JP2006057893A - Boiler control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a boiler control device for controlling combustion so as to prevent ash having a low melting point from adhering when combustion in a boiler furnace is executed by using a low-quality pulverized coal fuel such as subbituminous coal. <P>SOLUTION: This boiler control device is provided with: a means for calculating moisture of coal in a pulverized coal mill; a means for calculating a heat value of coal in process of combustion in the boiler furnace; and a means for determining a property of the coal to be burnt from the moisture of the coal and the heat value of the coal and thereby adjusting coal particle size at the exit of the pulverized coal mill. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a boiler control apparatus, and more particularly to a boiler control apparatus suitable for optimizing control characteristics for a large change in coal properties, particularly low-grade coal such as subbituminous coal and lignite, in a pulverized coal fired boiler. .

Coal combusted in a pulverized coal-fired boiler has different coal properties depending on the coal-producing area, and measures to stably control the pulverized-coal-fired boiler by burning a wide range of coal have become an important issue. Conventionally, charcoal with a high degree of carbonization called bituminous coal was often used because it has a large calorific value, but the coal property difference was not so large and devised to absorb the coal property difference, but it was a problem so much I didn't. However, in the future, sub-bituminous coal and lignite with low carbonization tend to be used, and technology development is urgently needed. In particular, subbituminous coal is characterized by low calorific value, low ash content, low sulfur content, and high volatile content. Low sulfur content results in low sulfur oxide emissions, high volatile content, and low carbon content. Therefore, there are many advantages such as low CO ₂ emission, but the ash melting point is low, and when burning in a normal boiler, slag adheres to the furnace, heat recovery characteristics deteriorate, and in the worst state, There was a problem that the furnace was blocked by slag.
JP 08-125953 A

  The problem of the present invention is to solve the above-mentioned problems of the prior art, and when burning in a boiler furnace using pulverized coal fuel, such as subbituminous coal, to which low melting point ash is likely to adhere, It is providing the boiler control apparatus which controls combustion so that it does not adhere easily.

In order to solve the above problems, the invention claimed in the present application is as follows.
(1) A pulverized coal mill, means for calculating the moisture of coal in the mill, means for calculating the calorific value of coal burned in a boiler furnace, and the amount of coal burned from the moisture of coal and the calorific value of coal The boiler control apparatus which has a means to determine a property, and a means to adjust the coal particle size of a pulverized coal mill exit from the property of this coal.
(2) The apparatus according to (1), wherein the coal is subbituminous coal or lignite.

(3) Calculate the heat input and output of the boiler from the coal inlet water temperature, outlet air temperature, mill casing temperature, coal temperature, coal flow rate, and mill inlet air flow rate, The apparatus according to (1) or (2), wherein the coal moisture is calculated from the balance.
(4) It has a measuring means for boiler main steam temperature, boiler main steam flow rate, boiler main steam pressure, and coal supply amount, and means for calculating the calorific value of coal based on the input of the measuring means. The device according to any one of (1) to (3).

  By reducing the number of revolutions of the pulverized coal mill's rotation classifier, the particle size of the pulverized coal is reduced, and the combustion time of the pulverized coal is lengthened, so that the temperature distribution in the boiler is moved to the downstream side, and the furnace By lowering the temperature, the boiler can be controlled and operated while preventing the ash from adhering to the furnace by operating the peak temperature in the furnace at a temperature lower than the low ash melting point temperature.

In the following examples, control was performed so as to reduce the fine particle size of the mill and lower the combustion temperature in the vicinity of the burner, but a similar effect can be expected by reducing the primary air amount of the mill or the secondary air amount of the burner. Therefore, it may be used in combination with these methods.
[Action]

  Coal that burns in a pulverized coal-fired boiler is pulverized into pulverized coal in the mill. However, if the particle size is fine, the contact area with air increases when burning in the burner, and apparently the mixing speed and combustion As the speed increases, the combustion temperature near the burner increases. The boiler is mainly composed of a furnace, a front heat transfer tube, and a rear heat transfer tube, but if the temperature near the burner is high, adhesion of molten ash in the furnace increases, so the amount of heat absorbed in the furnace decreases, As a result, the temperature at the inlet of the heat transfer tube rises, and the adhesion of molten ash to the front heat transfer tube also increases. If this vicious cycle continues, the molten ash adheres to the front heat transfer tube, and the heat absorption moves to the rear heat transfer tube. Usually, the ash removal is performed by the soot blower, so that there is no significant deterioration. However, the greater the ash adhesion before the soot blower operation, the greater the fluctuation in the endothermic balance after the soot blower operation, and the greater the disturbance to the boiler.

