Apparatus for converting gas using gliding plasma

An apparatus for converting gas using gliding plasma. The apparatus includes: a reaction chamber; an electrode member inside the reaction chamber and insulated from the reaction chamber; a power source applying electricity to the reaction chamber and the electrode member; a magnetic field generating unit installed outside the reaction chamber to rotate plasma induced inside the reaction chamber in a circumferential direction of the electrode member for forming a plasma region; and a gas supplying unit supplying material gas into the reaction chamber to allow the material gas to pass through the plasma region for converting the material gas into a different gas by energy received from the plasma. In the gas conversion apparatus, the plasma region can be widely formed in the reaction chamber to increase gas conversion rate.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2005-0115908, filed on Nov. 30, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for converting gas using gliding plasma, and more particularly, to an apparatus for converting material gas into desired gas by swirling gliding plasma arc.

2. Description of the Related Art

Various gas conversion apparatuses use plasma to change the molecular structure of gas (material gas) for converting the material gas into a different type of gas (post-reaction gas). Most of the gas conversion apparatuses have a similar structure and operate in a similar manner. That is, most of the gas conversion apparatuses have a mechanism for generating plasma in a closed reaction chamber and injecting material gas into the plasma to collide the molecules of the material gas with the electrons of the plasma for separating molecules of the material gas.

For example, methane, a main component of natural gas, can be converted into acetylene using the gas conversion apparatus. That is, acetylene can be produced from natural gas. As is well-known, the acetylene is a chemical intermediate that can be used in various fields as a starting material for various polymers such as a chlorinated vinyl monomer required for synthetic rubber, acetic acid, vinyl, or PVC.

The acetylene can be produced from the natural gas (specifically, methane) by a high temperature method (thermal treating method) or a low temperature method (non-thermal treating method).

Representative examples of the thermal treating method are an electric arc method and a partial oxidation method.

In the electric arc method, the natural gas is heated to a high temperature using the thermal energy of hot plasma to induce thermo-chemical reaction for obtaining acetylene from the natural gas. German Huel Company's commercial process can be taken as an example of the electric arc method.

In the partial oxidation method, 75% of reaction gas (methane) is burned to generate thermal energy, and then the thermal energy is applied to the remaining 25% of the methane to obtain acetylene by thermo-chemical reaction. BASF Company's partial oxidation combustion process can be taken as a representative example.

However, in producing the acetylene using the thermal treating method, the thermo-chemical reaction is performed at a temperature higher than above 3000K, and worse the thermo-chemical reaction further progresses after the acetylene is already produced to yield carbon and hydrogen from the acetylene. Therefore, the produced acetylene gas must be rapidly quenched to stop the reaction. However, as is well-known, it is difficult to rapidly quench the acetylene gas since gas has a low thermal capacity.

As described above, since the thermal treating method includes an extremely hot reaction process, it is difficult to select suitable materials for a reaction chamber and stop the decomposition reaction. Further, the conversion rate from the natural gas into the acetylene is not so high. Therefore, the non-thermal treating method has been introduced.

A representative example of the non-thermal treating method is a method using non-equilibrium plasma (low-temperature plasma). When methane gas is introduced into the low-temperature plasma, the molecules of the methane collide with electrons having a high energy of the low-temperature plasma, and thereby hydrogen atom is separated from the methane molecules to yield radicals such as methyl (CH3) and methylene (CH2).

The radicals may become ethane (C2H6) by recombining reaction. When energy is continuously applied, the methyl radical (CH3) may become methylene (CH2) or methylidyne (CH) radical by successive dehydrogenation. The CHx radicals obtained as described above make up C2 hydrocarbon such as ethane, ethylene, and acetylene through a recombination process.

FIG. 1shows a conventional gas conversion apparatus11using the gliding plasma, a kind of non-thermal treating method.

Referring toFIG. 1, the conventional gas conversion apparatus11includes a reaction chamber13providing a closed inner space and having a discharge hole17on a lower portion, anode and cathode plates23and25fixedly installed in the reaction chamber13, and a power source19supplying positive and negative currents to the anode and cathode plates23and25through power lines21.

