Microwave plasma converter

FIELD: power industry.

SUBSTANCE: invention may be used when producing carbon nanotubes and hydrogen. Microwave plasma converter comprises flow reactor 1 of radiotransparent heat-resistant material, filled with gas permeable electrically conductive material - catalyst 2 placed into the ultrahigh frequency waveguide 3 connected to the microwave electromagnetic radiation source 5, provided with microwave electromagnetic field concentrator, designed in the form of waveguide-coax junction (WCJ) 8 with hollow outer and inner conductors 9, forming discharge chamber 11 and secondary discharge system. Auxiliary discharge system is designed from N discharge devices 12, where N is greater than 1, arranged in a cross-sectional plane of discharge chamber 11 uniformly in circumferential direction. Longitudinal axes of discharge devices 12 are oriented tangentially with respect to the side surface of discharge chamber 11 in one direction. Nozzle 10 is made at outlet end of inner hollow conductor 9 of WCJ 8 coaxial. Each of discharge devices 12 is provided with individual gas pipeline 13 to supply plasma-supporting gas to discharge zone.

EFFECT: invention permits to increase the reaction volume, production capacity and period of continuous operation, stabilise burning of microwave discharge.

3 cl, 2 dwg

The invention relates to techniques for processing of hydrocarbon raw materials, particularly natural gas, and production of carbon and hydrogen.

One of the major problems of rational nature management is the deep processing of natural and associated gas production. Many variants are possible here: the transformation of the gas into the liquid fraction used as a source for electricity production, the conversion of such valuable products as carbon and hydrogen, for which demand is high enough. The yields of carbon evidenced great interest related to his main role in nanotechnology. In this regard, it should be noted the uniqueness of the known carbon modifications of fullerenes and nanotubes, opening wide possibilities of their application in pharmacology, materials science, electronics, automotive and aerospace, military, etc.

No less significant and the problem of hydrogen, the need for energy is difficult to overestimate. To obtain as the main raw materials used hydrocarbon gas.

Thus, confirms the relevance of the development of technologies and means of obtaining pure carbon and hydrogen, the efficiency of the processes.

A device that implements the method endothermically the heterophase reactions which is the reaction of dissociation of hydrocarbon molecules [microwave catalytic reactor for endothermic heterogeneous reactions. RF patent №2116826]. The novelty of the device is that the reactor is made in the form of a microwave resonator, and the working mixture is open to the penetration of the electromagnetic field. This allows for additional heating of the mixture of feedstock and catalyst dissipation of microwave energy to the resistive losses of the material. The device has the disadvantages inherent in the pyrolytic dissociation: low productivity, coking and, consequently, the short life of the catalyst.

Known apparatus for producing carbon and hydrogen from hydrocarbon gas (methane) [Ahibaii and other periodic-Pulsed microwave discharge as a catalyst for chemical reactions // ZH. - 2000. - T. - Vol. 11. - p.36-41], which implements the process of thermal dissociation of methane to carbon and hydrogen: CH₄→2H₂+When exposed to plasma periodic-pulsed microwave discharge in a pre-heated gas. The device includes a source of hot gas, a microwave generator, a ferrite circulator, a discharge chamber, a waveguide for supplying microwave energy into the discharge chamber. The disadvantages of the known devices: the need for additional external source of heat for pre-heating source is th hydrocarbon gas, i.e. the inevitable heat losses and the complexity of the design, and the relatively low degree of methane conversion and output of carbon and hydrogen.

