WO2013046961A1

WO2013046961A1 - Fresh water purification device

Info

Publication number: WO2013046961A1
Application number: PCT/JP2012/070530
Authority: WO
Inventors: 浩人横井; 晃治陰山; 豊三宮; 田所　秀之; 隆広舘
Original assignee: 株式会社日立製作所
Priority date: 2011-09-28
Filing date: 2012-08-10
Publication date: 2013-04-04
Also published as: JP2013071051A; JP5537528B2

Abstract

[Problem] To provide a device for purifying fresh water after absorption of water in a more semi-hyperosmotic solution for hyperosmosis than sea water using a forward osmosis membrane with sea water as the raw water. Also to be able to inhibit deposition of solids (ammonium carbamate) arising from NH₃ and CO₂ generated in the fresh water purification process, to separate this gas from the semi-hyperosmotic solution by a separation means, and reduce the device scale by making re-dissolving of the gas by a re-dissolving means more efficient. [Solution] A separation means (3) for a solute in the fresh water purification process has a plurality of recovery openings (4, 5) that recover solute components in a semi-hyperosmotic solution as a mixed gas and a carrier gas supply opening (6) and pump (10) that supply a carrier gas to the separation means (3). The gas recovered by the separation means (3) is re-dissolved in a re-dissolving means (14). Deposition of solids arising from NH₃ and CO₂ can be suppressed by a constitution that supplies gas supplied by the recovery openings (4, 5) to the re-dissolving means (14) from infusion openings (12, 13) that differ, respectively, along with the carrier gas.

Description

Fresh water purification equipment

The present invention relates to a fresh water purification apparatus for obtaining fresh water from a solution obtained by collecting water from seawater using a forward osmosis membrane.

In recent years, examples of applying seawater desalination technology using membranes to various systems and plants are increasing. For example, in the reverse osmosis membrane method, a pressure more than twice the osmotic pressure of seawater (about 2.5 MPa) is applied to a reverse osmosis membrane made of a material such as cellulose or polyamide, and salt does not permeate the membrane without passing through the membrane. Fresh water can be obtained by permeating only water.

On the other hand, in the forward osmosis membrane method, water in seawater is once recovered into a high osmotic pressure solution having a high solute concentration through a forward osmosis membrane made of a material such as cellulose, and the salt is removed from this solution. It is. Here, the quasi-high osmotic pressure solution refers to a high osmotic pressure solution obtained by once collecting water obtained from seawater as described above.

In this forward osmosis membrane method, not only can the driving force of osmotic pressure in the positive direction be utilized, but also the energy associated with freshwater production can be selected from the reverse osmosis membrane method by selecting a solute that can be easily separated from the hyperosmotic solution. Can also be reduced.

As a method for purifying fresh water from a quasi-high osmotic pressure solution, distillation, gas emission, electrodialysis, diffusion dialysis, crystallization, reverse osmosis membrane, forward osmosis membrane, and magnetic separation can be used independently depending on the substance to be solute. A process combining these can be applied. On the other hand, since it is necessary to obtain a high osmotic pressure, a substance having an affinity for water and thus a high solubility must be selected as the solute. Therefore, the establishment of a process for purifying fresh water from a quasi-high osmotic pressure solution, that is, the establishment of optimum process conditions is one of the problems in the development of a seawater desalination system using a forward osmosis membrane.

Under such circumstances, the NH ₃ / CO ₂ system solution of the high osmotic pressure solution has high solubility in water as ammonium hydrogen carbonate (NH ₄ HCO ₃ ), and NH ₃ gas is obtained by thermal decomposition at about 36 ° C. Since it can be separated and recovered as CO ₂ gas, it is one of the promising solute candidates that are being studied for application to seawater desalination by forward osmosis membrane treatment. For example, as described below, distillation has been proposed as a method for purifying fresh water from an NH ₃ / CO ₂ quasi-high osmotic pressure solution.

JP 2011-83663 A US Patent Application Publication No. 2009/0297431

[Patent Document 1] proposes a method of individually recovering a volatile cation (NH ₄ ⁺ ) and a volatile anion (CO ₃ ²⁻ ) by distillation. In such a distillation method using a distillation column, the NH ₃ concentration in the solution is usually determined according to the NH ₃ partial pressure in the gas phase. However, when a quasi-high osmotic pressure solution is used, when a normal distillation tower is applied, problems occur in terms of the amount of gas generated and the solute concentration in the liquid to be finally reached.

That is, since most of the solute in the solution having a concentration of several mol / L is finally separated as a mixed gas, in the initial stage, a large amount of mixed gas is generated with respect to the amount of the quasi-high osmotic pressure solution to be supplied. . On the other hand, in the lowermost layer of the distillation column, it is necessary to reduce the NH ₃ partial pressure sufficiently to reduce the NH ₃ concentration in the solution to several mg / L. Since this distillation is operated at a relatively low temperature, the vapor pressure of water is also low, and thus the total pressure of the gas phase in the lower layer is low. Even considering the recovery of the mixed gas generated in the initial stage, the pressure change to the lower stage due to the fluctuation of the operation occurs, so the purity of fresh water deteriorates. In particular, in the case of a packed tower, the gas phase is not divided on the shelf, so that the influence of the pressure change on the fresh water purity is increased. This requires a design with a predetermined level of safety factor, resulting in an increase in the size of the distillation column.

