Synthetic ammonia condensate treatment system and process thereof

Abstract

The invention provides a synthetic ammonia condensate treatment system and process, and relates to the technical field of inorganic chemical engineering. The system comprises a stripping tower, a carbonate blow-off tower, a biochemical pool, an air floatation pool, an ultrafiltration system and a reuse water pool, and volatile substances, carbonate ions, organic matters, suspended matters and small molecular particles in condensate water are removed step by step. Volatile substances in the stripping tower are removed through medium-pressure steam, and tail gas is used as raw material gas for synthesis ammonia production; the carbonate blowing tower is used for removing carbonate ions by heating compressed air, and tail gas is mainly carbon dioxide. The biochemical pool degrades organic matters, the air floatation pool removes suspended matters, the ultrafiltration system further filters small-molecular particles, and finally produced water is stored in the reuse water pool and serves as boiler make-up water or industrial reuse water. Through treatment, NH3-N in the condensate water is reduced from 1200 ppm to less than or equal to 5 ppm, COD is reduced from 1000 ppm to less than or equal to 50 ppm, and the conductivity is reduced from 4000 [mu] S / cm to less than or equal to 1000 [mu] S / cm. The device realizes efficient purification and recycling of condensate water, and is economical and environment-friendly.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic chemical industry, and in particular to a synthetic ammonia condensate treatment system and process thereof. Background Art

[0002] In the production process of synthetic ammonia, the process condensate is usually treated in a stripping tower in countercurrent contact with medium-pressure steam to remove ammonia (NH 3 ), methanol and formaldehyde and other impurities. The main indicators of the process condensate after stripping treatment are as follows: pH value: 6-9; NH 3 -N: ≤100ppm; Cl - : ≤700mg / L; conductivity: ≤4000μS / cm; COD: ≤400ppm; temperature: 50℃.

[0003] However, this part of the process condensate still has the problem of high conductivity, mainly because it contains carbonate ions (CO 3 2- ), and because it contains trace amounts of flammable gas, there are safety risks in recycling it into the circulating water system. This part of the condensate is difficult to directly reuse into the circulating water system or replace desalted water as boiler water, and is usually directly discharged into the sewage treatment system. This not only increases the burden of sewage treatment, but also causes a waste of water resources.

[0004] Existing treatment technologies (such as publication number CN1341695A, which discloses a synthetic ammonia condensate recovery process, using an anionic and cationic resin mixed bed to treat the synthetic ammonia process condensate) can reduce the conductivity to a certain extent, but have poor adaptability to water quality fluctuations, especially under production fluctuations or start-up and shutdown conditions, which easily leads to unstable treatment effects. At the same time, the mixed bed technology cannot effectively treat organic matter in the condensate. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a synthetic ammonia condensate treatment system and process thereof, which adopts the following technical solutions:

[0006] A synthetic ammonia condensate treatment system comprises a stripping tower and a carbonate removal tower, a biochemical pool, a flotation pool, an intermediate water pool, an ultrafiltration system, and a recycled water pool, which are sequentially pumped and connected. The stripping tower is used to remove volatile substances in the synthetic ammonia process condensate, and the volatile substances include NH 3 , methanol; the carbonate removal tower is used to remove CO in the condensate of the synthetic ammonia process by countercurrent contact with hot compressed air. 3 2-, to reduce the conductivity of the condensate of the synthetic ammonia process; the biochemical pool is used to remove organic matter; the flotation pool is used to remove suspended matter; the intermediate pool water is used to temporarily store the treated water produced by the flotation pool to provide stable water inlet conditions for the ultrafiltration system; the ultrafiltration system is used to remove small molecular particles; the reuse pool water is used to store the water produced by the ultrafiltration system.

[0007] Furthermore, the carbonate removal tower in the above system adopts a multi-layer floating valve tray structure.

[0008] Furthermore, the system also includes a compressed air heat exchanger, which is arranged before the air inlet at the bottom of the carbonate removal tower and is used to perform heat exchange on the compressed air entering the carbonate removal tower.

[0009] Furthermore, the compressed air heat exchanger is a steam heat exchanger, and the heat exchange medium of the steam heat exchanger is the medium-pressure steam entering the stripping tower.