The reaction chamber13includes a nozzle15in a top plate13. The nozzle15injects gas (hereinafter, referred to as material gas) into the reaction chamber13between the anode plate23and the cathode plate25for converting the material gas.

The anode plate23and the cathode plate25have a blade shape with a constant thickness and vertically fixed by separate supports (not shown). Specifically, the anode plate23and the cathode plate25face each other, and the facing surfaces of the anode plate23and the cathode plate25are curved so as to depart from each other further more as they go downward.

When an electricity is applied to the fixed anode and cathode plates23and25, plasma is induced between the fixed anode and cathode plates23and25. The plasma is a gliding plasma (or non-thermal plasma or low-temperature plasma) that glides downward when a downward force is applied by flow of material gas (G). The plasma is placed between the facing surfaces of the anode and cathode plates23and25.

However, the gas conversion rate of the conventional gas conversion apparatus11is not good since the plasma region (A) is not sufficient. That is, since the region (A) occupied by the induced plasma is very small when compared with the total space inside the reaction chamber13, a large portion of the material gas (G) injected into the reaction chamber13is not contacted with the plasma before the material gas (G) is discharged through the discharge hole17, thereby decreasing the gas conversion performance of the gas conversion apparatus11.

Further, since the plasma region (A) is narrow as described above, the material gas (G) injected from the nozzle15passes through the plasma region (A) in a very short time. To solve these problems, that is, to increase the time in which the material gas (G) passes through the plasma region (A), the injection amount of the material gas (G) or the injection speed of the material gas (G) is controlled. However, the gas conversion rate of the gas conversion apparatus is hardly increased by this control.

Referring to a thesis published about the gas conversion apparatus11, a maximal gas conversion rate of 40% is obtained by maximizing the plasma region (A) and optimally controlling the gas injection amount and the gas injection speed. In this case, 60% of the material gas (G) is discharged to the outside through the discharge hole17without reaction with the plasma.

Furthermore, it is very difficult to control the gas conversion rate of the gas conversion apparatus11. Practically, the gas conversion rate should be increased or decreased according to the kind of desired final object (converted gas). However, since the gas conversion rate of the gas conversion apparatus11is controlled by adjusting the injection amount or injection speed of the material gas, the sensitivity of the controlling is not good and the span of control is narrow, thereby precise controlling cannot be attained.

SUMMARY OF THE INVENTION

The present invention provides an apparatus for converting gas using gliding plasma. In the apparatus, gliding plasma is induced between an inner wall of a reaction chamber and an electrode member disposed at a center inside the reaction chamber, and the induced gliding plasma is forced to swirl down in the circumferential direction of the electrode member to form a plasma region between the electrode member and the inner wall of the reaction chamber, so that the plasma region can be widely formed in the reaction chamber to increase gas conversion rate. Particularly, since the gliding speed of the gliding plasma can be controlled, the contact time of the material gas and the gliding plasma can be adjusted to control the gas conversion rate and selectivity for the post-reaction materials.

According to an aspect of the present invention, there is provided an apparatus for converting gas using gliding plasma, the apparatus including: a reaction chamber including a cylindrical inner space and a discharge hole in a lower portion; an electrode member installed on the reaction chamber and extended downward in a downwardly tapered shape, the electrode member including a lower end disposed at the inner space of the reaction chamber and insulated from the reaction chamber; a power source applying electricity to the reaction chamber and the electrode member for inducing plasma between an inner wall of the reaction chamber and the electrode member; a magnetic field generating unit installed outside the reaction chamber to rotate the plasma induced inside the reaction chamber in a circumferential direction of the electrode member for forming a plasma region; and a gas supplying unit supplying material gas into the reaction chamber to allow the material gas to pass through the plasma region for converting the material gas into a different gas by energy supplied from the plasma.

The reaction chamber may include an openable top portion, and the electrode member is detachably installed on the reaction chamber.

The apparatus may further include an insulating electrode holder fixed to the electrode member and supported by the reaction chamber, the electrode holder including a connection rod therein, the connection rod being fixed to the electrode member in electrical connection with the electrode member and longitudinally extended for electrical connection with the power source.

