LT7065B - Plasma generator - Google Patents

Abstract

The invention relates to the field of electric arc thermal plasma generators (PG) and is intended for plasma waste and hazardous substances treatment systems. (PG) housing (1) consists of six stainless steel, coaxially arranged, insulated from each other, variable cross-section cylinders and nozzle (2), which are covered with a high-temperature aluminum oxide insulating protective coating (3), the cathode assembly is mounted on the body (1) inside with a holder (4) in the center of which a hafnium emitter (5) is pressed, an anode assembly consisting of a graphite plate with a liquid metal bath. The cooling system of the housing (1) consists of thin-walled stainless steel tubes inserted into the housing (1), into which the cooling fluid is supplied from the coolant supply channels (13), (14), (15) and exhaust channels (17), (18), (21), and for cooling the nozzle (2), the cooling fluid is fed through a milled channel (19). Graphite plate (25) with a liquid metal bath, on the surface, on the liquid metal or electrically conductive ceramic melt, a moving anodic spot is formed. The length of the electric arc between the cathode and the anode is variable and adjustable by employing a positioning device. The plasma-forming gas is supplied in the cathode-emitter zone, and the high-temperature aluminum oxide insulating coating (3), with the appropriate component composition, consists of an aluminum and/or titanium or an aluminum and/or zirconium oxide layer.

Description

TECHNICAL FIELD

The invention relates to the field of electric arc thermal plasma generators (PG) and is intended for use in plasma waste and hazardous material treatment systems.

STATE OF THE ART

A well-known constant current plasma generator with a hot cathode and stepped copper anode (US5363781A, 1994). A feature of such a PG is that it creates a high-temperature plasma environment for the decomposition of various materials. However, the plant is mainly designed to transport liquid or gaseous waste to a high temperature area where it is treated. Therefore, it is not suitable for plasma processing in plasma reactors due to the significant flux density and high speed, because the residence time of the material in the plasma device is very short (less than 100 ms). Other similar devices with linear PGs described in the applications are also not suitable for the neutralization of materials, especially hazardous waste, due to the insufficient time of material dislocation in the high-temperature reaction zone.

Among the existing plasma generators of similar designs are known and described in patents JP5226536B2, RU2036758 and US10076019B2. However, they are intended for mechanized and manual cutting, welding, spraying and other types of material processing in various industries. PG described in US10076019B2 can be considered as an analogue. However, the design includes a hollow electrode that is along the main axis of the PG. This can result in insufficient cooling by the plasma-forming gas and, at higher current values, there is a risk of burning. PGs of similar design are described in other patent applications, such as CN108770172, CN113811061A (2021), US2004000538A1 (B2) (2004), etc., but they are not suitable for processing materials that are crushed into granules larger than 1 mm in size.

In terms of construction, the closest technical solution and the best result achieved is JP3591233B2 and also CN112996211. The described PGs consist of a nozzle with an opening that serves as an outlet for the plasma flow. This PG has a cylindrical electrode, and the gas forming the plasma is blown through a vortex element with an external threaded part. When processing hazardous waste in this way, a plasma with a temperature of 2000-5000°C is created in the plasma generator with an electric arc. PG is directed to the reactor.

In the inventions KR100756642B1 (2007), US11032900B2 (A1) (2021),

CN103200757A (B) (2013) The PG consists of a cathode rod and an anode, an electric arc is initiated between the cathode and the first (intermediate) anode through which the gas forming the plasma is supplied. In such designs, too little attention is paid to cooling the cathode.

PG PSM-100 (RU2350052 C1) is described, which consists of a case, a tungsten cathode and an anode separated from the case by an insulating ring through which the working gas is supplied. The anode outlet nozzle is stepped, widening toward the outlet, and the anode outlet channel is cylindrical.

Patented PG has a number of disadvantages. Its cathode is made of a tungsten rod connected to a cooled housing through a sleeve clamp. The rod is cantilevered and has a fairly large overhang, so there may be additional difficulties in ensuring electrode alignment during fabrication and installation of the PG. In addition, tungsten oxidizes intensively in air, so additional inert gas or nitrogen must be used to protect it.

In most cases, the examined PGs use depleting cathodes. Due to the inevitable erosion of the cathode and the emission of material into the plasma-forming gas flow, the length of the rod gradually decreases, and after reaching a certain length, the rest of it becomes unsuitable for further use and must be removed. In this case, the electrode is replaced with a new one, which leads to an irrational use of the cathode material. In addition, the generated plasma stream is contaminated with erosion products of the electrode, which change its properties.

