JPH0613924B2 - Method for estimating unburned amount in ash - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for monitoring or controlling the combustion state of pulverized coal, CWM (coal / water slurry), etc., and particularly to unburned ash in boiler combustion. min (U n- B urnt C arbon, below, UBC
Abbreviated) regarding the estimation method of quantity.

[Background of the Invention]

Pulverized coal combustion technology, which is said to have been completed, is drawing attention in the review of coal as an alternative energy to oil. However, in recent years, new technical measures have been required to comply with regulations on environmental problems such as NO _x emissions and fly ash processing.

The increase in unburned content in ash due to the use of high-fuel ratio coal and low-grade coal as fuel for pulverized coal lowers boiler efficiency, so measures to reduce it are urgently needed.

For combustion of pulverized coal, pulverized coal is sent into the furnace together with primary air. The temperature of the coal particles rises due to the radiant heat from the high-temperature furnace wall and flame. Subsequently, the water is first evaporated, and then the volatile matter is ignited by vaporization. It burns until heat release and heat generation due to combustion are balanced, and a flame is formed due to a rapid temperature rise. Keep track of.

On the other hand, in the combustion process of fine powder particles, the decomposition and combustion of volatile matter proceed at the beginning of combustion, and then the residual carbonaceous matter of the coke (hereinafter,
Surface combustion).

It is considered that the time required for the surface combustion of the chaier is most of the time required for the fine powder particles to completely burn out.

Generally, pulverized coal combustion is greatly influenced by properties of the pulverized coal (fuel ratio, ash content, caking property, particle size distribution, etc.). Therefore, it is very difficult to estimate the UBC in the combustion process.

However, in order to reduce UBC, it is clear from experience that it is sufficient to make O ₂ excessive and burn it at once in a high temperature furnace. However, there are problems in terms of NO _x generation, control of furnace temperature distribution, and the like.

In the current commercial or industrial pulverized coal-fired boilers, the operation is performed to minimize the unburned ash content in order to improve the boiler efficiency. However, the reduction regulations such as NO _x, 2-stage combustion, Taking combustion methods such as slow combustion tends to temperature in the furnace is increased decreased UBC ( "thermal power" 34 -12, '83) [Object of the Invention] An object of the present invention is to provide a method for estimating the amount of unburned matter in ash in order to realize combustion that reduces UBC during pulverized coal combustion.

[Outline of Invention]

Fig. 1 shows three cases of flames having different flame shapes during pulverized coal combustion. Case (a) UBC has extremely few flames, case (b) UBC has extremely many flames, and case (c) UBC has flames between (a) and (b).

The flame, that is, the combustion region of pulverized coal, is mainly composed of the primary combustion region in which volatile matter is burned, and the solid carbon content is mainly burned in 2
It is divided into the next combustion zone. As a result of data analysis, it was found that there is an extremely high correlation between the distribution of luminance (or temperature) in these regions and the amount of UBC.

Therefore, the correlation between the luminance (or temperature) distribution of the flame and the UBC amount is obtained in advance, and the UBC amount generated from the actual flame is estimated using this correlation.

Example of Invention

As an example, the brightness distribution on the central axis of the burner in FIG. 1 (solid line BN1), the brightness distribution on the secondary air outlet axis (broken line BN2)
FIG. 2 shows the relationship between the UBC and NO _x .

In FIG. 2, in case (a), both the brightness distribution on the center axis of the burner and the brightness distribution on the secondary air outlet axis have a sharp rise from the tip of the burner and high brightness. At this time, the amount of NO _x is high and the amount of unburned fuel is low.

In case (b), the brightness on the central axis of the burner is low, and the distribution is almost unchanged. Also, the rise of the brightness distribution on the secondary air outlet axis is slower than that of (a) and (b). At this time, the amount of low NO _x and the amount of unburned fuel are high.

In case (c), the brightness distribution on the burner center axis rises gently, but the distribution on the secondary air outlet axis rises sharply and the brightness is high. At this time, both the unburned component and NO _x fall between cases (a) and (b).

On the other hand, the combustion atmosphere in each case during combustion is as follows.

