JPS60204A - Method and appatatus of burning pulverized coal - Google Patents

Abstract

PURPOSE:To control the forming of NOx and the burning efficiency by merely selecting burning conditions by means of controlling the mixture ratio of secondary air and primary fuel and the distribution of fuel between first and secondary fuels by utilizing a fuel dividing burner. CONSTITUTION:A dividing apparatus 9 divides a mixture flow of pulverized coal and air into two, and respective ducts for carrying the mixture flow are connected to a pulverized coal burner 11 through which the divided mixture flows are discharged into a pulverized coal burning apparatus 12 to be burnt therein by the burner 11. Meanwhile, an air duct 2 bypasses an air duct 3 that is connected to the inlet side of a mill 1, and an air duct 4 is provided that is connected to a mixing device 10 disposed in one of the mixture flow carrying ducts which are divided into two on the discharge side of the dividing apparatus 9. The opening of valves 5 and 7 is regulated by input signals from a control device 13, which also determined the function of the dividing apparatus. In this manner, the forming of NOx and the burning efficiency out of coals of different fuel ratio and coals having different N contents can be controlled by simply setting their burning conditions.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to pulverized coal combustion, and relates to a pulverized coal combustion method that can control NOx generation amount and combustion efficiency using the same burner for a wide variety of coals, and a pulverized coal combustion method therefor. This invention relates to a device for embodying the invention.

[Background of the invention]

Direct combustion of pulverized coal has a higher nitrogen content than gas or petroleum-based fuels, so it generates large amounts of nitrogen oxides and has many problems, including poor combustibility. In addition, thermal coal is highly dependent on overseas countries, and a wide variety of coals are imported and used as fuel.

In particular, the content of fixed carbon and volatile matter in coal, which greatly affects combustibility, varies widely, and even if all coals are combusted in the same combustion burner under the same conditions, the combustion efficiency will vary greatly. Generally, the ratio of fixed carbon content to volatile content is called the fuel ratio, and is used empirically to express combustibility. However, the fuel ratio is simply an indicator of combustibility; in addition, the N content in the fuel also varies greatly; also varies greatly. NOx is a substance subject to emission regulations, and countermeasures are required especially at emission sources such as thermal power plants whose emissions are regulated. Normally, at thermal power stations, etc., stone return electrodes are selected and used as fuel.
NO! In order to suppress the amount generated and meet strict regulatory values,
It is necessary to adopt a low NO8 combustion burner or modify the boiler.

On the other hand, in the past, low fuel ratio coal with high volatile content and good combustibility was used, but recently there has been a trend to use coal with a relatively high fuel ratio of around 2.0 to 2.5 as fuel. Meji, just the fuel ratio mentioned earlier is NO.

Since it is difficult to understand and evaluate the amount generated, it is necessary to evaluate the combustion state using both the fuel ratio and the N content as indicators. A particularly important point is that a wide variety of coals can be burned without changing the boiler structure, burner structure, etc.
There is a strong desire for a pulverized coal combustion method that can suppress the amount of NO generated and maintain high combustion efficiency.

FIG. 1 shows the structure of a two-stage combustion burner proposed as a conventional low NO8 combustion burner. This burner transports pulverized coal through primary air, and the pulverized coal is injected into a large furnace through a nozzle 1 under conditions of oxygen deficiency below the theoretical air amount and is combusted. Here, combustible substances such as CO, CH, H, etc. are generated from N in the coal, N compounds such as NHs, and others.

