Ammonia recovery method and ammonia recovery apparatus

Abstract

To provide an ammonia recovery method and recovery apparatus that use slaked lime as a chemical (alkali) to liberate ammonia, avoid complicating the device configuration and process, and suppress scale generation in a distillation process.SOLUTION: In an ammonia recovery method and a recovery apparatus of the present invention, slaked lime is added to a heated liquid to be treated, pH is adjusted to a range of 8 or more and 12 or less, and after a solid content is removed, the liquid to be treated from which the solid content has been removed is distilled in a distillation column, and in addition to recovery of ammonia contained in vapor at a top of the distillation column, an amount of the slaked lime added in a pH adjustment mechanism is controlled so that the ammonia concentration in a bottom liquid of the distillation column is 250 ppm or less, and also, an operating temperature in the distillation step should be lower than an operating temperature in the solid-liquid separation step by 5°C or more and 30°C or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an ammonia recovery method and recovery apparatus, and more particularly to an ammonia recovery method and ammonia recovery apparatus for recovering ammonia from an ammonia-containing liquid to be treated. [Background technology]

[0002] Ammonia is a substance that is widely used in a variety of applications and is also a waste product from a variety of processes. In recent years, a basic policy for reducing the total amount of nitrogen has been formulated, and wastewater containing ammonia is also subject to regulation.

[0003] Under such circumstances, various methods have been proposed to separate and recover ammonia from the ammonia-containing liquid to be treated. A representative method is known in which ammonia is recovered by distilling the liquid to be treated.

[0004] However, ammonia may exist not only in a free state in the aqueous solution but also in the form of ammonium ions, in which case it is necessary to add an alkali such as sodium hydroxide to liberate ammonia and then perform distillation.

[0005] As such, a method of adding an alkali to a liquid containing ammonia to liberate the ammonia and distill it is described in, for example, Patent Document 1 as follows: Supplying ammonium chloride alone, or a solid, liquid, or slurry containing ammonium chloride and a calcium content less than a chemical equivalent required for reaction with the ammonium chloride, to a preliminary blending tank; A liquid obtained by removing coarse solid matter from the liquid containing the reaction product is supplied to a finishing blending tank together with a solution or slurry containing ammonium chloride and / or calcium. A method for distilling ammonium chloride is disclosed in which the liquid containing the reaction product obtained is distilled to remove the coarse solid matter, and the coarse solid matter is returned to the preliminary blending tank. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 3-66248 Summary of the Invention [Problem to be solved by the invention]

[0007] However, this method requires a step of adding calcium at each of the two stages of preliminary blending and final blending, and also requires a step of removing the coarse solid matter after adding the calcium, resulting in a problem of complicated processes.

[0008] In addition, since a substance containing calcium is used as the alkaline component, there is a problem that scale is easily generated in the distillation apparatus.

[0009] The present invention is devised to solve the above-mentioned problems, and aims to provide an ammonia recovery method and recovery apparatus that uses hydrated lime as an agent (alkali) for liberating ammonia, while avoiding the equipment configuration and process from becoming complicated, and that is capable of suppressing the generation of scale in the distillation step. [Means for solving the problem]

[0010] In order to solve the above problems, the ammonia recovery method of the present invention comprises the steps of: a heating step of heating the liquid to be treated that contains ammonia; a pH adjustment step of adding slaked lime to the heated liquid to be treated to adjust the pH to a range of 8 to 12; A solid-liquid separation step of removing solids contained in the treated liquid after pH adjustment; A distillation step of distilling the liquid from which the solid content has been removed in a distillation column to separate the liquid into a top vapor containing ammonia at a higher concentration than the liquid to be treated and a bottom liquid containing ammonia at a lower concentration than the liquid to be treated; and a recovery step for recovering ammonia contained in the top vapor, The amount of slaked lime added in the pH adjustment step is controlled so that the ammonia concentration in the bottom liquid of the distillation column is 250 ppm or less, and The operation temperature in the distillation step is set to a temperature that is 5° C. or more and 30° C. or less lower than the operation temperature in the solid-liquid separation step. It is characterized by:

[0011] In the ammonia recovery method of the present invention, it is preferable that the liquid to be treated is heated to 70° C. or more and 100° C. or less in the heating step.

