used herein, the "power plant equipment" [0041] Herein, the medium-pressure feedwater heater includes (but not limited to): thermal power generation unit is provided between the low- pressure boiler feedwa- equipment, nuclear power plant equipment, biomass5 ter pump and high-pressure boiler feedwater pump. The power plant equipment, gas turbine power plant equip- medium-pressure feedwater heater unit may be com- ment, and other power plants. prised of one or more feedwater heaters. [0032] Unless defined or indicated otherwise, the [0042] Specially, said feedwater heater unit is com- terms used herein have the same meanings as they gen- prised of 2-3 feedwater heaters in one row or 4-6 feed- erally known by the person skilled in the art, for example 10 water heaters in two rows. the terms mentioned in the" thermal power plant equip- [0043] The feedwater heater may employ at least one ment, Zheng, Tikuan, China Electric Power PRESS, medium-pressure feedwater heater or optional high- 2001 Beijing, China". In addition, all the methods and pressure feedwater heater. Preferably, all of the feedwa- materials which are similar or equal to the described con- ter heaters are medium- pressure feedwater heaters. The tents can be used for the invention. 15 medium-pressure feedwater heaters of the invention are [0033] Detailed description of the aspects of the inven- well-known to a person skilled in the art. Specially, the tion: pressure of water side of said feedwater heater unit may be in a range of 5~24MPa. g based on the scale of the Boiler feedwater pump unit power plant. The method of determining the pressure of 20 water side may be carried out according to electrical en- [0034] In order to lower the cost and improve the ther- gineering handbook. mal efficiency, the boiler feedwater pump unit includes a [0044] A drain self- flowing pipe through which the drain low-pressure boiler feedwater pump and a high- pressure water flows automatically can be provided at the steam boiler feedwater pump provided along the upstream to side of one or each feedwater heater of said feedwater the downstream of the feedwater piping. 25 heater unit. The drain self-flowing pipe may be provided [0035] The low-pressure boiler feedwater pump and by conventional process in the art. For example, it may high-pressure boiler feedwater pump are relative terms. be provided according to the electrical engineering hand- [0036] Specially, the head of said low-pressure boiler books of the art. feedwater pump amounts to 30-60 percent of total head [0045] A drain water pump can be provided at the which is the sum of the heads of the low- pressure boiler 30 steam side of one or each feedwater heater of said feed- feedwater pump and the high-pressure boiler feedwater water heater unit. The drain water pump may be provided pump. by conventional process of the art. For example, it may [0037] Specially, the head of said high- pressure boiler be provided according to the electrical engineering hand- feedwater pump amounts to 40-70 percent of total head books in the art. which is the sum of the heads of the low- pressure boiler 35 [0046] When the feedwater heater unit is comprised of feedwater pump and the high-pressure boiler feedwater several (two or more than two) feedwater heaters, the pump. drain self-flowing pipe s may combined with the drain [0038] Specially, the pressure of low-pressure pumps. feedwater pump generally lower than that of the high- [0047] In prior art, since the pressure at the outlet of pressure boiler feedwater pump by 40-70%, preferably 40 the boiler feedwater pumps is high, the system must em- 40-60%, calculatedby the pressureof high- pressure boil- ploy high-pressure heaters. Said "high pressure" is well- er feedwater pump. known to the person skilled in the art. For example, the [0039] Specially, the head of said low-pressure boiler steam pressure of high- pressure heater is not lower than feedwater pump is 1200-2400m2 O; H preferably 1.5 MPa, including but not limited to 1.5 MPa to 10MPa; 45 1200-1800m H2O. Specially, the head of said high- pres- preferably, the pressure of the feedwater is 20 MPa to sure boiler feedwater pump is 1600-2800m H 2O; prefer- 40MPa.The pressure mentioned above can be adjusted ably 2200-2800m H2O.Specially, in the boiler feedwater according to engineering handbooks based on the scale pump unit, a feedwater booster pump can be provided of the power plant. on the upstream of the low-pressure boiler feedwater [0048] The inventors found that through reassigning pump. The head of said feedwater booster pump can 50 the total head of the boiler feedwater pumps, the total amounts to 5-10 percent of total head which is the sum head almost remains the same as the head of a conven- of the heads of the low-pressure boiler feedwater pump tional configuration, and it can satisfy the function of feed- and the high-pressure boiler feedwater pump. water system, while achieves lower the pressure of the [0040] Replacements or modifications to the embodi- feedwatersystem ofhigh- pressure heaters,thereby, low- ments of the invention are obvious to a person skilled in 55 eringthe cost ofthe feedwaterheater. And the drainwater the art. pump can be used, and the efficiency of thermal system can be improved.