[0010] At the same time, the present invention also proposes a synthetic ammonia condensate treatment process, which adopts the above-mentioned synthetic ammonia condensate treatment system and includes the following steps:

[0011] Step 1: The process condensate produced during the synthetic ammonia production process is pumped into a stripping tower to remove ammonia (NH 3 ), methanol and other volatile substances to obtain a condensate after stripping;

[0012] Step 2: The stripped condensate obtained in step 1 is pumped into the top of a carbonate removal tower, and countercurrently contacts with the heated compressed air entering from the bottom of the carbonate removal tower, and the carbonate ions in the stripped condensate are blown off to obtain a decarbonated condensate;

[0013] Step 3: sending the decarbonized condensate obtained in step 2 to a biochemical pool, adding microbial flora to the biochemical pool to degrade organic matter in the decarbonized condensate and remove part of the suspended matter, thereby obtaining a biochemical treatment liquid;

[0014] Step 4: sending the biochemical treatment liquid obtained in step 3 to the flotation tank, adding flocculants to the biochemical treatment liquid to aggregate the suspended matter, and then further removing the suspended matter and colloidal particles in the biochemical treatment liquid by releasing fine bubbles to obtain flotation water;

[0015] Step 5: temporarily store the flotation water obtained in step 3 in the intermediate pool water, pump it to the ultrafiltration system, remove small molecular particles and trace suspended matter in the condensate through the ultrafiltration membrane, further reduce the COD of the condensate, and obtain ultrafiltration water;

[0016] Step 6: Store the ultrafiltration water in a reuse water pool and use it as boiler feed water or to replace desalted water.

[0017] Furthermore, the product of the stripping tower in step 1 also includes stripping tail gas, the main component of which is ammonia (NH 3 ) Volatile substances such as methanol and formaldehyde can be introduced as raw gas into the second-stage hydrogenation converter of the synthetic ammonia production process to improve resource utilization efficiency.

[0018] Furthermore, in the above step 1, the pressure inside the stripping tower is 0.15 MPa, the medium-pressure steam temperature is 150° C., the stripping time is 1 to 2 hours, and the liquid-to-gas ratio is 1:0.8.

[0019] Furthermore, the product of the carbonate removal tower in step 2 also includes CO 2 , vented through the top of the carbonate removal tower.

[0020] Furthermore, in the above step 2, the temperature of the compressed air entering the carbonate removal tower is 80-100° C., the gas-liquid ratio is 1:2-1:3, and the residence time of the condensate in the carbonate removal tower is 20-30 minutes.

[0021] Furthermore, the dissolved oxygen (DO) concentration of the biochemical pool is controlled at 3 to 5 mg / L, and the hydraulic retention time (HRT) is 6 to 8 hours.

[0022] Through the above technical scheme, the present invention uses a multi-stage combined treatment process of a stripping tower, a carbonate removal tower, a biochemical pool, a flotation pool, and an ultrafiltration system to grade and remove volatile substances, carbonate ions, organic matter, and suspended particles in the condensate of the synthetic ammonia process. Compared with the prior art, the present invention can more efficiently reduce the chemical oxygen demand (COD) and conductivity in the condensate, making the treatment quality of the condensate of the synthetic ammonia process more stable and meeting the requirements of boiler water replenishment and industrial reuse. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of a system according to an embodiment of the present invention.

[0024] The accompanying drawings are numerals: 1. stripping tower; 2. carbonate removal tower; 3. biochemical pool; 4. flotation pool; 5. intermediate water pool; 6. ultrafiltration system; 7. recycled water pool; 8. heat exchanger. DETAILED DESCRIPTION

[0025] Hereinafter, the technology in the embodiments of the present invention will be described clearly and completely in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments; based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0026] Reference Figure 1 This embodiment provides a synthetic ammonia condensate treatment system and process thereof, which is a specific application of a condensate treatment system in a synthetic ammonia section of a chlor-alkali plant. The synthetic ammonia condensate comes from the process condensate generated in the synthetic ammonia process. The condensate mainly contains volatile substances (such as ammonia, methanol and formaldehyde), organic matter, carbonate ions and other impurities. The initial components of the condensate are: NH 3 -N 1200ppm, COD 1000ppm, Cl - 700mg / L, CO 3 2- 300ppm, conductivity 4000μS / cm, pH between 6 and 9.

[0027] In order to treat the above-mentioned condensed water, this embodiment adopts a multi-stage treatment system consisting of a stripping tower 1, a carbonate removal tower 2, a biochemical pool 3, a flotation pool 4, an intermediate water pool 5, an ultrafiltration system 6 and a reuse water pool 7, and combines the appropriate process flow to treat the condensed water step by step, ultimately achieving the goal of resource reuse.

