JP4417056B2 - Crystal recovery and transfer equipment - Google Patents

Description

The present invention relates to an apparatus for recovering specific ions from a liquid to be treated such as waste water, and in particular, phosphate ions, calcium ions, fluorine ions, carbonate ions, sulfate ions, manganese ions contained in various liquids. The present invention relates to an apparatus for recovering and transferring crystals that are efficiently and stably obtained by causing a chemical reaction to precipitate crystals of a hardly soluble salt.

  Conventionally, a crystallization method has been used as one of methods for recovering specific ions from various liquids to be treated. In the crystallization method, a compound that reacts with specific ions contained in the liquid to be treated to form a hardly soluble salt is added as a chemical to the liquid to be treated (hereinafter also referred to as “raw water”), or the pH of the liquid to be treated. This is a method in which the liquid to be treated is brought into a supersaturated state of ions by changing the value to precipitate and separate crystals containing specific ions.

As an example of the crystallization method, according to “Patent Document 1”, wastewater such as manure and sewage secondary treated water and return water from a sludge treatment system is treated water, and phosphate ions therein are In the case of recovery, a calcium compound is added to precipitate crystals of calcium phosphate (Ca ₃ (PO ₄ ) ₂ ) or hydroxyapatite (Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ; hereinafter referred to as “HAP”). It is shown. Also, wastewater from semiconductor factories often contains a lot of fluorine ions. When collecting fluorine ions from this wastewater, calcium compounds are added in the same manner to precipitate calcium fluoride (CaF ₂ ) crystals. By doing so, fluorine in the waste water can be recovered.

In addition, when calcium ions are removed from water, waste water, or leachate at the final disposal site, the ground water is used as raw water, and the crystal of calcium carbonate (CaCO ₃ ) is precipitated by increasing the pH or adding a carbonic acid source. be able to. Alternatively, by adding calcium ions or raising the pH to hard water containing a large amount of carbonate ions, the calcium carbonate crystals can be similarly prayed to reduce the hardness. Furthermore, in "Patent Document 2", magnesium is added to wastewater containing phosphate ions and ammonium in the liquid, such as filtrate of anaerobic digested sludge, return water from sludge treatment system, and fertilizer factory wastewater. It is shown that crystals of magnesium ammonium phosphate (hereinafter referred to as “MAP”) are precipitated.

  As the crystallization reactor, a fully mixed reactor, a fluidized bed reactor, or the like is used. In view of the solid-liquid separation performance, the latter method is preferable. In the fluidized bed reactor, the water to be treated is passed upward, and the product is precipitated on the surface of the crystal nuclei flowing in the fluidized bed, so that the crystals are settled by gravity while the treated water is fed from the top. By collecting, crystal formation reaction and solid-liquid separation can be performed simultaneously. The crystal nuclei are preferably the same as the product, but are not necessarily the same, and may be sand or zeolite, or those coated with the product.

Conventionally, the crystallized material that has increased due to production has been recovered from the bottom of the reactor by opening or closing a valve or using a pump. In addition to a mechanical pump, the pump used an air lift pump attached to the reactor.
An air lift pump is a system in which compressed air is blown into the lower end of an air lift pipe (also referred to as a pumped pipe) installed so that the lower end is arranged in the liquid of the water tank and the upper end is arranged above the liquid level. The apparent specific gravity of the bubble mixture in the pumping pipe is smaller than the specific gravity of the liquid outside the pipe, so that the liquid level in the pumping pipe rises above the liquid level in the water tank and exceeds the liquid level in the water tank. The liquid can be pumped.

Japanese Patent Publication No.57-34032 JP 2002-326089 A

However, in the recovery method by opening and closing the valve, a crystal substance is deposited in the vicinity of the valve, and the opening and closing of the valve becomes blunt, or the crystal substance is clogged. As a result, it has become difficult to recover a predetermined amount of crystals. In the case of a mechanical pump, crystals often precipitate inside the machine, and the load on the motor unit is often increased or the motor itself does not rotate.
On the other hand, the air lift pump has a simple structure with few mechanical parts, and includes an air lift pipe, a gas supply pipe, a gas separation section, and a slurry extraction section. Since the air lift pump has no moving parts and no contact points between the machinery and the crystal, the above problems such as blockage of the machinery are solved. However, after the air lift pump is terminated, there are cases where crystals remaining in the air lift pipe accumulate and gas cannot be supplied satisfactorily.

  The problem to be solved by the present invention is to provide a crystal recovery method and apparatus that solves the above problems in a crystal extraction method and apparatus using an air lift pump.

