JP2753839B2 - Method for monitoring and controlling combustion state - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for monitoring and controlling a combustion state of a furnace, and more particularly to a method for estimating an exhaust gas component at a furnace outlet of a pulverized coal-fired boiler.

[Conventional technology]

Substances contained in flue gas during boiler operation,
In particular, toxic substances such as NO _X , SO _X , dust and the like are regulated, and the operation must be performed with the amount of production below the regulated value.

On the other hand, it is desirable that the boiler be operated with the combustion efficiency always kept at a maximum, and the unburned portion contained in the exhaust gas is a guide for calculating this efficiency.

Conventionally, gas components during boiler operation have been detected by providing a detection end at a furnace outlet or a flue. During combustion, harmful substances (NO _X , SO _X ,
Etc.) are generated and contained in the exhaust gas, but it took a long time to separate and analyze the detected components, and online monitoring was not possible.

For this reason, in order to reduce the time, it was necessary to rely on the experience and intuition of the operator. In particular, NO _X (nitrogen oxides) that the production amount is being restricted, SO _X (sulfur oxides), or reduction of unburned affecting combustion efficiency, for like, an issue to be resolved quickly Despite the fact, at present, a method for quantitatively evaluating the combustion state has not been technically established.

Recently, the use of coal instead of gas and oil as fuel is being reviewed, and pulverized coal, CWM (coal / water slurry), COM (coal / oil slurry), and the like have started to be used as fuel in boilers.

While coal is being reviewed as an alternative energy to petroleum, pulverized coal combustion technology is attracting attention. It is said that this technology has already been completed, but the NO
_{Since the} amount of _X emissions, the amount of unburned ash remaining in the ash, etc., increase significantly compared to fuels such as gas and oil, the impact on the environment and efficiency is great.

Particularly when the coal as a fuel, since the nitrogen component contained in itself be converted to the NO _X by the combustion, the generation quantity becomes enormous. Furthermore, since the combustion speed is much slower than that of gas or oil, the residual amount of unburned ash in the ash tends to increase as the furnace temperature decreases.

The increase in unburned ash content lowers boiler efficiency and puts various restrictions on waste disposal. Furthermore, with the use of high-fuel-ratio coal (solid carbon / volatiles) and low-grade coal as the fuel for pulverized coal, measures to reduce unburned ash in ash are urgently needed. Therefore, new technical measures for reducing unburned ash are demanded.

In the combustion of pulverized coal, pulverized coal sent into the furnace together with the primary air receives radiant heat from the high temperature furnace wall and flame, the temperature of the coal particles rises, moisture evaporates, and then volatiles are generated. The temperature rises sharply by the combustion of the primary and secondary air and forms a flame before igniting and balancing the heat radiation and the heat generated by the combustion.

On the other hand, in the combustion process of the fine powder particles, the decomposition and combustion of volatile components advance at the beginning of the combustion, and then the surface combustion of coke-like residual carbonaceous material (hereinafter referred to as char) proceeds. The surface combustion of char is much slower than the decomposition combustion of volatiles,
Most of the time it takes to completely burn out is considered to be required for char burning on the surface.

From this, pulverized coal combustion has a high fuel ratio, ash content, caking property,
There are many factors related to the properties, such as particle size distribution, and it is very difficult to uniformly estimate unburned ash in the ash during the combustion process.

However, the combustion method for reducing the ash unburned is by the O ₂ to slightly excessive that it is sufficient to once burned in the furnace of high temperature atmosphere is evident from the experience, control over and safety thereof There is a problem with such a driving method.

At present, pulverized coal-fired boilers for business or industrial use are operated to reduce unburned ash in ash as much as possible to improve boiler efficiency. When a combustion method such as slow combustion is employed, the temperature in the furnace decreases, and the unburned ash in the ash tends to increase.

It has been found that many of these problems can be solved by improving the shape of the combustion flame and the like, and a method for reducing the unburned ash content by relating the flame to the unburned ash content has been disclosed in Japanese Patent Application Laid-Open No. 61-1986. This is proposed in Japanese Patent No. 93317. An outline of this conventional example will be described with reference to FIG.

FIG. 8 shows three cases of flames having different shapes during pulverized coal combustion. (A) The unburned ash content is low and NO _X is high, and the furnace temperature is high. (B) The ash unburned content is high and NO _X is between (a) and (c).
During furnace temperature is low flame, is (c) in the ash unburned (a) (b), NO X is reduced, the furnace temperature is flame, between (a) (b).

