US 20150033741A1

(19) United States (12) Patent Application Publication (10) Pub. No.: US 2015/0033741 A1

Iwasaki et al. (43) Pub. Date: Feb. 5, 2015

(54) TURBINE FACILITY AND WATER Publication Classi?cation TREATMENT METHOD FOR HEATER DRAINAGE WATER (51) Int- Cl

F01K 7/38 (2006.01) (71) Applicant: KURITA WATER INDUSTRIES (52) U-s- Cl

LTD Nakanwku Tokyo (Jp) CPC ...................................... .. F 01K 7/38 (2013.01) USPC ............................................. .. 60/646; 60/657

(72) Inventors: Mamoru Iwasaki, Nakano-ku (JP); (57) ABSTRACT NObllald Nagaof NalfanQ'ku (JP); Provided are a turbine facility, in Which iron oxide particle semehl TSUbaklzakl> Mlnato'ku (JP); scale that adheres to inner surfaces of boiler tubes and Masahalll Takada, Mlnato'ku (JP) impedes heat transfer can be e?iciently removed from heater

drainage water; and a water treatment method for heater (21) Appl. No.: 14/376,759 drainage water in the turbine facility. The turbine facility

includes a boiler 9, steam turbines 12 and 16, a condenser 1, (22) PCT Filed; Feb 19, 2013 feedwater heaters 5 and 8 Which are interposed in water

supply lines 4 and 6 that supply condensate condensed by the (86) PCT NO _ PCT/JP2013/053923 condenser 1 to the boiler 9, and in Which part of steam sup

" plied from the steam turbine 12 to a repeater is extracted as 371 (0X1), extraction steam, and the feedwater is heatedusing the extrac (2) Date: Aug 5, 2014 tion steam, and a ?ltration device 19 in Which heater drainage

water discharged from the low-pressure feedwater heater 5 is (30) Foreign Application Priority Data ?ltered and supplied to the water supply system for recovery.

The ?ltration device 19 includes a ?lter having a pore size of Feb. 29, 2012 (JP) ............................... .. 2012-043802 1 to 5 pm.

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US 2015/0033741A1

TURBINE FACILITY AND WATER TREATMENT METHOD FOR HEATER

DRAINAGE WATER

FIELD OF INVENTION

[0001] The present invention relates to a turbine facility, and more particularly relates to a turbine facility equipped with a mechanism that ?lters heater drainage water and recov ers water to a feed pipe. Furthermore, the present invention relates to a water treatment method for heater drainage water in the turbine facility.

BACKGROUND OF INVENTION

[0002] In thermal and nuclear power plants and the like, generated high-temperature, high-pressure steam is supplied to a turbine, and the turbine is driven by the steam to generate power. The steam which has driven the turbine is cooled and converted to the form of water by a condenser, and then the water is heated again and supplied to a boiler, nuclear reactor, or steam generator for reuse.

[0003] In large-scale power generation facilities, high pressure and low-pressure straight multi-stage steam turbines are used in many cases. The turbine is rotated by high-tem perature, high-pressure steam generated in a boiler or steam generator, and thus a power generator is rotated. As steam expands, its enthalpy decreases and the steam becomes wet steam. In the state of wet steam, the energy conversion ef? ciency in the turbine decreases, and therefore, partial of wet steam is performed at a predetermined stage of the turbine. The extraction steam has a large amount of energy including latent heat of vaporization. Accordingly, for the purpose of heat recovery, the bleed of steam from the predetermined stage of the turbine is led to a heat exchanger and subjected to indirect heat exchange with condensate, thus heating the con densate. A heat exchanger which heats the condensate using the extraction steam from a high-pressure turbine is referred to as a high-pressure heater, and a heat exchanger which heats the condensate using the extraction steam from a low pressure turbine is referred to as a low-pressure heater. [0004] The extraction steam from the low-pressure turbine is low in temperature and pressure compared with the extrac tion steam from the high-pressure turbine. Therefore, the condensate discharged from a condenser passes through a low-pressure heater ?rst, then passes through a deaerator, a high-pressure heater, and an economizer, and circulated again as feedwater to the boiler. Furthermore, high-pressure heater drainage generated by condensation in the high-pressure heater and low-pressure heater drainage generated by con densation in the low-pressure heater are led to a condensate main pipe, and recycled as boiler feedwater. [0005] In boilers, water quality management of feedwater is important in order to prevent damage on heat transmission tubes due to corrosion. Hitherto, for the purpose of maintain ing the pH of boiler feedwater on the alkali side, volatile amines and nitrogen compounds, such as hydrazine and ammonia, have been used. Furthermore, these pH adjustors also act as reducing agents and form a black oxide layer of magnetite (Fe3O4) on the boiler tube surface, thus exhibiting anti-corrosion behavior. Such a boiler water treatment method is referred to as AVT (All Volatile Treatment) and has long been considered as the standard for boiler water quality management.