Next, by introducing secondary air from nozzle 2 and tertiary air from nozzle 4, the unburned matter is combusted by the diffusion of these airs. The pulverized coal burner shown in Figure 1 can suppress the generation of NO by forming a low 02 combustion region, which lowers the combustion temperature and lowers the 02 partial pressure. No, this is because it suppresses the conversion rate. The inventors used the above-mentioned burner to maintain a constant N content of 0.99 to 1. lwt%
0, where only the fuel ratio can be used as a parameter.
We selected three types of coal in the range of 9 to 4.30 and used fuel prepared by adjusting these pulverized coals to 100 to 200 mesh to understand the effects of coals with different fuel ratios on the combustion efficiency. . FIG. 3 shows the relationship between the amount of NO generated and the fuel ratio measured under the conditions of a total air ratio of 1.4 and a primary air ratio of 0.2. As shown in curve A in the figure, as the fuel ratio increases,
NO, concentration increases. Therefore, the same combustion method cannot suppress the NO□ concentration generated from high fuel ratio coal. Next, the curve in the middle of FIG. 4 shows the combustion efficiency when burning with the burner of FIG. 1 under the same conditions as the curve of FIG. 3A. It can be seen that coal with a higher fuel ratio than this has poor combustibility and cannot be put to practical use under certain combustion conditions. Therefore, the results using the pulverized coal burner, which is one of the present inventions shown in FIG. 2, are shown below. This burner is a combustion type burner in which pulverized coal is divided into two parts, the primary ffi fuel nozzle 1 and the secondary fuel nozzle 7, to burn it, and the combustible noise was detected in correspondence with the burner shown in Fig. 1. The burner of the present invention shown in Fig. 2 injects and burns the primary fuel through the nozzle 1 with primary nitrogen gas that is less than the theoretical air amount, and injects and burns the secondary fuel with secondary air that is more than the theoretical air amount. . In particular, the mixed flow of secondary fuel and secondary air was spouted into the furnace while being swirled using a swirler 3. This burner uses 0.0% of primary fuel. A flame that generates NH8 etc. under conditions of shortage, and a flame that generates N under conditions of high 0□.
This is a low NO□ burner that simultaneously forms a flame that actively generates O, and promotes mixing of both flames on the downstream side to reduce NO. The results using this burner were compared with the 8 curves shown in FIGS. 3 and 4 with the A curve of the two-stage combustion burner shown in FIG. 1. As a result, NO□ for fuel ratio
The characteristics and combustion characteristics show relatively similar trends, but NO,
It is clear that both the amount generated and the combustion efficiency are significantly improved. However, it is difficult to obtain the same performance under the same combustion conditions even with the burner of the present invention. Therefore, the inventors found that due to the difference in fuel ratio, the amount of volatile N compounds that are produced as reducing agents for reducing NO8 is small in high fuel ratio coal with low volatile content, and that low 02, which is one of the reducing agents. It is thought that optimal combustion conditions exist depending on the type of coal, as the specific surface area of the char generated in the atmosphere differs depending on the fuel ratio. Therefore, the low NO! shown in Figure 2! Using a pulverized coal burner, which is one of the inventions effective for
The minute content is 0.9 to 1. Three coal cylinders with different fuel ratios of lwt316 were selected, and the influence of the -order air ratio (actually used primary air amount/theoretical air amount) was investigated. FIG. 5 shows the combustion characteristics when primary and secondary fuels with a total air ratio of 1.4 are supplied in equal parts. In the figure, the ho% property is the case where the fuel ratio is 11B, the property is fuel 2, and the property C is the case where the fuel ratio is 30 coal.

As a result of the inventors' studies, it is clear that there is an optimal air ratio depending on the fuel ratio.

Further, for the same three types of coal as shown in Fig. 5, the amount of NO□ generated when the supply ratio of -primary fuel and secondary fuel is changed is summarized in Fig. 6. From this experimental result, it is clear that there is an optimal fuel distribution ratio depending on the coal type. Based on these findings, the inventors used the fuel split type pulverized coal burner shown in FIG. 2, which is one of the embodiments of the present invention, to adjust the mixing ratio of primary fuel and primary air to a primary air ratio of 0. 2-0.5
By controlling the secondary fuel ratio within the range of 0.3 to 0.6, it became possible to burn coals with different fuel ratios in a single burner and suppress the amount of NOx produced.

Next, the fuel ratio is 1.5 and the N component is 0.8, 1.3°1.
Using the burner shown in Figure 2, we investigated the relationship between the N content in the coal and the amount of NO produced, as well as the effect on combustion efficiency, for three coal types of 9 daf% (dry, ash-free). The results are shown in FIG.

It has become clear that the combustion efficiency (carbon reaction rate) is dominated by the fuel ratio, and the N content has almost no effect on combustibility. To this, NO! The amount generated is N
The higher the N content, the higher the NO8
The concentration was also found to increase. This was a comparison under constant combustion conditions.Based on these results, we conducted further studies and found that there is an optimal combustion condition depending on the N content. Figure 8 shows the results. The curve of A is N minutes = 0. Bctaf%, the curve of B is 1.3 d a
f%, the C curve is the combustion characteristic of coal with 1.9 daf% l).For coal with a high N9 content, setting the primary air ratio to a low air region is effective in reducing NO. This is because a large amount of NH, which is a volatile N compound, is generated, and the amount of NO8 generated increases as the N content increases, so the amount of reducing agent generated can be increased.

[Purpose of the invention]

An object of the present invention is to provide a pulverized coal combustion system that can control NO, amount of generation, and combustion efficiency by simply selecting combustion conditions for coals with different fuel ratios and coals with different N contents.