[0028] Reference Figure 1 , the synthetic ammonia condensate treatment process steps of this embodiment are:

[0029] Step 1, stripping and degassing treatment: The condensed water is first pumped to the top of the stripping tower 1, and countercurrently contacts with the medium-pressure steam (150°C, 0.15MPa) entering from the bottom, and the volatile substances in the condensed water are removed by gas-liquid mass transfer. During the treatment process, ammonia, methanol and formaldehyde in the condensed water are stripped into the tail gas. After stripping treatment, the NH 3 -N concentration dropped to ≤100ppm, COD dropped to 700ppm, and the other components remained basically stable. The main components of the stripping tail gas are ammonia (accounting for 60% to 75%), methanol (accounting for 10% to 20%) and formaldehyde (accounting for 1% to 5%). The tail gas is transported to the second-stage hydrogenation converter of the synthetic ammonia process and recycled as raw gas.

[0030] Step 2, stripping and carbon removal treatment: The condensed water after stripping treatment is pumped to the top of the carbonate stripping tower 2, and countercurrently contacts with the heated compressed air entering from the bottom to further remove carbonate ions in the condensed water. The compressed air is heated by the compressed air heat exchanger 8 arranged at the bottom of the stripping tower, and the heat exchange medium is the medium-pressure steam used by the stripping tower 1. During the treatment process, CO in the condensed water 3 2-The concentration is reduced from 300ppm to ≤50ppm, and the conductivity is reduced to ≤3000μS / cm. The tail gas generated during the stripping process is mainly carbon dioxide (accounting for 70% to 90%), which is directly discharged through the top of the carbonate stripping tower 2, or the carbon dioxide is recycled as needed.

[0031] Step 3, biochemical treatment: The condensed water after decarbonization enters the biochemical pool 3, and the organic matter (such as methanol and formaldehyde) in the water is degraded by adding well-adapted microbial flora (such as salt-tolerant aerobic bacteria). Under the action of the aeration device, the dissolved oxygen concentration in the pool is maintained at 35 mg / L, and the hydraulic retention time is 68 hours to ensure that the organic matter is fully degraded. The COD of the treated biochemical liquid is reduced to 200ppm, and the suspended matter concentration is reduced to 50-100mg / L, providing stable water inlet for subsequent treatment.

[0032] Step 4, flotation treatment: The condensate after biochemical treatment is sent to the flotation tank 4, where the suspended matter is aggregated by adding flocculants (such as polyaluminium chloride) to the water, and the suspended matter floats to the water surface by releasing fine bubbles through dissolved air. The scum is cleaned in time by the scraper device, and the concentration of suspended matter in the produced water is reduced to ≤10mg / L, COD is reduced to 150ppm, and the water quality is further optimized.

[0033] Step 5, ultrafiltration treatment: The water after flotation treatment is temporarily stored in the intermediate water tank 5, and then pumped to the ultrafiltration system 6. The pore size of the ultrafiltration membrane is 0.01-0.05μm, which removes small molecular particles and trace suspended matter in the water by filtration, and further reduces the COD in the water. After treatment, the COD of the produced water is reduced to ≤50ppm, the suspended matter concentration is reduced to ≤1mg / L, and the conductivity is reduced to ≤1000μS / cm.

[0034] Step 6, recycled water treatment: The ultrafiltration water after ultrafiltration treatment is stored in the recycled water pool 7. The water quality indicators of the final water are: COD ≤ 50ppm, conductivity ≤ 1000μS / cm, suspended solids (SS) ≤ 1mg / L, pH between 6 and 8, which can be used as boiler feed water or desalted water alternative water source.

[0035] Through the above process flow, the main pollutants in the process condensate water in this embodiment are gradually removed, and the treated water quality meets the requirements of boiler feed water or industrial reuse: ammonia nitrogen (NH3-N): ≤5ppm; chemical oxygen demand (COD): ≤50ppm; conductivity: ≤1000μS / cm; suspended solids (SS): ≤1mg / L.

[0036] In addition, the stripping tail gas enters the second-stage hydrogenation converter of the synthetic ammonia process as raw gas. The main component of the stripping tail gas is carbon dioxide, which can be vented from the top or recycled to achieve effective recycling of resources.

[0037] This embodiment realizes efficient purification and resource utilization of synthetic ammonia condensate water through the combination of multi-stage treatment units: the combination of the stripping tower and the carbonate blow-off tower significantly reduces the concentration of volatile substances and carbonate ions in the condensate water; the biochemical pool has a strong ability to degrade organic matter, ensuring the deep removal of pollutants; the combination of flotation and ultrafiltration ensures the thorough removal of suspended matter and small molecular particles in the water; the overall system makes full use of thermal energy resources such as medium-pressure steam, reduces operating costs, and realizes the recycling of tail gas and water.

