Method and device for pretreating coal gasification ash water by pulse electrocoagulation / fenton-like coupling chemical precipitation

Abstract

The present application belongs to the technical field of coal gasification ash water treatment, and particularly relates to a method and device for pretreating coal gasification ash water by pulse electroflocculation / Fenton-like coupling chemical precipitation, which comprises a pulse electroflocculation / Fenton-like reaction, a chemical precipitation reaction, a flocculation coagulation growth and solid-liquid separation purification unit, etc. Compared with the prior art, the present application effectively inhibits electrode passivation and reduces energy consumption by controlling the electrode spacing, current pulse frequency, intermittent aeration and electrode exchange when treating coal gasification ash water; the present application simultaneously adds peroxide to construct a Fenton-like system in the pulse electroflocculation stage, significantly improves the organic matter removal effect and promotes the complex breaking of metal complexes; compared with the traditional simple chemical precipitation method, the present application has a lower reagent dosage, and the effluent after treatment can be directly reused in the coal gasification production process, greatly alleviating the scaling problem of the wastewater and reuse water pipeline of the coal gasification preparation facility, prolonging the equipment maintenance cycle, and having significant economic and social benefits.

Description

Technical Field

[0001] This invention belongs to the field of coal gasification ash water treatment technology, specifically a method and apparatus for pretreating coal gasification ash water by pulsed electrocoagulation / Fenton-like coupled chemical precipitation. Background Technology

[0002] Coal gasification is a way to utilize coal for high-value purposes. Coal gasification wastewater is generated during the high-temperature gasification process, mainly originating from the washing, condensation, and purification of coal gas. It is a typical industrial wastewater characterized by high hardness, high turbidity, high ammonia nitrogen, high organic matter content, and multiple pollutants. The supernatant after natural sedimentation of coal gasification wastewater is called ash water, which is characterized by high temperature, large volume, complex pollutant composition, and high hardness. Given the current water shortage situation in my country, the goal of coal gasification ash water treatment has shifted from meeting emission standards to purification and recycling. This makes it essential to develop new, efficient, and cost-effective coal gasification ash water treatment methods.

[0003] Typically, the pretreatment methods for coal gasification ash water mainly rely on physical or chemical precipitation, focusing on the selection of flocculants and dispersants, and paying attention to the removal effect of suspended solids and turbidity. However, for scaling phenomena on the inner walls of pipes or equipment caused by calcium carbonate, silicates, and borates, which have a greater impact, relying solely on dispersants and scale inhibitors is insufficient to solve the problems of deposition or precipitation of scaling ions under high-temperature conditions. Therefore, when pretreated coal gasification ash water is returned to the coal gasification production process, it easily leads to rapid scaling on the inner walls of equipment and process water pipelines, requiring frequent maintenance or component replacement, resulting in frequent shutdowns of the coal gasification facility and directly impacting efficiency. At present, the pretreatment of coal gasification ash water in China mostly adopts a combination process of "chemical softening + sedimentation" to remove suspended solids and total hardness in ash water. However, this method has a single type of pollutant removal, large amount of chemical reagents added, high salinity, and high pH of effluent. There are problems whether it is reused or enters the subsequent wastewater treatment process: (1) When the ash water after chemical hardening is reused in the production process, the problem of scaling on the inner wall of the equipment and pipes is still very prominent. Only excessive addition of dispersants can slow down the scaling rate. Not only is the consumption of reagents high, but the scale inhibition effect is also poor, and frequent maintenance is still required. (2) When the ash water enters the subsequent wastewater treatment unit, the scaling and frequent maintenance problems of the stripping unit are not alleviated. Toxic and harmful organic matter and various metal ions enter the subsequent biochemical treatment process, inhibiting the growth and activity of microorganisms. The pollutant removal efficiency is limited, and deep treatment is still required. The treatment process is long and the operating cost is high. Developing a new coal gasification ash water pretreatment method based on multi-target pollutant removal can not only improve the efficiency of ash water reuse, but also reduce the difficulty of biological treatment of coal gasification ash water.

[0004] In recent years, with the increasing complexity of industrial wastewater types and the growing demand for small-scale, high-efficiency integrated wastewater pretreatment equipment, electrocoagulation technology has gradually gained attention. The combination of electrocoagulation and chemical precipitation can effectively remove hardness or turbidity from coal gasification ash water and reduce the consumption of chemical reagents. However, conventional electrocoagulation and chemical precipitation methods suffer from limitations in removing a wide range of pollutants and are prone to electrode scaling and passivation.

[0005] Chinese patent CN105060580A discloses a method for treating heavy metal wastewater using electrocoagulation-chemical precipitation. The method includes the following steps: adjusting the pH of the wastewater, performing electrocoagulation treatment in an electrocoagulation reactor for 30-60 minutes, then adding a flocculant for settling for 10-30 minutes before effluent discharge. This invention first electrocoagulates heavy metal wastewater containing trace amounts of heavy metal ions. The ions generated by electrolysis hydrolyze to produce a large number of polyhydroxy compounds that react, adsorb, and chelate with the trace heavy metal ions to enrich most of them. Then, by adding a flocculant, the heavy metal ions are further enriched, working synergistically with electrocoagulation. Simultaneously, the resulting flocs begin to precipitate, ultimately ensuring the effluent meets discharge standards. However, this patent has an excessively long electrocoagulation treatment time, which can easily lead to passivation of the electrode plates, resulting in increased power consumption and reduced pollutant removal capacity. Furthermore, it treats a relatively simple type of pollutant with too low a concentration, making it unsuitable for treating heavy metal wastewater at various temperature ranges, with high impurity content, or industrial wastewater with more complex compositions.

[0006] In summary, given the characteristics of coal gasification ash water, such as high temperature, high ammonia, high hardness, complex types of pollutants, large differences in suspended solids content, and difficulty in treating organic matter, it is necessary to develop a novel electrocoagulation / Fenton-like coupled chemical precipitation technology to achieve comprehensive removal of multiple pollutants (macromolecular aromatics and humic acids) and significantly reduce power consumption and chemical reagent consumption.