The flame, that is, the combustion region of pulverized coal, is divided into a primary combustion region mainly composed of volatile components and a secondary combustion region mainly composed of solid carbon components. When focusing on unburned components, there is an extremely high correlation with the remaining amount. In FIG. 8, (a) the flame in the primary combustion region is large, and (b) the flame in the primary combustion region is (a).
(B). (C) The size of the flame in the primary combustion region is the smallest.

There are such features.

In the case of (a), the pulverized coal is diffused into a furnace in a high-temperature atmosphere in an appropriate manner so that the O ₂ distribution around the pulverized particles is optimized, thereby quickly igniting volatile components and maintaining the high-temperature atmosphere. Burns fine particles rapidly, and has low unburned content in ash.

In the case of (b), the pulverized coal and the O ₂ distribution are separated, and combustion proceeds only in the contact area between the two, so that a large amount of unburned fine powder particles remain as unburned components.

In case (c), to optimize pulverized coal and O ₂ distribution, 2
The secondary air is swirled to disperse the pulverized coal near the burner to promote combustion, and the swirl causes a negative pressure in the downstream part of the pulverized coal, so that pulverized coal and O ₂ are mixed and combustion proceeds. The unburned ash content is between (a) and (b).

Based on the phenomenon that the flame size in the primary combustion area and the flammability from the burner tip in the flame shape of FIG. 8 are effective in reducing the unburned ash in the ash, for example, the designation of the unburned ash in the ash The characteristic parameter (feature amount) of the flame shape for _{obtaining the} index (I _UBC ) is determined as shown in FIG.

In FIG. 9, the primary combustion region, that is, the region having high luminance is referred to as oxidizing flames A ₁ and A ₂ . Here, for example, as a characteristic parameter representing the oxidizing flame, the position of the oxidizing flame from the tip of the burner X = dZ / dB (1) the distance between the oxidizing flames Y = dX / dB (2) the thickness coefficient Z of the oxidizing flame = A / b (3) where, dB: burner diameter a: axial thickness of oxidizing flame b: thickness of oxidizing flame in radial direction In formulas (1) and (2), burner diameter dB and distance d
Although the ratio with Z, dX is used, the value of dZ, dX may be used as it is.

Here, using the formulas (1) to (3), an estimated index I _{UBC of} unburned ash in ash is defined by, for example, I _UBC = k × X ^-1 Y ^-1 .Z (4) I do. Here, k is a primary diameter coefficient.

On the other hand, the following parameters other than those described above can be used as the characteristic parameters representing the oxidizing flame.

X of FIG. 9, as G _1, defined beside the G ₂ representing the Y, the center of (1) G ₁ in FIG. 9, G ₂ and oxidizing flame.

(2) Let G ₁ and G ₂ be the positions closest to the oxidizing flame from the burner tip in FIG.

(3) The positions where the flame temperature is the highest are G ₁ and G ₂ .

(4) Obtain the oxidizing flame from the temperature distribution and determine the center of gravity as G ₁ , G ₂
And Further, Z may be a flame thickness in the burner radial direction, etc., but these are all parameters indicating the position or size of the oxidizing flame from the burner tip, and as long as Z is not necessarily the center of gravity or the thickness. However, the distribution of the luminance (or temperature) of the oxidizing flame is contoured, and its area changes according to the limit value of the extraction of the high-luminance area. It is considered appropriate to use the center of gravity as a feature parameter representing.

[Problems to be solved by the invention]

The above prior art qualitatively captures the characteristics of the flame shape shown in FIG. 8, and when burning with the same coal type,
The unburned ash content can be estimated relatively accurately. However, the type of coal burned in an actual boiler is not limited to one type, and rather, many types of coal must be burned in the current situation where most of the coal is imported from overseas. In the case where the coal type is changed or the burner type, the burner arrangement in the furnace, etc. is changed, the characteristic parameter of the combustion state extracted from the flame shape represents a physical quantity which is a universal parameter in the above-described conventional technology. Therefore, there is a problem that the estimation accuracy of the unburned portion in the ash is poor, and the above-described conventional technology cannot be applied as it is.

An object of the present invention is to estimate or estimate in a short time the amount of unburned ash in ash that has an effect on combustion efficiency contained in flue gas during boiler operation, and to monitor or control combustion for realizing an operation that reduces this. It is an object of the present invention to provide a method and an apparatus therefor.

[Means for solving the problem]

In order to achieve the above object, the present invention detects a flame temperature of a furnace, calculates energy generated from the flame temperature, and uses the energy as output energy of the flame, the amount of coal supplied to a burner, the amount of heat generated by the coal. Calculate the input energy from the amount, calculate the energy balance, calculate the combustion rate in the combustion flame, and based on this combustion rate, the amount of non-carbon supply to the burner, the amount of air supply, the preheated air temperature, A method and apparatus for controlling the amount of air supplied to the burner, the preheated air temperature, the ash content in coal, etc. so as to estimate the unburned content in the ash using the ash content in the coal and further reduce the unburned content in the ash. It is provided.

