JP2017064639A - Method and apparatus for recovering and using waste water from steam power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently process blow water, drain water, and sampling rack drainage water from a steam power plant to recover and use them as boiler makeup water.SOLUTION: The blow water, drain water, and sampling rack drainage water from a steam power plant are oxidized with an oxidant, subsequently, the oxidation treatment water is subjected to flocculation and solid-liquid separation, the separated water is desalinated, and the desalinated water is recovered to use as boiler makeup water. The desalting treatment is preferably carried out by ion exchange treatment, reverse osmosis membrane separation treatment, or electric deionization treatment, or a combination thereof, and solid-liquid separation is preferably carried out by membrane separation.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method and apparatus for treating blow water, drain water and sampling rack drainage generated at a steam power plant and recovering and using them as boiler make-up water.

  Steam power generation is a power generation method that generates power by driving a turbine with steam generated in a boiler. In the narrow sense, it refers only to thermal power generation, but in the broad sense, nuclear power generation, geothermal power generation, solar thermal power generation, ocean temperature difference power generation, etc. Is also included.

  FIG. 2 is a system diagram showing a configuration of a general steam power plant. In FIG. 2, a solid line indicates a water flow path, a dotted line indicates a steam flow path, and a broken line indicates a drainage flow path. In this power plant, steam generated by heating the water in the drum 1 by the boiler 4 is supplied to the steam turbine 2, and the steam turbine 2 is driven to generate power. The steam that has driven the steam turbine 2 is introduced into the condenser 3 and is condensed by exchanging heat with the cooling water in the condenser 3, and the condensed water (condensed water) is pumped out by a condensate pump (not shown). A steam cycle that is supplied to the steam turbine 2 through the deaerator and the heater (not shown), boosted by a feed water pump (not shown), circulated to the boiler drum 1, steam again in the boiler 4, and supplied to the steam turbine 2. Is formed.

In such a steam power plant, the following wastewater is generated.
(1) Blow water: Water obtained by blowing a part of the water in the system to maintain the water quality in the system. For example, drum blow water from the drum 1 and boiler blow water from the boiler 4.
(2) Drain water: Condensate water extracted from the steam piping system. For example, steam drain water extracted from the steam pipe from the boiler 4 to the steam turbine 2 or condensate drain water from the condenser 3.
(3) Sampling rack drainage: In a steam power plant, water sampled from each point (a, b, c in Fig. 2) is led to a water quality monitoring instrument through sampling pipes in order to measure water quality in the system. . In the analysis, the sampling pipe needs to be sufficiently flushed with sample water. There are various sampling points such as a condensate pump outlet, a deaerator inlet / outlet, and a boiler, and the water that flows from each sampling pipe at the time of flushing is joined and discharged as sampling rack drainage.
The waters of the above (1) to (3) are mixed with various wastewaters or are contaminated in the course of steam and water transfer, so they cannot be returned to the system as they are. Currently, these waters are discharged through wastewater treatment and are not collected and reused.

In recent years, effective use of water resources has been promoted in order to save water, and it is desired to collect and reuse wastewater even at steam power plants. In particular, there is a great demand for water conservation in steam power plants that are built in areas where water resources are limited and available water is low.
In addition, for example, in a gas-fired power plant, there is a great merit of collecting and using wastewater for the following reasons. That is, in gas-fired power plants, the amount of water used in the entire power plant is small and the amount of wastewater is small compared to heavy oil and coal-fired power plants, so the proportion of wastewater such as boiler makeup water and boiler drain water in the water supply and wastewater used is relative. Become expensive. For example, taking gas combined cycle power generation as an example, 30-40% of the water used for power generation is used as boiler makeup water, 70% of which is discharged as waste water. Therefore, if this wastewater can be recovered and used, it can be expected that the amount of water used will be reduced by about 20%.

  Conventionally, regarding treatment of thermal power plant wastewater, Patent Document 1 discloses that this wastewater is agglomerated and then separated into membranes, and the membrane permeate is discharged as treated water or advanced treatment as necessary to recover water. Has been proposed.

