KR101969832B1 - Boiler using micro plasma steam for eco-friendly burning of low grade fuel oil - Google Patents

Abstract

Provided in the present invention is a boiler, which uses microwave plasma in order to increase combustion efficiency of a low-grade fuel oil, which is a liquid fuel, and to reduce air pollution substances caused by the low-grade fuel oil to the maximum extent. The boiler comprises: a microwave generator providing a microwave so as to convert steam into plasma; a plasma steam burner connected to the microwave generator, and generating flame by using plasma steam containing an activated radical after making steam into plasma by means of the microwave; and a combustion unit heating water by means of the flame produced by the plasma steam burner. The plasma steam burner comprises: a burner main body, of which one side is provided with an inlet through which the low-grade fuel oil is introduced, and of which the other side is provided with an outlet through which the low-grade fuel oil is discharged; and the plasma steam generator attached after penetrating from the outside to the inside of the burner main body.

Description

 BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a boiler using microwave plasma steam for eco-friendly combustion of low-grade fuel oil,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler, and more particularly, to a boiler for inducing eco-friendly combustion of a low-grade fuel oil by microwave plasma steam, thereby increasing combustion efficiency and reducing air pollutants.

The boiler is a device that transfers heat generated by the combustion of fuel to water in a sealed container and supplies steam or hot water having a predetermined pressure and use. Generally, a boiler is composed of a combustion device, a fuselage, and an accessory device, and a solid raw material, a liquid raw material and a gas raw material are used as fuel and are used for power generation, heating, industrial use and home use. In recent years, it has been focused on minimizing air pollutants in addition to combustion efficiency in boilers including heating furnaces. Particularly, the regulation of nitrogen oxides (NOx) and particulate matter which are generated when burning solid and liquid fossil fuels becomes more strict according to exhaust gas emission standards.

Low-grade fuel oil such as bunker C oil, regenerated fuel oil, and heavy oil, which are liquid fuels, are used for domestic industrial use. Boilers using low fuel oil have a higher NOx emission than gas fuels and are accompanied by odor and pollutant emissions. Bunker C oil, which occupies a significant portion of crude oil, has a high viscosity, and the combustion efficiency is lowered due to the mousse formation due to entanglement at low temperature, and it may become a soot and exhaust gas factor due to incomplete combustion. In case of heavy oil, sufficient warm-up time relative to other fuels, combustion air, and additional power for combustion are required, and there is also concern about low temperature corrosion due to exhaust gas and sulfur substances due to nitrogen component in the component itself.

In order to reduce such nitrogen oxides, various methods such as exhaust gas recirculation, two-stage combustion, water / steam jet method, selective catalytic reduction method, and selective non-catalytic reduction method have been proposed. However, in the case of low-grade fuel oil, the above-mentioned method does not significantly reduce the NOx, and thus the reduction effect is not large. In order to solve this problem, a boiler using brown gas such as Korean Patent No. 10-1739651 and Korean Patent Laid-Open No. 2013-0041854 is proposed. However, even if Brown gas is used, a method of increasing the combustion efficiency of low-grade fuel oil, which is a liquid fuel, and minimizing air pollutants caused by low-grade fuel oil has not been specified yet. Japanese Patent No. 5,589,322 suggests a boiler for providing pure oxygen, but the effect of increasing combustion efficiency and reducing air pollutants is insufficient.

The object of the present invention is to provide a boiler which uses microwave plasma to increase the combustion efficiency of a low-grade fuel oil, which is a liquid fuel, and to reduce air pollutants caused by low-grade fuel oil to a maximum extent.

One example of a boiler for minimizing the amount of air pollutants due to a low fuel flow path to achieve the object of the present invention is a microwave generator for providing a microwave for converting steam into plasma, A plasma steam burner for converting the steam into plasma and generating a flame by using a plasma steam containing an activated radical, and a combustion unit for heating water by a flame by the plasma steam burner. At this time, the plasma steam burner includes a burner body having an injection port for injecting low-grade fuel oil on one side and a discharge port through which the low-grade fuel oil is injected on the other side, and a plasma steam generator penetrating from the outside to the inside of the burner body.

In one example of the present invention, the microwave generator includes a waveguide, and the waveguide may be tapered. At least one of the burner body or the plasma steam generator may be supplied with the emulsion fuel in which the low-grade fuel oil and the steam are emulsified. The input gas of the plasma steam generator is plasma steam. The input gas supplied to the burner body is plasma steam.

