JPS60194211A - Pulverized coal burner with arc type igniting torch - Google Patents

Abstract

PURPOSE:To contrive the simplifying of control operation and the stabilization of igniting by a method wherein an igniting torch and a burner are made into an integral structure. CONSTITUTION:A burner is composed of a electrode 14 having a needle-shaped top made of tungsten as a negative electrode and a nozzle 15 made of copper as a positive electrode, generates an electric arc between both poles by a high frequency power source 17. A jetting speed of pulverized coal/air flow is kept higher than a certain constant rate of flow, generally, set higher than 10m/s. The pulverized coal/air flow is set so that the jetting speed is kept higher than 10m/s. The weight of a flame holder 23 is adjusted so that the direction of the flame holder 23 is inclined toward the inner side of the torch side in case that the jetting speed is less than 17m/s. Thereby, the pulverized coal/air flow is easily contacted with a plasma arc flame 3, accordingly, the stable igniting for the pulverized coal can be achieved.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a pulverized coal combustion device, and in particular, it ignites pulverized coal at room temperature without using light oil or heavy oil as auxiliary fuel, and produces stable pulverized powder. This invention relates to a pulverized coal burner with a built-in arc-type ignition torch for forming a charcoal combustion flame.

[Background of the invention]

Conventionally, in pulverized coal boilers, petroleum-based fuels such as light oil and heavy oil are used as auxiliary fuels in addition to pulverized coal as fuel. The purposes of use of auxiliary fuel are broadly divided into boiler startup and stabilizing combustion conditions during load fluctuations. The former.

Pulverized coal has poor ignitability at room temperature, and conventionally used ignition torches are spark-type torches that are used for fuels that are relatively easy to ignite, such as gas fuel or petroleum-based fuel. It was difficult to ignite pulverized coal at room temperature. Therefore, petroleum-based fuels such as light oil and heavy oil with good combustibility are used to start up the boiler, and when the temperature inside the boiler rises, the petroleum-based fuel and pulverized coal are switched, and the operation shifts to pulverized coal-only combustion. The method was customary.

The use of these petroleum-based fuels requires a large amount of auxiliary fuel, and also imposes a large economic burden on the user, such as the cost of storage and supply equipment for the auxiliary fuel.

Therefore, a technology to stably burn pulverized coal by reducing or not using these auxiliary fuels was developed in the 1970s.
It is disclosed in Japanese Patent No. 8-1330.

As shown in Fig. 1, this new combustion method uses an arc ignition torch 2 (used in plasma arc welding machines, etc.) to generate a plasma arc flame 3 with pulverized coal/air ejected from a pulverized coal burner 1. In this method, pulverized coal is brought into contact with a stream 4 and ignited by a high-temperature flame 3. Ignition of pulverized coal using the arc type ignition torch 2 is considered to be an effective method for solving the conventional problems. However, this technique simply describes ignition within a specified range of ignition parameters defined by the ignition energy (and enthalpy) from the provided ignition torch side and the respective concentrations of the pulverized coal/air stream. However, as a result of experiments, the inventors found that when the plasma arc flame 3 from the arc type ignition torch 2 was brought into contact with the flow velocity of the pulverized coal/air flow, the concentration of each of the pulverized coal/air flow 4 and the plasma torch side simply increased. Even if the ignition energy was within the range of the ignition parameters described in the publication, stable ignition could not be achieved. This is due to the fact that the penetration power of the plasma arc flame is influenced by the flow velocity of the pulverized coal/air flow. The cause of this will be explained in detail based on FIG. 2, which is an example of the inventors' experimental results. Figure 2 (a) shows plasma arc flame 3.
FIG. 2 is a conceptual diagram showing a case where the pulverized coal/air flow 4 cannot be brought into sufficient contact with the pulverized coal/air flow 4 due to its high flow velocity, and the pulverized coal cannot be ignited stably. FIG. 2(b) is a conceptual diagram in which the flow velocity of the pulverized coal/air flow 4 is low, and conversely, the mixed flow avoids the high temperature part of the plasma arc flame 3 and passes through, making it impossible to stably ignite the pulverized coal. . In addition, if the arc type ignition daughter 2 is separated from the pulverized coal burner 1 and installed immediately after the pulverized coal/air flow is ejected as shown in Figure 1 above, the amount of pulverized coal supplied and the amount of air can be controlled by the operator However, on the downstream side of the ejection, the concentration of pulverized coal is not uniform due to the air flow and burner structure, and the operating conditions alone indicate that the concentration of pulverized coal is not uniform at the location where the arc flame from the torch is located, as described in the above publication. It is difficult to judge whether it is within the ignition region, and it is not necessarily within the ignition region. Therefore,
As in the past, the ignition region cannot be limited simply by the amount of pulverized coal, the amount of air, and the ignition energy.

