Method for reducing ammonia nitrogen content in acetylene purification wastewater

Abstract

The invention discloses a method for reducing ammonia nitrogen content in acetylene purification wastewater, and relates to the technical field of acetylene gas production, and the method comprises the following steps: purification discharged wastewater and water scrubber wastewater enter a wastewater buffer tank for preheating treatment, enter a high-efficiency desorption tower for negative pressure flash evaporation, and enter a high-efficiency desorption tower for high-efficiency desorption; the method comprises the following steps: separating out acetylene gas dissolved in wastewater, cooling the acetylene gas, feeding the cooled acetylene gas into a water washing tower for ammonia gas washing treatment, preheating ammonia-containing wastewater, feeding the preheated ammonia-containing wastewater into an ammonia distillation stripping tower from the top of an efficient desorption tower, introducing inert protective gas into the ammonia distillation stripping tower, and carrying out ammonia removal by a direct steam stripping method; according to the method, the content of ammonia nitrogen in the clean discharged reuse water can be effectively reduced, the on-site working environment is improved, the ammonia water generated by ammonia distillation can be recycled, economic benefits are achieved, the inert protective gas is introduced into the ammonia distillation stripping tower, then the ammonia is removed by adopting a direct steam stripping method, and the production cost is reduced. The steam usage amount in the ammonia distillation stripping tower can be effectively reduced, and the ammonia water yield is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of acetylene gas production, and particularly relates to a method for reducing the ammonia nitrogen content in acetylene purification wastewater. Background Art

[0002] At present, concentrated sulfuric acid is used for acetylene purification. The acetylene gas coming out from the positive water seal of dry acetylene first enters a water washing tower to cool the acetylene gas from 50°C to 35°C. In the first water washing tower, it is directly contacted with circulating cooling water for cooling and washing to completely remove the entrained carbide sludge, and then goes to the acetylene compressor. The compressed acetylene gas enters an alkali washing pre-cooling tower, where the acetylene gas is cooled from 35°C to 25°C and the CO 2 entrained in the acetylene gas is removed; the pre-cooled acetylene gas enters the second water washing tower, where it is cooled to ≤10°C. After removing most of the water entrained in the acetylene gas, it enters the concentrated sulfuric acid purification tower, where it is first dried and then purified. The purified acetylene gas enters a neutralization tower and is neutralized with 5-15% alkali solution to remove the impurity gas. After that, the purified and dried acetylene gas is sent to the next VCM synthesis process.

[0003] The crude acetylene gas undergoes processes such as water washing, sulfuric acid purification, and neutralization to remove impurities such as H 2 S, PH 3 and AsH 3 in the acetylene gas. During the production process, the amount of its purification liquid will continuously increase, and COD, ammonia nitrogen, etc. existing in the purification wastewater will gradually accumulate. Under certain conditions, ammonia gas will be precipitated, affecting the environment. Therefore, the present invention proposes a method for reducing the ammonia nitrogen content in acetylene purification wastewater to solve the deficiencies in the prior art. Summary of the Invention

[0004] Aiming at the above problems, the purpose of the present invention is to provide a method for reducing the ammonia nitrogen content in acetylene purification wastewater, which can effectively reduce the ammonia nitrogen content in the purified external recycled water, improve the on-site working environment, and the ammonia water generated by ammonia distillation can be recycled to achieve economic benefits. By introducing an inert protective gas into the ammonia distillation and stripping tower and then using the direct steam stripping method for ammonia removal, the steam consumption in the ammonia distillation and stripping tower can be effectively reduced, and the ammonia water output rate can be increased.

[0005] To achieve the above purpose, the present invention provides the following technical solutions: A method for reducing the ammonia nitrogen content in acetylene purification wastewater, comprising the following steps: Step 1: The purified external wastewater and the wastewater from the water washing tower enter a wastewater buffer tank for preheating treatment; Step 2: The purified external wastewater and the wastewater from the water washing tower after preheating treatment enter a high-efficiency stripping tower for vacuum flashing to strip out the dissolved acetylene gas in the wastewater; Step 3: The acetylene gas separated out is cooled down and then sent to a water washing tower for ammonia washing treatment. Step 4: The ammonia-containing wastewater generated in the negative pressure flash separation step is preheated and then enters the ammonia stripping column from the top of the high-efficiency stripping column. An inert protective gas is introduced into the ammonia stripping column, and then the direct steam stripping method is used for ammonia removal.

