JPH1094719A - Method for removing iron component in heater drain water in electric power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably and surely remove iron components such as iron oxide fine particles included in a heater drain water and to effectively prevent the iron components from entering into a steam generator or a boiler in an electric power plant. SOLUTION: Before the heater drain water in the electric power plant is supplied as steam producing water, the heater drain water is passed through a hollow fiber membrane 28 to remove the iron component essentially consisting of iron oxide fine particles in the water by the hollow fiber membrane 28. In this method, before the heater brain water is passed through the hollow fiber membrane, water added with γ-Fe2 O3 or Fe3 O4 fine particles having 1 to 10μm particle size as iron fine particles is passed through the hollow fiber membrane 28 to form a coating film D1 of iron oxide fine particles on the filtering face of the hollow fiber membrane 28.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing iron components in heater drain water in a power plant, for example, a pressurized water nuclear power plant (hereinafter, referred to as "PWR"), a boiling water nuclear power plant (hereinafter, "BWR"). ) And a method for removing iron components in heater drain water suitable for removing iron oxide contained in heater drain water of a thermal power plant.

[0002]

2. Description of the Related Art For example, in recent PWRs, impurities such as metal oxides containing iron oxide as a main component are introduced into a secondary side unit of a steam generator for producing steam for driving a turbine along with water supply. . Then, during the power generation, the impurities gradually adhere to the outer surface of the heat transfer tube of the steam generator, and the heat transfer efficiency of the steam generator decreases due to the attached matter. Moreover,
Since these impurities gradually increase and concentrate during the circulation of the feedwater, various measures have been conventionally studied to reduce the impurity concentration in the feedwater to the steam generator. Also, P
As in the case of the WR, in a thermal power plant, the above-mentioned impurities contained in the water supply to the boiler adhere to the heat transfer tubes of the boiler, and the deposit increases the pressure difference of the boiler.
Various measures for reducing the rise in the differential pressure have been conventionally studied.

[0003]

However, various iron removal methods for effectively removing impurities containing iron oxide as a main component brought into a steam generator or a boiler have been conventionally studied, but there is still a solid technique. It has not been established yet. Considering the sources of such impurities, it can be seen that they are roughly classified into those brought in from the condensate system and those brought in from various heater drain systems. However, the condensate system is generally equipped with a prefilter and a condensate desalination device, or a condensate purification device consisting of a condensate desalination device alone. Is relatively small. Therefore, in order to reduce the concentration of impurities brought into the water supply to the steam generator or the boiler, it is considered effective to reduce impurities brought in from various heater drain systems after the condensate purification system.

In order to effectively remove impurities from the heater drain water, a method of filtering the impurities using a filter such as an electromagnetic filter or a metal filter has been conventionally studied. Since iron components such as iron oxide are extremely fine particles and the filter removal performance is unstable, filters such as electromagnetic filters and metal filters have not yet been applied to power plants, Impurities due to various heater drain systems are not removed at all and are directly removed from the steam generator or into the boiler together with the feedwater, effectively removing impurities brought into the steam generator or boiler feedwater. Can not do it.

[0005] In addition to the above-mentioned filters, there is a membrane filter such as a hollow fiber membrane as a filter for removing fine particles. Removal performance is unstable. For this reason, it is known that the stability of the iron removal performance of the membrane filter is improved by pre-coating the membrane filter with iron oxide fine particles before water passage and forming a coating film of the iron oxide fine particles on the filtration surface.

However, when the water temperature is, for example, 60 to 70 ° C.
It has been found that in the case of the heater drain water reaching the temperature, the iron removal performance exhibits excellent iron removal performance only in the initial stage without sustainability, and the iron removal rate rapidly decreases in a short time. The mechanism of such a rapid decrease in the iron removal rate is that the presence form (oxidation state, crystal state, etc.) of the iron oxide fine particles in the precoat film is diverse and unique, in combination with the high temperature of the heater drain water. These factors remain unclear.
Therefore, a high iron removal rate cannot be stably maintained only by pre-coating the iron oxide fine particles, and in order to maintain a high iron removal rate, the pre-coating must be frequently re-coated. In addition to an increase in the amount of fine particles used, there was a problem that the operation of the filter had to be frequently stopped.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is intended to stably and reliably remove iron components such as iron oxide fine particles contained in heater drain water, and to provide a steam generator or boiler for a power plant. It is an object of the present invention to provide a method for removing an iron component in heater drain water in a power plant that can effectively prevent the introduction of an iron component into the water.

