JP6287666B2 - Waste water treatment method and waste water treatment equipment - Google Patents

Description

  The present invention relates to a wastewater treatment method and a wastewater treatment apparatus for treating wastewater discharged from a plant that incinerates waste.

  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. In addition, the waste water discharged from the incineration plant was added with a flocculant to separate the agglomerates, purified by microbial treatment and discharged.

  By the way, the waste incineration plant is provided with a circulating cooling water system for cooling the equipment. In this circulating cooling water system, water in the system is discharged from the cooling tower as blow water in order to prevent scale failure due to concentration of components that can become scale in the system (hereinafter referred to as scale components). The amount of water commensurate with water is replenished as make-up water. This blow water is water in which hardness components and scale components such as silica are concentrated to a high concentration, and recovering the water from this blow water and reusing it as makeup water for the circulating cooling water system increases the processing cost. .

  However, in recent years, as a wastewater treatment method for wastewater discharged from an incineration plant, it has been required to adopt a method in which purified water purified by wastewater treatment is not discharged to the outside as much as possible in order to cope with environmental problems.

  As a method of not releasing purified water as much as possible, for example, in Patent Document 1, in order to reduce the discharge flow rate of purified water, the purified water is sprayed into a temperature reducing device and vaporized, and the combustion exhaust gas is reduced in temperature by the heat of vaporization. Is described.

  Further, in Patent Document 2, in the method of decreasing the temperature by heat of vaporization, if the amount of spray water is large, the temperature decrease due to the heat of vaporization increases, and accordingly, the amount of heat recovered by the heat recovery device decreases and the amount of power generation decreases. Therefore, the amount of water sprayed by separating the wastewater with a reverse osmosis membrane and recycling the water that passed through the membrane as discharge or industrial water, and spraying only the concentrated water that did not pass through the membrane with a temperature reducing device A method of reducing the is described.

  However, since blow water discharged from the cooling tower of the circulating cooling water system is water in which scale components such as hardness components and silica have already been concentrated to the precipitation limit, if this blow water is directly processed by a reverse osmosis membrane treatment apparatus Concentration of scale components in the reverse osmosis membrane treatment apparatus immediately generates scale on the reverse osmosis membrane surface, making it impossible to continue the operation.

  In the thing of patent document 2, when processing the waste_water | drain containing apparatus cooling water blow water with a reverse osmosis membrane, in order to prevent that a deposit (scale) generate | occur | produces in a concentration port, on the reverse osmosis membrane inlet side. A scale inhibitor is added to the raw water. Components that can become scales contained in the raw water by adding a scale inhibitor to the raw water on the reverse osmosis membrane inlet side (hardness components such as ionic silica, calcium ions, magnesium ions, soluble evaporation residue, bicarbonate, etc.) Suppresses precipitation as a scale.

Usually, the blow timing and the blow water amount are controlled as follows.
The conductivity corresponding to the concentration rate at which no scale precipitation occurs in the system is set as the upper limit set value, and when the conductivity reaches the upper limit set value, the concentrated cooling water is blown from the bottom of the cooling tower. It is discharged and discharged, and the whole is diluted with make-up water, so that the circulating cooling water is operated and managed with a constant quality. Here, when the amount of blow water is increased and the scale component concentration in the system is lowered to operate, a large amount of makeup water is required, the cost of water increases, and the amount of blow water is decreased to perform high concentration operation. The scale component in the cooling water exceeds the solubility and the scale of the hardly soluble salt is precipitated.

  As mentioned above, equipment cooling water blow is intermittent operation by conductivity control, so the mixing ratio of equipment cooling water blow water and other waste water is not stable, the concentration of scale components temporarily increases, reverse osmosis There is a risk that raw water exceeding the capacity of the scale inhibitor flows into the membrane treatment apparatus and scale is generated.

JP 2003-74832 A JP 2010-64016 A

  An object of the present invention is to provide a wastewater treatment method and a wastewater treatment apparatus that prevent the generation of scale by suppressing the concentration fluctuation of the scale component of raw water for reverse osmosis membrane treatment.