  On the other hand, if the pulverized coal has a coarse particle size, the area of contact with air is reduced during combustion in the burner, and apparently the mixing speed and the combustion speed are reduced, and the combustion temperature in the vicinity of the burner is lowered. When the temperature in the vicinity of the burner falls, it becomes an operating point that does not melt even ash with a low melting point, so there is little ash adhering to the furnace, and the flame temperature is low, but heat absorption in the furnace is better than ordinary coal (bituminous coal) Also, the endotherm is slightly lower. Accordingly, the front heat transfer tube and the rear heat transfer tube can be continuously operated while maintaining a considerable amount of heat absorption at a temperature lower than the ash melting temperature.

  Thus, in coal with a low ash melting temperature, it is important to operate by lowering the flame temperature of the burner, and as a control method, if the property of the coal is detected and this property is low-grade coal, This can be achieved by reducing the fine particle size at the outlet.

  In the case of subbituminous coal, the coal moisture is 20% or more and the calorific value is 5500 kcal / kg. Therefore, the coal moisture is calculated from the heat balance of the mill, and the calorific value of the coal is calculated from the boiler output and the coal supply. By calculating, it can be determined whether the currently burning charcoal is subbituminous coal. Therefore, in the case of subbituminous coal, by reducing the fine particle size at the mill outlet, even with subbituminous coal having a low ash melting point, it is possible to stably operate with a normal boiler.

    FIG. 1 is an explanatory diagram of a boiler control apparatus showing an embodiment of the present invention. Based on the inputs of the mill inlet primary air flow meter 1, the mill inlet primary air thermometer 2, the mill outlet air thermometer 3, the coal feed meter 4, and the mill casing thermometer 5, the coal moisture calculator 6 Calculate moisture. The water content of coal is calculated from the balance of the heat input and output of the mill using the following formula.

Quantity of heat supplied to the mill: Qin
(1) Primary air: Ma, Ti, Ca
(2) Coal supply (dry coal), coal supply moisture: Mcd / Tc / Cc + Mcw / Tc / Cw
Heat stored in the mill: ΔQ
(1) Increase in coal holding temperature in the mill, increase in coal moisture temperature (2) Temperature rise in the mill casing Heat released from the mill: Qout
(1) Mill outlet air: Ma, To, Ca
(2) Coming coal (pulverized coal), combusting water, evaporating water: Mod, To, Co + Mow, To, Co
(3) Heat radiation from the mill casing to the outside: Qin · K
Except for rapid temperature fluctuations such as when the mill is started and when it is stopped, ΔQ = 0 in the state where the coal supply amount and the coal output amount are balanced, and the following equation holds.

Qin = Qout
Qin ＝ Ma ・ Ti ・ Ca + Mcd ・ Tc ・ Cc + Mcw ・ Tc ・ Cw
Qout = Ma, To, Ca + Mcd, To, Cc + Mcw, To, Co + Qin, K
Mcw = (Ma (Tik ¹ -To) Ca + Mc (Tck ¹ -To) Cc / ((Co-Cc) To- (Cw-Cc) k ¹ Tc)
Q (kJ / h): Mill heat storage Mcd (kg / h): Charging (dry coal)
Mcw (kg / h): Coal supply moisture Ma (kg / h): Primary air flow rate
Mc (kg / h): Coal supply (Mcd + Mcw)
Mod (kg / h): coal output (dry coal) Mow (kg / h): coal output moisture
Cc (J / kg ° C): Specific heat of coal Ca (J / kg ° C): Specific heat of air
Cw (J / kg ° C): Specific heat of water Co (J / kg ° C): Specific heat of outlet water / steam
Tc (℃): Coal feed temperature Ti (℃): Primary air temperature
To (° C): Mill outlet air temperature K (-): Emission coefficient
Mw (%): Coal moisture (Mcw / Mc × 100)
The calculated moisture value is compared with the set value (20% here) set by the coal moisture setting device 7 in the comparator 8, and it is determined that the moisture of the coal is equal to or more than the set value (20%).