ESSENCE OF THE INVENTION

The purpose of the invention is to expand the possibilities of using plasma generators in the conversion processes of hazardous materials and waste, to increase the service life of the electrodes and the possibility of obtaining non-equilibrium plasma of the required composition, low mobility, thermally and chemically active, to avoid the discharge to the reactor walls when an electrically conductive environment is formed in the chamber.

The purpose of the invention is achieved by the fact that in the plasma generator (PG), which consists of a cylindrical body (1), the walls of which are equipped with cooling fluid supply and drainage channels, plasma gas supply and plasma flow outflow channels, a cathode unit and an anode unit. The body (1), consisting of six stainless steel, coaxially arranged, insulated cylinders of variable cross-section, separated from each other by centering bushings, which are intended for the supply of gas forming the plasma and the circulation of cooling water, connected to the nozzle (2), which are coated with a high-temperature aluminum oxide insulating protective coating (3), the cathode unit is installed inside the body (1) with a holder (4), in the center of which a hafnium emitter (5) is pressed in, and an anode unit, consisting of graphite plates (25) with liquid metal bath.

Also, the cooling system of the PG housing (1) consists of thin-walled stainless steel tubes inserted into the housing (1), into which the coolant is fed from the coolant supply channels (13), (14), (15) and drained (17) ), (18), (21) channels, and for cooling the nozzle (2), the liquid is fed through a milled channel (19).

In addition, a special water-cooled holder (4) in the form of a truncated cone is attached to the cathode assembly, the angle of which forms an angle of 70°-90° with the axis.

Also, on the surface of the anode graphite plate (25) with a liquid metal bath, a moving anodic spot is formed on the liquid metal or electrically conductive ceramic melt, and the length of the electric arc between the cathode and the anode is variable and adjustable with the help of a positioning device (not shown in the drawing).

In addition, the plasma-forming gas is supplied to the cathode emitter (5) zone, and the high-temperature aluminum oxide insulating coating (3) consists of an aluminum and/or titanium or an aluminum and/or zirconium oxide layer, with the appropriate composition of components.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. the schematic diagram of the plasma generator PG is shown.

Fig. a general view of the PG body is shown, in the section view A-A, in the view

B - section of the tip.

The plasma generator (PG) (Fig. 1) consists of a stainless steel body (1) with a nozzle (2) covered with a high-temperature aluminum oxide protective coating (3), a cooled cathode holder (4) with a pressed-in hafnium emitter (5), a flow dynamic turning mechanism (6) with grooves, gas supply channel (7) with a pipe (8) directed to the end of the PG. The gas supply channel (7) consists of a cavity between the two outer tubes of the cathode assembly (9) and the cooling system channel (10), made of stainless steel. The gas is supplied through three coaxial centering bushings (11) with annular holes. The flow is turned using a special copper turning assembly (12) with a thread with a pitch of 4.25 mm.

Non-equilibrium plasma is generated to create an activating environment of reactive gases to increase the rate of chemical reactions by several hundreds of times.

The PG body (1), tip (2) and cathode assembly (9) are intensively cooled. For this, a special cooling system is used, which supplies coolant to the supply channels with supply (13), (14), (15) and drain (17), (18), (21) channels. The cooling shell of the body (1) consists of thin-walled stainless steel tubes, and the nozzle (2) has a milled channel (19) into which the outer tube (20) is threaded. The PG cathode cooling liquid flows through the central tube opening (21) through a channel directly from the entire cathode assembly.

The layout of the PG side plasma-forming gas and cooling water supply channels is shown in Fig. 2, which also shows the plasma-forming gas and electric arc discharge nozzle (22).

The cathode holder used in the PG plasma generator is made of high-quality copper, and the button-type emitter pressed into it is "hot" made of hafnium. In addition to the mentioned units and details, PG also consists of gas supply and measurement devices (not shown in the drawing), measurement holes, plasma flow discharge nozzles and fastening elements. PG is assembled and connected with ring nuts (23) with sealing gaskets (24). The body of the supply channel of plasma-forming gases is also used to supply electric current to the cathode emitter and is connected to a constant stabilized current 600 V and 300 A power supply source through terminal (-).

