JP5537528B2 - Fresh water purification equipment - Google Patents

Description

  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, the application of seawater desalination technology using membranes has increased. 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 materials such as cellulose and polyamide, so that salt does not permeate the membrane and pass water. Fresh water can be obtained.

  On the other hand, the forward osmosis membrane method is a method of removing salt from a semi-high osmotic pressure solution in which water in seawater is once recovered into a high concentration (high osmotic pressure) solution through an osmosis membrane made of a material such as cellulose. It is. Here, the quasi-high osmotic pressure solution refers to a high osmotic pressure solution obtained by collecting water.

  In this forward osmosis membrane method, not only utilizing the driving force in the positive direction, but also selecting the salt that can be easily separated from the solution as the salt to be added to the high osmotic pressure solution, the energy related to fresh water production can be reduced. There is a possibility that it can be reduced compared with the reverse osmosis membrane method.

  As a means of obtaining fresh water from a quasi-high osmotic pressure solution, depending on the substance to be solute, distillation, gas diffusion, electrodialysis, diffusion dialysis, crystallization, reverse osmosis membrane, magnetic separation can be used alone, or a combination of these processes. Applicable. Since the solute needs to obtain a high osmotic pressure, a substance having a high affinity (solubility) with water is selected. Therefore, establishing a process for purifying fresh water from a quasi-high osmotic pressure solution is one of the problems in a seawater desalination system using a forward osmosis membrane.

Among high osmotic pressure solutions, NH ₃ / CO ₂ solution has high solubility as ammonium bicarbonate (NH ₄ HCO ₃ ), and is separated and recovered as NH ₃ gas and CO ₂ gas by thermal decomposition at about 56 ° C. Therefore, it is one of the promising candidates for application to seawater desalination by forward osmosis membrane treatment. Distillation has been proposed as a method for purifying fresh water from a quasi-high osmotic pressure solution of the NH ₃ / CO ₂ system.

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. Of these, in the method of distillation using a distillation column, the NH ₃ concentration in the solution is usually determined according to the partial pressure of the gas phase. However, when a quasi-high osmotic pressure solution is used, there is a problem in terms of the amount of gas generated and the solute concentration in the liquid to be finally reached when a normal distillation tower is applied.

That is, since most of the solute in the solution of several mol / L is finally separated as a gas, a large amount of gas is generated in the initial stage with respect to the amount of the quasi-high osmotic pressure solution to be supplied. On the other hand, in the lowermost layer, it is necessary to reduce the NH ₃ partial pressure sufficiently to reduce the NH ₃ concentration in the liquid 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 generated gas at the initial stage, the influence of the pressure on the lower stage due to the fluctuation of operation occurs, and the purity of fresh water deteriorates. In particular, in the case of a packed tower, the influence is increased because the gas phase is not divided by the shelves. This requires a design with a 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. Therefore, clogging due to precipitation of solid (ammonium carbamate) in the piping and dissolution process, and fouling due to contamination in the forward osmosis membrane treatment process. There is a problem that a ring 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. Regarding gas separation, there is a problem similar to [Patent Document 1]. Further, since NH ₃ and CO ₂ gas are recovered at the same time, there is a high risk of solid precipitation, but there is no description about the dissolution of the separation gas.

  An object of the present invention is to provide a fresh water purifying apparatus in forward osmosis membrane treatment that can efficiently recover a gas component from a quasi-high osmotic pressure solution and suppress the precipitation of solids that hinders continuation of operation.

  In order to achieve the above object, the present invention provides a separation means for separating solute components from the quasi-high osmotic pressure solution obtained in the forward osmosis membrane treatment step to obtain fresh water. A plurality of recovery ports with different height positions for recovery as a gas and a carrier gas supply port into which a carrier gas supplied by a pump flows are provided, and the gas recovered by the separation means is dissolved in a quasi-high osmotic pressure solution. The re-dissolving means for performing the process includes a plurality of inlets for dissolving the gases recovered from the plurality of recovery ports of the separating means in descending order of partial pressure.

