CN103272696A - A method for particle diffusion charge thickening - Google Patents

Abstract

A method for particle diffusion charge thickening belongs to the technical field of environmental engineering and the like. The method is characterized in that PM0.1 primary particles and unipolar ions are injected into a high-frequency high-voltage alternating electric field together, and the unipolar ions are carried out in the high-frequency high-voltage alternating electric field by 10³～10⁴The particles do secondary up-and-down reciprocating motion, each PM0.1 particle and unipolar ions generate collision charge thickening for tens of thousands of times, even tens of thousands of times, and further the particle size of the particles is increased by 10-10³And then the mixture is condensed into primary particles with the particle size larger than 2 mu m. The invention has the advantages of providing an effective method for eliminating PM0.1 primary particle atmospheric pollutants, being also used for the diffusion, charge and condensation pretreatment of the ultrafine dust of a dust remover, greatly reducing the primary investment, the operation cost, the energy consumption and the like, and the like.

Description

A method for particle diffusion charge thickening

technical field

The invention belongs to the technical fields of gas discharge physics, plasma technology and environmental engineering, and relates to a method for thickening primary particles with a particle diameter of less than 0.1 μm by diffusion charging.

Background technique

my country is a rising economic power. Two-thirds of energy comes from coal, which is highly dependent. From 2005 to 2010, coal consumption increased by 44%. Fine dust, that is, primary particulate matter PM0.1 with a particle size of ≤0.1 μm. Due to its large specific surface area, strong activity, and strong adsorption, the surface of PM0.1 is very easy to accumulate heavy metals (As, Se, Pb, Cr, etc.) in the air and organic pollutants such as PAHs and VOCs; it is also easy to attach SO _2. NOx and its by-products such as sulfuric acid, nitric acid, sulfate, nitrate and other pollutants, these pollutants are mostly carcinogens or genotoxic mutagenic substances. These trace pollutants can further migrate and accumulate on the surface, which is extremely harmful. Controlling PM0.1 air pollution has become an urgent and major livelihood issue in my country.

The charge thickening of primary particles is realized by the collision of unipolar ions generated after gas ionization. The thickening mechanism is divided into two types. One is the charge thickening of electric field, and the gas unipolar ions move along the electric force line When the gas moves in a regular direction, the charge becomes thicker when it collides with the particles; the other kind of diffusion charge becomes thicker, and when the gas moves irregularly, the charge becomes thicker when it collides with the particles. The charging and thickening mechanism of primary particulate matter varies with the particle size. When the particle size > 1 μm, the coarsening by electric field charging is dominant; when the particle size is < 0.1 μm, the coarsening by diffusion charging is dominant. At present, the electrostatic precipitator technology is mainly based on electric field charging to thicken, and mainly captures particles with a particle size > 1 μm. Nothing can be done about PM0.1.

Contents of the invention

The invention solves the existing problem of collecting primary particles with a particle size of less than 0.1 μm, and provides a new method for thickening the primary particles with a particle size of less than 0.1 μm by diffusion charging. In this method, the gas containing PM0.1 primary particles and high-concentration unipolar ions are injected into the high-frequency and high-voltage alternating electric field, and the unipolar ions make 10 ³ to 10 ⁴ up and down reciprocating movements, PM0.1 primary particles and unipolar ions or charged PM0.1 primary particles diffuse and charge tens of thousands of times, or even hundreds of thousands of times; PM0.1 primary particles pass through high-frequency high-voltage alternating electric field After diffusion charging thickens, the particle size increases by 10 to 10 ³ times, and the charge condenses into primary particles with a particle size > 2 μm. It provides an effective method for eliminating PM0.1 primary particulate air pollutants, and has the advantages of greatly reducing primary investment, operating costs, and energy consumption.

The diffusion charging of PM0.1 primary particles is charged by the collision of ions in irregular thermal motion. The diffusion charging of dust particles with a particle size of <0.1 μm is related to various factors such as size, charge, ion thermal movement intensity, collision probability, movement speed and residence time in the electric field. The charging process of dust particles and the derivation of the calculation formula of the charging quantity follow the relevant theory of gas molecule motion.