[0012] In addition, the ammonia recovery apparatus of the present invention comprises: A heating mechanism for heating the liquid to be treated that contains ammonia; a pH adjustment mechanism that adds slaked lime to the heated liquid to be treated to adjust the pH to a range of 8 to 12; a solid-liquid separation mechanism for removing solids contained in the liquid to be treated after the pH adjustment by the pH adjustment mechanism; a distillation mechanism for distilling the liquid from which the solid content has been removed in a distillation column to separate the liquid into a top vapor containing ammonia at a higher concentration than the liquid to be treated and a bottom liquid containing ammonia at a lower concentration than the liquid to be treated; a recovery mechanism for recovering ammonia contained in the column top vapor, The amount of slaked lime added in the pH adjustment mechanism is controlled so that the ammonia concentration in the bottom liquid of the distillation column is 250 ppm or less, and The operation temperature in the distillation column is configured to be lower than the operation temperature in the solid-liquid separation mechanism by 5°C to 30°C. It is characterized by:

[0013] In the ammonia recovery apparatus of the present invention, it is preferable that the heating mechanism is configured to heat the liquid to be treated to 70° C. or higher and 100° C. or lower. Effect of the Invention

[0014] In the ammonia recovery method and recovery apparatus of the present invention, slaked lime is added to the heated liquid to be treated to adjust the pH to a range of 8 to 12, and the solids are removed. The liquid to be treated from which the solids have been removed is then distilled to separate it into a top vapor containing ammonia at a higher concentration than the liquid to be treated and a bottom liquid containing ammonia at a lower concentration than the liquid to be treated. The ammonia contained in the top vapor of the distillation tower is recovered, and the amount of slaked lime added in the pH adjustment mechanism is controlled so that the ammonia concentration of the bottom liquid of the distillation tower is 250 ppm or less. Furthermore, the operating temperature in the distillation tower (distillation process) is set to be lower than the operating temperature in the solid-liquid separation mechanism (solid-liquid separation process) by a range of 5°C to 30°C. This makes it possible to avoid complex processes and equipment configurations and to suppress the generation of scale in the distillation process. Hereinafter, in this specification, the ammonia concentration refers to the concentration of ammonia converted into NH3.

[0015] That is, the amount of slaked lime added in the pH adjustment mechanism is controlled so that the ammonia concentration in the bottom liquid of the distillation column is 250 ppm or less. This prevents the amount of slaked lime added from becoming excessive, and makes it possible to perform only solid-liquid separation of the liquid to be treated after pH adjustment. This eliminates the need to add calcium at each of the two stages, preliminary blending and finish blending, and to remove coarse solids at each of the two stages, as in the case of Patent Document 1 mentioned above, and therefore simplifies the process and equipment configuration.

[0016] Furthermore, taking into consideration the fact that calcium compounds such as calcium carbonate and calcium sulfate produced when slaked lime is used tend to become less soluble in water as the temperature increases and become more soluble in water as the temperature decreases, in the present invention, the operating temperature in the distillation column (distillation step) is set to be lower than the operating temperature in the solid-liquid separation mechanism (solid-liquid separation step) by a range of 5°C to 30°C, thereby making it possible to suppress the generation of scale in the distillation apparatus due to precipitation of calcium compounds, and a highly reliable ammonia recovery method and recovery apparatus can be provided.

[0017] In the ammonia recovery method and recovery apparatus of the present invention, it is preferable to heat the liquid to be treated to a temperature of 70°C or more and 100°C or less in the heating mechanism (heating step). This is because the addition of slaked lime makes it possible to promote the reaction that liberates ammonia, and also makes it easier to satisfy the requirement of the present invention that the operating temperature in the distillation mechanism (distillation step) be lower than the operating temperature in the solid-liquid separation mechanism (solid-liquid separation step) by a range of 5°C or more and 30°C or less. [Brief description of the drawings]

[0018] [Figure 1] 1 is a flow sheet showing a configuration of an ammonia recovery apparatus according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The features of the present invention will be described in more detail below with reference to the embodiments of the present invention.