In [Patent Document 1], volatile cations and volatile anions are individually recovered, but it is difficult to recover them completely individually. For this reason, a state in which high concentrations of NH ₃ and CO ₂ coexist is also generated, so blockage due to precipitation of solid (ammonium carbamate) in the piping and dissolution process, and further mixing of the solid into the forward osmosis membrane treatment process This causes a problem that fouling of the semipermeable membrane occurs.

[Patent Document 2] describes an apparatus for purifying fresh water from an NH ₃ / CO ₂ -based draw solution using a plurality of distillation columns. The use energy can be reduced by using the steam of the first tower as a heat source for the reboiler of the second tower. However, the separation of the mixed gas has the same problem as [Patent Document 1]. Further, since NH ₃ and CO ₂ gas are recovered at the same time, the risk of solid precipitation is high, but there is no description about the process of re-dissolving the separated mixed gas.

In view of the above problems, an object of the present invention is to perform forward osmosis membrane treatment that can efficiently recover a gas component from a quasi-high osmotic pressure solution and that can suppress precipitation of solids that hinders continuation of operation. It is to provide a fresh water purifier used.

In order to achieve the above object, the present invention provides a separation means for separating solute components from the semi-hyperosmotic solution obtained in the forward osmosis membrane treatment step to obtain fresh water, wherein the solute components of the semi-hyperosmotic solution are gasified. And a plurality of recovery ports having different height positions for recovery, and a carrier gas supply port through which a carrier gas supplied by a pump flows. Further, the re-dissolution means for re-dissolving the mixed gas recovered by the separation means in the semi-high osmotic pressure solution re-dissolves the mixed gas recovered from the plurality of recovery ports of the separation means in descending order of partial pressure. A plurality of inlets.

According to the present invention, NH ₃ partial pressure is reduced by adding a carrier gas to a mixed gas that is in an equilibrium state with fresh water recovered from the separation means, so that higher-purity fresh water can be obtained, and carbamine in the piping can be obtained. Formation of solids such as ammonium acid can be suppressed.

It is a block diagram of the fresh water refiner | purifier which concerns on 1st Embodiment of this invention. It is a block diagram of the fresh water refiner | purifier which concerns on 2nd Embodiment of this invention. It is a block diagram of the fresh water refiner | purifier which concerns on 3rd Embodiment of this invention. It is a block diagram of the fresh water refiner | purifier which concerns on 4th Embodiment of this invention. It is a flowchart which shows the process process in the operation control of a freshwater refiner | purifier. It is a flowchart which shows the process process in control of washing | cleaning operation of a freshwater refiner | purifier.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to these embodiments, and various modifications can be made.

[First Embodiment]
FIG. 1 is a block diagram of a freshwater purification apparatus for seawater according to a first embodiment of the present invention. As shown in FIG. 1, the seawater freshwater purification apparatus of the present embodiment includes a separation means 3 that separates a solute component as a gas from the quasi-high osmotic pressure solution 1 obtained in the forward osmosis membrane treatment step to obtain freshwater 7, The

recovery ports

4 and 5 and the carrier gas supply port 6 installed in the separation means 3 and the quasi-high osmotic pressure solution 2 obtained in the forward osmosis membrane treatment step are supplied, and NH ₃ and CO ₂ are sequentially dissolved to forward the osmosis membrane. Re-dissolution means 14 for obtaining a hyperosmotic solution 15 used in the treatment step. Further, the fresh water purifier includes a pipe connecting the recovery port 4 installed at the upper part of the separation means 3 and the injection port 13 installed at the lower part of the remelting means 14, the upper part of the remelting means 14 and the separation means 3. The carrier gas supply port 6 installed in the lower part of the pipe is connected via a valve 16 provided with a carrier gas filter 17, the carrier gas pump 10 and the valve 11, and the middle and upper recovery ports 4 of the separating means 3. Between the recovery port 5 and the injection port 12 installed at the middle position of the remelting means 14, and a pipe connecting the separation gas pump 8 and the valve 9.

The separation means 3 and the re-dissolution means 14 are supplied with the semi-high

osmotic pressure solutions

1 and 2 obtained in the forward osmosis membrane treatment step. In the forward osmosis membrane treatment step, seawater is used as raw water, and a semipermeable membrane is used. Water in seawater is recovered into a high osmotic pressure solution through a certain forward osmosis membrane. By this forward osmosis membrane treatment, the concentration of the high osmotic pressure solution is lower than the concentration when supplied to the forward osmosis membrane treatment step, but maintains a higher osmotic pressure than seawater and increases the driving force in the positive direction. Has enough osmotic pressure to maintain.

