JP2740970B2 - Operating method of coal boiler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a coal boiler having a flue gas desulfurization unit installed to reduce the concentration of sulfur oxides (hereinafter referred to as SO ₂ ) from flue gas. An operation method for controlling a desulfurization device in response to a change in boiler load, particularly to an operation method.

[Conventional technology]

At present, desulfurization systems for coal boilers, particularly power generation boilers, mainly use a desulfurization method called a limestone-gypsum method. The limestone - gypsum method is a lime in water was slurried by contacting with the exhaust gas, and at the same time fixed to the gypsum absorbs SO _2, a desulfurization method for reducing the SO ₂ concentration in the exhaust gas. The desulfurization reaction some elementary reaction as follows to secure the SO ₂ in the stable plaster.

_{SO 2 + H 2 O → H} + + HSO 3 - ...... (1) H + + HSO 3 - + 1 / 2O 2 → 2H + + SO 4 2- ...... (2) CaCO 3 + 2H + + SO 4 2- → CaSO 4 + 2H 2 _{O + CO 2 ...... (3)} H + + HSO 3 - 1 / 2O 2 → 2H + + SO 4 2- ...... (4) 2H + + SO 4 2- + CaCO 3 + H 2 O → CaSO 4 · 2H 2 O + CO 2 ...... ( 5) Summarizing these elementary reactions, Ca in the limestone slurry
CO ₃ reacts equimolarly with SO ₂ to produce gypsum (CaSO ₄ ).

CaCO ₃ + SO ₂ + 1 / 2O ₂ + 2H ₂ O → CaSO ₄ .2H ₂ O + CO ₂ … (6) Recent limestone-gypsum desulfurization equipment simultaneously blows air into the slurry in the absorption tower in order to streamline the equipment. It is common practice to oxidize sulfites and omit the oxidation tower.

Such limestone - limestone slurry in gypsum method as the control method (hereinafter, absorbent and referred) supply, conventionally, the amount of exhaust gas desulfurizer inlet, SO ₂ concentration in the exhaust gas, the slurry pH, etc. of the absorption tower tank Based on the detection result of
To cope with a change in the load of the boiler, an excessive amount of absorbent is preliminarily charged in advance.

In coal-fired power boiler, burning coal properties, days load change, because the SO ₂ concentration in the exhaust gas quantity and the exhaust gas changes due to adjustment of a stable combustion state corresponding to the coal type, the desulfurization device corresponding to these load changes Operation is required. When the boiler's daily load changes from 25% to 100% of the power generation boiler, the operation control of the desulfurization unit is based on the detection signal of the amount of exhaust gas, the concentration of SO _{2 in} the exhaust gas, and the pH of the slurry in the absorption tower tank. Control is being performed. In this method, there is a problem that the residence time in the path for supplying the absorbent, the residence time in the absorption tower, and the like are long and it is impossible to follow a load change.
Japanese Patent Application Laid-Open No. 63-315131 proposes to preliminarily control the supply amount of an absorbent to a desulfurization unit based on a signal obtained by analyzing the sulfur content in coal by an automatic analyzer.

[Problems to be solved by the invention]

In the conventional method, the supply amount of the absorbent to the desulfurization unit is controlled in advance by the analysis signal of the sulfur content in the coal by the automatic analyzer, so it is effective against fluctuations in fuel coal with different sulfur contents. However, this technique, however, does not take into account fluctuations in the load of the boiler, fluctuations in the operation amount of the combustion device, and the like.

For example, setting the optimal distribution of combustion air to reduce NOx generated in the boiler combustion section or improve the combustion rate is frequently performed during boiler operation, and the flow control system is set to a certain set value. However, since the flow rate always fluctuates within a certain range, it is important to promptly transmit the fluctuation to the controller for the supply amount of the absorbent in the desulfurization apparatus to adjust the supply amount of the absorbent.

Further at low load of the boiler, gas heats the exhaust gas desulfurizer outlet - due amount with leakage of air in the gas heat exchanger, the amount of exhaust gas introduced into the desulfurization apparatus, SO ₂ concentration from the sulfur content in coal Causes a problem that is different from the above-mentioned value, which leads to an excess / deficiency state of the absorbent, that is, an excessive supply or shortage state.