[0008]

The present inventors have conducted various studies on the method of removing the iron component of the heater drain water in a power plant, and in particular, on the iron removal performance of a filter precoated with iron oxide fine particles. I got
That is, heater drain water was passed through using filters precoated with various iron oxide fine particles, and as a result of examining the relationship between each iron oxide fine particle and the iron removal rate, α-Fe ₂ O ₃ ( In the case of hematite) and α-FeOOH (goethite), the iron removal rate with respect to high-temperature water such as heater drain water is poor, and although the iron removal rate is excellent at the beginning of the passage of water, the iron removal rate rapidly decreases in a short time. It turned out to be lower. However, among iron oxides, in the case of γ-Fe ₂ O ₃ (maghemite) or Fe ₃ O ₄ (magnetite), fine particles adjusted to a specific particle size show an extremely high iron removal rate, and furthermore, the iron removal rate is high. It was found that the iron ratio was stably maintained over a long period of time and was practically excellent.

The present invention has been made based on the above findings, and a method for removing an iron component in heater drain water in a power plant according to claim 1 is to remove the heater drain water before supplying the heater drain water as water for generating steam. A method for removing iron components in the heater drain water by passing water through a filter, wherein prior to passing the heater drain water through the filter, 1 to 10 μm of γ-Fe ₂ O ₃ as iron oxide fine particles is used. Alternatively, water to which fine particles of Fe ₃ O ₄ are added is passed through the filter, and a coating film of the iron oxide fine particles is formed on a filtration surface of the filter.

[0010] A method for removing an iron component from heater drain water in a power plant according to claim 2 of the present invention comprises:
In the invention according to claim 1, the coating amount of the iron oxide fine particles on the filter is 5 to 100 g (Fe equivalent).
/ M ² .

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As a filtration medium used in the present invention, in order to remove an Fe component in heater drain water by a fine particle layer of 1 to 10 μm of γ-Fe ₂ O ₃ or Fe ₃ O ₄ , a filtration surface is used. Γ-Fe ₂ O ₃ or Fe ₃
Any type of filtration medium can be used as long as it has a filtration accuracy capable of pre-coating the O ₄ fine particle layer and can transmit water through the pre-coat layer and the filtration layer. That is, as the filtration medium, a pleated filter, a ceramic filter, a sintered metal filter, a metal filter, or the like can be applied in addition to the hollow fiber membrane filter described in the present embodiment.

Hereinafter, the present invention will be described based on an embodiment shown in FIGS. 1 to 7 in the case where a hollow fiber membrane filter is used as a filtration medium. In each of the drawings, FIG. 1 is a configuration diagram showing an example of a filtration device suitably used in carrying out the method for removing an iron component in heater drain water of the present invention, and FIG. 2 is used in the filtration device shown in FIG. FIG. 3 is a cross-sectional view showing a hollow fiber membrane module, and FIG. 3 is a cross-sectional view showing a partially enlarged hollow fiber membrane to explain a state of the hollow fiber membrane when the heater drain water is filtered by the filtration device shown in FIG. FIG. 4 is a block diagram showing a system of a low-pressure feed water heater of a power plant to which the filtration device shown in FIG. 1 is applied. FIG. 5 is a diagram showing the fine particles of γ-Fe ₂ O ₃ and Fe ₃ O ₄ singly and individually. FIG. 6 is a graph showing the results of Example 1 in which the iron removal rate of the precoated hollow fiber membrane with respect to the heater drain water was experimentally examined. FIG.
FIG. 5 showing the results of Example 2 in which experiments were performed under the same conditions as in Example 1 except that the amounts of use of ₂ O ₃ and Fe ₃ O ₄ were reduced.
FIG. 7 is a diagram corresponding to FIG. 5 showing the results of Comparative Example 1 which was tested under the same conditions as Example 1 except that α-FeOOH microparticles were used.