As the high osmotic pressure solution, a solution in which NH ₃ and CO ₂ are dissolved is used. For example, when NH ₃ and CO ₂ are dissolved in equimolar amounts, an ammonium hydrogen carbonate (NH ₄ HCO ₃ ) solution is used in terms of chemical composition. The osmotic pressure of the solution can be calculated from the following (Equation 1).

Π = iRTC (Formula 1)

Here, Π is the osmotic pressure, R is the gas constant, T is the absolute temperature, C is the molar concentration of the solute, and i is the Phanto-Hoff coefficient. The Phanto-Hoff coefficient i is a coefficient for correcting the influence of ionization when the solute is an electrolyte. In order to drive a high osmotic pressure solution with an osmotic pressure greater than the osmotic pressure of seawater (2.5 MPa), a concentration of about 1 to 5 mol / L is required as the NH ₄ / CO ₂ composition. Therefore, when NH ₃ and CO ₂ are all released as a mixed gas from 1 L of 1 mol / L NH ₄ HCO ₃ solution, 44.8 L (0 ° C., 0.1013 MPa) is obtained.

As described above, the solute component of the semi-high osmotic pressure solution 1 is separated as a mixed gas by the separation means 3 to obtain fresh water 7. As the structure of the separating means 3, either a plate tower or a packed tower may be used. Separation performance varies depending on the tower height, diameter, tower type, packing shape, etc. If the dissolved concentrations of NH ₃ and CO _{2 in} the semi-high osmotic pressure solution 1 and fresh water 7 are appropriately set, A tower having equivalent performance can be designed by using an index of the number of transfer units (NTU).

The operating temperature is preferably 40 to 80 ° C., which is a temperature at which the solute can be separated as a mixed gas and lower than the boiling point of water. In order to set this temperature, a heating means (not shown) is provided at the inlet for supplying the quasi-high osmotic pressure solution 1 to the separation means 3. The higher the temperature at which the heating means is heated, the faster the separation rate is. On the other hand, energy for heating the quasi-high osmotic pressure solution 1 is required. Instead of the heating means, the separation means 3 may be decompressed by a vacuum device.

The

collection ports

4 and 5 and the carrier gas supply port 6 are installed at different heights in the height direction of the separation means 3. The collection port 4 is provided in the upper part of the tower, and collects a mixed gas whose CO ₂ partial pressure is higher than the NH ₃ partial pressure. The recovery port 5 is installed between the recovery port 4 and the carrier gas supply port 6. From the recovery port 5, a mixed gas whose NH ₃ partial pressure is higher than the CO ₂ partial pressure is recovered. The carrier gas supply port 6 is provided in the lower part of the tower, and the carrier gas pump 10 supplies the carrier gas to the separation means 3 through the valve 11.

By supplying the carrier gas, the gas-liquid ratio inside the separation means 3 increases, that is, the gas-liquid interface area between the carrier gas and the quasi-high osmotic pressure solution 1 increases, and the amount of absorption of the carrier gas into the solution increases. The separation rate of the mixed gas increases. As the carrier gas, any gas having low reactivity with CO ₂ or NH ₃ may be used, and air, N ₂ , Ar, He, or the like can be used. In this embodiment, the case where air is used is shown, and the carrier gas filter 17 filters the dust in the air and can be additionally supplied.

The position of the recovery port 5 is determined by the composition of the mixed gas obtained at the recovery port 4 and the recovery port 5. Since the mixed gas discharged from the recovery port 4 and the recovery port 5 contains both NH ₃ and CO ₂ , depending on the temperature conditions, NH ₃ , CO ₂ and H ₂ O such as ammonium carbamate and ammonium bicarbonate are used as raw materials. The compound to be precipitated. In order to suppress this precipitation, it is effective to separate NH ₃ and CO ₂ from each other. In a single system of NH ₃ and CO ₂ , the molar fraction in the liquid phase when the partial pressure is 50 kPa is very different from 2.66 × 10 ² and 3.4 × 10 ⁻⁴ , respectively. It appears that CO ₂ with low solubility can be easily separated.

However, a system in which NH ₃ and CO ₂ are mixed (NH ₃ / CO ₂ system) exhibits different solubility characteristics from the NH ₃ and CO ₂ single system, so that only the CO ₂ having a low solubility is mixed in the single system. It is difficult to recover from the top of the tower. The partial pressure in the NH ₃ / CO ₂ system is, for example, from the report of Misima et al. (K. Mishima et al., J. Chem. Eng. Japan, Vol. 28 (2), p144 (1995)). It can be seen that the partial pressures in the case of NH ₃ : CO ₂ = 1: 1 at 0.15 K and 0.1013 MPa are both about 0.03 MPa. This means that in the mixed system, CO ₂ has a high solubility even at a partial pressure as low as NH _3, and it is difficult to isolate CO _{2 in the} mixed system compared to the single system. Suggests.