[0006] A further improvement lies in that: in the said Step 1, a filter tank is also arranged at the wastewater buffer tank. The clean discharged wastewater and the wastewater from the water washing tower are first filtered by the filter tank and then discharged into the wastewater buffer tank for preheating treatment.

[0007] A further improvement lies in that: the filter tank consists of at least three levels of filter meshes with different filtration pore diameters and a zeolite adsorption unit. After the clean discharged wastewater and the wastewater from the water washing tower enter the interior of the filter tank, they are first filtered by the filter meshes and then enter the zeolite adsorption unit for static adsorption.

[0008] A further improvement lies in that: when the acetylene gas separated out in the said Step 3 is cooled down and then sent to a water washing tower for ammonia washing treatment, clean water is used for washing in the water washing tower to wash and remove the ammonia gas entrained in the acetylene gas. The qualified acetylene gas after washing is sent to the gas holder through the acetylene gas main pipe.

[0009] A further improvement lies in that: the unqualified acetylene gas after washing in the said Step 3 enters the water washing tower again through the circulation pipeline for secondary clean water washing until the qualified acetylene gas is sent to the gas holder through the acetylene gas main pipe.

[0010] A further improvement lies in that: when introducing the inert protective gas into the ammonia stripping column in the said Step 4, specifically nitrogen gas is introduced for protection, and the introduced nitrogen gas forms an effective path for steam in the ammonia stripping column for steam stripping.

[0011] A further improvement lies in that: after using the direct steam stripping method for ammonia removal in the said Step 4, the ammonia-containing steam at the top of the ammonia stripping column is condensed and recovered by a total condenser to form 20wt% ammonia water and sent to the production unit for reuse.

[0012] A further improvement lies in that: after using the direct steam stripping method for ammonia removal in the said Step 4, the deammoniated water (ammonia nitrogen content ≤ 100ppm) at the bottom of the ammonia stripping column is cooled down and then returned to the original factory wastewater pond for reuse.

[0013] A further improvement lies in that: after using the direct steam stripping method for ammonia removal in the said Step 4, the ammonia-containing tail gas at the top of the ammonia stripping column is introduced into the tail gas absorption tower and is spray-absorbed by the sulfuric acid spray system in the tail gas absorption tower and then discharged up to standard. The spray absorption liquid is discharged to the sewage treatment system for treatment.

[0014] A further improvement lies in that the pH value of the sulfuric acid solution sprayed by the sulfuric acid spraying system in the tail gas absorption tower is controlled to be 6.2 - 6.5.