According to the present invention, NH ₃ partial pressure is reduced by adding a carrier gas to a gas that is in equilibrium with fresh water discharged from the separation means, and fresh water with fewer impurities can be obtained, and carbamic acid in the pipe Generation of ammonium 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 in the operation control of a freshwater refiner | purifier. It is a flowchart which shows the process in control of washing | cleaning operation of a freshwater refiner | purifier.

  Embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram of a seawater desalination system according to a first embodiment of the present invention. As shown in FIG. 1, the seawater desalination system of the present embodiment includes a separation means 3 that separates a solute component from the quasi-high osmotic pressure solution 1 obtained in the forward osmosis membrane treatment step to obtain fresh water 7, and a separation means. 3, the recovery ports 4 and 5 and the carrier gas supply port 6 provided in 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. A re-dissolving means 14 for obtaining a high osmotic pressure solution 15 used in the processing step, a recovery port 4 provided at the upper part of the separating means 3 and an inlet 13 provided at the lower part of the re-dissolving means 14 are separated by a separation gas pump 8. And a pipe 16 connected via a separation gas pump 8, a carrier gas supply port 6 provided at an upper portion of the remelting means 14 and a lower portion of the separation means 3, a valve 16 provided with a carrier gas filter 17, and a carrier gas pump 10. And connection via valve 11 And a pipe connecting the recovery port 5 provided at the middle position of the separating means 3 and the inlet 12 provided at the middle position of the remelting means 14.

  The separation means 3 and the re-dissolution means 14 are supplied with the quasi-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 it is supplied to the forward osmosis membrane treatment step, but the osmotic pressure is higher than seawater and maintains the driving force in the quasi-direction. It has as much osmotic pressure as possible.

A solution in which NH ₃ and CO ₂ are dissolved is used as the high osmotic pressure solution. For example, an ammonium bicarbonate (NH ₄ HCO ₃ ) solution that dissolves NH ₃ and CO ₂ in equimolar amounts is used in terms of composition. The osmotic pressure of the solution can be calculated from Equation 1.
[Equation 1]
Π = iRTC (1)

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

The solute component of the semi-high osmotic pressure solution 1 is separated by the separation means 3 to obtain fresh water 7. The structure of the separation means 3 may be either a plate tower or a packed tower. Separation performance varies depending on column height, diameter, column type, and packing shape, etc. However, if the solubility concentration of NH ₃ and CO _{2 in} the quasi-high osmotic pressure solution 1 and fresh water 7 is set, the number of theoretical plates and the movement can be changed respectively. By using an index of the number of units (NTU), a tower with equivalent performance can be designed.

  The operation temperature is preferably 40 to 80 ° C., which is a temperature at which the solute can be separated as a gas and is lower than the boiling point of water. In order to obtain this temperature, a heating means (not shown) is provided at the inlet of the separating means 3. The higher the temperature obtained by the heating means, the faster the separation rate, but energy for heating the quasi-high osmotic pressure solution 1 is required. It is also conceivable to depressurize the separating means 3 with a vacuum device instead of the heating means.

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 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. A gas having a higher NH ₃ partial pressure than the CO ₂ partial pressure is recovered from the recovery port 5. The carrier gas supply port 6 is provided in the lower part of the tower, and the carrier gas is supplied to the separation means 3 through the valve 11 by the carrier gas pump 10.

When the gas-liquid ratio is increased by supplying the carrier gas, that is, when the contact area between the carrier gas and the quasi-high osmotic pressure solution 1 is increased, the gas separation rate is increased. 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 so that it can be additionally supplied.

The position of the recovery port 5 is determined by the gas composition obtained at the recovery port 4 and the recovery port 5. Since the 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 or H ₂ O such as ammonium carbamate or ammonium bicarbonate is used as a raw material. 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, the mixed system of NH ₃ and CO ₂ (NH ₃ / CO ₂ system) shows different solubility characteristics from the NH ₃ and CO ₂ single system, so only CO ₂ with low solubility is recovered from the top of the column. It is difficult to do. The partial pressure in the NH ₃ / CO ₂ system is, for example, 358 in 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 CO ₂ has high solubility even at a partial pressure as low as NH _3, and it is difficult to isolate CO ₂ in a mixed system compared to a single system. Yes.