  On the other hand, the coal supply amount (Kg) is obtained from the total coal flow meter 9, the boiler heat input (kcal) is obtained from the generator output meter 10, and these inputs are used to calculate the calorific value of the coal by the coal calorific value calculator 11. . The calorific value of coal is obtained by the following formula.

Hc = Q _FL / _Fc (kcal / Kg)
Hc: Calorific value (kcal / Kg) Q _FL : Boiler heat input (kcal) Fc: Coal supply (Kg)
The obtained calorific value may be corrected by an appropriate correction circuit. The calculated calorific value is less than the set value (5500 kcal if the coal is sub-bituminous coal) compared with the set value (here, 5500 kcal) set by the coal calorific value setter 12 in the comparator 13. Determine that there is.
These two results are processed by an AND (logical product) computing unit 14, and it is determined that the moisture of coal is 20% or more and the calorific value is 5500 kcal or less.

  The inverter 19 is set with the rotational speed setting value of the rotational classifier determined in advance by the rotational classifier rotational speed setting unit 17, and the rotational speed of the classifier motor 20 is determined. When the moisture of coal is 20% or more and the calorific value is 5500 kcal or less, the output of the AND calculator 14 becomes 1, so the rotation speed (10 rotations) set by the classifier reduction rotation speed setting device 15 is The subtractor 18 subtracts from the initial rotational speed, resulting in a lower rotational speed. By this treatment, when the moisture content of the coal is 20% or more and the calorific value is 5500 kcal or less, the classifier reduction rotational speed is reduced, and the original purpose can be achieved.

  According to the present invention, subbituminous coal with a low ash melting temperature, which is not much used at present but with a low reserve, is automatically identified during boiler combustion, and by controlling the mill so as to reduce the fine particle size at the mill outlet, The boiler can be stably controlled without melting the low-melt ash in the furnace.

Explanatory drawing of the boiler control apparatus which shows one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Mill inlet primary air flow meter, 2 ... Mill inlet primary air thermometer, 3 ... Mill outlet air thermometer, 4 ... Coal feed meter, 5 ... Mill casing thermometer, 6 ... Coal moisture calculator, 7 ... Coal Moisture setting device, 8 ... Comparator 1, 9 ... Total coal flow meter, 10 ... Generator output meter, 11 ... Coal heating value calculator, 12 ... Coal heating value setting device, 13 ... Comparator 2, 14 ... AND operation 15: classifier reduction speed setting device, 16: multiplier, 17 ... rotation classifier rotation speed setting device, 18 ... subtractor, 19 ... inverter, 20 ... classifier motor.

Claims (4)

A pulverized coal mill, means for calculating the water content of the coal in the mill, means for calculating the calorific value of the coal burned in the boiler furnace, and determining the property of the combusted coal from the water content of the coal and the calorific value of the coal And a means for adjusting the coal particle size at the outlet of the pulverized coal mill from the properties of the coal. The apparatus according to claim 1, wherein the coal is subbituminous coal or lignite. The moisture content of the coal is calculated from the balance by calculating the heat input and output heat of the boiler from the mill inlet air temperature, outlet air temperature, mill casing temperature, coal temperature, coal flow rate, and mill inlet air flow rate. 3. The apparatus according to claim 1, wherein the moisture of the coal is calculated. A boiler main steam temperature, a boiler main steam flow rate, a boiler main steam pressure, and a coal supply amount measuring means, and a means for calculating the calorific value of coal based on the input of the measuring means. Item 4. The apparatus according to any one of Items 1 to 3.

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