Electrostatic purification method of quartz wet grinding exhaust gas by charged water mist

Abstract

A charged water mist electrostatic purification method for quartz wet grinding waste gas involves introducing dust- and moisture-laden waste gas into a mixing chamber. A high-voltage electric field charges atomized droplets, which are then sprayed in a counter-current manner at an intersecting angle to contact quartz dust. Electrostatic attraction drives the droplets and dust to agglomerate, causing submicron-sized dust particles to combine and form agglomerates with increased particle size. The mixed gas flow then enters an electrostatic separation zone, where the agglomerates migrate directionally towards and deposit on the collecting electrode. The liquid phase components spread on the electrode surface, forming a wetting liquid film that encapsulates subsequently deposited dust, which is then carried away by the downward flow of the liquid film. This invention improves the charging and migration characteristics of fine dust through pre-agglomeration, while simultaneously using the liquid film to mechanistically suppress back corona discharge, maintaining stable dust removal efficiency over a long period under high humidity conditions.

Description

Technical Field

[0001] This invention belongs to the field of waste gas purification technology, specifically referring to a charged water mist electrostatic purification method for waste gas from quartz wet grinding. Background Technology

[0002] In the deep processing of quartz materials, the dust-laden exhaust gas generated by the wet grinding process is characterized by high moisture content and small dust particle size. The relative humidity of the exhaust gas typically reaches over 85%, and the dust particle size is mainly distributed in the submicron range. Due to the high free silica content of quartz dust, long-term inhalation can cause serious occupational diseases such as silicosis, necessitating effective purification of the dust-laden exhaust gas during production. However, submicron-sized quartz dust is difficult to fully charge in an electric field, resulting in low propagation velocity, and conventional electrostatic precipitators have limited collection efficiency for it.

[0003] Wet electrostatic precipitators are the primary technology for treating high-humidity, dust-laden waste gas. They rely on a water film on the surface of the collecting plates to remove deposited dust and maintain the plates' conductivity. However, under the high-humidity conditions of quartz wet grinding waste gas, fluctuations in the gas's moisture content and uneven distribution of the water film on the plates easily lead to the formation of localized dry spots on the collecting plates. After quartz dust deposits in these dry spots, it forms a high-resistivity dust layer. Charge accumulates within this layer, eventually triggering localized breakdown discharge and generating a back corona phenomenon. The positive ions generated by the back corona flow back into the corona region to neutralize the charge of the already charged particles, causing a sharp drop in dust removal efficiency within a short period. Existing processes that rely on the water film on the plates for dust removal occur after dust deposition, failing to prevent back corona at its source and lacking efficient pretreatment methods for capturing submicron-sized dust. Summary of the Invention

[0004] In view of the above situation and to overcome the defects of the prior art, the present invention provides a charged water mist electrostatic purification method for quartz wet grinding exhaust gas, which at least partially solves the above problems.

[0005] A method for electrostatic purification of quartz wet grinding exhaust gas using charged water mist includes the following steps: Dust- and moisture-laden waste gas is introduced into the mixing chamber; An atomizing nozzle is set in the mixing chamber, and the atomized droplets generated by the atomizing nozzle are charged by a high-voltage electric field to form charged droplets. Charged droplets are sprayed into the mixing chamber at an angle that is opposite to the direction of exhaust gas flow, so that the charged droplets come into full contact with the quartz dust in the exhaust gas. Inside the mixing chamber, the electrostatic attraction between charged droplets and dust drives the droplets and dust to coagulate, causing submicron-sized quartz dust to combine with charged droplets to form agglomerates with increased particle size. The mixed airflow carrying the agglomerates is introduced into the electrostatic separation zone, where the agglomerates migrate directionally toward the dust collecting plate and are deposited under the action of a high-voltage electric field. The liquid phase components contained in the deposited agglomerates spread on the surface of the dust collecting plate to form a wetting liquid film. The wetting liquid film encapsulates the subsequently deposited dust and flows downward with the liquid film, carrying the dust out of the electrostatic separation zone.

[0006] The core technological feature of the above-mentioned solution lies in advancing the charging process to the atomization stage, pre-agglomerating charged water mist and fine dust particles before electrostatic separation. Charged droplets carrying high-density charges attract, capture, and combine submicron-sized quartz dust particles under the influence of Coulomb forces, forming aggregates with increased particle size. This fundamentally improves the charging performance and electric field migration characteristics of the fine dust particles. After the agglomerates are deposited, their liquid components naturally spread on the surface of the collecting electrode to form a wetting film. This film's encapsulation and wetting of the deposited dust significantly reduces the overall resistivity of the dust layer, mechanistically suppressing back corona discharge caused by charge accumulation in high-resistivity dust layers.