[0020] In this embodiment, an ammonia recovery device will be described that recovers ammonia from a treated liquid (aqueous ammonia solution) mainly made of water and containing ammonia at a rate of 1.0 wt % (10,000 ppm), and discharges treated effluent containing ammonia at a low concentration to the outside.

[0021] As shown in FIG. 1, an ammonia recovery apparatus 100 according to an embodiment of the present invention includes: a) a heating mechanism (heater) 2 configured to heat the liquid to be treated supplied from a supply tank 1 storing the liquid to be treated containing ammonia to a predetermined temperature and return the liquid to the supply tank 1; b) a pH adjustment mechanism 3 for adding slaked lime to the liquid to be treated heated by the heating mechanism 2 to adjust the pH to a range of 8 to 12; c) a solid-liquid separation mechanism 4 for removing solids contained in the liquid to be treated, the pH of which has been adjusted by the pH adjustment mechanism 3; d) a distillation mechanism 5 that distills the liquid from which the solid content has been removed in the solid-liquid separation mechanism 4 in a distillation column 5a to separate the liquid into a column top vapor containing ammonia at a higher concentration than the liquid to be treated and a column bottom liquid containing ammonia at a lower concentration than the liquid to be treated; e) A recovery mechanism 6 is provided for recovering ammonia contained in the top vapor of the distillation column 5a.

[0022] Moreover, the ammonia recovery apparatus 100 according to one embodiment of the present invention is configured to control the amount of slaked lime added in the pH adjustment mechanism 3 so that the ammonia concentration in the bottom liquid of the distillation column 5a becomes 250 ppm or less.

[0023] The distillation mechanism 5 is configured such that the operating temperature in the distillation column 5a is lower than the operating temperature in the solid-liquid separation mechanism 4 by a range of 5° C. or more and 30° C. or less.

[0024] Next, the ammonia recovery apparatus 100 according to one embodiment of the present invention will be described in more detail.

[0025] In this ammonia recovery system 100, the supply tank 1 is a tank for storing the liquid to be treated that contains ammonia, and the liquid to be treated that has an ammonia concentration of 1.0 wt% is supplied at a rate of 8300 kg / hr. The amount of ammonia contained in the liquid to be treated is 83 kg / hr.

[0026] Furthermore, the heating mechanism (heater) 2 constituting the ammonia recovery apparatus 100 is configured to heat the liquid to be treated by a heat source (heat medium) so that the temperature of the liquid to be treated (liquid to be treated after pH adjustment) in a pH adjustment tank described below becomes 95° C. In this embodiment, the liquid to be treated heated by the heating mechanism (heater) 2 is circulated between the supply tank 1 and the heating mechanism (heater) 2, and a part of it is supplied to the pH adjustment tank 3b constituting the pH adjustment mechanism 3.

[0027] The heat source (heat medium) used for heating in the heating mechanism 2 and whose temperature has been reduced is configured to be heated again and supplied to the heating mechanism 2 as a heat source, although this is not shown in the figure.

[0028] The liquid to be treated heated by the heating mechanism 2 circulates between the supply tank 1 and the heating mechanism 2, and a part of the liquid is supplied to a pH adjustment tank 3b constituting a pH adjustment mechanism 3. In the present invention, the heating mechanism 2 is not limited to the above-mentioned configuration, and heating mechanisms of various configurations can be used.

[0029] The pH adjustment mechanism 3 also includes a slaked lime slurry tank 3a that prepares slaked lime slurry with a slaked lime concentration of 28 wt% by adding slaked lime to water and stirring it with an agitator 13a, and a pH adjustment tank 3b that mixes the liquid to be treated supplied from the supply tank 1 with the slaked lime slurry supplied from the slaked lime slurry tank 3a and stirs it with an agitator 13b to adjust the pH.

[0030] In this embodiment, the pH of the liquid to be treated in the pH adjustment tank 3b is adjusted to 8 or more and 12 or less (specifically, pH 10.8 to 11.5) by supplying slaked lime slurry with a slaked lime concentration of 28 wt% from the slaked lime slurry tank 3a to the pH adjustment tank 3b.

