JP2014030777A - Method and device for processing wastewater from incineration plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for processing wastewater discharged from an incineration plant, which solves problems associated with an MF membrane treatment, lowers cost of equipment and provides easy operation management.SOLUTION: The method for processing wastewater discharged from an incineration plant includes: an aggregation and sedimentation step of adding a coagulant and an alkali to the wastewater to form aggregate and depositing it; a neutralization step of adding an acid to a separated water away from the aggregate deposited in the aggregation and sedimentation step, such that the separated water has a pH value in the range of 7.5 to 9.5 and has Langelier index in the range of a negative; a sand filtration step of sand filtrating the processed water in the neutralization step; a pre-filtration step of treating the filtrate obtained in the sand filtration step with active carbon and then being filtrated with a prefilter; and a reverse osmosis membrane treatment step of treating the filtrate obtained in the pre-filtration step with a reverse osmosis membrane. The membrane concentrated water obtained in the reverse osmosis membrane treatment step is supplied to a temperature decreasing device, in the method and device for processing wastewater.

Description

  The present invention relates to a treatment method and treatment equipment for wastewater discharged from a waste incineration plant.

  In a waste incineration plant, in general, in addition to an incinerator, in order to effectively use the heat generated by combustion, a heat recovery device and a power generation device for combustion exhaust gas, and further reduce the temperature of the recovered combustion exhaust gas. A temperature reducing device, an exhaust gas treatment device, and the like are provided. The waste water discharged from the incineration plant was added with a flocculant to separate the agglomerates, purified by microbial treatment, and discharged.

  On the other hand, in order to reduce the discharge flow rate of purified water, purified water is sprayed into a temperature reducing device and vaporized, and the temperature of combustion exhaust gas is reduced by the heat of vaporization.

  However, in the method of reducing the temperature by the heat of vaporization, if the amount of spray water is large, the temperature decrease due to the heat of vaporization increases, and the amount of heat recovered by the heat recovery device is reduced accordingly, and the amount of power generation is reduced. Therefore, as a countermeasure, a method has been developed in which the wastewater is separated into membranes, the water that has passed through the membrane is discharged or reused as industrial water, and only concentrated water that has not passed through the membrane is sprayed with a temperature reducing device. (Patent Document 1).

  An example of this waste water treatment method is shown in FIG. As shown in the figure, the wastewater from the incineration plant is sent to a flocculating device to flocculate suspended matter, and then filtered through a sand filtering device. The filtered wastewater is sent to the MF membrane unit, filtered through a microfiltration membrane (MF membrane), and further purified by a reverse osmosis membrane (RO membrane) by the RO membrane unit. The purified water is reused as plant water, equipment cooling water, boiler raw water, and the like. The concentrated water that has not passed through the microfiltration membrane and the concentrated water that has not passed through the reverse osmosis membrane are vaporized by being sprayed by a temperature reducing device.

JP 2010-89071 A

  However, the method of using the MF membrane and the RO membrane has a high equipment cost of the MF membrane treatment equipment cost. In operation management of the MF membrane treatment facility, backwashing, chemical cleaning, and the like are required, which takes time and effort. In the neutralization tank after the coagulation sedimentation, the pH of the treated water of the RO membrane becomes 5.5 to 6.0 in order to make the pH about 7 neutral, compared with pH 6 to 8 which is the water quality standard of equipment cooling water. Too low. Furthermore, there was a problem that it was necessary to add a scale inhibitor before the RO membrane treatment.

  An object of the present invention is to provide a method for treating wastewater discharged from an incineration plant that solves the problems associated with the MF membrane treatment described above, lowers the equipment cost, and facilitates operation management.

  The present inventor has intensively studied to solve the above-mentioned problems, and firstly, the MF membrane treatment is eliminated, and the suspended matter is removed by the activated carbon treatment and the prefilter. And in order to prevent precipitation of calcium carbonate in the RO membrane, it was decided to adjust the pH in the neutralization tank so that the Langeria coefficient becomes negative. And in order to use RO membrane permeation water also for apparatus cooling water, pH in a neutralization tank was adjusted to 7.5-9.5.