  In Patent Document 2, as a method of recovering iron content by selectively separating and recovering dissolved iron from metal ion-containing wastewater containing divalent iron ions, divalent iron ions in the metal ion-containing wastewater are converted by iron-oxidizing bacteria. There has been proposed a method of separating and recovering by oxidizing to trivalent iron ions and precipitating them as iron hydroxide particles. The metal ion-containing wastewater treated by the method of Patent Document 2 contains divalent iron ions at a high concentration of several hundred mg / L, such as pickling wastewater and plating wastewater.

JP-A-10-28994 JP2012-228675A

The steam power plant effluents of (1) to (3) described above include iron, etc. that are eluted and mixed from piping in the system in addition to hydrazine, ammonia, and organic substances derived from chemicals and pollutants used in the system. Therefore, in order to recover and reuse these wastewater as boiler makeup water, etc., it is necessary to perform a desalting treatment after removing these mixed components, particularly fine iron.
However, the iron contained in these wastewater forms ferrous ions or unstable fine particles of iron colloid, and is separated and removed in a normal agglomeration process as described in Patent Document 1. I can't.

  The method of oxidizing divalent iron ions by iron-oxidizing bacteria and precipitating them as trivalent iron ions described in Patent Document 2 can achieve a certain degree of treatment efficiency for high-concentration iron-containing wastewater. Although it is considered, there is a possibility that stable treatment cannot be performed at a sufficient reaction rate for wastewater from steam power plants, which is generally low concentration iron-containing wastewater with an iron concentration of about 0 to 0.2 mg / L. .

  The present invention has been made in view of the above-described conventional situation, and provides a method and apparatus for efficiently treating blow water, drain water, and sampling rack waste water generated at a steam power plant and recovering and using them as boiler make-up water. The task is to do.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have conducted oxidation treatment with an oxidizing agent prior to coagulating solid-liquid separation of blow water, drain water, and sampling rack waste water generated at a steam power plant. It is possible to efficiently separate ionic iron and fine colloidal iron in waste water, which is difficult to separate into solid and liquid, and the water quality can be reused as boiler makeup water by desalting the separated water. It was found that treated water can be obtained.
The present invention has been achieved based on such findings, and the gist thereof is as follows.

[1] A method for recovering and using steam power plant wastewater containing at least one selected from the group consisting of blow water, drain water, and sampling rack waste water generated at a steam power plant, wherein the steam power plant waste water is oxidized Oxidized water is separated by agglomeration and solid-liquid separation, the separated water is desalted, and the desalted water is recovered and used as boiler make-up water. Method.

[2] The method of recovering and using steam power plant waste water according to [1], wherein the total iron concentration of the steam power plant waste water is 0 to 0.2 mg / L.

[3] In [1] or [2], the pH at the time of the oxidation treatment is 5 or more and less than 7, The method for recovering and using steam power plant wastewater.

[4] The steam power generation according to any one of [1] to [3], wherein the desalting process is performed by an ion exchange process, a reverse osmosis membrane separation process, an electrodeionization process, or a combination thereof. How to collect and use industrial wastewater.

[5] In any one of [1] to [4], the solid-liquid separation is performed by membrane separation.

[6] A steam power plant wastewater recovery and collection device including at least one selected from the group consisting of blow water, drain water, and sampling rack drainage generated at a steam power plant, and accepting the steam power plant wastewater Oxidation treatment means for oxidizing treatment with an oxidizing agent, agglomerated solid-liquid separation means for aggregating solid-liquid separation of the oxidation-treated water of the oxidation treatment means, and a desalination treatment means for desalting the separated water of the agglomerated solid-liquid separation means And a steam power plant wastewater recovery and utilization device, characterized in that the treated water of the desalination treatment means is supplied to the boiler feed water line of the steam power plant as boiler replenishment water.

[7] The steam power plant wastewater recovery and utilization device according to [6], wherein the total power concentration of the steam power plant wastewater is 0 to 0.2 mg / L.

