JP2013044464A - Exhaust gas treatment device and exhaust gas treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas treatment device capable of suppressing an increase of the generated amount of a sulfur oxide contained in exhaust gas discharged from a boiler even if an operation period of the boiler is prolonged.SOLUTION: The exhaust gas treatment device includes the boiler 5 for burning fuel F; an air supply part 16 for supplying air A to the boiler 5; an Osensor 25 capable of detecting the concentration of oxygen contained in the exhaust gas E discharged from the boiler 5; a correlation map showing a correlation among the operation period of the boiler 5, the concentration of oxygen, and a conversion ratio for converting to sulfur trioxide by bonding oxygen and sulfur contained in the exhaust gas E; and an operation control device 9 capable of adjusting the supply amount of the air A supplied to the boiler 5 by controlling the sir supply part 16. The operation control device 9 obtains a target oxygen concentration from the correlation map based on the target conversion ratio in accordance with the operation period of the boiler 5, and adjusts the supply amount of the air A to the boiler 5 so that the oxygen concentration detected by the Osensor 25 is the target oxygen concentration.

Description

  The present invention relates to an exhaust gas treatment apparatus and an exhaust gas treatment method for treating exhaust gas from a boiler that burns fuel.

  Conventionally, a heavy fuel fired boiler system having an ash fluidity measuring instrument for measuring ash fluidity downstream of an electric dust collector that removes dust contained in exhaust gas discharged from a heavy fuel fired boiler has been known. (For example, refer to Patent Document 1). In this heavy fuel fired boiler system, the supply amount of air supplied to the boiler is adjusted based on the ash fluidity information measured by the ash fluidity meter.

JP 2009-192100 A

Incidentally, in the exhaust gas discharged from the boiler, by binding oxygen and sulfur contained in the flue gas, sulfur oxides such as sulfur dioxide (SO ₂₎ and sulfur trioxide (SO ₃₎ is generated. Among these, the amount of sulfur trioxide generated increases as the boiler operation period becomes longer. In other words, when the operation period of the boiler becomes longer, dirt adheres to the heat transfer tube provided inside the boiler, thereby reducing the efficiency of heat exchange by the heat transfer tube, thereby increasing the temperature in the boiler. Sulfur trioxide is easily generated by the catalytic action of the attached ash.

  Here, an electric dust collector with an ammonia injection facility for collecting dust and ammonium sulfate in the exhaust gas may be connected to the discharge side of the boiler. This electrostatic precipitator adds ammonia to the inflowing exhaust gas and reacts sulfur trioxide and ammonia contained in the exhaust gas to produce ammonium sulfate, and removes the produced ammonium sulfate together with the soot and dust contained in the exhaust gas. ing. However, the produced ammonium sulfate includes acidic ammonium sulfate having strong adhesion due to lack of ammonia. This acidic ammonium sulfate is likely to adhere to the electrode (dust collecting electrode) of the electric dust collector. For this reason, as the production amount of sulfur trioxide increases, there is a possibility that acidic ammonium sulfate adheres to the electrode, thereby reducing the dust collection performance of the electric dust collector. In addition, in the electrostatic precipitator, the addition amount of ammonia is set to an addition amount that is sufficient when the production amount of sulfur trioxide is maximized. For this reason, an electric dust collector will add excess ammonia until the production amount of sulfur trioxide becomes the maximum.

  Accordingly, the present invention provides an exhaust gas treatment apparatus and an exhaust gas treatment method capable of suppressing an increase in the amount of sulfur trioxide contained in the exhaust gas discharged from the boiler even when the boiler operation period is long. The task is to do.

  The exhaust gas treatment apparatus of the present invention includes a boiler for burning fuel, an oxidant supply means for supplying an oxidant to the boiler, an oxygen concentration detection means capable of detecting the oxygen concentration contained in the exhaust gas discharged from the boiler, A correlation map representing the correlation between the operation period of the boiler, the oxygen concentration, and the conversion rate at which oxygen and sulfur contained in the exhaust gas are combined and converted to sulfur trioxide, and the oxidant supply means are controlled. And a control means capable of adjusting the supply amount of the oxidant supplied to the boiler, the control means acquiring the target oxygen concentration from the correlation map based on the target conversion rate according to the boiler operation period. The supply amount of the oxidant to the boiler is adjusted so that the oxygen concentration detected by the oxygen concentration detection means becomes the target oxygen concentration.