Another object of the present invention is to provide a microwave generator for generating microwave for converting steam into plasma, a microwave generator connected to the microwave generator, A plasma steam burner for generating the flame by using the plasma steam containing the activated radical by making the steam into plasma, and a combustion unit for heating water by the flame by the plasma steam burner. The plasma steam burner may include a first injection path disposed in the body of the steam burner and injecting and discharging the plasma steam, and a plurality of circulation pumps arranged in a concentric circle outside the first injection path, 2 injection path and a plurality of mixing flow paths located between the first injection path and the second injection path and into which the plasma steam is injected. Also, a communication path is provided between the mixing flow path and the second injection path to provide a mixing region in which the plasma steam and the fuel oil are mixed.

In another example of the present invention, the first injection path may include a venturi area for increasing the flow rate of the plasma steam, and an extension area for diverging and expanding the discharge of the plasma steam. The inside of the mixing flow path may include a margin region for smooth mixing in the mixing region. The steam burner may further include a plurality of third injection paths disposed concentrically with the second injection path and injecting the low-grade fuel oil without mixing with the plasma steam.

In another preferred embodiment of the present invention, the mixed fuel in the second injection path is sprayed by the first discharge port, the low-grade fuel oil in the third injection path is sprayed from the second discharge port, and the length of the first discharge port The lower fuel oil may be emulsified with the steam.

According to the boiler using the microwave plasma steam for eco-friendly combustion of the fuel of the present invention, the combustion efficiency of the low-grade fuel oil is increased and the air pollutant caused by the low-grade fuel oil is reduced as much as possible. By blocking or minimizing the injection of air, thermal NOx, Prompt NOx, which is nitrogen oxides, can be originally eliminated or greatly reduced. In addition, it promotes decomposition of low-grade fuel oil and suppresses the generation of Fuel NOx to the maximum.

FIG. 1 is a diagram schematically illustrating a process of generating thermal NOx, Prompt NOx, and Fuel NOx, which may affect a boiler according to the present invention.
2 is a block diagram for explaining a boiler using microwave plasma steam according to the present invention.
FIG. 3 is a view schematically showing the microwave generator of FIG. 2. FIG.
4 is a conceptual view showing a combustion process of a general fuel and an emulsion fuel.
Fig. 5 is a perspective view showing the plasma steam burner of Fig. 2;
6 is a cross-sectional view illustrating the plasma steam generator of FIG.
FIG. 7 is a cross-sectional view and a side sectional view illustrating a plasma steam burner for multi-stage combustion according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments described below can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention. On the other hand, terms pointing to positions such as top, bottom, front, and the like only relate to those shown in the drawings. In fact, the boiler can be used in any optional orientation, and the spatial orientation in actual use varies with the direction and rotation of the boiler.

The embodiment of the present invention proposes a boiler for increasing the combustion efficiency of the low-grade fuel oil and reducing the air pollutant due to the low-grade fuel oil to the utmost by utilizing the microwave plasma steam. To this end, the structure of the boiler using the microwave plasma steam will be described in detail, and the process of burning by the microwave plasma steam will be described in detail. Here, the low-grade fuel turbulence is a liquid fuel such as bunker C oil, regenerated fuel oil, heavy oil and the like. Accordingly, it can be considered that the microwave plasma steam is mixed with the low-grade fuel oil and burned.

FIG. 1 is a diagram schematically illustrating a process of generating thermal NOx, Prompt NOx, and Fuel NOx, which may affect a boiler according to an embodiment of the present invention.

Referring to FIG. 1, the nitrogen source of nitrogen oxide, which is an air pollutant, is nitrogen contained in air and fuel. The source of nitrogen produces nitrogen oxides such as Thermal NOx, Prompt NOx, and Fuel NOx during the combustion process. The fuel NOx is converted into a low molecular weight nitrogen compound such as NH ₃ , HCN, and CN through pyrolysis before the nitrogen component contained in the chemical component of the fuel is introduced into the combustion region, and these substances are generated by reacting with oxygen. In the case of heavy oil, it is known that about 10 to 20% of the nitrogen component is converted and produced, and when it is burned, it is affected by the oxygen concentration, the nitrogen content in the fuel, the volatile content. On the other hand, if air is kept at a low level at the beginning of the reaction, the probability of conversion to nitrogen (N ₂ ) increases, which is effective for reducing NO x.