[Purpose of the invention]

An object of the present invention is to provide a pulverized coal burner equipped with an arc type ignition torch.

[Summary of the invention]

The key points of the present invention are that the contact between the plasma arc flame and the pulverized coal/air stream is efficiently carried out, and that the pulverized coal/air stream is within the ignition range of the pulverized coal under the operating conditions. In order to simplify the operation and stably ignite the pulverized coal, the arc type ignition torch is integrated with the pulverized coal burner.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail with reference to FIGS. 3 to 8.

FIG. 3 is an overall configuration diagram of a pulverized coal burner equipped with an arc type ignition torch according to an embodiment of the present invention. If the burner is cylindrical, the arc type ignition torch 2 is installed in the center.

On the outside there is a pulverized coal/air flow jet nozzle 8;
A secondary air nozzle 9 and a tertiary air nozzle 1o are arranged on the outer peripheral side. The secondary air nozzle 9 and the tertiary air nozzle 1o each have a swirler 11.1 for giving swirling motion to the air.
4 shows the detailed structure of the arc type ignition torch used in the pulverized coal burner 1 of the present invention, in which the torch 2 is arranged. In the burner of the present invention, a tungsten electrode 14 with a needle-like tip is used as one pole, a copper nozzle 15 is used as the electrode, and a high frequency power source 17 generates an electric arc between the two poles. In the present invention, argon gas (Δr) 21 is used as plasma gas.
A plasma arc flame 3 was formed using the following. The plasma arc section 3' is in a high temperature region of 8000C or higher, but the temperature at the tip of the arc frame 3 is 8000C or lower. Effective contact of the pulverized coal/air stream with this plasma arc flame 3 is a prerequisite. Also.

Since the arc generating part becomes high temperature, a tungsten electrode 14 is used.
And nozzle J5 is a cooling structure 1, cooling water 20.21
A shield cap 16 is supported by an insulating tube 18 at the outer peripheral part where the gas can flow into the inside of the nozzle, and a shield gas 19 can flow out between the nozzle 15 and the shield cap, and air is usually used as the shield gas 19.

The length of the plasma flame 3 depends on the plasma arc output determined by the flow rate of the plasma gas 21 and the output from the high frequency power source 17. According to the inventors' experimental results, the ejection flow velocity of the nozzle 15 is 3 m /
s or more, and the plasma arc output is 1
．． Plasma arc flame 3 is good if it is 5KW or more
It has been confirmed that it can be formed. The arc-type ignition torch has been described as being located at the center of the cylindrical pulverized coal burner 1, but the pulverized coal is ignited in a jetting state of pulverized coal/air flow.

