TWI636968B - Method for recovering ammonia-containing wastewater - Google Patents

Abstract

A method for recovering ammonia-containing wastewater, the ammonia-containing nitrogen wastewater is an alkaline wastewater containing ammonia, and the recovery method comprises: (a) introducing the alkaline wastewater and an inert gas into a first rotating packed bed, respectively, through the gas Extracting a first gas containing ammonia gas and an alkaline waste liquid; (b) mixing the first gas with dilute hydrochloric acid and reacting to obtain a second gas containing ammonium chloride particles and a chlorination a first recovery liquid of ammonium; and (c) introducing a process water and the second gas into a second rotating packed bed, respectively, and capturing a second ammonium chloride-containing particle by capturing ammonium chloride particles in the second gas Recycled liquid. The method for recovering ammonia-containing nitrogen wastewater of the present invention can effectively separate the ammonia nitrogen component in the ammonia-containing nitrogen wastewater by the steps of stripping, reacting and capturing, and obtain a high concentration ammonium chloride recovery liquid.

Description

Method for recovering ammonia-containing wastewater

The invention relates to a method for recovering wastewater, in particular to a method for recovering ammonia-containing wastewater.

Industrially produced ammonia-containing wastewater (such as etching waste liquid produced by printed circuit board factories), if directly discharged into water bodies such as lakes, rivers, and oceans, may not only pose a risk of heavy metal pollution, but ammonia nitrogen will cause maintenance. The problem is solved, so it needs to be properly recycled.

The existing industrial ammonia-containing nitrogen wastewater recovery method is generally carried out by gas stripping or conversion into ammonium sulfate for recycling, or by distillation to produce ammonia water. However, the industrial application value of ammonium sulfate is low, and it has become a large amount of secondary pollutants, and at the same time, a large amount of clear freight is derived. In addition, the process of producing ammonia water also has the disadvantage of large energy consumption, and is limited by the problem that the concentration of ammonia nitrogen in the wastewater may result in low ammonia concentration without recycling benefit.

TW 342382 discloses a method for recovering copper-containing waste liquid of a printed circuit board, which is used for recycling and recycling copper-containing substances through a plurality of procedures such as precipitation, separation, strong acid type cation exchange resin (RH), adding additives, heating and evaporation, and extraction. At the same time, ammonium chloride is recovered. However, the ion exchange resin is expensive, and the added additive is also ammonium chloride and ammonia water, which not only requires a heating and evaporation process of subsequent energy consumption, but also increases the cost of the raw material and the ammonium chloride content in the waste liquid.

Accordingly, it is an object of the present invention to provide a method for recovering ammonia-containing wastewater which overcomes the disadvantages of the prior art described above.

Therefore, in the method for recovering ammonia-containing wastewater according to the present invention, the ammonia-containing nitrogen wastewater is an alkaline wastewater containing ammonia, and the recovery method comprises the steps of: (a) introducing the alkaline wastewater and an inert gas into the first a rotating packed bed, gas stripping to obtain a first gas containing ammonia gas and an alkaline waste liquid; (b) mixing the first gas with dilute hydrochloric acid and reacting to obtain a chlorination a second gas of ammonium fine particles and a first recovered liquid containing ammonium chloride; and (c) introducing a process water and the second gas into a second rotating packed bed, respectively, by trapping the The ammonium chloride fine particles in the second gas give a second recovered liquid containing ammonium chloride.

The invention has the effect that the method for recovering ammonia-containing wastewater of the present invention can effectively separate the ammonia nitrogen component by the steps of stripping, reacting and capturing, and obtain a high concentration ammonium chloride recovery liquid.

Hereinafter, the present invention will be described in detail. Preferably, the alkaline waste water is neutralized by an acidic wastewater containing ammonium ions and heavy metal ions and an excess of alkali, and is obtained by filtration.

Preferably, in the step (b), the first gas is first mixed with ice water, and then mixed with the diluted hydrochloric acid to carry out a reaction. More preferably, the ice water is the process water from the step (c).

Preferably, in the step (c), the process water is combined with a supplementary water and then returned to the second rotating packed bed to continue the ammonium chloride particles in the second gas. Capture.

Preferably, in the step (b), the dilute hydrochloric acid is obtained by combining the first recovered liquid with concentrated hydrochloric acid to react with the first gas.