The present invention has solved the above problems by the following means.
(1) Using a crystallization reactor, a compound that reacts with the ions to be removed to form a sparingly soluble salt is supplied to the liquid to be treated to precipitate the sparingly soluble salt crystal, and the sparingly soluble crystal is recovered and transferred. A rinsing water supply pipe that is provided with an air lift pipe in the crystallization reactor, provided with a gas supply pipe that supplies gas to a lower portion of the air lift pipe, and for cleaning the air lift pipe in order from the bottom on the air lift pipe; A crystal recovery and transfer device, wherein a valve and a gas separation unit are installed, and a slurry discharge unit is installed in the gas separation unit.
(2) The crystal recovery and transfer device according to (1 ), wherein the washing water supply pipe is located above the water surface of the crystallization reactor.

  According to the present invention, a method is provided in which a compound that reacts with ions to be removed to form a hardly soluble salt is supplied to a liquid to be treated, crystals of the hardly soluble salt are precipitated by a crystallization method, and the hardly soluble salt crystals are recovered. In this case, the hardly soluble salt crystal is recovered and transferred by using an air lift pump provided in a reactor for generating the hardly soluble salt crystal, or after the hardly soluble salt crystal is recovered and transferred, or recovered. -Immediately before the end of transfer, it is possible to provide a method and an apparatus for recovering and transferring crystals efficiently and stably by washing the air lift pipe by passing the wash water downward through the air lift pipe. As a result, the maintenance of the apparatus became easy and the operation efficiency was greatly improved.

The best mode for carrying out the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments and examples.
The crystal recovery method and apparatus will be described below.
FIG. 1 shows a schematic diagram of a crystal recovery and transfer apparatus of the present invention applied to a reactor comprising a crystal grain growth tank 1. At the bottom of the crystal grain growth tank 1, a raw water supply pipe 3 for supplying raw water 2, a circulating water supply pipe 5 for supplying circulating water 4 (including a compound that reacts with ions to be removed in the raw water), and particles in the reactor The air supply pipe 7 for agitating the air and the tip part of the air lift pipe 8 constituting a part of the air lift pump are connected. In addition to the air lift pipe 8, the air lift pump includes a gas (air) supply pipe 9, a gas separation part 10, a slurry discharge part 11, and a wash water supply pipe 13. In the method and apparatus of FIG. 1, the example in which the air lift pipe 8 is installed outside the reactor is shown, but it may be installed inside the reactor. An outflow pipe 15 for the treated water 14 is connected to the upper part of the crystal grain growth tank 1.

  The crystal grain growth tank 1 is filled with seed crystals in advance, and is flowed by the upward flow of the raw water 2 and the circulating water 4 and the air 6. As described above, the seed crystal (= same meaning as the crystal nucleus) is preferably the same as the product, but is not necessarily the same, and may be sand, zeolite, or those coated with the product. The compound that reacts with the ions to be removed in the raw water and the ions to be removed in the circulating water reacts on the surface of the seed crystal and precipitates on the surface of the seed crystal. That is, seed crystals grow (also referred to as enlargement). The treated water 14 flows out from the upper part of the crystal grain growth tank 1.

Crystal particles grown from the seed crystal are collected by an air lift pump in a timely manner. The apparent specific gravity in the air lift pipe 8 is smaller than the specific gravity in the crystal grain growth tank by the gas 9 supplied into the air lift pipe, and the liquid in the crystal grain growth tank 1 flows out through the air lift pipe 8. At that time, the crystals rise with the outflow of the liquid, and the crystals can be recovered. In addition, the gas separation part 10 which comprises an air lift pump is an apparatus which isolate | separates slurry (mixed liquid of a liquid and a crystal | crystallization) and the supplied gas 9, The slurry discharge part 11 is an apparatus which discharges | releases a slurry, Product crystal Get 12.
During the operation of the air lift pump, it is preferable to supply the raw water 2 and the circulating water 4 in order to prevent the water level in the crystal grain growth tank from decreasing.

  When the air lift pump is terminated, the crystals rising up the air lift pipe 8 are deposited in the air lift pipe. In the present invention, the wash water (2, 4, 14) is supplied from the wash water supply pipe 13 installed on the upper part of the air lift pipe. Supply applicable). By doing so, the crystals of the downflow washing water deposited in the air lift pipe are pushed out to the crystal particle growth tank side, and the problem of clogging of the air lift pipe 8 due to the crystals is solved.