[0007] Therefore, the present invention provides a method and apparatus for pretreating coal gasification ash water by pulsed electrocoagulation / Fenton-like coupled chemical precipitation. Summary of the Invention

[0008] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0009] The technical solution adopted by this invention to solve its technical problem is: the method for pretreating coal gasification ash water by pulsed electrocoagulation / Fenton-like coupled chemical precipitation as described in this invention includes the following steps: S1: Pulse electrocoagulation / Fenton-like reaction: Coal gasification ash water enters the bipolar pulse electrocoagulation / Fenton-like reactor, with iron as the electrode, hydrogen peroxide is added simultaneously, and intermittent aeration is carried out for pulse electrolysis; S2: Chemical precipitation reaction: Add a precipitation regulator to the effluent, adjust the pH, and stir the reaction rapidly; S3: Floc growth aid: Add floc growth aid and stir slowly to promote floc growth; S4: Solid-liquid separation: After sedimentation, take the supernatant to obtain the treated ash water; In the pulsed electrocoagulation / Fenton-like reaction, the reactor used is a bipolar pulsed electrocoagulation / Fenton-like reactor with an electrode plate spacing of 5-30 mm and an inlet water temperature of 10-80℃ for coal gasification ash water. In the pulsed electrocoagulation / Fenton-like reaction, the current density is 6–40 mA / cm², the pulse frequency is 500–5000 Hz, the duty cycle is 20%–100%, the pulsed electrocoagulation reaction time is 0.5–5 min, the peroxide dosage is 50 mg / L–200 mg / L, the amount of peroxide added is 50–200 mg / L, aeration is performed every 0.5–2 min for 0.5–2 min, and the flow rate is 1.0 L / min.

[0010] Preferably, in the pulsed electrocoagulation / Fenton-like reaction, the bipolar pulsed electrocoagulation / Fenton-like reactor is cylindrical or cuboid in shape, with a gas collection hood or collection pipe at the top, and the flow pattern of the bipolar pulsed electrocoagulation / Fenton-like reactor is plug flow or baffle flow, with a flow velocity in the range of 0.2 to 1.0 m / s.

[0011] Preferably, in the pulsed electrocoagulation / Fenton-like reaction, the peroxides are hydrogen peroxide, ozone, sodium percarbonate, and potassium persulfate.

[0012] Preferably, the chemical precipitation reaction includes: adding a precipitation regulator to the pulse electrocoagulation / Fenton-like effluent and stirring the reaction to obtain the chemical precipitation reaction effluent; The precipitation regulator includes one or more of sodium carbonate, sodium bicarbonate, sodium sulfate, or sodium hydroxide. By adding the precipitation regulator, the pH is adjusted to 8-10. During the stirring reaction, the stirring speed is 100-300 rpm and the stirring time is 2-10 min.

[0013] Preferably, the floc coagulation and growth aid includes: adding a coagulant to the effluent from the chemical precipitation reaction and stirring the reaction to obtain the effluent from the floc coagulation and growth aid. The coagulant aid includes one of polyacrylamide or a natural polymeric coagulant aid, wherein the natural polymeric coagulant aid includes at least one of cellulose, chitosan, chitin, gelatin or bone glue, and the dosage of the coagulant aid is 2×10-4~10×10-3 g / L of chemically precipitated effluent.

[0014] Preferably, the stirring reaction includes: a stirring speed of 50-150 rpm and a stirring time of 5-10 min; the solid-liquid separation includes: after the flocs coagulate and grow, they are settled by gravity, and the resulting supernatant is the treated coal gasification ash water.

[0015] Preferably, the solid-liquid separation is performed by gravity sedimentation, inclined plate sedimentation, or mechanical clarification, with a sedimentation time of 30 min to 60 min.

[0016] A pulsed electrocoagulation / Fenton-like coupled chemical precipitation pretreatment device for coal gasification ash water, which is applicable to the above-mentioned pulsed electrocoagulation / Fenton-like coupled chemical precipitation pretreatment method for coal gasification ash water, includes a raw water tank, a pump, an aeration device, a pulsed electrocoagulation / Fenton-like reactor, a chemical precipitation reactor, a flocculation stirring reactor, and a solid-liquid separator arranged in series. The raw water tank, pump, aeration device, and pulse electrocoagulation / Fenton-like reactor constitute a pulse electrocoagulation reaction unit. The chemical precipitation reactor, flocculation stirring reactor, and solid-liquid separator constitute a chemical reaction and solid-liquid separation unit.

[0017] Preferably, the pulse electrocoagulation / Fenton-like reactor is provided with an electrode plate inside. The pair of electrode plates located on the outermost side inside the pulse electrocoagulation / Fenton-like reactor are fixedly connected with mounting blocks by fasteners. A lifting frame is provided below the mounting block. Disassembly blocks can be detachably connected to the bottom of the mounting block and the top of the lifting frame. The same rubber telescopic belt is fixedly connected between the pair of disassembly blocks in the vertical direction. The inner wall of the lifting frame is provided with an inner wall groove, and a scraper is movably inserted inside the inner wall groove. The inner wall of the scraper is engraved with friction texture, and the inner wall of the scraper abuts against the outer side of the electrode plate. Adjustable blocks are detachably connected to all four sides of the lifting frame. A round block is fixedly connected to one end of the adjustable block. A magnetic coating is applied to the side of the round block away from the adjustable block. A magnetic coating is applied to all four sides of the scraping frame, which is magnetically repelled by the magnetic coating. A pair of motors are fixedly connected to the inner bottom wall of the flocculation stirring reactor. A spool is fixedly connected to the output end of the motors. A pull rope is fixedly connected between the spool and the lifting frame. The lifting frame has a hollow interior and is equipped with a pump. The inner wall of the lifting frame has a dust inlet hole that communicates with the interior of the lifting frame. Both sides of the bottom of the lifting frame are fixedly connected to a sealing plate by fasteners, and the sealing plate has a filter hole.

[0018] Preferably, the lifting frame is equipped with a controller and a sensor inside, and an indicator light is fixedly connected to the outside of the lifting frame. Both the indicator light and the sensor are electrically connected to the controller via wires.