  According to this configuration, the control unit can adjust the supply amount of the oxidant to the boiler so that the oxygen concentration detected by the oxygen concentration detection unit becomes the target oxygen concentration. For this reason, the control means can make the conversion rate to sulfur trioxide the target conversion rate according to the operation period of the boiler. Thereby, even if the operation period of a boiler becomes long, the conversion rate of sulfur trioxide can be made constant. Therefore, when an electrostatic precipitator with ammonia injection equipment is connected to the boiler, the increase of sulfur trioxide in the exhaust gas flowing into the electrostatic precipitator can be suppressed, and the inflow amount of sulfur trioxide in the exhaust gas flowing into the electrostatic precipitator is constant. Can be. For this reason, it is possible to make the electrode of the electric dust collector difficult to get dirty, and it is possible to extend the operation of the electric dust collector. Moreover, since the inflow amount of sulfur trioxide flowing into the electrostatic precipitator can be made constant, the addition amount of ammonia can be made constant, thereby suppressing the addition of excess ammonia.

  In this case, the conversion map preferably has a constant conversion rate by decreasing the oxygen concentration as the boiler operation period becomes longer.

  According to this structure, the conversion rate to sulfur trioxide can be made constant by reducing the supply amount of the oxidant to the boiler and lowering the oxygen concentration as the operation period of the boiler becomes longer.

  In this case, the oxidant is preferably air.

  According to this structure, since the conversion rate to sulfur trioxide can be made constant, an increase in the amount of ammonium sulfate produced by the reaction of sulfur trioxide and ammonia can be suppressed. Moreover, by using air as an oxidant, the boiler can burn fuel while air is supplied.

  In the exhaust gas treatment method of the present invention, the operation period of the boiler to which the oxidant is supplied, the oxygen concentration contained in the exhaust gas discharged from the boiler, and the oxygen and sulfur contained in the exhaust gas are combined to form sulfur trioxide. An exhaust gas treatment method for treating exhaust gas discharged from a boiler using a correlation map representing a correlation with a conversion rate to be converted into a boiler, an operation period acquisition step for acquiring a boiler operation period, and a boiler operation period A target conversion rate acquisition step of acquiring a target conversion rate, which is a target conversion rate according to the target, and a target oxygen concentration acquisition step of acquiring a target oxygen concentration from a correlation map based on the boiler operation period and the target conversion rate; An oxygen concentration detection step for detecting the oxygen concentration, and an oxidant supply for adjusting the supply amount of the oxidant to the boiler so that the oxygen concentration detected in the oxygen concentration detection step becomes a target oxygen concentration. Characterized by comprising a quantity adjusting step.

  According to this configuration, in the oxidant supply amount adjustment step, the oxidant supply amount to the boiler can be adjusted so that the oxygen concentration detected in the oxygen concentration detection step becomes the target oxygen concentration. For this reason, the conversion rate to sulfur trioxide can be made into the conversion rate used as the target according to the operation period of a boiler. Thereby, even if the operation period of a boiler becomes long, the conversion rate of sulfur trioxide can be made constant.

  According to the exhaust gas treatment apparatus and the exhaust gas treatment method of the present invention, the conversion rate to sulfur trioxide contained in the exhaust gas discharged from the boiler can be made constant even when the operation period of the boiler becomes long. The increase in sulfur trioxide can be suppressed.

FIG. 1 is a schematic configuration diagram of an exhaust gas treatment apparatus according to the present embodiment. FIG. 2 is an explanatory diagram of a correlation map showing the correlation between the operation period of the boiler, the oxygen concentration, and the conversion rate to sulfur trioxide. FIG. 3 is an explanatory diagram of a graph showing the conversion rate to sulfur trioxide that changes in accordance with the operation period of the boiler. FIG. 4 is a flowchart showing a series of control operations related to the exhaust gas treatment method.

