JP2010096431A - Combustion control method and combustion control device of fine powder-like fuel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustion control device of fine powder-like fuel capable of achieving low NOx combustion while effectively utilizing solid fuel other than bituminous coal which has not been satisfactorily used from a practical point of view, in a boiler which mixes and burns the fine powder-like fuel formed of a plurality of kinds of solid fuel. <P>SOLUTION: The combustion control device includes a computing unit 8 and coal supply amount adjusting devices 3, 3. The computing unit collects data of a past fuel ratio of fine powder coal C formed of two kinds of mixed/crushed coals A, B, and a past NOx concentration in exhaust gas D to obtain NOx a peak concentration and a NOx peak fuel ratio, sets a NOx acceptable concentration beforehand based on the NOx peak concentration, compares a present NOx concentration measured by a gas analyzer 7 with the NOx acceptable concentration, and when the present NOx concentration exceeds the NOx acceptable concentration, issues a command of changing the combination rate of the coals A, B so as to lower the NOx concentration in the exhaust gas D to be the same as or lower than the NOx acceptable concentration by adjusting the fuel ratio of the fine powder coal C to be farther from the NOx peak fuel ratio. The coal supply amount adjusting devices change supply amounts of the coals A, B based on the command. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a combustion control technique in a boiler using pulverized fuel such as pulverized coal as fuel.

  Coal is roughly classified into anthracite, bituminous coal, subbituminous coal, and lignite in descending order of the fuel ratio. However, in the present pulverized coal combustion boiler, the fuel ratio of mainly bituminous coal is 1.0 to 1.5. High-grade coal in the range is used. Here, the fuel ratio, which is an evaluation index of coal, is a value defined by fixed carbon / volatile matter (mass ratio), and the fuel ratio becomes smaller as the lignite is called low grade.

  The problem in combustion of pulverized coal is the generation of NOx and SOx. Particularly, the reduction of NOx is one of the most important issues, and various countermeasures have been conventionally taken.

  For example, as proposed in Patent Documents 1 and 2, low NOx has been realized by devising the structure of the pulverized coal combustion burner part.

  On the other hand, from the viewpoint of depleting high-grade resources and increasing supply costs in the future, it is required to use coal other than bituminous coal in the boiler.

  However, when burning coal with a high fuel ratio, there is a problem that the ignitability and combustibility are inferior because the ratio of the fixed carbon content is higher than the volatile content. Therefore, in Patent Document 3, in the combustion method of co-firing high fuel specific coal with a high fixed carbon content and low fuel specific coal with a low fixed carbon content, the particle size of the high fuel specific coal is set to be smaller than the particle size of the low fuel specific coal. Although a method for promoting combustion in a finer manner has been proposed, there remains a problem that the energy required for pulverization increases and the cost increases.

  On the other hand, lignite is included in the types of coal with a low fuel ratio, but lignite is not in practical use due to its high water content. However, for example, if the dehydration technique in oil disclosed in Patent Document 4 is used, the high moisture content can be removed from lignite and reformed into a fuel with a low moisture content and a low fuel ratio. Technology for using modified lignite is being studied.

Further, in Patent Document 5, in a combustion furnace in which many types of coal are co-fired, the coal fuel ratio and the N content in the fuel are input to the control circuit, and the O ₂ concentration in the exhaust gas, the unburned ash content, NH ₃ A method of controlling NOx by controlling the amount of air for two-stage combustion from an injection amount factor is disclosed. However, this technique controls NOx by controlling the amount of air for two-stage combustion under a predetermined fuel blending condition, and does not use the fuel blending condition itself as a control means as in the present invention. Both technical ideas are completely different.
JP 2001-82706 A JP-A-6-272810 Japanese Patent Publication No. 5-17445 JP 7-233383 A JP-A 63-207894

  Accordingly, an object of the present invention is to effectively use a solid fuel other than bituminous coal, which has not been sufficiently used in practice, in a boiler for co-firing finely pulverized fuels composed of a plurality of types of solid fuels. An object of the present invention is to provide a combustion control method and a combustion control device for finely pulverized fuel capable of realizing combustion.