[0019] The beneficial effects of this invention are as follows: 1. The pulse electrocoagulation unit in this invention mainly consists of three physicochemical unit processes or reactions: electrocoagulation, chemical precipitation, air flotation separation, and oxidation-reduction. It effectively combines three technologies: electrochemical reaction, chemical coagulation and precipitation, and electroflotation. For coal gasification ash water with complex inorganic ion composition, high hardness and suspended solids content, and a large amount of organic macromolecules, the above technical solution can effectively reduce hardness, remove various ions and organic pollutants under short time and low energy consumption conditions. Moreover, the process is simple to operate, has a fast processing rate, good effect, low cost, small equipment size, and is easy to automate.

[0020] 2. The pulse electrocoagulation unit of this invention is followed by a chemical reaction and solid-liquid separation unit. This is a water treatment method that involves adding chemical agents to convert soluble substances in the water into insoluble substances, causing them to precipitate. Examples of substances to be removed include calcium, magnesium, iron, manganese, silicon, and boron. The method described in this invention is simple and fast. Electrocoagulation itself alters the ionic valence state and morphology of the system, facilitating precipitation. After adding coagulant aids, the system loses or reduces its stability through mechanisms such as double-layer compression and charge neutralization, generating micro-flocs. These micro-flocs then grow into large flocs through adsorption bridging and precipitate trapping, thereby accelerating the removal of insoluble substances from the water and enhancing the efficiency of co-precipitation or chemical precipitation. Pretreatment of coal gasification ash water using pulse electrocoagulation / Fenton-like coupled chemical precipitation is simple to operate, overcomes the high agent consumption of simple chemical precipitation or hardening reactions, has good effects, and produces non-toxic chemical sludge such as calcium carbonate, magnesium carbonate, calcium silicate, and borate. The removal of organic matter is improved, the disposal method is simple, it can be directly landfilled, and the overall treatment cost is low.

[0021] 3. Periodically start the motor to rotate the spool at its output end, which will then wind up the pull rope. Simultaneously, the rubber telescopic belt will be stretched, pulling the lifting frame and scraper up and down on the electrode plate. The scraper will then remove the scale and foreign matter adhering to the electrode plate. At the same time, start the extraction pump to draw the scraped scale and foreign matter into the lifting frame through the dust inlet, and discharge the liquid mixed with the scale and foreign matter through the filter hole. Finally, remove the lifting frame from the electrode plate and clean the scale and foreign matter inside the lifting frame. This facilitates the cleaning of the electrode plate, solves the passivation problem, ensures long-term stable current efficiency, and reduces downtime maintenance. Attached Figure Description

[0022] The invention will now be further described with reference to the accompanying drawings.

[0023] Figure 1 This is a schematic diagram of the structure of a pulsed electrocoagulation / Fenton-like coupled chemical precipitation pretreatment device for coal gasification ash water according to the present invention. Figure 2 This is a comparison chart showing the total hardness removal effect of Examples 1-4 and Comparative Examples 1 and 2 on coal gasification ash water; Figure 3 The graph shows a comparison of the turbidity removal effects of Examples 1-4 and Comparative Examples 1 and 2 on coal gasification ash water. Figure 4 The graph shows a comparison of the NPOC removal effects of Examples 1-4 with Comparative Example 1 and Comparative Example 2 on coal gasification ash water. Figure 5 Comparison of COD removal effects of Examples 1-4 and Comparative Examples 1 and 2 on coal gasification ash water; Figure 6 The graph shows a comparison of the ammonia nitrogen removal effects of Examples 1-4 and Comparative Examples 1 and 2 on coal gasification ash water. Figure 7 This is a comparison chart showing the boron removal effect of Examples 1-4 on coal gasification ash water with Comparative Examples 1 and 2; Figure 8 Comparison of the silicon removal effects of Examples 1-4 and Comparative Examples 1 and 2 on coal gasification ash water; Figure 9 Comparison of manganese removal effects of Examples 1-4 and Comparative Examples 1 and 2 on coal gasification ash water; Figure 10 Comparison of the barium removal effect of Examples 1-4 with Comparative Examples 1 and 2 on coal gasification ash water; Figure 11 The graph shows a comparison of the suspended solids removal effects of Examples 1-4 with Comparative Examples 1 and 2 on coal gasification ash water. Figure 12 This is a comparison chart of power consumption during the coal gasification ash water treatment process in Examples 2 and 4; Figure 13 This is a flowchart of the method of the present invention; Figure 14 This is a schematic diagram of the lifting frame in this invention; Figure 15 This is a schematic diagram of the scraping frame in this invention; Figure 16 This is a schematic diagram of the sealing plate in this invention; Figure 17 This is the present invention. Figure 16 A magnified view of a portion of point A in the middle.

[0024] In the diagram: 1. Raw water tank; 2. Pump; 3. Aeration device; 4. Pulse electrocoagulation / Fenton-like reactor; 5. Chemical precipitation reactor; 6. Flocculation stirring reactor; 7. Solid-liquid separator; 8. Mounting block; 9. Lifting frame; 10. Disassembly block; 11. Rubber telescopic belt; 12. Inner wall groove; 13. Scraper frame; 14. Round block; 15. Magnetic coating one; 16. Magnetic coating two; 17. Motor; 18. Bollard; 19. Pull rope; 20. Dust inlet; 21. Sealing plate; 22. Filter hole; 23. Indicator light; 24. Adjusting block; Figure 2-12 In the examples: A. Example 1: Pulsed electrocoagulation / Fenton-like unit; B. Example 1: Chemical reaction and solid-liquid separation unit; C. Example 2: Pulsed electrocoagulation / Fenton-like unit; D. Example 2: Chemical reaction and solid-liquid separation unit; E. Comparative Example 1: Chemical reaction and solid-liquid separation unit only; F. Example 3: Pulsed electrocoagulation / Fenton-like unit; G. Example 3: Chemical reaction and solid-liquid separation unit; H. Example 4: DC electrocoagulation / Fenton-like stage; I. Example 4: Chemical reaction and solid-liquid separation unit; J. Comparative Example 2: Chemical reaction and solid-liquid separation unit only, without the addition of coagulant polyacrylamide. Detailed Implementation