[0031] In this pH adjustment process, 646 kg / hr of slaked lime slurry with a slaked lime concentration of 28 wt% is added to 8,300 kg / hr of the liquid to be treated. The amount of slaked lime contained in the 646 kg / hr of slaked lime slurry added is 181 kg / hr. In this embodiment, the temperature of the liquid to be treated after the pH adjustment is set to 95° C. as described above.

[0032] In the ammonia recovery apparatus 100 according to the present embodiment, a filter having an organic, ceramic, or metallic filter material is used as the solid-liquid separation mechanism 4. It is possible to use a filter having various configurations, such as a membrane having an opening size of 100 nm to 10 μm.

[0033] Then, the liquid to be treated, which has been pH-adjusted by the above-mentioned pH adjustment mechanism 3 and has a temperature of 95° C., is sent to this solid-liquid separation mechanism 4, where the solid content is separated and removed.

[0034] The filtration flow rate (filtrate volume) is 8,850 kg / hr, and the separated solids (including adhering liquid) are 96 kg / hr ((8,300 kg / hr + 646 kg / hr) - 8,850 kg / hr = 96 kg / hr). The ammonia concentration in the filtrate is 0.94 wt% (9400 ppm).

[0035] Then, the filtrate (8,850 kg / hr) at a temperature of 95° C. from which the solid content has been separated and removed in the solid-liquid separation mechanism 4 is sent to the distillation mechanism 5.

[0036] In the ammonia recovery apparatus 100 according to this embodiment, the distillation mechanism 5 includes a packed distillation column 5a, a thin film falling reboiler (heater) 5b, and a condenser 5c that cools and condenses the top vapor of the distillation column 5a.

[0037] The distillation column 5a is not limited to a packed column, and various known types can be used.

[0038] Moreover, the reboiler 5b is not limited to the thin film falling type, and various known types can be used.

[0039] In this distillation mechanism 5, the liquid to be treated from which solids have been removed in the solid-liquid separation mechanism 4 is distilled in the distillation column 5a and separated into a column top vapor containing ammonia at a higher concentration than the liquid to be treated and a column bottom liquid containing ammonia at a lower concentration than the liquid to be treated.

[0040] Further, distillation column 5a is configured such that the operating temperature is operated at a temperature lower than the temperature of the filtrate in solid-liquid separation mechanism 4 by controlling the pressure within the system (operating pressure).

[0041] Specifically, the liquid to be treated is distilled in the distillation tower 5a, so that an overhead vapor having an ammonia concentration of 49.5 wt % is taken from the top of the tower, and a bottom liquid having an ammonia concentration of 10 ppm is taken from the bottom of the tower.

[0042] In this embodiment, the operation pressure of distillation column 5a is controlled to 61 kPaA, so that the temperature of the bottom liquid of distillation column 5a is 90° C. In other words, distillation column 5a is operated at a temperature (90° C.) that is 5° C. lower than the operation temperature in solid-liquid separation mechanism 4 (the temperature of the filtrate (95° C.)).

[0043] The overhead vapor of the distillation column 5a is cooled by a condenser 5c, and the condensed liquid (water) is returned to the top of the distillation column 5a as a reflux liquid.

[0044] On the other hand, the non-condensed gas that is not condensed in the condenser 5c is recovered as a gas containing a high concentration of ammonia, and is configured to be able to be utilized for an appropriate purpose.

[0045] However, it is also possible to provide an absorption device (not shown in FIG. 1) so as to absorb the ammonia contained in the non-condensable gas into water and recover it as ammonia water having a predetermined concentration.

[0046] Therefore, when the non-condensed gas in the condenser 5c is recovered as a gas containing a high concentration of ammonia, the condenser 5c also functions as the recovery mechanism 6 for recovering the ammonia.

[0047] Furthermore, as described above, when the ammonia in the uncondensed gas in the condenser 5c is absorbed in water by an absorption device and recovered as ammonia water of a predetermined concentration, the absorption device functions as a recovery mechanism 6 for recovering ammonia.