The present invention solves the above problems by taking these measures,
An incinerator for combusting waste, a heat recovery device for recovering the heat of the combustion exhaust gas discharged from the incinerator, and a temperature reducing device for further reducing the temperature of the combustion exhaust gas recovered by the heat recovery device are provided. A method for treating wastewater discharged from an incineration plant,
A flocculant and an alkali are added to the waste water to precipitate the generated aggregate, and an acid is added to the separated water from which the aggregate precipitated in the aggregate precipitation step is separated, and the pH value of the separated water is adjusted. It is obtained within the range of 7.5 to 9.5 and the neutralization step for adjusting the Langelia index to a negative range, the sand filtration step for sand filtration of the treated water in the neutralization step, and the sand filtration step. The obtained filtrate is subjected to activated carbon treatment, and then has a prefiltration step of filtering with a prefilter, and a reverse osmosis membrane treatment step of treating the filtrate obtained in the prefiltration step with a reverse osmosis membrane, wherein the reverse osmosis membrane treatment step A wastewater treatment method, characterized in that the membrane concentrated water obtained in (1) is supplied to the temperature reducing device;
An incinerator for combusting waste, a heat recovery device for recovering the heat of the flue gas discharged from the incinerator, and a temperature reducing device for further reducing the temperature of the flue gas recovered by the heat recovery device are provided. A facility for treating wastewater discharged from an incineration plant,
A coagulating and precipitating device for pre-drain water provided with a coagulant and alkali addition means, an acid addition means, and the pH value of the separated water separated by the pre-coagulation precipitator in the range of 7.5 to 9.5, and , A neutralizer for adjusting the Langeria index to a negative range, a sand filtration device for treated water treated by the neutralizer, an activated carbon treatment device for the filtrate obtained from the sand filtration device, and the activated carbon treatment device A pre-filter for filtering the treated water treated in step 1 and a reverse osmosis membrane treatment device for treating the filtrate of the pre-filter with a reverse osmosis membrane, and the membrane concentrated water obtained by the reverse osmosis membrane treatment device The present invention provides a wastewater treatment facility characterized by having means for supplying to a temperature reducing device.

  In the present invention, since the MF membrane treatment is not performed, the equipment cost and the operation cost relating to the MF membrane treatment are unnecessary, and since only the membrane concentrated water for the RO membrane treatment is sent to the temperature reducing device, it is sent to the temperature reducing device. The amount of water decreases, the amount of heat recovered by the heat recovery device increases, and the amount of power generation can be increased. RO membrane permeated water can be widely used as industrial water and can also be used as equipment cooling water. Since the Langelier index is made negative in the neutralization process, there is no problem of scale adhesion to the RO membrane, and as a whole, exhaust heat from the incineration plant can be efficiently recovered and waste water can be effectively reused.

It is a figure which shows the structure of an example of the incineration plant to which this invention is applied. It is a block diagram which shows the process of the waste_water | drain. It is a graph which shows the relationship between pH of a neutralization tank, and pH of RO membrane process water. It is a block diagram which shows an example of the processing process of the conventional waste_water | drain.

Mode for carrying out the invention

  The incineration plant of the present invention is a plant for incinerating waste, and has an incinerator, a heat recovery device, and a temperature reducing device.

  The type of waste is not limited, but it is general waste mainly composed of household waste, or industrial waste mainly discharged from various factories.

  As the incinerator, a general incinerator that burns waste can be applied, for example, a stoker type, a kiln type, a fluidized bed type, or a shaft type gasification melting furnace.

  The heat recovery device is a device that recovers heat from the combustion exhaust gas emitted from the incinerator, and uses a waste heat boiler, an economizer, and the like. In the heat recovery apparatus, the temperature of the combustion exhaust gas of about 850 to 950 ° C is usually lowered to about 200 to 300 ° C.

  The temperature reduction device is a device that further reduces the temperature of the combustion exhaust gas recovered by the heat recovery device. Usually, a two-fluid nozzle for water spraying is installed inside the temperature-decreasing tower and the temperature-decreasing tower. A device that lowers the exhaust gas temperature by the heat of vaporization of water is used by injecting water and compressed air into the temperature reducing tower and bringing it into contact with the incineration exhaust gas.

  A general exhaust gas treatment system such as a filter type dust collector (bag filter), a denitration reaction tower, and an activated carbon adsorption tower is used for the exhaust gas exiting the temperature reducing tower. Main ash and fly ash generated from the incinerator are treated in the conventional manner.

Examples of waste water discharged from this incineration plant include boiler blow water, equipment cooling water, car wash water, and floor wash water.
Coagulation and precipitation process The coagulation and precipitation process is a process of adding a flocculant and alkali to the waste water discharged from the incineration plant, and precipitates the agglomerate produced by ferric chloride (FeCl ₃ ) and sulfuric acid. Ferrous iron (FeSO ₄ ), sulfuric acid band (Al ₂ (SO ₄ ) ₃ ), PAC (polyaluminum chloride) and the like are used. The purpose of alkali is to remove heavy metals. For example, caustic soda is added to precipitate and precipitate heavy metals as hydroxides. The pH is about 8-10.

