U.S. patent application number 14/376759 was filed with the patent office on 2015-02-05 for turbine facility and water treatment method for heater drainage water.
The applicant listed for this patent is KURITA WATER INDUSTRIES LTD.. Invention is credited to Mamoru Iwasaki, Nobuaki Nagao, Masaharu Takada, Senichi Tsubakizaki.
Application Number | 20150033741 14/376759 |
Document ID | / |
Family ID | 49082372 |
Filed Date | 2015-02-05 |
United States Patent
Application |
20150033741 |
Kind Code |
A1 |
Iwasaki; Mamoru ; et
al. |
February 5, 2015 |
TURBINE FACILITY AND WATER TREATMENT METHOD FOR HEATER DRAINAGE
WATER
Abstract
Provided are a turbine facility, in which iron oxide particle
scale that adheres to inner surfaces of boiler tubes and impedes
heat transfer can be efficiently removed from heater drainage
water; and a water treatment method for heater drainage water in
the turbine facility. The turbine facility includes a boiler 9,
steam turbines 12 and 16, a condenser 1, feedwater heaters 5 and 8
which are interposed in water supply lines 4 and 6 that supply
condensate condensed by the condenser 1 to the boiler 9, and in
which part of steam supplied from the steam turbine 12 to a
repeater is extracted as extraction steam, and the feedwater is
heated using the extraction steam, and a filtration device 19 in
which heater drainage water discharged from the low-pressure
feedwater heater 5 is filtered and supplied to the water supply
system for recovery. The filtration device 19 includes a filter
having a pore size of 1 to 5 .mu.m.
Inventors: |
Iwasaki; Mamoru; (Nakano-ku,
JP) ; Nagao; Nobuaki; (Nakano-ku, JP) ;
Tsubakizaki; Senichi; (Minato-ku, JP) ; Takada;
Masaharu; (Minato-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KURITA WATER INDUSTRIES LTD. |
Nakano-ku, Tokyo |
|
JP |
|
|
Family ID: |
49082372 |
Appl. No.: |
14/376759 |
Filed: |
February 19, 2013 |
PCT Filed: |
February 19, 2013 |
PCT NO: |
PCT/JP2013/053923 |
371 Date: |
August 5, 2014 |
Current U.S.
Class: |
60/646 ;
60/657 |
Current CPC
Class: |
F01K 7/40 20130101; C02F
2101/203 20130101; C02F 1/488 20130101; C02F 1/42 20130101; C02F
2303/22 20130101; C02F 1/20 20130101; F01K 7/38 20130101; C02F
1/444 20130101 |
Class at
Publication: |
60/646 ;
60/657 |
International
Class: |
F01K 7/38 20060101
F01K007/38 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 29, 2012 |
JP |
2012-043802 |
Claims
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 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 filtration device in
which heater drainage water discharged from the feedwater heater is
filtered and supplied to the water supply system for recovery,
characterized in that the filtration device includes a filter
having a pore size of 1 to 5 .mu.m.
2. The turbine facility according to claim 1, characterized in
that, in the filtration device, the total amount of the heater
drainage water is filtered 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 drainage
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 extraction steam extracted from part of steam supplied from
the steam turbine to a reheater; and filtering heater drainage
water which is generated by cooling 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 filtered with a
filter having a pore size of 1 to 5 .mu.m.
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 filtered with the
filter 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.
Description
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 filters heater drainage water and recovers 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-temperature,
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 efficiency 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
condensate. 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 extraction steam from
the high-pressure turbine. Therefore, the condensate discharged
from a condenser passes through a low-pressure heater first, 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 condensation 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 maintaining 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 (Fe.sub.3O.sub.4) 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.
[0006] As the thickness of the magnetite layer increases
excessively, the heat-transfer coefficient decreases. Furthermore,
magnetite forms a wavelike oxide layer on the boiler tube surface
and increases the water flow resistance of boiler water, resulting
in a decrease in comprehensive energy conversion efficiency.
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 prevention of boiler tubes and
decreases in resistance of heat transfer and water flow resistance
can be achieved.