Therefore, at the collection port 4 and the collection port 5, a gas in which CO ₂ and NH ₃ are mixed is collected. Even in the NH ₃ / CO ₂ system, CO ₂ is more easily separated than NH ₃ , so
The ratio of O ₂ : NH ₃ is larger than the ratio of CO ₂ : NH ₃ at the recovery port 5. At this time, considering the dissolution efficiency and mass balance in the subsequent remelting means 14, the ratio of CO ₂ : NH ₃ in the recovery port 4 becomes the same value as the ratio of NH ₃ : CO ₂ in the recovery port 5, In addition, it is desirable to provide the recovery port 4 at a position where the ratio value becomes substantially maximum.

This position varies depending on the operating temperature and the composition of the quasi-high osmotic pressure solution 1, but can be determined using partial pressure data in a mixed system as shown in the above document. The actual height of the separation means 3 varies depending on the type of separation means (for example, a tower column or a packed tower). This is simply because the separation performance per stage or unit height is different. Here, the position of the

recovery ports

4 and 5 satisfying the composition condition of the mixed gas is examined by normalizing by the number of stages (or unit height).

The separating means 3 is considered to be divided into two parts, from the collecting port 4 to the upper end of the collecting port 5 (upper part of the separating means 3) and from the collecting port 5 to the carrier gas supply port 6 (lower part of the separating means 3). Then, an equilibrium mixed gas (a mixed gas of CO ₂ and NH ₃ ) is recovered at the upper upper end of the separation means 3. At the upper part of the separating means 3, the solution concentration at the lower end is calculated on the assumption that the substance is separated from the solution by the amount of the mixed gas recovered at the upper end. Further, it is assumed that the concentration of the solution is the same at the lower end of the upper part of the separating means 3 and the upper end of the lower part of the separating means 3, and there is no transfer of the mixed gas from the lower part of the separating means 3 to the upper part of the separating means 3.

The partial pressures of NH ₃ and CO ₂ at equilibrium are the NH ₃ —H ₂ O system, CO ₂ —H ₂ O system, and data reported by Misima et al. (Partial pressure of each gas and mole fraction in solution). Based on the relationship, the total dissolution amount of NH ₃ and CO ₂ was corrected and calculated. The temperature of the separation means 3 was 358.15 K, and the concentrations of NH ₃ and CO _{2 in} the solution supplied to the top of the separation means 3 were both 1.5 mol / L. The NH ₃ concentration in fresh water 7 was 5.9 × 10 ⁻⁵ mol / L (1 mg / L), and the CO ₂ concentration was 2.3 × 10 ⁻⁵ mol / L (1 mg / L).

Under these calculation conditions, the CO ₂ : NH ₃ ratio at the recovery port 4 is approximately the same as the NH ₃ : CO ₂ ratio at the recovery port 5, and the ratio value is approximately the maximum value. As a result, the height of the upper part of the separating means 3: the height of the lower part of the separating means 3 was 1: 6. That is, when the recovery port 4 is set at the upper end of the separating means 3 and the carrier gas supply port 6 is set at the lower end, the recovery port 5 may be installed at a position 1/7 from the recovery port 4 during this period. At this time, the CO ₂ : NH ₃ ratio in the gas mixture obtained from the recovery port 4 was 17: 1, while the NH ₃ : CO ₂ ratio in the gas obtained from the recovery port 5 was calculated as 25: 1. .

Even when the operating temperature or the concentration of the quasi-high osmotic pressure solution 1 supplied to the separation means 3 is different, the data of the partial pressure of CO ₂ , NH ₃ , H ₂ O and the concentration in the solution are used, The opening position can be set.

The mixed gas discharged from the recovery port 4 is supplied from an injection port 13 installed at the lower part of the remelting means 14 through a pipe. Further, the mixed gas containing the carrier gas discharged from the recovery port 5 is supplied from the injection port 12 installed in the middle stage of the remelting means 14 after the pressure is adjusted via the separation gas pump 8 and the valve 9. The air volume of the separation gas pump 8 is the sum of the supply amount of the carrier gas pump 10 and the generation amount of the mixed gas of NH ₃ and CO ₂ separated below the recovery port 5 of the separation means 3 or smaller. This is to prevent the gas separated in the upper stage from flowing into the lower stage and lowering the separation performance, particularly when using a packed tower.

As the remelting means 14, a plate tower or a packed tower can be used as in the separation means 3. The quasi-high osmotic pressure solution 2 is sprayed from above, and NH ₃ and CO ₂ in the mixed gas obtained by the separating means 3 are dissolved successively. Although operation at a low temperature is more advantageous for dissolution of the mixed gas, it is desirable that the operating temperature range of the separating means 3 is at least from 0 ° C. The specifications of the re-dissolution means 14 are the carrier gas flow rate, the operating temperature, the partial pressure of the mixed gas of NH ₃ and CO _{2 at} the

inlets

12 and 13, the solute concentration and flow rate of the quasi-high osmotic pressure solution 2, and the high osmotic pressure. Determined by the solute concentration of the solution 15.