The thermal NOx is generated by the reaction of the nitrogen component in the air with the free oxygen for combustion at 1,200 DEG C or higher, and is related to the combustion chamber temperature and the reaction time. Particularly, when the temperature is high and the concentration of oxygen in the combustion region is high, a large amount is generated when the residence time of the combustion gas in the high temperature region is long. That is, the thermal NOx is suppressed by reducing the combustion temperature and the residence time in the combustion region and lowering the oxygen concentration. In the combustion process, the Prompt NOx generates hydrocarbon intermediates such as HCN and CN through the reaction of nitrogen in the air and HC radicals generated by the flame. Then, the nitrogen produced by the conversion into NO is converted into nitrogen monoxide Oxide.

Nitrogen oxides in combustion account for most of the thermal NOx. The process of generating the thermal NOx is important, and the process of generating NO from atmospheric nitrogen is explained by the Zeldovich mechanism. The mechanism has steps of O ₂ ↔ 2O, N ₂ + O ↔ NO + N, N + O ₂ ↔ NO + O and N + OH ↔ NO + H. Oxygen molecules in the combustion gas generate oxygen atoms by the decomposition reaction of O ₂ at temperatures around 1,700 ° C. The separated oxygen atoms react with the nitrogen molecules to generate NO, and the separated nitrogen atoms react with oxygen molecules to produce NO. Again, a cascade reaction occurs in which the separated oxygen atoms react with the nitrogen molecule.

One of the ways to reduce nitrogen oxides from burning low fuel oil is to reduce the amount of air entering the boiler. Because nitrogen in the air is the source of thermal NOx, Prompt NOx. In particular, it is noted that the thermal NOx, which is the mainstream of nitrogen oxides, is highly related to nitrogen in the air. The other is useful for reducing the NO x emissions because the probability of conversion to nitrogen (N ₂ ) increases when the air is kept as low as possible at the beginning of the reaction. Therefore, if the air is not added at all or the amount of the air is minimized, the effect of reducing the nitrogen oxides can be obtained.

2 is a block diagram illustrating a boiler using a microwave plasma steam according to an embodiment of the present invention.

Referring to FIG. 2, the boiler of the present invention includes a microwave generator 100, a plasma steam burner 200, and a combustion unit 300. The microwave generator 100 supplies energy for plasma steam. A microwave is an electromagnetic wave including a sub-millimeter wave near a far-infrared ray having a wavelength of 1 m or less to 1 mm or less. Since microwaves have higher frequencies and shorter wavelengths than microwave, properties such as linearity, reflection, refraction, and interference are almost similar to light. When the microwave comes into contact with the object to be heated, frictional heat is generated in the process of rapidly changing the arrangement direction of the axis of the dipole constituting the object to be heated by the electric field of the microwave, so that the object to be heated is heated.

The plasma steam burner 200 generates steam by using a microwave and generates a flame by using activated radicals such as H *, OH *, and O *. The plasma steam burner 200 will be described later in detail. The combustion unit 300 includes a combustion chamber, a steam collection unit, and the like. Since the combustion chamber, the steam collecting unit, and the like are well known, a detailed description thereof will be omitted.

3 is a view schematically showing the microwave generator 100 of FIG.

3, the microwave generator 100 includes a magnetron 10, an isolator 11, a focusing tube 12, a tuner 13, and a waveguide 14. The operation and control of the microwave generator 100 can be observed through the monitor 15 and performed necessary actions. The magnetron 10, the isolator 11, the focusing tube 12, the tuner 13, and the monitor 15 can be all known ones, and a detailed description thereof will be omitted here. The waveguide 14 is tapered and can be implemented in a stepped manner as shown in the figure. That is, the width of the step is gradually reduced to form a tapered shape as a whole. When the waveguide 14 is inclined, it provides the direction in which the microwave advances.

That is, the low-grade fuel oil of the present invention may be a general low-grade fuel oil, but more preferably an emulsion fuel in which low-grade fuel oil and steam are emulsified. FIG. 4 is a conceptual view showing a general combustion process by the common low-grade fuel oil and an emulsion combustion process of the emulsion fuel.