A device for plasma-chemical conversion of hydrocarbon gas (methane) to hydrogen and carbon [RF Patent №2393988, publ. 10.07.2010. Bull. No. 19], in which preheating and subsequent decomposition of the hydrocarbon gas into carbon and hydrogen in the plasma of RF discharge exercise combined effect of microwave electromagnetic fields and matter-initiator (catalyst). On set of technical characteristics of this analogue is selected as a prototype of the present invention. The device comprises a flow reactor with separate entrance hydrocarbon gas and the release of carbon and hydrogen, made of a radiation transparent heat-resistant material, for example quartz glass, filled with a catalyst, provided with a hub of microwave electromagnetic field and placed in a S-shaped waveguide of rectangular cross-section through the center perpendicular to the broad walls. To the outlet of the reactor adjacent the hub of microwave electromagnetic fields, made in the form of a waveguide-coaxial transition (BCP) with a hollow inner conductor, in which the axially posted by high voltage electrode connected to a source of high voltage is tion and forming with the inner conductor of the coaxial BCP system auxiliary discharge (electric gas discharger), when this high voltage electrode is made in the form of a tube plugged at the outlet end, and is equipped with a system diametrically opposite holes. In the inner conductor of the coaxial BCP implemented system of radial holes. Both holes are isolated from each other tight dielectric septum located in the cross section of the inner conductor of the coaxial BCP. The cavity bounded by the end face of the inner conductor and the inner side surface of the outer conductor of the coax, forms a discharge chamber.

The device prototype works as follows. After purging the reactor with nitrogen to push out its volume of oxygen in the S-shaped waveguide is fed microwave energy from the microwave generator (magnetron), operating in continuous mode. When exposed to microwave energy in the reactor is heated catalyst due to energy dissipation in resistive losses up to temperatures of 400÷700°C. In the second stage of work on high-voltage electrode system auxiliary discharge is fed to the pulse from the high voltage source, which in the space between the high voltage electrode and the inner conductor of the coaxial BCP lights glow discharge. This category plays an auxiliary role to create the initial concentration of the emission of the plasma, sufficient to initiate and maintain in the future the microwave discharge. Part of the microwave energy after passing through the catalyst enters the area of the glow discharge. When a sufficient level of strength of the electric component of the electromagnetic field penetrates the gas (nitrogen) and ignited microwave discharge. In the third phase in the reactor is methane (VLF) and shuts off the supply of nitrogen. Passing the heated catalyst, the methane is heated, which leads to pre-excitation of the molecules and the formation of unsaturated hydrocarbons (ethylene, acetylene). These products are made in the area of microwave discharge plasma which is the final decomposition of unsaturated hydrocarbons to carbon and hydrogen.

During the experimental test conditions, of igniting and maintaining auxiliary (glow) and a body (CB₄) discharges was installed that used in the prototype design system auxiliary discharge provides a stable initiation and maintenance of the basic microwave discharge in a mixture of nitrogen - methane at the expense of methane up to 1 m³per hour and microwave power invested in a range of about 2000 watts. When increasing the flow rate of methane in excess of 1 m³per hour to ensure the highest conversion rates need to increase the level of microwave power introduced into the discharge zone. At high power dissipated in the etrade, problems with heating and erosion of the inner conductor of the coax (electrode) up to its melting. Reducing power to eliminate overheating of the electrode can lead either to failure initiation microwave discharge, or to its extinction.

The disadvantage of the system auxiliary discharge implemented in the prototype is also "bind" auxiliary discharge to a certain point electrode that violates the spatial uniformity of the plasma initiation of a microwave discharge in atmospheric pressure due to its contraction, resulting in reduced efficiency of the conversion process.

On the other hand, when increasing the flow rate of the methane passing through the discharge zone may not be sufficient amount of energy input auxiliary discharge to create the initial, required to initiate the plasma concentration. In all modes of decomposition of methane (flow rate, temperature, energy input) power auxiliary discharge must be less than the capacity, put in the microwave discharge. This condition is dictated by the overall efficiency of the system.

The disadvantages include the fact that when increasing the capacity of the auxiliary discharge and consumption of methane preheated to a high temperature electrode of a spark gap in the presence of methane, the formation of carbon as carbon bridge overlaps the bit period until the breakdown of the subsidiary and, as a consequence, the main microwave discharge.