4 7 EP 2 520 855 A1 8

Feedwater system for medium-pressure heater used in performed under conventional conditions, or according power plant to the manufacturer’s instructions.

[0049] The feedwater system for heaters used in the Embodiments power plant of the invention includes a feedwater piping, 5 a boiler feedwater pump unit and a water feed heater [0057] Fig 2~6 show theembodiments of the feedwater unit, wherein the boiler feedwater pump unit is comprised and draining system for medium-pressure heater used of a low- pressure boiler feedwater pump and a high- pres- in power plant of the invention. The feedwater and drain- sure boiler feedwater pump provided along the upstream ing system for medium- pressure heaters used in a power to the downstream of the feedwater piping, and the water 10 plant constitute a part of the thermal cycling system of feed heater unit is provided between the low-pressure turbine. Figs 2~6 show 3 full- capacity heaters in one row, boiler feedwater pump and the high- pressure boiler feed- 2 full-capacity heaters in one row, 4 half capacity heaters water pump. The feedwater heater unit is comprised of in two rows (2 heaters in each row), 6 half capacity heat- one or more feedwater heaters. ers in two rows (3 heaters in each row), or other combi- 15 nations are also suitable. Medium-pressure heater drain water system used in [0058] The feedwater and draining system for heaters power plant used in a power plant mainly comprised of:

[0050] The heater drain water system used in the pow- 1) low-pressure boiler feedwater pump(s) 203; er plant of the invention includes drain water piping, drain 20 2) medium-pressure boiler feedwater heater unit water pump(s) provided along the drain water piping. The 300; drain water piping is provide at the steam side of each 3) high-pressure boiler feedwater pump 204; feedwater heaters, and a drain water pump is provided 4) optional heater drain water pump 206; on each of or one of said feedwater heater drain water 5) feedwater piping 100; piping. 25 6) optional heater drain water piping, that is, drain self-flowing pipe 205; Supercritical pressure generator set or an ultra-super- 7) optional feedwater booster pump 201. critical pressure generator set and power plant [0059] Fig. 2 shows a embodiment of the feedwater [0051] The invention also provides a supercritical pres- 30 system for heaters used in power plant of the invention. sure generator set or an ultra- supercritical pressure gen- The system includes a feedwater piping 100, a boiler erator set including said feedwater and draining system feedwater pump unit 200 provided on feedwater piping, for medium-pressure heaters used in a power plan. and a medium-pressure feedwater heater unit 300. Said [0052] Said supercritical pressure generator set or an boiler feedwater pump unit 200 includes a low-pressure ultra-supercritical pressure generator set can be config- 35 boiler feedwater pump 203 and a high-pressure boiler ured according to conventional method, except that the feedwater pump 204 provided along the upstream to the feedwater and draining system for medium-pressure downstream of the feedwater piping 100. Said medium- heaters used in power plant of the invention is used. Said pressure feedwater heater unit is provided between said supercritical pressure generator set or an ultra- supercrit- low-pressure boiler feedwater pump 203 and said high- ical pressure generator set and configuration thereof are 40 pressure boiler feedwater pump 204 and is comprised of well-known to the person skilled in the art. a first medium-pressure feedwater heater 301, a second [0053] The invention also provides a power plant medium-pressure feedwater heater 302, and a medium- equipment including the feedwater and draining system pressure feedwater heater 303. for medium-pressure heaters used in power plant of the [0060] There are low-pressure heaters and high- pres- invention. 45 sure heaters in the conventional power plant. Generally, [0054] Said power plant equipment can be configured the low-pressure heaters refer to the heaters between according to conventional method, except that the feed- the condensate pumps and deaerator, the pressure of water and draining system for medium- pressure heaters water side of which is less than 5 MPa. G; and the high- used in power plant of the invention is used. pressure heaters refer to the heaters between the feed- [0055] Other aspects of the invention will become ap- 50 water pumps and boiler, the pressure of water side of parent to the person skilled in the art based on the dis- which is higher than 24 MPa. g. The pressure of water closure of the specification. side of the heaters is in a range of 5~24 MPa. g, therefore, [0056] The present invention will be further illustrated the heaters are medium-pressure heaters. below with reference to the specific examples. It should [0061] In other alternative embodiments, the feedwa- be understood that these examples are only used to de- 55 ter heater unit 300 may also be comprised of one or more scribe the invention but not to limit the scope of the in- (not limited to 3) feedwater heaters. The pressure of wa- vention. The experimental methods with no specific con- ter side of each feedwater heater in the feedwater heater ditions described in the following examples are generally unit 300 is generally in a range of 5~24 MPa. g. Drain