  In the description of FIG. 1, a solution (referred to as circulating water) in which a compound (chemical 16 in FIG. 1) that forms a sparingly soluble salt by reacting with ions to be removed is used as cleaning water. 2 or treated water 14 may be used. As a cleaning water supply method, the circulating water supply valve 17 is switched after the air lift pump ends or immediately before the end so that the circulating water 4 flows through the cleaning water supply pipe 13. The amount of water to be washed is at least one time the amount of air lift pipe volume, preferably 2 to 3 times, and 10 times to completely clean the air lift pipe 8. In this case, to completely clean the air lift pipe 8 is to completely eliminate crystals in the air lift pipe. The supply time of the washing water is the time for supplying the above-mentioned predetermined amount of water. After a predetermined time has elapsed, the circulating water supply valve 17 is switched again to supply the circulating water 4 directly to the reactor. During cleaning, the upper part of the air lift pipe is closed by the valve 18 so that the cleaning water does not flow out from the upper part of the air lift pipe.

FIG. 2 includes a crystal grain growth tank 1 and a seed crystal production tank 19. The crystal grain growth tank 1 is the same as that shown in FIG. The seed crystal generation tank 19 is a tank for generating seed crystals to be supplied to the crystal particle growth tank 1. Similar to the crystal grain growth tank 1, the seed crystal generation tank 19 is a raw water supply pipe 3 (indicated by * A), a circulating water supply pipe 5, an air supply pipe 7, and a seed crystal transfer pipe 8b (which constitutes an air lift pump). A fine crystal transfer pipe 20 and an outflow pipe 15 for the treated water 14.
The seed crystal generation tank 19 generates a seed crystal by transferring the fine crystal floating above the crystal particle growth tank 1 and growing the fine crystal so that the seed crystal is efficiently generated. The compound that reacts with the ions to be removed in the raw water and the ions to be removed in the circulating water reacts and precipitates on the surface of the fine crystals. That is, fine crystals grow (also referred to as enlargement). The treated water 14 flows out from the upper part of the seed crystal production tank.

  The fine crystal grown to a predetermined particle size is transferred to the crystal particle growth tank 1 as a seed crystal. The transfer method in this case is also an air lift pump like the crystal grain growth tank. When the air lift pump is actuated, the seed crystals in the seed crystal production tank ascend the air lift pipe 8b and flow into the crystal grain growth tank 1 from the gas separator 10 through the fine crystal discharge part 21. At the same time, the slurry containing fine crystals floating above the crystal grain growth tank flows into the seed crystal production tank 19 through the fine crystal transfer pipe 20.

After the transfer is completed or just before the end, the air lift pipe 8b is cleaned. The fine crystal transfer pipe air lift pump is washed by supplying wash water from a wash water supply pipe 13 (indicated by * C) installed at the upper part of the air lift pipe after the air lift pump is finished, Pushes the crystals deposited in the air lift pipe 8b to the seed crystal production tank 19 side. As the washing water, a liquid (referred to as circulating water), raw water 2 or treated water 14 to which a compound (chemical 16 in FIG. 2) which reacts with ions to be removed to form a hardly soluble salt is added to the treated water. In the washing water supply method, after the air lift pump is finished, the circulating water supply valve 17 is switched so that the circulating water flows through the washing water supply pipe. The amount of cleaning water is at least one time the amount of air lift pipe volume, preferably 2 to 3 times, and 10 times to clean the air lift pipe 8b completely. In this case, to completely clean the air lift pipe 8b is to completely eliminate crystals in the air lift pipe. The supply time of the washing water is the time for supplying the above-mentioned predetermined amount of water. After a predetermined time has elapsed, the circulating water supply valve 17 is switched again to supply the circulating water directly to the seed crystal production tank 19. During cleaning, the upper part of the air lift pipe is closed by the valve 18 so that the cleaning water does not flow out from the upper part of the air lift pipe 8b.
In FIG. 2, * A, * B, and * C indicate that the pipes are connected if they have the same sign.

  EXAMPLES In the following, the present invention will be described in more detail with reference to examples, but the scope of the present invention is not limited by these examples.

Example 1
In this example, phosphorus was recovered by precipitating hydroxyapatite (hereinafter referred to as “HAP”) from phosphorus in the separated liquid in which the excess sludge was concentrated using a treatment flow as shown in FIG.
The operating conditions are shown in Table 1. The reactor was filled with bone charcoal as seed crystals in advance, and circulating water in which Ca was added to the raw water and treated water was passed upward from the bottom of the reactor. HAP deposited on the surface of the bone charcoal was collected together with the bone charcoal using an air lift pump. Raw water and circulating water were supplied even during operation of the air lift pump. At the end of the air lift, the circulating water supply valve was switched, and the circulating water was passed as washing water from the upper part of the air lift pipe in a downward flow. The amount of washing water was 1.5 times the air lift tube volume.
When extraction was performed once a day for one year, there was no trouble such as blockage. Further, as shown in Table 2, the extraction amount was about 200 L (liter) / d, and it was possible to stably extract without large fluctuation.