[0025] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0026] Example 1: As Figure 13 As shown, the method for pretreating coal gasification ash water using pulsed electrocoagulation / Fenton-like coupled chemical precipitation includes the following steps: S1: Pulse electrocoagulation / Fenton-like reaction: Coal gasification ash water enters the bipolar pulse electrocoagulation / Fenton-like reactor 4, with iron as the electrode, hydrogen peroxide is added simultaneously, and intermittent aeration is carried out for pulse electrolysis; S2: Chemical precipitation reaction: Add a precipitation regulator to the effluent, adjust the pH, and stir the reaction rapidly; S3: Floc growth aid: Add floc growth aid and stir slowly to promote floc growth; S4: Solid-liquid separation: After sedimentation, take the supernatant to obtain the treated ash water; In the pulsed electrocoagulation / Fenton-like reaction, the reactor used is a bipolar pulsed electrocoagulation / Fenton-like reactor 4, the electrode plate spacing is 5-30 mm, and the inlet water temperature of the coal gasification ash water is 10-80 ℃. In the pulsed electrocoagulation / Fenton-like reaction, the current density is 6–40 mA / cm², the pulse frequency is 500–5000 Hz, the duty cycle is 20%–100%, the pulsed electrocoagulation reaction time is 0.5–5 min, the peroxide dosage is 50 mg / L–200 mg / L, the amount of peroxide added is 50–200 mg / L, aeration is performed every 0.5–2 min for 0.5–2 min, and the flow rate is 1.0 L / min.

[0027] In the aforementioned pulsed electrocoagulation / Fenton-like reaction, the bipolar pulsed electrocoagulation / Fenton-like reactor 4 is cylindrical or cuboid in shape, with a gas collection hood or collection pipe at the top. The flow pattern of the bipolar pulsed electrocoagulation / Fenton-like reactor 4 is plug flow or baffle flow, with a flow velocity in the range of 0.2 to 1.0 m / s.

[0028] In the pulsed electrocoagulation / Fenton-like reaction, the peroxides include hydrogen peroxide, ozone, sodium percarbonate, and potassium persulfate.

[0029] The chemical precipitation reaction includes: adding a precipitation regulator to the pulse electrocoagulation / Fenton-like effluent and stirring the reaction to obtain the chemical precipitation reaction effluent; The precipitation regulator includes one or more of sodium carbonate, sodium bicarbonate, sodium sulfate, or sodium hydroxide. By adding the precipitation regulator, the pH is adjusted to 8-10. During the stirring reaction, the stirring speed is 100-300 rpm and the stirring time is 2-10 min.

[0030] The floc coagulation and growth process includes: adding a coagulant to the effluent from the chemical precipitation reaction and stirring the reaction to obtain the effluent from the floc coagulation and growth process. The coagulant aid includes one of polyacrylamide or a natural polymeric coagulant aid, wherein the natural polymeric coagulant aid includes at least one of cellulose, chitosan, chitin, gelatin or bone glue, and the dosage of the coagulant aid is 2×10-4~10×10-3 g / L of chemically precipitated effluent.

[0031] The stirring reaction includes: a stirring speed of 50-150 rpm and a stirring time of 5-10 min. The solid-liquid separation includes: after the flocs coagulate and grow, they are settled by gravity, and the resulting supernatant is the treated coal gasification ash water.

[0032] The solid-liquid separation is performed by gravity sedimentation, inclined plate sedimentation or mechanical clarification, with a sedimentation time of 30 min to 60 min.

[0033] The present invention is used in the following steps: Step 1: Assemble electrode plates with a total area of ​​700 cm2 in a cuboid pulse electrocoagulation / Fenton-like reactor 4 with a gas collection hood on top. The plate spacing is 5 mm, and multiple electrode plates are connected in a bipolar manner. The supernatant from the ash water tank in the 25℃ coal gasification process is continuously fed into the carbon steel pulse electrocoagulation / Fenton-like reactor 4. The ash water to be treated has a total hardness of 900 mg / L, turbidity of 36 NTU, suspended solids of 67 mg / L, ammonia nitrogen of 300 mg / L, COD of 600 mg / L, and manganese ions, barium ions, boron ions, and silicon ions of 40 mg / L each. The flow rate of grey water in the pulse electrocoagulation / Fenton-like reactor 4 was 0.2 m / s. The DC rectangular pulse power supply was started, the pulse current mode was unidirectional pulse, the current density was adjusted to 8 mA / cm2, the pulse frequency was 500 Hz, the duty cycle was 20%, and the pulse electrocoagulation reaction was carried out for 0.5 min. The hydrogen peroxide dosage was 100 mg / L, and aeration was carried out every 3 min for 1 min at a flow rate of 1.0 L / min. Step 2: The effluent from Step 1 enters the chemical reaction and solid-liquid separation unit, which consists of three stages: chemical precipitation reaction, floc coagulation and growth, and solid-liquid separation. In the chemical precipitation reaction stage, a precipitation regulator consisting of sodium hydroxide and sodium bicarbonate in a molar ratio of 1.32:1 was added to adjust the pH to 8. The mixture was then rapidly stirred at 100 r / min for 5 min. Finally, 2 × 10⁻⁴ g / L of chitosan was added to the chemical precipitation effluent for the floc-aiding coagulation and growth stage. The mixture is slowly stirred at 50 r / min for 5 min. After sedimentation and floc growth, the solid-liquid mixture enters the sedimentation zone and stays for 10 min. The supernatant is recycled for production or enters subsequent processing stages. Sludge is periodically discharged from the bottom of the sedimentation zone.

[0034] This invention can also be used in other pretreatment processes for industrial wastewater characterized by high organic matter and high hardness.

[0035] This invention not only effectively reduces the total hardness of coal gasification ash water, removes suspended impurities and various pollutants, overcomes or reduces the rate of electrode passivation, and enables the reuse of ash water in the production process, but also reduces the risk of scaling and pipe blockage, and lowers the difficulty of subsequent biochemical treatment. Specifically, based on conventional electrocoagulation treatment, this invention uses bidirectional or unidirectional alternating pulsed currents, adds peroxides to construct a Fenton-like system, and electrolyzes and electrocoagulates the wastewater under certain water flow conditions, changing the valence state or occurrence form of metal ions and groups to generate oxidative free radicals. Then, chemical precipitants and pH adjusters are added to synergistically remove various pollutants from coal gasification ash water, avoiding electrode passivation.