According to Fig. 4, the general combustion takes place only in the first atomization (1). For example, the combustion temperature and ignition temperature of heavy oil are about 530 ° C, and the pyrolysis temperature (300 ° C or higher) is low, resulting in solid carbonation due to incomplete combustion. On the other hand, the emulsion combustion takes place in the primary atomization (1) and the secondary atomization (2). For example, since the vaporization explosion point (250 ° C or less) of the water vapor is lower than the pyrolysis temperature (300 ° C or higher) of heavy oil, contact with steam is increased due to secondary atomization (②) before pyrolysis, Contaminants such as soot are reduced.

The combustion process of the emulsion fuel is as follows. First, the steam particles in the fuel droplet are overheated due to the boiling point and become unstable. Thereafter, the difference in boiling point with the fuel causes the steam particles to evaporate first and expand. The expansion of the steam particles explosively destroys the fuel droplet, which causes the fuel to become finer. The feature of the emulsion combustion is that the rotation of the air is increased and the contact with the steam is increased by the increase of the fuel spray momentum. Water evaporation also increases premixing due to ignition delay. By the above-mentioned emulsion combustion, the maximum combustion temperature, ineffective flame reduction, and the combustion gas molar number become large.

Hereinafter, an example of a plasma steam burner according to an embodiment of the present invention will be described. The above case will be described mainly with reference to a case where air is completely replaced with plasma steam. Also, when the air is completely replaced by plasma steam, a steam burner for multi-stage combustion is also presented. It is to be understood that the invention is not limited to the disclosed examples and that various changes and modifications may be made by those skilled in the art without departing from the gist of the present invention.

FIG. 5 is a perspective view showing the plasma steam burner 200 of FIG. 2, and FIG. 6 is a sectional view for explaining the plasma steam generator 23 of FIG. For convenience of explanation, a part of the discharge port 22 of FIG. 5 is cut out and represented. At this time, it is assumed that the lower fuel oil is an emulsion fuel.

5 and 6, the plasma steam burner 200 has an inlet 21 through which the emulsion fuel is injected at one side of the burner body 20 and an outlet 22 through which the emulsion fuel is ejected at the other side . The discharged emulsion fuel is ignited by the plasma ignition region (a) to cause the plasma flame (b). Further, for the combustion of the emulsion fuel, a swirl gas which proceeds while generating a swirl can be supplied into the inlet 21. Embodiments of the present invention utilize plasma steam as input gas instead of conventional air. The discharge port 22 is in the form of a funnel whose width widens toward the outside so as to be radiated while expanding the plasma flame b. At one side of the burner body 20, a plasma steam generator 23 for generating plasma by microwave (MW) is installed. The plasma generator 23 penetrates from the outside to the inside of the burner body 20 and is attached thereto.

The plasma steam generator 23 includes a discharge tube 23a, a microwave waveguide 23b, and an igniter 23c. The microwave waveguide 23b is preferably tapered as described in FIG. The waveguide 23b is attached to the discharge tube 23a and the igniter 23c is located on the side of the discharge port 22 side. Emulsion fuel is injected into the discharge tube 23a, and plasma steam is used as input gas of the path (c). The microwave transmitted from the microwave waveguide 23b converts the steam into plasma. The plasma steam is ignited by the igniter 23c together with the emulsion fuel ejected from the discharge port 22 to form the plasma ignition region a and to trigger the plasma flame b.

Conventional plasma forming methods include a corona induction method using electrodes, a dielectric discharge method, and an arc induction method. However, the microwave induction type plasma of the present invention does not use an electrode. Accordingly, unlike the conventional method, the microwave induction method does not need to worry about replacement or damage of the electrode. In addition, the plasma according to the embodiment of the present invention enables the continuous injection of the emulsion fuel into the plasma flame (b) by using plasma steam instead of air as the input gas (swirl gas). Furthermore, the flame is larger and the efficiency of electricity is improved as compared with the conventional arc induction type plasma.

The plasma steam burner 200 according to an embodiment of the present invention is a plasma burning technique that uses plasma steam as an oxidizing agent. When the steam is in the plasma state, water molecules dissociate to form radicals of O ^* , H ^* and OH ^* . In particular, the OH ^* improves combustion efficiency when injecting emulsion fuel as a strong oxidizing agent. Since the plasma combustion technique has no heat loss during ignition and flame formation, the thermal efficiency is greatly improved as compared with the classical combustion technique. In the microwave-induced plasma, the steam can be used as an input gas, and thus all the air generating nitrogen oxides can be replaced. In this case, the amount of nitrogen is extremely reduced because there is no amount of air to be injected. When the plasma steam is used, a stable flame (b) is formed, thereby reducing heat loss and improving thermal efficiency. Furthermore, the plasma steam can coexist with low-grade fuel oil to realize environment-friendly combustion.