An object of the present invention is to solve the above-mentioned problems of the prior art, and captures a great deal of information on exhaust gas on the upstream side of a desulfurization device and transmits the information to the desulfurization device to reduce the load change. It is an object of the present invention to provide a method of operating a coal boiler that enhances responsiveness and smoothly controls the supply amount of an absorbent.

[Means for solving the problem]

The above object is to provide a moving bed flue gas desulfurization device for bringing solid particles into contact with flue gas of a coal boiler and absorbing or adsorbing sulfur oxides in the flue gas to the solid particles to reduce the sulfur oxide concentration. In the operating method of the provided coal boiler, a set value or a measured value of an operation factor such as a coal amount and an air supply amount for controlling a combustion state of the coal boiler,
By the value based on the analysis value of the sulfur content in the coal,
Controlling the solid particle supply rate in the moving bed flue gas desulfurization unit, and analyzing the sulfur content in the flue gas at the inlet of the moving bed flue gas desulfurization unit and the sulfur content in the coal based on the detected value of the amount of flue gas. If necessary, the value based on the value or the like is corrected, and the control signal based on the corrected value is used as a setting signal of the solid particle supply speed in the moving bed flue gas desulfurization apparatus, and the method for operating a coal boiler is characterized in that Achieved.

[Action]

In a normal coal-fired boiler, the operation is repeated within several hours from the maximum load to a quarter of the load in order to adjust the daily power generation. The change in the boiler load is performed by adjusting the amount of supplied coal and the amount of supplied air. The amount of exhaust gas, SO
To variations in ₂ concentrations, always in the desulfurization apparatus to maintain a predetermined desulfurization rate, it can be said that it is important so as not to discharge the SO ₂ from the system.

For this purpose, it can be said that the responsiveness of the desulfurization device is increased in accordance with the load amount, and the control of the supply amount of the absorbent is the operation factor which can be most easily handled. In order to increase the responsiveness of the desulfurization unit, it is necessary to quickly detect the load change amount of the boiler and transmit the signal to the absorbent supply system of the desulfurization unit to respond. As the means, detecting the boiler combustion conditions and the sulfur content in the burnt coal and transmitting the signal to the absorbent supply system eliminates the time delay of the desulfurization device and leads to the improvement of the responsiveness. In particular, in a fine coal boiler, the amount of exhaust gas is determined by converting the amount of air supplied from a burner into the furnace and the amount of coal supplied. Normally, the boiler load is changed at a rate of 3% to 8% per minute by changing the coal supply and air supply, but by detecting the rate of increase of the coal supply and air supply, the desulfurization unit is started. Advance control is possible.

Sulfur oxide generated by combustion of coal is caused by sulfur oxide contained in coal. Since the sulfur content in coal varies considerably even for the same coal type, it is necessary to detect the average value of sulfur concentration by continuous analysis for many sample points. It can be said that this analysis technique has already been established. Based on the exhaust gas amount of the signal obtained from the sulfur analysis signal and the coal supply quantity and air supply quantity calculating the SO ₂ concentration for use as absorbent feed amount of the signal to the desulfurization unit. Particularly when the load varies, the coal supply amount is changed, so this with the combustion air amount needs to be changed, the amount of exhaust gas, SO ₂
The concentration changes.

According to the configuration of the present invention, a moving bed flue gas desulfurization apparatus having a very simple configuration can be realized by directly controlling the moving speed of the solid particles. In addition, SO ₂
By controlling the solid particle supply rate of the desulfurization unit by regulating the concentration, not only the control corresponding to the load change can be performed quickly, but also the SOx in the exhaust gas at the desulfurization unit inlet can be controlled.
₍₂₎ It has an excellent effect that the concentration and exhaust gas amount can be detected and the operating factor and the sulfur content in coal can be back-checked from the combustion state, thereby preventing malfunction of the desulfurization unit. it can.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a system diagram of each component of a typical coal boiler and pulverized coal boiler system. The components of the coal-fired power generation boiler system are boiler 2, denitration equipment 4, electric precipitator 6,
It is constituted by a desulfurization device 8. The boiler 2 includes an air supply facility, a fuel supply facility, and a boiler body 2A.

