阅读说明：本技术 电子发射体及其制法与包含该电子发射体的粉尘荷电装置 (Electron emitter, manufacturing method thereof and dust charging device comprising electron emitter ) 是由 顾中铸 席剑飞 蔡杰 陆洋 吴晶晶 于 2021-08-19 设计创作，主要内容包括：本发明公开了一种电子发射体,为圆锥体,电子发射体包括2～3wt％的三元稀土氧化物,余量为钨,三元稀土氧化物包括以下质量百分数的物质：CeO-(2) 15～20wt％,La-(2)O-(3) 15～25wt％,其余为Y-(2)O-(3)。本发明还公开了一种电子发射体的制备方法,包括以下步骤：将仲钨酸铵与硝酸铈、硝酸镧、硝酸钇的水溶液进行掺杂,烘干,大温度梯度还原后,制成钨粉,再经混料、压型、预烧结,垂熔烧结、塑性加工制成。本发明还公开了一种粉尘荷电装置,包括壳体,壳体接地,壳体内设置放电阴极,放电阴极为狼牙棒型。本发明在高温环境、常温和中低温环境下均能高效、稳定地工作,提高微细粉尘荷电量,提高静电聚并及电场捕集效率。(The invention discloses an electron emitter which is a cone, wherein the electron emitter comprises 2-3 wt% of ternary rare earth oxide, and the balance is tungsten, and the ternary rare earth oxide comprises the following substances in percentage by mass: CeO (CeO) 2 15～20wt％，La 2 O 3 15 to 25 wt%, and the balance Y 2 O 3 . The invention also discloses a preparation method of the electron emitter, which comprises the following steps: ammonium paratungstate is doped with aqueous solution of cerium nitrate, lanthanum nitrate and yttrium nitrate, the mixture is dried and reduced at a large temperature gradient to prepare tungsten powder, and the tungsten powder is prepared by mixing, pressing, pre-sintering, vertical sintering and plastic processing. The invention also discloses a dust charging device which comprises a shell, wherein the shell is grounded, and a discharge cathode is arranged in the shell and is of a wolf tooth rod shape. The invention is inThe device can work efficiently and stably in high-temperature environment, normal-temperature environment and medium-low temperature environment, improves the charge capacity of fine dust, and improves the electrostatic coalescence and electric field trapping efficiency.)

1. An electron emitter, comprising: the material is a cone and comprises 2-3 wt% of ternary rare earth oxide, and the balance is tungsten, wherein the ternary rare earth oxide comprises the following substances in percentage by mass: CeO (CeO)₂ 15～20wt％，La₂O₃15 to 25 wt%, and the balance Y₂O₃。

2. The method of claim 1, comprising the steps of: ammonium paratungstate is doped with aqueous solution of cerium nitrate, lanthanum nitrate and yttrium nitrate, the doped solution is dried and reduced at a large temperature gradient to prepare tungsten powder, and the tungsten powder is subjected to material mixing, compression molding, pre-sintering, vertical sintering and plastic processing.

3. The method of claim 2, wherein: the large temperature gradient is 240-960 ℃.

4. The method of claim 2, wherein: the temperature of the vertical melting sintering is 1150-1950 ℃.

5. A dust charging device is characterized in that: including casing (2), casing (2) ground connection, set up discharge cathode (1) in casing (2), discharge cathode (1) is wolf tooth stick type, links to each other with high-voltage pulse power supply (4) through insulating ceramic sleeve pipe (3), discharge cathode (1) includes electron emitter (11) and metal support pole (12), electron emitter (11) are the cone.

6. A dust charging device according to claim 5, wherein: the electron emitters (11) are uniformly distributed along the metal support rod (12) at intervals.

7. A dust charging device according to claim 6, wherein: the taper of the electron emitter (11) is 1: 2-4: 5, and the taper tip distance is 15-25 mm.

8. A dust charging device according to claim 5, wherein: the electron emitter (11) comprises 2-3 wt% of ternary rare earth oxide, and the balance is tungsten.