[8] The steam power plant wastewater recovery and utilization device according to [6] or [7], wherein the pH during the oxidation treatment is 5 or more and less than 7.

[9] In any one of [6] to [8], the desalting means is an ion exchange device, a reverse osmosis membrane separation device, an electrodeionization device, or a combination of these devices. A steam power plant wastewater collection and utilization device.

[10] In any one of [6] to [9], the aggregated solid-liquid separation means includes a membrane separation device.

  According to the present invention, blow water, drain water, and sampling rack drainage of steam power plants that have been discharged and discarded can be efficiently processed and used effectively as boiler make-up water. For this reason, according to the present invention, it is possible to reduce the amount of makeup water from outside the system in the power plant of the steam power plant, and thus reduce the amount of industrial water and clean water used as raw water for makeup water, Savings and water costs can be reduced.

It is a systematic diagram showing an example of a steam power plant that employs a recovery and utilization device for steam power plant drainage of the present invention. It is a distribution diagram showing a general steam power plant.

  Embodiments of the method and apparatus for recovering and using steam power plant wastewater of the present invention will be described in detail below.

  In the present invention, blow water, drain water and sampling rack waste water generated at a steam power plant are treated in the order of (1) oxidation treatment with an oxidizing agent, (2) flocculation solid-liquid separation, and (3) desalination treatment. The treated water is collected and reused as boiler makeup water.

[Steam power plant drainage]
The steam power plant wastewater to be treated in the present invention is drum blow water, boiler blow water, etc., blow water, steam drain water, condensate drain water, etc. drain water, sampling rack waste water, etc., generated at the aforementioned steam power plant. .
In the present invention, only one of these wastewaters may be treated, or two or more of these wastewaters may be treated. Preferably, by treating all of the blow water, drain water, and sampling rack waste water generated at the steam power plant, the amount of water discarded can be sufficiently reduced and the water recovery rate can be increased.

As described above, these steam power plant effluents contain iron, hydrazine, ammonia, organic matter, and other ions, and the water quality is usually as follows.
<Water quality of steam power plant>
pH: 6.3 to 9.3
Electrical conductivity: 2.0-40mS / m
Total iron: 0-0.2 mg / L, especially 0-0.1 mg / L, especially 10 μg / L-0.1 mg / L
Ammonia: 0 to 2.0 mg / L
Hydrazine: 0 to 0.5 mg / L
TOC: 0 to 5 mg / L
Total silica: 1-10mg / L

[Oxidation treatment]
Iron in the above steam power plant wastewater exists as ferrous ions (Fe ²⁺ ) or fine and unstable colloidal iron particles, and is difficult to remove as it is by coagulation solid-liquid separation. In the present invention, the waste water is oxidized with an oxidizing agent prior to the flocculated solid-liquid separation. The oxidation treatment of waste water, the iron in the waste water, a stable iron hydroxide (Fe _{(OH) 3,} etc.) is oxidized to iron oxide _{(Fe 2 O 3, Fe 3} O 4 , etc.), can be agglomerated solid-liquid separation It becomes.
In addition, hydrazine and ammonia are originally present in the system, but their concentration is controlled in the system, and if they are contained in recovered water and replenished in the system, the concentration management becomes complicated. Therefore, it is decomposed by oxidation treatment.
In addition, since the organic matter causes organic fouling when desalting is performed later, the organic matter in the wastewater is also removed by oxidative decomposition.

The waste water is oxidized by adding an oxidizing agent to the waste water. As the oxidizing agent, one or more of chlorine-based oxidizing agent, ozone, hydrogen peroxide and the like can be used, but it is preferable to use a chlorine-based oxidizing agent such as sodium hypochlorite from the viewpoint of easy handling. .
As described above, in the oxidation treatment with iron-oxidizing bacteria as described in Patent Document 2, there is a possibility that the low concentration iron-containing waste water targeted in the present invention cannot be stably treated at a sufficient reaction rate. However, if it is an oxidation treatment with an oxidizing agent, even if it is a low-concentration iron-containing wastewater, the oxidation treatment can be reliably and efficiently performed.