In case (a), the pulverized coal is appropriately diffused and sent into the furnace in a high temperature atmosphere so that the O ₂ distribution around the fine powder particles is optimized. For this reason, the ignition of volatilization becomes faster, and the fine powder particles burn rapidly to reduce UBC.

In case (b), the distributions of pulverized coal and O ₂ are separated, and combustion proceeds only in the contact area between the two. Therefore, a large amount of fine powder particles that do not burn out remain as UBC.

Case (c) optimizes the contact between pulverized coal and O ₂ .
The secondary air is swirled to scatter pulverized coal near the tip of the burner to promote combustion. By turning, a negative pressure is generated in the wake portion, so that the pulverized coal and O ₂ are mixed and combustion proceeds. From this, it is considered that UBC is between (a) and (b).

From the relationship between the above luminance distribution and the combustion atmosphere, the present invention measures a flame image in the vicinity of the burner, and a zone on the burner center axis in the burner axial direction of the flame image (the pulverized coal of the burner and the air ejection direction). Relative brightness distribution with other bands,
Focusing on the fact that it has a high correlation with UBC, the UBC is estimated by pre-storing the relationship between the relative brightness from the burner tip and UBC as a mathematical expression or numerical table (eg, a figure or table). is there.

One embodiment of the present invention is shown in FIG. In FIG. 3, 1
Is a furnace, 2 is a burner, 3 is a flame, 4 is a cooling device, 5 is an image fiber, and 6 is an ITV (Industrial Television).
A camera, 7 is an image signal, 8 is an A / D conversion device, 9 is a frame memory, 10 is a processor, and 11 is a display device.

An image fiber 5 is attached to the sight window of the boiler furnace 1 so that a flame image near the pulverized coal barter 2 can be measured. The image fiber 5 has a structure in which the head is cooled with water or air so as to withstand a high temperature atmosphere, and air is jetted from the outer periphery of the front surface to prevent the combustion ash of pulverized coal from adhering.
The flame image is converted into an electric signal by the ITV camera 6 via the image fiber 5, and is transmitted to the A / D converter 8 as an image signal 7. The image signal digitized by A / D conversion is stored in the frame memory 9.

The processor 10 processes the image data stored in the frame memory 9 in the following manner (fourth example).
Figure).

Flame image data input 100; Flame image data X (i,
j) is taken into the frame memory 9.

Flame brightness distribution calculation 110: Calculation of brightness distribution on the burner central axis (BN1) and brightness distribution on the secondary air outlet axis (BN2). The brightness distribution on the secondary air outlet axis is set because a high brightness area, that is, an oxidizing flame is formed on this axis. FIG. 5 (a) shows a schematic flow for calculating the luminance distribution.

BN1 (i) = X (i, j ₁ ) ... (1) j ₁ ; burner radial position (here, burner central axis position) i; axial distance (i = 1 to I) X; flame Image data BN2 (i) = X (i, j ₂ ) ... (2) j ₂ ; Burner radial direction position (here, secondary air outlet position) In addition, the luminance distribution was obtained here, As described above, since the temperature distribution and the UBC amount also have a correlation, the temperature distribution may be obtained. In this case, in the following description, it is necessary to treat brightness as temperature.

Calculating unburned ash content index 120; BN1 and BN2 are compared with respective limit values LIMT1 and LIMT2. Limit value LIMT1, L
IMT2 is determined as, for example, the ratio of the high-luminance region to the total area of the luminance distribution on the axis.

BN1 (i) LIMT1 ………… (3) BN2 (i) LIMT2 ………… (4) i; Axial distance (i = 1 to I) As a result of comparison with Eqs. (3) and (4), 1 point However, if the expressions (3) and (4) are satisfied, the half-threshold value processing is performed with the limit value (Sixth
Figure).

Half-threshold processing means that the value below (or less than) the limit value is 0.
It is a process of clearing and storing the value more than (or exceeding) as it is (hatching part in FIG. 6).

Next, as shown in FIG. 6, the deviation of the portion exceeding the limit value of the areas [I] and [II] above the limit value from the burner tip is calculated (Equation (5)) and FIG. Then, the base amount is removed with the limit value LIMT3.