9. A dust charging device according to claim 8, wherein: the ternary rare earth oxide comprises the following substances in percentage by mass: CeO (CeO)₂ 15～20wt％，La₂O₃15 to 25 wt%, and the balance Y₂O₃。

10. A dust charging device according to claim 5, wherein: the shell (2) is provided with a flue gas inlet (5) and a flue gas outlet (6).

Technical Field

The invention relates to a flue gas purification device and a manufacturing method thereof, in particular to an electron emitter, a manufacturing method thereof and a dust charging device comprising the electron emitter.

Background

As an international problem in the fields of electric power, metallurgy, chemical industry, and the like, flue gas purification is attracting more and more attention, and among them, removal of fine particulate matters is a difficult point. The electrostatic dust removal technology has the advantages of high dust removal efficiency, small resistance loss, large flow of treated gas, wide application range and the like, so the electrostatic dust removal technology is widely applied to the fields of ventilation dust removal, flue gas purification and the like, but the traditional electrostatic dust remover has good dust removal effect on fine particulate matters, particularly PM2.5, although the comparison between the traditional electrostatic dust remover and larger particles is limited by the working voltage and the cathode discharge intensity. In order to improve the purification effect of the fine dust, the discharge performance of the cathode of the electrostatic dust collector is enhanced, and the current density of a charged area is improved, so that the charged quantity of the fine dust is increased; secondly, the fine dust is charged with different polarities (part of the fine dust is charged with positive charges, and the other fine dust is charged with negative charges), and the fine dust is polymerized and enlarged by static electricity. In recent years, people use a high-voltage pulse power supply to replace a power frequency or high-frequency power supply of a traditional electrostatic dust collector, and because the pulse power supply uses narrow pulse high voltage in a short time, pulse discharge can generate high-density low-temperature plasma, so that the charge effect of dust particles is improved.

However, the existing discharge cathode is made of common metal or alloy material (such as stainless steel or titanium alloy, etc.), because the surface work function is high (more than 4 ev), the internal free electrons are difficult to overcome the surface constraint and are emitted, and the cathode discharge performance is influenced; therefore, the domestic Nanjing university and Beijing university of industry use powder metallurgy technology to prepare the tungsten-based functional composite material (rare earth tungsten) added with rare earth oxide, the surface work function of the rare earth tungsten is low (about 3 ev), and free electrons can be emitted under certain external voltage or after the rare earth tungsten is heated to a certain temperature, so that the dust is charged.

At present, the rare earth tungsten cathode is only applied to the high-temperature direct-current power supply electrostatic dust removal technology, but in a normal-temperature or medium-low-temperature environment, because the direct-current power supply is used in the prior related technology and the cathode adopts a rare earth tungsten round rod structure, the initial discharge voltage of gas is high, a stable and high-strength discharge process is difficult to maintain, and the efficient collection of PM2.5 cannot be realized.

Disclosure of Invention

The purpose of the invention is as follows: in order to overcome the defects in the prior art, the invention aims to provide an electron emitter with significantly reduced work function and good gas discharge performance, and the invention also aims to provide a simple and convenient preparation method of the electron emitter, and further aims to provide a dust charging device capable of promoting the heteropolarity charging of fine dust.

The technical scheme is as follows: the electron emitter is a cone, the electron emitter comprises 2-3 wt% of ternary rare earth oxide, and the balance is tungsten, and the ternary rare earth oxide comprises the following substances in percentage by mass: CeO (CeO)₂ 15～20wt％，La₂O₃15 to 25 wt%, and the balance Y₂O₃. The work function of the electron emitter is reduced to 2.74ev, which is reduced by more than 30% compared with common metal cathodes of the existing corona type electrostatic dust collector, such as stainless steel, titanium alloy and the like, and is reduced by about 10% compared with rare earth tungsten cathodes in the existing thermionic emission type particle charging device, thereby obviously enhancing the electron emission and gas discharge performance of the cathodes. The ternary rare earth tungsten material has low work function, good wear resistance and corrosion resistance, and is not easy to damage in a dust-containing smoke environment.

The preparation method of the electron emitter comprises the following steps: doping ammonium paratungstate with aqueous solution of cerium nitrate, lanthanum nitrate and yttrium nitrate, drying, reducing at a large temperature gradient to prepare tungsten powder, mixing, pressing, presintering, sintering at a vertical melting point, and performing plastic processing to prepare the electron emitter.