  As a result of investigations to solve the above-mentioned problems, the present inventor has not performed conductivity control but timer control for equipment cooling water blow water blow control that contains a component (scale component) that can be a high-concentration scale. It is found that the above problem can be solved by blowing equipment cooling water at a high frequency and mixing it with other wastewater generated quantitatively at all times to suppress concentration fluctuations. Completed the invention.

The present invention is a wastewater treatment method and a wastewater treatment apparatus as described below.
(1) A wastewater treatment method for treating wastewater containing equipment cooling water blow water and boiler blow water discharged from a waste incineration plant having a boiler using a reverse osmosis membrane treatment device,
Supply the equipment cooling water blow water and boiler blow water discharged every fixed time by timer control to the raw water tank, mix and store it, and use it as raw water for reverse osmosis membrane treatment,
The supply amount of the equipment cooling water blow water to the raw water tank and the supply amount of the boiler blow water to the raw water tank are such that the concentration of the scale component in the raw water for reverse osmosis membrane treatment does not exceed a predetermined set value. Such a ratio,
A wastewater treatment method, wherein reverse osmosis treatment is performed by supplying raw water for reverse osmosis membrane treatment in the raw water tank to the reverse osmosis membrane treatment apparatus.
(2) A bypass path for supplying equipment cooling water blow water to the reuse water tank is provided in the middle of the path for supplying equipment cooling water blow water to the raw water tank , and boiler blow water is provided in the middle of the path for supplying boiler blow water to the raw water tank. the providing a bypass path for supplying the pure water reproducing drainage tank, and characterized in that to adjust the flow rate to each of the raw water tank of the reverse osmosis membrane device cooling water blow water into the processing apparatus and Boiraburo water The waste water treatment method according to (1).
(3) A waste water treatment apparatus for treating waste water including equipment cooling water blow water and boiler blow water discharged from a waste incineration plant having a boiler,
Equipment cooling water blowing means for discharging a part of equipment cooling water of the incineration plant at regular intervals by timer control;
Boiler blow means,
A raw water tank in which the equipment cooling water blow water discharged by the equipment cooling water blow means and the boiler blow water discharged by the boiler blow means are supplied as raw water;
A reverse osmosis membrane treatment apparatus for treating the raw water with a reverse osmosis membrane,
The equipment cooling water blow means and the boiler blow means blow the equipment cooling water blow water and the boiler blow water so that the concentration of the scale component in the raw water in the raw water tank does not exceed a predetermined set value. Wastewater treatment equipment.
(4) A bypass path for supplying equipment cooling water blow water to the reuse water tank is provided in the middle of the path for supplying equipment cooling water blow water to the raw water tank , and boiler blow water is provided in the middle of the path for supplying boiler blow water to the raw water tank. The waste water treatment apparatus as set forth in (3), wherein a bypass path is provided for supplying the water to the pure water regeneration drainage tank.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the scale in a reverse osmosis membrane processing apparatus can be prevented by suppressing the density | concentration fluctuation | variation of the scale component of the raw | natural water supplied to a reverse osmosis membrane processing apparatus.

It is a figure which shows schematic structure of an example of the waste water treatment apparatus for enforcing the waste water treatment method of this invention. It is a figure which shows schematic structure of an example of the waste water treatment equipment of this invention. It is a figure which shows the density | concentration fluctuation | variation of the silica component in the raw water for reverse osmosis membrane processing at the time of implementing the waste water treatment method of this invention.

(Mixing of equipment cooling water blow water and boiler blow water)
In the present invention, the blow water of the equipment cooling water and the boiler blow water discharged from the boiler are mixed, and if necessary, mixed with other waste water as raw water for reverse osmosis membrane treatment, which is used as the reverse osmosis membrane. Process with processing equipment.
Equipment cooling water blow water and boiler blow water are generated intermittently. For this reason, in order to make the raw water uniform, it is necessary to secure the capacity of the raw water tank.
Hereinafter, the reverse osmosis membrane may be referred to as “RO membrane”, and the reverse osmosis membrane treatment apparatus may be referred to as “RO membrane treatment apparatus”.

