JPH1057947A - Separating and recovering method of ammonia of the like from liquid containing ammonia or the like - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and surely separate and recover ammonia with a reduced space by micronizing a liq. containing ammonia, etc., in a gas phase to dissipate the ammonia, etc., in a gas phase. SOLUTION: A stripping device 11 is composed of rooms 15-17, and an ammonia-containing waste water supplied to the rooms 15 is fluidized while overflowing to the rooms 16 and 17. Each room 15-17 is provided with a circular disk 19 rotating at high speed with a motor 18 so that its lower part is immersed in the ammonia-containing waste water and the ammonia-containing waste water is scraped with the circular disk 19 to micronize the waste water in the gas phase and thus to cause gas-liq. contact to dissipate ammonia. And in each chamber 15-17, the ammonia is discharged from the chamber 15 together with the air flow so that the air supplied to the gas phase from the chamber 17 is allowed to flow in the chambers 16 and 15. The discharged ammonia is supplied to a demister device 12, and the mist is removed here, and the ammonia with the mist removed is sent to a scrubber 13, and the ammonia is absorbed to a circulating liq.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating ammonia and the like from a liquid containing the same and a method for recovering the same.

[0002]

2. Description of the Related Art The discharge of nutrients of nitrogen and phosphorus into rivers, lakes and marshes, and sea areas causes abnormal reproduction of phytoplankton and algae due to eutrophication, and has recently caused red tide and the like. The revision of the Water Pollution Control Law on October 1, 1993 determined the regulation of nitrogen and phosphorus emissions, and a provisional grace period of five years was set for 55 industries. The industry is desperately thinking, "What is the best technology?" There are four types of nitrogen, namely, organic nitrogen / ammonia nitrogen, nitrate nitrogen, and nitrite. The present invention relates to a method for separating and recovering nitrogen from ammonia. The main method of treating ammonia nitrogen is by a microorganism. NH under aerobic conditions (aeration _{^{tank) 4 + 1.5O 2 → 2H +}} + H 2 O + NO 2 - (1) NO 2 + 1 / 2O 2 → NO 3 - (2) oxidizing the ammonia by the action of microorganisms, It is nitritized and further nitrated. Thereafter, under anaerobic conditions, NO ₃ ⁻ +0.33 CH ₃ OH = NO ₂ ⁻ +0.67 H ₂ O (3) NO ₂ ⁻ +0.5 CH ₃ OH = 0.5 N ₂ +0.5 CO ₂ + 0.5H ₂ O + OH ⁻ (4) Due to the action of microorganisms, NO ₃ ⁻ and NO ₂ ⁻ become N ₂ gas and go out of the system. CH ₃ OH (methanol) is N
It is generally added as a hydrogen donor for the reduction of O ₃ ⁻ and NO ₂ . Generally, the nitrification (nitrification) rate of ammonia is lower than the denitrification rate, and the aeration tank 1
load _NH 4 -N in m ³ per day or less 0.2 Kg. The denitrification rate is also about 1 kg. Therefore, ammonia treatment by microorganisms requires a large tank and power for aerating or stirring the tank. Moreover,
As can be seen from equations (3) and (4), a hydrogen donor such as methanol is required. One mole of ammonia requires 0.83 moles of methanol. Therefore, in the case of high-concentration ammonia drainage, there is a large space and a large amount of methanol and the like, and the total cost increases. If the ammonia concentration is high, raise the pH of the wastewater, gasify the ammonia in the liquid phase by aeration or gas-liquid contact in a packed tower, discharge it to the gas phase, absorb it into a class bar, etc., recover the ammonia, Alternatively, a method of performing combustion treatment by introducing into a combustion facility has been performed. FIG. 10 shows a separation method using an aeration tank as a conventional ammonia separation method, and FIG. 11 similarly shows a separation method using a gas-liquid contact tower.