In the re-dissolution means 14, first, a gas mixture having a high solubility of NH ₃ is supplied to raise the pH of the quasi-high osmotic pressure solution 2. That is, the partial pressure of NH ₃ is higher than the partial pressure of CO ₂ (that is, greater proportion proportion of CO ₂ NH ₃₎ supplying a gas mixture from the recovery port 5, before other gas mixture. Subsequently, the partial pressure of CO ₂ is higher than the partial pressure of NH ₃ (i.e., the ratio of CO ₂ ratio greater than NH ₃₎ the gas mixture from the recovery port 4 is supplied from the inlet 13 in the bottom.

An effect of increasing the partial pressure of any gas in the separation means 3 is to improve the efficiency of re-dissolution. When the supply pressure to the remelting means 14 is constant, the partial pressure of each gas increases or decreases according to the composition ratio of NH ₃ and CO ₂ . When NH ₃ : CO ₂ = 2: 1 at the recovery port 5, if the ratio of carrier gas: (NH ₃ + CO ₂ ) is constant, compared with the case where the entire amount is recovered (NH ₃ : CO ₂ = 1: 1) Thus, the redissolving efficiency is 1.33 times. Thereby, the amount of dissolution at each stage of the tower increases, and the dissolution efficiency of the entire tower improves.

Adjustment of the NH ₃ : CO ₂ ratio leads to an improvement in dissolution efficiency in the re-dissolution means 14 from the viewpoint of pH. CO ₂ can than be dissolved in neutral water, is better to be dissolved in high pH solution are dissolved a greater amount at a lower partial pressure of CO _2. This is because in an alkaline solution, CO ₂ + OH ⁻ → HCO ₃ ⁻ and HCO ₃ ⁻ + OH ⁻ → CO ₃ ² + + H ₂ O reactions proceed and are easily dissolved as bicarbonate ions or carbonate ions.

Therefore, in this embodiment, the mixed gas in the recovery port 5 is supplied to the inlet 12 so that the pH at the position of the inlet 12 can be increased, that is, the NH ₃ partial pressure is high and the NH ₃ : CO ₂ ratio is large. ing. It is desirable to adjust the composition of the mixed gas so that the pH at the inlet 12 is alkaline, preferably pH ≧ 9.

NH ₃ and CO ₂ are dissolved in the quasi-high osmotic pressure solution, but most of the carrier gas reaches the upper part of the redissolving means 14 without being dissolved and is discharged to the pipe. In the valve 16, the inflow of the mixed gas from the remelting means 14 and the inflow of the carrier gas from the carrier gas filter 17 are adjusted and supplied to the separation means 3 via the carrier gas pump 10.

With such a configuration, fresh water with less impurities can be obtained, and generation of ammonium carbamate and the like in the pipe can be suppressed. Also, the partial pressure is high recovery gas mixture compared to the partial pressure of CO ₂ of the NH ₃ in the re-dissolving means (mixed gas of NH ₃ and CO _2), can be dissolved before other gas mixture, The pH of the quasi-hyperosmotic solution is increased, and the dissolution of CO _{2 in} the solution gas mixture (NH ₃ and CO ₂ gas mixture) to be subsequently supplied can be promoted.

[Second Embodiment]
FIG. 2 is a block diagram of a fresh water purification apparatus according to the second embodiment of the present invention. In addition to the configuration of the first embodiment, the fresh water purifying apparatus of the present embodiment is provided with a carrier gas supply port 18 at a position above the recovery port 5 of the separation means 3, and the carrier gas supply port 18 has a carrier gas pump 20 and a valve 21. A carrier gas filter 19 is connected via Further, the quasi-high osmotic pressure solution 1 is supplied to the separation means 3 via the valve 22, and the fresh water 7 is recovered from the separation means 3 via the valve 23.

In the processing of the fresh water purification apparatus in the present embodiment, the

valves

22 and 23 are opened, the quasi-high osmotic pressure solution 1 is supplied from the upper part of the separation means 3, and the fresh water 7 is recovered from the lower part of the separation means 3.

The same carrier gas as that supplied by the carrier gas pump 10 is supplied from the supply port 18 by the carrier gas pump 20. The supply port 18 is installed at a position higher than the collection port 5. When the separating means 3 is a tray tower, the supply port 18 and the recovery port 5 are provided in different stages. In the case of a packed tower, it is desirable that the distance from the supply port 18 to the recovery port 4 is shorter than the distance from the supply port 18 to the recovery port 5. Thereby, generation | occurrence | production of the backflow (downward flow) of carrier gas can be suppressed. The carrier gas may be branched from the valve 11 and used.

The flow rate of each pump is set so as not to lower the NH ₃ : CO ₂ ratio of the mixed gas at the recovery port 5. That is, the flow rate of the separation gas pump 8 = the flow rate of the pump 10+ (unit time recovery amount of NH ₃ and CO ₂ from the low part to the recovery port 5).

On the other hand, the flow rate of the carrier gas pump 20 takes into account the pressure increase due to the generation of gas at each stage between the supply port 18 and the recovery port 4 and the pressure loss due to the shelf or packed tower. The condition is set so that 5 is not reached.