First, an embodiment in which the method for removing iron from the heater drain water of the present invention is applied to a filtration device attached to a low-pressure water heater in a power plant will be described. That is, the filtration device 10 is attached to a low-pressure feed water heater of a power plant to be described later, filters drain water generated in the low-pressure heater (hereinafter, referred to as “heater drain water”), and removes impurities, particularly iron oxide fine particles, from the heater drain water. It is configured to remove iron components such as.

[0014] As shown in FIG.
A filtration tower 11 for filtering the heater drain water by a hollow fiber membrane module in which a number of external pressure type hollow fiber membranes to be described later are bundled, and a hollow fiber membrane module of the filtration tower 11 is provided with water to which iron oxide fine particles are added to allow water to flow. A coating film forming apparatus 12 for forming a coating film of iron oxide fine particles on the filtration surface of the yarn membrane;
And a water to which iron oxide fine particles are added is filtered through the circulation pipe 13 through the circulation pipe 13.
And a circulating pump 14 for circulating the water.

As shown in FIG. 1, the filtration tower 11 includes a closed vessel 15 and an upper chamber 16 and a lower chamber 1 inside the closed vessel 15.
7, and a plurality of hollow fiber membrane modules 19 having an upper end fixed to the partition plate 18 and a lower end hanging down to the lower chamber 17 side, from an inflow pipe 20 connected to the lower chamber 17. The heater drain water flowing into the lower chamber 17 is filtered by a number of hollow fiber membranes 28 (see FIG. 2) constituting each hollow fiber membrane module 19 to filter an iron component mainly composed of iron oxide fine particles. The water is configured to flow out of the outflow pipe 21 connected to the upper chamber 16.

A baffle plate 22 is disposed at the center near the bottom of the lower chamber 17 so as to face the inlet of the heater drain water.
The heater drain water flowing into the inside 7 is dispersed. A distribution mechanism 23 is disposed between the baffle plate 22 and the lower end of the hollow fiber membrane module 19. The distribution mechanism 23 once receives the heater drain water from the baffle plate 22, and then continuously supplies the hollow fiber membrane module 19 with each other. The heater drain water is distributed. That is, the distribution mechanism 23 has a flat inverted cup shape as a whole,
7 has an outer diameter smaller than the inner diameter. Further, on the upper surface of the distribution mechanism 23, distribution pipes 24 facing the lower ends of the respective hollow fiber membrane modules 19 are provided, and heater drain water is supplied from the respective distribution pipes 24 to the respective hollow fiber membrane modules 19. is there. The portion other than the distribution pipe 24 of the distribution mechanism 23 functions as an air bubble receiver during scrubbing cleaning, which will be described later. The air collected in the air bubble receiver rises upward as air bubbles from a hole 24A formed in the distribution pipe 24, and becomes hollow. It flows into the thread membrane module 19.

An air pipe used for scrubbing and cleaning impurities adhering to the hollow fiber membrane 28 constituting the hollow fiber membrane module 19 is connected to the closed vessel 15. The air pipe includes an air inlet pipe 25 connected to a lower part of the lower chamber 17 and an air outlet pipe 26 connected to an upper part of the lower chamber 17. And each pipe 25, 26
Are fitted with valves 25A and 26A, respectively. In addition, a drain pipe 27 is provided at the lower end of the closed container 15.
Is connected, and the cleaning wastewater containing impurities mainly composed of iron oxide fine particles is drained through the drain pipe 27. 27A is a valve attached to the drain pipe 27.

Next, the hollow fiber membrane module 19 will be described with reference to FIG. As shown in the figure, the hollow fiber membrane module 19 includes about 100 to 50,000 hollow fiber membranes 28, and a protective cylinder 29 that bundles and stores the hollow fiber membranes 28. Each hollow fiber membrane 28 is formed as a hollow fiber having an outer diameter of 0.3 to 5 mm and an inner diameter of 0.2 to 4 mm by a resin thin film having fine pores of, for example, 0.01 to 0.3 μm. Further, a flange portion 29A is formed at the upper end of the protection cylinder 29, and the flange portion 2A is formed.
At 9A, it hangs down on the partition plate 18.