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 NH ₃ / CO ₂ system, since CO ₂ is easily separated as compared with NH _3, CO ₂ in the recovery port 4: The ratio of NH ₃ is, CO ₂ in the recovery port 5: the ratio of NH ₃ Bigger than that. At this time, considering the dissolution efficiency and mass balance in the subsequent re-dissolution means 14, the ratio of CO ₂ : NH ₃ in the recovery port 4 becomes approximately the same as the ratio of NH ₃ : CO ₂ in the recovery port 5, In addition, it is desirable to provide the recovery port 4b at a position where a large ratio value can be obtained.

  This position varies depending on the operating temperature and the composition of the quasi-hyperosmotic pressure solution 1, but can be determined using partial pressure data in a mixed system as shown in the above-mentioned 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 positions of the recovery ports 4 and 5 satisfying the above gas composition conditions are examined by standardizing 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 gas (a mixed gas of CO ₂ and NH ₃ ) is obtained at the upper end of the upper stage of the separation means 3. In the upper part of the separation means 3, the solution concentration at the lower end is calculated on the assumption that the amount of the gas recovered at the upper end is separated from the solution. Further, it is assumed that the concentration of the solution is the same at the lower end of the upper part of the separation means 3 and the upper end of the lower part of the separation means 3, and there is no gas transfer from the lower part of the separation means 3 to the upper part of the separation means 3.

The partial pressures of NH ₃ and CO ₂ at equilibrium are the data reported in the NH ₃ —H ₂ O system, CO ₂ —H ₂ O system, and Misima et al. (Mol fraction of solution and partial pressure of each gas). 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. Further, the NH ₃ concentration in the fresh water 7 was set to 5.9 × 10 ⁻⁵ mol / L (1 mg / L), and the CO ₂ concentration was set to 2.3 × 10 ⁻⁵ mol / L (1 mg / L). .

Under this calculation condition, the ratio of CO ₂ : NH ₃ in the recovery port 4 is the same as the ratio of NH ₃ : CO ₂ in the recovery port 5, and the position where the ratio value can be greatly obtained is obtained. 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 obtained from the recovery port 4 is calculated as 17: 1, and the NH ₃ : CO ₂ ratio in the gas obtained from the recovery port 5 is calculated as 25: 1.

Even when the temperature and the concentration of the quasi-high osmotic pressure solution 1 supplied to the separation means 3 are different, the opening position of the recovery port is determined by using the same CO ₂ , NH ₃ , H ₂ O solution and partial pressure data. Can be set.

The gas discharged from the recovery port 4 is supplied from an injection port 13 installed under the remelting means 14 through a pipe. Further, the gas containing the carrier gas discharged from the recovery port 5 is supplied from the inlet 12 provided 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 quantity of the carrier gas pump 10 and the generation quantity 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 a packed tower is used.

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 separation means 3 are dissolved sequentially. Although operation at a low temperature is advantageous for gas dissolution, it is desirable that the operation temperature is in the range of at least 0 ° C. to the operation temperature of the separation means 3. 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 concentration and flow rate of the quasi-high osmotic pressure solution 2, and the high osmotic pressure solution 15. Determined by the concentration of

In the re-dissolution means 14, first, a mixed gas having a high NH ₃ ratio with high solubility 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 (greater percentage of the percentage of NH ₃ is CO ₂₎ First supplies a gas recovery port 5. Subsequently, the partial higher pressure (the ratio of CO ₂ is greater than the ratio of NH ₃₎ recovery port 4 of the gas partial pressure of NH ₃ CO _2, is supplied from the inlet 13 in the bottom.

As an effect of increasing the partial pressure of any gas in the separation means 3, there is an increase in efficiency of re-dissolution. When the supply pressure to the remelting means 14 is constant, the partial pressure of each gas increases or decreases depending on the composition 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) And 1.33 times. This increases the amount of dissolution at each stage of the tower, improving the efficiency of the entire tower.