  In order to solve the above problems, the inventors firstly, in a pulverized coal combustion test furnace (furnace inner diameter 400 mm, furnace effective height 3650 mm), the amount of heat input to the solid fuel is 600 kW, and the primary air and Using secondary air preheated to 300 ° C, bituminous coal A as the reference fuel, and four types of solid fuels (B, C, D, E) with different fuel ratios were changed in order, respectively. A test for co-firing was conducted, and changes in the NOx concentration in the exhaust gas collected at the furnace outlet were investigated.

Table 1 below shows the fuel ratio of each solid fuel used in the combustion test and the N content in the fuel.

The results of the combustion test are shown in FIGS. FIG. 2 shows the relationship between the fuel ratio of the pulverized fuel after mixing and the NOx concentration in the exhaust gas, and FIG. 3 shows the N content in the fuel and the NOx concentration in the exhaust gas after mixing. This shows the relationship. Here, the fuel ratio of the pulverized fuel after mixing and the N content in the fuel are values obtained by weighted averaging of the fuel ratio of each blended solid fuel and the N content in the fuel, respectively. Further, the NOx concentration in the exhaust gas (O ₂ : 6 volume% conversion) is converted from the measured NOx concentration and O ₂ concentration in the exhaust gas using the following formula (1).

[NOx concentration (O ₂ : 6 vol% conversion) (ppm)] = [actual NOx concentration (ppm)] × (21−6) / (21− [actual O ₂ concentration (capacity%)]) Equation (1 )

  As shown in FIG. 2, it is recognized that the fuel ratio of the pulverized fuel and the NOx concentration in the exhaust gas are in a substantially constant relationship regardless of the type of fuel to be co-fired. The NOx concentration in the exhaust gas shows a peak value when the fuel ratio of the pulverized fuel is between 1.0 and 1.5 (about 1.2 in this example), and the fuel ratio shows the peak value. It has been found that the NOx concentration decreases as the distance increases (both on the low and high fuel ratio sides).

  On the other hand, as shown in FIG. 3, it can be seen that the NOx concentration in the exhaust gas is hardly influenced by the N content in the fuel of the finely divided fuel.

  Considering the results shown in FIG. 2 and FIG. 3 comprehensively, the NOx concentration in the exhaust gas decreases when the blending ratio of the modified lignites C and D with a small N content is simply increased after mixing. It can be determined that this is not due to a decrease in the N content in the fuel of the pulverized fuel but to a decrease in the fuel ratio of the pulverized fuel after mixing.

  On the other hand, although the fuel ratio of the pulverized fuel after mixing is higher on the side where the NOx concentration becomes higher than the fuel ratio at which the peak value is reached, this test result shows that pulverized coal (pulverized fuel) Contrary to the conventional technical common sense that the NOx concentration in the exhaust gas increases as the fuel ratio increases (for example, refer to FIG. 7 of Patent Document 5 and page 2, left column 20-28 of Patent Document 3). It has become a trend. The reason why the test result different from the conventional technical common sense is obtained is assumed as follows.

  That is, at the time of the above-mentioned Patent Documents 3 and 5, since the pulverized coal was completely burned by blowing one stage of air in the burner part of the boiler, the volatile matter decreased when the fuel ratio of the pulverized coal increased, and the atmosphere The reduction property of NOx decreased and NOx production increased (see the second column, left column, lines 20 to 28 of Patent Document 3).

On the other hand, in recent years, in order to suppress the generation of NOx, air is blown into multiple stages (usually two stages or three stages) in the burner section (see, for example, Patent Document 1). Thereby, the generation of NOx is suppressed by making the atmosphere more reducible by incompletely burning the pulverized coal in the first stage air blowing section. When high-fuel ratio pulverized coal is co-fired in a boiler operating under such conditions, NOx generated in the first stage air blowing section and unburned high-fuel ratio pulverized coal derived Combustion char is brought into the air blowing section after the second stage, and NOx is reduced using the unburned char as a reducing material (2NOx + xC → N ₂ + xCO), so that the NOx concentration in the exhaust gas decreases. Conceivable.

  As a result of further investigation based on the above findings, the following invention has been completed.