Further, the large temperature gradient is 240 ℃ to 960 ℃. The temperature of the vertical melting sintering is 1150-1950 ℃.

A dust charging device comprises a shell, wherein the shell is grounded and serves as an anode of a discharging area, an additional high-voltage pulse electric field is formed between a discharging cathode and the anode, the discharging cathode is arranged in the shell and is of a wolf tooth rod shape and is connected with a high-voltage pulse power supply through an insulating ceramic sleeve, the high-voltage electric insulation problem is solved, the discharging cathode comprises an electron emitter and a metal support rod, and the electron emitter is a cone.

Furthermore, the electron emitters are uniformly arranged along the metal support rod at intervals. The taper of the electron emitter is 1: 2-4: 5, and the taper distance is 15-25 mm. So as to generate local high field intensity, further obtain higher energy from the source electrons emitted by the emitter, and improve the discharge intensity of the flue gas; the flue gas flows longitudinally through the discharge area, so that the dust in the flue gas is fully charged.

Further, the electron emitter comprises 2-3 wt% of ternary rare earth oxide, and the balance is tungsten. The ternary rare earth oxide comprises the following substances in percentage by mass: CeO (CeO)₂ 15～20wt％，La₂O₃15 to 25 wt%, and the balance Y₂O₃。

Further, a smoke inlet and a smoke outlet are arranged on the shell.

The working principle is as follows: the ternary rare earth tungsten composite material is made into a cone-shaped electron emitter and is uniformly embedded on a metal support rod to construct a wolf tooth rod type discharge cathode. Under the action of an external high-voltage pulse electric field, the wolf tooth rod-shaped discharge cathode can stably emit source electrons with high density, the source electrons have higher initial kinetic energy, and then the external pulse electric field obtains more energy to accelerate and impact smoke molecules to enable the smoke molecules to strongly discharge, so that a similar 'dispersion discharge' phenomenon is formed, and a large-area uniform low-temperature plasma is generated, so that high-density free electrons, negative ions and positive ions are arranged in the whole electric field channel, and the full and uniform heteropolarity charge of fine dust particles is facilitated. The dust longitudinally flows through the discharge area along with the flue gas, one part of the dust collides with free electrons and negative ions and captures the free electrons and the negative ions to become particles with negative charges, and other dust collides with positive ions and captures the free electrons and the negative ions to become particles with positive charges, so that the flue gas particle group generates heteropolar charges, the heteropolar charge quantity of the fine dust can be obviously improved, and the electrostatic coalescence and electric field trapping efficiency of the fine dust can be improved.

Has the advantages that: compared with the prior art, the invention has the following remarkable characteristics:

1. the electrostatic precipitator is suitable for a high-temperature environment, can work efficiently and stably in a normal-temperature environment and a medium-low-temperature environment, and generates large-area uniform low-temperature plasma by forming a similar 'dispersion discharge' phenomenon, so that high-density free electrons, negative ions and positive ions are arranged in a whole electric field channel, dust particle groups can generate heteropolarity charge, part of the dust particle groups are charged with positive charges, and other dust particle groups are charged with negative charges, the charge capacity of fine dust is obviously improved, and the electrostatic precipitation and electric field trapping efficiency is improved;

2. the work function of an electron emitter of the prepared ternary rare earth tungsten composite material is reduced to 2.74ev, the cathode of the ternary rare earth tungsten composite material is reduced by more than 30% compared with common metals of the existing corona type electrostatic dust collector, such as stainless steel, titanium alloy and the like, and the cathode of the ternary rare earth tungsten composite material is reduced by about 10% compared with the rare earth tungsten cathode of the existing thermionic emission type electrostatic dust collector, so that the electron emission and gas discharge performance of the cathode are obviously enhanced;

3. simple structure, low energy consumption, and more than 50% reduction than direct current corona discharge.

Drawings

FIG. 1 is a schematic view of the structure of a discharge cathode 1 according to the present invention;

fig. 2 is a schematic structural diagram of the present invention.