The technical result of the invention is to improve efficiency by increasing the reaction volume, stability "burning" microwave discharge and vortex stabilizing action on the plasma torch microwave discharge, increasing the yield of target products, performance and duration of continuous operation of the Converter.

This technical result is achieved by the fact that in the proposed microwave plasma Converter containing, as a prototype, the flow reactor of the radiation transparent heat-resistant material filled with gas-permeable electrically conductive substance is a catalyst, placed in a microwave waveguide connected to a source of microwave electromagnetic radiation, provided with a hub microwave electromagnetic field, is made in the form of a waveguide-coaxial transition (BCP) with a hollow outer and inner conductors forming the discharge chamber and the auxiliary discharge, unlike the prototype, the system auxiliary discharge is made of N arresters, where N>1, located in the plane the cross-section of the discharge chamber uniformly on its circumference, with the longitudinal axis of the spark gap is oriented tangentially with respect to the side surface of the bit is the ameres in the same direction.

It is advisable that in the inner hollow conductor of the coaxial CPSU at its output end was made nozzle.

It is advisable that each of the gaps was provided by individual pipeline for supplying a plasma-forming gas into the discharge zone.

Compared to the system auxiliary discharge prototype of the proposed execution of the system in the form N arresters, first, increases plasma volume of the auxiliary discharge, thereby ensuring the reliability of initiation of the main microwave discharge, secondly, the tangential location of dischargers in the same direction relative to the normal to the side surface of the discharge chamber creates a swirling flow of plasma gas (nitrogen), increasing the reaction volume of the plasma formation, the time of interaction convertible natural gas (methane) with the plasma, increasing the stability of the "burning" of the microwave discharge, and providing a vortex stabilizing effect on the plasma torch microwave discharge.

Due to this design of the system auxiliary discharge increases the efficiency of conversion, the output of carbon and hydrogen at elevated (>1.0 m³/hour) cost convertible gas, requiring higher energy input in the discharge.

Figure 1 schematically illustrates the construction of the inventive device. In figure 2, not only the but the cross-section of the discharge chamber with the auxiliary system discharge.

The proposed device comprises a reactor 1, is made of tubular radiation transparent heat-resistant material, for example quartz glass, filled with a granular mass of substance - 2 catalyst, such as iron filings. The reactor 1 is installed across (for example, S-shaped) of the waveguide 3 of rectangular cross-section, through the middle of its wide walls (in particular, perpendicular to the walls in the maximum electric field intensity of the wave H₁₀in a waveguide of rectangular cross-section). The input waveguide 3 through the circulator 4 is connected to a source of microwave electromagnetic radiation (magnetron) 5. The waveguide 3 is equipped outrageous circular waveguide 6, which prevents the radiation of microwave energy to the outside. The output end of the waveguide 3 has a movable short piston 7. Granular matter - the catalyst 2 is placed in the cavity of the reactor 1 in the associated (aggregated) state that provides effective end-to-end flow of gas. To the output end of the reactor adjacent the hub of the microwave electromagnetic energy is made in the form of a waveguide-coaxial transition (BCP) 8, with a hollow inner conductor 9, the output end of the nozzle 10. The cooled discharge chamber 11 bounded by the outer conductor of the coaxial BCP contains the system auxil telego discharge, consisting of N, where N>1, level 12, each of which has an individual pipeline 13 for supplying a plasma-forming gas in the discharge (electrode) period and contains isolated from each other, the outer 14 and inner electrodes 15.

The gaps 12 are evenly spaced around the circumference and oriented with their longitudinal axes tangentially to the lateral surface of the discharge chamber 11 in the same direction.

The proposed device operates as follows.

In the first stage reactor 1 is purged with inert gas (nitrogen) to the exclusion of its volume of oxygen. Then in the waveguide 3 from the magnetron 5 is supplied microwave energy, which in the reactor 1 is heated particles of catalyst 2 under the action of the induced eddy currents and dissipative energy losses up to temperatures of 500-800°C. however, the catalyst particles 2 possible electrical micro-discharges and autoelectronic emission, passing, with increasing temperature of the particles in thermionic emission.