Preferably, in the step (c), the second recovered liquid is obtained, accompanied by obtaining a third gas, and the third gas is combined with the inert gas in the step (a) and then circulated to continue Carry out this step (a).

Preferably, in the step (a), the alkaline waste liquid is refluxed to the first rotating packed bed.

Preferably, step (b) is carried out in a scrubber or a third rotating packed bed.

More preferably, the pH of the alkaline wastewater obtained by filtration is 11 or more to ensure that the ammonia nitrogen in the alkaline wastewater is mainly in the form of ammonia molecules (NH _{3 (aq)} ).

Preferably, the pH of the dilute hydrochloric acid in the step (b) is 6 or less. More preferably, the pH of the dilute hydrochloric acid in the step (b) is 2-6.

Preferably, in the step (b), the mixing flow ratio of the first gas to the dilute hydrochloric acid is from 10:1 to 1000:1. If the flow ratio is too low, it means that the flow rate of dilute hydrochloric acid is too large, which will cause an increase in equipment and operation cost; if the flow rate ratio is too high, the efficiency of ammonia reaction in the first gas to form ammonium chloride will be low.

Preferably, in the step (c), the mixing flow ratio of the second gas to the process water is from 3:1 to 500:1. If the flow ratio is too low, it means that the flow rate of the process water is too large, which will increase the required volume and operation cost of the equipment; if the flow rate ratio is too high, the efficiency of capturing the ammonium chloride particles into the second recovered liquid will be low.

1‧‧‧Alkaline wastewater

2‧‧‧Inactive gases

3‧‧‧First rotating packed bed

31‧‧‧First gas

32‧‧‧Alkaline waste liquid

4‧‧‧Concentrated hydrochloric acid

41‧‧‧Diluted hydrochloric acid

5‧‧‧ Washing tower

51‧‧‧second gas

52‧‧‧First recovery liquid

6‧‧‧Process water

7‧‧‧Second rotating packed bed

71‧‧‧ Third gas

72‧‧‧Second recovery liquid

8‧‧‧Supply water

9‧‧‧Ice water absorption device

a~c‧‧‧step

Other features and effects of the present invention will be apparent from the following description of the drawings, wherein: FIG. 1 is a schematic view showing a recycling method of the first embodiment of the present invention.

Before the present invention is described in detail, it should be noted that in the following description, similar elements are denoted by the same reference numerals.

The invention is further described in the following examples, but it should be understood that these examples are for illustrative purposes only and are not to be construed as limiting.

Referring to Figure 1, a first embodiment of the method for recovering ammonia-containing wastewater of the present invention comprises the following steps:

[pre-processing]

An acidic wastewater containing ammonium ions and heavy metal ions is neutralized with an excess of alkali, and filtered to obtain an alkaline wastewater 1. In this embodiment, the acidic wastewater is dilute hydrochloric acid (HCl) wastewater containing ammonium chloride (NH ₄ Cl) and cobalt ions. The base is an aqueous solution of sodium hydroxide (NaOH) so that the pH of the filtered alkaline wastewater is 11 or more.

[Air stripping step (a)]

The above alkaline wastewater 1 and an inert gas 2 are introduced into a first rotating packed bed 3 at a flow rate of 15 L/min and 30 m ³ /min, respectively (the inner diameter of the packed bed is 370 mm, and the outer diameter of the packed bed is 670 mm, packed bed). The axial height is 315 mm, the rotational speed is 1100 rpm, the filler is a stainless steel mesh, and the stainless steel mesh has a specific surface area of 850 m ² /m ³ ), and a first gas 31 containing ammonia gas and an alkaline waste liquid 32 are obtained by gas stripping. The ammonia nitrogen in the alkaline wastewater 1 is thereby stripped into the first gas 31 in the form of ammonia gas (NH _{3 (g)} ).

In the present embodiment, the inert gas 2 is air. The alkaline waste liquid 32 can be further refluxed to the first rotating packed bed 3 to increase the efficiency of stripping, followed by waste liquid discharge.