A skirt portion 29B is formed at the lower end of the protective cylinder 29, and the skirt portion 29B collects gas flowing in at the time of cleaning. At the upper end of the protective cylinder 29, an upper joint 30 is formed by bonding and fixing the upper ends of the hollow fiber membranes 28 with an adhesive or the like. At the lower end, the lower end of each hollow fiber membrane 28 is joined to the upper end. A lower joining portion 31 joined and fixed in the same manner as described above is formed. Each hollow fiber membrane 28 is open at the upper joint 30 and each hollow fiber membrane 28 is closed at the lower joint 31 so that the filtered water flows out of the opening of the hollow fiber membrane 28 and collects in the upper chamber 16. It is. When water is collected from both ends of each hollow fiber membrane 28, the lower end is also opened in the same manner as the upper end, and a lower water collecting chamber (not shown).
Is provided. In addition, the lower joint portion 31 has a flow hole 31A.
Is formed, and the gas collected in the skirt portion 29B flows into the hollow fiber membrane module 19 through the flow hole 31A. Further, the upper joint 30 of the protective cylinder 29
Flow holes 29C and 29D are formed slightly below and slightly above the lower joining portion 31, respectively.
The heater drain water flows into the hollow fiber membrane module 19 via C and 29D.

As shown in FIG. 1, a coating film forming apparatus 12 attached to the filtration tower 11 includes a storage tank 12A for storing water to which iron oxide fine particles are added, and a storage tank 12A for storing the water.
A and a circulating pipe 13 are connected to a pipe 12B, and an injection pump 12C that is sequentially arranged in the pipe 12B from the upstream side.
And a valve 12D. In addition, the circulation pipe 13
Is connected to the inflow pipe 20 of the filtration tower 11 on the downstream side of the valve 20A, and the other end is connected to the outflow pipe 21 by the valve 21.
A is connected on the upstream side of A. Therefore, in the coating film forming apparatus 12, the valve 12D is opened, and the water containing the iron oxide fine particles in the storage tank 12A is supplied to the pipe 1 by driving the injection pump 12C.
2B, the circulation pipe 13 is supplied to the filtration tower 11 via a certain the coating film D ₁ and the iron oxide fine particles are adhered to the outer surface of the hollow fiber membrane 28 so as to form, as shown in FIG. 3 .
In some cases, a compressed gas is used as a driving force instead of the injection pump 12C.

The fine iron oxide particles are γ-F
Fine particles of e ₂ O ₃ (maghemite) or Fe ₃ O ₄ (magnetite) are used. γ-Fe ₂ O ₃ or Fe ₃
The fine particles of O ₄ can maintain a stable iron removal rate over a long period of time as described in Example 1. Also, γ-
Even if the fine particles of Fe ₂ O ₃ or Fe ₃ O ₄ adhere to the surface of the hollow fiber membrane 28, they are easily peeled off in the scrubbing backwashing step described later, and the handling is easy. The particle size of the γ-Fe ₂ O ₃ or Fe ₃ O ₄ fine particles is 1 to 10 μm,
m is more preferred. If the particle diameter of the γ-Fe ₂ O ₃ or Fe ₃ O ₄ fine particles is less than 1 μm, the releasability from the hollow fiber membrane 28 is reduced, and in some cases, there is a possibility that the fine pores of the hollow fiber membrane 28 may pass through. If it exceeds 10 μm, the iron oxide fine particles contained in the heater drain water permeate the voids of the coating film D ₁ ,
Possibility that the coating film D ₁ can not be captured iron oxide particles not preferable. preferably 5 to 100 g (Fe terms) / m ² as coated amount of the fine particles of γ-Fe ₂ O ₃ or Fe ₃ O _4, 20~100g (Fe terms) / m ² is more preferable. When the coating amount is less than 5 g (in terms of Fe) / m ² , the film thickness is so small that the coating film D ₁ is insufficient and the iron oxide fine particles can be trapped at the initial stage of water passage. , And a stable iron removal rate cannot be maintained for a long time. In addition, the coating amount is 100 g (Fe conversion)
/ M ² , it is possible to maintain a high iron removal rate, but even if the precoat amount is further increased, there is no great difference in the maintenance time of the iron removal rate, and there is no need to use a large amount of excess precoat agent. . Incidentally, commercially available iron oxide fine particles of γ-Fe ₂ O ₃ or Fe ₃ O ₄ can be used.