[0048] In this embodiment, the amount of uncondensed gas that was not condensed in the condenser 5c is 166 kg / hr, the ammonia concentration is 49.5 wt%, and the amount of ammonia recovered is 82.1 kg / hr. In other words, 82.1 kg / hr of the 83 kg / hr of ammonia contained in the liquid to be treated is recovered.

[0049] The bottom liquid of the distillation column 5a is supplied to the top of the reboiler (heater) 5b and heated again, and a part of the bottom liquid supplied to the top of the reboiler (heater) 5b is discharged to the outside of the system at a rate of 8684 kg / hr as wastewater with an ammonia concentration of 10 ppm. The amount of ammonia discharged is 0.9 kg / hr.

[0050] In the ammonia recovery apparatus 100 of the present embodiment, the pH is adjusted to 10.8 to 11.5 by the pH adjustment mechanism 3, while the amount of slaked lime added by the pH adjustment mechanism 3 is controlled so that the ammonia concentration of the bottom liquid of the distillation column 5a becomes 10 ppm. Even in this case, it has been confirmed that the pH of the liquid to be treated in the pH adjustment tank 3b falls within the range of pH 10.8 to 11.5.

[0051] Therefore, in the ammonia recovery apparatus 100 according to this embodiment, the pH adjustment mechanism 3 functions as a preliminary mechanism for adjusting the amount of slaked lime added to a roughly appropriate amount, and the final amount of slaked lime added is controlled based on the detection result of the ammonia concentration of the column bottom liquid of the distillation column 5a.

[0052] As described above, in the ammonia recovery apparatus 100 according to the present embodiment, slaked lime is added to the heated liquid to be treated by the pH adjustment mechanism 3 to adjust the pH to a range of 8 to 12 (more specifically, pH 10.8 to 11.5), the solid content is removed by the solid-liquid separation mechanism 4, and then the liquid to be treated from which the solid content has been removed is distilled by the distillation mechanism 5. At the same time, the amount of slaked lime added by the pH adjustment mechanism 3 is controlled so that the ammonia concentration of the bottom liquid of the distillation tower 5a is 250 ppm or less (10 ppm in this embodiment), and the operating temperature in the distillation tower 5a (distillation step) is set to be lower than the operating temperature in the solid-liquid separation mechanism 4 (solid-liquid separation step) by a range of 5°C to 30°C (5°C lower in this embodiment), so that it is possible to avoid the process and equipment configuration from becoming complicated and to suppress the generation of scale in the distillation step.

[0053] That is, in this embodiment, the amount of slaked lime added by the pH adjustment mechanism 3 is controlled so that the ammonia concentration of the bottom liquid of the distillation column 5a is 10 ppm or less, thereby preventing the amount of slaked lime added from becoming excessive, and as a result, it becomes unnecessary to add calcium at each of the two stages of preliminary blending and final blending and to remove coarse solids at each of the two stages, as in the case of the above-mentioned Patent Document 1. As a result, it becomes possible to simplify the process and the equipment configuration.

[0054] Furthermore, in the ammonia recovery apparatus 100 according to this embodiment, calcium compounds such as calcium carbonate and calcium sulfate that may be generated when slaked lime is used to liberate ammonia tend to have a lower solubility in water as the temperature increases and a higher solubility in water as the temperature decreases. In consideration of this, the operating temperature in the distillation column 5a is set to be 5° C. lower than the operating temperature in the solid-liquid separation mechanism 4, so that it is possible to suppress the generation of scale in the distillation column 5a due to precipitation of calcium compounds, and it is possible to provide a highly reliable ammonia recovery apparatus 100.

[0055] In addition, in the case of the above embodiment, the distillation column 5a is operated in a state in which 10 ppm of ammonia capable of reacting with slaked lime is present in the bottom liquid thereof. This reduces the possibility that slaked lime remains without reacting with ammonia, and thus reduces the load on the solid-liquid separation mechanism 4.

[0056] When the ammonia concentration in the bottom liquid of the distillation column 5a can be made higher than 10 ppm in relation to the wastewater conditions, etc., the possibility that slaked lime will remain without reacting with ammonia is further reduced, making it possible to further suppress the generation of scale in the distillation column 5a.