[0015] The beneficial effects of the present invention are as follows: The method of the present invention can effectively reduce the ammonia nitrogen content in the recycled water discharged from the acetylene purification process, improve the on-site working environment, and the ammonia water generated by ammonia distillation can be recycled to achieve economic benefits. By introducing an inert protective gas into the ammonia distillation stripping tower and then using the direct steam stripping method for ammonia removal, the steam consumption in the ammonia distillation stripping tower can be effectively reduced, the ammonia water output rate can be increased, and the pressure in the ammonia distillation stripping tower can be stabilized. The method of the present invention can also reduce the sulfuric acid consumption in the purification process, having good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic flow diagram of the method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0018] According to Figure 1 as shown, this embodiment proposes a method for reducing the ammonia nitrogen content in the acetylene purification wastewater, including the following steps: Step 1: A filter tank is set at the wastewater buffer tank. The purified wastewater discharged externally and the wastewater from the water washing tower first pass through the filter tank for filtration treatment, and then the purified wastewater discharged externally and the wastewater from the water washing tower enter the wastewater buffer tank for preheating treatment. The preheating treatment can adjust the temperature and viscosity of the wastewater to facilitate subsequent treatment of the wastewater. The filter tank consists of at least three levels of filter meshes with different filtration pore diameters and a zeolite adsorption unit. After the purified wastewater discharged externally and the wastewater from the water washing tower enter the interior of the filter tank, they first pass through the filter mesh for filtration and then enter the zeolite adsorption unit for static adsorption. In this embodiment, the zeolite in the zeolite adsorption unit is also subjected to modification treatment. The zeolite is boiled with an NaCl solution and then rinsed to neutral to remove impurities in the zeolite and increase its selectivity for NH4+, thereby improving the ammonia nitrogen purification ability of the zeolite adsorption unit; Step 2: The purified wastewater discharged externally and the wastewater from the water washing tower after preheating treatment enter the high-efficiency desorption tower for negative pressure flashing to desorb the dissolved acetylene gas in the wastewater. In the present invention, the connecting pipeline between the wastewater buffer tank and the high-efficiency desorption tower is a connecting pipeline provided with a heat preservation structure to ensure that the purified wastewater discharged externally and the wastewater from the water washing tower after preheating treatment do not lose heat when entering the interior of the high-efficiency desorption tower, avoiding the problem of preheating failure; Step 3: The desorbed acetylene gas is cooled and then sent to a water scrubber for ammonia washing. In the water scrubber, the acetylene gas is washed with clean water to remove the ammonia entrained in the acetylene gas. The qualified acetylene gas after washing is sent to the gas holder through the acetylene gas main pipe. The unqualified acetylene gas after washing enters the water scrubber again through the circulation pipeline for secondary washing with clean water until the qualified acetylene gas is sent to the gas holder through the acetylene gas main pipe; Step 4: The ammonia-containing wastewater generated in the negative pressure flashing desorption step is preheated and then enters the ammonia stripping column from the top of the high-efficiency desorption column. In the present invention, the ammonia stripping column also needs to be preheated by steam before startup to prevent local temperature drop at the top, which may lead to a decrease in the partial pressure at the top, and an inert protective gas is introduced into the ammonia stripping column, specifically nitrogen gas for protection. The introduced nitrogen gas forms an effective path for the steam in the ammonia stripping column, and then the direct steam stripping method is used for ammonia removal; after ammonia removal by the direct steam stripping method, the ammonia-containing steam at the top of the ammonia stripping column is condensed and recovered by a total condenser to form 20 wt% ammonia water and sent to the production unit for reuse. The deammoniated water (ammonia nitrogen content ≤ 100 ppm) at the bottom of the ammonia stripping column is cooled and then returned to the original factory wastewater tank for reuse. The ammonia-containing tail gas at the top of the ammonia stripping column is introduced into the tail gas absorption tower and is spray-absorbed by the sulfuric acid spray system in the tail gas absorption tower and then discharged up to standard. The spray absorption liquid is discharged to the sewage treatment system for treatment. During the process, the pH value of the sulfuric acid solution sprayed by the sulfuric acid spray system in the tail gas absorption tower is controlled at 6.2 - 6.5. By controlling the pH value of the sulfuric acid solution sprayed by the sulfuric acid spray system in the tail gas absorption tower at 6.2 - 6.5 to maintain a weak acidity, it can prevent excessive acidity from affecting the sulfuric acid content in the discharged tail gas and causing too high a temperature in the tail gas absorption tower, which will increase the corrosion of the fan and its connecting parts.

[0019] In this embodiment, by introducing nitrogen protective gas into the ammonia stripping column to form an effective path for the steam, the steam consumption can be effectively reduced. When nitrogen protective gas is not introduced, the processing capacity of the ammonia stripping tower is 50 m 3 / h, the steam consumption is 6.4 T / h, the top temperature needs to be controlled at 93 °C, and the top pressure is controlled at atmospheric pressure. At this time, the production of 20% ammonia water is the largest. However, it is found in the daily production process that when controlled according to these data, the pressure in the ammonia stripping tower cannot be guaranteed, and the pressure fluctuates violently frequently. At the same time, the steam consumption is nearly 1.2 times more than the theoretical value, greatly increasing the use cost. At the same time, the ammonia water concentration cannot be guaranteed, and long-term reflux concentration is required. During this process, ammonia gas will overflow, greatly affecting the on-site environment. After nitrogen filling in the ammonia stripping tower, by additionally supplementing non-reactive gas, the effective path of steam in the tower can be effectively guaranteed, and the pressure in the ammonia stripping tower can be stably and efficiently balanced, and the steam consumption can be reduced, and the output rate of ammonia water can be increased. The steam consumption is reduced from 6.4 T / h to 1.6 T / h, greatly saving the cost.