[Reaction step (b)]

The first gas 31 obtained in the stripping step (a) is introduced into an ice water absorption device 9 and mixed with ice water to absorb a part of the ammonia gas in the first gas 31 into the ice water, and the first gas discharged. 31 and then introduced into a wet scrubber 5 (washing tower diameter of 600 mm, washing tower height of 3.5 m, filling material of plastic material, plastic material specific surface area of 168 m ² /m ³ ) at a flow rate of 30 m ³ /min And dilute hydrochloric acid 41 (pH 2 to 6) is introduced into the top of the scrubbing tower 5 at a flow rate of 250 L/min, and the dilute hydrochloric acid 41 flows down the scrubbing tower 5 with the first gas in the countercurrent flow The mixture was contacted with 31 and reacted (HCl + NH ₃ → NH ₄ Cl) to obtain a second gas 51 (white smoke) containing ammonium chloride particles and a first recovery liquid 52 containing ammonium chloride. This second gas 51 is discharged from the top end of the washing tower 5. The first recovered liquid 52 is discharged from the bottom end of the washing column 5, and a solution containing ammonium chloride is collected after heat exchange.

In the present embodiment, the ice water absorption device 9 is a rotating packed bed. After the first recovery liquid 52 is discharged from the washing column 5 and combined with the concentrated hydrochloric acid 4, dilute hydrochloric acid 41 is obtained to be refluxed to continue the reaction with the first gas 31 in the washing column 5, thereby lifting the first recovery. The concentration of ammonium chloride in liquid 52.

[Capture Step (c)]

Introducing a process water 6 and the second gas 51 obtained in the above reaction step (b) into a second rotating packed bed 7 at a flow rate of 600 L/min and 30 m ³ /min, respectively (packing bed size, rotation speed, and filling and the first a rotating packed bed 3 is the same), the fine particles in the second gas 51 are captured by gas-liquid contact, and the ammonium chloride particles in the second gas 51 are captured into the liquid phase to obtain an ammonium chloride-containing solution. The second recovered liquid 72 is accompanied by a third gas 71.

In the present embodiment, the third gas 71 is circulated after being combined with the air in the stripping step (a) to continue the stripping step (a) in the first rotating packed bed 3, whereby A trace amount of ammonium chloride fine particles, a trace amount of ammonia gas, a trace amount of hydrogen chloride vapor or water vapor which may be present in the third gas 71 is avoided to escape to the external environment, and the recovery rate of ammonia nitrogen is effectively improved. The process water 6 is obtained by combining the second recovery liquid 72 with a make-up water (H ₂ O) 8 and undergoing heat exchange, and is returned to the second rotating packed bed 7 to continue the second gas 51. The fine particles in the medium are captured, thereby increasing the ammonia nitrogen recovery rate of the recovery method of the ammonia-containing nitrogen wastewater of the present invention. Meanwhile, in the present embodiment, a part of the process water 6 may be introduced into the ice water absorption device 9 to absorb part of the ammonia gas in the first gas 31 as ice water.

[Recovery calculation]

Taking the acidic wastewater containing about 15000 ppm of ammonia nitrogen as an example, after the ammonia nitrogen-containing wastewater recovery method of the above first embodiment is performed for 600 minutes, about 1600 kg of a recovery liquid containing no cobalt ions and containing 30% by weight of ammonium chloride can be obtained, and the ammonia nitrogen is calculated. The recovery rate is approximately 94%.

The second embodiment of the method for recovering ammonia-containing nitrogen wastewater of the present invention is different from the above-described first embodiment in that the stripping step (a) and the reaction step are separately performed using three rotating packed beds of the same specification ( b) (instead of the washing tower 5) and the capturing step (c) (the inner diameter of the packed bed is 22 mm, the outer diameter of the packed bed is 140 mm, the axial height of the packed bed is 20 mm, the rotational speed is 1200 rpm, the filling is stainless steel mesh, stainless steel mesh The specific surface area is 850 m ² /m ³ ): the alkaline wastewater 1 and the inert gas 2 (air) of the first embodiment described above are introduced into a first rotating packed bed at a flow rate of 0.1 L/min and 6 L/min, respectively. Performing the stripping step (a), introducing the first gas 31 obtained by stripping into a third rotating packed bed at a flow rate of 6 L/min, and diluting hydrochloric acid 41 (pH 4-6) at 0.5 L/min. The flow rate is introduced into the third rotating packed bed to carry out the reaction step (b) to obtain a second gas 51 (in the form of white smoke) and a first recovered liquid 52. Then, a process water 6 and a second gas 51 obtained by the reaction are respectively introduced into a second rotating packed bed 7 at a flow rate of 2 L/min and 6 L/min to perform a capturing step (c), whereby the chlorine in the second gas 51 is made. The ammonium phosphate particles are captured into the second recovery liquid 72. Taking 60 L of acidic wastewater containing about 26,600 ppm of ammonia nitrogen as an example, after the 540 min recovery method of the ammonia-containing nitrogen wastewater of the second embodiment described above, about 18 kg of a recovery liquid containing no cobalt ions and containing 30 wt% of ammonium chloride can be obtained. The recovery of ammonia nitrogen is approximately 90%.