The gas supplying unit may include at least one nozzle injecting the material gas between the inner wall of the reaction chamber and the electrode member, the nozzle being positioned such that the material gas injected from the nozzle moves downward while swirling around the electrode member.

The apparatus may further include a heat exchanger inside the reaction chamber for cooling the material gas after the material gas passes through the plasma region in a downward direction.

The magnetic field generating unit may include: a coil enclosing the reaction chamber; a power source supplying power to the coil; and a controller connected to the power source for controlling the power to the coil.

The electrode member may have a conical shape.

The electrode member may have a convexly curved outer surface or a concavely curved outer surface.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2shows an overall structure of an apparatus41for converting gas using gliding plasma according to an embodiment of the present invention.

Referring toFIG. 2, the gas conversion apparatus41includes: a reaction chamber43providing a cylindrical inner space having a predetermined diameter; a gas supplying unit45installed on a top of the reaction chamber43for supplying material gas into the reaction chamber43; an electrode unit71detachably supported on the reaction chamber43through the gas supplying unit45; and a magnetic field generating unit53enclosing the reaction chamber43for generating a magnetic field inside the reaction chamber43in a predetermined direction.

The reaction chamber43has a cylindrical shape with an open top. The reaction chamber43includes a coolant circulation passage49bin a lateral wall. The coolant circulation passage49bis a coolant jacket cooling the reaction chamber43when plasma is generated inside the reaction chamber43. For this, the coolant circulation passage49bincludes a coolant inlet49aon one end and a coolant outlet49con the other end. Coolant is introduced through the coolant inlet49ato cool the reaction chamber43while passing through the coolant circulation passage49b.After cooling the reaction chamber43, the coolant is discharged to the outside through the coolant outlet49c.

The reaction chamber43includes an inner wall43ahaving a predetermined inside diameter for defining the inner space of the reaction chamber43. Inside the inner space, an electrode member47(described later) is vertically positioned, and a plasma region (z) is formed between the inner wall43aand the electrode member47.

The reaction chamber43includes a discharge hole67in a lower portion. The material gas supplied into the reaction chamber43through the gas supplying unit45passes through the plasma region (z), and then discharged to the outside through the discharge hole67.

The gas supplying unit45receives material gas from an outside gas source and injects the material gas into the reaction chamber43downwardly in a tangential direction of the electrode member71, such that the injected material gas moves down while swirling around the electrode member71. Gliding plasma (G) (described later) generated between the electrode member71and the inner wall43ais pushed down while being swirled around the electrode member71by the flow of the material gas.

The gas supplying unit45coupled to the top end of the reaction chamber43includes a casing45ahaving an inner space, a plurality of nozzles45bfixed in the casing45afor injecting the material gas into the reaction chamber43toward the plasma region (z), and a gas supplying pipe45cand a ring-shaped pipe45e(refer toFIG. 3) that supply the material gas from an outside to the nozzles45b.

FIG. 3is a cross-sectional view showing a detail structure and operation of the gas supplying unit45.

Referring toFIG. 3, the ring-shape pipe45eis positioned at the inner space inside the casing45a. The ring-shaped pipe45eis curved in a ring shape and connected with the nozzles45bthrough connecting tubes45f. The gas supplying pipe45cis also connected with the ring-shaped pipe45eto supply the material gas to the nozzles45b. Therefore, the material gas is introduced into the ring-shaped pipe45ethrough the gas supplying pipe45cand supplied to each of the nozzles45bwhile being flowed inside the ring-shaped pipe45e, so that the material gas can be injected through the nozzles in a designed direction.

In the embodiment shown inFIGS. 2 and 3, the ring-shape pipe45eor the plurality of nozzles45bare used to inject the material gas into the plasma region (z). However, this structure can be modified or changed so long as the material gas can be injected in a desired direction.

Referring again toFIG. 2, the casing45aof the gas supplying unit45is formed with a female thread portion45d. The female thread portion45dis formed on an inner surface of the casing45afor coupling with a male thread portion59aof a cap59(described later) to close the reaction chamber43.