In the present embodiment, not only the fresh water purification process but also the operation for pipe cleaning can be performed periodically. This is for the purpose of decomposing the substances deposited on the piping between the recovery port 4 and the injection port 13, the piping between the recovery port 5 and the injection port 12, the pump and the valve. These pipes and devices are maintained at the same temperature as that of the separation means 3 because NH ₃ and CO ₂ exist as gases.

However, when a high concentration of NH ₃ or CO ₂ circulates for a long period of time, a solid such as ammonium carbamate tends to precipitate. Therefore, the following cleaning operation is performed.

The valve 23 and the valve 22 are closed. On the other hand, the

carrier gas pumps

10 and 20 and the separation gas pump 8 are continuously operated. By this operation, the concentrations of NH ₃ and CO _{2 in} the

recovery ports

4 and 5 are both gradually lowered, and the ratio of the carrier gas in the gas phase is increased. As a result, no further precipitation from the gas phase to the solid deposited on the piping or equipment occurs, and conversely, the precipitate can be decomposed and removed by maintaining a predetermined temperature necessary for the decomposition of the precipitate. .

The above operation for cleaning pipes and the like is performed while maintaining a predetermined operating temperature after the NH ₃ and CO ₂ concentrations in the carrier gas are reduced to 1/10 or less of the concentration in the separation operation. It is desirable to carry out for about 24 hours.

With such a configuration, when the operation at atmospheric pressure is assumed in the upper stage of the separation means 3 (part where CO ₂ is mainly recovered), the CO ₂ partial pressure in the gas phase is reduced more than in the first embodiment. Therefore, CO ₂ can be separated and recovered more efficiently.

In addition, since the partial pressure of NH ₃ and CO ₂ in the piping and the like is reduced and the cleaning operation of the piping and the like is performed, the compound of NH ₃ and CO ₂ such as ammonium carbamate as a raw material is used. Generation / growth suppression and removal are possible.

In the separation means 3 of this embodiment, the recovery port and the carrier gas supply port are set at two locations for one tower, but the tower is divided into two, and the recovery port and the carrier gas supply are supplied to each tower. It is good also as a structure which provided the opening | mouth. Thereby, the height of the tower and the scale of the building can be reduced.

[Third Embodiment]
FIG. 3 is a block diagram of a fresh water purification apparatus according to the third embodiment of the present invention.

In the fresh water purifying apparatus of this embodiment, in addition to the configuration of the first embodiment, a heater 25 and a carrier gas filter 26 are connected to the recovery port 4 via a valve (three-way valve) 24, and the rest of the valve (three-way valve) 24 is connected. One of these is connected to the inlet 13 via the carrier gas pump 27 and the valve 28. Further, the semi-high osmotic pressure solution 1 is supplied to the separation means 3 through the valve 22, and the fresh water 7 is recovered from the separation means 3 through the valve 23.

In the processing of the fresh water purifying apparatus in the present embodiment, the semi-high osmotic pressure solution 1 is supplied to the separation means 3 and the mixed gas is recovered from the

recovery ports

4 and 5, respectively, as in the first embodiment. The carrier gas is supplied to the separation means 3 only by the pump 10.

The mixed gas discharged from the recovery port 4 and the carrier gas are mixed by a valve (three-way valve) 24 and supplied to the remelting means 14 by a carrier gas pump 27. The carrier gas supplied at this time is processed by the carrier gas filter 26 and then heated by the heater 25 to the same temperature as that maintained in the pipe. A pressure adjusting valve is provided on the discharge side of the carrier gas pump 27 so that the partial pressure of the mixed gas of CO ₂ and NH ₃ is adjusted to be lower than the partial pressure in the recovery port 5 and then supplied to the inlet 13. .

As in the case of Embodiment 2, the pipes, equipment, etc. are periodically cleaned. At this time, the

valves

22 and 23 are closed, and the valve (three-way valve) 24 is operated so that only the carrier gas can be supplied to the carrier gas pump 27. As in the second embodiment, it is desirable to set the cleaning time for piping and the like to 1-24 hours while maintaining a predetermined operating temperature. The carrier gas may be branched from the valve 11 and used.

With such a configuration, in addition to the effects of the first embodiment, the piping and the like can be washed with a carrier gas, and the removal performance of a compound using NH ₃ and CO ₂ such as ammonium carbamate as raw materials can be improved. Since the partial pressures of NH ₃ and CO _{2 in} the carrier gas are lower than those in the second embodiment, higher removal performance can be expected.

[Fourth Embodiment]
FIG. 4 is a block diagram of a fresh water purifying apparatus according to the fourth embodiment of the present invention. In this embodiment, control of carrier gas supply and backwashing by sensing is performed.

In addition to the configuration of the third embodiment, the fresh water purification apparatus of the present embodiment has a configuration including a control means 51, sensors 29 to 33, 35, and 38, pumps 34 and 36, and a valve 37. Based on the information from the sensors 29 to 33, 35, and 38, each pump and valve are controlled in order to satisfy the required amount of fresh water purification and the water quality.