  The invention according to claim 1 is a combustion control method in a boiler that co-fires fine powder fuel composed of a plurality of types of solid fuel, and the fuel ratio of the fine powder fuel and the boiler obtained from past operation results. The NOx concentration peak value (hereinafter referred to as “NOx peak concentration”) and the fuel ratio indicating the NOx peak value (hereinafter referred to as “NOx peak fuel ratio”). Based on the NOx peak value, an allowable value of the NOx concentration (hereinafter referred to as “NOx allowable concentration”) is set in advance, and the NOx concentration in the exhaust gas measured in the current operation is determined. When the NOx allowable concentration is exceeded, the blending ratio of the plurality of types of solid fuels is changed to adjust the fuel ratio of the pulverized fuel in a direction away from the NOx peak fuel ratio. A combustion control method pulverulent fuel, characterized in that to reduce the NOx concentration in the gas below the NOx allowable concentration.

  According to a second aspect of the present invention, the pulverized fuel is composed of a main fuel having a fuel ratio of 1.0 to 1.5 and an auxiliary fuel having a fuel ratio of less than 1.0. 2. The method for controlling combustion of fine powder fuel according to claim 1, wherein the adjustment is performed by increasing the blending ratio of the auxiliary fuel.

  According to a third aspect of the present invention, the pulverized fuel is composed of a main fuel having a fuel ratio of 1.0 to 1.5 and a secondary fuel having a fuel ratio of more than 1.5. 2. The method for controlling combustion of fine powder fuel according to claim 1, wherein the adjustment is performed by increasing the blending ratio of the auxiliary fuel.

  The invention according to claim 4 is a combustion control device in a boiler that co-fires finely pulverized fuel composed of a plurality of types of solid fuel, the gas analyzing means for measuring the NOx concentration in the exhaust gas of the boiler, and the past operation The fuel ratio of the pulverized fuel (hereinafter referred to as “past fuel ratio”) and the NOx concentration in the exhaust gas (hereinafter referred to as “past NOx concentration”) measured by the gas analyzer are used as data. Based on the relationship between the past fuel ratio and the past NOx concentration, the past NOx concentration peak value (hereinafter referred to as “NOx peak concentration”) and the fuel ratio indicating the NOx peak concentration (hereinafter referred to as “NOx peak”). Fuel ratio ”)), and a preset allowable value of NOx concentration in the exhaust gas (hereinafter referred to as“ NOx allowable concentration ”) based on the NOx peak concentration, The NOx concentration (hereinafter referred to as “current NOx concentration”) measured by the gas analyzing means in operation is compared with the NOx allowable concentration. When the current NOx concentration exceeds the NOx allowable concentration, A command to change the blending ratio of the plurality of types of solid fuels so as to lower the NOx concentration in the exhaust gas below the allowable NOx concentration by adjusting the fuel ratio of the pulverized fuel away from the NOx peak fuel ratio. And a fuel supply amount adjusting means for changing supply amounts of the plurality of types of solid fuel based on the command.

  According to the present invention, various solid fuels can be controlled by changing the blending ratio of a plurality of types of solid fuels and adjusting the fuel ratio of the finely divided fuel to keep away from the peak value of the NOx concentration in the exhaust gas. Low NOx combustion can be realized more reliably while effectively utilizing the.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG.

  FIG. 1 is a schematic flow diagram showing an embodiment of a pulverized fuel combustion apparatus according to the present invention.

  Reference numerals 1 and 2 are coal hoppers respectively holding two types of coals A and B having different fuel ratios, and reference numerals 3 and 3 are coal supply amounts for adjusting the cut-out amounts of the coals A and B from the coal hoppers 1 and 2. Adjusting device (fuel supply amount adjusting means), reference numeral 4 is a mixer for mixing the two types of cut coals A and B, reference numeral 5 is a pulverizer for pulverizing the mixed coal into pulverized coal C, reference numeral Reference numeral 6 denotes a boiler that burns pulverized coal C blown together with air, and reference numeral 7 denotes a gas analyzer (gas analysis means) that measures the NOx concentration in the exhaust gas D from the boiler 7.