[Summary of the invention]

The key point of the present invention is to use a fuel split burner to control the mixing ratio of secondary air and primary fuel and the distribution ratio of secondary fuel and secondary fuel.

[Embodiments of the invention]

An embodiment of the pulverized coal combustion apparatus of the present invention will be described in detail using FIG. 9.

In the pulverized coal combustion device 12, a plurality of pulverized coal burners are arranged on the furnace wall. Here, the explanation will focus on one pulverized coal burner 11. First, a pretreatment system for supplying pulverized coal to the pulverized coal burner 11 will be described.

Since the coal is usually lump coal, 15 pieces of coal can be introduced into the mill 1, and it is usually pulverized to 80% by weight under a sieve of 200 meshes. An air pipe 3 branched from an air pipe 2 for combustion of pulverized coal is directly connected to the mill l.
A valve whose opening degree can be adjusted and a flow meter 6 for measuring the amount of air are arranged. The coal (pulverized coal) pulverized by the mill 1 is conveyed by air and introduced into the dividing device 9. The mixed flow of pulverized coal and air is divided into two by the dividing device 9, each mixed flow conveying pipe is connected to the pulverized coal burner 11, and the divided state is combusted in the pulverized coal combustion device 12 from the pulverized coal burner 11. be done. On the other hand, on the inlet side of the mill 10, the air pipe 2 bypasses the mill l outside the air pipe 3 directly connected to the mill l, and is installed on one side of the mixed flow conveying pipe divided into two on the downstream side of the dividing device 9. An air pipe 4 is arranged which is connected to a mixing device IO. Similarly to the air pipe 3, this air pipe 4 is also provided with an air flow meter 8 and a valve whose opening degree can be adjusted. Furthermore, the valves 5.7 arranged in the air pipes 3 and 4, the flow meters 6, 8, and the dividing device 9 are connected to the control device 13, and the valves 5 and 7 are opened by an input signal from the control device 13. is adjusted and the function of the dividing device 9 is determined. The control device 13 further stores a burning profile according to the type of coal, and when the properties of the coal are input, it selects a burning profile that matches the properties of the coal, and thereby sends a command signal for combustion conditions to the control device 13. A storage device 14 for sending data is connected.

The specific operating conditions for these apparatus configurations will be explained in relation to the properties of coal. Table 1 shows Table 1 Analysis value calorific value of domestic A coal (Kcal/Ky) 6370 C (9) 63.31 H (X) 5.04 0 (%) 18.62 S (9) 0.40 Fixed carbon (9) 38.80 Volatile content (9) 39.10 Ash content (9) 13.90 This is the analysis value for domestic A coal. If this domestic coal A is used as fuel, this analysis value is input into the storage device 14. The storage device 14 reads this analysis value and uses the calorific value as an index to determine the heat input to the pulverized coal combustion device 12, and indirectly determines the total amount of pulverized coal supplied to the combustion device 12. It is used as a factor for The two values particularly utilized in the present invention are the nitrogen content N and the fuel ratio, and these can be used as indicators for determining combustion conditions. Therefore, in the storage device 14, the N minute and fuel ratio are extracted and compared, and a burning profile corresponding to each value is drawn on the display device 16. Further, since the total supply amount of pulverized coal is determined in consideration of the analytical value of the calorific value, the performance (function) of the mill 1 is also determined. Table 2 shows an example of display when domestic A coal is used as fuel.

As shown in Table 2-, the primary air ratio λ□ and the secondary fuel ratio f in each single burner are determined according to the N content rate and fuel ratio stored in advance.
, is determined, and the predicted value of NO, and the predicted value of combustion efficiency are set out. This is intended to notify the operator and is utilized for confirmation. These setting conditions are input to the control device 13, and the performance of the mill 1 and dividing device 9, and the opening degrees of the valves 5 and 7 are automatically determined as the flow rate. Feedback control is performed from the signals of the devices 6 and 8. In this way, the amount of pulverized coal introduced into the splitting device 9 is controlled, but depending on the input signal to the splitting device 9, the splitting amount and bypass air amount flow from the mixer 10, and the primary air ratio λ1 is adjusted. The configuration is such that The above describes the operation for domestic A coal, but in addition to domestic A coal, various coals with fuel ratios up to 3.4 and different N coal contents are used, and the combustion conditions are changed according to the coal type. control,
As a result of measuring NO, generation amount, and combustion efficiency during combustion, as shown in Figure 10, even coals with different fuel ratios and N content
It is possible to suppress the amount of No. 8 generated, achieve low NO emissions, and maintain high combustion efficiency.