In seawater desalination using membranes, clogging (fouling) of membranes due to inorganic substances, organic substances, and living organisms in seawater and additive drugs occurs. In the case of reverse osmosis membrane treatment, the supply amount can be adjusted by a high-pressure pump, so that it is possible to relatively easily cope with an increase in transmembrane pressure difference caused by fouling.

On the other hand, in forward osmosis membrane treatment using the osmotic pressure difference as a driving force and not having a high-pressure pump, the progress of fouling adversely affects the treatment amount and the water quality obtained by forward osmosis membrane treatment. When the transmembrane pressure difference becomes large, for example, an operation of increasing the supply amount of the high osmotic pressure solution and maintaining the osmotic pressure difference at a high value is assumed. At this time, a quasi-high osmotic pressure solution having a higher concentration is supplied in the fresh water purification step.

Therefore, the optimum operating conditions in the separation means 3 and the remelting means 14 change. In order to cope with this in the fourth embodiment, various sensors are installed, and the supply of the semi-osmotic solution and the carrier gas and the execution of the cleaning operation are controlled based on the sensor information. The sensor 35 has a conductivity meter and a flow meter. The sensor 29 has a flow meter, a thermometer, a pressure gauge, a CO ₂ concentration meter, and an NH ₃ concentration meter. The sensor 30 has a pressure gauge. The sensor 32 has a pressure gauge. The sensor 31 has a flow meter, a thermometer, a pressure gauge, a CO ₂ concentration meter, and an NH ₃ concentration meter. The sensor 38 includes a pressure gauge, a flow meter, a thermometer, a CO ₂ concentration meter, and an NH ₃ concentration meter. The sensor 33 has a conductivity meter. The measured value of each sensor is transmitted to the control means 51 online.

In the control of the fresh water purification device, fresh water purification treatment control (carrier gas and quasi-high osmotic pressure solution flow rate control) and cleaning operation control are performed.

FIG. 5 shows a processing flow of fresh water purification processing control by the control means 51. The treatment is divided into a part relating to the separating means 3 and a part relating to the remelting means 14.

In S501, the measurement values of the

sensors

35 and 33 are acquired. In S502, the concentration of NH ₃ and CO ₂ and the load amount of the quasi-high osmotic pressure solution 1 to the separation means 3 are calculated from the flow rate and conductivity of the sensor 35. The correlation between the NH ₃ and CO ₂ concentrations and the conductivity can be prepared in advance or estimated from the molar conductivity of ions.

In S503, the flow rate of the carrier gas is calculated using the processing model related to the separation means 3, the load obtained in S502, and the target fresh water quality. Depending on the flow rate of the carrier gas, the gas-liquid ratio in the separation means 3 can be changed to adjust the separation performance. The treatment model uses vapor-liquid equilibrium data, NTU, etc., and is a basic model of chemical engineering.

In S504, the carrier gas pump 10 is adjusted according to the calculated value in S503. Next, it is determined whether or not the measured value of the conductivity of the sensor 33 is within a target value. If it is lower than the target value, the carrier gas flow rate is reduced. On the other hand, if it exceeds the target value, it is determined whether or not it is the upper limit of the supply of the carrier gas, and then the carrier gas flow rate is increased. The supply amount of the osmotic pressure solution 1 is reduced.

In the re-dissolution means 14, the carrier gas flow rate or the supply amount of the quasi-high osmotic pressure solution 2 is similarly controlled. In S511, the measurement values of the

sensors

29, 32, 31, and 38 are collected. In S512, the amount of NH ₃ and CO ₂ substances, that is, the load on the remelting means 14 is calculated from the flow rate, temperature, pressure, NH ₃ concentration, and CO ₂ concentration using the relationship between the equation of state and mass balance. To do.

In S513, based on the dissolution model of the remelting means 14 and the load in S512, the flow rate of the carrier gas pump 27 necessary for the NH ₃ and CO ₂ concentrations in the exhaust gas mixture to satisfy a predetermined target value. The maximum value of is calculated. In S514, the carrier gas flow rate is actually adjusted. In S515, the actual exhaust concentrations of NH ₃ and CO ₂ are obtained from the measured values of the sensor 38, and it is determined whether or not the target values are actually satisfied. If satisfied, reduce carrier gas. Otherwise, after determining whether or not the carrier gas supply upper limit is reached, the carrier gas is increased or the pump 36 for adjusting the supply amount of the quasi-high osmotic pressure solution 2 is adjusted.

FIG. 6 shows a processing flow of cleaning operation control by the control means 51. In S601, the measurement values (pressures) of the

sensors

30 and 32 are acquired. In step S602, the change amount (ΔP) of the differential pressure is calculated from the latest measured value and the measured value that is the previous time τ. τ is a period from 1 day to 6 months. In step S603, the value of ΔP is compared with the set value, and if the value of ΔP is large, a cleaning operation of the pipe or the like is performed. If not, continue driving.

