Coal-fired power plant flue gas calcium carbide slag wet desulfurization system and method

Abstract

A wet desulfurization system and method for flue gas from a coal-fired power plant using calcium carbide slag, the desulfurization system comprising: a filter screen, a drum screen, a vibrating screen, an iron remover, a calcium carbide slag slurry pool, a desulfurization tower, a calcium sulfate crystallization pool, and a disc dewatering machine. The method comprises the following steps: (1) filtering the calcium carbide slag sequentially through the filter screen, drum screen, and vibrating screen to remove coarse slag, and then sending the fine slag to the iron remover to remove iron, obtaining calcium carbide screening slag; (2) sending it to the calcium carbide slag slurry pool, adding water, stirring and slurrying to obtain calcium carbide slag slurry; (3) sending it to the top of the desulfurization tower, sending sulfur-containing flue gas to the middle of the desulfurization tower, sending air to the bottom of the desulfurization tower, and pulse stirring reaction; (4) circulating the calcium carbide slag desulfurization slurry to the top of the desulfurization tower, or partially sending it to the calcium sulfate crystallization pool for crystallization and dehydration to obtain dehydrated gypsum. The calcium carbide slag slurry concentration in the desulfurization system of this invention is stable, the desulfurization efficiency is high and stable, and the desulfurization tower is not prone to scaling. The method of this invention is simple, low-cost, and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to a desulfurization system and method, specifically to a wet desulfurization system and method for flue gas from coal-fired power plants using calcium carbide slag. Background Technology

[0002] More than 80% of the flue gas from coal-fired boilers in thermal power plants uses limestone wet desulfurization technology. The desulfurization slurry and oxidation slurry are processed in one pool. The primary byproduct, calcium sulfite, can be oxidized into gypsum byproduct, which has better dehydration properties. However, the desulfurization tower is prone to scaling, and the desulfurization effect is unstable.

[0003] Calcium carbide slag is an industrial waste residue produced after the hydrolysis of calcium carbide to obtain acetylene gas. Because it contains large amounts of calcium oxide and silicon dioxide, it not only requires significant storage space but also poses certain safety and environmental pollution risks. Therefore, in recent years, calcium carbide slag has been increasingly used for desulfurization. However, during the desulfurization process, the concentration of the calcium carbide slag slurry is unstable due to the varying particle sizes, with larger particles not completely dissolved. Continuous use of calcium carbide slag slurry for flue gas desulfurization leads to an increasing concentration of sulfur dioxide in the desulfurized flue gas. Furthermore, scaling is a common problem during desulfurization in the desulfurization tower.

[0004] In summary, there is an urgent need to find a wet desulfurization system and method for flue gas from coal-fired power plants using calcium carbide slag that has a stable slurry concentration, high and stable desulfurization efficiency, is not prone to scaling in the desulfurization tower, has a simple process, low cost, and is suitable for industrial production. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a wet desulfurization system for flue gas of coal-fired power plants with carbide slag, which has stable concentration of carbide slag slurry, high and stable desulfurization efficiency, and is not prone to scaling in the desulfurization tower.

[0006] The further technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a simple, low-cost, and industrially suitable wet desulfurization method for flue gas from coal-fired power plants using calcium carbide slag.

[0007] This invention provides a wet desulfurization system for flue gas from a coal-fired power plant using calcium carbide slag, comprising: a filter screen, a drum screen, a vibrating screen, an iron separator, a calcium carbide slag slurry pool, a desulfurization tower, a calcium sulfate crystallization pool, and a disc dewatering machine; the fine slag from the calcium carbide slag raw material after being screened by the filter screen is fed into the drum screen; the fine slag from the drum screen is fed into the vibrating screen, and the fine slag after being screened by the vibrating screen is then fed into the iron separator, and the calcium carbide slag screened by the iron separator after removing iron is fed into the calcium carbide slag slurry pool; the calcium carbide slag slurry pool is connected to the top of the desulfurization tower; sulfur-containing flue gas is fed into the middle of the desulfurization tower and discharged from the top, and air is fed into the lower part of the desulfurization tower and discharged from the top; the calcium carbide slag desulfurization slurry in the desulfurization tower is circulated to the top of the desulfurization tower, or the calcium carbide slag desulfurization slurry discharged from the lower part of the desulfurization tower is sent into the calcium sulfate crystallization pool for crystallization, and the crystallized slurry enters the disc dewatering machine for dewatering.

[0008] Preferably, the wastewater generated by the calcium sulfate crystallization tank and the disc dewatering machine is sent to an electrocoagulation treatment tank for treatment.

[0009] Preferably, the limestone slurry tank is connected in parallel with the carbide slag slurry pool and is connected to the top of the desulfurization tower.

[0010] Preferably, both the carbide slag slurry tank and the limestone slurry tank are equipped with a stirring slurry generator.

[0011] Preferably, slurry circulation pumps are provided between the carbide slag slurry tank and the limestone slurry tank and the desulfurization tower, as well as between the lower and upper parts of the desulfurization tower, and flow rate valves are provided on the output pipes.

[0012] Preferably, the filter screen has a pore size of 180–240 μm. The filter screen can retain larger carbide slag particles above the screen, allowing only smaller particles to pass through the pores, thereby achieving the screening of carbide slag.

[0013] Preferably, the mesh size of the drum screen is 70–100 μm. Calcium carbide slag often contains particles of various sizes, and the mesh size of the drum screen can be adjusted according to the size and characteristics of different calcium carbide slag particles in order to separate different particles.

[0014] Preferably, the mesh size of the vibrating screen is 50–65 μm. Using a vibrating screen to ultimately screen out carbide slag of suitable particle size is more beneficial for pulping.

[0015] Preferably, the height-to-diameter ratio of the desulfurization tower is 3 to 5:1.

[0016] Preferably, a slurry inlet pipe is provided on one side of the top of the desulfurization tower, and the upper end of the slurry inlet pipe is connected to the lower end of the output pipe of the carbide slag slurry pool and the limestone slurry tank.

[0017] Preferably, the desulfurization tower is provided with a flue gas inlet pipe in the middle.

[0018] Preferably, the lower part of the desulfurization tower is provided with a desulfurization slurry output pipe, which is connected to the slurry inlet pipe and the calcium sulfate crystallization pool respectively.

[0019] Preferably, the desulfurization tower is provided with a desulfurization flue gas discharge pipe at the top center.