The combustion air is supplied by a fan and heated to a predetermined temperature by heat exchange with combustion gas in an air preheating device (not shown), and then the primary air used for transporting coal and other combustion air are used. Separated with air. Primary air is introduced into a crusher (not shown) by a primary air fan,
Is pulverized into pulverized coal, transported to a burner (not shown), and charged into a furnace (not shown) from a pulverized coal nozzle in the burner. Combustion gas generated in the furnace is heated as heat exchange with water or steam in a group of heat exchangers installed between the furnace outlet and the outlet of the boiler 2, and then heated and discharged as an exhaust gas 12 outside the boiler 2. Is done.

The outlet of the boiler body 2A, denitration unit 4, an electrostatic precipitator 6, elements equipment desulfurizer 8 is installed, the combustion gas line after the NOx contained therein, dust, the concentration of SO ₂ is reduced
It is led to the chimney from 14 and discharged out of the system.

The concentration of NOx, SO ₂ , O ₂ , CO, etc. in the combustion gas depends on the denitration device 4
A part is used as a control factor of each component device in which the combustion gas is sampled at the inlet of the desulfurization device 8 and the concentration is measured by each analyzer. Combustion gas is also sampled and measured downstream of the exhaust gas flow from these flue gas treatment facilities.

The coal 10 is pulverized and supplied to the boiler 2. In this embodiment, the coal immediately after being introduced into the burner from the outlet of the coal crusher is sampled, and the sulfur content is determined by the analyzer 16. This sulfur analysis signal 18, the operation signal 20 such as the coal supply amount and the air supply amount of the boiler body 2 </ _b > A, and SO ₂ in the exhaust gas 22 of the desulfurization unit 8.
An exhaust gas property signal 24 such as concentration is taken into a calculator 26, and a control signal 28 from the calculator 26 is sent to a controller 30 to adjust the supply amount of the absorbent to the desulfurization device 8.

Although Figure 2 shows the relationship between the SO ₂ concentration in the exhaust gas when burned in air ratio in the same sulfur content in coal (humidity-based), the SO ₂ concentration coal species Since the air ratio is slightly different depending on the heat generation amount, the SO ₂ concentration corrected by the computer is used. By sending the set value signals of the sulfur content in the coal burned in the boiler, the amount of coal supplied, and the amount of air supplied to the arithmetic unit, and using the relationship shown in FIG.
The amount of exhaust gas at the inlet of the desulfurization unit and the concentration of SO _{2 are} calculated and transmitted as a control signal for the supply amount of the absorbent to the desulfurization unit.

In this embodiment, the operation of the coal supply and the air supply for controlling the combustion state of the boiler and the signal of the analysis result of the sulfur content in the coal are used to control the amount of the absorbent supplied to the desulfurization unit. It can be controlled in advance.

FIG. 3 shows a boiler load, an exhaust gas treatment amount, a limestone slurry supply amount, and a slurry amount when a flue gas treatment of a coal boiler incorporating the limestone-gypsum method desulfurization apparatus shown in FIG. pH and desulfurization rate are shown together. According to this figure, although the boiler load changes and the exhaust gas amount changes accordingly, the limestone slurry supply also follows the boiler load, minimizing the effect on the desulfurization rate of the desulfurization unit. It can be said that the load is suppressed and the load is tracked well.

FIG. 4 shows a limestone-gypsum which adjusts a supply amount of a limestone slurry 32 as an absorbent by a controller 30 based on a control signal 28, desulfurizes the exhaust gas 22 with the limestone slurry 32, and discharges it to the line 14. It is a desulfurization unit 8 of the method.

Further, it is also possible to control the amount of air blown into the slurry in the absorption tower of the desulfurization device by using the operation factor of the combustion state and the analysis value signal of the sulfur content in the coal. Limestone-
In the gypsum method desulfurization apparatus, an oxidation tower for the purpose of oxidizing a sulfite is omitted, and a method of blowing air into slurry in a tank is mainly used. Sulfite ions in the slurry tend to increase as the boiler load increases. As the sulfite ion concentration in the slurry increases, the desulfurization performance decreases, so it is necessary to oxidize it to reduce it to sulfate ions. It can be controlled by the analysis signal of the sulfur content.