Detailed Description

As shown in fig. 1, the discharge cathode 1 is a wolf tooth bar type, and includes a plurality of electron emitters 11 and a metal support rod 12, wherein the electron emitters 11 are uniformly arranged along the metal support rod 12 at intervals. The electron emitter 11 is a cone with a taper of 1: 2-4: and 5, the distance between conical tips is 15-25 mm. The metal support rod 12 is made of a stainless steel material. The electron emitter 11 comprises 2-3 wt% of a ternary rare earth oxide, with the balance being tungsten. The ternary rare earth oxide comprises the following substances in percentage by mass: CeO (CeO)₂15～20wt％，La₂O₃15 to 25 wt%, and the balance Y₂O₃. The work function of the electron emitter 11 is reduced to 2.74ev, which is higher than that of the existing corona type electrostatic precipitatorCommon metal cathodes, such as stainless steel, titanium alloy and the like, have the reduction of more than 30 percent of barbed wires, sawtooth wires, needle-punched wires and the like, and are reduced by about 10 percent compared with rare earth tungsten cathodes in the existing thermionic emission type particulate matter charging device, so that the electron emission and gas discharge performance of the cathodes are obviously enhanced. The ternary rare earth tungsten material has low work function, good wear resistance and corrosion resistance, and is not easy to damage in a dust-containing smoke environment.

A method of making an electron emitter 11 comprising the steps of: ammonium paratungstate and aqueous solution of cerium nitrate, lanthanum nitrate and yttrium nitrate are doped, dried and reduced at two stages of 240-960 ℃ with large temperature gradient to prepare tungsten powder, and then the tungsten powder is mixed, pressed, presintered, sintered at 1150-1950 ℃ in a vertical melting mode and subjected to plastic processing to prepare the electron emitter 11. If the reduction temperature is not in the range of 240-960 ℃, rare earth oxide fine particles and uniform dispersion thereof are difficult to form; the temperature of the vertical melting sintering is not in the range of 1150-1950 ℃, which leads to low density of the billet and uneven distribution of the rare earth elements in the billet. Both of the above-mentioned cases cause a decrease in the electron emission capability of the electron emitter 11.

As shown in fig. 2, the housing 2 of the dust charging device is grounded. The discharge cathode 1 shown in fig. 1 is arranged in the shell 2 and is connected with a high-voltage pulse power supply 4 through an insulating ceramic sleeve 3. The cone-shaped electron emitter 11 is uniformly embedded on the metal support rod 12 to form the wolf tooth rod-shaped discharge cathode 1, and the wolf tooth rod-shaped discharge cathode 1 is connected to the negative electrode of the high-voltage pulse power supply 4. The shell 2 is also provided with a flue gas inlet 5 and a flue gas outlet 6 which are respectively positioned at the lower part and the upper part of the shell 2.

The cone-shaped low work function ternary rare earth tungsten functional composite material for emitting electrons is embedded on a common metal (such as stainless steel) support rod to be made into a wolf tooth rod type discharge cathode 1, and the purpose is as follows: firstly, expensive ternary rare earth tungsten functional composite materials are saved as much as possible; secondly, the field electron emission performance of the low work function ternary rare earth tungsten functional composite material is fully exerted; thirdly, the discharge performance of the smoke is strengthened under the coupling action of electron emission and an external high-voltage pulse electric field, similar 'dispersion discharge' is formed, large-area uniform low-temperature plasma is generated, and the heteropolarity charge of the fine dust is promoted.

Performance testing

Ten sets of devices were set according to the process parameter values of table 1 below, and the peak current densities were tested separately, as can be seen: the pulse power supply parameters (e.g., rising edge, pulse frequency, peak voltage) and the discharge cathode 1 structure (e.g., electron emitter 11 taper, taper pitch) have an effect on the soot charge performance. When the rising edge, the pulse frequency and the peak voltage of the high-voltage pulse power supply 4 are respectively 800ns, 50Hz and 60.8KV, and the taper interval distribution of the electron emitter 11 of the discharge cathode 1 are 4: the discharge current density is maximum (up to 3.24 mA/cm) at 5 and 20mm²) The dust charging effect is optimal.

TABLE 1 Performance testing of electron emitters 11 of different tapers, taper pitches