[0020] Preferably, a display panel is provided in the middle of the desulfurization tower.

[0021] Preferably, the display panel is electrically connected to the temperature probe and pH probe inside the desulfurization tower.

[0022] Preferably, the lower part of the desulfurization tower is equipped with an axial flow oxidation fan, and the part extending into the desulfurization tower is a gas distribution pipe.

[0023] Preferably, a pulse pump is provided at the bottom of the inner cavity of the desulfurization tower.

[0024] Preferably, the slurry inlet pipe is provided with a downward spray head at the bend at the end of the pipe located in the middle of the top of the desulfurization tower cavity.

[0025] Preferably, a waisted flue gas demister, which is wide at both ends and narrow in the middle, is fixedly installed in the inner cavity of the desulfurization tower below the spray head.

[0026] Preferably, the middle part of the flue gas demister is a through hole, and a ring-shaped swirling corrugated plate is provided at the through hole. The upper inner wall of the flue gas demister is spirally provided with a descaling guide groove.

[0027] The technical solution adopted by the present invention to further solve its technical problem is as follows: A wet desulfurization method for flue gas from coal-fired power plants using calcium carbide slag, comprising the following steps:

[0028] (1) The calcium carbide slag is filtered through a filter screen, a drum screen and a vibrating screen in sequence to remove coarse slag, and then the resulting fine slag is sent to an iron remover to remove iron, thus obtaining calcium carbide screening slag.

[0029] (2) The calcium carbide screening slag obtained in step (1) is sent into the calcium carbide slag slurry tank, water is added, and the mixture is stirred and slurried to obtain calcium carbide slag slurry.

[0030] (3) The calcium carbide slag slurry obtained in step (2) is sent to the top of the desulfurization tower, the sulfur-containing flue gas is sent to the middle of the desulfurization tower, and the air is sent to the bottom of the desulfurization tower. After pulse stirring reaction in the desulfurization tower, calcium carbide slag desulfurization slurry is obtained and desulfurization flue gas is discharged.

[0031] (4) Circulate the calcium carbide slag desulfurization slurry obtained in step (3) to the top of the desulfurization tower, or send part of it into the calcium sulfate crystallization pool for crystallization and dehydration to obtain dehydrated gypsum.

[0032] Preferably, in step (1), the main components and their mass fractions of the carbide slag are as follows: CaO 80-95%, SiO2 2-8%, Fe2O3 0.5-1.5%, with a total mass fraction ≤100%. The carbide slag used in this invention originates from the solid waste generated during the production of polyvinyl chloride. The CaO contained in the carbide slag will generate a large amount of strongly alkaline Ca(OH)2 after slurrying, which is a good sulfur dioxide absorbent. Experimental results show that the desulfurization capacity of carbide slag is 20% higher than that of commercial Ca(OH)2, while the product cost is only one-third of that of commercial Ca(OH)2.

[0033] Preferably, in step (1), the magnetic field strength for iron removal is 1500–2200 kA / m. Iron removal can remove iron-containing components from carbide slag, reducing the wear of desulfurization equipment caused by iron-containing components.

[0034] Preferably, in step (2), the mass ratio of water to the calcium carbide screening slag is 2.2–3.6:1 (more preferably 2.3–3.0:1). When the water-to-material ratio is low, the slurry viscosity is high and the fluidity is poor, which is not conducive to the subsequent desulfurization reaction; when the water-to-material ratio is high, the slurry viscosity is low and the fluidity is good, which easily causes slurry deposition.

[0035] Preferably, in step (2), the stirring speed is 200-400 rpm and the time is 1-3 hours. During the stirring process, the carbide slag particles interact with water molecules to form a uniformly dispersed mixture composed of carbide slag particles and water molecules, namely, carbide slag slurry. Specifically, the principle of stirring and slurrying of carbide slag slurry includes the following aspects: 1) Dispersion of carbide slag particles: During the stirring process, mechanical energy can disperse the carbide slag particles evenly, avoiding particle aggregation and accumulation; in addition, stirring can also destroy the hard shell layer and binding material on the surface of carbide slag particles, increasing the particle surface area and reaction rate; 2) Dissolution of water molecules: Stirring can also make water molecules contact the surface of carbide slag particles, and undergo ion exchange reaction with calcium ions on the surface of carbide slag, dissolving Ca 2+ Ions and OH - Ions form calcium hydroxide slurry; 3) Stirring speed adjustment: During the stirring and slurrying process of carbide slag slurry, if the stirring speed is too fast, the viscosity of the slurry will decrease; if the stirring speed is too slow, the dispersibility and stability of the slurry will be affected.

[0036] Preferably, in step (3), the flow rate of the carbide slag slurry t / h = E * the flow rate of sulfur-containing flue gas m 3 / h* Concentration of sulfur dioxide in sulfur-containing flue gas (mg / m³) 3 *10 -9Wherein, E = 3.2–4.7 (more preferably 3.8–4.6), and the flow rate of the calcium carbide slag slurry is adjusted within the E value range to achieve a pH value of 4.2–4.8 in the absorber slurry. The flow rate of the calcium carbide slag slurry depends on factors such as the sulfur dioxide content in the flue gas, the flue gas flow rate, and the calcium carbide slag concentration in the slurry (parameter E). Compared with the conventional limestone-gypsum wet process, the calcium carbide slag-gypsum process has a lower liquid-to-gas ratio, a faster desulfurization reaction rate, and higher desulfurization efficiency.

[0037] Preferably, in step (3), the flow rate of the sulfur-containing flue gas is 50,000 to 2,000,000 m³ / s. 3 / h. The amount of flue gas processed is affected by the size of the absorption tower; if the amount of flue gas processed is too large, it will affect the desulfurization efficiency.

[0038] Preferably, in step (3), the concentration of sulfur dioxide in the sulfur-containing flue gas is 500–5000 mg / m³. 3 Sulfur-containing flue gas originates from coal-fired power plants. Excessive sulfur dioxide concentration can lead to excessively high sulfur dioxide concentrations in desulfurization flue gas, making it difficult to meet emission standards.

[0039] Preferably, in step (3), the pulse pump flow rate for the pulse stirring reaction is 2000–5000 m³ / h. 3 / h. Pulse pumps can reduce wear and tear on equipment caused by impurities in carbide slag. If the pulse pump flow rate is too low, slurry sedimentation will occur; if the pulse pump flow rate is too high, excessive power consumption will result.