The contact of the plasma arc flame is the most important factor. FIG. 5 shows the detailed structure of the tip of the pulverized coal/air flow nozzle 8 of the pulverized coal burner of the present invention. The flame stabilizer 23 at the tip of the pulverized coal/air flow nozzle was a structure that could move inside and outside of the torch 2 depending on the ejection speed of the pulverized coal/air flow. Since pulverized coal is ignited at room temperature under harsh conditions with no radiation from the furnace walls, the ignition area is narrow. Therefore,
The movable flame holder 23 was invented to ensure stable ignition at all times. The jetting speed of the pulverized coal/air stream is kept above a certain flow rate to prevent backfire. This requires that the pulverized coal be ejected at a speed faster than the propagation speed of the pulverized coal combustion flame. Generally, it is set to 10 m/s or more. Therefore, in the present invention, the pulverized coal/air flow is set so that the ejection speed is 10 m/s or more, and the ejection speed is 17 m/s or more.
Below s, the weight of the flame holder 23 was adjusted so that the direction of the flame holder 23 was inclined inward toward the torch side. With this configuration, the pulverized coal/air flow can easily come into contact with the plasma arc flame 3, and the pulverized coal can be ignited stably. During the period when the plasma arc flame 3 is being formed, ignition energy is given to the pulverized coal, so that the pulverized coal can be stably combusted. Since the temperature of the pulverized coal combustion flame increases as the pulverized coal ignites, the more time passes, the more stable the pulverized coal can be burned by radiation from the flame surface. When igniting pulverized coal from room temperature in this way, it is preferable that the ejection flow velocity is small, but from the standpoint of flashback, it is preferably 10 m/s or more.
The inventors have found that setting the velocity to 17 m/S or less is advantageous for ignition at room temperature. Therefore, regarding the ignition conditions from room temperature, in addition to the ignition limit caused by the concentration of pulverized coal, the ejection speed is one of the factors that influences ignition. In addition, at the time of ignition, the pulverized coal/air flow is ejected in the region of 10 to 17 m/s, but once the nozzle structure is decided, it is necessary to increase the amount of pulverized coal supplied from a single burner. As a result, the amount of primary air also increases, and the ejection speed naturally increases. Therefore, in the present invention, when the speed exceeds about 17 m/s, the flame stabilizer 2
The weight of the flame holder 23 was determined so that the pressure at the time of ejection was high, overcoming the weight of No. 3, and the flame holder 23 was directed outward. The angle θ of the flame stabilizer 23 toward the outside is restricted by the support plate 24 provided on the outside of the flame stabilizer 23, and θ is 10
It was set up so that the temperature was higher than that.

In order to obtain the flame stabilizing effect of the flame stabilizer 23 in this way, the flame stabilizer 23 should be oriented outward so that the pulverized coal spreads outward immediately after the pulverized coal is ejected, and the flame stabilizer 23 is Since a part of the secondary air is involved in the pulverized coal/air flow, a flame is formed from the vicinity of the flame stabilizer 23, and the pulverized coal is burnt well. The irradiation time of the plasma arc flame 3 is determined based on the point in time when the flame temperature increases, the temperature of the atmosphere such as the furnace wall increases, and conditions are reached where the flame of the pulverized coal can continue due to radiation.

Next, using Figures 6 and 7, we will discuss the ignition limit of pulverized coal determined by the pulverized coal concentration and plasma arc output, and the limits for stopping the plasma arc flame after one ignition and continuing to form a flame. The conditions will be explained based on experimental results. The experimental results shown in Figures 6 and 7 were obtained using domestic Pacific coal as the pulverized coal.

The particles used were adjusted so that the particle size was 80% less than 200 mesh (74 μm). The volatile content in coal is approximately 38
%, fixed and fixed carbon content is approximately 38-39%, and ash content is 14%.
It is about %. Pulverized coal/air flow jetting speed is 15m/s
The pulverized coal concentration was constant and varied by adjusting the pulverized coal supply rate. Moreover, the air temperature was 10°C. The structure of the pulverized coal burner uses the burner of the present invention shown in FIG. 3, with a negative air amount of 3ONrrr/h, a secondary air amount of 4ONnf/h, and a tertiary air amount of 6ONn? /h. The horizontal axis in FIG. 6 shows the ratio of pulverized coal/-primary air conveying air).