The electrode unit71includes: the electrode member47having a conical shape and disposed at a center of the inner space defined by the inner wall43aof the reaction chamber43; an electrode holder57coupled to a top of the electrode member47and placed on the casing45a; a connection rod55having a lower end fixed to the electrode member47, an upper end connected to a power line62of a power source61, and extended portion between the lower and upper ends through the electrode holder57, for supplying power from the power source61to the electrode member47; and the cap59enclosing the electrode holder57and thread-coupled with the casing45a. The connection rod55may be fixed to the electrode member47by thread-coupling.

The electrode member47has a reversed conical shape. Particularly, the electrode member47is coaxial with the inner space formed by the inner wall43aof the reaction chamber43. Further, since the electrode member47is symmetric with respect to its center line, an outer sloped surface47aof the electrode member47departs from the inner wall43amuch more as it goes downward. The minimal distance between the sloped surface47aand the inner wall43ais selected such that plasma can be generated when an electricity is applied between the sloped surface47aand the inner wall43a. The maximal distance between the sloped surface47aand the inner wall43ais defined between a lower end of the electrode member47and the inner wall43a. That is, the maximal distance is equal to the inner radius of the inner wall43a.

The electrode holder57is formed of an electrically insulating material, and the electrode member47is fixed to a lower portion of the electrode holder57. The electrode holder57may be formed of various insulating materials including synthetic resin and soft rubber. Particularly, a lower edge of the electrode holder57is tightly held by the casing45ato hermetically close the reaction chamber43located below.

The cap59covers the electrode holder57and includes the male thread portion59aon a lower outside end surface. The male thread portion59acouples with the female thread portion45dof the casing45a. The male thread portion59aand the female thread portion45dcan be selectively engaged with and disengaged from each other. Therefore, the electrode unit71can be detached from the reaction chamber43. That is, elements of the electrode unit71such as the electrode member47can be replaced with new one by unscrewing the electrode unit71away from the reaction chamber43.

In the embodiment shown inFIG. 2, the electrode unit71is thread-coupled to the casing45a. However, the coupling can be modified and changed.

A heat exchanger51is provided under the electrode member47. The heat exchanger51is a water-cooled type heat exchanger for cooling gas pushed down from the plasma region (z). The heat exchanger51is connected with a cooling water pipe51a, and cooling water circulates inside the heat exchanger51when the heat exchanger51operates.

The magnetic field generating unit53includes a coil53aenclosing the outer surface of the reaction chamber43, a power source53bapplying an electricity to the coil53a, and a controller53dconnected to the power source53bfor controlling the current to the coil53a.

The magnetic field generating unit53induces a magnetic field inside the plasma region (z), so that the gliding plasma (G) formed in the plasma region (z) can be rotated by Lorentz force. As is well-known, plasma is attracted by a magnetic force. Therefore, the gliding plasma (G) can be moved in the direction of magnetic flux by forming a magnetic field in the plasma region (z).

The moving speed of the gliding plasma (G) increases in proportion to the strength of the magnetic field. Further, since the current applied to the coil53ais controlled by the controller53d, the moving speed of the gliding plasma (G) can be controlled by the controller53d.

Therefore, the plasma region (z) is divided up and down by the gliding plasma (G) which is formed like disk shape when the speed of the gliding plasma (G) moving around the electrode member47is increased by the controller53d.

For reference, when the gliding plasma (G) is placed in a flow of gas, the gliding plasma (G) is moved by a pressure applied by the gas flow as well as the magnetic force. Therefore, for example, when the material gas is injected into the reaction chamber43through the nozzles45bwhile the magnetic field generating unit53does not operate, the gliding plasma (G) is moved in the gas injection direction (i.e., the gliding plasma (G) is moved down while being swirled around the electrode member47).