5 9 EP 2 520 855 A1 10 self-flowing pipe 205 through which the drain water flows booster pump 201 and the low- pressure boiler feedwater automatically is provided at the steam side of each feed- pump 203 can be combined into a single pump or pump water heater of said feedwater heater unit 300. set (see fig.3), according to different cases. [0062] The head of said low- pressure boiler feedwater [0070] The high-pressure boiler feedwater pump 204, pump 203 amounts to 30-60 percent of total head which 5 low-pressure boiler feedwater pump 203, and feedwater is the sum of the heads of the low-pressure boiler feed- booster pump 201 can be driven either by the same motor water pump 203 and the high-pressure boiler feedwater or small steam turbine, or by different motors or small pump 204.The head of said low- pressure boiler feedwa- steam turbines. ter pump 203 is 1200-2400m H 2O.The head of said high- [0071] Self-Flowing in a stepwise manner can be em- pressure boiler feedwater pump 204 is 1600-2800m10 ployed for the medium-pressure heaters without provid-

H2O.In said boiler feedwater pump unit 200, a feedwater ing drain water pump 206 (see fig.2-3), or each of the booster pump 201 is provided on the upstream of the medium-pressure heaters is fitted with drain water pump low-pressure boiler feedwater pump 203.In other option- 206 (see fig.4), or some of the medium- pressure heaters al embodiments, feedwater booster pump 201 can be are fitted with the drain water pump (see fig. 5-6), in order combined with feedwater pump 203, as shown in fig.3. 15 to improve the efficiency of the thermal system. [0063] Figure 4 is a feedwater system for heaters used [0072] The effects of the invention are indicated as fol- in power plant according to one embodiment of the in- lows: vention, wherein drain water pumps 206 are provided on [0073] The key point of the invention is that the boiler the steam side of each feedwater heater of feedwater feedwater pumps in front of the feedwater heater are sep- heater unit 300.If the feedwater heaters are fitted with 20 arated into at least 2 pumps in series. The pressure at drain waterpumps, the drain subcooling zoneof theboiler the outlet of the pump(s) in front of the heaters is lower feedwater heaters can be cancelled, thereby lowering (for example, for a 1000 MW supercritical pressure gen- the cost of the feedwater heaters, while improving the erator set, the pressure at the outlet is about 13 MPa. g), efficiency of the thermal system. therefore, the pump is called low-pressure boiler feed- [0064] Figure 5 is a feedwater system for heaters used 25 water pump 203; the pressure at the outlet of the pump in power plant according to one embodiment of the in- (s) behind the heaters is relatively higher (for example, vention. Two drain water pumps 206 and a drain self- for a 1000 MW supercritical pressure generator set, the flowing pipe 205 are successively provided on the steam pressure at the outlet is about 36 MPa. g), therefore, the side of each feedwater heater of feedwater heater unit pump is called high- pressure boiler feedwater pump 203. 