Example 2
In this example, phosphorus and ammonium in a filtrate obtained by dewatering digested sludge were collected with magnesium ammonium phosphate (hereinafter referred to as “MAP”) using a treatment flow as shown in FIG.
The treatment process consists of a seed crystal production tank, a MAP particle growth tank, and an Mg dissolution tank.
Table 3 shows the operating conditions of the dephosphorization process. Circulating water in which Mg was added to the raw water and treated water was passed upward from the bottom of both reactors. The fine MAP crystal floating in the upper part of the MAP particle growth tank was transferred to the seed crystal production tank through a fine MAP crystal transfer pipe once every three days. Along with the transfer of the fine MAP, the entire amount of seed crystals produced in the seed crystal production tank was returned to the MAP particle growth tank by an air lift pump installed in the seed crystal production tank. In the MAP particle growth tank, MAP was collected once a day by an air lift pump installed in the MAP particle growth tank.

Both reactors supplied raw water and circulating water during the operation of the air lift pump. At the end of the air lift, the circulating water supply valve was switched, and the circulating water was passed as washing water from the upper part of the air lift pipe in a downward flow. The amount of washing water was 1.5 times the air lift tube volume.
When the extraction of the MAP particle growth tank was continued once a day for one year, there was no trouble such as blockage. Further, even if the transfer of the seed crystal generation tank once every three days was continued for one year, there was no trouble such as clogging. As shown in Table 4, the extraction amount of the MAP particle growth tank was about 200 L / d, and could be extracted stably without a large fluctuation.

Comparative Example 1
Below, the comparative example with respect to Example 1 is shown.
In this comparative example, phosphorus was recovered by precipitating phosphorus in the separated liquid obtained by concentrating excess sludge as HAP using a treatment flow as shown in FIG. The water flow conditions are the same as in Table 1. The increased HAP was collected from the bottom of the reactor once a day together with the bone charcoal. The recovery was successful for 2 weeks from the start of operation, but after 4 weeks, the vicinity of the valve was blocked, and extraction was not possible after 6 weeks.

Comparative Example 2
Below, the comparative example with respect to Example 2 is shown.
In this comparative example, phosphorus and ammonium in the filtrate from which the digested sludge was dehydrated were recovered by MAP using a treatment flow as shown in FIG.
The water flow conditions are the same as in Table 3. The increased MAP was collected once a day from the bottom of the MAP growth tank. The recovery was successful for 2 weeks from the start of operation, but after 2 weeks, the vicinity of the valve was blocked, and extraction was not possible in the 3rd week.

  Since the present invention can efficiently treat wastewater containing phosphorus such as sewage, human waste and industrial wastewater and recover phosphorus as an effective resource, it is expected to be used in sewage treatment plants and various wastewater treatment facilities. The

It is a flowchart which shows one Embodiment of the waste water treatment equipment of this invention which consists of a crystal grain growth tank. It is a flowchart which shows one Embodiment of the waste water treatment equipment of this invention which consists of a crystal grain growth tank and a seed crystal production tank. It is a flowchart which shows embodiment of the waste water treatment equipment used in the comparative example 1. It is a flowchart which shows embodiment of the waste water treatment equipment used in the comparative example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crystal grain growth tank 2 Raw water 3 Raw water supply pipe 4 Circulating water 5 Circulating water supply pipe 6 Air 7 Air supply pipe 8 Air lift pipe 8a, 8b Air lift pipe 9 Gas 10 Gas separation part 11 Slurry discharge part 12 Product crystal 13 Washing water supply Pipe 14 Treated water 15 Treated water outflow pipe 16 Chemical 17 Circulating water supply valve 18 Valve 19 Seed crystal generation tank 20 Fine crystal transfer pipe 21 Fine crystal discharge part A, B, C

Claims (2)

A device that uses a crystallization reactor to supply a compound that reacts with the ions to be removed to form a sparingly soluble salt by depositing a sparingly soluble salt crystal into a liquid to be treated, and collects and transports the sparingly soluble crystal. The crystallization reactor is provided with an air lift pipe, a gas supply pipe for supplying gas to the lower part of the air lift pipe is provided, and a washing water supply pipe, a valve, and a gas for cleaning the air lift pipe in order from the bottom on the air lift pipe A crystal recovery and transfer device, wherein a separation unit is installed, and a slurry discharge unit is installed in the gas separation unit. 2. The crystal recovery and transfer device according to claim 1, wherein the washing water supply pipe is located above the water surface of the crystallization reactor.

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