Advanced treatment system and treatment process for carbon black wastewater of natural gas cracking acetylene preparation device

Abstract

The invention discloses an advanced treatment system and treatment process for carbon black wastewater of a natural gas cracking acetylene preparation device. The system comprises a carbon black water storage tank, an automatic dosing system, a mixer, a thickener, a stripping tower, a biochemical pool, a membrane separation system, a circulating water system and a torch system. The wastewater is subjected to flocculating settling to remove carbon black particles, volatile gas is removed through a stripping tower, COD and ammonia nitrogen are degraded through a biochemical pool, the wastewater enters a membrane separation system to be deeply filtered, purified water is recycled to a circulating cooling system, and concentrated water flows back to a thickener. The system further comprises a homogenizing tank and a centrifugal dehydrator which are used for dehydrating the carbon black mud, and dried mud cakes are produced and used for incineration. The membrane separation system integrates a waste membrane regeneration process, the service life of the membrane is prolonged, and the operation cost is reduced. Through multi-stage treatment, efficient purification and resource utilization of the carbon black wastewater are achieved, the effluent quality reaches the industrial reuse water standard, and the method is suitable for wastewater treatment in the field of natural gas chemical industry.

Description

Technical Field

[0001] The invention relates to the technical field of natural gas chemical industry, and in particular to a carbon black wastewater deep treatment system and treatment process of a natural gas cracking acetylene production device. Background Art

[0002] In the field of natural gas chemical industry, in the process of using natural gas to crack acetylene, natural gas and oxygen undergo partial oxidation reaction in the acetylene furnace to generate acetylene and acetylene tail gas while carbon black is produced. These reaction gases are washed and purified with desalted water or softened water to produce sewage containing a large amount of carbon black particles, which is called carbon black water in the industry. In the production process, a large amount of carbon black water will be used as circulating cooling water for the cracking reaction. In order to ensure the water quality index of the circulating water, it is necessary to continuously add a certain amount of fresh water to the system, and at the same time, about 5% of the carbon black water should be discharged to the outside of the system. About 50 tons / hour. Components: PH = 8.8, COD ≤ 450mg / L, volatile components carbon dioxide about 0.19%, CH4 0.003%, C2H4 4.13ppm, C2H2 0.11%, C4H2 0.004% temperature about 40℃. Since the discharged carbon black water contains about 30-50mg / L of carbon black and contains flammable media, it will affect subsequent utilization and can generally only be discharged as sewage. With the improvement of environmental protection and water conservation goals, it is urgent to consider the recycling of carbon black water. The traditional separation process is generally carried out through flocculation, flotation, sublimation and other steps. Since the carbon black particles are small, less than 10 microns, it is difficult to completely separate them by sedimentation and centrifugation. The carbon black water does not need to be reused after treatment, but is sent to the sewage treatment system. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a deep treatment system and treatment process for carbon black wastewater from a natural gas cracking acetylene production device, which adopts the following technical solutions:

[0004] A deep treatment system for carbon black wastewater from a natural gas cracking acetylene production unit includes a carbon black water storage tank, an automatic dosing system, a mixer, a thickener, a stripping tower, a biochemical pool, and a membrane separation system. Each part is pumped and connected in sequence to form a complete treatment process. Specifically:

[0005] The carbon black water storage tank is used to store carbon black wastewater from the natural gas cracking acetylene production unit, providing a stable source of wastewater;

[0006] The automatic dosing system promotes the flocculation and sedimentation of carbon black particles by adding flocculant solution to the wastewater;

[0007] The mixer is used to achieve full mixing of carbon black wastewater and flocculant to ensure uniform flocculation effect;

[0008] The thickener receives the mixed wastewater and separates the carbon black particles by gravity sedimentation to obtain clarified wastewater and concentrated carbon black sludge;

[0009] The stripping tower is used to remove combustible volatile components from clarified wastewater, including methane and ethylene;

[0010] The biochemical pool receives the wastewater treated by the stripping tower and removes organic pollutants such as COD and ammonia nitrogen in the wastewater through microbial degradation;

[0011] The membrane separation system deeply filters the wastewater through an organic membrane to remove residual carbon black particles and trace organic matter, so that the water quality meets the reuse standards.