[0007] For about 20 years, a boiler water quality management
technique referred to as "CWT (Combined Water Treatment)" has been
prevalent mainly in Europe and North America. In this method,
feedwater including both condensate 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 feedwater is controlled to about 5 ppb. In the initial phase
of transition 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 (Fe.sub.2O.sub.3),
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 flow 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 condensate, the
high-pressure heater drainage, and the low-pressure 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 turbine
facility, in which CWT treatment was carried out, was made to flow
through a filter unit in which membrane filters with effective
filter pore sizes of 3, 1, 0.45, 0.2, and 0.1 .mu.m were arranged
in series, it was found that 90% or more of iron oxide scale were
retained by the membrane filter with an effective filter pore size
of 3 .mu.m. In the present invention, the pore size of the filter
(which may be described as the effective filter pore size) is
indicated by the absolute filter 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 fine 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 fine particles were
separated, and form identification was performed by Mossbauer
spectrometric analysis. As a result, it was found that composite
oxides, such as .alpha.-Fe.sub.2O.sub.3, .gamma.-Fe.sub.2O.sub.3,
and .alpha.-FeOOH were present in 80% or more, which confirmed the
formation of acicular crystals.
[0012] In the CWT treatment, the oxygen dissolved in feedwater is
consumed for oxide layer formation when being passed through boiler
tubes, and the dissolved oxygen concentration gradually decreases.
High-temperature, high-pressure 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 130.degree. C. or lower. In the low-pressure heater, since
the extraction steam from the low-pressure turbine is condensed,
developed turbulent flow occurs in the heater. Therefore, it is
believed that a situation arises where a stable hematite layer is
difficult to form on the heating surface of the low-pressure
heater. Furthermore, since the temperature of the low-pressure
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 difficult. 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
sufficiently proceed. Accordingly, it is believed that dissolution
of iron from the base material (corrosion) proceeds. Such a form of
corrosion is known as FAC (Flow Accelerated Corrosion).
[0013] Iron oxide fine particles in the low-pressure drainage 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 fine
particles in boiler feedwater have been proposed (Patent
Literatures 1 to 3).
[0015] Patent Literature 1 describes that condensate is filtered
with a membrane having a pore size of 0.01 to 0.3 .mu.m. Patent
Literature 2 describes that condensate is filtered with a membrane
having a pore size of 1 .mu.m. However, Patent Literatures 1 and 2
do not describe filtration treatment of low-pressure heater
drainage.
[0016] Patent Literature 3 describes a turbine facility configured
to filter 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 concentration is low, iron is removed with a
filter and the filtrate is used as part of boiler feedwater. The
reason for this is that, since drainage water basically contains
fine iron particles that cannot be filtered, except for the case
where the iron concentration is equal to or less than the
predetermined concentration, the iron content exceeds the allowable
limit for boiler feedwater even if filtration treatment is
performed. In such a configuration of Patent Literature 3, in
addition to the problem 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 9-206567
A
[0018] Patent Literature 2: Japanese Patent Publication 2000-218110
A
[0019] Patent Literature 3: Japanese Patent Publication 2008-25922
A
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
efficiently 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 filtration device in which heater drainage water
discharged from the feedwater heater is filtered and supplied to
the water supply system for recovery, in which the filtration
device includes a filter having a pore size of 1 to 5 .mu.m.
[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 filtering heater drainage water which is generated by
cooling the extraction steam in the feedwater heater so as to be
recovered to a water supply system, in which the heater drainage
water is filtered with a filter having a pore size of 1 to 5
.mu.m.
[0023] In the present invention, preferably, the total amount of
heater drainage water is filtered and supplied to the water supply
system. The feedwater heater for filtering drainage water is
preferably a low-pressure feedwater heater.
ADVANTAGEOUS EFFECTS OF INVENTION
[0024] In the present invention, since iron oxide fine particles
are efficiently removed from heater drainage water by filtering the
heater drainage water using a filter having a pore size of 1 to 5
.mu.m, adhesion of iron oxide fine 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 drainage 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 filtered and supplied to the water supply
system, and thus the water recovery rate is high.
[0027] Most of the iron oxide fine particles introduced into boiler
feedwater are attributed to low-pressure heater drainage. In
general, a filter has an appropriate flow velocity for use. When
low-pressure heater drainage is subjected to filtration treatment,
the amount of treated water is about one tenth compared with the
case where the total amount of condensate is subjected to
filtration treatment. Consequently, it is possible to provide a
compact filtration device which has a small number of filters
installed.
[0028] Many of the iron oxide fine particles generated in the
low-pressure heater are acicular crystals that can be retained by a
membrane with an effective filter pore size of 3 .mu.m. Therefore,
by using a filter with an effective filter pore size of 1 to 5
.mu.m, the particles can be retained sufficiently. Since the filter
pore size is large at 1 to 5 .mu.m and the shape of fine particles
is acicular, the flow 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 condenser 1 is supplied
through an electromagnetic filter 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 high-pressure
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 flowing 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 effluent
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-pressure heater drainage water is
supplied via a line 18 to a filtration device 19, and after being
filtered, 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 inflow side of the low-pressure
feedwater heater 5 or the line 6 on the outflow side.