300. 30 The low-pressure boiler feedwater pump 203 is arranged [0065] Figure 6 is a feedwater system for heaters used in front of feedwater heater 300, the high- pressure boiler in power plant according to one embodiment of the in- feedwater pump 204 is arranged behind feedwater heat- vention. One drain water pump 206 and two drain self- er 300, and the total head of boiler feedwater pumps is flowing pipe s 205 are successively provided on the reassigned, thereby the total head remaining almost the steam side of each feedwater heater of feedwater heater 35 same as that of a conventional configuration. unit 300 in order. [0074] The head of the boiler feedwater pump(s) in [0066] The procedure of the system is shown as fol- front of the feedwater heater 300 both satisfies the re- lows: quirement for undercooling behind feedwater heaters [0067] The feedwater with low pressure from deaerator and net positive suction head (NPSH) of boiler feedwater 1 passes through low- pressure boiler feedwater pump (s) 40 pump behind feedwater heaters as well. The pressure at 203, and then the pressure of the feedwater increases the outlet of high-pressure boiler feedwater pump 204 to medium pressure. The feedwater with medium pres- satisfies the requirement for feedwater of the boiler. In sure passes through every stage of medium-pressure the configuration, feedwater heaters are provided behind heater 300, and the temperature of the feedwater grad- low-pressure boiler feedwater pump(s) and in front of ually increase. Finally, the feedwater passes through 45 high-pressure boiler feedwater pump (s), the pressure of high-pressure boiler feedwater pump 204, and then the water side of feedwater heaters is relatively low, which pressure of the feedwater increases to high pressure, leads to a relatively lower cost of the feedwater heaters, thereby satisfying the requirement of feedwater of the and the cost of piping is relative low due to the pressure boiler 4. of feedwater piping (including pipes, valves, etc) in front [0068] The steam in medium- pressure feedwater heat- 50 of and behind the feedwater heaters as well as between er 300 condenses into water after heat exchanging, the the low-pressure boiler feedwater pump and high-pres- water is pressurized by drain water pump 206 and then sure boiler feedwater pump is lower. Thus, the overall enters feedwater piping 100, thereby improving the effi- cost could be lowered. ciency of the thermal efficiency. [0075] At the same time, if the invention is employed, [0069] The low-pressure boiler feedwater pump(s) in 55 the pressure of the feedwater downstream of the feed- front of the medium-pressure heaters can be separated water heaters will be lowered, a drain water pump can into a feedwater booster pump 201 and a low-pressure be readily provided to the feedwater heaters to transfer boiler feedwater pump 203 (see fig.2), or the feedwater the drain water to feedwater downstream of the feedwa-