[0012] Furthermore, the system also includes a homogenization tank and a centrifugal dehydrator. The homogenization tank is used to perform secondary mixing on the concentrated carbon black mud to optimize the subsequent dehydration effect; the centrifugal dehydrator dehydrates the carbon black mud after secondary mixing in the homogenization tank to produce dry carbon black mud and separation liquid.

[0013] Furthermore, the gas phase outlet at the top of the stripping tower is connected to a flare system for treating the combustible volatile components generated during the stripping process.

[0014] Furthermore, the concentrate outlet pump of the membrane separation system is connected to the feed inlet of the thickener, so that the concentrate of the membrane separation system can flow back to the thickener.

[0015] At the same time, the present invention also proposes a natural gas cracking acetylene device carbon black wastewater deep treatment process, using the natural gas cracking acetylene device carbon black wastewater deep treatment system, comprising the following steps:

[0016] Step 1, carbon black water storage and preliminary mixing: the carbon black wastewater enters the carbon black water storage tank through a pipeline for storage, the wastewater in the storage tank is added with a flocculant solution through an automatic dosing system, and is fully mixed in a mixer to form a uniform mixed solution;

[0017] Step 2, thickener sedimentation: the mixed liquid enters the thickener, and the clarified wastewater and concentrated carbon black mud are separated by gravity sedimentation. The clarified wastewater overflows from the top of the thickener and enters the stripping tower for treatment. The concentrated carbon black mud is concentrated by the scraper and discharged from the bottom;

[0018] Step 3, stripping tower to remove volatile components: the clarified wastewater separated by the thickener enters the stripping tower, and the combustible volatile components in the wastewater, such as methane (CH4), ethylene (C2H4), etc., are removed by stripping;

[0019] Step 4, biochemical treatment: the wastewater treated by the stripping tower enters the biochemical pool, where the organic pollutants, COD and ammonia nitrogen in the wastewater are further degraded by microorganisms;

[0020] Step 5, membrane separation deep treatment: the wastewater after biochemical treatment enters the membrane separation system and is further filtered through the organic membrane to completely remove carbon black particles and trace organic matter;

[0021] Step 6, recycling and reuse: The treated carbon black wastewater meets the desalted water standard and enters the circulating water system for recycling in production equipment to replace desalted water.

[0022] Furthermore, the organic membrane in step 5 uses a waste reverse osmosis membrane from a water treatment device in a thermal power plant, and the waste reverse osmosis membrane can be converted and regenerated. After cleaning the contamination layer on the membrane surface, the polyamide skin layer is oxidized to make the regenerated membrane show nanofiltration or ultrafiltration performance, and the carbon black particles are removed with water.

[0023] Furthermore, it also includes step 7, homogenization mixing and dehydration treatment: the concentrated carbon black mud at the bottom of the thickener in the above step 2 enters the homogenization tank from the bottom of the thickener, and is mixed with the flocculant for the second time to enhance the dehydration effect. After dehydration by a centrifugal dehydrator, carbon black mud and separation liquid are obtained. The separation liquid is returned to the carbon black water storage tank. After the carbon black mud is dried, it can be transported to heat incineration.

[0024] 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

[0025] Figure 1 It is a process flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0026] 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.

[0027] Embodiment 1:

[0028] Reference Figure 1 This embodiment provides a deep treatment system for carbon black wastewater from a natural gas cracking acetylene production unit, including a carbon black water storage tank, an automatic dosing system, a mixer, a thickener, a homogenizer, a centrifugal dehydrator, a stripping tower, a biochemical pool, a membrane separation system, a circulating water system, and a flare system. Each part is pumped and connected in sequence to form a complete treatment process.

[0029] The carbon black water storage tank is used to store carbon black wastewater from the acetylene production section. The storage tank is made of corrosion-resistant materials and has a designed volume of 50m 3 , which can stably receive wastewater containing carbon black particles and ensure uniform wastewater flow. The storage tank is equipped with a liquid level sensor to monitor the liquid level and transport the carbon black wastewater to the mixer through the outlet pipe and pump;

[0030] The automatic dosing system is arranged on the pipeline between the carbon black water storage tank and the mixer. The system includes a metering pump and a flocculant storage tank. The metering pump injects flocculant (such as polyaluminium chloride solution) from the flocculant storage tank into the wastewater at a concentration of 100-200ppm according to the flow ratio. The flocculant and the wastewater are preliminarily mixed in the pipeline to promote the flocculation of carbon black particles.