[0035] The filter used in the filtration device 19 has a pore size
(effective filter pore size) of 1 to 5 .mu.m, preferably 1 to 4
.mu.m, more preferably 2 to 4 .mu.m, and still more preferably 2 to
3 .mu.m. When the pore size of the filter is less than 1 .mu.m, the
flow pressure loss increases. When the pore size is more than 5
.mu.m, retention of iron oxide fine particles becomes insufficient.
The LV of the filtration 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 filter is not particularly limited.
However, since the temperature of low-pressure heater drainage
water is 80.degree. C. to 130.degree. C., the material is
preferably endurable for use in this temperature range for a
minimum of one year. Specifically, a nonwoven fabric composed of
polyphenylene sulfide fibers or fluororesin fibers is suitably
used. When a nonwoven fabric filter alone is used, deposition of
the filter cake and flow of filter fluid may cause distortion of
the fiber layer, and the predetermined filtration efficiency may
not be obtained in some cases. Therefore, the filter to be used
preferably has a three-layer structure in which a nonwoven fabric
is sandwiched at both surfaces between spunbonded sheets having a
mechanical strength, and these layers are integrated by
embossing.
[0037] According to this embodiment, since iron oxide fine
particles are sufficiently removed from low-temperature heater
drainage water, adhesion of iron oxide fine particles to inner
surfaces of boiler tubes can be prevented (which also includes
suppression). Since the total amount of low-pressure heater
drainage water is filtered, the water recovery rate is high, and
the configuration of supplying water to the filtration 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 flow through a filter unit, in which first to fifth
membrane filters with effective filter pore sizes of 3, 1, 0.45,
0.2, and 0.1 .mu.m were arranged in series, from the 3-.mu.m
membrane side at a flow linear velocity (LV) of 2.3 cm/min for 4
Hr. The distribution of the amount of iron oxide retained by the
filters with the respective pore sizes was measured. The result
thereof is shown in Table 1.
TABLE-US-00001 TABLE 1 Weight percentage Filter of total iron
(effective filter pore size) retained (%) First membrane filter (3
.mu.m) 95.3 Second membrane filter (1 .mu.m) 1.64 Third membrane
filter (0.45 .mu.m) 0.82 Fourth membrane filter (0.2 .mu.m) 1.31
Fifth membrane filter (0.1 .mu.m) 0.95
[0039] The sum total of the amount of iron oxide retained by the
first to fifth membrane filters was divided by the integrated flow
rate and converted into the amount of Fe (iron). The calculation
result was 25 .mu.g-Fe/L. The total iron concentration in the
filtrate passed through all of the first to fifth membrane filters
was 1.4 .mu.g-Fe/L.
Experimental Example 2
[0040] Boiler drainage at 125.degree. C. (pressure 0.25 MPa (G))
was made to flow at 580 mL/min through a pleated filter (effective
filter pore size: 2 .mu.m) with a diameter of 70 mm and an
effective length of the filter surface of 25 mm, which was produced
by folding three SMS sheets, each being obtained by sandwiching a
nonwoven fabric composed of polyphenylene sulfide thin filaments
spun by a melt blow method between spunbonded sheets, followed by
embossing. The total iron concentration of the influent water was
48 .mu.g-Fe/L, and the total iron concentration in the filtrate at
the outlet of the pleated filter was 2.0 .mu.g-Fe/L.
[0041] The particle size distribution of the filter 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 .mu.m. The cumulative
content of particles having a particle size of 1 .mu.m or less was
about 5% by weight, and the cumulative content of particles having
a particle size of 5 .mu.m or less was about 40% by weight. This
shows that even when a filter with an effective filter pore size of
less than 1 .mu.m is used, the particle retention rate is not
improved, and that when a filter with an effective filter pore size
of more than 5 .mu.m 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 .mu.g-Fe/L is made to pass through the
filter 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 specific embodiments, it will be apparent to those
skilled in the art that various changes and modifications may be
made therein without departing from the spirit and scope of the
invention.
[0044] This application claims the benefit of Japanese Patent
Application No. 2012-043802, filed Feb. 29, 2012, which is hereby
incorporated by reference herein in its entirety.
* * * * *