The waste incineration plant is provided with a heat recovery device for combustion exhaust gas. As this heat recovery device, a boiler (steam generation means) that generates steam by heat exchange with the combustion exhaust gas is used.
The water (canned water) supplied to the boiler is heated to generate steam. After the steam is used as power, a part or all of the steam is returned to the water supply tank as condensate and circulated for use as water supply.
The can water in the boiler produces steam and the can water itself is concentrated. In order to prevent scale generation, a portion of boiler water is discharged from the bottom of the boiler as boiler blow water. In addition to boiler bottom blow water, boiler blow water includes continuous blow water.

The reverse osmosis membrane may be clogged when the concentration of the silica component in the raw water is about 200 mg / L. In addition, as a result of membrane treatment by the RO membrane treatment apparatus, the concentration of the silica component in the concentrated water becomes higher than the concentration of the silica component in the raw water.
Usually, the cooling water in the cooling tower is operated at a concentration ratio of 3 to 4 times. Therefore, in the RO membrane treatment apparatus, if the treatment is performed at a concentration ratio lower than the concentration ratio of the cooling water, for example, about 2 times, the RO membrane The concentrated water can be sufficiently used together with the raw cooling water as makeup water for the cooling water system.
And when making a concentration magnification into 2 times, it is necessary to control the silica density | concentration in the raw | natural water which flows into RO membrane processing apparatus to 100 mg / L or less normally.

Since the concentration of the scale component of the boiler blow water is lower than the scale component concentration of the equipment cooling water, the silica concentration of the raw raw water mixed by mixing the equipment blow water with the equipment cooling water blow water It can be made lower than the silica concentration.
Then, by appropriately managing the ratio of the equipment cooling water blow water and boiler blow water supplied to the raw water tank, the concentration of the scale component is set to a predetermined value or less, and the concentration fluctuation of the scale component in the raw water is suppressed. Thus, scale generation can be prevented even if the scale component is concentrated by membrane separation treatment in the reverse osmosis membrane treatment apparatus.

(Timer control of equipment cooling water blow)
In order to make the quality of the raw water uniform, it is preferable to frequently blow the apparatus cooling water blow water by narrowing the blow interval.
Conventionally, equipment cooling water is blown on and off by the conductivity of the cooling water, but in that case, the frequency of blowing is reduced and even if the interval can be shortened, it is limited to once a day. is there. Since the capacity of the equipment cooling water receiving tank is large, replenishment of new water is started after about 20 m ³ of blow is performed, and when about 20 m ³ is blown at a time, the amount of blow water is reduced to the membrane treatment system raw material. The capacity of the water tank will be exceeded, which is impossible in terms of capacity, and the quality of the raw water cannot be made uniform.

  Therefore, in the present invention, the blow interval is narrowed by controlling the blow interval of the equipment cooling water with a timer. In the case of the timer control, if the timer is set according to the summer season when the equipment cooling water is easy to concentrate, excessive blow will occur in the winter season. Therefore, when performing timer control, the operator checks the conductivity trend data periodically and adjusts the timer set value periodically and every season so that the blow amount does not become excessive. .

(Ratio between can bottom blow and continuous blow)
In order to make the raw water quality uniform, it is necessary to discharge boiler blow water as uniformly as possible.
There are two types of boiler blows: can bottom blow and continuous blow. In order to make the raw water quality uniform, it is preferable to reduce the amount of blow at the bottom of the can once and increase the amount of continuous blow per day to the amount of blow at the bottom of the can per day.
At present, the ratio between can bottom blow and continuous blow is set as follows, for example.
Can bottom blow: 130 kg / h Blow once every 12 hours Continuous blow: 50 kg / h
In the present invention, in order to make the properties of the raw RO water uniform, the ratio of can bottom blow and continuous blow can be set as follows, for example.
Can bottom blow: 80 kg / h Blow once every 12 hours Continuous blow: 100 kg / h

One embodiment of the present invention will be described with reference to FIG.
Equipment cooling water blow water (CB) is supplied to the raw water tank 1 at regular time intervals by timer control. As for the boiler blow water (BB), can bottom blow water and continuous blow water are also supplied to the raw water tank 1.
The equipment cooling water blow water and boiler blow water in the raw water tank 1 are made uniform in the raw water tank 1 and supplied to the activated carbon filtration device 2 by the feed pump P1. The raw water discharged from the activated carbon filter 2 is supplied to the prefilter 3.

