JP2761903B2 - Plasma type pulverized coal ignition burner, its anode structure and ignition method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid fuel combustion apparatus, and more particularly to a plasma type pulverized coal suitable for igniting a burner with low energy, stable and high efficiency, and performing continuous combustion. The present invention relates to an ignition burner, an anode structure thereof, and an ignition method.

[Conventional technology]

In the conventional plasma-type pulverized coal ignition burner, the device is large and the profitability is poor, and it has not been applied as an industrial combustion device.

In recent years, demand for pulverized coal-fired boilers has been rapidly increasing due to instability of oil fuel prices. Auxiliary fuels used in pulverized coal-fired boilers are mainly light oils and heavy oils with good ignitability.Although the ratio of these oil fuels is lower than when oil is used as the main fuel, BACKGROUND ART In recent years, boilers for power generation frequently use intermediate loads, the frequency of ignition and startup is higher than before, and the ratio of fuel cost to main fuel is also increasing. In coal-fired boilers,
In addition to the main fuel coal, three types of fuels are generally used, such as heavy oil for starting and light oil for ignition.

Therefore, studies on reducing the amount of oil fuel in coal-fired boilers are being actively conducted. On the other hand,
There is a plan to switch from conventional oil to coal as a burner fuel for ignition and startup. If it is possible to switch to coal as the fuel for ignition and startup, the use ratio of oil can be reduced, running costs can be reduced, and there are many advantages especially for boilers operating in intermediate loads. As ignition and starting fuel,
When the amount of oil used is 0%, that is, 100% pulverized coal-operated boiler, the conventional tank and its system are not required, so that the initial cost can be reduced, and the industrial boiler can be made exclusively for coal.

In response to such needs, direct ignition of pulverized coal has been tried, but direct ignition of pulverized coal by plasma is a typical example, and ignition of pulverized coal is possible at high temperatures exceeding 10,000 ° C. is there.

However, the conventional pulverized coal direct ignition torch by plasma is intended for direct ignition of the main burner.
As shown in FIG. 25 and FIG. 25, the plasma ignition torch 26 had a mounting structure with an angle with respect to the pulverized coal jet from the pulverized coal line 20. A plasma mark 11 is formed from the continuous plasma generator 13 exposed at the tip, and the other end is connected to the DC power supply 10. On the other hand, the pulverized coal from the pulverized coal line 20 circulates in the venturi 19, the center of which is provided with an oil-activated burner 17 inserted and an oil-flame flame stabilizer at its tip. Then
In order to make the plasma and pulverized coal contact efficiently, a huge power supply and electric power were required. Therefore, although direct ignition of pulverized coal was technically possible, it was far from practical.

[Problems to be solved by the invention]

In the conventional plasma pulverized coal ignition burner, the ratio of closing initial costs and lining costs is high because pulverized coal fuel is directly ignited to the pulverized coal main burner by the plasma generator, and the device is also upsized. Therefore, it could not be applied to commercial and industrial fuel systems.

An object of the present invention is to provide a plasma type pulverized coal ignition burner having a heat capacity comparable to the capacity of an ignition burner using oil or gas, in which plasma and pulverized coal are efficiently in contact with each other, and a plasma electrode is protected. It is in.

[Means for solving the problem]

In order to achieve the above object, a plasma pulverized coal ignition burner according to the present invention and an anode structure and an ignition method thereof are provided.
In a plasma pulverized coal ignition burner in which a solid fuel is used as a main fuel and a fixed fuel is ignited by a continuous plasma generator and the plasma arc is formed in a flame holder,
The solid fuel flows between the anode and the cathode of the continuous plasma generator, and the anode and the cathode are arranged on the upstream side of the flame stabilizer. The plasma is applied to the solid fuel and the carrier air for carrying the solid fuel. A heat exchange fin for transferring the heat of the arc and cooling the anode and the cathode is arranged between the respective electrodes.

In the anode structure, one end of the flame stabilizer is used as a secondary anode facing the primary anode, and at least one slit is provided in the radial direction of the secondary anode, and is formed of conductive ceramic.

Further, the ignition method is configured such that the continuous plasma generator is inserted into the pulverized coal flow passage to form an ignition burner or an ignition torch, and the main fuel of the main burner is ignited by the ignition burner or the ignition torch. .