In the second phase of work on the gaps 12 are high-voltage pulses from a source (not shown)under the action of which is between the electrodes 14, 15 of the spark gap 12 is illuminated glow discharge. The flow of nitrogen is supplied into the discharge gap of each spark gap, the discharge plasma is blown inside the discharge-and the camera 11. The concentration of this plasma is sufficient to initiate and maintain in the future the main microwave discharge. The proportion of microwave energy, not pegloticase substance - catalyst 2, flows through the waveguide 3 in the auxiliary discharge discharge chamber 11. When a sufficient level of strength of the electric component of the electromagnetic microwave field penetrates the gas in the discharge chamber 11 in the region of the end of the inner hollow conductor 9 of the coaxial BCP occurs microwave discharge. Configuring BCP on the optimal mode of operation is carried out using a rolling short piston 7.

Previously created by the system of the auxiliary spark gap set of glow discharge facilitates the ignition of the microwave discharge, which alleviates problems associated with erosion and heating of the inner conductor 9, which is characteristic for the device of the prototype.

In the third phase in the reactor 1 is methane (CH₄and shuts down the flow of nitrogen into the reactor. Passing the heated substance - catalyst 2 methane is heated, which leads to the formation of unsaturated hydrocarbons (ethylene, acetylene), and active particles (radicals, ions, excited molecules), promotes the decomposition of the hydrocarbon chain reactions. Converted and the remaining gases, hydrocarbon products are made in the area of the hub microwave electric the magnetic field, where both burn microwave gas discharge and initiating his glow discharge. Here in plasma gas microwave discharge is the final decomposition of unsaturated hydrocarbons to carbon and hydrogen, which are submitted to intensive gas flow from the zone of plasma-chemical reactions. For the proposed device, as and for the prototype, presumably part of the substance 2 catalyst chemical reaction, which resulted in the above-mentioned temperatures on its surface is formed of crystalline carbon (nanotubes), At the expense of plasma micro-discharges induced between the individual particles of the catalyst of the microwave electromagnetic field, crystalline carbon strays from the surface of the catalyst particles and is carried away from the reactor gas stream. This allows you to increase the "life" of the substance of the catalyst and to increase the efficiency of conversion of natural gas.

During the experimental verification of the conditions of ignition and stability of the subsidiary (glow) and the main microwave (MW) discharge, it was found that both types of discharges steadily burn in nitrogen atmosphere. When switching to nitrogen-methane mixture or pure methane recorded that the stability of the discharge, until its extinction due to the formation of the carbon bridge between the electrodes in place binding of discharge. When premikanje ele is trudov auxiliary discharge is extinguished and, accordingly, turns off the main microwave discharge. The device prototype, this problem is partially removed due to the construction of the spark gap, providing a combustion auxiliary discharge mainly in a nitrogen atmosphere, and microwave discharge in the environment of methane. However, with increasing consumption of methane to values that are of practical interest for a fixed auxiliary discharge the nitrogen flow, dramatically increases the rate of formation of carbon material on the electrodes, resulting in quenching of the discharge. This problem is solved by the proposed system design the auxiliary discharge.

In accordance with the drawing tangentially located on the periphery of the discharge chamber 11 dischargers 12 auxiliary discharge and hollow conductor 9, through which the discharge chamber is methane and the area which is lit microwave discharge, spatially separated. In addition, the location of dischargers and their implementation provide rotational stabilization of the plasma torch microwave discharge flow of inert gas (nitrogen), pressing it against the walls of the discharge chamber. Due to this decrease the probability of formation of carbon deposits on the electrode arresters and their shorting.