[0003]

By the way, in the aeration method shown in FIG. 10, when a large amount of air is blown, the air must be blown against the pressure loss from the water depth, and the power becomes large. The contact time of bubbles is large and difficult to take.
Further, the gas-liquid contact area depends on the number and size of the bubbles. Making the bubbles finer is advantageous for gas-liquid contact, but increases the pressure loss. When slaked lime (Ca (OH) ₂ ) is used as an alkaline agent, it reacts with carbon dioxide in the air, and as shown in equation (5), Ca (OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O (5) calcium carbonate A sediment may form, which may clog the injection nozzle. With the method as shown in FIG. 11, the gas-liquid contact time can be made longer than in the aeration method. Also, the static pressure of the blower can be reduced. However, a large tower is required due to the necessity of a high tower, and the power of a pump for lifting drainage to the top of the tower increases. Also, as with the aeration method, when slaked lime is used as an alkaline agent, calcium carbonate precipitates in the filler, which often blocks and reduces the stripping efficiency due to scale generation. It is difficult to use slaked lime or carbide slag as an alkaline agent. The reaction of the formula (5) does not occur if a force soda is used, but the cost is high. Therefore, an object of the present invention is to provide a method for separating and recovering ammonia from an ammonia-containing liquid, which can efficiently and reliably separate and recover ammonia in a space-saving manner.

[0004]

Means for Solving the Problems In order to solve the above-mentioned problems, a first aspect of the present invention is to disperse ammonia and the like into the gas phase by atomizing a liquid containing ammonia and the like in the gas phase. Is adopted. The invention according to claim 2 is a scooping member in which a plurality of separation tanks are provided in multiple stages, the liquid containing ammonia or the like and the gas flow are opposed to the multi-stage separation tank, and the liquid containing ammonia or the like is rotated at high speed in each separation tank. In this case, a structure is adopted in which the fine particles are lifted into a gas phase to be miniaturized and diffused into the gas phase. According to a third aspect of the present invention, there is provided a configuration in which ammonia or the like released into the gas phase by the separation method according to the first or second aspect is treated by a demister and a scrubber.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a recovery apparatus used for carrying out the recovery method of the present invention.
, A demister device 12, a first scrubber 13 and a second scrubber 14, and the stopping device 11 includes a first chamber 15, a second chamber 16, and a third chamber 17. The ammonia-containing wastewater supplied to the chamber flows while overflowing to the second chamber 16 and the third chamber 17, and a disk 19 rotated at a high speed by a motor 18 is immersed in each chamber in the lower part of the ammonia-containing wastewater. The disk 19 is provided as a scraping member, and scrapes ammonia-containing waste water into fine particles in a gas phase, and makes gas-liquid contact to diffuse ammonia into the gas phase. Each of the rooms 15, 16, and 17 has a third room 1
7 is supplied to the second chamber 16 and the first chamber 15 so as to be opposed to the flow of the ammonia-containing wastewater. The removed ammonia is supplied to the demister device 12, the mist is removed in the demister device 12, and water droplets are returned to the first chamber 15 by drain or sent to another drain tank.

The ammonia from which the mist has been removed is
And is absorbed by a circulating fluid containing sulfuric acid, hydrochloric acid, or the like. The unremoved ammonia is likewise absorbed in the second scrubber 14, and the treated exhaust gas is discharged to the outside or, if there is no problem, returned to the stripping device to form a gas circulation system. In the liquid management of the first scrubber 13, the acid is supplied by operating the pump according to the instruction of the pH meter. It should be noted that a very small amount of acid is quantitatively put into the second scrubber 14 using a pump. Water is quantitatively pumped to the second scrubber 14 by a pump so that the circulating liquid of the first scrubber 13 is not saturated with ammonium salt, and overflows toward the first scrubber 13 therefrom. With such a method, the concentration of ammonia salt can be relatively easily increased without lowering the ammonia removal efficiency of the scrubber.