[Action]

According to the present invention, the solid fuel flows between at least one anode and one cathode of the continuous plasma generator of the plasma type powder ignition burner, and both electrodes are arranged on the upstream side of the flame stabilizer; By using one end of the flame stabilizer as a secondary anode facing the primary anode, the plasma arc is difficult to be affected by the carrier air of the solid fuel (pulverized coal) at the time of startup, and the optimum concentration region of the pulverized coal particles is quickly determined. It is formed. At the optimum weight ratio (C / A) of pulverized coal and carrier air, the pulverized coal is dispersed by the slit structure of the primary anode and the secondary anode, and the pulverized coal particles heated to a high temperature are subjected to plasma. The arc flows selectively. Since the pulverized coal and the plasma arc are easily in contact with each other, the anode is made of conductive ceramic to prevent its burning.The heat exchange fins take away the heat of the electrode, and the heat is transferred to the pulverized coal and the carrier air. Heat is transferred to. Thus, the ignition burner or the ignition torch is ignited by controlling the ignition delay, and then the main fuel of the main burner is ignited.

〔Example〕

One embodiment of the present invention will be described with reference to FIGS.

As shown in FIG. 1, a solid fuel (pulverized coal) 7 is used as a main fuel, the solid fuel 7 is ignited by a continuous plasma generator 13, and a plasma arc 11 is formed in the flame stabilizer 1. In the pulverized coal ignition burner, the solid fuel 7 flows between the anodes 3 and 12 of the continuous plasma generator 13 and the cathode 2, and at least one anode 3 and 12 and the cathode 2 are connected to the upstream side of the flame stabilizer 1. It is the structure arranged in.

The cathode 2 is inserted into the continuous plasma generator 13 to generate a plasma arc 11 from the plasma arc nozzle 25 at the tip, and the other end is connected to the DC power supply 10. The cathode 2 is supported by an insulating insulator 4, around which a plasma working gas 8 flows in the direction of the arrow, and the other end of the cathode 2 is connected to a DC power supply 10 via a high-frequency starter 9.

In commercial pulverized coal-fired boilers, the structure of the main burner for pulverized coal is usually configured coaxially with the startup burner using oil fuel. On the other hand, the startup burner has a boiler load of about 25
% And the fuel is charged and burned until the furnace temperature reaches about 600 ° C. Conventional ignition burners have a heat input capacity of about 3% of the main burner, and are used for extinguishing these main burners. As shown in FIGS. 24 and 25,
The conventional plasma ignition torch 26 has been used in place of the oil ignition burner of the oil starter burner 71 or as a direct ignition device for the pulverized coal main burner. The plasma ignition torch according to the present invention does not directly ignite the start-up burner or the main burner, but uses the same pulverized coal as the main burner, instead of the fuel for the ignition burner which has conventionally mainly used oil fuel. It is characterized by having done. In the present invention, plasma is used as the ignition energy for the pulverized coal. FIG. 1 shows the configuration of a pulverized coal burner using the plasma generator according to the present invention. The electrode is composed of a cathode 2 and a primary anode 3 and a secondary anode 12 opposite to the primary anode 3 at one end of the flame holder 1, and discharges during this period.
The plasma arc 11 is generated by the activation of the high-frequency starter 9, and is then replaced by the power supply 10 with a direct current. On the other hand, the working fluid flows as indicated by arrows using air or inert gas 8, and a plasma arc 11 is formed to blow off the plasma. As shown in FIG. 2, the structure of the secondary anode 12 is provided with a plurality of slits 27 in order to easily disturb the pulverized coal flow. The plasma arc 11 is generated when the high-frequency starter 9 is started, and is then switched to DC by the DC power supply 10. The plasma exits the cathode 2 and eventually falls to the secondary anode 12,
Immediately after the start, since the plasma arc 11 is unstable, the primary anode 3 which becomes a resistance is provided so that it is hardly affected by the primary air flow 7 for conveying pulverized coal. This configuration ensures that the plasma arc 11 starts and falls to the secondary anode 12, which is part of the flame stabilizer.

FIG. 3 shows the relationship between the weight ratio (C / A) of the pulverized coal C and the air A for transporting the pulverized coal and the ignition delay of the pulverized coal. When the pulverized coal concentration is low (C / A is low), the distance between the pulverized coal particles is small, and the air ratio of the flammable mixture consisting of volatiles and air released from the particles falls within the flammable mixture range. There is no ignition because there is no. On the other hand, when the pulverized coal concentration is high, ignition does not occur due to large heat release from the heated fine powder particles. Therefore, optimal C / A to minimize ignition delay
Value exists.