When the gas supplying unit45and the magnetic field generating unit53operated at the same time, the gliding plasma (G) swirls around the electrode member47by the pressure (horizontal direction) of the gas flow and Lentz force, and at the same time the gliding plasma (G) gradually moves down by the vertical pressure of the gas flow. The gliding plasma (G) as it moves down meets the lower end of the electrode member47and disappears after the lower end. The gliding plasma (G) appears again at the top end of the electrode member47.

Eventually, by injecting the material gas downward and applying the magnetic field inside the reaction chamber, the gliding plasma (G) can be moved from a top to a bottom of the plasma region (z) to apply energy to the material gas, so that the material gas (pre-reaction gas) can be converted into desired gas (post-reaction gas).

The amount of energy applied to the material gas by the gliding plasma (G) is proportional to the mean density of the gliding plasma (G) filled in the plasma region (z). The mean density varies according to the swirling speed and the downwardly-moving speed of the gliding plasma (G). As the swirling speed of the gliding plasma (G) around the electrode member47increases and the downwardly-moving speed of the gliding plasma (G) along the electrode member47increases, the mean density of the gliding plasma (G) per unit time increases inside the plasma region (z).

Therefore, the amount of energy applied to the material gas can be controlled by adjusting the swirling speed and/or the downwardly-moving speed of the gliding plasma (G).

FIGS. 4A and 4Bare front views showing differently-shaped electrode members that can be applied to the gas conversion apparatus41depicted inFIG. 2.

In the gas conversion apparatus41according to the embodiment of the present invention, the shape of the electrode member can be modified or changed so long as the cross section of the electrode member decreases downwardly.

A method of converting gas using the gas conversion apparatus41will now be described.

When power is supplied from the power source61, gliding plasma (G) is induced in the plasma region (z). The power source61supplies a positive current to the reaction chamber43and a negative current to the electrode member47, such that the gliding plasma (G) is induced between the top end of the sloped surface47aof the electrode member47and the inner wall43afacing the top end.

After the gliding plasma (G) is induced, a magnetic field is formed in the plasma region (z) by manipulating the controller53d. The magnetic field formed in the plasma region (z) applies a magnetic force (Lorenz force) to the gliding plasma (G) to rotate the gliding plasma (G) around the electrode member47. The rotating speed of the gliding plasma (G) is controlled by the controller53d, generally at about several hundred revolutions per second.

When the gliding plasma (G) is rotated at a speed enough for supplying sufficient energy, material gas to be reacted with the gliding plasma (G) is injected downward through the nozzles45bof the gas supplying unit45. The material gas injected downward by the nozzles45bis directed in the tangential direction of the electrode member47, such that the material gas swirls around the electrode member47and moves down, for example, along a three-dimensional spiral path. While the material gas swirls down, the gliding plasma (G) is moved down by a pressure applied by flow of the material gas.

Particularly, since the material gas moves downward more fast than the gliding plasma (G), the injected material gas receives energy from the gliding plasma (G) while passing through the thickness of the downwardly-moving gliding plasma (G). The material gas is converted by the energy received from the gliding plasma (G) and then discharged through the discharge hole67.

Experiments are performed using the gas conversion apparatus according to the embodiment of the present invention to convert methane into acetylene.

Methane (material gas) is diluted with nitrogen gas to a concentration of 20%, and a total flow rate of the material gas is set to 10 liters/minute. The power from the power source is set to 600 watts, the magnetic flux density for rotating the gliding plasma is set to 833 Gausses, and a Gas Chromatography (GC, HP 5890 series) is used as an analyzing device for analyzing post-reaction gas. The entire reaction is performed at a room temperature and an atmospheric pressure. The result of the experiment 1 is shown in Table below.

All experimental conditions are the same as the experiment 1 except that the magnetic flux density is set to 1100 gausses.

Comparison Experiment Example

This comparison experiment is performed using the gas conversion apparatus11ofFIG. 1under the same conditions as the experiment 1.

Referring to Table above, according to the gas conversion apparatus of this embodiment, the conversion rate (moles of methane gas after reaction/moles of injected methane gas) is higher than 75%, and the yield (2*moles of acetylene gas/moles of injected methane gas) is higher than 35%. The experimental results show that the conversion rate and the yield are much higher in the present invention than in the related art.