Next, FIGS. 2 to 5 show different examples of the disc 19 used in the stripping device 11. FIG.
The disk 19 in the example shown in FIG. 2 has a structure in which a circular plate is formed in a radial waveform, and a boss 21 for attaching to a rotating shaft is provided at a central portion. Raised and scattered at the wavy part. 3 (A) and 3 (B), an annular plate 23 having a ring-shaped band is fixed to the outer periphery of the disk body 22. A large number of through holes 24 are formed in the annular plate 23. They are provided at regular intervals in the circumferential direction, and have a structure in which a boss 25 for attachment to a rotating shaft is provided at the center of the disc body 22. FIG. 4 (A),
The disk 19 in the example shown in (B) has a large number of scraping plates 28 fixed in a radial arrangement on the outer periphery of a disk 27 fixed on the outer periphery of a boss 26. 5 (A) and 5 (B), the disk 19 is fixed to the outer periphery of the boss 29 at fixed intervals, and the both ends of the scraping plate 31 group are fixed to the ring plate 32. Are combined. When these discs 19 are rotated at a high speed in a state where the lower part is immersed in the ammonia-containing wastewater, the wastewater can be scraped up to a gas phase to be finely divided.

Next, the separation and recovery of ammonia from the ammonia-containing wastewater will be specifically described. As shown in FIG.
Ammonia-containing wastewater is introduced into the first chamber 15 from the inlet, and rotates at a high speed in the first chamber 15 by a disk 19 (100 to 3000).
(RPM) and is finely divided and stays in the air.
Contact with air coming from chamber 16. At this time, if the number of rotations is increased, the size of the wastewater can be more effectively reduced, the gas-liquid contact area increases, and ammonia in the liquid is easily gasified.
Ammonia gasifies into the air coming from the second chamber 16 while the wastewater stays in the first chamber 15 for a certain period of time, is discharged to the demister device 11 while exhibiting a certain ammonia partial pressure, and is sent to a scrubber. After the drainage stays in the first chamber 15 for a certain period of time, it continuously overflows into the second chamber 16.
Since the water level is slightly lower in the second chamber 16, there is no water flow in the opposite direction. Since the wastewater that has entered the second chamber 16 is considerably stripped of ammonia in the first chamber 15, the ammonia concentration has decreased. Similarly to the first chamber 15, the ammonia comes into contact with the air coming from the third chamber 17 while staying for a certain period of time, and ammonia is gasified and sent to the first chamber 15. On the other hand, the wastewater flows into the third chamber 17 after staying for a certain time. In the third chamber 17, although the ammonia concentration in the wastewater is considerably reduced, the ammonia is miniaturized by the rotating disk 19 while staying for a certain period of time, and comes into contact with fresh air entering from outside to be stripped. It is discharged from the overflow port to the outside of the device as treated water. In general, gas solubility follows Henry's law. As shown in FIG. 1, when the ammonia partial pressure P ₁ in the first chamber 15, the ammonia concentration in the liquid is C ₁ , and H is Henry's constant, P ₂ = HC ₂ P ₃ = HC ₃ as in P ₁ = HC _1. . Suppose that the residence time in one chamber is 20 minutes, the removal rate of ammonia is 90%, and there is no concentration dependency of the Henry constant and the removal rate of ammonia. _{C 2 = 0.1C 1 C 3 =} 0.1C 2 = 0.01C 1 becomes _{P 2 = HC 2 = 0.1HC 1} = 0.1P 1 P 3 = HC 3 = 0.01HC 1 = 0.01P 1 Becomes On the other hand, the ammonia gas-containing air accompanied by the mist discharged from the first chamber 15 is removed by the mist catcher of the demister device 12 installed on the way, and then introduced into the scrubber, and the collected liquid of the scrubber is collected. The air absorbed by (water or acid) and from which ammonia has been removed is discharged outside. The ammonia scrubber can be treated in one stage, but when it is made in multiple stages, a small amount of gas can be treated with the collected liquid.