  Reference numeral 8 denotes a computing unit (calculating means), which is the fuel ratio of pulverized coal C (hereinafter referred to as “past fuel ratio”) in the past operation, and the exhaust gas D measured by the gas analyzer 7. NOx concentration (hereinafter referred to as “past NOx concentration”) is accumulated as data, and the peak value of the NOx concentration (hereinafter referred to as “NOx peak”) obtained from the relationship between the past fuel ratio and the past NOx concentration. And a fuel ratio indicating the peak value (hereinafter referred to as “NOx peak fuel ratio”), and an allowable value of the NOx concentration in the exhaust gas D (hereinafter referred to as “NOx peak fuel ratio”). The NOx concentration measured by the gas analyzer 7 in the current operation (hereinafter referred to as “current NOx concentration”) and the NOx allowable concentration are compared. The current NOx concentration is N When the x allowable value is exceeded, the fuel ratio of the pulverized coal C is adjusted in a direction away from the NOx peak fuel ratio so that the NOx concentration in the exhaust gas D is reduced to be equal to or less than the NOx allowable concentration. It is a calculator (calculation means) which issues a command to change the blending ratio to the coal supply amount adjusting devices 3 and 3.

  For example, the coal hopper 1 holds bituminous coal A having a fuel ratio of 1.0 to 1.5 as a main fuel, and the coal hopper 2 holds reformed lignite B having a fuel ratio of less than 1.0 as a secondary fuel. Keep it. Then, the main fuel A and the auxiliary fuel B are cut out from the coal hoppers 1 and 2 by adjusting the blending ratio by the coal supply amount adjusting devices 3 and 3, mixed by the mixer 4, and then predetermined by the grinder 5. Crush to particle size to make pulverized coal C. The pulverized coal C is blown into the boiler 6 together with air and burned.

  The exhaust gas D after combustion is measured for NOx concentration (current NOx concentration) by the gas analyzer 7.

  Here, in the calculator 8, the fuel ratio (past fuel ratio) of the pulverized coal C in the past operation and the NOx concentration (past NOx concentration) in the exhaust gas D measured by the gas analyzer 7 are used as data. From the relationship between the past fuel ratio and the past NOx concentration, a peak value of the past NOx concentration (NOx peak concentration) and a fuel ratio indicating the peak value (NOx peak fuel ratio) are obtained (FIG. 4), an allowable value of NOx concentration (NOx allowable concentration) in the exhaust gas D is set in advance based on the NOx peak concentration.

  The allowable NOx concentration may be set as appropriate in consideration of the environmental regulation value or the like at the installation location of the pulverized fuel combustion device, but may be set to a certain ratio (for example, 80%) of the NOx peak concentration. The NOx peak concentration may be set to a value obtained by subtracting a constant concentration. In addition, as shown in the schematic diagram of FIG. 4, the relationship between the past fuel ratio and the past NOx concentration varies somewhat depending on the combination of the types of solid fuels used and has a certain range. The NOx peak fuel ratio may be set so as to fall within the range of the maximum NOx concentration (matching the NOx peak concentration) and the minimum NOx concentration.

  Further, the computing unit 8 compares the NOx concentration (current NOx concentration) measured by the gas analyzer 7 in the current operation with the NOx allowable concentration, and the current NOx concentration exceeds the NOx allowable concentration. When changing the fuel ratio of pulverized coal C in a direction away from the NOx peak fuel ratio, the blending ratio of coals A and B is changed so that the NOx concentration in the exhaust gas D is reduced below the allowable NOx concentration. Issue a command.

  The coal supply amount adjusting devices 3 and 3 that have received a command from the computing unit 8 adjust the cutout amounts of the coals A and B based on the command.

  As a result, since the NOx concentration in the exhaust gas D is always controlled to be kept below the allowable NOx concentration, low NOx combustion can be realized more reliably while effectively using solid fuel other than bituminous coal. .

(Modification)
In the above embodiment, coal having a fuel ratio of less than 1.0 (modified lignite in this example) is exemplified as the auxiliary fuel. Instead, bituminous coal or anthracite having a fuel ratio of more than 1.5 should be used. You can also.

  In the above embodiment, bituminous coal and modified lignite are exemplified as the solid fuel, but are not limited to these, and any solid fuel containing hydrocarbons can be used. For example, wood chips, biomass, waste plastic, waste, etc. can be used.

  Moreover, in the said embodiment, although the case where two types of solid fuels were mixed-fired was illustrated, it is applicable also when three or more types are mixed-fired. For example, when three types of solid fuels are co-fired, if the same control as in the above embodiment is performed with the mixing ratio of the two types being constant and these being used as the main fuel and the remaining one as the sub fuel, Good.

  Moreover, although the example which grind | pulverizes after mixing two types of solid fuel was shown in the said embodiment, for example, when one type is originally a fine powder form among two types of solid fuel, only one other type is used. What is necessary is just to mix after grind | pulverizing, for example, when two types are fine powder forms, what is necessary is just to mix by omitting a grind | pulverization.