[0036] The principle of this invention is to use metallic iron or metallic aluminum as electrodes in the pulse electrocoagulation / Fenton-like reactor 4, and to optimize its structure. Multiple electrode plates are fixed in slots. A gas collection hood is provided above the pulse electrocoagulation / Fenton-like reactor 4 to facilitate the collection of gases generated during the electrocoagulation reaction and prevent environmental pollution. A turbulent flow field of ash water is constructed in the pulse electrocoagulation / Fenton-like reactor 4 and its flow rate is controlled to improve the contact and mass transfer between the electrodes and the wastewater. Using unidirectional or bidirectional pulsed currents at the positive and negative electrodes of iron and aluminum, the coal gasification ash water repeatedly undergoes polarity reversal between the positive and negative electrodes during its flow in the reactor, resulting in various electrochemical reactions: (1) The metal ions generated on the anode by the metal electrode combine with the OH- generated by the dissociation of the aqueous solution to form hydrates or nascent hydroxides with complex valence states. These hydrates then flocculate with organic and inorganic impurities in the ash water, changing the surface potential of suspended solids, colloidal particles, etc., destabilizing them, and making them more likely to precipitate or become crystal nuclei for subsequent hardening reactions. (2) The metal element at the anode generates new ecological groups or active ions with redox properties during the electrolysis process. These can react with certain anions and cations already present in the wastewater to change their valence state and occurrence form, making them easier to precipitate. The added peroxide will generate new ecological groups or active ions such as atomic oxygen and hydroxyl radicals, which will directly react with organic matter or reducing inorganic components to remove NPOC and COD from the water. At the same time, it can also cause the chain breaking reaction of the difficult-to-degrade macromolecular organic pollutants to generate easily degradable small molecule organic matter, thereby improving the biodegradability of the ash water. (3) Hydrogen gas is generated when the cathode of the electrode electrolyzes water. It escapes in the form of tiny bubbles, which can carry flocculent matter and oily substances in the ash water, producing a flotation effect to achieve separation and purification.

[0037] This invention enables rapid hardening and turbidity removal while ensuring compliant emissions. It also prevents scale buildup in pipelines and equipment before the purified ash water re-enters the production process. Furthermore, it effectively removes various other pollutants during subsequent gas stripping and ammonia removal, improving the biodegradability of the effluent and reducing the risks of scaling and excessive sediment accumulation in the biological treatment tank. This invention features simple and easy-to-maintain equipment, clean and pollution-free operation, low reagent usage, and low cost, making it suitable for large-scale industrial-scale coal gasification ash water pretreatment.

[0038] This method is also applicable to the pretreatment of industrial wastewater with high temperature, high turbidity, high hardness, and various complex organic and inorganic components.

[0039] The coal gasification ash water, processed using the method described in this invention, forms a large amount of metal oxides and polyhydroxy iron, aluminum, and other complex components after being subjected to pulsed current for several minutes. Under the action of added pH adjusters and coagulants, it undergoes oxidation-reduction, precipitation, adsorption, and coagulation reactions, rapidly forming precipitates such as calcium, magnesium, barium, manganese, silicon, and boron. Co-precipitation is enhanced through the coagulation process of iron and aluminum-based hydroxides. Further solid-liquid separation achieves high-efficiency removal of various cations, significantly reducing hardness and turbidity. The active groups generated during the electrolytic flocculation / Fenton-like process oxidize the macromolecular organic matter in the coal gasification wastewater and remove NPOC and COD.

[0040] Example 2: A method for pretreating coal gasification ash water using pulsed electrocoagulation / Fenton-like coupled chemical precipitation, comprising the following steps: S1: Assemble an electrode plate with a total area of ​​400 cm2 in a cuboid pulse electrocoagulation / Fenton-like reactor 4 with a gas collection hood on top. The plate spacing is 15 mm. Multiple electrode plates are connected in a bipolar manner. Take 40℃ coal gasification ash water and continuously enter the stainless steel pulse electrocoagulation / Fenton-like reactor 4. The total hardness of the grey water to be treated was 880 mg / L, the turbidity was 30 NTU, the suspended solids were 78 mg / L, the ammonia nitrogen was 300 mg / L, the COD was 620 mg / L, and the manganese ion, barium ion, boron ion and silicon ion were 40 mg / L each. The flow rate of grey water in the pulse electrocoagulation / Fenton-like reactor 4 was 0.5 m / s. A unidirectional DC rectangular pulse power supply was started, and the current density was adjusted to 25 mA / cm2, the pulse frequency to 3000 Hz, and the duty cycle to 50%. The pulse electrocoagulation / Fenton-like reaction was carried out for 3 min. The sodium percarbonate dosage was 100 mg / L. Aeration was performed every 1.5 min for 0.5 min at a flow rate of 1.0 L / min. S2: The effluent after step S1 enters the chemical reaction and solid-liquid separation unit, which consists of three stages: chemical precipitation reaction, floc coagulation and growth, and solid-liquid separation. In the chemical precipitation reaction stage, a precipitation regulator consisting of sodium hydroxide and sodium carbonate in a molar ratio of 1.06:1 is added to adjust the pH to 9. The mixture is then rapidly stirred at 300 rpm for 5 min to achieve uniformity. Subsequently, 5 × 10⁻³ g / L of polyacrylamide is added to the effluent for chemical precipitation to promote floc growth. The mixture is then slowly stirred at 100 rpm for 8 min. After the precipitation reaction and floc growth, the solid-liquid mixture enters the sedimentation zone and remains there for 30 min. The supernatant is recycled for production or used in subsequent treatment stages. Sludge is periodically discharged from the bottom of the sedimentation zone.