[0057] In the above embodiment, the case where the liquid to be treated is an aqueous solution containing 1.0 wt % ammonia has been described, but the present invention can be effectively applied to the case where ammonia is recovered from a liquid to be treated containing 0.1 to 5 wt % ammonia.

[0058] In addition, in the above embodiment, the operating temperature of distillation column 5a is set to 90°C, which is 5°C lower than the operating temperature of solid-liquid separation mechanism 4, which is 95°C. However, the operating temperature of distillation column 5a may be set to a temperature lower than the operating temperature of solid-liquid separation mechanism 4 in the range of 5°C to 30°C.

[0059] In addition, the configurations and operating conditions (various amounts, temperatures, ammonia concentrations) of the heating mechanism 2, the pH adjustment mechanism 3, the solid-liquid separation mechanism 4, the distillation mechanism 5, and the recovery mechanism 6 described in the above embodiment or shown in FIG. 1 are merely examples, and the present invention does not exclude cases where those values ​​are different from those in the above embodiment.

[0060] The present invention is not limited to the above-described embodiment in any other respects either, and applications and modifications can be made within the scope of the invention. [Explanation of symbols]

[0061] 100 Ammonia recovery device 1 Supply Tank 2 Heating mechanism 3 pH adjustment mechanism 3a Slaked lime slurry tank 3b pH adjustment tank 4 Solid-liquid separation mechanism 5 Distillation mechanism 5a Distillation column 5b Reboiler (heater) 5c capacitor 6. Collection Mechanism 13a Mixer 13b Mixer

Claims

1. a heating step of heating the liquid to be treated that contains ammonia; a pH adjustment step of adding slaked lime to the liquid to be treated heated in the heating step to adjust the pH to a range of 8 to 12; a solid-liquid separation step of removing solids contained in the pH-adjusted liquid to be treated; A distillation step of distilling the liquid from which the solid content has been removed in a distillation column to separate the liquid into a top vapor containing ammonia at a high concentration and a bottom liquid containing ammonia at a low concentration; a recovery step for recovering ammonia contained in the top vapor, The amount of slaked lime added in the pH adjustment step is controlled so that the ammonia concentration of the bottom liquid of the distillation column is 250 ppm or less, and The temperature of the bottom liquid is set to a temperature that is 5° C. or more and 30° C. or less lower than the operation temperature in the solid-liquid separation step. The ammonia recovery method according to claim 1,

2. 2. The method for recovering ammonia according to claim 1, wherein the liquid to be treated is heated to 70° C. or higher and 100° C. or lower in the heating step.

3. A heating mechanism for heating the liquid to be treated that contains ammonia; a pH adjustment mechanism that supplies a heated liquid to be treated from the heating mechanism and adds slaked lime to the heated liquid to be treated to adjust the pH to a range of 8 to 12; a solid-liquid separation mechanism for removing solids contained in the liquid to be treated after the pH adjustment by the pH adjustment mechanism; a distillation mechanism for distilling the liquid from which the solid content has been removed in a distillation column to separate the liquid into a top vapor containing ammonia at a high concentration and a bottom liquid containing ammonia at a low concentration; a recovery mechanism for recovering ammonia contained in the column top vapor, The amount of slaked lime added in the pH adjustment mechanism is controlled so that the ammonia concentration in the bottom liquid of the distillation column is 250 ppm or less, and The temperature of the bottom liquid of the column is set to be lower than the operating temperature of the solid-liquid separation mechanism by a range of 5° C. to 30° C. An ammonia recovery apparatus comprising:

4. 4. The ammonia recovery apparatus according to claim 3, characterized in that the heating mechanism is configured to heat the liquid to be treated to 70° C. or higher and 100° C. or lower.

5. An ammonia recovery method as described in claim 1 or 2, wherein the temperature of the bottom liquid is set to a temperature that is 5°C or more and 30°C or less lower than the temperature at which the treated liquid from which the solids have been removed is supplied to the distillation tower.

6. An ammonia recovery apparatus as described in claim 3 or 4, wherein the temperature of the bottom liquid is configured to be lower by a range of 5°C to 30°C than the temperature at which the treated liquid from which the solids have been removed is supplied to the distillation tower.

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