Adjustment of the NH ₃ : CO ₂ ratio leads to an improvement in dissolution efficiency in the redissolving means from the viewpoint of pH. More CO ₂ can be dissolved at a lower CO ₂ partial pressure by dissolving it in a solution having a higher pH than in neutral water. This is because CO ₂ + OH ⁻ → HCO ₃ ⁻ + and HCO ₃ ⁻ + OH ⁻ → CO ₃ ² + + H ₂ O proceed in the solution 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 injection port 12 so that the pH at the position of the injection port 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 gas composition so that the pH at the inlet 12 level 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. In the valve 16, the inflow from the remelting means 14 and the inflow 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. Further, in re-dissolving means can dissolve the partial pressure is higher stripping gas than the partial pressure of CO ₂ NH ₃ (gas mixture of NH ₃ and CO ₂₎ above, pH of the quasi-hyperosmotic solution It is possible to promote the dissolution of CO _{2 in} the recovery gas (mixed gas of NH ₃ and CO ₂ ) that is raised and subsequently supplied.

[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 semi-high osmotic pressure solution 1 is supplied to the separation means 3 through the valve 22, and the fresh water 7 is obtained from the separation means 3 through the valve 23.

  In the processing of the fresh water purifying apparatus in this embodiment, the valves 22 and 23 are opened, the quasi-high osmotic pressure solution 1 is supplied from the upper part of the separating means 3, and the fresh water 7 is recovered from the lower part of the separating means 3.

  The same gas as that supplied by the carrier gas pump 10 is supplied from the supply port 18 by the carrier gas pump 20. The installation position of the supply port 18 is installed above 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 ratio of NH ₃ : CO ₂ of the gas at the recovery port 5. That is, the flow rate of the separation gas pump 8 = the flow rate of the pump 10+ (the amount of NH ₃ and CO ₂ recovered between the low part and 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. The purpose of this is to decompose the substances deposited on the piping between the recovery port 4 and the injection port 13 and 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 operations are 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 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. .

It is desirable that the above operation for cleaning pipes and the like is performed for about 1-24 h after the concentration of NH ₃ and CO _{2 in} the carrier gas is reduced to 1/10 or less of the concentration in the separation operation.

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. As a result, 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 a carrier gas pump 27 and a 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 obtained from the separation means 3 through the valve 23.

  In the processing of the fresh water purification apparatus in the present embodiment, the semi-high osmotic pressure solution 1 is supplied to the separation means 3 and the 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 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, and each 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 sent to the inlet 13. .

  As in the case of the second embodiment, the piping, equipment, and the like 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. The cleaning time for piping and the like is desirably 1 to 24 h as in the second embodiment. 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 refining device of the present embodiment includes a control means 51, sensors 29 to 33, 35, 38, pumps 34, 36, and a valve 37. Based on the information of the sensors 29 to 33, 35, and 38, each pump and valve are controlled in order to satisfy the necessary amount of fresh water purification and the water quality.

  In seawater desalination using a membrane, clogging (fouling) of the membrane due to inorganic substances, organic substances, and living organisms in seawater and additive chemicals 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 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 separating means 3 and the remelting means 14 change. In the fourth embodiment, in order to cope with this, 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 has a pressure, flow rate, temperature, CO ₂ concentration meter, and 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.

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

  In FIG. 5, the processing flow of the fresh water refinement | purification process control by the control means 51 is shown. 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 load amounts of NH ₃ and CO ₂ and 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 NH ₃ , CO _2, and conductivity can be created in advance or estimated from the molar conductivity of ions.

  In step S503, the flow rate of the carrier gas is calculated using the processing model related to the separation unit 3, the load obtained in step S502, and the target fresh water quality. The flow rate of the carrier gas can change the gas-liquid ratio in the separation means 3 and 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 of S503. Next, it is determined whether the measured value of the conductivity of the sensor 33 is within a target value. When lower than the target value, the carrier gas is reduced. On the other hand, when the target value is exceeded, after determining whether the upper limit of the supply of the carrier gas, the carrier gas is increased or the quasi-high osmotic pressure solution 1 of the pump 34 is increased. Reduce supply.

In the re-dissolution means 14, the carrier gas flow rate or the 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 acquired. In step S512, the NH ₃ and CO ₂ substance amounts, that is, the load on the remelting means 14 are calculated from the flow rate, temperature, pressure, NH ₃ concentration, and CO ₂ concentration using the relationship between the state equation and the material balance. .