Here, Henry's law will be described. Henry's Law The diffusion / absorption operation is a sequential process in which solutes in the liquid phase move from the liquid phase to the gas-liquid interface, evaporate into the gas phase, and then diffuse into the gas phase body. In this case, the problem is the distribution relationship of solute gas at the gas-liquid interface, that is, the solubility of gas (the opposite of the degree of emission) is well known by Henry's law (“Gas that dissolves in a certain amount of liquid at a certain temperature. The mass is proportional to the partial pressure of the gas. "). P = HC (6) where, P: madness of dissolved gas (atm) H: Henry's constant (atm · m ³ / kg-mol) C: concentration of dissolved gas in liquid (kg-mol / m ³ ) Comparison Henry's law does not hold for gaseous ammonia, hydrogen chloride, etc., which are easily soluble in water. However, even when these gases have a low partial pressure, they can be considered to approximately follow Henry's law. In general, the Henry's law constant increases as the temperature increases, that is, the higher the temperature, the lower the solubility of the gas becomes and the easier it is to dissipate. Table 1 shows NH ₃ −
Henry's law constant of H ₂ O system, and Table 2 shows vapor-liquid equilibrium data of ammonia-water system. FIG. 6 shows the solubility of each gas in water.

[Table 1] The double membrane theory is a useful theory when considering the rate of gas absorption and emission. According to this theory, as shown in FIG. 7, a thin boundary film without disturbance is formed on the gas side and the liquid side along the interface where the gas phase and the liquid phase are in contact with each other. The slow diffusion leads to mass transfer resistance. The driving force for the diffusion in the film is the difference between the solute concentration in the boundary and the liquid body and the difference in partial pressure between the gas body and the diffused substance in the boundary. Movement amount N _A (kg) per unit time and unit area on liquid side and gas side
−mol / m ² Hr) are equal, so the following equation holds. N _A = k _G (p-pi) = k _L (Ci-C) (7) where k _L : liquid phase mass transfer coefficient (m / Hr) Ci: concentration of solute at interface (kg-mol / m) ³ ) pi: partial pressure of the solute at the interface (atm, Pa) k _G : gas phase mass transfer coefficient (kg-mol / m ² · atm)
· Hr) C: solute concentration in the body ^{(kg-mol / m 3)} p: partial pressure of the solute gas body (atm, Pa) The value of _{k G} and _{k L,} of the solute in the gas-side and a liquid phase The diffusion coefficient is related to the effective thickness of the film. Pi and Ci must be measured in order to directly determine k _G and k _L from gas absorption experiments. However, since this is almost impossible, a generalization coefficient represented by the following equation is used. To _{N A = K G (p-} pe) = K L (Ce-C) (8) _{where, K} L: liquidus overall mass transfer coefficient (m / Hr), Ce: equilibrium to gas body concentration (kg-mol /
m ³⁾ pe: equilibrium partial pressure for the liquid body (atm, Pa) _{K G:} vapor phase overall mass transfer coefficient ^{(kg-mol / m 2 ·} a
_{tm · Hr) K G, K} L and _k G, the relationship of _{k L} is as follows. 1 / K _G = 1 / k _G + H / k _L (9) 1 / K _L = 1 / k _L + 1 / Hk _G (10) where H is Henry's constant p _i / C _i , and Henry's law is not applied when is the _{(p i -pe) / (C} i -C e). When the solubility is large, H is small, so that H / k _L can be neglected, and K _G = k _G , and the resistance on the gas side becomes dominant.

[0010] Ammonia stripping and p
H The ammoniacal nitrogen in the water is composed of ammonia ions (N
H ₄ ⁺ ) and free ammonia (NH ₃ ) are present in equilibrium, but as the pH increases, the proportion of free ammonia increases. In this equation, as the pH increases, the equilibrium tilts to the right and pH 1
Above zero, most are in the form of free ammonia. The ratio of ammonia ions to free ammonia in water is p
H, which is affected by the water temperature, can be determined by the following equation. Here, _Kb is the dissociation constant of ammonia ion, 1.8 × 10 ⁻⁵ mol at 25 ° C., (H ⁺ ) is the hydrogen ion concentration, and _KW is the dissociation constant of water, (OH ⁻ ) (H ⁺ ) = 10
⁻¹⁴ (mol) ^{2 From} this, the NH ₃ ratio at 25 ° C. and pH 10.0 is calculated. Becomes FIG. 8 shows the relationship between NH ₃ and NH ₄ ⁺ at each pH. Ammonia that has been released by raising the pH of water is in a state where it can easily escape to the outside, and comes out of the water into the atmosphere when a physical stimulus such as stirring or aeration is given. To facilitate this, an ammonia stripping method is used. In the ammonia stripping method, generally, water to be treated is sprayed from the top of a high tower, and a plastic filler is added to increase the gas-liquid contact area. From equation (8), since the mass transfer amount is per unit Na contact area, the mass transfer amount is proportional to the gas-liquid contact area. In other words, the efficiency of ammonia stripping can be increased by increasing the gas-liquid interface.This time, focusing on this point, the conventional high tower method and aeration method were stopped, and the water to be treated was A method of miniaturizing and extremely increasing the gas-liquid contact area was considered. At the same time, it was possible to prevent calcium carbonate from sticking, which tends to occur when slaked lime is used as an alkaline agent, which was a disadvantage of the conventional method. Note that the separation and recovery method can also be used for a method in which free chlorine in a chlorine-containing liquid is gasified and taken out.