The above-mentioned filtration device 10 is attached to a low-pressure water heater of a power plant as shown in FIG. 4, for example. As shown in FIG. 4, the low-pressure heater system includes a low-pressure turbine 1 driven by receiving steam from a steam generator (not shown), a condenser 2 for returning the steam of the low-pressure turbine 1 to water, and a condenser A desalination device 4 for desalinating the condensed water sent from the vessel 2 by the pump 3;
And a low-pressure heater 6 for heating the treated water after desalination through a pump 5 with steam supplied from the low-pressure turbine 1. Then, the treated water heated in the low-pressure heater 6 is sent to a steam generator via a high-pressure heater (not shown) or the like. As shown in the drawing, the low-pressure heater 6 is provided with the above-described filtering device 10.
The heater drain water is filtered by 0 to remove impurities mainly composed of iron oxide particles from the heater drain water, and the filtered water joins with the condensate heated in the low-pressure heater 6.

Next, a method for removing an iron component from the heater drain water of the present invention using the above-mentioned filtration device 10 will be described. When carrying out the iron removal method of the present invention, water to which fine particles of γ-Fe ₂ O ₃ or Fe ₃ O ₄ have been added as iron oxide fine particles before passing the heater drain water through the filtration tower 11 is filtered. Water is passed through the filtration tower 11, and a coating film D ₁ of fine particles of γ-Fe ₂ O ₃ or Fe ₃ O ₄ is formed on the filtration surface of the hollow fiber membrane 28. First, the inside of the upper chamber 16 and the lower chamber 17 of the filtration tower 11 is filled with water, and then the storage tank 12A is filled with water.
Fine particles of γ-Fe ₂ O ₃ or Fe ₃ O ₄ of 10 to 10 μm are dispersed and mixed in water to prepare a suspension of a predetermined concentration. Next, when the valves 14C and 14D of the circulation pipe 13 are opened and the circulation pump 14B is started, the water in the filtration tower 11 circulates through the filtration tower 11 via the circulation pipe 13 to form a circulation loop. As the water for filling the upper and lower chambers 16 and 17 of the filtration tower and the water for dispersing the fine particles of γ-Fe ₂ O ₃ or Fe ₃ O ₄ , pure water usually used in power plants can be used. preferable.

Next, the valve 12D of the coating film forming apparatus 12
Is opened, and when the injection pump 12C is started, γ-Fe ₂ O ₃
Alternatively, the suspension of Fe ₃ O ₄ fine particles flows into the lower chamber 17 of the filtration tower 11 through the pipe 12B and the circulation pipe 13. As a result, the fine particles of γ-Fe ₂ O ₃ or Fe ₃ O ₄ are suspended in the hollow fiber membrane module 19 in the lower chamber 17 of the filtration tower 11.
Γ-Fe ₂ O ₃ or F
e ₃ O ₄ fine particles are filtered and γ-Fe ₂ O ₃ or Fe ₃
Coating of O ₄ of particle film D ₁ is the hollow fiber membrane 2 as shown in FIG. 3
8 on the filtration surface. And γ-Fe on the filtration surface
_When the coating amount of the fine particles of ₂ O ₃ or Fe ₃ O ₄ reaches a predetermined amount (for example, 20 to 50 g (Fe conversion) / m ² ), the valve 12D is closed, and the injection pump 12C is stopped. After the fine particles of γ-Fe ₂ O ₃ or Fe ₃ O ₄ are precoated on the hollow fiber membrane 28 in this manner, the iron removal treatment of the heater drain water is performed.