[0041] Example 3: A method for pretreating coal gasification ash water by pulsed electrocoagulation / Fenton-like coupled chemical precipitation, comprising the following steps: S1: Assemble electrode plates with a total area of ​​200 cm2 in a cuboid pulsed electrocoagulation / Fenton-like reactor 4 with a gas collection hood on the top. The plate spacing is 30 mm. Multiple electrode plates are connected in a bipolar manner. 70°C coal gasification ash water continuously enters the carbon steel pulsed electrocoagulation / Fenton-like reactor 4. The total hardness of the grey water to be treated was 850 mg / L, the turbidity was 36 NTU, the suspended solids were 65 mg / L, the ammonia nitrogen was 280 mg / L, the COD was 640 mg / L, and the manganese ion, barium ion, boron ion and silicon ion were 40 mg / L each. The flow rate of grey water in the pulse electrocoagulation / Fenton-like reactor 4 was 1.0 m / s. A unidirectional AC pulse power supply was started, the pulse current mode was unidirectional pulse, the current density was adjusted to 40 mA / cm2, the pulse frequency was 5000 Hz, the duty cycle was 80%, and the pulse electrocoagulation reaction was carried out for 5 min. The potassium persulfate dosage was 200 mg / L, and aeration was carried out every 2 min for 0.5 min at a flow rate of 1.0 L / min. S2: The effluent after step S1 enters the chemical reaction and solid-liquid separation unit, which consists of three stages: chemical precipitation reaction, floc coagulation and growth, and solid-liquid separation. In the chemical precipitation reaction stage, a combination of sodium hydroxide and sodium sulfate in a molar ratio of 2.54:1 is added as a precipitation regulator to adjust the pH to 10. The mixture is then rapidly stirred at 200 rpm for 5 min to achieve uniformity. Subsequently, 10 × 10⁻³ g / L of cellulose is added to the chemical precipitation effluent for floc coagulation and growth. The mixture is then slowly stirred at 150 rpm for 10 min. After the precipitation reaction and floc growth, the solid-liquid mixture enters the sedimentation zone and remains there for 60 min. The supernatant is recycled for production or enters subsequent treatment stages. Sludge is periodically discharged from the bottom of the sedimentation zone.

[0042] Example 4: A method for pretreating coal gasification ash water using pulsed electrocoagulation / Fenton-like coupled chemical precipitation, comprising the following steps: S1: An electrode plate with a total area of ​​400 cm2 is assembled in a cuboid pulse electrocoagulation / Fenton-like reactor 4 with a gas collection hood on top. The plate spacing is 30 mm. Multiple electrode plates are connected in a bipolar manner. 40 ℃ coal gasification ash water continuously enters the stainless steel pulse electrocoagulation / Fenton-like reactor 4. The total hardness of the ash water to be treated was 800 mg / L, the turbidity was 30 NTU, the suspended solids were 74 mg / L, the ammonia nitrogen was 280 mg / L, the COD was 600 mg / L, and the manganese, barium, boron and silicon ions were 40 mg / L each. The flow rate of the ash water in the electrocoagulation reactor was 0.5 m / s. The pulse power supply was started, the current density was adjusted to 25 mA / cm2, the pulse frequency was 3000 Hz, the duty cycle was 100%, and pulse electrocoagulation / Fenton-like reaction was carried out for 3 min. The hydrogen peroxide dosage was 100 mg / L, and aeration was carried out every 1 min for 0.5 min at a flow rate of 1.0 L / min. S2: The effluent from step S1 enters the chemical reaction and solid-liquid separation unit. The chemical reaction and solid-liquid separation unit consists of three stages: chemical precipitation reaction, floc coagulation and growth, and solid-liquid separation. In the chemical precipitation reaction stage, a precipitation regulator consisting of sodium hydroxide and sodium carbonate in a molar ratio of 1.06:1 is added to adjust the pH to 9. The mixture is then rapidly stirred at 300 rpm until homogeneous. Next, 5×10⁻³ g / L of polyacrylamide is added to the chemical precipitation effluent for floc coagulation and growth. The mixture is then slowly stirred at 100 rpm for 8 minutes. After the precipitation reaction and floc growth, the solid-liquid mixture enters the sedimentation zone and remains for 30 minutes. The supernatant is recycled for production or enters subsequent treatment stages. Sludge is periodically discharged from the bottom of the sedimentation zone.

[0043] Comparative Example 1: A method for chemical precipitation coupled treatment of coal gasification ash water, which differs from Example 2 only in that it does not contain step S1, and is otherwise the same as Example 2.

[0044] Comparative Example 2: A method for chemical precipitation coupled treatment of coal gasification ash water, which differs from Example 2 only in that: no coagulant polyacrylamide is added, and the rest is the same as Example 2.

[0045] Example 5: This embodiment investigates the turbidity, total hardness, COD, ammonia nitrogen, silicon, and boron of the supernatants obtained in Examples 1-4 and the comparative examples. The testing methods for each index are as follows: total hardness was determined by EDTA titration (GB7477-87); turbidity was determined by a turbidimeter; suspended solids content was determined by gravimetric method; ammonia nitrogen was determined by Nessler's reagent spectrophotometry (HJ535-2009); NPOC was determined by a TOC analyzer; COD was determined by the potassium dichromate method (GB / T 11914-1989); and silicon, boron, barium, and manganese were determined by ICP-OES 5110. The results are as follows. Figure 2 As shown.

[0046] from Figure 2-10It can be seen that the pulse electrocoagulation / Fenton-like coupled chemical precipitation in Examples 1-3 and the DC electrocoagulation / Fenton-like coupled chemical precipitation in Example 4 for pretreatment of coal gasification ash water can effectively remove turbidity, total hardness, suspended solids, silicon, boron, manganese, and barium from the ash water in a short time, with removal rates of over 80%, 60%, 70%, 55%, 60%, 90%, and 90%, respectively. They can all meet the discharge standards for ash water hardness reduction and turbidity removal, and also have good removal effects on COD and ammonia nitrogen. Moreover, the chemical reaction and solid-liquid separation unit has a significantly improved effect on the treatment of each index compared with the pulse electrocoagulation unit. Example 2 also has a significant improvement effect compared with Comparative Examples 1 and 2. This shows that the method for removing multiple pollutants from coal gasification ash water using pulse electrocoagulation / Fenton-like coupled chemical precipitation provided by the present invention has a very good effect, especially the addition of coagulant to accelerate the settling rate of flocs and improve the removal rate of each pollutant. DC electrocoagulation typically suffers from electrode passivation when the energizing time is long. In contrast, pulse power supply uses an "on-off-on" power supply method for electrolysis, which is beneficial for diffusion on the electrode surface and reduces electrode passivation. During the pulse intervals, the actual energizing time is much shorter than the total reaction time of electrocoagulation. Therefore, pulse electrocoagulation units can significantly reduce energy consumption compared to DC electrocoagulation units. Furthermore, it is essential to perform pulsed electrocoagulation / Fenton-like treatment before the chemical reaction and solid-liquid separation unit. This method has good application prospects in the field of coal gasification ash water with high temperature, high hardness, high turbidity, high ammonia nitrogen and multiple pollutant components.