[0031] The mixer is used to further evenly mix the carbon black wastewater and flocculant after dosing. The wastewater retention time flowing through the mixer is 30 seconds to ensure that it is evenly mixed and then enters the thickener through the pipeline;

[0032] The design flow rate of the thickener is 50m 3 / h, mainly separating carbon black particles by gravity settling. The wastewater is divided into two parts in the thickener: clarified wastewater overflows from the top and enters the stripping tower for subsequent treatment, while concentrated carbon black sludge is discharged from the bottom;

[0033] The stripping tower receives the clarified wastewater discharged from the top of the thickener, and removes the combustible volatile components (such as CH4 and C2H4) in the wastewater under the conditions of operating pressure of 0.1-0.3MPa and operating temperature of 40-60℃. The combustible volatile components are discharged through the gas phase outlet at the top of the stripping tower;

[0034] The biochemical pool receives the wastewater treated by the stripping tower and uses microorganisms to degrade the COD and ammonia nitrogen in the wastewater. The biochemical pool is equipped with an aeration device to control the dissolved oxygen concentration to 2 mg / L. The removal rates of COD and ammonia nitrogen reach over 90% and 85% respectively.

[0035] The membrane separation system uses a regenerative reverse osmosis membrane (RO membrane) to deeply filter the wastewater after biochemical treatment to remove trace carbon black particles and organic matter. The operating pressure is 1MPa and the purified water recovery rate is 75%. The concentrated water produced by membrane separation is returned to the thickener inlet through a reflux pump.

[0036] Preferably, the system also includes a homogenizing tank and a centrifugal dehydrator. The homogenizing tank receives the concentrated carbon black mud discharged from the bottom of the thickener, and adds an appropriate amount of flocculant (concentration 50-100ppm) for secondary mixing. The homogenizing tank is provided with an agitator with a stirring speed of 60rpm to ensure uniform distribution of mud and water and optimize the subsequent dehydration effect. The centrifugal dehydrator is used to dehydrate the carbon black mud after secondary mixing in the homogenizing tank. The centrifugal dehydrator is designed as a high-speed horizontal centrifugal device with an operating speed of 3000rpm, which can dehydrate the concentrated carbon black mud to a moisture content of less than 40%. The dehydrated products include: dry carbon black mud and separation liquid. The dry carbon black mud can be transported by a screw conveyor and incinerated or recycled as a heating fuel. The separation liquid returns to the carbon black water storage tank through a reflux pipe and is mixed with new wastewater for reprocessing.

[0037] Preferably, the gas phase outlet at the top of the stripping tower is connected to a flare system for treating the combustible volatile components generated during the stripping process. The flare system burns and treats the volatile gas to ensure environmental protection and safety.

[0038] Preferably, the concentrate produced by the membrane separation system is returned to the thickener through a reflux pump and mixed with new wastewater from the thickener for treatment, thereby reducing the amount of concentrate discharged and improving the water recovery rate.

[0039] Embodiment 2:

[0040] This example describes a treatment process for carbon black wastewater based on the system provided in Example 1, which is mainly applicable to small and medium-sized natural gas cracking acetylene production units. The process flow is as follows:

[0041] Step 1, carbon black water storage tank stores wastewater:

[0042] The carbon black water storage tank is used to store carbon black wastewater from the acetylene production unit. The carbon black particle concentration in the wastewater is 31.5-47.8 mg / L, the COD concentration is 447.6 mg / L, and the ammonia nitrogen concentration is 39.2 mg / L. The carbon black wastewater is pumped to the mixer to ensure stable water supply. Through the automatic dosing system, 110-195 ppm of polyaluminium chloride (PAC) solution is added in proportion according to the wastewater flow rate to promote the flocculation of carbon black particles. The wastewater then enters the mixer. After the flocculant is fully mixed with the wastewater, the particle size increases from 0.1-2 μm to 5-20 μm, creating conditions for the subsequent separation process.

[0043] 2. Thickener sedimentation separation:

[0044] The mixed wastewater enters the thickener, where the carbon black particles are separated by gravity settling. The separated clarified wastewater overflows from the top of the thickener, the COD concentration is reduced to 296.3-308.7 mg / L, the carbon black particle concentration is reduced to 1.6-4.2 mg / L, and is pumped to the stripping tower for further treatment; the concentrated carbon black sludge is discharged from the bottom for standby treatment.