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 to satisfy a predetermined target value is determined. Calculate the maximum value. 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 value of the sensor 38, and it is determined whether or not the target values are actually satisfied. If satisfied, reduce carrier gas. If not, it is determined whether the supply upper limit of the carrier gas is reached, and the pump 36 that adjusts the gas increase amount or 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 set 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.

  With 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 a carrier gas to a gas that is in equilibrium with the fresh water discharged from the separation means, and fresh water with fewer impurities can be obtained. At the same time, production of ammonium carbamate in the pipe can be suppressed.

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

Further, since the recovery gas having a high NH ₃ partial pressure is first dissolved in the re-dissolution means, the pH of the quasi-high osmotic pressure solution rises. Therefore, dissolution of CO _{2 in} the recovered gas to be supplied next can be promoted.

Furthermore, by decomposing in accordance with the closed condition of the pipe due monitoring, precipitates causing the partial pressure of NH ₃ and CO ₂ by a low carrier gas, it is possible to maintain the health of the plant.

1, 2 Semi-high osmotic pressure solution 3 Separation means 4, 5 Recovery port 6 Carrier gas supply port 7 Fresh water 8 Separation gas pumps 9, 11, 21, 22, 23, 24, 28 Valves 10, 20, 27 Carrier gas pumps 12, 13 Inlet 14 Remelting means 15 Osmotic pressure solution 17, 26 Carrier gas filter 25 Heaters 29-33, 35, 38 Sensor 51 Control means

Claims (6)

Separation means for separating the solute component from the quasi-high osmotic pressure solution obtained in the forward osmosis membrane treatment step to obtain fresh water collects the solute component of the quasi-high osmotic pressure solution as a mixed gas of NH ₃ and CO ₂ Re-dissolution means for dissolving the gas recovered by the separation means in a quasi-high osmotic pressure solution, comprising a plurality of recovery ports at different height positions, and a carrier gas supply port through which carrier gas supplied by a pump flows Is provided with a plurality of inlets for dissolving the mixed gas recovered from the plurality of recovery ports of the separation means in the order of the mixed gas in which the partial pressure of NH ₃ is higher than the partial pressure of CO _2. Fresh water purification equipment. 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 gas having a NH ₃ partial pressure higher than the CO ₂ partial pressure is set low. A fresh water purifier characterized by being provided at a position.   2. The fresh water purifier according to claim 1, wherein a plurality of the carrier gas supply ports are provided, at least one carrier gas supply port is provided below any of the recovery ports, and a plurality of other carrier gas supply ports are provided. It is installed between the collection ports of the fresh water. 2. The fresh water purifier according to claim 1, wherein a gas having a partial pressure of NH ₃ higher than a partial pressure of CO ₂ is supplied to the re-dissolution means out of the gas discharged from each recovery port of the separation means. The fresh water purifier according to claim 1, wherein the inlet is provided at a position where the inlet first comes into contact with the quasi-hyperosmotic solution supplied to the re-dissolution means among the plurality of inlets . 2. The fresh water purification apparatus according to claim 1, wherein a gas discharged from a recovery port of the separation means during fresh water purification operation 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 a carrier gas containing these at a partial pressure lower than the partial pressures of NH ₃ and CO ₂ is connected, and solids deposited on the pipe, pump, or valve are decomposed. Fresh water purification equipment. The fresh water purification apparatus according to claim 1, wherein the semi-high osmotic pressure solution obtained in the forward osmosis membrane treatment step, the fresh water conductivity obtained by the separation means, the gas discharged from the recovery port, the injection The pressure , temperature, flow rate, NH ₃ concentration, and CO ₂ concentration of the gas injected into the inlet and the gas discharged from the remelting means are measured and discharged from the separation means and the remelting means using the measurement results. that water or NH ₃ concentration in the gas, and CO ₂ to estimate the concentration, based on these estimates or measurements, fresh water purification, characterized in that it comprises means for controlling the supply amount of the carrier gas and the solution apparatus.