ΔBN (i) = BN2 (i) −BN1 (i) ………… (5) BNR (i) = ΔBN (i) −LIMT3 ……… (6) As a result of removing the base of BNR (i); ΔBN (i), the maximum brightness y of BNR (i) and the distance x from the burner tip to the position of maximum brightness are obtained.

Estimating unburned ash content 130: Estimate the UBC value using, for example, equations (7) and (8) or a numerical table corresponding thereto.

Ash unburned content estimation index I _UBC f (x, y, G ₁ ) (7) x; distance to maximum brightness y of deviation y; maximum brightness of deviation G ₁ ; primary air amount unburned ash content UBC = K · I _UBC (8) K; constant Eq. (7) showing the correlation between the ash unburned content estimation index I _UBC and (x, y, C ₁ ), and ash unburned content Estimated index I
_The equation (8) for calculating the amount of unburned ash in _UBC is stored in advance in the memory of the processor 10.

Display 140: A flame image used for I _UBC calculation, shape characteristic parameters x, y, I _UBC , UBC, etc. are displayed on the display device.

By repeating the above process periodically or continuously, the UBC during boiler operation can be accurately estimated, high efficiency operation can be realized, and the combustion state of the boiler can be satisfactorily monitored. Furthermore, although the instant image data is used in the present embodiment, it is also possible to use the average value of a plurality of image data in order to improve and stabilize the estimation accuracy.

Another embodiment of the present invention is shown in FIG. FIG. 8 is an example of a multi-burner monitoring device in which FIG. 3 which is one embodiment of the present invention is applied to each stage of a boiler. In FIG. 8, 12
Is a channel switching device of the ITV camera 6, and 13 is a channel switching signal. The basic processing is the same as that of the first embodiment of the present invention, but since it is a multi-burner, equation (7) is represented by equation (7 ') and equation (8) is represented by equation (8'). Become.

A, B, C: Suffixes representing each stage, and the process of the processor 10 is carried out by sequentially estimating UBC (unburned components in ash) of all channels (all stages) as shown in FIG. It is possible to monitor the combustion state of each stage and realize fine and highly efficient operation.

When considering the brightness distributions of the burner center axis and the secondary air outlet axis in the first embodiment and the other embodiments, it is possible to use not the brightness distribution on the line but the average brightness of a band having a width in the burner radial direction. Is. For example, in equations (1) and (2), It is also possible to use j ₁ ; burner center axis position j ₂ ; secondary air outlet axis position i; axial distance (i = 1 to I).

〔The invention's effect〕

By carrying out the present invention, the amount of UBC (unburned ash content) can be estimated.

[Brief description of drawings]

FIG. 1 is a diagram comparing flame shapes that are the basis of the present invention,
FIG. 2 is a diagram showing the difference in the luminance distribution of the flame in the burner axis direction, FIG. 3 is an apparatus configuration showing one embodiment of the present invention, FIG. 4 is its processing flow, and FIG. ) (b) shows a schematic procedure of the processing flow, and FIG.
FIG. 8 shows a relative luminance deviation, FIG. 8 shows an apparatus configuration showing another embodiment of the present invention, and FIG. 9 shows a processing flow thereof. 1 ... furnace, 2 ... burner, 3 ... flame, 5 ... image fiber, 6 ... ITV camera, 7 ... image signal,
8 ... A / D converter, 9 ... Frame memory, 10 ...
... Processor, 11 ... Display device.

Claims (1)

[Claims] 1. A method for estimating an unburned amount in ash from an image of a flame formed by combustion of pulverized coal ejected from a burner, the unburned amount in ash being estimated on a central axis of the burner. Brightness (or temperature) distribution,
The brightness (or temperature) distribution at a position distant from the center axis of the burner and the correlation between the amount of unburned matter in ash are obtained in advance, the image of the flame is measured, and from the image signal, The brightness (or temperature) distribution is obtained on the center axis of the burner and at a position separated from the burner by a predetermined distance, and based on the obtained brightness (or temperature) distribution and the previously obtained correlation, A method for estimating an unburned amount in ash, which comprises estimating an unburned amount.