FIG. 6 shows an application example of the present embodiment when a moving bed desulfurization device 36 filled with solid particles (absorbent) 34 is incorporated. FIG. 5 shows the daily load of the boiler for this example. FIG. 9 shows the behavior of the desulfurization rate by the advance control of the present example under the condition where the change amount changes from 35% to 100%. SO ₂ concentration in the exhaust gas 22 introduced into the desulfurization apparatus 36 from 616Ppm 8
The solid particles 3 in the moving bed desulfurization unit 36
The moving speed of 4 was controlled from 0.07 to 0.119 m / h. It can be seen that the desulfurization rate favorably follows the load.

As described above, by controlling the desulfurization device in the present embodiment,
It has been clarified that the SO ₂ concentration in the exhaust gas can be reduced to a predetermined concentration or less in response to a change in boiler load. Furthermore, merged with the control of the desulfurization apparatus according to the present embodiment, the amount of exhaust gas in the exhaust gas introduced into the desulfurization apparatus, the detection signal, such as SO ₂ concentration,
By controlling the amount of the absorbent supplied to the desulfurization device, malfunctions can be prevented even for abnormal values of sulfur analysis in boiler coal.

〔The invention's effect〕

As described above, according to the present invention, as a smooth control of a desulfurization device of a flue gas treatment system of a coal boiler, particularly a power generation boiler, the sulfur content in coal of a boiler fuel for coal-fired power is clarified, and the boiler Air supply, which is the operating factor of
Since the set value of the coal supply is used as an adjustment signal for the solid particle supply speed of the desulfurization unit, the desulfurization unit can be controlled in advance of changes in boiler load and changes in coal type, reducing the sulfur concentration in the exhaust gas. it can.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram showing an outline of a boiler system in one embodiment of the present invention, FIG. 2 is a graph showing a relationship between a sulfur content in coal and an SO ₂ concentration in exhaust gas, FIG. 3 is a graph showing the following relationship of each factor when this embodiment is applied to a limestone-gypsum method desulfurization apparatus, FIG. 4 is a schematic diagram of a limestone-gypsum method desulfurization apparatus, and FIG. 5 uses solid particles. FIG. 6 is a graph showing a change in desulfurization rate with a change in load when this embodiment is applied to a moving bed desulfurization apparatus. FIG. 6 is a schematic diagram of the moving bed desulfurization apparatus. 2 boiler, 4 denitrifier, 8,36 desulfurizer, 10 coal, 12,22 exhaust gas, 16 sulfur analyzer, 18 sulfur analysis value signal, 20 boiler Operating factor signal, 24: exhaust gas property signal, 26: arithmetic unit, 28: control signal, 30: controller.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Ichiichi Saito 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Inside the laboratory (72) Inventor Shigeru Nozawa 6-9 Takara-cho, Kure City, Hiroshima Prefecture Inside the Kure Factory of Babcock Hitachi Ltd. (56) References JP-A-63-315131 (JP, A) JP-A-63-224719 (JP) , A) JP-A-64-47426 (JP, A)

Claims (1)

(57) [Claims] A moving bed flue gas desulfurization apparatus for bringing solid particles into contact with flue gas from a coal boiler, and absorbing or adsorbing sulfur oxides in the flue gas to the solid particles to reduce the sulfur oxide concentration. In a method for operating a coal boiler comprising: based on set values or measured values of operation factors such as a coal amount and an air supply amount for controlling a combustion state of the coal boiler, and an analysis value of a sulfur content rate in the coal Controlling the solid particle feed rate in the moving bed flue gas desulfurization unit according to the value, and detecting the sulfur oxide concentration in the flue gas at the entrance of the moving bed flue gas desulphurization unit and the detected value of the amount of sulfur contained in the coal. A coal boiler wherein a value based on an analysis value of the rate is corrected, if necessary, and a control signal based on the corrected value is used as a setting signal of a solid particle supply speed in the moving bed flue gas desulfurization apparatus. Driving method.