The particle concentration distribution of the pulverized coal in the burner nozzle portion immediately after the start of the pulverized coal conveyance varies both temporally and pneumatically.
This is because the passage concentration of the aggregated particles changes because the particle concentration in the pipe increases with time. FIGS. 4 and 5 show a high-concentration region 16, a low-efficiency region 14, and an optimum-concentration region 15 as a change state of the particle concentration distribution in the cross-section of the burner nozzle. The plasma arc exits the nozzle 25 and falls on the secondary anode 12. At this time, the plasma arc
The ignition delay can be minimized by passing through the optimum concentration region 15, but in fact, as shown in FIGS. 4 and 5, there is only one secondary anode 12 because it fluctuates. In this case, the plasma arc does not always pass through the optimum concentration region 15. Further, when the secondary anode has an orifice structure, heat diffusion is performed relatively favorably inside the anode, so that local heating does not occur unlike the slit structure. In the present invention, the pulverized coal is dispersed by the slit structure, and the effect of heating and igniting the pulverized coal by the secondary anode is intended. On the other hand, the plasma arc has a pinch effect,
Since there is a characteristic that a current passes through a high-temperature region even a little, the plasma arc is heated and flows selectively to the high-temperature particles. Therefore, the ignition delay can be minimized without mechanically changing the radial distance between the nozzle 25 and the secondary anode 12 or rotating the plasma arc by a magnetic field.

6 to 8 show an anode structure, and FIG. 9 shows another embodiment in which a plasma-type pulverized coal ignition burner is incorporated in a pulverized coal burner. FIG. 6 shows a cross-sectional view of the vicinity of a plasma electrode. .

In this embodiment, since the pulverized coal fuel passes between the two electrodes of the primary anode 3 and the secondary anode 12, it is desirable that the pulverized coal and the plasma arc are easily brought into contact with each other, and the electrode and its surroundings are easily heated. For this reason, it is necessary to prevent burnout, and the material of the primary anode 3 is made of conductive ceramic, and the structure is a columnar structure so that the pulverized coal particles and the plasma arc are easily in contact with each other.

The plasma arc exits from the cathode and falls to the anode, but both the plasma portion and the electrodes are exposed to high temperatures due to the flow of a large current, and cause abrasion problems due to contact with the pulverized coal. Therefore, in order to increase the heat resistance and the service life, it is effective to select a material of the electrode, cool the electrode, and the like. As a means for this, the material of the anode is made of conductive ceramics, and in order to cool both electrodes,
The structure was provided with heat exchange fins. Further, since the pulverized coal burner is ignited with a minimum ignition delay, a method of increasing the surface area of the high-temperature portion in contact with the pulverized coal is effective. For this reason, the anode is used as a part of the flame stabilizer of the pulverized coal burner, and the surface temperature of the flame stabilizer in the low particle velocity part of the pulverized coal nozzle is increased. I ignite in the area.

FIG. 10 shows the effect of the pulverized coal concentration (C / A) on the primary air temperature T for pulverized coal transport on the ignition. By increasing the primary air temperature T, the C / A was lowered. You can see that it can ignite. Further, FIG. 11 shows a change in C / A with respect to time H after the start of pulverized coal conveyance. From FIGS. 10 and 11, by increasing the primary air temperature T from T1 to T2. the C / a can be reduced from p1 to p2, and the time H in ignition delay can be suppressed from r ₁ to the r _2. Reducing the ignition delay time is a technique necessary for suppressing an increase in furnace pressure during ignition and for suppressing unburned components. In pulverized coal combustion, the delay of the supply system reaching the rated flow rate is remarkable as compared with other fuels. Therefore, it is necessary to fill this gap by adjusting the combustion reaction system.

Next, regarding the method of raising the temperature of the primary air, ignition of pulverized coal is often performed in a state where the furnace is cooled. Therefore, it is effective to effectively use the heat loss due to the plasma arc in order not to complicate the combustion system. FIG. 8 shows another embodiment in which heat exchange fins 21 are provided around the cathode.

In the heat exchange by the plasma arc, the amount of heat transmitted to the base side of the electrode by heat conduction is said to be about 30% of the total input energy. The adoption of these heat exchange fins 21
As shown in FIG. 12, the rise of the next air temperature T is shorter in the case of the fins F than in the case of the fins N, thereby suppressing the ignition delay.