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[0006] As the thickness of the magnetite layer increases excessively, the heat-transfer coef?cient decreases. Further more, magnetite forrns a wavelike oxide layer on the boiler tube surface and increases the water ?ow resistance of boiler water, resulting in a decrease in comprehensive energy con version e?iciency. Therefore, in power generation facilities, once in three to four years, chemical cleaning is performed during the periodic maintenance so that excessive growth of magnetite oxide layers can be controlled and corrosion pre vention of boiler tubes and decreases in resistance of heat transfer and water ?ow resistance can be achieved. [0007] For about 20 years, a boiler water quality manage ment technique referred to as CWT (Combined Water Treat ment) has been prevalent mainly in Europe and North America. In this method, feedwater including both conden sate and makeup water is treated with a deaerator, in which oxygen, inert gases, and the like are removed, and then by adding pure oxygen, the oxygen concentration in the feedwa ter is controlled to about 5 ppb. In the initial phase of transi tion to CWT, combined treatment using ammonia together with oxygen was mainly carried out. In recent years, oxygen treatment in which oxygen only is added has become the mainstream. By the oxygen treatment, a layer of hematite (Fe203), which is more oxidized than magnetite, is formed on the boiler tube surface. The hematite layer is very dense, the surface thereof is smoother than that of the magnetite layer, and therefore, the hematite layer does not increase water ?ow resistance. Furthermore, the hematite layer is also chemically stable and has a high anti-corrosion effect. Therefore, CWT less frequently requires chemical cleaning than AVT. For these reasons, the number of boilers to which CWT treatment is applied has been increasing in large-scale thermal power plants in Japan. [0008] As described above, the condensate from the turbine is heated by a feedwater heater which uses the extraction steam as a heat source. The drainage from the feedwater heater joins the condensate and recycled as feedwater. [0009] In the turbine facility in which CWT treatment was carried out, when the total iron concentration in the conden sate, the high-pressure heater drainage, and the low-pres sure heater drainage was measured, the iron concentration in the low-pressure heater drainage was markedly higher than that of other water. Thus, it became evident that the cause for increasing the iron concentration in the boiler feedwater was the low-pressure heater drainage. [0010] When the low-pressure heater drainage in the tur bine facility, in which CWT treatment was carried out, was made to ?ow through a ?lter unit in which membrane ?lters with effective ?lter pore sizes of 3, l, 0.45, 0.2, and 0.1 pm were arranged in series, it was found that 90% or more of iron oxide scale were retained by the membrane ?lter with an effective ?lter pore size of 3 pm. In the present invention, the pore size of the ?lter (which may be described as the effective ?lter pore size) is indicated by the absolute ?lter pore size that allows particles with a target particle size to be removed at a probability of 99% or more.

[0011] When the iron oxide ?ne particles were observed with an electron microscope, they were found to be acicular crystals having a very high ratio of length to cross-sectional diameter of the particle (shape ratio). The iron oxide ?ne particles were separated, and form identi?cation was per formed by Mossbauer spectrometric analysis. As a result, it was found that composite oxides, such as (x-Fe203, y-Fe203,