6 11 EP 2 520 855 A1 12 ter heaters, and the efficiency of the thermal system can should be understood that after reading the above teach- be improved. ing, many variations and modifications may be made by [0076] As mentioned above, the invention can achieve the skilled in the art, and these equivalents also fall within the function of feedwater system and lower the pressure the scope as defined by the appended claims. of the feedwater system of high-pressure heaters, there- 5 by lowering the cost of the feedwater heater. And the drain water pump can be used, and the efficiency of ther- Claims mal system can be improved. [0077] In particular, for a 1000 MW ultra-supercritical 1. A feedwater and draining system for medium-pres- pressure generator set, the total head of the boiler feed- 10 sure heaters used in a power plant, said feedwater water pumps is about 3600 mH 2O. According to the prior and draining system comprises a feedwater piping art, the design pressure of the heaters behind the boiler (100) and a boiler feedwater pump unit (200) provid- feedwater pumps is 36 MPa. g, therefore, the heaters ed on the feedwater piping (100), are high-pressure heaters. If the boiler feedwater pump wherein, set are separated into low-pressure boiler feedwater 15 pump(s) and high-pressure boiler feedwater pump(s), - said feedwater pump unit (200) includes a low- the low-pressure boiler feedwater pump can be arranged pressure boiler feedwater pump (203) and a in frontof feedwater heaters, and thehigh- pressure boiler high-pressure boiler feedwater pump (204) pro- feedwater pump can be arranged behind feedwater heat- vided along the upstream to the downstream of ers. The head of the low-pressure boiler feedwater 20 the feedwater piping (100); pumps is about 1300 mH20, and the head of the high- - a medium-pressure feedwater heater unit pressure boiler feedwater pumps is about 2300 mH20. (300) is provided between said low-pressure The design pressure of the heaters between the feedwa- boiler feedwater pump (203) and said high- pres- ter pumps can be lowered to about 13 MPa. g, therefore, sureboiler feedwater pump (204), and said feed- the heaters are low-pressure heaters. The cost of the 25 water heater unit (300) is comprised of one or feedwater heaters of each power generator set can be more feedwater heaters. lowered by 3 million CNY, the cost of feedwater piping can be lowered by 3 million CNY, and the total cost of 2. The system according to claim 1, wherein the head the system can be lowered by 6 million CNY. The cost of said low-pressure boiler feedwater pump(203) will change with the market, and the numbers that men- 30 amounts to 30-60 percent of total head which is the tioned above are only for reference. Whatever, the cost sum of the heads of the low- pressure boiler feedwa- can be lowered significantly. ter pump(203) and the high- pressure boiler feedwa- [0078] At the same time, if the invention is employed, ter pump(204). the pressure of the feedwater downstream of the feed- water heaters will be lowered, a drain water pump can 35 3. The system according to claim 1, wherein the head be readily provided to the feedwater heaters to transfer of said low-pressure boiler feedwater pump (203) is the drain water at steam side to the feedwater down- 1200-2400m H2O; preferably 1200-1800m H2O. stream of feedwater heaters, and the efficiency of the thermal system can be improved. 4. The system according to claim 1, wherein the head [0079] For example, for a 1000 MW ultra-supercritical 40 of said high-pressure boiler feedwater pump (204) pressure generator set,if the feedwater heater unit are is 1600-2800m H2O; preferably 2200-2800m H2O. fitted with drain water pumps, the efficiency of thermal system will increase by 0.2%, thereby saving 3000 tons 5. The system according to claim 1, wherein the pres- of coal for every unit every year.In other word, it can save sure of water side of said feedwater heater unit (300) 2 million CNY. More importantly, the invention provides 45 is in a range of 5~24MPa. g. a technical solution which is more environment-friendly. [0080] The above examples are merely the preferred 6. The system according to claim 1, wherein said feed- examples for the invention, and such examples are not water heater unit (300) is comprised of 2-3 feedwater intended to limit the scope of the invention. The substan- heaters in one row or 4-6 feedwater heaters in two tial technical contents according to the present invention 50 rows. are broadly defined in the claims, and any entities or methods accomplished by others which are the same as 7. The system according to claim 1, wherein a drain those or the equivalents thereof defined by the claims self-flowing pipe (205) is provided at the steam side should be considered as falling within the scope as de- of one or each feedwater heater of said feedwater fined by the claims. 55 heater unit(300). [0081] All documents mentioned in the present appli- cation are incorporated by reference herein, as though 8. The system according to claim 1, wherein a drain individually incorporated by reference. Additionally, it water pump (206) is provided at the steam side of

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said feedwater heater unit (300).

9. A supercritical pressure generator set or an ultra- supercritical pressure generator set including the feedwater and draining system for medium- pressure 5 heaters used in a power plant according to claim 1.

10. A power plant equipment including the feedwater and draining system for medium-pressure heaters used in a power plant according to claim 1. 10

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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Non-patent literature cited in the description

• ZHENG, TIKUAN. thermal power plant equipment. China Electric Power PRESS, 2001 [0032]

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