13 and 14 show another embodiment in which a pulverized coal ignition burner using a plasma torch is incorporated in a pulverized coal main burner. The ignition burner is installed in the center of the main burner, and the ignition sequence is as follows: first, the plasma is generated, the pulverized coal ignition burner is ignited, and finally, the main burner is ignited. According to this ignition method, it is possible to ignite and start the pulverized coal main burner with the minimum ignition delay and the minimum igniter (plasma) energy. When starting or igniting the main burner with a pulverized coal ignition burner using a fuel other than pulverized coal, a plasma type pulverized ignition burner according to the present invention is used instead of the plasma ignition torch 26 shown in FIG. The configuration includes a generator 13, a pulverized coal flow path 22 for an ignition burner, an air flow path 23 for an ignition burner, and a pulverized coal flow path 24 for a main burner. According to this method, the load can be increased at a room temperature, that is, at the time of cold start of the boiler, while maintaining low pollution and high reliability.

15 and 16 show a pulverized coal burner according to the present invention attached to the pulverized coal burner shown in FIG. The pulverized coal main burner having the pulverized coal passage 26 for the starting burner or the main burner is arranged in a vertical line, and a plasma type pulverized coal ignition burner equipped with a plasma generator 13 is attached to the center of the central burner.

Further, another embodiment of the present invention will be described with reference to FIGS. 17 and 18.

As shown in FIGS. 17 and 18, the electrode is composed of a cathode 2 and an anode 30, and discharges between them. Arc is cathode 2
And the arc drop point 32 is formed. On the other hand, the plasma is blown off by the insulating ceramic nozzle 33 and is formed inside the cylindrical opening 29. The gas heated by the plasma is efficiently exhausted by the diffuser 31.

FIG. 1 shows a structure in which the plasma igniter according to the present invention is incorporated in an ignition torch using pulverized coal.
The igniter has a structure inserted into the center of the ignition torch so that the plasma easily contacts the pulverized coal stream. This configuration ensures that the arc starts and falls to the secondary anode, which is part of the flame stabilizer.

FIG. 20 shows the nozzle structure, and FIG. 21 shows the axial length of the ceramic and the stability of the plasma.

The vertical axis in FIG. 21 is the arc voltage V with respect to the ceramics 34 in FIG. Generally, arc length is compared with V / Lo
Since constant current is a normal operating condition, a larger value indicates that the vehicle is operating under the rated condition.

The horizontal axis represents the ratio of the nozzle length Lc to the nozzle diameter Do. As this value is smaller, the plasma is more likely to travel straight, but a higher voltage is required for operation.

Therefore, as the operation time becomes longer, the nozzle diameter
Do gets damaged and grows, and Do / Lc increases with time.

In this figure, the ceramic insertion length of the nozzle part is Lc
Shown as / Lo. When Lc / Lo is 0, there is no ceramic, and when Lc / Lo is 1, it indicates that all are made of ceramic.
In the case of 1, plasma cannot be started. On the other hand, if the value is 0, the nozzle is damaged in a short time, and V / Lo is reduced in a short time.

In this figure, V / Lo deformation indicates that the arc fall position has changed.

 Experiments have shown that Lc / Lo is preferably between 0.2 and 0.8.

Further, depending on the voltage, the generation of plasma is limited to near the nozzle. For this reason, by operating for a long time, the surrounding anode is melted and blown off by radiation and heat conduction, and when observed in cross section, it becomes just circular. The falling point of the plasma and beam showed that this circle had a stable anode structure.

Therefore, the electrode structure in the plasma generation region is cylindrical on the inside due to restrictions on electrode processing. In Figure 22,
The state of plasma and arc formation in the case where the anode structure is extended in the axial direction is shown. Arc current is cathode 2
And falls to the anode 35. At this time, a plasma 36 is formed by the working air. Under normal operating conditions, the arc is more stable at lower voltages, so it falls to a location near the tip of the plasma 36, at which time the voltage becomes V1.
However, if the anode 35 is significantly damaged, not only the anode 35 but also the nozzle 25 will be deformed, and the plasma flow will not flow in the axial direction. Under these conditions, the arc is
Since the voltage falls to the vicinity and the voltage becomes V2, generally V1> V2, the plasma output becomes unstable temporally.

In response to such a phenomenon, FIG. 23 shows an anode 37 structure in which a gap is formed concentrically so that the voltage is always constant. In this structure, the voltage of each part is V1 = V2 = V3 =
Become V4. For this reason, the anode 37 is uniformly damaged, and the life can be extended. Further, as compared with FIG. 22, the structure is less susceptible to direct radiation and convection heat transfer from the plasma.

In the downstream part of the plasma, the diffuser 38
Having. With the structure having the acceleration portion, a large amount of ambient air can be sucked in, and the electrode can be efficiently cooled. Further, pulverized coal flowing around the anode 37 can be efficiently introduced into the high temperature portion of the plasma center. For this reason, it can be expected that the ignition performance of pulverized coal also increases as the life of the electrode becomes longer.