US 2015/0033741A1

and (x-FeOOH were present in 80% or more, which con?rmed the formation of acicular crystals. [0012] In the CWT treatment, the oxygen dissolved in feed water is consumed for oxide layer formation when being passed through boiler tubes, and the dissolved oxygen con centration gradually decreases. High-temperature, high-pres sure steam generated in the boiler decreases in temperature and pressure as being expanded in the turbine. In the low pressure heater, the saturation temperature becomes 1300 C. or lower. In the low-pressure heater, since the extraction steam from the low-pressure turbine is condensed, developed turbulent ?ow occurs in the heater. Therefore, it is believed that a situation arises where a stable hematite layer is dif?cult to form on the heating surface of the low-pressure heater. Furthermore, since the temperature of the low-pres sure heater is lower than that of the boiler tubes, the oxidation reaction rate of the base material the heat transmission tube decreases, and the formation of the hematite oxide layer further becomes dif?cult. As described above, on the heating surface of the low-pressure heater, there is a situation where, physically and chemically, formation of the hematite layer is unlikely to suf?ciently proceed. Accordingly, it is believed that dissolu tion of iron from the base material (corrosion) proceeds. Such a form of corrosion is known as FAC (Flow Accelerated Corrosion). [0013] Iron oxide ?ne particles in the low-pressure drain age are believed to be formed because the dissolved iron is subjected to oxidation in the drain bulk and precipitated as hematite or geothite (FeOOH) particles which have a low solubility and which are chemically stable. [0014] Techniques for the purpose of removing iron oxide ?ne particles in boiler feedwater have been proposed (Patent Literatures l to 3). [0015] Patent Literature 1 describes that condensate is ?l tered with a membrane having a pore size of 0.01 to 0.3 pm. Patent Literature 2 describes that condensate is ?ltered with a membrane having a pore size of 1 pm. However, Patent Lit eratures l and 2 do not describe ?ltration treatment of low pressure heater drainage. [0016] Patent Literature 3 describes a turbine facility con ?gured to ?lter low-pressure heater drainage and supply water to a water supply system and a water treatment method of heater drainage water in the turbine facility. In Patent Literature 3, when the iron concentration of drainage water exceeds a predetermined concentration, the drainage water is discharged out of the system. Only when the iron concentra tion is low, iron is removed with a ?lter and the ?ltrate is used as part of boiler feedwater. The reason for this is that, since drainage water basically contains ?ne iron particles that can not be ?ltered, except for the case where the iron concentra tion is equal to or less than the predetermined concentration, the iron content exceeds the allowable limit for boiler feed water even if ?ltration treatment is performed. In such a con?guration of Patent Literature 3, in addition to the prob lem that large-scale equipment is required, there are other problems in that the water recovery rate from heater drainage water decreases because drainage water having a high iron content is discharged out of the system, and the amount of discharge water increases.

LIST OF LITERATURES

[0017] Patent Literature 1: Japanese Patent Publication 9-206567A

Feb. 5, 2015

[0018] Patent Literature 2: Japanese Patent Publication 2000-218110A [0019] Patent Literature 3: Japanese Patent Publication 2008-25922A

OBJECT AND SUMMARY OF INVENTION

[0020] It is an object of the present invention to provide a turbine facility in which iron oxide particle scale that adheres to inner surfaces of boiler tubes and impedes heat transfer can be ef?ciently removed from heater drainage water, and a water treatment method for heater drainage water in a turbine facility. [0021] A turbine facility according to the present invention includes a boiler in which steam is generated by heat from a heat source, a steam turbine which is driven by the steam of the boiler, a condenser which condenses steam from the steam turbine, a water supply system which supplies condensate condensed by the condenser as feedwater to the boiler side, a feedwater heater which is interposed in the water supply system and in which part of steam supplied from the steam turbine to a reheater is extracted as extraction steam, and the feedwater is heated using the extraction steam, and a ?ltration device in which heater drainage water discharged from the feedwater heater is ?ltered and supplied to the water supply system for recovery, in which the ?ltration device includes a ?lter having a pore size of l to 5 pm. [0022] A water treatment method for heater drainage water in a turbine facility according to the present invention includes vaporizing and superheating feedwater in a boiler by heat from a heat source, driving a steam turbine by means of generated steam, condensing steam discharged from the steam turbine with a condenser to form feedwater, supplying the feedwater to the boiler side, heating the feedwater in a feedwater heater using extraction steam extracted from part of steam supplied from the steam turbine to a reheater, and ?ltering heater drainage water which is generated by cooling the extraction steam in the feedwater heater so as to be recov ered to a water supply system, in which the heater drainage water is ?ltered with a ?lter having a pore size of l to 5 pm. [0023] In the present invention, preferably, the total amount of heater drainage water is ?ltered and supplied to the water supply system. The feedwater heater for ?ltering drainage water is preferably a low-pressure feedwater heater.

ADVANTAGEOUS EFFECTS OF INVENTION

[0024] In the present invention, since iron oxide ?ne par ticles are ef?ciently removed from heater drainage water by ?ltering the heater drainage water using a ?lter having a pore size of l to 5 pm, adhesion of iron oxide ?ne particles to inner surfaces of boiler tubes can be prevented. [0025] In the present invention, there is no need for a mechanism to measure the iron concentration in heater drain age water and accordingly change the destination to which heater drainage water is supplied. [0026] In the present invention, the total amount of heater drainage water can be ?ltered and supplied to the water sup ply system, and thus the water recovery rate is high. [0027] Most of the iron oxide ?ne particles introduced into boiler feedwater are attributed to low-pressure heater drain age. In general, a ?lter has an appropriate ?ow velocity for use. When low-pressure heater drainage is subjected to ?ltra tion treatment, the amount of treated water is about one tenth compared with the case where the total amount of condensate

US 2015/0033741A1

is subjected to ?ltration treatment. Consequently, it is pos sible to provide a compact ?ltration device which has a small number of ?lters installed. [0028] Many of the iron oxide ?ne particles generated in the low-pressure heater are acicular crystals that can be retained by a membrane with an effective ?lter pore size of 3 pm. Therefore, by using a ?lter with an effective ?lter pore size of 1 to 5 pm, the particles can be retained su?iciently. Since the ?lter pore size is large at 1 to 5 pm and the shape of ?ne particles is acicular, the ?ow pressure loss is unlikely to increase even when continuously used.