By adopting the configuration as described above, in addition to the effects of the third embodiment, fresh water with good quality can be supplied even when the composition and flow rate of the quasi-high osmotic pressure solution are changed.

As described above, according to each embodiment, the NH ₃ partial pressure is reduced by adding the carrier gas to the mixed gas that is in equilibrium with the solution in the separation means 3, and fresh water with fewer impurities is obtained. And the production of ammonium carbamate in the piping can be suppressed.

In addition, compared to the case where NH ₃ and CO ₂ are recovered at the same time, a mixed gas having a low ratio is handled, so that the production of ammonium carbamate can be suppressed.

Further, since the recovered mixed gas having a high NH ₃ partial pressure is dissolved in the re-dissolving means 14 before the other mixed gases, the pH of the quasi-high osmotic pressure solution 2 supplied to the re-dissolving means 14 is increased. . Therefore, dissolution of CO _{2 in} the recovered mixed gas supplied next can be promoted.

Also, the safety and operation of freshwater purification equipment can be achieved by circulating the carrier gas with a low partial pressure of NH ₃ and CO ₂ to remove the causative deposits according to the blocking situation of piping etc. based on sensing. Efficiency can be maintained.

1, 2 Semi-high osmotic pressure solution 3 Separation means 4, 5

Recovery port

6, 18 Carrier gas supply port 7 Fresh water 8

Separation gas pumps

9, 11, 16, 21, 22, 23, 24, 28, 37

Valves

10, 20, 27

Carrier gas pumps

12 and 13 Inlet 14 Re-dissolution means 15 High

osmotic pressure solutions

17, 19 and 26 Carrier gas filter 25 Heaters 29 to 33, 35 and 38

Sensors

34 and 36 Pump 51 Control means

Claims

In fresh water purification equipment,
Equipped with multiple recovery ports with different height positions for recovering solute components of quasi-high osmotic pressure solutions as a mixed gas, and carrier gas supply ports for flowing in carrier gas supplied by a pump, and forward osmosis from raw water Separation means for separating the solute component from the quasi-high osmotic pressure solution obtained in the membrane treatment step to obtain fresh water;
A re-dissolution means comprising a plurality of inlets for dissolving the mixed gas recovered from the plurality of recovery ports of the separation means in the semi-high pressure solution in order of high partial pressure;
A fresh water purification apparatus comprising:
2. The fresh water purification apparatus according to claim 1, wherein the quasi-high osmotic pressure solution is an aqueous solution in which NH 3 and CO 2 are dissolved, and a recovery port for recovering a mixed gas having a NH 3 partial pressure higher than the CO 2 partial pressure is provided. A fresh water purifying apparatus, which is installed between a middle position of the separation means and an upper recovery port, and is connected to an inlet port located at a middle position of the re-dissolution means via a pipe.
2. The fresh water purifier according to claim 1, wherein a plurality of the carrier gas supply ports are installed in the separation means, and at least one carrier gas supply port is installed at a position lower than any of the recovery ports, and another carrier is provided. A fresh water purification apparatus, wherein a gas supply port is installed between a plurality of recovery ports.
2. The fresh water purifier according to claim 1, wherein a gas whose NH 3 partial pressure is higher than the partial pressure of CO 2 among the mixed gas discharged from each recovery port of the separation means is supplied to the re-dissolution means. The fresh water purifier according to claim 1, wherein the injection port is installed at a position where the quasi-high osmotic pressure solution supplied to the re-dissolution means is dissolved before the other mixed gas.
The fresh water purifying apparatus according to claim 1, wherein the mixed gas discharged from the recovery port of the separation means during fresh water purification operation is connected to a pipe connecting the separation means and the re-dissolution means, a pump or a valve attached to the pipe. A pump that periodically supplies and supplies a carrier gas containing these at a partial pressure lower than the partial pressure of NH 3 and CO 2 is connected, and the solid deposited on the pipe, pump, or valve is decomposed and removed. A fresh water purifier characterized by.
The fresh water purification apparatus according to claim 1, wherein the semi-high osmotic pressure solution obtained in the forward osmosis membrane treatment step, fresh water collected by the separation means, a mixed gas discharged from the collection port, and a mixture supplied to the injection port Measure the pressure, temperature, flow rate, NH 3 concentration, CO 2 concentration, conductivity of the gas, water discharged from the re-dissolving means or mixed gas, and use the results of the measurement to collect fresh water recovered from the separating means Estimate or measure the water quality and the impurity concentration in the mixed gas discharged from the separation means and the re-dissolution means, and based on these estimated values or measured values, supply the carrier gas and the quasi-hyperosmotic solution supply amount A fresh water purifier having control means for controlling.
2. The fresh water purification apparatus according to claim 1, wherein fresh water purification treatment control and cleaning operation control are performed, and the control is performed by a control means based on a measurement value obtained by sensing with a plurality of sensors or an estimated value based on the measurement value. A fresh water purifying apparatus characterized by:
8. The fresh water purifier according to claim 7, wherein the washing operation control includes backwash control to prevent fouling.