[0047] Example 6, as Figure 1 As shown, a pulsed electrocoagulation / Fenton-like coupled chemical precipitation pretreatment device for coal gasification ash water is applicable to the above-mentioned pulsed electrocoagulation / Fenton-like coupled chemical precipitation pretreatment method for coal gasification ash water. The device includes a raw water tank 1, a pump 2, an aeration device 3, a pulsed electrocoagulation / Fenton-like reactor 4, a chemical precipitation reactor 5, a flocculation stirring reactor 6, and a solid-liquid separator 7 arranged in series. The raw water tank 1, pump 2, aeration device 3 and pulse electrocoagulation / Fenton-like reactor 4 constitute a pulse electrocoagulation reaction unit. The chemical precipitation reactor 5, the flocculation and stirring reactor 6, and the solid-liquid separator 7 constitute a chemical reaction and solid-liquid separation unit.

[0048] like Figure 14-17As shown, the pulse electrocoagulation / Fenton-like reactor 4 is equipped with an electrode plate inside. The pair of electrode plates located on the outermost side of the pulse electrocoagulation / Fenton-like reactor 4 are fixedly connected to an installation block 8 by fasteners, specifically bolts. A lifting frame 9 is provided below the installation block 8. The bottom of the installation block 8 and the top of the lifting frame 9 are detachably connected to a disassembly block 10, specifically a threaded connection. The same rubber telescopic belt 11 is fixedly connected between the pair of disassembly blocks 10 in the vertical direction. The inner wall of the lifting frame 9 is provided with an inner wall groove 12, and a scraping frame 13 is movably inserted inside the inner wall groove 12. The inner wall of the scraping frame 13 is engraved with friction texture, and the inner wall of the scraping frame 13 abuts against the outer side of the electrode plate. Adjustment blocks 24 can be detachably connected to all four sides of the lifting frame 9. A round block 14 is fixedly connected to one end of the adjustment block 24. A magnetic coating 15 is coated on the side of the round block 14 away from the adjustment block 24. A magnetic coating 16 that is magnetically repelled by the magnetic coating 15 is coated on all four sides of the scraping frame 13. In use, the adjusting block 24 can be rotated to adjust the distance between the circular block 14 and the scraping frame 13, thereby adjusting the magnitude of the repulsive force between the magnetic coating one 15 and the magnetic coating two 16, and thus adjusting the cleaning intensity of the scraping frame 13 on the electrode plate surface.

[0049] A pair of motors 17 are fixedly connected to the inner bottom wall of the flocculation stirring reactor 6. A controller is provided on the motors 17. A spool 18 is fixedly connected to the output end of the motors 17. A pull rope 19 is fixedly connected between the spool 18 and the lifting frame 9. The interior of the lifting frame 9 is hollow and equipped with a pump body. A dust inlet 20 is provided on the inner wall of the lifting frame 9, and the dust inlet 20 communicates with the interior of the lifting frame 9. Both sides of the bottom of the lifting frame 9 are fixedly connected to a sealing plate 21 by fasteners, specifically bolts. A filter hole 22 is provided on the sealing plate 21.

[0050] When using this invention, the motor 17 needs to be started periodically so that its output end drives the spool 18 to rotate in order to wind up the pull rope 19. At the same time, the rubber telescopic belt 11 will be stretched, thereby pulling the lifting frame 9 and the scraping frame 13 to move up and down on the electrode plate (represented by P in the figure). The scraping frame 13 is used to scrape off the scale and foreign matter attached to the electrode plate. Simultaneously, the extraction pump is started to draw the scraped scale and foreign matter into the lifting frame 9 through the dust inlet 20, and the liquid mixed with the scale and foreign matter is discharged from the filter hole 22. Finally, the lifting frame 9 is removed from the electrode plate, and the scale and foreign matter inside the lifting frame 9 are cleaned. This makes it easier for personnel to clean the electrode plate, solve the passivation problem, ensure long-term stable current efficiency, and reduce downtime maintenance.

[0051] like Figure 15 As shown, the lifting frame 9 is equipped with a controller and a sensor inside. An indicator light 23 is fixedly connected to the outside of the lifting frame 9. Both the indicator light 23 and the sensor are electrically connected to the controller through wires. When the lifting frame 9 collects a certain amount of dirt and foreign matter, the indicator light 23 will light up to remind personnel to clean the inside of the lifting frame 9.

[0052] The terms "front," "back," "left," "right," "top," and "bottom" all refer to the figures in the accompanying drawings. Figure 1 Based on the perspective of the observer, the side of the device facing the observer is defined as the front, the left side of the observer is defined as the left, and so on.

[0053] In the description of this invention, it should be understood that the terms "center", "longitudinal", "lateral", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

[0054] 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 to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for pretreating coal gasification ash water using pulsed electrocoagulation / Fenton-like coupled chemical precipitation, characterized in that, Includes the following steps: S1: Pulse electrocoagulation / Fenton-like reaction: Coal gasification ash water enters the bipolar pulse electrocoagulation / Fenton-like reactor (4), with iron as the electrode, hydrogen peroxide is added simultaneously, and intermittent aeration is carried out for pulse electrolysis; S2: Chemical precipitation reaction: Add a precipitation regulator to the effluent, adjust the pH, and stir the reaction rapidly; S3: Floc growth aid: Add floc growth aid and stir slowly to promote floc growth; S4: Solid-liquid separation: After sedimentation, take the supernatant to obtain the treated ash water; In the pulse electrocoagulation / Fenton-like reaction, the reactor used is a bipolar pulse electrocoagulation / Fenton-like reactor (4), the electrode plate spacing is 5-30 mm, and the inlet water temperature of coal gasification ash water is 10-80℃. In the pulsed electrocoagulation / Fenton-like reaction, the current density is 6–40 mA / cm², the pulse frequency is 500–5000 Hz, the duty cycle is 20%–100%, the pulsed electrocoagulation reaction time is 0.5–5 min, the peroxide dosage is 50 mg / L–200 mg / L, the amount of peroxide added is 50–200 mg / L, aeration is performed every 0.5–2 min for 0.5–2 min, and the flow rate is 1.0 L / min.