[0007] In the above method, the preferred way to charge the atomized droplets is to set a corona electrode near the outlet of the atomizing nozzle and apply a DC high-voltage corona discharge to the atomized droplets generated by the atomizing nozzle, so that the droplets carry a charge at the same time as they are generated.

[0008] In the above method, the injection angle between the charged droplets and the direction of exhaust gas flow is preferably 90 to 150 degrees, allowing the charged droplets to traverse the cross-section of the exhaust gas flow and make multiple cross-contacts with dust particles. Through this injection angle setting, the quartz fine dust and charged droplets agglomerate in the mixing chamber, forming agglomerates with a particle size larger than the original quartz fine dust particles. The particle size growth process of these agglomerates is completed before they enter the electrostatic separation zone.

[0009] In the above method, the charging treatment in the mixing chamber is only for the atomized droplets generated by the atomizing nozzle. The quartz dust in the exhaust gas does not undergo independent pre-charging treatment, but is captured by the electrostatic attraction of the charged droplets and combines with the droplets to form agglomerates.

[0010] In the above method, after the agglomerates are deposited on the surface of the dust collecting electrode, their liquid phase components spread on the surface of the dust collecting electrode to form a wetting liquid film. To further ensure the continuity of the liquid film, the continuity of the wetting liquid film can be maintained by intermittently or continuously supplying replenishing liquid to the surface of the dust collecting electrode, and the collected dust is carried out of the electrostatic separation zone by flowing downward with the wetting liquid film. By maintaining the continuity of the wetting liquid film, the dust deposited on the surface of the dust collecting electrode is fully mixed with the liquid film to form a slurry layer. The conductivity of this slurry layer is higher than that of the original dry accumulation layer of quartz fine dust, which can suppress the back corona discharge caused by the accumulation of charge in the dust layer on the surface of the dust collecting electrode.

[0011] The above method also includes dust recovery and water recycling steps: the dust slurry deposited on the surface of the dust collecting plate is peeled off from the dust collecting plate and discharged from the collection tank; the discharged dust slurry is subjected to solid-liquid separation treatment, the separated liquid phase is returned to supply the atomizing nozzle, and the separated solid phase is collected as recycled quartz powder.

[0012] In the above method, the relative humidity of the dust- and moisture-laden waste gas when it is introduced into the mixing chamber is above 85%; the water vapor contained in the waste gas coexists with the charged droplets in the mixing chamber, which is beneficial to maintaining the charge stability of the charged droplets during the coagulation process.

[0013] In the above method, the electrostatic separation zone and the mixing chamber are two functional zones within the same device. The mixing chamber is located upstream of the airflow in the electrostatic separation zone. After the exhaust gas completes pre-agglomeration in the mixing chamber, it directly enters the electrostatic separation zone for separation without passing through other separation or treatment units in between.

[0014] The beneficial effects of this invention are: by pre-agglomerating fine quartz dust at the electrostatic separation front end with charged water mist, the particle size of submicron dust particles is increased, effectively solving the problem of low collection efficiency of submicron particles in traditional electrostatic dust removal; after the pre-agglomerated agglomerates spread on the surface of the dust collecting plate, a uniform wetting liquid film layer is naturally formed, which inhibits the occurrence of back corona phenomenon from the mechanism, and can maintain a stable dust removal efficiency for a long time under high humidity conditions. Attached Figure Description

[0015] Figure 1 This is a flowchart of a method for electrostatic purification of quartz wet grinding exhaust gas using charged water mist, as described in an embodiment of the present invention.

[0016] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0017] The following will refer to the appendices in the embodiments of the present invention. Figure 1The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] The quartz wet grinding exhaust gas purification method of the present invention can be operated in practical applications as follows: First, the dust- and moisture-laden exhaust gas generated by the quartz wet grinding equipment is collected centrally through a gas collection hood and an exhaust pipe, and then introduced into the mixing chamber. The temperature of this exhaust gas is typically between 25°C and 40°C, and the relative humidity is generally above 85%, even approaching saturation. The quartz dust particles carried in the exhaust gas are mostly distributed in the submicron to micron range of 0.1μm to 2μm, with a total dust concentration of approximately 25mg / m³ to 50mg / m³. Due to the high humidity, the large amount of water vapor contained in the exhaust gas coexists with the charged droplets in the subsequent mixing chamber, which is actually beneficial to maintaining the stability of the charge carried by the droplets.