  Hereinafter, an exhaust gas treatment apparatus and an exhaust gas treatment method according to the present invention will be described with reference to the accompanying drawings. The present invention is not limited to the following examples. In addition, constituent elements in the following embodiments include those that can be easily replaced by those skilled in the art or those that are substantially the same.

  FIG. 1 is a schematic configuration diagram of an exhaust gas treatment apparatus according to the present embodiment. The exhaust gas treatment apparatus 1 of the present embodiment uses air as an oxidant, burns bad fuel such as heavy oil in a boiler, and purifies exhaust gas discharged from the boiler.

  The exhaust gas treatment device 1 controls a boiler 5, a denitration device 6 connected to the boiler 5, an electric dust collector 7 connected to the denitration device 6, a desulfurization device 8 connected to the electric dust collector 7, and these operations. An operation control device (control means) 9 is provided.

  A fuel supply unit 15 that supplies fuel F and an air supply unit 16 that supplies air A as an oxidant are connected to the boiler 5. Further, a heat transfer tube 17 is provided inside the boiler 5, and the heat transfer tube 17 exchanges heat by being heated by heat generated in the boiler 5. When the air A is supplied from the air supply unit 16 to the boiler 5 and the fuel F is supplied from the fuel supply unit 15 to the boiler 5, the boiler 5 uses the air A to burn the fuel F, so that the boiler The heat transfer tube 17 provided in 5 is heated. The boiler 5 discharges the exhaust gas E generated after combustion toward the denitration device 6. At this time, in the exhaust gas E discharged from the boiler 5, oxygen and sulfur contained therein are combined to generate sulfur oxides. The air supply unit 16 is connected to the operation control device 9 and adjusts the supply amount of the air A supplied to the boiler 5 under the control of the operation control device 9.

Note that an O ₂ sensor 25 is provided between the boiler 5 and the denitration device 6 to detect the oxygen concentration in the exhaust gas E discharged from the boiler 5. The O ₂ sensor 25 is connected to the operation control device 9 and outputs the detected oxygen concentration to the operation control device 9.

The denitration device 6 is for removing nitrogen oxides contained in the exhaust gas E. The denitration device 6 has a denitration catalyst layer (not shown) in its interior, and when the exhaust gas E comes into contact with the denitration catalyst layer, nitrogen oxides in the exhaust gas E are converted into nitrogen gas (N ₂ ) and water. Decomposed and removed to (H ₂ O).

The electric dust collector 7 is an electric dust collector 7 with an ammonia injection facility 21. When ammonia is added from the ammonia injection facility 21, sulfur trioxide in the exhaust gas E reacts with ammonia to produce ammonium sulfate. Then, an electrostatic precipitator 7, to remove the dust contained in the exhaust gas E after denitrification to remove ammonium sulfate produced by adding ammonia (NH _3). The electrostatic precipitator 7 has a discharge electrode and a dust collection electrode. The dust and ammonium sulfate in the exhaust gas E are charged to the cathode side by the electric charge discharged from the discharge electrode, and the exhaust gas E in the exhaust gas E charged to the cathode side is charged. Dust and acid ammonium sulfate are collected by attracting them to the dust collecting electrode on the anode side.

  The desulfurizer 8 removes sulfur oxides contained in the exhaust gas E after dust collection. The denitration apparatus 8 has an absorption tower (not shown), and, for example, lime slurry is used as an absorbing liquid that absorbs sulfur oxides. In the absorption tower, the exhaust gas E and the lime slurry are brought into contact with each other to remove sulfur oxides in the exhaust gas E, whereby the exhaust gas E is purified. The purified exhaust gas E is discharged as a purified gas from the absorption tower of the desulfurization device 8 and discharged from the chimney 22 connected to the absorption tower to the outside air.

The operation control device 9 controls the operations of the boiler 5, the denitration device 6, the electrostatic precipitator 7, and the desulfurization device 8, respectively. For example, the operation control device 9 is connected to the air supply unit 16 and is also connected to the O ₂ sensor 25. Based on the oxygen concentration detected by the O ₂ sensor 25, the operation control device 9 is transferred from the air supply unit 16 to the boiler 5. The flow rate of air A to be supplied is adjusted.