To perform the iron removal treatment, first, the valve 20A of the inflow pipe 20 and the valve 21A of the outflow pipe 21 are opened,
The heater drain water flows from the inflow pipe 20 to the lower chamber 1 of the filtration tower 11.
Flow into 7 By this operation, the hollow fiber membrane module 1
9, the iron oxide fine particles in the heater drain water are filtered,
The filtered water flows out of the outflow pipe 21 through the upper chamber 16.
At this time, the iron oxide fine particles in the heater drain water firstly become γ-Fe ₂ O ₃ or Fe ₃ of the coating film D _{1 on} the filtration surface of the hollow fiber membrane 28.
The particles adhere to the surface of the O ₄ fine particles, and are then adsorbed and captured by the fine particles of γ-Fe ₂ O ₃ or Fe ₃ O ₄ while moving through the voids in the coating film D ₁ , and the filtered water of the hollow fiber membrane 28 Contains only a small amount of iron oxide fine particles. When thereafter continues filtration heater drain water, the adhesion layer D ₂ iron oxide fine particles filtered from the heater drain water in the coating film D ₁ of the outer surface laminated gradually as shown in FIG. 3 of the hollow fiber membrane 28 formed, the adhesive layer D ₂ by gradually increases filtration differential pressure heater drain water in the filtration tower 11, the coating film D ₁ at the time it reaches the specified differential pressure by air scrubbing backwash
And the adhesion layer D ₂ is removed from the hollow fiber membrane 28.

To perform the air scrubbing backwash, first, the valve 20A of the inflow pipe 20 and the valve 21A of the outflow pipe 21 are closed, and the heater drain water is supplied to the lower chamber 17 and the filtered water is supplied to the upper chamber 16 respectively. When the valve 25A of the air inflow pipe 25 and the valve 26A of the air outflow pipe 26 are opened with the water being full, compressed air flows in from the air inflow pipe 25. The compressed air temporarily accumulates in the bubble receiver of the distribution mechanism 23, and then forms bubbles from the holes 24A of the distribution pipes 24 and flows into the skirts 29B of the hollow fiber membrane modules 19, and then flows through the holes 31A of the lower joint 31. From each of the hollow fiber membrane modules 19. Hollow fiber membrane module 1
In 9, each hollow fiber membrane 28 is vibrated by the bubbles due to the rise of the bubbles, and the water in the hollow fiber membrane module 19 is stirred by the bubbles, so that the adhesion layer D ₂ and the coating film D _{1 on the} surface of each hollow fiber membrane 28 are formed. The iron oxide fine particles are separated from each other in the filtration tower 1
1 in the lower chamber 17. This air bubble then flows out of the hollow fiber membrane module 19 through the flow hole 29C of the hollow fiber membrane module 19, and then flows from the air vent pipe 26 to the filtration tower 1
1 Outflow. Prior to air scrubbing backwash,
It is also possible to take measures to lower the temperature of the heater drain water in the lower chamber 17 of the filtration tower 11.

The iron oxide fine particles separated by the air scrubbing backwashing and dispersed in the water in the lower chamber 17 of the filtration tower 11 flow out of the filtration tower 11. When the valve 25A of the air inlet pipe 25 is closed while the valve 26A of the air outlet pipe 26 is opened, and the valve 27A of the drain pipe 27 is opened, the cleaning waste liquid in which the iron oxide fine particles are dispersed in the lower chamber 17 is opened. Flows out of the drainage pipe 27 to the outside of the filtration tower 11. In this step in which the washing waste liquid flows out, a head difference is used. However, when compressed air is introduced from the air outflow pipe 26 or the air inflow pipe 25, the cleaning waste liquid in the filtration tower 11 is quickly discharged by the compressed air. Can be done. After the stirring with the compressed air and the blowing of the washing wastewater are completed, the above-mentioned γ-Fe ₂ O ₃ or Fe
After formation of the coating film D ₁ of the ₃ O ₄ by fine particles, it was filtered of heater drain water, repeated filtration in this order.