[0045] 3. Stripping tower removes volatile gases:

[0046] The clarified wastewater enters the stripping tower, where volatile gases such as methane and ethylene are removed by stripping at 0.21-0.28 MPa and 48.2-55.4°C, with a removal efficiency of 91.2%-93.6%. The gas phase outlet at the top of the stripping tower is connected to the flare system to burn volatile gases and avoid environmental pollution.

[0047] 4. Biochemical pools degrade pollutants:

[0048] The wastewater treated by steam stripping is pumped into the biochemical pool, where microbial metabolism degrades COD and ammonia nitrogen in the wastewater. The aeration device controls the dissolved oxygen concentration at 1.9-2.3 mg / L, and the COD removal rate reaches 83.5%-86.8%, and the ammonia nitrogen removal rate is 78.7%-81.9%.

[0049] 5. Membrane separation depth filtration:

[0050] The wastewater after biochemical treatment enters the membrane separation system, using an organic membrane to further remove trace carbon black particles and organic matter at a pressure of 0.92-1.15 MPa. The recovery rate of purified water is 74.5%-76.3%, and the concentrated water is returned to the thickener for further treatment.

[0051] 6. Recycling water system to reuse purified water:

[0052] The purified wastewater enters the circulating water system and is used as cooling circulating water for the acetylene unit, replacing fresh water sources and realizing wastewater resource utilization.

[0053] Through the above treatment process, the final effluent water quality of this embodiment meets the following standards: COD concentration ≤47.2-52.5 mg / L; ammonia nitrogen concentration ≤4.8-5.3 mg / L; carbon black particle concentration ≤0.9-1.3 mg / L; purified water resource reuse rate is about 75%, and the concentrated water discharge volume is reduced by about 70%.

[0054] Preferably, the organic membrane in step 5 adopts the waste reverse osmosis membrane from the water treatment device of the thermal power plant, and the waste reverse osmosis membrane can be converted and regenerated. The specific treatment steps include: taking out the waste reverse osmosis membrane from the membrane assembly, using a cleaning solution to remove the contamination layer on the membrane surface, the cleaning solution components include an alkaline solution (NaOH, concentration 0.5-1wt%), an acidic solution (citric acid, concentration 0.2-0.5wt%); the cleaned membrane is immersed in a sodium hypochlorite (NaClO, concentration 500-1000ppm) solution for 5-10 minutes, the solution pH is 6-7, the temperature is 20-25°C, and the membrane performance is ensured to be restored to 80%-90% of the original performance, and the water flux is 40-60L / m 2 h, interception rate (COD ≥ 80%, carbon black particles ≥ 90%); the regenerated membrane is reloaded into the membrane separation system for use.

[0055] Embodiment 2:

[0056] On the basis of Example 1, this example optimizes the carbon black mud processing part of the thickener, adds a homogenizing tank and a centrifugal dehydrator, and improves the processing efficiency and resource utilization level of the carbon black mud.

[0057] The steps of this embodiment are the same as those of the process of embodiment 1. After the wastewater is stored in the carbon black water storage tank and the flocculant is added to the automatic dosing system, it is processed by the mixer, the thickener and the stripping tower in sequence to complete the flocculation, sedimentation and volatile gas removal of the wastewater. The steps also include the following steps:

[0058] 7. Secondary mixing in homogenizing tank

[0059] The concentrated carbon black mud discharged from the bottom of the thickener enters the homogenizing tank, where 50-100ppm flocculant solution is added through the automatic dosing system and fully mixed. The stirring speed of the homogenizing tank is 50-100rpm. The mud particles are evenly distributed and the concentration is stable at 15.8-20.4wt%, providing good conditions for the subsequent dehydration process.

[0060] 8. Deep dehydration by centrifugal dehydrator

[0061] The concentrated carbon black mud after homogenization enters the centrifugal dehydrator for high-speed centrifugal dehydration, with an operating speed of 2950-3100rpm. The moisture content of the carbon black mud after dehydration is reduced to 38.2%-41.7%, which is convenient for transportation or incineration; the separated liquid is returned to the carbon black water storage tank for recycling. The moisture content of the mud cake after dehydration is reduced to ≤41.7%, and the calorific value reaches 19.7-20.5MJ / kg, which can be used as fuel for incineration; the concentration of carbon black particles in the separated liquid is reduced to 85-112ppm.