[0019] The aforementioned mixing chamber and the downstream electrostatic separation zone are actually two functional zones arranged one after the other within the same equipment. The mixing chamber is located upstream of the airflow, and the exhaust gas directly enters the electrostatic separation zone after pre-agglomeration here, without needing to pass through other separation or treatment units in between. This simplifies the process and reduces system resistance.

[0020] Several atomizing nozzles are installed on the top or side wall of the mixing chamber. Ultrasonic atomizing nozzles or dual-fluid atomizing nozzles are commonly used, and the median particle size of the atomized droplets is preferably controlled between 30μm and 50μm. Corona electrodes are placed near the outlet of each nozzle, connected to an external high-voltage DC power supply. By applying a high-voltage DC corona discharge to the droplets just generated by the nozzle, the droplets are charged instantly upon generation, forming charged droplets. Within the entire mixing chamber, only the atomized droplets are charged; the quartz dust contained in the exhaust gas introduced from the front end does not undergo any independent pre-charging treatment upon entering the mixing chamber. This single-sided charging method is simpler than the traditional method that requires separate dual-channel charging of dust and droplets, and avoids the problem of uneven charging caused by differences in the dielectric constant of individual dust particles.

[0021] Subsequently, charged droplets are injected into the mixing chamber at a certain angle to the main flow direction of the exhaust gas, either in the opposite direction or at an angle. The angle between the injection direction and the exhaust gas flow direction is generally between 90 and 150 degrees, so that the droplets can cross the cross section of the exhaust gas flow and have multiple cross-contacts with the dust particles therein, greatly increasing the chance of collision.

[0022] The flow velocity of the exhaust gas in the mixing chamber can be maintained at 4 m / s to 8 m / s, with a gas-liquid volume ratio of approximately 1000:1 to 3000:1. By controlling the corona voltage, the charge-to-mass ratio of the charged droplets can be achieved to 0.5 mC / kg to 2.0 mC / kg, and the droplet number concentration can be maintained at 10. 3 10 per cm³ 4 The number of droplets per cm³ is the level. The charge-to-mass ratio directly determines the magnitude of the Coulomb attraction between the droplets and the dust, while the droplet number concentration affects the collision probability of the particles. In practical applications, these two parameters can be adjusted according to the concentration and particle size distribution of dust in the exhaust gas.

[0023] Within the mixing chamber, charged droplets and fine quartz dust in the exhaust gas come into full contact and coalesce. Here, "coalescing" refers to the process by which fine particles in the dispersed phase combine and aggregate into larger particles under physical forces. In this method, coalescing is primarily achieved through three synergistic mechanisms: firstly, electrostatic coalescing, where the charge on the droplet surface induces a mirror charge on the dust surface when the charged droplet approaches an uncharged or weakly charged dust particle, creating a short-range attraction. Simultaneously, the potential difference between the two drives charge migration, further strengthening the binding force; secondly, collisional coalescing, where the ejected droplets, with a velocity of 5 m / s to 30 m / s, collide with suspended dust particles, directly capturing the dust inside the droplet or attaching it to the droplet surface; and thirdly, diffusion coalescing, targeting ultrafine quartz dust with a particle size less than 0.1 μm. These dust particles move randomly in the gas under the influence of Brownian motion, and the high-density charged droplets in the mixing chamber provide numerous collision surfaces, enabling the effective capture of even ultrafine dust. Through the synergistic effect of these three mechanisms, submicron-sized quartz dust particles with a diameter of only 0.1 μm to 2 μm combine with charged droplets to form aggregates with a significantly increased particle size.

[0024] The effective length of the mixing chamber is typically designed to be between 1.5m and 2.5m, and the residence time of the exhaust gas in the mixing chamber is approximately 0.2s to 0.5s, which is sufficient to complete the pre-agglomeration process. At this point, the particle size of the agglomerates formed is significantly larger than that of the quartz fine dust before agglomeration, in most cases increasing to 5μm to 50μm, with a particle size increase of ten to one hundred times. Moreover, this particle size growth process is completely completed before entering the electrostatic separation zone.