[0040] Preferably, in step (3), the air flow rate m 3 / h = sulfur-containing flue gas flow rate (m) 3 / h* Concentration of sulfur dioxide in sulfur-containing flue gas (mg / m³) 3 *10 -6 *0.25 / (k*0.2315kg / m 3 ), where k = 0.18~0.28. In the formula, 0.25 indicates that 0.25 kg of oxygen is needed to oxidize 1 kg of sulfur dioxide, and k represents the air utilization rate of oxidation, 0.2315 kg / m³. 3 Indicates 1m 3 The air contains 0.2315 kg of oxygen.

[0041] Preferably, in step (3), when the concentration of sulfur dioxide in the desulfurization flue gas is ≥60 mg / m³, 3 Alternatively, when the moisture content of dehydrated gypsum is ≥15%, limestone slurry is added to the desulfurization tower until the concentration of sulfur dioxide in the desulfurization flue gas is <30mg / m³. 3 Alternatively, the moisture content of the dehydrated gypsum can be less than 15%. The purpose of adding it is to stabilize the pH value of the absorber slurry.

[0042] Preferably, the flow rate of the limestone slurry is 0.1 to 0.4 times (more preferably 0.20 to 0.35 times) that of the carbide slag slurry.

[0043] Preferably, the density of the limestone slurry is 1180–1250 kg / m³. 3 The density of the limestone slurry allows for more effective control of the pH value of the absorber slurry.

[0044] Preferably, in step (4), the sum of the flow rates of the carbide slag desulfurization slurry circulation, the fresh carbide slag slurry, and the limestone slurry, and the liquid-to-gas ratio (L / m) of the sulfur-containing flue gas, is... 3 ≥8 (more preferably 10 to 20).

[0045] Preferably, in step (4), the flow rate of the carbide slag desulfurization slurry fed into the calcium sulfate crystallization tank is equivalent to 1.01 to 1.20 times the sum of the flow rates of the fresh carbide slag slurry and the limestone slurry.

[0046] Preferably, in step (4), the pH value of the crystallization is 4.2 to 4.8.

[0047] Preferably, in step (4), the solid content of the gypsum slurry before dehydration is 25-40%, and the water content of the dehydrated gypsum is 5-14%. If the solid content of the gypsum slurry before dehydration is too low, the dehydration effect will be poor, and the water content of the dehydrated gypsum will be high; if the solid content of the gypsum slurry before dehydration is too high, it will affect the dehydration speed and may even cause problems such as equipment blockage.

[0048] Preferably, in step (4), the wastewater generated from crystallization and dehydration is neutralized by electrocoagulation.

[0049] Preferably, the electrocoagulation neutralization treatment specifically involves: first adjusting the pH of the wastewater generated during crystallization and dehydration to 6.5–7.5 using waste alkaline solution, then performing electrocoagulation. After the sludge and wastewater are separated, the sludge is reintroduced into a disc dewatering machine for further dewatering. The flocculation effect is optimal when the pH is within the range of 6.5–7.5.

[0050] The beneficial effects of this invention are as follows:

[0051] (1) The desulfurization system of the present invention uses three layers of calcium carbide slag raw material screening. The filter screen, drum screen and vibrating screen can remove large particles of impurities in the calcium carbide slag. At the same time, the iron is removed by the iron remover, ensuring that the calcium carbide slag entering the calcium carbide slag slurry pool is all small slag, improving the dissolution efficiency and obtaining a stable limestone solution concentration. This can reduce the wear and blockage of equipment and pipelines caused by impurities in subsequent processes, improve the service life of the equipment, and also improve the purity of the calcium carbide slag slurry.

[0052] (2) The design of the flue gas demister in the desulfurization tower of the desulfurization system of the present invention enables the atomized spray slurry to form an atomization area above the swirl corrugated plate, so that the flue gas passing through can be mixed and treated. The liquefied flue gas will flow down along the swirl corrugated plate and return to the slurry at the bottom of the tower. The descaling guide channel enables the spray liquid to swirl in a directional manner, thereby flushing the dirt attached to the swirl corrugated plate and achieving the effect of automatic descaling.

[0053] (3) The method of the present invention has a stable concentration of carbide slag slurry, and the desulfurization efficiency can reach up to 99.5% and remain stable, and the desulfurization tower is not prone to scaling.

[0054] (4) The method of the present invention uses carbide slag instead of limestone for flue gas desulfurization. The process is simple, can reduce the desulfurization operation cost, and has good economic, environmental and social benefits. It is suitable for industrial production. Attached Figure Description

[0055] Figure 1 These are schematic diagrams of the process structure of the wet desulfurization system for flue gas from coal-fired power plants using calcium carbide slag, as described in Embodiments 1-3 of this invention.

[0056] Figure 2 This is a schematic diagram of the upper right front axis view of the desulfurization tower in the wet desulfurization system of flue gas from coal-fired power plants using calcium carbide slag, as described in Embodiments 1-3 of the present invention.

[0057] Figure 3 This is a schematic diagram of the lower right front axis view of the desulfurization tower in the wet desulfurization system of flue gas from coal-fired power plants using calcium carbide slag, as described in Embodiments 1-3 of the present invention.

[0058] Figure 4 This is an axial view structural diagram of the upper part of the desulfurization tower in the wet desulfurization system of flue gas from a coal-fired power plant using calcium carbide slag, as described in Embodiments 1-3 of the present invention, in the state of upward movement.

[0059] Figure 5 yes Figure 4 A magnified structural diagram of part A in the middle;

[0060] Figure 6 This is a schematic diagram of the lower axial view of the upper part of the desulfurization tower in the wet desulfurization system of flue gas from a coal-fired power plant using calcium carbide slag, as described in Embodiments 1-3 of the present invention.