[0020] The method of the present invention can effectively reduce the ammonia nitrogen content in the recycled water discharged from the purification process, improve the on-site working environment, and the ammonia water generated by ammonia distillation can be recycled to achieve economic benefits. By introducing an inert protective gas into the ammonia distillation stripper and then using the direct steam stripping method for ammonia removal, the steam consumption in the ammonia distillation stripper can be effectively reduced, the ammonia water production rate can be increased, and the pressure in the ammonia distillation stripper can be stabilized. The method of the present invention can also reduce the consumption of purified sulfuric acid and has good economic benefits.

[0021] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only used to illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for reducing the ammonia nitrogen content in acetylene purification wastewater, characterized in that: The following steps are involved: Step 1: The cleaned wastewater and the water washing tower wastewater enter the wastewater buffer tank for preheating treatment; Step 2: The clean effluent and the water washing tower wastewater after preheating treatment enter the high-efficiency desorption tower for negative pressure flash evaporation to desorb the acetylene gas dissolved in the wastewater; Step 3: The acetylene gas separated out is sent to a water scrubber for ammonia scrubbing after cooling; Step 4: The ammonia-containing wastewater generated in the negative pressure flash stripping step is preheated and then enters the ammonia stripping tower from the top of the high-efficiency stripping tower, and an inert protective gas is introduced into the ammonia stripping tower, and then ammonia is removed by direct steam stripping.

2. A method for reducing ammonia nitrogen content in acetylene purification wastewater according to claim 1, characterized in that: The step one also includes setting a filter tank at the wastewater buffer tank, and the clean external wastewater and the water washing tower wastewater are first filtered through the filter tank and then discharged into the wastewater buffer tank for preheating treatment.

3. A method for reducing ammonia nitrogen content in acetylene purification wastewater according to claim 2, characterized in that: The filter tank is composed of at least 3 levels of filter screens with different filter apertures and zeolite adsorption units. After the clean external wastewater and the water washing tower wastewater enter the filter tank, they are first filtered through the filter screen and then enter the zeolite adsorption unit for static adsorption.

4. A method for reducing ammonia nitrogen content in acetylene purification wastewater according to claim 3, characterized in that: The acetylene gas separated out in the step 3 is sent to a water scrubber for ammonia scrubbing after being cooled. Clean water is used for scrubbing in the water scrubber to remove ammonia entrained in the acetylene gas. The qualified acetylene gas after scrubbing is sent to the gas cabinet through the acetylene gas main pipe.

5. A method for reducing ammonia nitrogen content in acetylene purification wastewater according to claim 1, characterized in that: The unqualified acetylene gas after washing in step three enters the water washing tower again through the circulation pipeline and is washed with clean water for the second time, until the washed qualified acetylene gas is sent to the gas cabinet through the acetylene gas main pipe.

6. A method for reducing ammonia nitrogen content in acetylene purification wastewater according to claim 5, characterized in that: In the step 4, when an inert protective gas is introduced into the ammonia stripping tower, specifically nitrogen is introduced for protection, and the introduced nitrogen is used to form an effective path for steam in the ammonia stripping tower to provide steam for stripping.

7. A method for reducing ammonia nitrogen content in acetylene purification wastewater according to claim 6, characterized in that: After ammonia is removed by direct steam stripping in step 4, the ammonia-containing vapor at the top of the ammonia stripping tower is condensed and recovered through a total condenser to form 20 wt% ammonia water which is sent to the production unit for reuse.

8. A method for reducing ammonia nitrogen content in acetylene purification wastewater according to claim 7, characterized in that: After ammonia is removed by direct steam stripping in step 4, the deammonified water (ammonia nitrogen content ≤ 100 ppm) in the bottom of the ammonia stripping tower is returned to the original wastewater pool for reuse after cooling.

9. A method for reducing ammonia nitrogen content in acetylene purification wastewater according to claim 8, characterized in that: After ammonia is removed by direct steam stripping in step 4, the ammonia-containing tail gas at the top of the ammonia stripping tower is introduced into the tail gas absorption tower, sprayed and absorbed by the sulfuric acid spray system in the tail gas absorption tower, and then discharged in compliance with the standards, and the spray absorption liquid is discharged to the sewage treatment system for treatment.

10. A method for reducing ammonia nitrogen content in acetylene purification wastewater according to claim 9, characterized in that: The pH value of the sulfuric acid solution sprayed by the sulfuric acid spraying system in the tail gas absorption tower is controlled to be 6.2-6.5.

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