[0025] The pre-agglomerated airflow then carries these enlarged agglomerates into the downstream electrostatic separation zone. The electrostatic separation zone can employ a wire-plate or wire-tube structure. Taking the common wire-plate structure as an example, the corona electrode wire is connected to a high-voltage DC power supply, while the dust collection electrode is grounded. Depending on the actual needs, negative or positive corona discharge can be selected. Negative corona discharge has a lower initiation voltage and a larger corona current, making it suitable for applications requiring high dust removal efficiency; positive corona discharge produces less ozone, making it suitable for production environments with strict ozone generation limits. The operating voltage range is generally -40kV to -70kV for negative corona discharge and +30kV to +50kV for positive corona discharge. The inter-electrode spacing is typically set between 150mm and 300mm, the electric field velocity is controlled between 1.0m / s and 2.0m / s, and the effective residence time is 3s to 6s. Under the action of a high-voltage electric field, corona discharge occurs near the corona electrode, generating a large number of gas ions. Driven by the electric field force, the gas ions migrate towards the dust collection electrode plate. Along the way, they encounter the agglomerates and charge them. The charged agglomerates also move directionally to the surface of the dust collection electrode plate and are deposited under the same electric field force.

[0026] After the agglomerates deposit on the surface of the dust collecting plates, the liquid components they contain naturally spread out, forming a wetting film. This film can encapsulate the subsequently deposited dust particles, and as the film flows downwards, it carries the captured dust out of the electrostatic separation zone. Under typical operating conditions where the relative humidity of the exhaust gas remains stable above 85% and the dust concentration is between 25 mg / m³ and 50 mg / m³, the amount of liquid entering the electrostatic separation zone with the agglomerates is sufficient to maintain the continuity of the wetting film on the plate surface, achieving effective dust removal and plate self-cleaning without the need for additional liquid replenishment.

[0027] However, under unfavorable operating conditions, such as low relative humidity of the exhaust gas, a sudden increase in dust concentration, or uneven liquid distribution due to the wide surface area of ​​the dust collecting plates, the liquid carried by the agglomerates themselves may not be sufficient to maintain complete liquid film coverage for an extended period, and so-called "dry spots" may appear in certain areas. Here, "dry spots" refer to localized areas on the plate surface that are not covered by the water film and are directly exposed. Quartz dust accumulates in these areas, forming a high-resistivity dust layer, which easily triggers back corona discharge. "Back corona discharge" refers to the phenomenon of localized breakdown discharge within the high-resistivity dust layer due to the inability to dissipate accumulated charge. The positive ions generated flow back into the corona region, neutralizing the charge of the already charged particles and causing a sharp decrease in dust removal efficiency.

[0028] To avoid the aforementioned situation, a separate liquid supply path, independent of the front-end spray, can be used to provide supplementary liquid to the surface of the dust collecting plates. The supplementation method can be intermittent or continuous, depending on the needs. For example, liquid can be supplied every 1 to 2 hours, each time lasting 2 to 5 minutes; or a continuous supply method can be used, with a flow rate of 0.1 L / (m·min) to 0.5 L / (m·min) per unit width of the dust collecting plates for uniform distribution. This supplementary liquid can be delivered to the plate surface through supply pipelines such as spray pipes, overflow troughs, or porous distribution plates located above the dust collecting plates, where it merges with the deposited liquid film to maintain a continuous wetted state on the plate surface. The supplementary liquid can be sourced from external industrial water or directly from the supernatant recovered after solid-liquid separation of the subsequent dust slurry, thus achieving cascade utilization of water resources.

[0029] By maintaining the continuity of the liquid film, the dust deposited on the electrode surface mixes thoroughly with the liquid, forming a slurry layer with good conductivity. Quartz fine dust itself is a high resistivity material, with a resistivity typically ranging from 10¹² Ω·cm to 10... 14 The resistivity is on the order of Ω·cm, and it easily accumulates charge and generates back corona during dry stacking. However, when dust is mixed with liquid, the resistivity of the slurry layer can be significantly reduced to 10 Ω·cm. 6 Ω·cm to 10 8 With a charge on the order of Ω·cm, the charge can be promptly transferred and carried away through the continuous liquid medium, preventing it from accumulating continuously inside the dust layer. Therefore, the occurrence of back corona discharge is effectively suppressed from a mechanistic perspective.

[0030] The dust slurry deposited on the dust collecting plates flows downwards along the plate surface into a collection tank located at the bottom of the electrostatic separation zone under the influence of gravity. The slurry discharged from the collection tank then undergoes solid-liquid separation treatment, such as natural sedimentation in a settling tank or dehydration using a centrifugal dewatering machine. The separated supernatant can be returned to the front-end atomizing nozzle for recycling as atomizing water supply; the separated solid phase is recovered quartz powder, which can be returned to the quartz processing production line as raw material, reducing raw material waste.