By the way, when most of the impurities contained in the heater drain water is gamma-Fe ₂ O ₃ or Fe ₃ O ₄ is, gamma-Fe ₂ in the present invention O ₃ or Fe ₃ O ₄
Upon which the forming a coating film D ₁ of the particles, it can be used as it is iron oxide contained in the heater drain water without the addition of iron oxide particles from the coating film forming apparatus 12. Further, if most of the iron oxide fine particles in the condensate are γ-Fe ₂ O ₃ or Fe ₃ O ₄ fine particles in another system in the power plant, for example, the condensate purification system, a filter capable of capturing the iron oxide fine particles is used. installed, it may be used iron oxide particles of the condensate water that is trapped by the filter as a coating film D ₁ of the hollow fiber membrane 28.

As described above, according to the present embodiment,
When the heater drain water is filtered by the filtration device 10 in the power generation plant, before the water is passed through the hollow fiber membrane 28 of the filtration tower 11 and filtered, 1 to 10 μm γ-Fe ₂ O as iron oxide fine particles is used. Water containing fine particles of ₃ or Fe ₃ O ₄ is passed through the hollow fiber membrane 28 and the γ-Fe ₂
A coating film D ₁ with fine particles of O ₃ or Fe ₃ O ₄ at a predetermined coating amount;
The iron oxide contained in the heater drain water of the power plant is removed stably and reliably over a long period of time, and the iron oxide is taken into the steam generator or boiler of the power plant. It can be effectively prevented.

[0030]

Next, the present invention will be described based on specific examples of the above embodiment. Example 1 In this example, a small experimental filtration tower was manufactured with the following specifications as the filtration device shown in FIG. 1, and the following experiment was performed using this small experimental filtration tower. First, the following γ-Fe ₂ O ₃ and Fe
The fine particles of ₃ O ₄ were dispersed in water in different storage tanks to prepare suspensions of γ-Fe ₂ O ₃ and Fe ₃ O ₄ , respectively. Next, after forming a water circulation loop with the filtration tower and the circulation pipe, suspension water to which fine particles of γ-Fe ₂ O ₃ or Fe ₃ O ₄ are added is injected into the circulation loop from the storage tank, and each hollow fiber is formed. By passing water from the outside to the inside of the membrane, γ-Fe ₂ O ₃ and Fe
A coating film of fine particles of ₃ O ₄ was formed. Next, drain water of the low pressure heater of the power plant (water temperature: 60 ° C to 70 ° C)
Was passed through each filtration tower on which a coating film of fine particles of γ-Fe ₂ O ₃ and Fe ₃ O ₄ was formed, and the change with time of the iron removal rate was tracked. The results are shown in FIG. The secondary system of this power plant performs water quality management by volatile treatment using ammonia and hydrazine.

According to the results shown in FIG. 5, when iron components such as iron oxide fine particles are removed from high-temperature water such as heater drain water, fine particles of γ-Fe ₂ O ₃ are applied to the hollow fiber membrane of the filtration tower. It was found that when the coating amount was 50 g / m ² , a stable iron removal rate of about 90% or more could be maintained over a long period of 700 hours from the initial stage of filtration. In addition, when the fine particles of Fe ₃ O ₄ were precoated at a coating amount of 50 g / m ^{2 on} the hollow fiber membrane of the filtration tower,
It has been found that a stable iron removal rate of about 90% or more can be maintained over a long period of 650 hours from the initial stage of filtration.

[Specifications of Small Experimental Filtration Tower] 1. Hollow fiber membrane module Hollow fiber membrane; Micropore: around 0.2 μm Outer diameter: 1 mm Inner diameter: 0.7 mm Length: 1.1 m Number: 250 Protective cylinder diameter: 25 mm 2. Number of hollow fiber membrane modules used: 1 _3. γ-Fe ₂ O ₃ or Fe ₃ O ₄ fine particles Particle size: 1 to ₃ μm Coating amount: 50 g (in terms of Fe) / m ² (hollow fiber membrane) Filtration speed: 0.5 m / hour

Example 2 In this example, a flow test of heater drain water was carried out under the same conditions as in Example 1 except that the coating amount of γ-Fe ₂ O ₃ or Fe ₃ O ₄ fine particles was changed to 20 g / m ^2. The change over time in the iron removal rate was tracked, and the results are shown in FIG.