[0061] Figure 7 This is a schematic diagram of the axial view of the flue gas demister in the wet desulfurization system of coal-fired power plant flue gas and calcium carbide slag in Embodiments 1-3 of the present invention;

[0062] List of reference numerals in the attached diagram:

[0063] 1. Filter screen; 2. Rotary drum screen; 3. Vibrating screen; 4. Iron separator; 5. Calcium carbide slag slurry tank; 6. Desulfurization tower; 601. Slurry inlet pipe; 60101. Spray head; 602. Flue gas inlet pipe; 603. Desulfurization slurry outlet pipe; 604. Desulfurization flue gas outlet pipe; 605. Display panel; 606. Axial flow oxidation fan; 607. Pulse pump; 608. Flue gas demister; 60801. Swirl corrugated plate; 60802. Descaling guide channel; 7. Calcium sulfate crystallization tank; 8. Disc dewatering machine; 9. Electrocoagulation treatment tank; 10. Limestone slurry tank. Detailed Implementation

[0064] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0065] The calcium carbide slag used in this embodiment of the invention is derived from calcium carbide slag solid waste generated during the production of polyvinyl chloride. The main components and mass fractions of the calcium carbide slag are as follows: CaO 87.28%, SiO2 5.81%, Fe2O3 0.85%. Unless otherwise specified, the raw materials or chemical reagents used in this embodiment of the invention are obtained through conventional commercial channels.

[0066] Examples 1-3 of a wet desulfurization system for flue gas from a coal-fired power plant using calcium carbide slag

[0067] like Figures 1-7 As shown, a wet desulfurization system for flue gas from a coal-fired power plant using calcium carbide slag includes: a filter screen 1, a drum screen 2, a vibrating screen 3, an iron remover 4, a calcium carbide slag slurry pool 5, a desulfurization tower 6, a calcium sulfate crystallization pool 7, and a disc dewatering machine 8. Fine slag from the calcium carbide slag raw material, after being screened by the filter screen 1, is fed into the drum screen 2. The fine slag from the drum screen 2 is then fed into the vibrating screen 3, and the fine slag after being screened by the vibrating screen 3 is further fed into the iron remover 4. The calcium carbide slag screened by the iron remover 4, after iron removal, is fed into the calcium carbide slag slurry pool 5. The calcium carbide slag slurry pool 5 is connected to the top of the desulfurization tower 6. Sulfur-containing flue gas is fed into the middle of the desulfurization tower 6 and discharged from the top, while air is fed into the lower part of the desulfurization tower 6 and discharged from the top. The calcium carbide slag desulfurization slurry in the desulfurization tower 6 is circulated to the top of the desulfurization tower 6, or the calcium carbide slag desulfurization slurry discharged from the lower part of the desulfurization tower 6 is fed into the calcium sulfate crystallization pool 7 for crystallization. The crystallized slurry then enters the disc dewatering machine 8 for dewatering.

[0068] Furthermore, the wastewater generated by the calcium sulfate crystallization tank 7 and the disc dewatering machine 8 is sent to the electrocoagulation treatment tank 9 for treatment; the limestone slurry tank 10 is connected in parallel with the carbide slag slurry tank 5 and is connected to the top of the desulfurization tower 6; both the carbide slag slurry tank 5 and the limestone slurry tank 10 are equipped with stirring slurry devices; slurry circulation pumps are installed between the carbide slag slurry tank 5 and the limestone slurry tank 10 and the desulfurization tower 6, as well as between the lower and upper parts of the desulfurization tower 6, and flow rate valves are installed on the output pipes. This is to ensure the desulfurization effect of the carbide slag. When the desulfurization effect of the carbide slag is not good, the limestone slurry tank 10 can be put into operation immediately to improve the desulfurization effect.

[0069] The filter screen 1 has a pore size of 200 μm; the drum screen 2 has a pore size of 80 μm; and the vibrating screen 3 has a pore size of 60 μm.

[0070] The desulfurization tower 6 has a height-to-diameter ratio of 4:1. A slurry inlet pipe 601 is located on one side of the top of the desulfurization tower 6, with its upper end connected to the lower ends of the output pipes of the carbide slag slurry pool 5 and the limestone slurry tank 10. A flue gas inlet pipe 602 is located in the middle of the desulfurization tower 6. A desulfurization slurry outlet pipe 603 is located at the bottom of the desulfurization tower 6, and is connected to the slurry inlet pipe 601 and the calcium sulfate crystallization pool 7, respectively. A desulfurization flue gas outlet pipe 604 is located at the top center of the desulfurization tower 6. A display panel 605 is located in the middle of the desulfurization tower 6. The display panel 605 is electrically connected to a temperature probe and a pH probe inside the desulfurization tower 6 for real-time observation of the composition within the tower. An axial flow oxidation fan 606 is located at the bottom of the desulfurization tower 6, with the portion extending into the tower as a gas distribution pipe. A pulse pump 607 is located at the bottom of the inner cavity of the desulfurization tower 6 for stirring the slurry.

[0071] The slurry inlet pipe 601 has a downward-facing spray head 60101 at its end bend at the top center of the desulfurization tower 6 cavity, used to atomize and spray the slurry. Below the spray head 60101, a waist-shaped flue gas demister 608, wider at both ends and narrower in the middle, is fixedly installed in the desulfurization tower 6 cavity. The flue gas demister 608 has a through hole in the middle, with annularly distributed swirling corrugated plates 60801 at the through hole. The upper end of the flue gas demister 608... The cavity sidewall is spirally provided with a descaling guide groove 60802. The atomized spray slurry can form an atomization area above the swirl corrugated plate 60801, so that the flue gas passing through can be mixed and treated. The liquefied flue gas will flow down along the swirl corrugated plate 60801 and return to the slurry at the bottom of the tower. The descaling guide groove 60802 can make the spray liquid swirl in a directional manner, thereby flushing the dirt attached to the swirl corrugated plate 60801 and achieving the effect of automatic descaling.

[0072] The specific usage and function of this embodiment: In the wet desulfurization system of flue gas from a coal-fired power plant using calcium carbide slag, after the calcium carbide slag raw material is screened by filter screen 1, the small slag is sent to drum screen 2, and the waste slag is discharged. The small slag screened by drum screen 2 is sent to vibrating screen 3. The small slag screened by vibrating screen 3 is then sent to iron remover 4 to remove iron slag, so as to reduce the wear on subsequent desulfurization equipment. The iron-removed small slag in iron remover 4 is sent to calcium carbide slag slurry tank 5, water is added, and it is stirred and slurried. The calcium carbide slag slurry in calcium carbide slag slurry tank 5 is sent to the top of desulfurization tower 6. At the same time, sulfur-containing flue gas is sent to the middle of desulfurization tower 6, and air is sent to the bottom of desulfurization tower 6. After the desulfurization reaction, the desulfurized flue gas is discharged from the top of desulfurization tower 6, and the calcium carbide slag desulfurization slurry is discharged from the bottom of desulfurization tower 6. It is circulated to the top of desulfurization tower 6, or part of it is sent to calcium sulfate crystallization tank 7 for crystallization. The crystallized slurry is sent to disc dewatering machine 8 for dewatering. Wastewater from calcium sulfate crystallization tank 7 and disc dewatering machine 8 can also be sent to electrocoagulation treatment tank 9 for further treatment. After the sludge and wastewater are separated in electrocoagulation treatment tank 9, the sludge is sent back to disc dewatering machine 8 for further dewatering. When the concentration of sulfur dioxide in the desulfurization flue gas is ≥60mg / m³... 3 Alternatively, when the moisture content of the dehydrated gypsum is ≥15%, the limestone slurry in the limestone slurry tank 10 is sent to the top of the desulfurization tower 6.