Assume that the number of unipolar ions in the unit body in the electric field is quite far away from the dust particles, N; the number of ions close to the dust particles is N1. According to the theory of gas molecular motion, the expression of the relationship between the two can be obtained:

N ₁ =N×exp (-eV/kT) Formula 1

In the formula: e is the electric charge of the ion; V is the electric potential where the dust particle is located; k is Botzmann’s constant; T is _the gas temperature; when

${\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">N</figure-callout>}}_2={\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">N</figure-callout>}}_1\sqrt{\frac{\mathrm{<figure-callout\; id="2"\; label="kT"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">kT</figure-callout>}}{2\mathrm{\&pi;<figure-callout\; id="2"\; label="m\; Formula"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">m</figure-callout>}}}$ Formula 2

In the formula: m is the mass of the ion. According to Gauss's theorem, the electric field strength in the peripheral area of dust particles is

${\mathrm{E.}}_2=\frac{{\mathrm{<figure-callout\; id="4"\; label="q\; p"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">q</figure-callout>}}_p}{4\mathrm{\&pi;}{\mathrm{\&epsiv;}}_0{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">r</figure-callout>}}^2}$ Formula 3

In the formula: q _p is the charge amount of the primary particle; E ₂ is the electric field strength when the charge amount on the periphery of the dust particle is q _p ; ε ₀ is the vacuum dielectric constant; r is the charge radius on the periphery of the particle. Integrate the differential form of Equation 3 with respect to r, and then get the potential at the radius r after the dust particle is charged

$V=\frac{{\mathrm{<figure-callout\; id="4"\; label="q\; p"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">q</figure-callout>}}_p}{4\mathrm{\&pi;}{\mathrm{\&epsiv;}}_0\mathrm{<figure-callout\; id="4"\; label="r\; Formula"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">r</figure-callout>}}$ Formula 4

Substituting Equation 4 into Equation 1, then

${\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">N</figure-callout>}}_1=N\&times;\exp (-\frac{{\mathrm{<figure-callout\; id="4"\; label="eq\; p"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">eq</figure-callout>}}_p}{4\mathrm{\&pi;}{\mathrm{\&epsiv;}}_0\mathrm{kTr}})$ Formula 5

At r=a on the outer surface of the dust particle, the number of ions N _1a per unit volume is

$N_{1a}=N\&times;\exp (-\frac{{\mathrm{<figure-callout\; id="4"\; label="eq\; p"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">eq</figure-callout>}}_p}{4\mathrm{\&pi;}{\mathrm{\&epsiv;}}_0\mathrm{kT}})$ Formula 6

Calculate the charge rate on the particle surface by using Equation 6

$\frac{{\mathrm{<span\; class="notranslate">\; dq</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;e</span>}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; a</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;ea</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; a</span>}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="kT"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">kT</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;m</span>}}}$

$<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; e</span>}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; \&pi;kT</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}}{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; Next</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="4"\; label="eq\; p"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">eq</figure-callout></span><figure-callout\; id="4"\; label="eq\; p"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; kT</span>}}<span\; class="notranslate">\; )</span>$

Formula 7

where m is the mass of the ion. Integrating Equation 7 with the boundary conditions of t=0, _qp =0, the charge of PM0.1 can be obtained:

$q_p=\frac{2\mathrm{\&pi;}{\mathrm{\&epsiv;}}_0{d}_{\mathrm{<figure-callout\; id="1"\; label="p\; kT\; e"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">p</figure-callout>}}\mathrm{kT}}{e}1\mathrm{no}(1+\frac{d_p{\mathrm{Ne}}^2\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">t</figure-callout>}}{{2\mathrm{\&epsiv;}}_0\sqrt{2\mathrm{m\&pi;kT}}})$ Formula 8

代入上式，上式则改写为average velocity of ions

Substituting into the above formula, the above formula can be rewritten as

$q_p=\frac{2\mathrm{\&pi;}{\mathrm{\&epsiv;}}_0{d}_{\mathrm{<figure-callout\; id="1"\; label="p\; kT\; e"\; filenames="HDA00003312951600013.png"\; state="\{\{state\}\}">p</figure-callout>}}\mathrm{kT}}{e}1\mathrm{no}(1+\frac{d_p\stackrel{-}{u}{\mathrm{Ne}}^{2}t}{8{\mathrm{\&epsiv;}}_0\mathrm{kT}})$ Formula 9