 FIG. 19 shows the anode structure.

As shown in FIG. 19, a Laval nozzle 41 (supersonic nozzle) is provided between the cylindrical opening 29 and the diffuser 40.
Was installed.

Since the plasma temperature exceeds 10,000 ° C., the flow velocity of the plasma locally becomes supersonic even when the original pressure of the working air is 1 atg or less. Since the structure behind the nozzle is open to the atmosphere, it does not accelerate to supersonic speed, but can be efficiently expanded by the structure of the diffuser 40. However, if there is an acute structure between the cylindrical opening 29 and the diffuser section 40, the flow separates and the effect of the diffuser decreases. For this reason, a Laval nozzle 41 having a curvature is provided at this location to adjust the flow.

〔The invention's effect〕

According to the present invention, a solid fuel (pulverized coal) flows between at least one anode and a cathode of a continuous plasma generator for a plasma-type pulverized coal ignition burner, and one end of a flame stabilizer is formed as a secondary anode. By doing so, the high temperature portion of the plasma arc and the pulverized coal particles can be efficiently brought into contact with each other, so that the pulverized coal ignition burner is compactly configured, the ignition delay is minimized, and the electric capacity of the continuous plasma apparatus is reduced by about 1%. / 100, and the initial cost and running cost can be greatly reduced.

Further, the use of the plasma torch according to the present invention enables direct ignition of gas and oil fuel having other good combustibility of pulverized coal.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG.
FIG. 3 is a graph showing the relationship between ignition delay and C / A, FIGS. 4 and 5 are diagrams for explaining the operation of the present embodiment, and FIG. 6 is a diagram showing the present invention. Sectional view showing another embodiment of the
FIG. 7 is a front view of FIG. 6, FIGS. 8 and 9 are cross-sectional views showing another embodiment of the present invention, FIGS. 10 to 12 are graphs for explaining the operation of the other embodiment, 13 is a cross-sectional view showing another embodiment of the present invention, FIG. 14 is a front view of FIG. 13, FIG. 15 is a cross-sectional view showing another embodiment of the present invention, FIG. 16 is FIG. FIG. 17 is a cross-sectional view of the tip of a plasma igniter showing another embodiment of the present invention, FIG. 18 is a plan view of FIG. 17, and FIG.
Figure is a sectional view of a plasma anode showing another embodiment of the present invention,
20 is a cross-sectional view of the nozzle of FIG. 19, FIG. 21 is a view for explaining the effect of the embodiment of FIG. 20, and FIGS. 22 and 23 are plasma anodes showing another embodiment of the present invention. Sectional view, FIG. 24 and FIG.
FIG. 25 is a sectional view showing a conventional technique. 1 ... flame stabilizer, 2 ... cathode, 3 ... primary anode, 7 ... solid fuel,
11 ... plasma arc, 12 ... secondary anode, 13 ... continuous plasma generator.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Nobuo Nakazawa, Inventor, No. 3-36, Takara-cho, Kure-shi, Hiroshima Pref. Inside the Kure Research Laboratory, Babkotsuk Hitachi Ltd. (56) References JP-A-1-244216 (JP, A) JP-A-Hei 2-13718 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F23Q 13/00

Claims (6)

(57) [Claims] 1. A plasma-type pulverized coal ignition burner in which a solid fuel is used as a main fuel, the solid fuel is ignited by a continuous plasma generator, and the plasma arc is formed in a flame holder. A pulverized coal ignition burner, characterized in that the solid fuel flows between a fuel cell and a cathode, and at least one of the anode and the cathode is disposed upstream of the flame stabilizer. 2. A heat exchange fin for transferring heat of a plasma arc to a solid fuel and a carrier air for carrying the solid fuel and cooling an anode and a cathode is provided between the respective electrodes. The burner according to claim 1. 3. An anode structure for a plasma-type pulverized coal ignition burner according to claim 1, wherein one end of the flame stabilizer is a secondary anode facing the primary anode. 4. The anode structure of a plasma pulverized coal ignition burner according to claim 3, wherein at least one slit is provided in a radial direction of the secondary anode. 5. An anode structure according to claim 3, wherein the anode is formed of a conductive ceramic. 6. A method for igniting a plasma type pulverized coal ignition burner according to claim 1 or 2, wherein a continuous plasma generator is inserted into a flow path of the pulverized coal to form an ignition burner or an ignition torch. An ignition method characterized by igniting main fuel of a main burner by an ignition torch.