[0031] In practice, some key parameters can be flexibly adjusted according to the specific conditions of the exhaust gas. For example, when the relative humidity of the exhaust gas is 90% to near saturation and the dust concentration is around 25mg / m³ to 35mg / m³, a cross-flow injection angle of 90 to 120 degrees is used, and the exhaust gas stays in the mixing chamber for 0.2 to 0.3 seconds, which is sufficient for the agglomerates to grow sufficiently. When the humidity of the exhaust gas is low, such as between 85% and 90%, or when the dust concentration rises to 35mg / m³ to 50mg / m³, in order to improve the coagulation efficiency, the injection angle can be adjusted to a counter-current oblique injection of 120 to 150 degrees. At the same time, the residence time of the exhaust gas in the mixing chamber is extended to 0.4 to 0.7 seconds. This can be combined with the aforementioned external liquid replenishment measures to ensure that high dust removal efficiency and good operational reliability can be maintained stably under various operating condition fluctuations.

[0032] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for electrostatic purification of waste gas from wet quartz grinding using charged water mist, characterized in that, Includes the following steps: Dust- and moisture-laden waste gas is introduced into the mixing chamber; An atomizing nozzle is set in the mixing chamber, and the atomized droplets generated by the atomizing nozzle are charged by a high-voltage electric field to form charged droplets. Charged droplets are injected into the mixing chamber at an angle that intersects with the direction of exhaust gas flow. Inside the mixing chamber, the electrostatic attraction between charged droplets and dust drives the droplets and dust to coagulate, forming agglomerates with increased particle size. The mixed airflow carrying agglomerates is introduced into the electrostatic separation zone, where the agglomerates migrate directionally toward the dust collection plate and are deposited under the action of a high-voltage electric field. The liquid phase components contained in the deposited agglomerates spread on the surface of the dust collecting plate to form a wetting liquid film. The wetting liquid film encapsulates the subsequently deposited dust and flows downward with the liquid film, carrying the dust out of the electrostatic separation zone.

2. The method according to claim 1, characterized in that, The method for charging the atomized droplets is as follows: a corona electrode is set near the outlet of the atomizing nozzle, and a DC high-voltage corona discharge is applied to the atomized droplets generated by the atomizing nozzle, so that the droplets carry a charge at the same time as they are generated.

3. The method according to claim 2, characterized in that, The angle between the charged droplets and the direction of exhaust gas flow is 90 to 150 degrees.

4. The method according to claim 3, characterized in that, Submicron-sized quartz dust particles and charged droplets coagulate in the mixing chamber to form agglomerates, making the particle size of the agglomerates larger than that of the quartz dust particles before coagulation; the particle size growth process of the agglomerates is completed before entering the electrostatic separation zone.

5. The method according to claim 2, characterized in that, Within the mixing chamber, only the atomized droplets generated by the atomizing nozzle are charged, without independently pre-charging the quartz dust in the exhaust gas; the charged droplets capture and combine the quartz dust to form agglomerates through electrostatic attraction.

6. The method according to claim 1, characterized in that, After the agglomerates are deposited on the surface of the dust collecting plate, the liquid phase components contained in the agglomerates spread on the surface of the dust collecting plate to form a wetting liquid film. The continuity of the wetting liquid film is maintained by intermittently or continuously supplying replenishing liquid to the surface of the dust collecting plate, and the collected dust flows downward with the wetting liquid film and is carried out of the electrostatic separation zone.

7. The method according to claim 6, characterized in that, By maintaining the continuity of the wetting liquid film, the dust deposited on the surface of the dust collecting electrode plate is fully mixed with the liquid film to form a slurry layer; the conductivity of the slurry layer is higher than that of the original dry and accumulated quartz fine dust layer, so as to suppress the back corona discharge caused by the accumulation of charge in the dust layer on the surface of the dust collecting electrode plate.

8. The method according to claim 1, characterized in that, It also includes the following steps: The dust slurry deposited on the surface of the dust collecting plate is peeled off the dust collecting plate and discharged from the collection tank; After being discharged, the dust slurry undergoes solid-liquid separation treatment, and the separated liquid phase is returned to supply the atomizing nozzles. The separated solid phase is collected as recycled quartz powder.

9. The method according to claim 1, characterized in that, The relative humidity of the dust- and moisture-laden exhaust gas introduced into the mixing chamber is above 85%; the coexistence environment of water vapor contained in the exhaust gas and charged droplets in the mixing chamber is utilized to maintain the charge stability of the charged droplets during the coagulation process.

10. The method according to claim 1, characterized in that, The electrostatic separation zone and the mixing chamber are two functional zones within the same device; the mixing chamber is located upstream of the airflow in the electrostatic separation zone, and the exhaust gas directly enters the electrostatic separation zone for separation after pre-agglomeration in the mixing chamber, without passing through other separation or treatment units in between.

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