Claims

1. A deep treatment system for carbon black wastewater from a natural gas cracking acetylene production device, characterized in that: It includes a carbon black water storage tank, an automatic dosing system, a mixer, a thickener, a stripping tower, a biochemical pool, and a membrane separation system, and each part is pumped and connected in sequence. The carbon black water storage tank is used to store carbon black wastewater from a natural gas cracking acetylene production device, providing a stable source of wastewater; The automatic dosing system promotes the flocculation and sedimentation of carbon black particles by adding flocculant solution to the wastewater; The mixer is used to achieve full mixing of carbon black wastewater and flocculant to ensure uniform flocculation effect; The thickener receives the mixed wastewater and separates the carbon black particles by gravity sedimentation to obtain clarified wastewater and concentrated carbon black mud; The stripping tower receives clarified wastewater and is used to remove combustible volatile components in the clarified wastewater; The biochemical pool receives the wastewater treated by the stripping tower and removes organic pollutants such as COD and ammonia nitrogen in the wastewater through microbial degradation; The membrane separation system deeply filters the wastewater through an organic membrane to remove residual carbon black particles and trace organic matter, so that the water quality meets the reuse standards.

2. A natural gas cracking acetylene production device carbon black wastewater deep treatment system according to claim 1, characterized in that: The system also includes a homogenizing tank and a centrifugal dehydrator. The homogenizing tank is used to perform secondary mixing on the concentrated carbon black mud; the centrifugal dehydrator is used to dehydrate the carbon black mud after secondary mixing in the homogenizing tank to produce dry carbon black mud and separation liquid.

3. The deep treatment system for carbon black wastewater from a natural gas cracking acetylene production device according to claim 1 is characterized in that: The gas phase outlet at the top of the stripping tower is connected to a flare system for treating the combustible volatile components generated during the stripping process.

4. The deep treatment system for carbon black wastewater from a natural gas cracking acetylene production device according to claim 1 is characterized in that: The concentrate outlet of the membrane separation system is pumped and connected to the feed inlet of the thickener.

5. A process for deep treatment of carbon black wastewater from a natural gas cracking acetylene production unit, characterized in that: The carbon black wastewater deep treatment system of the natural gas cracking acetylene production device according to any one of claims 1 to 4 comprises the following steps: Step 1: The carbon black wastewater is pumped from the carbon black water storage tank to the mixer through a pipeline, and the wastewater in the pipeline is added with a flocculant solution through an automatic dosing system and fully mixed in the mixer to form a uniform mixed liquid; Step 2: The mixed liquid is pumped into the thickener by the mixer, and the clarified wastewater and concentrated carbon black mud are separated under the action of gravity sedimentation. The clarified wastewater overflows from the top of the thickener and enters the stripping tower for treatment. The concentrated carbon black mud is concentrated by the scraper and discharged from the bottom of the thickener; Step 3: The clarified wastewater separated by the thickener enters the stripping tower, and the combustible volatile components in the clarified wastewater are removed by stripping; Step 4: The wastewater after biochemical treatment enters the membrane separation system and is further filtered through the organic membrane to completely remove carbon black particles and trace organic matter; Step 5: The wastewater after biochemical treatment enters the membrane separation system and is further filtered through the organic membrane to completely remove carbon black particles and trace organic matter; Step 6: The treated carbon black wastewater meets the desalted water standard and enters the circulating water system for recycling in the production equipment to replace desalted water.

6. A process for deep treatment of carbon black wastewater from a natural gas cracking acetylene production plant according to claim 5, characterized in that: The organic membrane in step 5 adopts the waste reverse osmosis membrane from the water treatment device of the thermal power plant, and the waste reverse osmosis membrane can be converted and regenerated. After cleaning the pollution layer on the surface of the membrane, the polyamide skin layer is oxidized to make the regenerated membrane show the performance of nanofiltration or ultrafiltration, and the carbon black particles are removed by water.

7. A process for deep treatment of carbon black wastewater from a natural gas cracking acetylene production plant according to claim 6, characterized in that: The process also includes: Step 7: The concentrated carbon black mud in step 2 is discharged from the bottom of the thickener into the homogenization tank, mixed with the flocculant for a second time, and then dehydrated by a centrifugal dehydrator to obtain carbon black mud and separation liquid. The separation liquid is returned to the carbon black water storage tank. After the carbon black mud is dried, it can be transported to heat incineration.

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