和一次颗粒物荷电时间t方可增加PM0.1荷电量。由于气体温度T、一次颗粒物荷电时间t增加量很有限，而单极性粒子数N及其平均速度可成

数量级式增加，可采用增加单极性粒子数N和单极性离子平均速度方法

来增加PM0.1一次颗粒物的电荷量。In the formula: _dp is the diameter of PM0.1; is the average ion velocity. The above formula is applicable to the calculation of the diffusion charge of primary particles with a particle size d _p <0.1 μm. It can be seen from the formula that only by increasing the number N of unipolar ions, the gas temperature T, and the average velocity of ions

And the charging time t of the primary particulate matter can increase the charging capacity of PM0.1. Due to the limited increase in the gas temperature T and the charging time t of primary particles, the number N of unipolar particles and their average velocity can be

The order of magnitude increases, and the method of increasing the number N of unipolar particles and the average velocity of unipolar ions can be used

To increase the charge of PM0.1 primary particles.

The method for thickening the PM0.1 primary particulate matter by diffusion charging will be described in detail below.

Increasing the number of unipolar ions and their moving speed is the key to the charge thickening of PM0.1 primary particles. The output voltage of the high-frequency high-voltage alternating power source 8 is applied to the high-voltage electrode 11, and a high-frequency high-voltage charge-thickened alternating electric field 3 is formed between the high-voltage electrode 11 and the ground electrode 10, and the electric field strength is 0.8kV-40kV. Inject unipolar ions 1 (negative ions or positive ions) with a concentration as high as 10 ¹⁰ /cm ³ to 10 ¹⁴ /cm ³ and gas containing PM0.1 primary particulate matter 2 together into a 0.1m to 4m long high-frequency high-voltage charging In thickening the alternating electric field 3, the number of unipolar ions per 1 cm ³ of gas reaches 10 ¹⁰ -10 ¹⁴ . Unipolar ions 1 move at an average speed of 2 km/s in the high-frequency, high-voltage charged and thickened alternating electric field 3, and move 10 ³ to 10 in the gap between the high-voltage electrode 11 and the ground electrode 10 at a speed of 2 km/s. ⁴ times of up and down reciprocating motion, its motion track is shown as 4 in Fig. 1. Every PM0.1 particle 2 collides with unipolar ions 1 every second for tens of thousands or even hundreds of thousands of times. The thickening trajectory of M0.1 primary particles in the alternating electric field is shown as 5 in Figure 1. After PM0.1 primary particles are thickened by high-frequency high-voltage charging and alternating electric field 3, the particle size increases by 10 to 10 ³ times, and the saturated charge condenses into primary particles with a particle size > 2 μm7.

High-frequency high-voltage charged thickening alternating electric field 3 includes Al ₂ O ₃ sheet 9, grounding electrode 10, and high-voltage electrode 11, and the gap distance is 10 cm to 60 cm; grounding electrode 10 and high-voltage electrode 11 are all made of 304 stainless steel sheets formed rectangular plates. The frequency range of the high-frequency and high-voltage alternating power supply 8 is 80Hz-12kHz, and the range of the output voltage amplitude is 10kV-600kV.

In the present invention, the PM0.1 primary particles are saturated and charged through a high-frequency and high-voltage alternating electric field, and then condensed and thickened into primary particles with a particle diameter > 2 μm. This solves the problem of PM0.1 primary particle capture and purification, and provides a feasible and effective new method for diffusion charging and condensation thickening. The present invention can also be applied to the pretreatment of dust collectors such as electrostatic precipitators, cloth bags, and sedimentation. After pre-charging and condensing into primary particles with large particle diameters, the purification of dust collectors such as electrostatic precipitators, cloth bags, and sedimentation will be greatly improved. efficiency. At the same time, the volume of the dust collector can be greatly reduced, and the amount of steel used can be reduced, thereby reducing the primary investment and operating costs, and reducing energy consumption.

Description of drawings

The present invention will be further described below in conjunction with drawings and embodiments.

Figure 1 is a schematic diagram of the principle of charging thickening method for PM0.1 primary particulate matter.