From the results shown in FIG. 6, it can be seen that there is a limit plasma arc output depending on the pulverized coal concentration, and that as the plasma arc output is increased, the single ignition limit shifts to the lower concentration side. However, there is a region where the plasma arc cannot ignite even if the output is increased, and the ratio of pulverized coal to primary air is 0.15.
0.15 is the ignition limit determined from the pulverized coal concentration because it will not ignite below the In this case, it becomes impossible to ignite regardless of the concentration, and the ignition limit is determined from the plasma arc output. Therefore, as shown in FIG. 6, it is necessary to determine the pulverized coal concentration and plasma arc output within the ignition region. Figure 7 shows the flame holding effect in blocking the plasma arc flame and stably continuing the flame.
The figure shows ignition at room temperature under the same conditions as in Figure 6, the plasma arc flame is brought into contact with the pulverized coal air flow, the temperature at the burner tip is measured with a thermocouple, and the temperature at the burner tip and the plasma arc flame are measured. A television camera (ITV) was installed near the burner to observe whether a flame was formed or extinguished when the burner was shut off. As a result, it was found that when the temperature at the tip of the burner was about 50° C. or lower, the plasma arc flame would be blown out if it was cut off. In the range of approximately 50 to 100 degrees Celsius, there are times when flame exists and times when it blows out, making it an unstable region.
When the temperature at the tip of the burner reaches 100° C. or higher, the flame remains stably and becomes a flame-holding region.

Therefore, if the temperature at the tip of the burner is used as a control factor for shutting off the plasma arc flame, the operation of the plasma arc flame after ignition of pulverized coal can be controlled, and there will be no wasted time or ε that consumes energy.

〔Effect of the invention〕

According to the present invention, the contact between the plasma arc flame and the pulverized coal/air flow can be efficiently carried out, and control aspects such as being within the pulverized coal ignition region under the operating conditions of the pulverized coal/air flow can be achieved. This simplifies the operation and enables stable ignition of pulverized coal.

[Brief explanation of drawings]

Figure 1 is a conventional configuration diagram, Figure 2 is an explanatory diagram of conventional problems,
Figures 3 to 5 are block diagrams of a pulverized coal burner incorporating the arc-type ignition torch of the present invention, and Figures 6 and 7 are diagrams of experimental results showing the conditions necessary for ignition and flame holding of pulverized coal. It is. 1...pulverized coal burner, 2...arc type ignition torch,
8...Pulverized coal/air flow nozzle, 9...Secondary air nozzle, 1 3rd color at the edge of the figure 4th mouth 1'? f1 t Continued from page 1 0 Inventor Ina 1) Toru @ Inventor Norio Arashi @ Inventor Otsuka Kaoruzo @ Inventor Masai Tadahisa 3-1-1 Saiwaimachi, Hitachi City Hitachi Research Co., Ltd. 3-1-1 Saiwai-cho, Hitachi City Hitachi Research Institute, Hitachi, Ltd. 3-1-1 Saiwai-cho, Hitachi, Ltd. Hitachi Research Laboratory, Hitachi, Ltd.

Claims (1)

[Claims] 1. An ignition plasma torch capable of emitting an electric arc flame is arranged in the center, and a nozzle for ejecting pulverized coal and primary air is provided outside the torch, and two A pulverized coal burner equipped with an arc type ignition torch characterized by the arrangement of secondary air and secondary air nozzles. 2. The pulverized coal equipped with an arc type ignition torch according to claim 1, characterized in that the tips of the pulverized coal and the primary air flow nozzle are configured to be able to change their directions inwardly and outwardly. Burna. 3. A pulverized coal burner equipped with an arc type ignition torch according to claim 1, characterized in that a swirler for imparting rotational motion to the air is disposed in the secondary air and tertiary air nozzles. 4. In claim 1, the ignition torch includes an arc set between a pair of electrodes, an inert gas, air,
Alternatively, it is characterized by comprising a means for passing a mixed gas of both through an arc generation location of a plasma torch, and a means for forming a plasma arc flame by heating the gas to a high temperature and bringing it into contact with pulverized coal and a primary air stream. A pulverized coal burner equipped with an arc-type ignition torch.