[Action]

The energy generation rate E that is generated by the combustion flame is the sum of the energy E ₂ generated by the energy E ₁ and the flame due to the temperature rise of the supplied combustion gas (含未燃固body min), E = E ₁ + E ₂ (K cal / h) ... (5) This is the energy of the coal output by the flame.

On the other hand, the energy E ₀ supplied to the burner is given by the following equation based on the coal supply amount Gcoal and the calorific value Hcoal of the coal.

E ₀ = Gcoal · Hcoal (k cal / h) (6) From the energy balance of the equations (5) and (6), the combustion rate x in the combustion flame is given by the following equation (7).

Equation (7) is the combustion rate in the field of view downstream end being observed, different from the combustion ratio x _F at furnace exit. Then, the burning rate x obtained for each stage of the furnace is xi (i indicates the number of stages).
Considering the combustion at the gas retention time Δti from the vicinity of the burner to the furnace outlet (or the region where the temperature is reduced to a negligible extent), the combustion rate xi at the furnace outlet xi of the combustion rate xi at each stage is considered. _F is given by xi _F = f (xi, Δti) (8)

Therefore, the average burn rate x _F at the _{outlet, x F = zyi · xi F} ...... (9) where, yi: coal supply weight next to the i-th stage, the estimated ash in unburned UBC at the outlet Here, A: given by the ash content in the coal.

Therefore, if the burner operation amount such as the amount of coal supplied to each burner, the amount of supplied air, the calorific value of the coal, the preheated air temperature, etc. and the temperature and radiant energy of the combustion flame are measured, the unburned UBC in the ash at the furnace outlet is Can be estimated.

These quantities are physical quantities and include the effect of burner type, burner configuration, and coal type.

〔Example〕

 Hereinafter, the present invention will be described based on embodiments shown in the drawings.

FIGS. 1 and 2 relate to an embodiment of the present invention, and FIG. 1 shows a case in which monitoring and diagnosis of unburned ash UBC in a single burner are performed. In FIG. A cooling pipe 5 is inserted and arranged in the viewing window 3 formed in the furnace wall 2. The cooling pipe 5 is provided with an image fiber 8 connected to an ITV camera 6, and the ITV camera 6 is connected to a combustion state monitoring device shown in FIG. A burner 9 to which primary air and pulverized coal are supplied is provided in the upper part of the furnace 1. Around this burner 9, a secondary air supply pipe 10 and a tertiary air supply pipe 11 are provided, and an air introduction hole 12 is provided below the furnace 1.

Then, an image fiber 8 cooled with water or air by the cooling pipe 5 from the viewing window 3 was inserted into the furnace 1, and the image of the combustion flame 13 was guided to the outside of the furnace 1 by the image fiber 8, and was guided to the outside of the furnace 1. The flame image is converted into an electric signal by the ITV camera 6.

In FIG. 1, 15 is a swirler for swirling air, and 16 is a filter. In addition, image fiber 8
Alternatively, a wide-angle lens may be used.

FIG. 2 shows an example of a combustion state monitoring device.
The analog video signal 18 from the ITV camera 6 is converted to an A / D converter 19
Is converted into a digital video signal 20, and this signal 20 is written to the frame memory 21. The written image data 22 is taken into the processor 23, and the processor 23
Calculates the combustion rate x at the downstream end of the flame, which is observed in the above. The manipulated variables and the measured variables (coal supply, air supply, coal heating, preheated air temperature, etc.) 25 are input to the processor 23 as digital signals 28 via the process I / O 26, and are written in the processor 23 in advance. It is substituted into the equations (5) to (10) and calculated as the estimated unburned ash in the ash UBC.

In Fig. 2, 29 is the data of unburned UBC in ash, and 30 is
Is a display device for the data 28.

As described above, the apparatus according to the present embodiment includes an image fiber 8 as an image detection unit that detects a flame image of the furnace 1,
An ITV camera 6 is provided, and a temperature calculating means for calculating a flame temperature from a flame image, a burning rate calculating means for calculating a burning rate at the furnace 1 outlet from the flame temperature, and an ashes in the ash for calculating an unburned portion in the ash from the burning rate. A processor 23 is provided as unburned content calculating means and control means for controlling the amount of coal supplied to the burner 9, the amount of air supplied, the preheated air temperature, and the like so as to reduce the unburned content in the ash.