Figure 2 is a graph showing the influence of alternating electric field frequency on the mass occupancy rate of primary particles with a particle size of 0.1 μm.

Figure 3 is a graph showing the influence of alternating electric field strength on the mass occupancy rate of primary particulate matter with a particle size of 0.1 μm.

In the figure: 1 unipolar ion; 2PM0.1 primary particulate matter; 3 high-frequency high-voltage charging thickening alternating electric field; 4 unipolar ion trajectory; 5PM0.1 primary particulate matter charging thickening trajectory in alternating electric field ; 6 Charged and thickened primary particles; 7 Saturated charge condenses into primary particles with a particle size > 2 μm; 8 High-frequency high-voltage alternating power supply; 9 Al ₂ O ₃ flakes; 10 Grounding electrode; 11 High-voltage electrode.

Detailed ways

Describe the embodiment of the present invention in detail below in conjunction with technical scheme and accompanying drawing:

The schematic diagram of the method for charging and thickening PM0.1 primary particles of the present invention is shown in FIG. 1 . The output voltage of the high-frequency high-voltage alternating power supply 8 is applied to the high-voltage electrode 11, and a high-frequency high-voltage charge thickening alternating electric field 3 is formed between the high-voltage electrode 11 and the ground electrode 10, and the concentration is as high as 10 ¹⁰ /cm ³ to 10 ¹⁴ Unipolar ions 1/cm ³ and gas containing PM0.1 primary particulate matter 2 are injected into the 0.1m-4m long high-frequency high-voltage charge thickening alternating electric field 3, that is, the unipolar ion in every 1cm ³ of gas The number of ions reaches 10 ¹⁰ to 10 ¹⁴ or more. The unipolar ion 1 reciprocates 10 ³ to 10 ⁴ times up and down in the gap between the high-voltage electrode 11 and the ground electrode 10 at a speed of 2 km/s in the high-frequency high-voltage charging thickening alternating electric field 3 , and each PM0 .1 The opportunity for particle 2 to collide with unipolar ion 1 to charge and thicken is tens of thousands to hundreds of thousands of times per second. PM0.1 primary particles are thickened by high-frequency and high-voltage charging in alternating electric field 3 and thickened by diffusion charging, the particle size increases by 10 to 10 ³ times, and the saturated charge condenses into primary particles with a particle size > 2 μm 7 .

The implementation results of the present invention are shown in Figures 2 and 3. From the influence curve of alternating electric field frequency on the mass occupancy rate of primary particles with a particle size of 0.1 μm in Figure 2, it can be seen that under the condition of high frequency and high voltage electric field strength of 5 kV/cm, when the alternating electric field frequency is 10 kHz, the particle size is 0.1 μm The mass occupancy rate of primary particulate matter is about 28%, that is, 72% of the primary particulate matter with a particle size of 0.1 μm is charged and thickened, which shows that the effect of agglomeration and thickening is obvious. It can be seen from the influence curve of alternating electric field intensity on the mass occupancy rate of primary particles with a particle size of 0.1 μm in Fig. The mass occupancy rate of primary particles with a diameter of 0.1 μm is about 28%. It can be seen that 72% of the primary particles with a diameter of 0.1 μm are charged and thickened under this parameter.

Claims (2)

1. a particle diffusional charging increases thick method, it is characterized in that concentration up to 10 ¹⁰/ cm ³～10 ¹⁴/ cm ³The unipolarity ion injects long 0.1m～4m together with the gas that contains the PM0.1 primary particulate, electric-field intensity is the high-frequency and high-voltage alternating electric field of 0.8kV～40kV; After the PM0.1 primary particulate increased slightly by high-frequency and high-voltage alternating electric field diffusional charging, its particle diameter increased 10～10 ³Doubly, the charged particle diameter＞2 μ m primary particulates that are condensed into.

2. method according to claim 1 is characterized in that, described high-frequency and high-voltage alternating electric field comprises Al ₂O ₃Thin slice (9), earthing pole (10), high-field electrode (11), its clearance distance is 10cm～60cm; The rectangle pole plate that earthing pole (10), high-field electrode (11) all adopt 304 stainless sheet metals to process; High-frequency and high-voltage alternating source (8) frequency range is 80Hz～12kHz, and the output voltage amplitude scope is 10kV～600kV.

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