BRIEF DESCRIPTION OF DRAWINGS

[0029] FIG. 1 is a block diagram of a turbine facility according to an embodiment. [0030] FIG. 2 is a graph showing experimental results.

DESCRIPTION OF EMBODIMENTS

[0031] The present invention will be described in more detail below with reference to the drawings. [0032] FIG. 1 shows a turbine facility according to an embodiment. Water (condensate and makeup water) in a con denser 1 is supplied through an electromagnetic ?lter 2 and a deionizer 3 including ion exchange resins, via a line 4, to low-pressure feedwater heaters 5, and heated. The heated water is supplied via line 6 to a deaerator 7, subjected to deaeration treatment, then heated by hi gh-pres sure feedwater heaters 8, and supplied to a boiler 9. Steam generated in the boiler 9 is superheated by a superheater 10, and then supplied via a steam line 11 to a high-pressure turbine 12. [0033] Steam ?owing out of the high-pressure turbine 12 is sent via a steam line 13 to a reheater 14, reheated, and then supplied via a steam line 15 to a low-pressure turbine 16. The e?luent steam therefrom is returned to the condenser 1. [0034] An extraction steam line 17 branches off from the steam line 13. Part of steam is separated from the line 11, supplied to the heat source side of the low-pressure feedwater heater 5, and heat-exchanged with water to form drainage water (low -pressure heater drainage water). The low-pres sure heater drainage water is supplied via a line 18 to a ?ltration device 19, and after being ?ltered, supplied via a return line 20 to the water side of the low-pressure feedwater heater 5. The return line 20 may be connected to the line 4 on the in?ow side of the low-pressure feedwater heater 5 or the line 6 on the out?ow side. [0035] The ?lter used in the ?ltration device 19 has a pore size (effective ?lter pore size) of 1 to 5 pm, preferably 1 to 4 pm, more preferably 2 to 4 pm, and still more preferably 2 to 3 pm. When the pore size of the ?lter is less than 1 pm, the ?ow pressure loss increases. When the pore size is more than 5 pm, retention of iron oxide ?ne particles becomes insu?i cient. The LV of the ?ltration device 19 is 0.2 to 1.2 m/Hr, and particularly preferably about 0.3 to 1.0 m/ Hr. [0036] The material for the ?lter is not particularly limited. However, since the temperature of low-pres sure heater drain age water is 80 C. to 130 C., the material is preferably endurable for use in this temperature range for a minimum of one year. Speci?cally, a nonwoven fabric composed of polyphenylene sul?de ?bers or ?uororesin ?bers is suitably used. When a nonwoven fabric ?lter alone is used, deposition of the ?lter cake and ?ow of ?lter ?uid may cause distortion of the ?ber layer, and the predetermined ?ltration e?iciency may not be obtained in some cases. Therefore, the ?lter to be

Feb. 5, 2015

used preferably has a three-layer structure in which a non woven fabric is sandwiched at both surfaces between spun bonded sheets having a mechanical strength, and these layers are integrated by embossing. [0037] According to this embodiment, since iron oxide ?ne particles are su?iciently removed from low-temperature heater drainage water, adhesion of iron oxide ?ne particles to inner surfaces of boiler tubes can be prevented (which also includes suppression). Since the total amount of low-pres sure heater drainage water is ?ltered, the water recovery rate is high, and the con?guration of supplying water to the ?ltration device 19 is simple and low cost.

EXAMPLES

Experimental Example 1 [0038] Low-pressure heater drainage in a turbine facility of a thermal power plant, in which CWT treatment was carried out, was made to ?ow through a ?lter unit, in which ?rst to ?fth membrane ?lters with effective ?lter pore sizes of 3, 1, 0.45, 0.2, and 0.1 pm were arranged in series, from the 3-um membrane side at a ?ow linear velocity (LV) of 2.3 cm/min for 4 Hr. The distribution of the amount of iron oxide retained by the ?lters with the respective pore sizes was measured. The result thereof is shown in Table 1.