[0073] Example 1 of a wet desulfurization method using calcium carbide slag for flue gas from a coal-fired power plant

[0074] (1) 10t of calcium carbide slag was filtered through a filter screen, a drum screen and a vibrating screen in sequence to remove coarse slag. The resulting fine slag was then sent to an iron remover to remove iron under a magnetic field strength of 1800kA / m, resulting in 9.9t of calcium carbide screening slag.

[0075] (2) The 9.9t calcium carbide screening slag obtained in step (1) is sent into the calcium carbide slag slurry tank, 24t of water is added, and the mixture is stirred and slurried at 300rpm for 2h to obtain calcium carbide slag slurry.

[0076] (3) The calcium carbide slag slurry obtained in step (2) is discharged at a flow rate of 10 t / h (calcium carbide slag slurry flow rate t / h = 4.43 * 1137322 m³ / h). 3 / h*1985mg / m 3 *10 -9 The slurry in the absorption tower is controlled to have a pH of 4.6 before being fed into the top of the desulfurization tower. The sulfur-containing flue gas (concentration of 1985 mg / m³) is then introduced into the tower. 3 With a flow rate of 1,137,322 m³ / h 3 The air is fed into the middle of the desulfurization tower at a flow rate of 12190 m³ / h. Inside the desulfurization tower, an axial flow oxidation fan distributes air through a distribution pipe. 3 / h (air supply flow rate in m) 3 / h=1137322m 3 / h*1985mg / m 3 *10-6 *0.25 / (0.2*0.2315kg / m 3 The solution is fed into the lower part of the desulfurization tower at a pulse pump flow rate of 4000 m³ / h. 3 After pulse stirring reaction at / h, calcium carbide slag desulfurization slurry is obtained and desulfurization flue gas is discharged;

[0077] (4) Circulate the desulfurization slurry obtained in step (3) to the top of the desulfurization tower (the sum of the circulation flow rate of the desulfurization slurry and the flow rate of the fresh desulfurization slurry, and the liquid-to-gas ratio of the sulfur-containing flue gas L / m 3 The gypsum slurry (solid content 35.2%) was partially fed into a calcium sulfate crystallization tank at a flow rate of 11 t / h. Crystallization was carried out at a pH of 4.6. The gypsum slurry (solid content 35.2%) was dehydrated to a water content of 11.8% using a disc dewatering machine to obtain dehydrated gypsum.

[0078] In step (4), the wastewater generated from crystallization and dehydration is neutralized by electrocoagulation. Specifically, the pH value of the wastewater generated from crystallization and dehydration is adjusted to 7.0 by using waste alkaline solution from the power plant, and then electrocoagulation is performed. After the sludge and wastewater are separated, the sludge is sent back to the disc dewatering machine for dewatering.

[0079] The concentration of sulfur dioxide in the desulfurization flue gas discharged in step (3) was found to be 10 mg / m³. 3 The desulfurization rate is 99.5%.

[0080] Example 2 of a wet desulfurization method using calcium carbide slag for flue gas from a coal-fired power plant

[0081] (1) 12t of calcium carbide slag was filtered through a filter screen, a drum screen and a vibrating screen in sequence to remove coarse slag. The resulting fine slag was then sent to an iron remover to remove iron under a magnetic field strength of 2000kA / m, resulting in 11.88t of calcium carbide screening slag.

[0082] (2) The 11.88t calcium carbide screening slag obtained in step (1) is sent into the calcium carbide slag slurry tank, 33t of water is added, and the mixture is stirred and slurried at 400rpm for 1.5h to obtain calcium carbide slag slurry.

[0083] (3) The calcium carbide slag slurry obtained in step (2) is discharged at a flow rate of 11 t / h (calcium carbide slag slurry flow rate t / h = 4.3 * 1536732 m³ / h). 3 / h*1667mg / m 3 *10 -9 The slurry in the absorption tower (with a pH value controlled at 4.4) is fed into the top of the desulfurization tower, where sulfur-containing flue gas (concentration of 1667 mg / m³) is introduced. 3 With a flow rate of 1,536,732 m³ / h 3 The air is fed into the middle of the desulfurization tower at a flow rate of 12575 m³ / h. Inside the desulfurization tower, an axial flow oxidation fan distributes air through a distribution pipe. 3 / h (air supply flow rate in m) 3 / h=1536732m 3 / h*1667mg / m 3 *10 -6 *0.25 / (0.22*0.2315kg / m 3 The solution is fed into the lower part of the desulfurization tower at a pulse pump flow rate of 4500 m³ / h. 3 After pulse stirring reaction at / h, calcium carbide slag desulfurization slurry is obtained and desulfurization flue gas is discharged;

[0084] When the concentration of sulfur dioxide in the desulfurization flue gas is ≥60 mg / m³ 3 At that time, 3 t / h of limestone slurry (density 1200 kg / m³) was added to the desulfurization tower. 3 The concentration of sulfur dioxide in the desulfurization flue gas is <30 mg / m³. 3 ;

[0085] (4) Circulate the carbide slag desulfurization slurry obtained in step (3) to the top of the desulfurization tower (the sum of the flow rate of the carbide slag desulfurization slurry circulation, the flow rate of the fresh carbide slag slurry, and the flow rate of the limestone slurry, and the liquid-to-gas ratio of the sulfur-containing flue gas L / m 3 The gypsum slurry (solid content 35.2%) was partially fed into the calcium sulfate crystallization tank at a flow rate of 12t / h (15.5t / h when limestone slurry was added). Crystallization was carried out at a pH of 4.4. The gypsum slurry (solid content 35.2%) was dehydrated to a water content of 11.7% using a disc dewatering machine to obtain dehydrated gypsum.