7 is a cross-sectional view (a) and a side sectional view (b) simultaneously illustrating the plasma steam burner 200a for multi-stage combustion. Here, the cross-sectional view is taken along the line VII-VII of the side sectional view, and the side sectional view is viewed from the direction in which the emulsion fuel and the plasma steam are injected.

7, the plasma steam burner 200a includes a burner body 30, a first injection path 31, a plurality of mixing flow paths 32, a plurality of second injection paths 34, (35). The first injection path 31 is located at the center and the mixing flow path 32 and the second and third injection paths 34 and 35 are located in concentric circles having different diameters respectively and the second and third injection paths 34 , 35) are located on a concentric circle having a large diameter. In other words, the second and third injection paths 34 and 35 are located at the outermost side and the mixing flow path 32 is provided between the first injection path 31 and the second and third injection paths 34 and 35 .

The first injection path 31 located at the center of the burner body 30 is a path through which plasma steam is injected and ejected. Inside the first injection path 31, there is a venturi area e for increasing the flow velocity, and an end thereof is a funnel-like extension area f in which the plasma steam is expanded and ejected. That is, the plasma steam increases in velocity by the venturi region e, and is emitted while expanding and expanding in the expansion region f. To this end, the expanded region f has a funnel shape in which the diameter gradually increases toward the spraying direction. The greater the extent of extension (the diameter of the extreme end) of the extension region f, the greater the extensibility in the lateral direction y, but the smaller the extensibility in the frontal direction x. The second injection path 34 is a passage through which the emulsion fuel is supplied.

The mixing flow path 32 is a path through which plasma steam is supplied for mixing with the emulsion fuel supplied to the second injection path 34. The mixing flow path 32 is communicated with the second injection path 34 by the communication path 33. The communication passage (33) is preferably located adjacent to the first discharge port (36). The periphery of the communication path 33 is a mixing region d in which the plasma steam of the mixing flow path 32 and the emulsion fuel of the second injection path 34 are mixed. The mixed region (d) is formed near the first discharge port (36). In other words, the second injection path 34 refers to a passage having the mixing region d communicated with the mixing flow path 32.

The mixing flow path 32 includes a margin region g on the inner side where the space for allowing the mixing of the emulsion fuel and the plasma steam in the mixing region d to occur smoothly occurs. The size of the margin area g is adjusted in consideration of the size of the plasma steam burner 200a of the present invention, the amount of emulsion fuel, the amount of plasma steam, and the like. The plasma steam is injected into the first injection path (31) and the mixing flow path (32). Of course, the first injection path 31 and the mixing flow path 32 are spatially blocked. The mixed fuel mixed in the mixing region (d) is discharged through the first discharge port (36). The mixed fuel is a mixture of plasma steam and the emulsion fuel.

The third injection path 35 is a passage through which the emulsion fuel is injected without communicating with the mixing flow path 32 and without the mixing region d. When the number of the third injection paths 35 is increased, the emulsion fuel is supplied more than the mixed fuel mixed with the plasma steam. Thus, the extent to which the third injection path 35 is occupied determines the proportion of the total fuel occupied by the emulsion fuel. The emulsion fuel of the third injection path 35 is discharged through the second discharge port 37. The diameter of the third injection path 35 can be variously changed. In the drawing, a third injection path 35a having a relatively large diameter and a third injection path 35b having a relatively small diameter are shown as an example. This difference in diameters may vary depending on the amount of emulsion fuel required for combustion.

As described above, the first discharge port 36 is where the mixed fuel is injected, and the second discharge port 37 is where the emulsion fuel is injected. The first discharge port 36 has a first length L1 and the second discharge port 37 has a second length L2 and the first length L1 is smaller than the second length L2. The lengths L1 and L2 of the discharge ports 37 and 37 determine the spraying distance of the mixed fuel or the emulsion fuel to be injected. For example, the second discharge port 37 of the second length L2 can inject fuel farther than the first discharge port 36 of the first length L1. That is, the emulsion fuel is injected farther than the mixed fuel. In this case, the plasma steam burner 200a according to the embodiment of the present invention realizes multi-stage combustion.