TABLE 1

Weight percentage Filter of total iron (effective ?lter pore size) retained (%) First membrane ?lter (3 pm) 95.3 Second membrane ?lter (1 pm) 1.64 Third membrane ?lter (0.45 pm) 0.82 Fourth membrane ?lter (0.2 pm) 1.31 Filth membrane ?lter (0.1 pm) 0.95

[0039] The sum total of the amount of iron oxide retained by the ?rst to ?fth membrane ?lters was divided by the inte grated ?ow rate and converted into the amount of Fe (iron). The calculation result was 25 ug-Fe/L. The total iron concen tration in the ?ltrate passed through all of the ?rst to ?fth membrane ?lters was 1.4 ug-Fe/L.

Experimental Example 2 [0040] Boiler drainage at 125 C. (pressure 0.25 MPa (G)) was made to ?ow at 580 mL/min through a pleated ?lter (effective ?lter pore size: 2 pm) with a diameter of 70 mm and an effective length of the ?lter surface of 25 mm, which was produced by folding three SMS sheets, each being obtained by sandwiching a nonwoven fabric composed of polyphe nylene sul?de thin ?laments spun by a melt blow method between spunbonded sheets, followed by embossing. The total iron concentration of the in?uent water was 48 ug-Fe/L, and the total iron concentration in the ?ltrate at the outlet of the pleated ?lter was 2.0 ug-Fe/L. [0041] The particle size distribution of the ?lter cake obtained by continuously passing water was measured by an ultrasonic particle size analyzer. As a result, as shown in FIG. 2, the 50% by weight average particle size was 7 to 8 pm. The cumulative content of particles having a particle size of 1 pm or less was about 5% by weight, and the cumulative content of particles having a particle size of 5 pm or less was about 40% by weight. This shows that even when a ?lter with an effective

US 2015/0033741A1

?lter pore size of less than 1 pm is used, the particle retention rate is not improved, and that When a ?lter With an effective ?lter pore size of more than 5 pm is used, the particle retention rate decreases. [0042] Furthermore, it has become evident that, in this state, even if water passing is continued for 120 days, the differential pressure is about 5 kPa, and even When drainage having a concentration of about 20 ug-Fe/L is made to pass through the ?lter for one year, the differential pressure does not increase to such an extent that passing of water is impeded. [0043] Although the present invention have been described in detail on the basis of speci?c embodiments, it Will be apparent to those skilled in the art that various changes and modi?cations may be made therein Without departing from the spirit and scope of the invention. [0044] This application claims the bene?t of Japanese Patent Application No. 2012-043802, ?led Feb. 29, 2012, Which is hereby incorporated by reference herein in its entirety.

1. A turbine facility comprising: a boiler in Which steam is generated by heat from a heat

source; a steam turbine Which is driven by the steam of the boiler; a condenser Which condenses steam from the steam tur

bine; a water supply system Which supplies condensate con

densed by the condenser as feedwater to the boiler side; a feedwater heater Which is interposed in the water supply

system and in Which part of steam supplied from the steam turbine to a reheater is extracted as extraction steam, and the feedwater is heated using the extraction steam; and

a ?ltration device in Which heater drainage water dis charged from the feedwater heater is ?ltered and sup plied to the water supply system for recovery,

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characterized in that the ?ltration device includes a ?lter having a pore size of 1 to 5 pm.

2. The turbine facility according to claim 1, characterized in that, in the ?ltration device, the total amount of the heater drainage water is ?ltered and supplied to the water supply system.

3. The turbine facility according to claim 1, characterized in that the heater drainage water is low-pressure heater drain age water.

4. A water treatment method for heater drainage water in a turbine facility comprising:

vaporizing and superheating feedwater in a boiler by heat from a heat source;

driving a steam turbine by means of generated steam; condensing steam discharged from the steam turbine With

a condenser to form feedwater; supplying the feedwater to the boiler side; heating the feedwater in a feedwater heater using extrac

tion steam extracted from part of steam supplied from the steam turbine to a reheater; and

?ltering heater drainage water Which is generated by cool ing the extraction steam in the feedwater heater so as to be recovered to a water supply system,

characterized in that the heater drainage water is ?ltered With a ?lter having a pore size of 1 to 5 pm.

5. The water treatment method for heater drainage water in a turbine facility according to claim 4, characterized in that the total amount of the heater drainage water is ?ltered With the ?lter and recovered to the water supply system.

6. The water treatment method for heater drainage water in a turbine facility according to claim 4, characterized in that the heater drainage water is low-pressure heater drainage water.