The PG anode is a graphite plate (Fig. 1, 25) with a liquid metal bath (Fig. 1, 26) installed in a plasma chemical reactor. This also makes this PG different from the prototype. The gas forming the plasma is heated together with the processed material in the reaction zone of the electric arc, where organic materials are decomposed and gasified, and inorganic materials are melted. The gas forming the plasma is heated by the plasma generator, supplied with a flow of 0.9-1.2 g/s through bushings with annular holes (Fig. 2, 11) arranged evenly around the entire circumference of the outlet nozzle of the plasma generator, after which it enters through the copper turning assembly (12) into the outlet nozzle (22). In the reaction zone of the arc, the gases forming the plasma may contain various types of components and mixtures thereof, including carbon dioxide, air, water vapor, argon, hydrogen and other gases and mixtures thereof.

In the internal structure of the PG, six coaxial coaxial cylinders can be distinguished, separated from each other by centering sleeves, which are used for the supply of plasma-forming gases and cooling water circulation. The cathode holder, the tip of which is in the form of a truncated cone, the component of which forms an angle of 70-90° with the axis, is screwed into the water-cooled cathode assembly. The inlet sleeve for plasma-forming gases is made of glass textolite and has an inner diameter of 20 mm. As a result of the dynamic and thermal processes of the gas, which take place after the plasma column flows towards the anode, an arc spot is formed on the graphite plate (25), the diameter of which is directly proportional to the distance between the electrodes and depends on the composition and flow rate of the blown gas. The metal in its cavity melts and forms a bath of liquid metal (26). Under the influence of gas dynamic and electromagnetic forces, the spot constantly moves on the surface of graphite and liquid metal (steel). It has a relatively large surface area where the heat of the anode zone of the arc is released, which guarantees a high resistance of the anode to thermal shocks.

DESCRIPTION OF IMPLEMENTATION OF THE INVENTION

The plasma generator PG works on the following principle:

coolant (water) starts to be supplied from the cooling system reservoir pumps through channels (13), (14) and (15). At the same time, plasma-forming gas is supplied through the supply channel (7) through the nozzle (8) and sleeves (11), which enters the pre-cathode zone. Next, with the help of a positioning device (not shown in the drawing), a minimum distance of 5-10 mm is determined between the PG cathode and the anode (graphite plate (25) with the not yet melted metal in its bath (26). A gap of 5-6 mm is selected to excite the electric arc and between the PG and the graphite plate is supplied with voltage and the oscillator is briefly switched on, which gives a voltage pulse of 15 kV. The gas in the gap is ionized and the electric arc is initiated between the anode and the cathode. After the arc is ignited, the required distance of 150200 mm is determined by the positioning device, at which the PG works stably, and its voltammetric characteristics become rising, which also shows the difference of this PG from existing analogues.

The stream of cold plasma-forming gases surrounds the pre-cathode zone of the arc and moves along the central axis of the PG towards the anode. The gas moving through the channel of the nozzle (2) intensively expands and the arc together with it, leaves the cylindrical nozzle through the central channel (22) and moves to the metal bath of the graphite plate (26), where the metal is melted. This nature of the arc combustion ensures its stability, uniform heating of plasma-forming gases along the axis and periphery, and uniform temperature distribution in the cross-section of the plasma current at various PG operating parameters. In this way, the arc acquires a rising voltammetric characteristic.

The heat released in the cathode-emitter zone is intensively removed by flowing water and the current surrounding the arc. This design ensures long-term operation of the PG at a current of up to 300 A. The main characteristics of the patented PG operation are stable and strictly regulated. The average size of the arc current is 160-180 A. It depends on the efficiency of the plasma process, the speed and quality of material processing, as well as the power of the plasma device. The size of the current is selected based on the composition and amount of pollutants to be treated.

The voltage of the arc depends on its length, it can vary between 280-235 V, depending on the set distance and arc current. It also determines the power of the device and has a direct influence on the voltammetric characteristics of the PG.

Arc power is one of the defining parameters of an electric arc and is expressed as the product of arc current and voltage. In the patented device, it is 37.6-44.8 kW.

One of the defining parameters is the flow of plasma-forming gases. In this PG, it is 0.9-1.1 g/s, while in the examined prototypes it is significantly higher and reaches up to 50 g/s. This parameter is very important because it ensures the long-term dislocation of contaminants in the plasma environment. This is also an advantage of this PG.