As the prefiltration device 3, a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane) can be used. In the case where a sand filtration device is provided in the previous stage and the floating substance can be sufficiently removed, a pincushion type check filter having an opening of 1 to 3 μm may be used, which is preferable in terms of cost reduction.
The raw water discharged from the prefiltration device 3 is mixed with the scale inhibitor supplied from the scale inhibitor solution tank 11 and then supplied to the reverse osmosis membrane treatment device 4 by the high-pressure pump P2.

The reverse osmosis membrane treated water obtained by the treatment with the reverse osmosis membrane treatment apparatus 4 is mixed with the caustic soda solution from the caustic soda solution tank 12 and with the sodium hypochlorite solution from the sodium hypochlorite solution tank 13. To the reverse osmosis membrane treated water tank 5.
The caustic soda solution is added to the reverse osmosis membrane treated water, and the sodium hypochlorite solution is added to the reverse osmosis membrane treated water as a disinfectant.
Caustic soda solution tank 12 is replenished with caustic soda from caustic soda storage tank 14.

The reverse osmosis membrane treated water mixed with the chemical solution is sent from the reverse osmosis membrane treated water tank 5 to the equipment cooling water receiving tank 7 by the reverse osmosis membrane treated water supply pump P3. The reverse osmosis membrane treated water stored in the equipment cooling water receiving tank 7 is reused as equipment cooling water.
On the other hand, the reverse osmosis membrane treated concentrated water discharged from the reverse osmosis membrane treatment apparatus 4 is stored in the reverse osmosis membrane treated concentrated water tank 6. The stored water in the reverse osmosis membrane treatment concentrated water tank 6 is sent to the sewage tank in the plant system by the reverse osmosis membrane treatment concentrated water pump P4. The concentrated water in the sewage tank may be sprayed in a temperature reducing device that further reduces the temperature of the combustion exhaust gas recovered by the heat recovery device.
Further, the reverse osmosis membrane treated concentrated water tank 6 may be provided with a supply path for supplying backwash wastewater generated when the activated carbon filtration device 2 is backwashed as shown in FIG.

The system configuration upstream of the membrane treatment system raw water tank is preferably the one shown in FIG.
In the equipment cooling water blow water system, “KS” indicates ON / OFF control of blow by the timer, and “QISA” indicates control by the conductivity of the cooling water.
In the wastewater treatment method of the present invention, blow ON / OFF control is performed by a timer. However, in order to increase the degree of freedom of operation of the wastewater treatment facility, control by conductivity may be possible depending on the facility.

In the equipment cooling water blow water system, the equipment cooling water blow water is recirculated in the middle of the path for supplying equipment cooling water blow water to the raw water tank so that the amount of equipment cooling water blow water flowing into the RO membrane treatment device can be adjusted. It is preferable to provide a bypass path for supplying the water tank.
In the boiler blow water system, a bypass path for supplying boiler blow water to the pure water regeneration drainage tank in the middle of the path for supplying boiler blow water to the raw water tank so that the amount of boiler blow water flowing into the RO membrane treatment device can be adjusted. Is preferably provided.
By providing the bypass path in this way, it is possible to cope with a failure of the reverse osmosis membrane processing apparatus.

(simulation)
The effects of the present invention will be verified by showing the simulation results below.
The technical scope of the present invention is not limited to the following simulation conditions.

The amount of raw material boiler blow water and equipment cooling water blow water was set as follows.
[Boiler blow water]
Design treated water volume: 15.6 m ³ / day [equipment cooling water blow water]
Designed water volume: 10.4 m ³ / day

When the treatment capacity of the reverse osmosis treatment apparatus is 26 m ³ / day and the concentration rate is 2 times, the balance of the inlet and outlet of the reverse osmosis membrane treatment apparatus on the design specifications is as follows.
(entrance)
Boiler blow water: 15.6 m ³ / day Equipment cooling blow water: 10.4 m ³ / day Total 26 m ³ / day (exit)
Membrane treated water: 13.0 m ³ / day Membrane treated water: 13.0 m ³ / day [raw water quality]
The raw water quality was as shown in Table 1 below.
[Processed water quality]
The treated water quality was set to the level of the water supply.