[0086] In step (4), the wastewater generated from crystallization and dehydration is neutralized by electrocoagulation. Specifically, the pH value of the wastewater generated from crystallization and dehydration is adjusted to 7.0 by using waste alkaline solution from the power plant, and then electrocoagulation is performed. After the sludge and wastewater are separated, the sludge is sent back to the disc dewatering machine for dewatering.

[0087] The concentration of sulfur dioxide in the desulfurization flue gas discharged in step (3) was found to be 15 mg / m³. 3 The desulfurization rate is 99.1%.

[0088] Example 3 of a wet desulfurization method using calcium carbide slag for flue gas from a coal-fired power plant

[0089] (1) 8.2t of calcium carbide slag was filtered through a filter screen, a drum screen and a vibrating screen in sequence to remove coarse slag. The resulting fine slag was then sent to an iron remover to remove iron under a magnetic field strength of 1500kA / m to obtain 8.1t of calcium carbide screening slag.

[0090] (2) The 8.1t calcium carbide screening slag obtained in step (1) is sent into the calcium carbide slag slurry tank, 20t of water is added, and the mixture is stirred and slurried at 300rpm for 2.5h to obtain calcium carbide slag slurry.

[0091] (3) The calcium carbide slag slurry obtained in step (2) is discharged at a flow rate of 5.46 t / h (calcium carbide slag slurry flow rate t / h = 4.2 * 856322 m³ / h). 3 / h*1519mg / m 3 *10 -9 The pH of the absorber slurry (controlled to 4.6) is fed into the top of the desulfurization tower, where sulfur-containing flue gas (concentration 1519 mg / m³) is introduced. 3 With a flow rate of 856322m 3 The air is fed into the middle of the desulfurization tower at a flow rate of 7804 m³ / h. Inside the desulfurization tower, an axial flow oxidation fan distributes air through a distribution pipe. 3 / h (air supply flow rate in m) 3 / h=856322m 3 / h*1519mg / m 3 *10 -6 *0.25 / (0.18*0.2315kg / m 3 The solution is fed into the lower part of the desulfurization tower at a pulse pump flow rate of 3500 m³ / h. 3 After pulse stirring reaction at / h, calcium carbide slag desulfurization slurry is obtained and desulfurization flue gas is discharged;

[0092] When the moisture content of the dehydrated gypsum is ≥15%, add 1.8 t / h of limestone slurry (density 1200 kg / m³) to the desulfurization tower. 3 The moisture content of the dehydrated gypsum is less than 15%.

[0093] (4) Circulate the carbide slag desulfurization slurry obtained in step (3) to the top of the desulfurization tower (the sum of the flow rate of the carbide slag desulfurization slurry circulation, the flow rate of the fresh carbide slag slurry, and the flow rate of the limestone slurry, and the liquid-to-gas ratio of the sulfur-containing flue gas L / m 3 The gypsum slurry (solid content 34.8%) was partially fed into the calcium sulfate crystallization tank at a flow rate of 6t / h (8.2t / h when limestone slurry was added). Crystallization was carried out at a pH of 4.5. The gypsum slurry (solid content 34.8%) was dehydrated to a water content of 11.9% using a disc dewatering machine to obtain dehydrated gypsum.

[0094] In step (4), the wastewater generated from crystallization and dehydration is neutralized by electrocoagulation. Specifically, the pH value of the wastewater generated from crystallization and dehydration is adjusted to 7.0 by using waste alkaline solution from the power plant, and then electrocoagulation is performed. After the sludge and wastewater are separated, the sludge is sent back to the disc dewatering machine for dewatering.

[0095] The concentration of sulfur dioxide in the desulfurization flue gas discharged in step (3) was found to be 11 mg / m³. 3 The desulfurization rate is 99.3%.

[0096] Comparative Example 1

[0097] (1) 10t of calcium carbide slag was filtered through a filter screen, a drum screen and a vibrating screen in sequence to remove coarse slag. The resulting fine slag was then sent to an iron remover to remove iron under a magnetic field strength of 1800kA / m, resulting in 9.9t of calcium carbide screening slag.

[0098] (2) The 9.9t calcium carbide screening slag obtained in step (1) is sent into the calcium carbide slag slurry tank, 24t of water is added, and the mixture is stirred and slurried at 300rpm for 0.5h to obtain calcium carbide slag slurry.

[0099] (3) The calcium carbide slag slurry obtained in step (2) is discharged at a flow rate of 11 t / h (calcium carbide slag slurry flow rate t / h = 4.9 * 1137322 m³ / h). 3 / h*1985mg / m 3 *10 -9 The slurry in the absorption tower (with a controlled pH of 5.0) is fed into the top of the desulfurization tower, where sulfur-containing flue gas (concentration of 1985 mg / m³) is introduced. 3 With a flow rate of 1,137,322 m³ / h 3 The air is fed into the middle of the desulfurization tower at a flow rate of 12190 m³ / h. Inside the desulfurization tower, an axial flow oxidation fan distributes air through a distribution pipe. 3 / h (air supply flow rate in m) 3 / h=1137322m 3 / h*1985mg / m 3 *10 -6 *0.25 / (0.2*0.2315kg / m 3 The solution is fed into the lower part of the desulfurization tower at a pulse pump flow rate of 4000 m³ / h. 3 After pulse stirring reaction at / h, calcium carbide slag desulfurization slurry is obtained and desulfurization flue gas is discharged;

[0100] (4) Circulate the desulfurization slurry obtained in step (3) to the top of the desulfurization tower (the sum of the circulation flow rate of the desulfurization slurry and the flow rate of the fresh desulfurization slurry, and the liquid-to-gas ratio of the sulfur-containing flue gas L / m 3 The gypsum slurry (solid content 35.2%) was partially fed into a calcium sulfate crystallization tank at a flow rate of 12.1 t / h. Crystallization was carried out at a pH of 4.9. The gypsum slurry (solid content 35.2%) was dehydrated to a water content of 11.8% using a disc dewatering machine to obtain dehydrated gypsum.

[0101] In step (4), the wastewater generated from crystallization and dehydration is neutralized by electrocoagulation. Specifically, the pH value of the wastewater generated from crystallization and dehydration is adjusted to 7.0 by using waste alkaline solution from the power plant, and then electrocoagulation is performed. After the sludge and wastewater are separated, the sludge is sent back to the disc dewatering machine for dewatering.