Due to the proposed design of the system auxiliary discharges ignite and burn mainly in nitrogen atmosphere. G is the way they are blown into the volume of the discharge chamber and initiate the microwave discharge zone end of the inner conductor 9 of the coaxial BCP with the predominance in it of methane concentration. This embodiment of system auxiliary discharge increases the volume of plasma formation, improves the stability of the microwave discharge and spatial homogeneous plasma, increases the yield of the conversion products (carbon and hydrogen) and the efficiency of the Converter.

In a particular example implementation of the present invention, the inner conductor 9 of the coaxial BCP, which is the electrode of the discharge chamber, made of stainless steel hollow tube with a diameter of 16 mm and length l, determined from the condition$$l=(2m+1)\frac{{\lambda }_0}{4}$$,

where m=0,1,2,3... are integers, λ₀/4 - quarter of the operating wavelength of the microwave generator.

When the value of the operating frequency of the microwave generator f₀=2450 MHz, λ₀=12,24 see this condition selection electrode length is dictated by the need of the location of the end face of the electrode in the antinodes of the electric intensity microwave field.

The output end of the electrode is provided with a tapered expanding nozzle for forming a plasma torch. The outer conductor of the coaxial BCP, which is a cylindrical discharge chamber, equipped with a four-electrode system auxiliary discharge, in his continuation is all Volnov the house with an inner diameter of 40 mm, a second wave of the microwave generator λ₀=12,24 see due to the formation of the reflected wave from the exorbitant waveguide increases, the electric field at the end of the electrode to the breakdown, which increases the stability of the ignition microwave discharge and increases the efficiency of the conversion process. Supply microwave energy to the discharge chamber is supplied from the microwave generator with adjustable output power 5 through the circulator 4 and the waveguide of rectangular cross-section 90×45 mm as the microwave generator used magnetron type M-168 with output power up to 5 kW in continuous mode, and as a circulator ferrite valve type VFW-39. Both of these instrument of domestic production.

Enter convertible gas (methane) into the reactor through the beyond the round waveguide (aka pipe) 6.

The high voltage pulses from source 15 kV with a frequency of 100 Hz is served on the Central electrodes 75 arresters 12 through the high-voltage inputs, representing automotive spark plugs, for example AD, have removed the side electrode (not shown). Each of the spark gap 12 is equipped with individual gas for feeding into the interelectrode gap of the plasma-forming gas (nitrogen). From the discharge chamber, the reaction products come in collections of carbon and hydrogen (not shown).

In the Converter PR is gusmorino water cooling of the discharge chamber.

Thus, the new system design auxiliary discharge is allowed to reach the main technical result of the claimed invention - improving the efficiency of the Converter due to the following factors.

1. The increase in the plasma formation (reaction volume) in the discharge chamber.

2. Improved stability of initiating and maintaining microwave discharge.

3. The stabilizing effect of the vortex gas flow to the plasma torch microwave discharge.

4. Increased deposition of energy in the microwave discharge at high costs convertible gas.

5. Increasing the yield of the target products (carbon and hydrogen).

6. Improving the performance and duration of continuous operation of the Converter.

1. Microwave plasma Converter containing the flow-through reactor of radiation transparent heat-resistant material filled with gas-permeable electrically conductive substance is a catalyst, placed in a microwave waveguide connected to a source of microwave electromagnetic radiation, provided with a hub microwave electromagnetic field, is made in the form of a waveguide-coaxial transition (BCP) with a hollow outer and inner conductors forming the discharge chamber and the auxiliary discharge, characterized in that the system auxiliary discharge is made of N p is Zrodnikov, where N>1, located in the plane of the cross-section of the discharge chamber uniformly on its circumference, with the longitudinal axis of the spark gap is oriented tangentially with respect to the side surface of the discharge chamber in the same direction.

2. Microwave plasma Converter according to claim 1, characterized in that in the inner hollow conductor of the coaxial CPSU at its output end of the completed nozzle.

3. Microwave plasma Converter according to claim 1, characterized in that each of the gaps provided by individual pipeline for supplying a plasma-forming gas into the discharge zone.