[0011]

EXAMPLE A wastewater containing ammonia was put into a stripping device as shown in FIG. 9 (15 L), valves at the inlet and outlet were stopped, constant air was sent, and a liquid to be treated was sampled from a lower drain at regular time intervals. And ammonia was measured. At the same time, the air flow was measured from the measurement port of the blown air duct with a hot wire anemometer to measure the air supply. The liquid temperature was raised by a heater installed in the apparatus, and measured by a temperature sensor. Further, an alkaline agent was added according to the instruction of the pH meter, and the pH was adjusted to 11 or more. The results are shown in Tables 2 and 3. For comparison, FIG. 12 shows the conventional removal rate by the gas-liquid contact tower shown in FIG. As ammonia water, ammonium sulfate was dissolved in water to make experimental wastewater.

[Table 2]

[Table 3]

[0012]

As described above, according to the present invention, the liquid containing ammonia or the like is dispersed in the gas phase by making it finer in the gas phase. Separation of ammonia and the like from a liquid containing such as can be performed efficiently, ammonia and the like can be separated at a low pH, a low temperature, and a small amount of air, thereby reducing the processing cost and equipment cost. In addition, it is possible to reduce the size and space of equipment for separating ammonia and the like, to increase the collection rate of ammonia and the like, and to prevent the adhesion of calcium carbonate.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a recovery apparatus for implementing a recovery method of the present invention.

FIG. 2 is a perspective view showing an example of a disk.

3A is a front view showing an example of a disk, and FIG. 3B is a side view thereof.

FIG. 4A is a longitudinal sectional front view showing an example of a disk, and FIG.

5A is a longitudinal sectional front view showing an example of a disk, and FIG. 5B is a side view of the same.

FIG. 6 is a graph showing the solubility of gas in water.

FIGS. 7A and 7B are explanatory diagrams showing movement of a substance at a gas-liquid interface.

FIG. 8 is an explanatory diagram showing the relationship between free ammonia and ammonium ions at each pH.

FIG. 9 is an explanatory view of an apparatus used in an example.

FIG. 10 is an explanatory view showing a conventional separation method.

FIG. 11 is an explanatory view showing another conventional separation method.

FIG. 12 is a graph showing a relationship between a conventional gas-liquid ratio and a removal rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Stripping apparatus 12 Demister apparatus 13 1st scrubber 14 2nd scrubber 15 1st chamber 16 2nd chamber 17 3rd chamber 18 Motor 19 Disk

Claims (3)

[Claims] 1. A method for separating ammonia from an ammonia-containing liquid, wherein the ammonia or the like is diffused into the gas phase by atomizing the liquid such as ammonia in the gas phase. 2. A plurality of separation tanks are provided in multiple stages, a flow of a liquid containing ammonia and the like flowing in the multi-stage separation tank is opposed to each other, and a gas-raising member which rotates the liquid containing ammonia and the like in each separation tank at a high speed is used for gas separation. A method for separating ammonia or the like from a liquid containing ammonia or the like, characterized in that the solution is scraped into a phase, finely divided and diffused into a gas phase. 3. A method for recovering ammonia or the like from a liquid containing ammonia or the like, wherein the ammonia or the like released into the gas phase by the separation method according to claim 1 or 2 is treated with a demister and a scrubber.