According to the results shown in FIG. 6, a high iron removal rate of 80% or more was obtained from the initial stage of filtration to about 200 to 300 hours, and thereafter, the iron removal rate gradually decreased.
It was found that the iron removal rate was reduced to about 0%. Therefore, 2
It was found that a high iron removal rate could be maintained if the coating amount was 0 g / m ² for about 200 to 300 hours.

Comparative Example 1 In this comparative example, α-FeOOH was used instead of Fe ₃ O ₄ fine particles.
A water drainage test was conducted for 150 hours by passing heater drain water through the filtration tower under the same conditions as in Example 1 except that the hollow fiber membrane was coated with the fine particles of 20 g / m ^{2 at} a coating amount of 20 g / m ² . The change with time was tracked, and the results are shown in FIG.

According to the results shown in FIG. 7, the iron removal rate was high only in the initial stage of the filtration (about 10 hours), but thereafter, the iron removal rate rapidly decreased, and after 50 hours, the iron removal rate reached 60%.
It was found that the iron removal rate decreased to about 30% after 150 hours.

The present invention is not limited to the above embodiment. For example, in addition to a hollow fiber membrane filter, a pleated filter, a ceramic filter, a metal filter, a sintered metal filter, a disk filter, or the like can be used as the filtration medium as described above.

[0038]

According to the method for removing iron components in the heater drain water in the power plant according to the first and second aspects of the present invention, the iron components such as the iron oxide fine particles contained in the heater drain water can be stably removed. In addition, the iron component can be reliably removed and the iron component can be effectively prevented from being brought into the steam generator or the boiler of the power plant.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of a filtration device suitably used in carrying out a method for removing an iron component in heater drain water of the present invention.

FIG. 2 is a cross-sectional view showing a hollow fiber membrane module used in the filtration device shown in FIG.

FIG. 3 is a partially enlarged cross-sectional view of the hollow fiber membrane for explaining a state of the hollow fiber membrane when filtering the heater drain water with the filtration device shown in FIG. 1;

4 is a configuration diagram showing a system of a low-pressure water heater of a power plant to which the filtration device shown in FIG. 1 is applied.

FIG. 5 is a graph showing the results of Example 1 in which the iron removal ratio of a hollow fiber membrane precoated individually and individually with γ-Fe ₂ O ₃ and Fe ₃ O ₄ microparticles with respect to heater drain water was experimentally determined. .

FIG. 6 is a diagram corresponding to FIG. 5 showing the result of Example 2 which was tested under the same conditions as Example 1 except that the amounts of γ-Fe ₂ O ₃ and Fe ₃ O ₄ used were reduced compared to Example 1. is there.

FIG. 7 is a diagram corresponding to FIG. 5, showing the result of Comparative Example 1 which was tested under the same conditions as Example 1 except that α-FeOOH fine particles were used.

[Explanation of symbols]

10 filtration device 11 filtration tower 12 coating film forming apparatus 13 circulation pipe 28 hollow fiber membrane (filter) D ₁ coated film

Claims (2)

[Claims] The heater drain water is passed through a filter before the heater drain water is supplied as water for generating steam.
A method for removing an iron component in heater drain water by this filter, wherein iron oxide fine particles are 1 to 10 μm before passing the heater drain water through the filter.
Water containing fine particles of γ-Fe ₂ O ₃ or Fe ₃ O ₄ is passed through the filter, and a coating film of the iron oxide particles is formed on a filtration surface of the filter. A method for removing iron components in heater drain water in a power plant. 2. The method for removing an iron component from heater drain water in a power plant according to claim 1, wherein the coating amount of the iron oxide fine particles on the filter is 5 to 100 g (in terms of Fe) / m ^2. .