The mixed fuel injected from the first discharge port 36 causes primary combustion in the primary flame zone h. The emulsion fuel injected from the second discharge port 37 causes a reburn and a burn out in the secondary flame region i. At this time, the plasma steam expanded from the first injection path 31 is diffused into the primary and secondary flame regions h, i, and radicals of O ^* , H ^* and OH ^* , especially OH ^* Further supply of radicals to increase combustion efficiency. Without the supply of air, the nitrogen content is also reduced. If the nitrogen content is reduced, the amount of nitrogen compounds that are the main cause of air pollution is reduced. That is, it is possible to reduce air pollutants through improvement of combustion efficiency and reduction of nitrogen content.

Meanwhile, although the case of completely replacing the air with the plasma steam has been described above, it is necessary to inject the minimum amount of air substantially for the combustion efficiency. Although not shown, air can be supplied through an air damper or the like. The air is limited to an auxiliary role in the combustion using the plasma steam according to the embodiment of the present invention. The boiler according to the embodiment of the present invention can essentially eliminate or substantially reduce the thermal NOx, Prompt NOx, which is the mainstream of air pollutants, by blocking or minimizing the injection of air.

On the other hand, the plasma serves as a catalyst for promoting the destruction of the molecular bond of the fuel oil. In other words, the low-grade fuel oil mainly dissolves molecular bonds due to heat energy, and plasma accelerates the decomposition. Plasma is generated at high temperatures through the activation of intense electric fields or strong magnetic fields. At this time, the releasing free electrons get energy from the active electric field and lose the energy through collision. In this process, the free electrons destroy the molecular bond of the lower fuel oil. In this case, decomposition of the low-grade fuel oil is made sufficiently, and the generation of the fuel NOx is suppressed to the maximum. That is, the Fuel NOx is reduced by reducing the air or decomposing by the plasma.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but many variations and modifications may be made without departing from the spirit and scope of the invention. It is possible.

10; Magnetron 12; Focusing tube
14; Waveguides 20, 30; Burner body
21; An inlet 22; Outlet
23; Plasma steam generator
31, 34, 35; The first to third injection paths
32; A mixing flow path 33; A communication path
36, 37; The first and second discharge ports
a; Ignition zone b; Plasma flame
c; Input gas path d; Mixed region
e; Venturi area f; Extended area
g; Margin area h; Primary flame zone
i; Secondary flame zone
100; Microwave generators 200, 200a; Plasma steam burner
300; Combustion part

Claims (11)

delete delete delete delete delete A microwave generator for providing a microwave for converting steam into plasma;
A plasma steam burner connected to the microwave generator and generating the flame by using the plasma steam containing the activated radical by making the steam into plasma by the microwave; And
And a combustion section for heating the water by the flame by the plasma steam burner,
In the plasma steam burner,
A first injection path disposed in the body of the steam burner and through which the plasma steam is injected and ejected;
A plurality of second injection paths which are arranged concentrically outside the first injection path and into which low-grade fuel oil is injected; And
And a plurality of mixing flow paths located between the first injection path and the second injection path and into which the plasma steam is injected,
Wherein a communication path is provided between the mixing flow path and the second injection path to provide a mixing region in which the plasma steam and the fuel oil are mixed,
Wherein the steam burner includes a plurality of third injection paths arranged in the same concentric circle as the second injection path and in which the low-grade fuel oil is injected without mixing with the plasma steam. Boiler using microwave plasma steam. The microwave oven according to claim 6, wherein the first injection path includes a venturi area for increasing the flow rate of the plasma steam and an expansion area for diverging and expanding the plasma steam. Plasma steam boiler. 7. The boiler according to claim 6, wherein the mixing channel includes a margin region inside the mixing channel for smooth mixing in the mixing zone. delete 7. The fuel cell system according to claim 6, wherein the mixed fuel in the second injection path is sprayed by a first discharge port, the low-grade fuel oil in the third injection path is sprayed from a second discharge port, Wherein the length of the discharge port is smaller than the length of the discharge port. 7. The boiler according to claim 6, wherein the low-grade fuel oil is emulsified with the steam.

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