[0102] The concentration of sulfur dioxide in the desulfurization flue gas discharged in step (3) was found to be 54 mg / m³. 3The desulfurization rate was 97.3%, indicating that pH value has a significant impact on the desulfurization effect of carbide slag.

Claims

1. A wet desulfurization system for flue gas from a coal-fired power plant using calcium carbide slag, characterized in that, include: The system consists of a filter screen (1), a drum screen (2), a vibrating screen (3), an iron remover (4), a carbide slag slurry pool (5), a desulfurization tower (6), a calcium sulfate crystallization pool (7), and a disc dewatering machine (8). Fine slag from the carbide slag raw material after being screened by the filter screen (1) is fed into the drum screen (2). The fine slag in the drum screen (2) is fed into the vibrating screen (3), and the fine slag after being screened by the vibrating screen (3) is then fed into the iron remover (4). The carbide slag removed from the iron in the iron remover (4) is fed into the carbide slag slurry pool (5). The carbide slag slurry pool (5) is connected to the top of the desulfurization tower (6). Sulfur-containing flue gas is fed into the middle of the desulfurization tower (6) and discharged from the top. Air is fed into the lower part of the desulfurization tower (6) and discharged from the top. The carbide slag in the desulfurization tower (6) is desulfurized. The slurry is circulated to the top of the desulfurization tower (6), or the calcium carbide slag desulfurization slurry discharged from the bottom of the desulfurization tower (6) is sent to the calcium sulfate crystallization tank (7) for crystallization. The crystallized slurry is then sent to the disc dewatering machine (8) for dewatering. The wastewater generated by the calcium sulfate crystallization tank (7) and the disc dewatering machine (8) is sent to the electrocoagulation treatment tank (9) for treatment. The limestone slurry tank (10) is connected in parallel with the calcium carbide slag slurry tank (5) and is connected to the top of the desulfurization tower (6). Both the calcium carbide slag slurry tank (5) and the limestone slurry tank (10) are equipped with stirring slurry generators. Slurry circulation pumps are installed between the calcium carbide slag slurry tank (5) and the limestone slurry tank (10) and the desulfurization tower (6), as well as between the bottom and top of the desulfurization tower (6), and the output pipes are equipped with slurry circulation pumps. Flow rate valve; the filter screen (1) has a mesh size of 180-240 μm; the drum screen (2) has a mesh size of 70-100 μm; the vibrating screen (3) has a mesh size of 50-65 μm; the height-to-diameter ratio of the desulfurization tower (6) is 3-5:1; a slurry inlet pipe (601) is provided on one side of the top of the desulfurization tower (6), and the upper end of the slurry inlet pipe (601) is connected to the lower end of the output pipes of the carbide slag slurry pool (5) and the limestone slurry tank (10); a flue gas inlet pipe (602) is provided in the middle of the desulfurization tower (6); a desulfurization slurry output pipe (603) is provided at the bottom of the desulfurization tower (6), and is connected to the slurry inlet pipe (601) and the calcium sulfate crystallization pool (7) respectively; the top of the desulfurization tower (6) A desulfurization flue gas discharge pipe (604) is provided in the middle of the end; a display panel (605) is provided in the middle of the desulfurization tower (6); the display panel (605) is electrically connected to the temperature probe and pH probe inside the desulfurization tower (6); an axial flow oxidation fan (606) is provided at the bottom of the desulfurization tower (6), and the part extending into the desulfurization tower (6) is a gas distribution pipe; a pulse pump (607) is provided at the bottom of the inner cavity of the desulfurization tower (6); a downward spray head (60101) is provided at the end bend of the slurry inlet pipe (601) located in the middle of the top of the inner cavity of the desulfurization tower (6); a waisted flue gas demister (608) that is wide at both ends and narrow in the middle is fixedly installed in the inner cavity of the desulfurization tower (6) below the spray head (60101).The flue gas demister (608) has a through hole in the middle, and a ring-shaped swirling corrugated plate (60801) is provided at the through hole. A descaling guide groove (60802) is spirally provided on the inner wall of the upper end of the flue gas demister (608).

2. A wet desulfurization method using calcium carbide slag for flue gas from a coal-fired power plant based on the desulfurization system described in claim 1, characterized in that, Includes the following steps: (1) The calcium carbide slag is filtered through a filter screen, a drum screen and a vibrating screen in sequence to remove coarse slag, and then the resulting fine slag is sent to an iron remover to remove iron, thus obtaining calcium carbide screening slag. (2) The calcium carbide screening slag obtained in step (1) is sent into the calcium carbide slag slurry tank, water is added, and the mixture is stirred and slurried to obtain calcium carbide slag slurry. (3) The calcium carbide slag slurry obtained in step (2) is sent to the top of the desulfurization tower, the sulfur-containing flue gas is sent to the middle of the desulfurization tower, and the air is sent to the bottom of the desulfurization tower. After pulse stirring reaction in the desulfurization tower, calcium carbide slag desulfurization slurry is obtained and desulfurization flue gas is discharged. (4) Circulate the calcium carbide slag desulfurization slurry obtained in step (3) to the top of the desulfurization tower, or send part of it into the calcium sulfate crystallization pool for crystallization and dehydration to obtain dehydrated gypsum.

3. The wet desulfurization method using calcium carbide slag for flue gas from coal-fired power plants according to claim 2, characterized in that: In step (1), the main components and their mass fractions of the carbide slag are as follows: CaO 80-95%, SiO2 2-8%, Fe2O3 0.5-1.5%, with a total mass fraction ≤100%; the magnetic field strength for iron removal is 1500-2200 kA / m.

4. The wet desulfurization method using calcium carbide slag for flue gas from coal-fired power plants according to claim 2 or 3, characterized in that: In step (2), the mass ratio of water to the calcium carbide screening slag is 2.2 to 3.6:1; the stirring speed is 200 to 400 rpm and the time is 1 to 3 hours.