As an example of the above processing, an outline of the internal processing flow of the processor 23 will be described with reference to FIG.

Step 100: Input Flame Image Data The flame image data IM (i, j) is input to the processor 23 (i = 1 to I, j = 1 to J).

Step 110: Averaging of flame image data A flame shape having the highest probability indicating the combustion state is obtained (an example is shown in equation (11)).

Step 120: Calculate the temperature of the flame Using the principle of a two-wavelength thermometer, calculate the temperature of the flame,
Calculate the average temperature.

Step 130: Calculate energy Using the flame temperature calculated in step 120, energy due to temperature rise of the supplied combustion gas (including unburned solids)
The E ₁ and energy E ₂ generated by the flame is calculated by the following equation.

E ₁ = f ₁ (Gcoal, Gair, T ₀ , T)… (12) E ₂ = f ₂ (T) …… (13) where, Gcoal: coal supply amount Gair: air supply amount T: flame temperature T ₀ : Preheated air temperature Energy E ₀ associated with the coal supplied to the burner is calculated by equation (6).

Step 140: Calculation of combustion rate x Input energy E ₀ to the burner calculated in step 130
And the energy E = E ₁ + E ₂ generated by combustion (7)
By substituting into the equation, the combustion rate x at the downstream end of the combustion flame
Can be calculated.

Step 150: the average combustion rate calculation step 120 and 140 at the calculated flame temperature at the furnace outlet, the combustion rate and the operation amount, using a metered amount, an average burn rate x _F at furnace exit by the following equation.

x _F = f ₃ (x, Tair, Δt, Gcoal, Gair, y) …… (14) where, Tair: average flame temperature Δt: temperature falls from near the burner to the furnace outlet (or to the extent that combustion can be ignored) Todokotamari time to reach region) y: the distribution a of the average burn rate X _F and coal in furnace exit calculated in calculation step 150 in the ash unburned: coal supply weight step 160 for each stage Calculate the estimated unburned portion UBC at the exit by substituting into equation (10).

Step 170: Output of estimation result of unburned ash in ash The estimated value UBC of unburned ash in ash is output to the output device.

Step 180: Judgment of the result of estimation of unburned ash in ash It is judged whether or not the estimated value UBC of unburned ash in ash in step 170 is appropriate. Here, if the determination is YES, the program ends, but if the determination is NO, that is, if the estimated value of the unburned ash in the ash is large, the air supply amount to the burner 9, the preheated air temperature, the ash content in the coal And the like to execute the program according to the above-described procedure.

As described above, the method according to the present embodiment includes: (a) a first step: a step of detecting a flame temperature of the furnace 1, (b) a second step: a step of calculating energy generated from the flame temperature, (C) Third step: The energy is used as the output energy of the flame, the input energy is calculated from the amount of coal supplied to the burner 9 and the calorific value of the coal, the energy balance is obtained, and the combustion rate in the combustion flame 13 is calculated. (D) fourth step: the amount of coal supplied to the burner 9, the amount of air supplied, and the preheating based on the combustion rates obtained in the first to third steps. A process of estimating the unburned portion of the ash at the outlet of the furnace 1 using the air temperature and the ash content of the coal, and monitoring the combustion state of the furnace 1 based on the estimated unburned portion of the ash; : Air supply to burner 9 so that unburned ash in the ash decreases, preheated air Process for controlling air temperature and ash content in lime.

As described above, the flame temperature and the energy generated in the flame are calculated from the flame image, the combustion rate is calculated from the balance of the coal energy supplied to the burner, and the unburned ash in the ash is estimated from the manipulated variables and the measured variables. It becomes possible to accurately estimate or predict the unburned portion in the ash at the position.

As another embodiment, FIG. 4 shows a case where a plurality of different burners are monitored by the combustion state monitoring device according to the present invention. In this case, a method of switching the image input unit of the combustion state monitoring device at the time of each image input of the A, B, and C stages (FIG. 5 (a)), the A / D converter and the frame memory are respectively A, B, C Prepare for the step, 3
Method of inputting an image to the frame memory 21 at the same time (step 5
Figure (b) is conceivable. The internal processing of the processor 23 is
It is basically the same as FIG.

For example, by using the present invention to monitor the combustion state of an actual boiler, the burner combustion state of each stage, that is, the boiler operation state can be monitored, and a fine and highly efficient operation taking into account the influence of after-air can be realized. Also, from the estimated value of unburned ash in the ash of the present invention, the manipulated variable (air supply, air ratio, etc.)
, The burden on the operator can be further reduced. 4 and 5, reference numeral 31 denotes an after-airport, and 32 denotes a video signal switching device.