  Although the addition amount of an oxidizing agent changes with content of the oxidizable substance in waste_water | drain, in the case of a chlorine-type oxidizing agent, it is about 5-20 mg / L normally as a chlorine conversion addition amount, for example.

The pH of the wastewater during this oxidation treatment is preferably 5 or more and less than 7, that is, 5 ≦ pH <7, more preferably 5.5 ≦ pH <7, and even more preferably 6.0 ≦ pH <7. . The reason for setting the weakly acidic condition below pH 7 is as follows.
That is, in the present invention, the oxidation-treated water is subjected to flocculated solid-liquid separation, and the separated water is desalted with a reverse osmosis membrane separator or the like. In this desalting treatment, the pH is preferably weakly acidic in order to prevent the occurrence of scale. For this reason, it is preferable to perform the oxidation treatment at a pH of less than 7 as described above. For this reason, when the pH of the steam power plant drainage is 7 or more, an acid is appropriately added to adjust the pH to less than 7. However, if the pH is excessively low, the amount of acid agent used for pH adjustment increases, and it may be necessary to adjust the pH again when using desalted water as boiler makeup water. The pH is preferably at least the above lower limit.

  The oxidation treatment is preferably performed while ensuring a reaction time of about 15 to 30 minutes in order to sufficiently oxidize the oxidizable substance in the waste water.

[Agglomerated solid-liquid separation]
The oxidized water then removes iron oxidized by coagulation solid-liquid separation and SS in waste water.
When the load of drainage iron or SS is low, water can be passed through the ion exchange apparatus and RO membrane separation apparatus in the subsequent stage as it is, but when these loads are high, the apparatus is likely to be blocked due to water flow, so these SS Is removed by agglomeration solid-liquid separation prior to desalting.

  As the flocculant, for example, inorganic flocculants such as sulfate band, polyaluminum chloride (PAC), ferrous sulfate, ferric chloride, slaked lime, calcium chloride, and magnesium compounds can be suitably used. As necessary, anionic polymer flocculants such as sodium alginate, carboxymethylcellulose, polyacrylamide partial hydrolyzate salts, cationic polymer flocculants such as polyethyleneimine, polythiourea, polydimethyldiallylammonium chloride, poly Separation can be improved by using a nonionic polymer flocculant such as acrylamide. These flocculants may be used individually by 1 type, and may be used in combination of 2 or more type.

  The amount of the inorganic flocculant added varies depending on the water quality of the waste water and the presence or absence of the combined use of the polymer flocculant, but is usually preferably about 5 to 50 mg / L.

  The aggregation treatment pH may be any suitable pH value for the inorganic flocculant used, and is usually about 5.5 to 8.0 for an aluminum flocculant and usually 4 or more for an iron flocculant. However, as described above, the pH is preferably less than 7 for the subsequent desalting treatment.

  This agglomeration treatment may be performed by providing an agglomeration tank and securing a reaction time of about 5 to 30 minutes, or may be a treatment performed by injecting a flocculant into a pipe.

As solid-liquid separation means of the flocculated water, a precipitation tank, a floating tank, a filter, a membrane separation device, or the like can be used.
However, flocs are likely to leak when starting and stopping in the sedimentation tank and levitation tank. In addition, the filter has a large opening and iron leakage tends to increase.

A microfiltration (MF) membrane having a pore size of about 0.01 to 0.2 μm, or a molecular weight cut off of 5000 to 5000 in that the colloidal particles that do not have such problems and can be flocated or cannot be adsorbed to the flocs by the aggregation treatment can be removed. It is preferable to use an ultrafiltration (UF) membrane separator of about 18000. According to these membrane separation apparatuses, there is an advantage that not only the quality of the solid-liquid separation water but also the operation of the desalting treatment in the subsequent stage can be stabilized.
There is no restriction | limiting in particular in the type of these separation membrane elements, For example, a flat membrane clamping type | mold, a flat membrane spiral winding type | mold, a tubular membrane, a hollow fiber membrane etc. can be used. The type of the membrane separation device is not particularly limited, and for example, an external pressure type, an internal pressure type, a pressure type, a pressure reduction type, or the like can be appropriately selected and used.