5. The wet desulfurization method using calcium carbide slag for flue gas from a coal-fired power plant according to claim 2 or 3, characterized in that: In step (3), the flow rate of the carbide slag slurry t / h = E * sulfur-containing flue gas flow rate m 3 / h* Concentration of sulfur dioxide in sulfur-containing flue gas (mg / m³) 3 *10 -9 Wherein, E = 3.2–4.7, and the flow rate of the calcium carbide slag slurry is adjusted within the E value range to make the pH value of the slurry in the absorption tower 4.2–4.8; the flow rate of the sulfur-containing flue gas is 50,000–2,000,000 m³ / s. 3 / h; the concentration of sulfur dioxide in the sulfur-containing flue gas is 500–5000 mg / m³. 3 The pulse pump flow rate for the pulse stirring reaction is 2000–5000 m³ / h. 3 / h; the air flow rate m 3 / h = sulfur-containing flue gas flow rate (m) 3 / h* Concentration of sulfur dioxide in sulfur-containing flue gas (mg / m³) 3 *10 -6 *0.25 / (k*0.2315kg / m 3 ), where k = 0.18~0.28; when the concentration of sulfur dioxide in the desulfurization flue gas is ≥60mg / m³ 3 Alternatively, when the moisture content of dehydrated gypsum is ≥15%, limestone slurry is added to the desulfurization tower until the concentration of sulfur dioxide in the desulfurization flue gas is <30mg / m³. 3 Alternatively, the moisture content of the dehydrated gypsum may be <15%; the flow rate of the limestone slurry may be 0.1 to 0.4 times that of the carbide slag slurry; and the density of the limestone slurry may be 1180 to 1250 kg / m³. 3 .

6. The wet desulfurization method using calcium carbide slag for flue gas from a coal-fired power plant according to claim 4, characterized in that: In step (3), the flow rate of the carbide slag slurry t / h = E * sulfur-containing flue gas flow rate m 3 / h* Concentration of sulfur dioxide in sulfur-containing flue gas (mg / m³) 3 *10 -9 Wherein, E = 3.2–4.7, and the flow rate of the calcium carbide slag slurry is adjusted within the E value range to make the pH value of the slurry in the absorption tower 4.2–4.8; the flow rate of the sulfur-containing flue gas is 50,000–2,000,000 m³ / s. 3 / h; the concentration of sulfur dioxide in the sulfur-containing flue gas is 500–5000 mg / m³. 3 The pulse pump flow rate for the pulse stirring reaction is 2000–5000 m³ / h. 3 / h; the air flow rate m 3 / h = sulfur-containing flue gas flow rate (m) 3 / h* Concentration of sulfur dioxide in sulfur-containing flue gas (mg / m³) 3 *10 -6 *0.25 / (k*0.2315kg / m 3 ), where k = 0.18~0.28; when the concentration of sulfur dioxide in the desulfurization flue gas is ≥60mg / m³ 3 Alternatively, when the moisture content of dehydrated gypsum is ≥15%, limestone slurry is added to the desulfurization tower until the concentration of sulfur dioxide in the desulfurization flue gas is <30mg / m³. 3 Alternatively, the moisture content of the dehydrated gypsum may be <15%; the flow rate of the limestone slurry may be 0.1 to 0.4 times that of the carbide slag slurry; and the density of the limestone slurry may be 1180 to 1250 kg / m³. 3 .

7. The wet desulfurization method using calcium carbide slag for flue gas from a coal-fired power plant according to claim 2 or 3, characterized in that: In step (4), the sum of the flow rates of the carbide slag desulfurization slurry circulation, the fresh carbide slag slurry, and the limestone slurry, and the liquid-to-gas ratio (L / m) of the sulfur-containing flue gas, is... 3 ≥8; the flow rate of the calcium carbide slag desulfurization slurry fed into the calcium sulfate crystallization tank is equivalent to 1.01 to 1.20 times the sum of the flow rates of fresh calcium carbide slag slurry and limestone slurry; the pH value of the crystallization is 4.2 to 4.8; the solid content of the gypsum slurry before dewatering is 25% to 40%, and the water content of the dewatered gypsum is 5% to 14%; the wastewater generated from crystallization and dewatering is neutralized by electrocoagulation; the electrocoagulation neutralization treatment specifically involves: first adjusting the pH value of the wastewater generated from crystallization and dewatering to 6.5 to 7.5 with waste alkali solution, then performing electrocoagulation, and after the sludge and wastewater are separated, the sludge is reintroduced into the disc dewatering machine for dewatering.

8. The wet desulfurization method using calcium carbide slag for flue gas from coal-fired power plants according to claim 4, characterized in that: In step (4), the sum of the flow rates of the carbide slag desulfurization slurry circulation, the fresh carbide slag slurry, and the limestone slurry, and the liquid-to-gas ratio (L / m) of the sulfur-containing flue gas, is... 3 ≥8; the flow rate of the calcium carbide slag desulfurization slurry fed into the calcium sulfate crystallization tank is equivalent to 1.01 to 1.20 times the sum of the flow rates of fresh calcium carbide slag slurry and limestone slurry; the pH value of the crystallization is 4.2 to 4.8; the solid content of the gypsum slurry before dewatering is 25% to 40%, and the water content of the dewatered gypsum is 5% to 14%; the wastewater generated from crystallization and dewatering is neutralized by electrocoagulation; the electrocoagulation neutralization treatment specifically involves: first adjusting the pH value of the wastewater generated from crystallization and dewatering to 6.5 to 7.5 with waste alkali solution, then performing electrocoagulation, and after the sludge and wastewater are separated, the sludge is reintroduced into the disc dewatering machine for dewatering.

9. The wet desulfurization method using calcium carbide slag for flue gas from coal-fired power plants according to claim 5, characterized in that: In step (4), the sum of the flow rates of the carbide slag desulfurization slurry circulation, the fresh carbide slag slurry, and the limestone slurry, and the liquid-to-gas ratio (L / m) of the sulfur-containing flue gas, is... 3 ≥8; the flow rate of the calcium carbide slag desulfurization slurry fed into the calcium sulfate crystallization tank is equivalent to 1.01 to 1.20 times the sum of the flow rates of fresh calcium carbide slag slurry and limestone slurry; the pH value of the crystallization is 4.2 to 4.8; the solid content of the gypsum slurry before dewatering is 25% to 40%, and the water content of the dewatered gypsum is 5% to 14%; the wastewater generated from crystallization and dewatering is neutralized by electrocoagulation; the electrocoagulation neutralization treatment specifically involves: first adjusting the pH value of the wastewater generated from crystallization and dewatering to 6.5 to 7.5 with waste alkali solution, then performing electrocoagulation, and after the sludge and wastewater are separated, the sludge is reintroduced into the disc dewatering machine for dewatering.

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