Additional gases of various compositions can be supplied to the PG pre-cathode zone, which are designed to create a protective atmosphere for the cathode emitter. Additional gas, with a flow of up to 10-15 g/s, is supplied to the near-anode zone inside the plasma chemical reactor, in case it is desired to increase the enthalpy of the gases in the reaction zone, as well as to create an atmosphere of the required composition in the reactor. Supplying additional gas can also reduce the temperature and velocity of the plasma environment, as well as the enthalpy of the environment (e.g., by supplying water vapor).

Using a positioning device with a plasma generator, the initial distance between the cathode and the anode is determined by calculating the minimum thickness of the piercing layer and knowing the electrical conductivity of the additional gas supplied to the reaction zone at ambient temperature. Next, using the same positioning device, the working distance between the cathode and the anode is determined, and by changing it, the power and characteristics of the electric arc are regulated.

The parameters of the plasma current depend on the geometrical dimensions of the arc, especially on the diameter of the discharge nozzle and the length of the arc. As the diameter of the nozzle increases, the length of the plasma jet decreases and the diameter increases. As the arc length increases, the average mass enthalpy of the plasma stream decreases and the plasma plume becomes more concentrated, while the angle of expansion of the stream decreases.

In order to avoid electrical contact between the cathode, the generated conductive gas, and the metal parts of the walls of plasma chemical devices where the PG is installed, its body (1) and nozzle (2) are covered with a high-temperature aluminum oxide insulating protective coating (3), which consists, with the appropriate composition of components, from aluminum and/or titanium or aluminum and/or zirconium oxide 250 μm thick layer, which prevents the arc from closing on the wall or lining of the plasma chemical reactor in the plasma environment.

An electric arc burning in a confined space (reactor) is considered free, although its development in space is somewhat limited by the walls of the reactor. The form and behavior of the arc are not limited by the plasma-forming and shielding gases, and the flow of additional gases stabilizes it. Air, as a plasma-forming gas, is supplied to the PG from the cathode side. The object of the invention, PG, in addition to waste treatment, can also be used in plasma-chemical reactors for various purposes, for the synthesis of materials, their melting and the formation of various products, such as granules and fibers. Together with the reactor, it can be successfully used for hydrogen synthesis in water vapor plasma technology, metallurgy, etc.

INDUSTRIAL SUITABILITY

A new set of structural elements, thanks to the fact that the plasma generator, in which the coaxially installed water-cooled elements of variable cross-section, are isolated from each other, allows the generation of a stationary arc pillar with stable and fully adjustable parameters, which allows to achieve the goal of the invention.

Claims (8)

1. A plasma generator consisting of a cylindrical body, the walls of which are equipped with coolant supply and drainage channels, gas supply and plasma flow gas inlet and outlet channels, a cathode assembly and an anode assembly, but differs in that the casing (1) consists of six stainless steel coaxially insulated cylinders of variable cross-section, separated from each other by centering bushings for the supply of plasma-forming gases and cooling water circulation, and the nozzle (2), which are covered with a high-temperature aluminum oxide insulating protective coating (3), the cathode assembly (9) is mounted inside the housing (1) with a cathode holder (4) in the center of which a hafnium emitter (5) is pressed in and, at the tip (2) separately arranged at an adjustable distance, an anode assembly consisting of a graphite plate (25) with liquid metal bath (26). 2. The plasma generator according to claim 1, but differs in that the cooling system of the body (1) is composed of thin-walled stainless steel tubes inserted into the body (1), into which the coolant is supplied from the coolant supply channels (13), (14) , (15) and is led through channels (17), (18), (21). 3. The plasma generator according to claim 1, which differs in that the liquid is fed through a milled channel (19) for cooling the nozzle (2) of the body (1). 4. The plasma generator according to point 1, but differs in that the cathode unit is fixed in a special water-cooled truncated cone-shaped holder (4), the angle of which forms an angle of 70°-90° with the axis. 5. The plasma generator according to claim 1, which differs in that a moving anodic spot is formed on the surface of the graphite plate with a liquid metal bath, on the liquid metal or electrically conductive ceramic melt. 6. The plasma generator according to claim 1, which differs in that the length of the electric arc between the cathode and the anode is variable and adjustable with the help of a positioning device. 7. The plasma generator according to claim 1, which differs in that the gas forming the plasma is supplied in the area of the cathode emitter (5). 8. The plasma generator according to claim 1, which differs in that the high-temperature aluminum oxide insulating coating consists of an aluminum and/or titanium, or an aluminum and/or zirconium oxide layer, in the presence of a suitable composition of components.