A tank or a pond provided with a coagulant and alkali addition means is used for this coagulation sedimentation apparatus.
Neutralization step In the neutralization step, an acid is added to the separated water from which the aggregates have been separated in the coagulating sedimentation step, so that the pH of the separated water is in the range of 7.5 to 9.5 and the Langeria index is negative. Adjust to range.

  As the acid, hydrochloric acid, sulfuric acid and the like can be used. The pH is 7.5 to 9.5, preferably 7.7 to 8.2.

  The Langeliar Saturation Index (LSI) is an index represented by the following formula (1).

LSI = pH-pHs (1)
pH is the actual pH value of water, and pHs is the theoretical pH value when in an equilibrium state where calcium carbonate does not dissolve or precipitate in water.

pHs = 8.313−log (Ca ²⁺ ) −log (A) + S
Ca ²⁺ (meq / L)… Ca ²⁺ (mg / L) ÷ (40.1 ÷ 2)
A (total alkalinity) (meq / L) ... total alkalinity (mg / L) ÷ (100 ÷ 2)
Total alkalinity is an index of alkali content such as bicarbonate, carbonate or hydroxide contained in water. The total alkalinity in natural water is mainly composed of carbonates or bicarbonates, and when the total alkalinity is high, there are many substances that combine with the hardness components of Ca and Mg to produce precipitates. Show. Total alkalinity (mg / L) can be analyzed by titration with hydrochloric acid or sulfuric acid.

S… 2√μ ÷ (1 + √μ) μ ＝ 2.5 × 10-5 × sd sd is soluble substance concentration (mg / L)
In the present invention, the Langellia index is preferably in the range of −0.5 to less than 0 so as to be negative. When the Langelia index is positive, the scale component is deposited, and the reverse osmosis membrane is likely to be clogged. On the other hand, when the Langeria index is too lower than −0.5, it is assumed that the pH of the reverse osmosis membrane treatment water is lower than 6 and it is necessary to inject an alkaline agent such as caustic soda into the RO membrane treatment water. .

  In order to adjust the Langelia index to be less than 0 (zero), for example, when any of the pH value of the treated water, the soluble substance concentration, the calcium concentration, and the total alkalinity increases, the Langeria Since the index is in the direction of increasing, the Langeria index can be adjusted to decrease by increasing the amount of the acidic agent added by the pH adjuster adding device.

Sand filtration step The sand filtration step is a step of sand filtering the treated water in the neutralization step, and in this step, suspended matter of about several tens of μm in the treated water is filtered off.
Pre-filtration process In the pre-filtration process, the sand-filtered water is first filtered with activated charcoal to adsorb and remove organic substances and some inorganic substances, and the medium suspended particles with a particle size of about 5μm are filtered out. Is filtered off.

As the prefilter, a check filter in which cotton yarn or the like is spirally reciprocated and wound so as to cross each other can be used. There are various types of check filter having a pore diameter of about 0.5 to 3 μm, and they are commercially available under trade names such as “RO wind”.
Reverse osmosis membrane treatment step In the reverse osmosis membrane treatment step, the filtrate filtered in the prefiltration step is permeated through the reverse osmosis membrane. Commercially available reverse osmosis membranes and devices for mounting them can be used. The permeated water of the reverse osmosis membrane can be used as industrial water for equipment cooling water or the like. On the other hand, the membrane concentrated water remaining without passing through the reverse osmosis membrane is sprayed by the temperature reducing tower to reduce the temperature of the combustion exhaust gas discharged from the heat recovery device, but a part thereof may be discharged into the sewage.

  The incineration plant having the configuration shown in FIGS.

  As shown in Fig. 1, this incineration plant is equipped with an incinerator, boiler, economizer, temperature reducing tower, filtration dust collector, denitration reaction tower, and chimney in this order. Waste is incinerated in the incinerator. The remaining main ash is taken out and landfilled.

  The combustion exhaust gas is first recovered by a boiler and further recovered by an economizer, and then the RO membrane concentrated water is sprayed by a temperature reducing tower to reduce the temperature. Thereafter, fly ash is collected and removed by a filtration type dust collector (bag filter), NOX contained in the exhaust gas is removed by a denitration reaction tower, and then released into the atmosphere through a chimney. In addition to the denitration reaction tower, an activated carbon adsorption tower is also used.

  As shown in the upper part of FIG. 1, the water used in this plant first receives clean water in a reuse water tank, which is used for plant water, equipment washing water, boiler raw water, and the like. Wastewater after use is treated with wastewater treatment equipment.