[Desalination]
The separated water obtained by the above-mentioned coagulation solid-liquid separation is then desalted.
That is, since the above solid-liquid separated water contains various ions and organic substances derived from the waste water, it is necessary to desalinate the water for reuse as boiler makeup water.

As the desalting treatment means, an ion exchange device (ion exchange resin tower), a reverse osmosis (RO) membrane separation device, an electrodeionization device or the like can be used. These are appropriately selected and used according to the target water quality, that is, the water quality to be recovered and used as boiler make-up water, and only one type may be used or two or more types may be used in combination. Further, one type of device may be connected in series in two stages.
For example, a two-stage RO membrane separation process may be performed, or an electrodeionization process may be performed after the RO membrane separation process.

  In the present invention, it is preferable to obtain treated water having an electrical conductivity of 0.1 mS / m or less, total iron of 10 μg / L or less, and ammonia, hydrazine and TOC below the detection limit by such desalting treatment. If it is treated water with a good water quality, it can be effectively used as boiler makeup water.

  According to the present invention, from the mixed drainage of steam power plant blow water, drain water and sampling rack drainage, it is possible to obtain treated water of the above water quality at a water recovery rate of about 40 to 90%, By using the collected water as boiler make-up water, the amount of make-up water from outside the system can be greatly reduced.

[Application to power plants]
FIG. 1 is a system diagram showing an application example of a steam power plant wastewater recovery and utilization apparatus of the present invention to a power plant. In FIG. 1, members having the same functions as those in FIG. It is. Similarly to FIG. 2, the solid line indicates the water flow path, the dotted line indicates the steam flow path, the broken line indicates the drainage flow path, and the alternate long and short dash line indicates the recovered water flow path.

  In FIG. 1, drum blow water, steam drain water, condensate drain water, and sampling rack drain water are respectively introduced into a water recovery apparatus 10 that is a recovery and utilization apparatus for steam power plant drainage according to the present invention. It is treated by the steps of) oxidation treatment with an oxidizing agent, (2) flocculated solid-liquid separation, and (3) desalination treatment, and the desalted water is collected and returned to the water supply line as boiler makeup water.

As this water treatment device 10, a drainage tank in which the respective wastewaters provided as needed are combined, an oxidation reaction tank in which an oxidant is added to the wastewater from the drainage tank and reacted, and an oxidation treatment water from the oxidation reaction tank Coagulation tank for adding coagulant to flocculation process, UF or MF membrane separator for solid-liquid separation of coagulated water from coagulation tank, and ion exchange for desalting the permeated water of UF or MF membrane separator Examples thereof include an apparatus, an RO membrane separation apparatus, an electrodeionization apparatus, or a desalination treatment apparatus composed of a combination thereof. While the treated water of the desalinating apparatus is recovered as boiler make-up water, wastewater such as concentrated water is discharged out of the system.
In addition, this water collection | recovery apparatus 10 may have the circulation piping which circulates the backwashing means of a membrane separation apparatus, a part of membrane concentrated water, and backwash waste_water | drain to a preceding stage drainage tank suitably.

  Hereinafter, the present invention will be described more specifically with reference to examples.

<Example 1>
The mixed waste water of boiler blow water, steam drain water, condensate drain water, and sampling rack waste water discharged from the steam power plant of the steam power plant shown in FIG. 1 was treated according to the present invention.
The water quality of this mixed waste water is as shown in Table 1 below.