[Effects of the Invention] According to the present invention, even if the coal types are different, NO, generation amount, and combustion efficiency can be controlled using the same pulverized coal burner and the same pretreatment device, and high performance can be maintained.

[Brief explanation of the drawing]

Figure 1 is a sectional view of a conventional low NO burner, Figure 2 is a block diagram of a pulverized coal burner of the present invention, and Figures 3 to 8 are graphs showing experimental results on the combustion characteristics of the conventional burner and the burner of the present invention. , FIG. 9 is a system diagram of the pulverized coal combustion apparatus of the present invention, the 1st θ
The figure is a combustion characteristic diagram of the present invention. 1...mil, 2,3.4...air pipe, 5,7...
Valve, 6° 8... Flow device, 9... Dividing device, 10...
・Mixer, ll...Pulverized coal burner, 13...Control device, 14...Memory cylinder 1 Back cover 2 Hard No. 3 Inu Kuri Ruishi・Harutamabari tea can 1 Dividing leather 4 Diagram No. 5 C Mi 2 N Daikazen 1 call thi (=fx/f, +fyu) 87 Inichibuki Tsutomuhikusa? Continuation of Figure 10, Page 1 0 Inventor Kaoru Inuzuka 3-1-1 Saiwai-cho, Hitachi City Stock % Formula % Hitachi Laboratories, Hitachi, Ltd. 3-1-1 Saiwai-cho, Hitachi City 0 Application People Babcock Hitachi Co., Ltd. 2-6-2-21 Otemachi, Chiyoda-ku, Tokyo

Claims (1)

[Claims] 1. A step of pulverizing lump coal, a step of conveying the pulverized coal obtained in this pulverizing step by air, a step of dividing the mixed fluid of the pulverized coal and the conveying air, and a step after the division. The ratio of the amount of pulverized coal to the amount of air in the mixed fluid after division is as follows:
One side is adjusted to a range that is less than the theoretical air amount, and the other is subadjusted to a range that is more than the theoretical air amount. A method for burning pulverized coal, characterized in that the amount of air introduced into one side of the dividing and conveying process on the downstream side of the dividing process can be controlled by changing the supply amount of the air. 2. In claim 4, paragraph 1, the mixing ratio of the pulverized coal and the air is ``a fuel ratio defined by the nitrogen content of coal used as fuel and the ratio of fixed carbon content to volatile content. The mixed flow of the pulverized coal and the air ejected in a region below the theoretical air amount has an air ratio of 0.
．． The proportion of the pulverized coal in the mixed flow conveyance process of the pulverized coal divided into two and the air is adjusted to be in the range of 2 to 0.5, and the ratio of the pulverized coal on the side to be conveyed is equal to or higher than the theoretical air amount. A method for combustion of pulverized coal, characterized in that conditions are set according to the type of coal so that the amount of coal is in the range of 0.3 to 0.6 with respect to the total amount of pulverized coal supplied. & A mill for crushing the lump coal, a first trachea introduced directly into this mill, and a second trachea, bypassing said mill.
air pipes, valves with adjustable openings installed in the two series, a mixed flow dividing device for pulverized coal and air located on the downstream side of the mill, pulverized coal burners placed on the furnace wall, and fuel A conveying pipe for a mixed flow of the pulverized coal and the air on the downstream side of the splitting device, comprising a storage device that stores a burning profile according to the type of coal and a control device that is activated by a signal from the storage device. After a third air pipe that bypasses the mill is directly connected to one of the pulverized coal burners, the two series of mixed flow conveying pipes of the pulverized coal and the air are connected to a pulverized coal burner, and further, the control device , the first air pipe directly connected to the mill and the second air pipe bypassed are connected so that signals can be input to valves and a dividing device, and the amount of air is adjusted by adjusting the opening degree of each valve. A pulverized coal combustion apparatus, characterized in that the pulverized coal is configured to control the amount of pulverized coal supplied by the splitting device so that the pulverized coal can be ejected and combusted into the two series of furnaces. 4. In claim 3, the pulverized coal burner is of a concentric cylindrical shape, and has a first portion in the center of which spouts the mixed flow conveyed with air less than or equal to the theoretical air amount of the pulverized coal. A combustion device for pulverized coal, characterized in that a nozzle and a nozzle for ejecting a mixed flow of the pulverized coal and the air adjusted to a theoretical air amount or higher are disposed outside the nozzle.