In summary, the method for recovering ammonia-containing nitrogen wastewater of the present invention, by using the stripping step (a), the reacting step (b), and the capturing step (c), only using the inert gas 2, the concentrated hydrochloric acid 4, The low-cost raw material such as the supplementary water 8 can completely separate the heavy metal ions in the waste water, effectively recover the first recovered liquid 52 containing a high concentration of ammonium chloride, and can avoid the discharge of ammonium chloride particles, ammonia gas, hydrogen chloride. The exhaust gas is suitable for industrial continuous processing, so that the object of the present invention can be achieved.

However, the above is only the embodiment of the present invention, and the scope of the invention is not limited thereto, and all the equivalent equivalent changes and modifications according to the scope of the patent application and the patent specification of the present invention are still The scope of the invention is covered.

Claims (12)

A method for recovering ammonia-containing wastewater, the ammonia-containing wastewater is an alkaline wastewater containing ammonia, comprising the steps of: (a) introducing the alkaline wastewater and an inert gas into a first rotating packed bed, respectively, through gas stripping Obtaining a first gas containing ammonia gas and an alkaline waste liquid; (b) mixing the first gas with dilute hydrochloric acid and reacting to obtain a second gas containing ammonium chloride particles and one containing ammonium chloride The first recovered liquid, wherein the diluted hydrochloric acid is obtained by combining the first recovered liquid and concentrated hydrochloric acid to react with the first gas; and (c) introducing a process water and the second gas into the first A second rotating packed bed is obtained by capturing ammonium chloride particles in the second gas to obtain a second recovered liquid containing ammonium chloride. The method for recovering ammonia-containing wastewater according to claim 1, wherein the alkaline wastewater is neutralized by an acidic wastewater containing ammonium ions and heavy metal ions and an excess of alkali, and is obtained by filtration. The method for recovering ammonia-containing wastewater according to claim 1, wherein in the step (b), the first gas is first mixed with ice water, and then mixed with the diluted hydrochloric acid to carry out a reaction. The method for recovering ammonia-containing wastewater according to claim 1, wherein in the step (c), the process water is combined with a supplementary water and returned to the second rotating packed bed to continue The ammonium chloride microparticles in the second gas are captured. The method for recovering ammonia-containing wastewater according to claim 3, wherein the ice water is the process water from the step (c). The method for recovering ammonia-containing nitrogen wastewater according to claim 1, wherein, in the step (c), the second recovered liquid is obtained, accompanied by obtaining a third gas, and the third gas is associated with the step (a) The inactive gases in the mixture are combined and recycled to continue the step (a). The method for recovering ammonia-containing wastewater according to claim 1, wherein in the step (a), the alkaline waste liquid is refluxed to the first rotating packed bed. The method for recovering ammonia-containing wastewater according to claim 1, wherein the step (b) is carried out in a washing column or a third rotating packed bed. The method for recovering ammonia-containing wastewater according to claim 2, wherein the pH of the alkaline wastewater obtained by filtration is 11 or more. The method for recovering ammonia-containing wastewater according to claim 1, wherein the pH of the dilute hydrochloric acid in the step (b) is 6 or less. The method for recovering ammonia-containing wastewater according to claim 1, wherein in the step (b), the mixing flow ratio of the first gas to the dilute hydrochloric acid is from 10:1 to 1000:1. The method for recovering ammonia-containing wastewater according to claim 1, wherein in the step (c), the mixing flow ratio of the second gas to the process water is from 3:1 to 500:1.