First, sodium hypochlorite 5 mg-Cl ₂ / L was added to 100 L of mixed waste water in a reaction tank, and the mixture was reacted for 15 minutes with stirring under the condition of pH 6.7. PAC 10 mg / L was added to the oxidation-treated water, and the mixture was agglomerated with stirring for 10 minutes. The pH of this agglomerated water was 6.4. The agglomerated water was subjected to membrane separation with an MF membrane separation device having a pore size of 0.02 μm. The quality of the obtained permeated water was as shown in Table 1 below.
Next, the membrane permeated water is subjected to two-stage desorption using an RO membrane separation device ("K-RO-A-203V" manufactured by Kurita Kogyo Co., Ltd.) and an electrodeionization device ("KCDI-H30" manufactured by Kurita Kogyo Co., Ltd.). Salt treatment was performed (water recovery rate of desalting treatment was 80%), and 80 L of desalted water (about 80% water recovery rate for the entire apparatus) shown in Table 1 was obtained.
The obtained desalted treated water sufficiently satisfied the target value as boiler makeup water shown in Table 1.

By applying the power plant are operating water recovery of this embodiment up water usage ^24m 3 / day, in wastewater ^16m 3 / day, to obtain the recovered water ^13m 3 / day from wastewater ^16m 3 / day, which Can be used as boiler make-up water, so that the amount of use of make-up water from outside the system can be reduced to 11 m ³ / day.

<Comparative Example 1>
In Example 1, flocculation and membrane filtration were attempted in the same manner as in Example 1 without oxidizing the mixed waste water, but sufficient flocculation flocs could not be formed in the flocculation process, and iron was 19 μg in the membrane permeated water. / L remained, and water quality capable of operating the RO membrane separation device and the electrodeionization device could not be obtained.

1 Drum 2 Steam Turbine 3 Condenser 4 Boiler 10 Water Recovery Device

Claims (10)

  A method for recovering and using steam power plant wastewater containing at least one selected from the group consisting of blow water, drain water and sampling rack waste water generated at a steam power plant, wherein the steam power plant wastewater is oxidized with an oxidizing agent. After that, a method for recovering and using steam power plant wastewater is characterized in that the oxidized water is subjected to flocculated solid-liquid separation, the separated water is desalted, and the desalted water is recovered and used as boiler makeup water.   The method for recovering and using steam power plant wastewater according to claim 1, wherein the total iron concentration of the steam power plant wastewater is 0 to 0.2 mg / L.   The method for recovering and using steam power plant wastewater according to claim 1 or 2, wherein the pH during the oxidation treatment is 5 or more and less than 7.   4. The steam power plant wastewater according to claim 1, wherein the desalting treatment is performed by an ion exchange treatment, a reverse osmosis membrane separation treatment, an electrodeionization treatment, or a combination thereof. 5. Collection and usage method.   5. The method of recovering and using steam power plant wastewater according to claim 1, wherein the solid-liquid separation is performed by membrane separation.   An apparatus for recovering and using steam power plant wastewater containing at least one selected from the group consisting of blow water, drain water, and sampling rack waste water generated at a steam power plant, which receives the steam power plant wastewater by an oxidizing agent Oxidation treatment means for oxidation treatment, agglomeration solid-liquid separation means for aggregating solid-liquid separation of the oxidation treated water of the oxidation treatment means, a desalination treatment means for desalting the separated water of the aggregation solid-liquid separation means, A steam power plant wastewater recovery and utilization device, characterized by having a feed water pipe that feeds the treated water of the desalination treatment means to the boiler feed water line of the steam power plant as boiler makeup water.   The steam power plant wastewater recovery and utilization device according to claim 6, wherein the total iron concentration of the steam power plant wastewater is 0 to 0.2 mg / L.   In Claim 6 or 7, pH at the time of the said oxidation process is 5 or more and less than 7, The recovery utilization apparatus of the steam power station waste water characterized by the above-mentioned.   9. The demineralization treatment means according to claim 6, wherein the desalting means is an ion exchange device, a reverse osmosis membrane separation device, an electrodeionization device, or a combination of these devices. Steam power plant wastewater collection and utilization equipment.   10. The steam power plant wastewater recovery and utilization device according to any one of claims 6 to 9, wherein the agglomerated solid-liquid separation means includes a membrane separation device.

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