2. The method for pretreating coal gasification ash water according to claim 1 using pulsed electrocoagulation / Fenton-like coupled chemical precipitation, characterized in that: In the pulse electrocoagulation / Fenton-like reaction, the bipolar pulse electrocoagulation / Fenton-like reactor (4) is cylindrical or cuboid in shape, with a gas collection hood or collection pipe at the top. The flow pattern of the bipolar pulse electrocoagulation / Fenton-like reactor (4) is plug flow or baffle flow, with a flow velocity in the range of 0.2 to 1.0 m / s.

3. The method for pretreating coal gasification ash water according to claim 1, characterized in that: In the pulsed electrocoagulation / Fenton-like reaction, the peroxides include hydrogen peroxide, ozone, sodium percarbonate, and potassium persulfate.

4. The method for pretreating coal gasification ash water according to claim 1 using pulsed electrocoagulation / Fenton-like coupled chemical precipitation, characterized in that: The chemical precipitation reaction includes: adding a precipitation regulator to the pulse electrocoagulation / Fenton-like effluent and stirring the reaction to obtain the chemical precipitation reaction effluent; The precipitation regulator includes one or more of sodium carbonate, sodium bicarbonate, sodium sulfate, or sodium hydroxide. By adding the precipitation regulator, the pH is adjusted to 8-10. During the stirring reaction, the stirring speed is 100-300 rpm and the stirring time is 2-10 min.

5. The method for pretreating coal gasification ash water according to claim 1 using pulsed electrocoagulation / Fenton-like coupled chemical precipitation, characterized in that: The floc coagulation and growth process includes: adding a coagulant to the effluent from the chemical precipitation reaction and stirring the reaction to obtain the effluent from the floc coagulation and growth process. The coagulant aid includes one of polyacrylamide or a natural polymeric coagulant aid, wherein the natural polymeric coagulant aid includes at least one of cellulose, chitosan, chitin, gelatin or bone glue, and the dosage of the coagulant aid is 2×10-4~10×10-3 g / L of chemically precipitated effluent.

6. The method for pretreating coal gasification ash water according to claim 1 using pulsed electrocoagulation / Fenton-like coupled chemical precipitation, characterized in that: The stirring reaction includes: a stirring speed of 50-150 rpm and a stirring time of 5-10 min. The solid-liquid separation includes: after the flocs coagulate and grow, they are settled by gravity, and the resulting supernatant is the treated coal gasification ash water.

7. The method for pretreating coal gasification ash water according to claim 1 using pulsed electrocoagulation / Fenton-like coupled chemical precipitation, characterized in that: The solid-liquid separation is performed by gravity sedimentation, inclined plate sedimentation or mechanical clarification, with a sedimentation time of 30 min to 60 min.

8. A pulsed electrocoagulation / Fenton-like coupled chemical precipitation pretreatment device for coal gasification ash water, the device being applicable to the pulsed electrocoagulation / Fenton-like coupled chemical precipitation pretreatment method for coal gasification ash water as described in claims 1-7, characterized in that: It includes a raw water tank (1), a pump (2), an aeration device (3), a pulse electrocoagulation / Fenton-like reactor (4), a chemical precipitation reactor (5), a flocculation stirring reactor (6), and a solid-liquid separator (7) arranged in series. The raw water tank (1), pump (2), aeration device (3) and pulse electrocoagulation / Fenton-like reactor (4) constitute a pulse electrocoagulation reaction unit. The chemical precipitation reactor (5), the flocculation stirring reactor (6), and the solid-liquid separator (7) constitute a chemical reaction and solid-liquid separation unit.

9. The pulsed electrocoagulation / Fenton-like coupled chemical precipitation pretreatment device for coal gasification ash water according to claim 8, characterized in that: The pulse electrocoagulation / Fenton-like reactor (4) is equipped with an electrode plate. The pair of electrode plates located on the outermost side of the pulse electrocoagulation / Fenton-like reactor (4) are fixedly connected to an installation block (8) by fasteners. A lifting frame (9) is provided below the installation block (8). A disassembly block (10) can be detachably connected to the bottom of the installation block (8) and the top of the lifting frame (9). The same rubber telescopic belt (11) is fixedly connected between the pair of disassembly blocks (10) in the vertical direction. The inner wall of the lifting frame (9) is provided with an inner wall groove (12), and a scraper (13) is movably inserted inside the inner wall groove (12). The inner wall of the scraper (13) is engraved with friction texture, and the inner wall of the scraper (13) abuts against the outer side of the electrode plate. The lifting frame (9) is detachably connected to an adjustment block (24) on all four sides. One end of the adjustment block (24) is fixedly connected to a round block (14). The side of the round block (14) away from the adjustment block (24) is coated with a magnetic coating first (15). The scraping frame (13) is coated with a magnetic coating second (16) that is magnetically repelled by the magnetic coating first (15). A pair of motors (17) are fixedly connected to the inner bottom wall of the flocculation stirring reactor (6). A spool (18) is fixedly connected to the output end of the motor (17). A pull rope (19) is fixedly connected between the spool (18) and the lifting frame (9). The interior of the lifting frame (9) is hollow and is equipped with a pump body. A dust inlet hole (20) is provided on the inner wall of the lifting frame (9). The dust inlet hole (20) is connected to the interior of the lifting frame (9). Both sides of the bottom of the lifting frame (9) are fixedly connected with a sealing plate (21) by fasteners. A filter hole (22) is provided on the sealing plate (21).

10. The pulsed electrocoagulation / Fenton-like coupled chemical precipitation pretreatment device for coal gasification ash water according to claim 9, characterized in that: The lifting frame (9) is equipped with a controller and a sensor inside. An indicator light (23) is fixedly connected to the outside of the lifting frame (9). Both the indicator light (23) and the sensor are electrically connected to the controller through wires.

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