Claims

1. A synthetic ammonia condensate treatment system, comprising a stripping tower and a carbonate blow-off tower, a biochemical tank, a flotation tank, an intermediate water tank, an ultrafiltration system, and a recycled water tank, which are sequentially pumped and connected, wherein the stripping tower is used to remove volatile substances in the synthetic ammonia process condensate, wherein the volatile substances include NH3 and methanol; the carbonate blow-off tower is used to blow off CO3 in the synthetic ammonia process condensate by countercurrent contact with hot compressed air. 2- , to reduce the conductivity of the condensate of the synthetic ammonia process; the biochemical pool is used to remove organic matter; the flotation pool is used to remove suspended matter; the intermediate pool water is used to temporarily store the treated water produced by the flotation pool to provide stable water inlet conditions for the ultrafiltration system; the ultrafiltration system is used to remove small molecular particles; the reuse pool water is used to store the water produced by the ultrafiltration system.

2. A synthetic ammonia condensate treatment system according to claim 1, characterized in that: The carbonate removal tower adopts a multi-layer floating valve tray structure.

3. A synthetic ammonia condensate treatment system according to claim 2, characterized in that: The system further comprises a compressed air heat exchanger, which is arranged before the air inlet at the bottom of the carbonate removal tower and is used for performing heat exchange on the compressed air entering the carbonate removal tower.

4. A synthetic ammonia condensate treatment system according to claim 3, characterized in that: The compressed air heat exchanger is a steam heat exchanger, and the heat exchange medium of the steam heat exchanger is the medium-pressure steam entering the stripping tower.

5. A process for treating synthetic ammonia condensate, characterized in that: The synthetic ammonia condensate treatment system as claimed in claim 4 comprises the following steps: Step 1: Pumping the process condensate generated in the synthetic ammonia production process into a stripping tower to remove ammonia, methanol and other volatile substances in the process condensate to obtain a stripped condensate; Step 2: The stripped condensate obtained in step 1 is pumped into the top of a carbonate removal tower, and countercurrently contacts with the heated compressed air entering from the bottom of the carbonate removal tower, and the carbonate ions in the stripped condensate are blown off to obtain a decarbonated condensate; Step 3: sending the decarbonized condensate obtained in step 2 to a biochemical pool, adding microbial flora to the biochemical pool to degrade organic matter in the decarbonized condensate and remove part of the suspended matter, thereby obtaining a biochemical treatment liquid; Step 4: sending the biochemical treatment liquid obtained in step 3 to the flotation tank, adding flocculants to the biochemical treatment liquid to aggregate the suspended matter, and then further removing the suspended matter and colloidal particles in the biochemical treatment liquid by releasing fine bubbles to obtain flotation water; Step 5: temporarily store the flotation water obtained in step 3 in the intermediate pool water, pump it to the ultrafiltration system, remove small molecular particles and trace suspended matter in the condensate through the ultrafiltration membrane, further reduce the COD of the condensate, and obtain ultrafiltration water; Step 6: Store the ultrafiltration water in a reuse water pool and use it as boiler feed water or to replace desalted water.

6. A synthetic ammonia condensate treatment process according to claim 5, characterized in that: The product of the stripping tower in step 1 also includes stripping tail gas, and the stripping tail gas can be introduced into the second-stage hydrogenation converter of the synthetic ammonia production process as raw gas.

7. A synthetic ammonia condensate treatment process according to claim 5, characterized in that: In step 1, the pressure in the stripping tower is 0.15 MPa, the temperature of the medium-pressure steam is 150° C., the stripping time is 1 to 2 hours, and the liquid-to-gas ratio is 1:0.

8.

8. The process for treating synthetic ammonia condensate according to claim 5, characterized in that: The product of the carbonate removal tower in step 2 also includes CO2, which is discharged through the top of the carbonate removal tower.

9. A synthetic ammonia condensate treatment process according to claim 5, characterized in that: In the step 2, the temperature of the compressed air entering the carbonate removal tower is 80-100° C., the gas-liquid ratio is 1:2-1:3, and the residence time of the condensate in the carbonate removal tower is 20-30 minutes.

10. A synthetic ammonia condensate treatment process according to claim 5, characterized in that: In step 3, the dissolved oxygen concentration of the biochemical pool is controlled at 3-5 mg / L, and the hydraulic retention time is 6-8 hours.

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