It is a schematic flowchart which shows one Embodiment of the pulverized fuel combustion apparatus which concerns on this invention. It is a graph which shows the relationship between the fuel ratio of a pulverized fuel, and the NOx density | concentration in waste gas. It is a graph which shows the relationship between N content in the fuel of a pulverized fuel, and the NOx density | concentration in waste gas. It is a graph which shows typically the method of calculating | requiring NOx peak concentration and NOx peak fuel ratio from the relationship between the past fuel ratio of pulverized fuel, and the past NOx density | concentration in waste gas.

Explanation of symbols

1, 2: Coal hopper 3: Coal supply amount adjusting device (fuel supply amount adjusting means)
4: Mixer 5: Crusher 6: Boiler 7: Gas analyzer (gas analysis means)
8: Calculator (calculation means)
A, B: Coal (solid fuel)
C: Pulverized coal (pulverized fuel)
D: exhaust gas

Claims (4)

A combustion control method in a boiler that co-fires finely pulverized fuel composed of multiple types of solid fuel,
From the relationship between the fuel ratio of the pulverized fuel and the NOx concentration in the exhaust gas of the boiler obtained from the past operation results, the peak value of the NOx concentration (hereinafter referred to as “NOx peak concentration”) and the A fuel ratio indicating the NOx peak concentration (hereinafter referred to as “NOx peak fuel ratio”) is obtained, and an allowable value of the NOx concentration (hereinafter referred to as “NOx allowable concentration”) is preset based on the NOx peak concentration. Aside,
When the NOx concentration in the exhaust gas measured in the current operation exceeds the NOx allowable concentration, the blending ratio of the plurality of types of solid fuels is changed to change the fuel ratio of the pulverized fuel to the NOx peak fuel ratio. A combustion control method for pulverized fuel, characterized in that the NOx concentration in the exhaust gas is reduced below the allowable NOx concentration by adjusting in a direction away from the NOx.   The pulverized fuel is composed of a main fuel having a fuel ratio of 1.0 to 1.5 and an auxiliary fuel having a fuel ratio of less than 1.0, and the adjustment of the fuel ratio of the pulverized fuel is performed by adjusting the mixing ratio of the auxiliary fuel. The method for controlling the combustion of a pulverized fuel according to claim 1, wherein the combustion control method is performed by raising   The pulverized fuel is composed of a main fuel having a fuel ratio of 1.0 to 1.5 and an auxiliary fuel having a fuel ratio of more than 1.5, and the adjustment of the fuel ratio of the pulverized fuel is performed by adjusting the mixing ratio of the auxiliary fuel. The method for controlling the combustion of a pulverized fuel according to claim 1, wherein the combustion control method is performed by raising A combustion control device for a boiler that co-fires finely pulverized fuel composed of multiple types of solid fuel,
Gas analysis means for measuring the NOx concentration in the exhaust gas of the boiler;
The fuel ratio of the pulverized fuel in the past operation (hereinafter referred to as “past fuel ratio”) and the NOx concentration in the exhaust gas measured by the gas analysis means (hereinafter referred to as “past NOx concentration”). From the relationship between the past fuel ratio and the past NOx concentration, the peak value of the past NOx concentration (hereinafter referred to as “NOx peak concentration”), and the fuel ratio indicating the NOx peak concentration (hereinafter referred to as “NOx peak concentration”). "NOx peak fuel ratio") is determined, and an allowable value of NOx concentration in the exhaust gas (hereinafter referred to as "NOx allowable concentration") is set in advance based on the NOx peak concentration, and the current operation is performed. The NOx concentration measured by the gas analyzer (hereinafter referred to as “current NOx concentration”) is compared with the allowable NOx concentration, and the current NOx concentration exceeds the allowable NOx concentration. The blending ratio of the plurality of types of solid fuels so as to lower the NOx concentration in the exhaust gas below the allowable NOx concentration by adjusting the fuel ratio of the pulverized fuel away from the NOx peak fuel ratio. Computing means for issuing a command to change
Fuel supply amount adjusting means for changing the supply amounts of the plurality of types of solid fuels based on the command;
A combustion control apparatus for finely pulverized fuel, comprising:

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