(Changes in silica concentration in raw water)
FIG. 3 is a diagram showing a simulation result of fluctuations in silica concentration in raw water in a raw water tank of mixed water of equipment cooling water blower water and boiler blow water.
FIG. 3A is a graph showing the relationship between the elapsed time when blown every 24 hours with conductivity control and the silica concentration, and FIG. 3B shows the elapsed time when blown every hour with timer control. It is a graph which shows the relationship with a silica concentration.
As shown in the graph, the variation range of the silica concentration is 20 ppm according to the conductivity control, whereas the variation range of the silica concentration can be suppressed to within 10 ppm according to the timer control.
The simulation conditions were as follows.

(Timer control)
Equipment cooling water blow water Blow water volume 8m ³ / day (354kg / h)
Inflow frequency Once per hour → 354 kg / time Boiler blow water Continuous blow generation rate 100 kg / h / furnace Can bottom blow generation rate 960 kg / time / furnace Can bottom blow frequency Once every 12 hours (conductivity control)
The same conditions as the timer control were used except that the inflow frequency of the equipment cooling water blow water under the timer control conditions was 24 hours.

DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Activated carbon filtration apparatus 3 Pre filtration apparatus 4 Reverse osmosis membrane treatment apparatus 5 Reverse osmosis membrane treatment water tank 6 Reverse osmosis membrane treatment concentration water tank 7 Equipment cooling water receiving tank 10 Waste water treatment apparatus 11 Scale inhibitor solution tank 12 Caustic soda solution tank 13 Sodium hypochlorite solution tank 14 Caustic soda storage tank P1 Feed pump P2 High pressure pump P3 Reverse osmosis membrane treated water supply pump P4 Reverse osmosis membrane treated concentrated water supply pump BB Boiler blow water CB Equipment cooling water blow water

Claims (4)

A wastewater treatment method for treating wastewater containing equipment cooling water blow water and boiler blow water discharged from a waste incineration plant having a boiler using a reverse osmosis membrane treatment device,
Supply the equipment cooling water blow water and boiler blow water discharged every fixed time by timer control to the raw water tank, mix and store it, and use it as raw water for reverse osmosis membrane treatment,
The supply amount of the equipment cooling water blow water to the raw water tank and the supply amount of the boiler blow water to the raw water tank are such that the concentration of the scale component in the raw water for reverse osmosis membrane treatment does not exceed a predetermined set value. Such a ratio,
A wastewater treatment method, wherein reverse osmosis treatment is performed by supplying raw water for reverse osmosis membrane treatment in the raw water tank to the reverse osmosis membrane treatment apparatus. A bypass path for supplying the equipment cooling water blow water to the reuse water tank is provided in the middle of the path for supplying the equipment cooling water blow water to the raw water tank , and the boiler blow water is pure water in the middle of the path for supplying the boiler blow water to the raw water tank. The bypass path for supplying to the regeneration drainage tank is provided , and the inflow amount of the equipment cooling water blow water and the boiler blow water to the reverse osmosis membrane treatment apparatus is adjusted to each raw water tank. The waste water treatment method according to 1. A wastewater treatment apparatus for treating wastewater including equipment cooling water blow water and boiler blow water discharged from a waste incineration plant having a boiler,
Equipment cooling water blowing means for discharging a part of equipment cooling water of the incineration plant at regular intervals by timer control;
Boiler blow means,
A raw water tank in which the equipment cooling water blow water discharged by the equipment cooling water blow means and the boiler blow water discharged by the boiler blow means are supplied as raw water;
A reverse osmosis membrane treatment apparatus for treating the raw water with a reverse osmosis membrane,
The equipment cooling water blow means and the boiler blow means blow the equipment cooling water blow water and the boiler blow water so that the concentration of the scale component in the raw water in the raw water tank does not exceed a predetermined set value. Wastewater treatment equipment. A bypass path for supplying the equipment cooling water blow water to the reuse water tank is provided in the middle of the path for supplying the equipment cooling water blow water to the raw water tank , and the boiler blow water is pure water in the middle of the path for supplying the boiler blow water to the raw water tank. The wastewater treatment apparatus according to claim 3, wherein a bypass path for supplying the regeneration drainage tank is provided.

Images