  As shown in FIG. 2 for details of the wastewater treatment facility, the wastewater after use is first sent to a flocculating device, and caustic soda and a flocculating agent are charged and precipitated in a settling tank. The supernatant water is sent to a neutralization tank, where neutralization and Langerian coefficient are measured and filtered with a sand filter. The filtrate is passed through an activated carbon tower to adsorb and remove organic matters and finer fine particles are removed with a check filter. The filtered water of the check filter is sent to the RO membrane device. The RO membrane filtered water can be recycled for equipment cooling water and the like, and is sent to a reuse water tank for circulation. On the other hand, the concentrated water remaining without permeating the RO membrane is sprayed in a temperature reducing tower or discharged into the sewer.

  The fly ash collected by the filtration type dust collector of FIG. 1 is insolubilized by adding clean water and a chelating agent, and is landfilled.

The wastewater from this incineration plant was put into a coagulation tank, caustic soda was added to adjust the pH to 8-9, and ferric chloride (FeCl ₃ ) was further added to precipitate the aggregate. The supernatant was transferred to a neutralization tank and neutralized by adding hydrochloric acid. The incineration plant (FIGS. 1 and 2) was continuously operated while controlling the pH of the neutralization tank and the amount of hydrochloric acid injected so that the Langeria coefficient was in the range of 0 to -0.5.

  The treatment liquid of this neutralization step was filtered through a sand filtration tank, and further passed through a fixed bed type activated carbon tower filled with activated carbon commercially available for wastewater treatment.

  As the prefilter, 6 RO winds with a pore diameter of 3 μm, which are commercially available for wastewater treatment, were installed. After passing this, reverse osmosis membrane treatment was carried out in which three commercially available reverse osmosis membrane modules for wastewater treatment were placed in series in a high-pressure vessel to obtain RO membrane treated water and RO membrane concentrated water. .

  Table 1 shows the pH of the neutralization tank, the estimated value of the Langeria coefficient, and the pH of the RO membrane treated water. By operating at a Langelia coefficient of 0 to -0.5, the generation of scale was suppressed and stable operation was possible. FIG. 3 shows the pressure data. As the cleaning liquid, a caustic soda aqueous solution having a pH of 11 to 12 and / or a hydrochloric acid aqueous solution having a pH of 2 to 3 were used. Table 2 shows the water quality test results of the incineration plant wastewater, RO membrane treated water and RO membrane concentrated water in the test. It was possible to control the pH of RO membrane treated water to a value suitable for the standard value (6-8) of equipment cooling water (make-up water, circulation system). RO membrane concentrated water could be sprayed stably without spraying on the cooling tower and causing clogging in the piping and nozzles.

  Since the wastewater treatment method of the present invention can be effectively used internally without discharging the wastewater discharged from the incineration plant in the waste incineration plant, it can be widely used in the waste incineration plant.

Claims (2)

An incinerator for combusting waste, a heat recovery device for recovering the heat of the combustion exhaust gas discharged from the incinerator, and a temperature reducing device for further reducing the temperature of the combustion exhaust gas recovered by the heat recovery device are provided. A method for treating wastewater discharged from an incineration plant,
A flocculant and an alkali are added to the waste water to precipitate the generated aggregate, and an acid is added to the separated water from which the aggregate precipitated in the aggregate precipitation step is separated, and the pH value of the separated water is adjusted. It is obtained within the range of 7.5 to 9.5 and the neutralization step for adjusting the Langelia index to a negative range, the sand filtration step for sand filtration of the treated water in the neutralization step, and the sand filtration step. The obtained filtrate is subjected to activated carbon treatment, and then has a prefiltration step of filtering with a prefilter, and a reverse osmosis membrane treatment step of treating the filtrate obtained in the prefiltration step with a reverse osmosis membrane, wherein the reverse osmosis membrane treatment step A wastewater treatment method characterized by supplying the membrane concentrated water obtained in step 1 to the temperature reducing device and / or discharging the sewage. An incinerator for combusting waste, a heat recovery device for recovering the heat of the flue gas discharged from the incinerator, and a temperature reducing device for further reducing the temperature of the flue gas recovered by the heat recovery device are provided. A facility for treating wastewater discharged from an incineration plant,
A coagulating and precipitating device for pre-drain water provided with a coagulant and alkali addition means, an acid addition means, and the pH value of the separated water separated by the pre-coagulation precipitator in the range of 7.5 to 9.5, and , A neutralizer for adjusting the Langeria index to a negative range, a sand filtration device for treated water treated by the neutralizer, an activated carbon treatment device for the filtrate obtained from the sand filtration device, and the activated carbon treatment device A pre-filter for filtering the treated water treated in step 1 and a reverse osmosis membrane treatment device for treating the filtrate of the pre-filter with a reverse osmosis membrane, and the membrane concentrated water obtained by the reverse osmosis membrane treatment device A wastewater treatment facility comprising means for supplying to a temperature reducing device and / or discharging sewage.

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