Furthermore, the invention is not dependent on the type of burner. For example, when the combustion flame is measured from the cross section direction of the burner even if the burner type is different as shown in FIGS. 6 and 7, it is clear from the fact that the flame formed has the same shape in both FIGS. is there.

Further, in the present embodiment, when calculating the combustion temperature and the energy generated by the flame, the image of the combustion flame is used by the image fiber 8, but other temperature measurement methods can be more simply used.
For example, it goes without saying that a similar effect can be expected even if a radiation thermometer, a dual-wavelength thermometer, or the like, or a radiation energy measuring device is used as a sensor.

〔The invention's effect〕

According to the present invention, the combustion rate is obtained from the energy balance of the energy supplied to the burner and the energy generated by the combustion flame, and the unburned ash in the ash at the furnace outlet can be accurately estimated, thereby controlling the burner operation amount. This has the effect of increasing combustion efficiency.

[Brief description of the drawings]

1 to 3 relate to an embodiment of the present invention, FIG. 1 is a longitudinal sectional view of a furnace part, FIG. 2 is a schematic configuration diagram of a combustion state monitoring device, and FIG. 3 is a schematic process of a processor. Flowchart,
FIG. 4 (a) is a schematic front view of a furnace part according to another embodiment,
FIG. 4 (b) is a plan view of FIG. 4 (a), and FIG.
The figure shows an example of an image input method according to another embodiment. FIGS. 6 (a) and 7 (a) are schematic front sectional views of a burner part according to another embodiment, FIGS. 6 (b) and 6 (b). 7 (b) is a plan view of those shown in FIGS. 6 (a) and 7 (a), FIG. 8 is a diagram comparing flame shapes, and FIG. 9 is a feature extracted from a flame shape of a conventional example. It is a figure showing a parameter. 1 ... furnace, 5 ... cooling pipe, 6 ... ITV camera, 8 ... image fiber, 9 ... burner, 10 ... secondary air supply pipe, 11 ... tertiary air supply pipe, 13 ... flame , 18: analog video signal, 19: A / D converter, 20: digital video signal, 21: frame memory, 22: image data, 23: processor, 25: operation amount and measurement amount.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Jinichi Tomuro 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Inside the Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Toru Kimura 5-2-1 Omika-cho, Hitachi City, Ibaraki Stock (72) Inventor Hisanori Miyagaki 5-2-1 Omika-cho, Hitachi City, Ibaraki Prefecture In-house Hitachi Omika Plant (72) Inventor Hiroshi Inada 2-6-1 Otemachi, Chiyoda-ku, Tokyo No. Babcock Hitachi Co., Ltd. (72) Inventor Yoshio Watanabe 1-7-33 Kashiwagi, Sendai City, Miyagi Prefecture (72) Inventor Naokatsu Sakuma 3-1-1-17 Yoshinari, Sendai City, Miyagi Prefecture (56) References JP JP-A-60-228818 (JP, A) JP-A-60-263013 (JP, A) JP-A-56-130525 (JP, A) JP-A-56-100224 (JP, A)

Claims (3)

(57) [Claims] 1. A method for detecting a flame temperature of a furnace of a pulverized coal-fired boiler, calculating energy generated from the flame temperature,
The energy is used as the output energy of the flame.On the other hand, the energy supplied to the burner is calculated from the amount of coal supplied to the burner and the calorific value of the coal, and the calculated energy is used as the input energy, and the balance between the input energy and the output energy is calculated. A method for monitoring a combustion state, comprising calculating a combustion rate in a combustion flame and monitoring a combustion state of the furnace based on the calculated combustion rate. 2. The method according to claim 1, wherein:
Using the air supply amount to the burner, the preheated air temperature, the ash content in the coal, etc., estimate the unburned content in the ash at the furnace outlet, and monitor the combustion state of the furnace based on the estimated unburned content in the ash. Characteristic combustion state monitoring method. 3. Detecting the flame temperature of the furnace of the pulverized coal-fired boiler, calculating the energy generated from the flame temperature,
The energy is used as the output energy in the flame.On the other hand, the energy supplied to the burner is calculated from the amount of coal supplied to the burner, the calorific value of the coal, etc., and this is used as the input energy, and the balance between the input energy and the output energy is calculated. The combustion rate in the combustion flame is calculated, and the air supply amount to the burner based on the combustion rate, the preheated air temperature, the unburned ash content in the ash at the furnace outlet using the ash content in the coal, etc. are estimated, A method for controlling a combustion state, comprising controlling an air supply amount to a burner, a preheated air temperature, an ash content in coal, and the like so as to reduce the unburned content in the ash.