Therefore, the exhaust gas treatment device 1 supplies the fuel F and the air A from the fuel supply unit 15 and the air supply unit 16 toward the boiler 5 while being controlled by the operation control device 9. Then, in the boiler 5, the heat transfer tube 17 provided in the boiler 5 is heated by burning the fuel F using the supplied air A. The exhaust gas E generated after the combustion is discharged toward the denitration device 6. The exhaust gas E heading for the denitration device 6 has an oxygen concentration detected by the O ₂ sensor 25, and the detected oxygen concentration is output to the operation control device 9. The exhaust gas E flowing into the denitration device 6 is discharged toward the electrostatic precipitator 7 after the nitrogen oxides are removed. The exhaust gas E that has flowed into the electric dust collector 7 is added with ammonia from the ammonia injection facility 21, so that sulfur trioxide contained in the exhaust gas E reacts with ammonia to generate ammonium sulfate. The exhaust gas E flowing into the electric dust collector 7 is discharged toward the desulfurization device 8 after dust and ammonium sulfate are collected by the electric dust collector 7. The exhaust gas E flowing into the desulfurization device 8 is discharged from the chimney 22 to the outside air after the sulfur oxide is removed.

  In the exhaust gas treatment apparatus 1 configured as described above, when the boiler 5 is operated for a long period of time, dirt adheres to the heat transfer tubes 17. If dirt adheres to the heat transfer tube 17, the efficiency of heat exchange decreases, and the temperature in the boiler 5 rises. When the temperature in the boiler 5 rises or the catalytic action of the attached ash is activated, sulfur trioxide is easily generated, so that the amount of sulfur trioxide generated in the exhaust gas E discharged from the boiler 5 increases. When the sulfur trioxide in the exhaust gas E increases, the amount of acidic ammonium sulfate contained in the generated ammonium sulfate increases due to the ammonia added in the electric dust collector 7, and the acidic ammonium sulfate adhering to the dust collecting electrode of the electric dust collector 7 adheres. The amount increases and the dust collection performance of the electric dust collector 7 decreases. For this reason, in the exhaust gas treatment apparatus 1 of the present embodiment, the operation controller 9 controls the air supply unit 16 to suppress the increase in sulfur trioxide in the exhaust gas E discharged from the boiler 5, so that the boiler 5 The supply amount of air A to be supplied is adjusted. Hereinafter, the operation control device 9 will be described in detail with reference to FIGS. 2 to 4.

FIG. 2 is an explanatory diagram of a correlation map showing the correlation between the operation period of the boiler, the oxygen concentration, and the conversion rate to sulfur trioxide. FIG. 3 is an explanatory diagram of a graph showing the conversion rate to sulfur trioxide that changes in accordance with the operation period of the boiler. FIG. 4 shows a series of control operations related to the exhaust gas treatment method. The operation control device 9 controls the air supply unit 16 based on the correlation map M prepared in advance, so that sulfur oxides in the exhaust gas E discharged from the boiler 5, particularly sulfur trioxide (SO ₃ ). The conversion rate is constant.

  A correlation map M shown in FIG. 2 is stored in the operation control device 9. This correlation map M represents the correlation between the operation period of the boiler 5, the oxygen concentration in the exhaust gas E, and the conversion rate at which oxygen and sulfur contained in the exhaust gas E are combined and converted to sulfur trioxide. Yes. Here, in the correlation map M, the horizontal axis is the operation period of the boiler 5, and the vertical axis is the oxygen concentration. In the correlation map M, L1 is a line with a predetermined rate of conversion to sulfur trioxide, and L2 is a line with a higher rate of conversion to sulfur trioxide than L1.

  The correlation map M is generated based on the graph shown in FIG. In the graph shown in FIG. 3, the horizontal axis represents the operation period of the boiler 5, and the vertical axis represents the conversion rate to sulfur trioxide. In the graph shown in FIG. 3, M1 is a line representing a change in conversion rate when the oxygen concentration is the first oxygen concentration. Similarly, M2 is a line representing a change in conversion rate when the oxygen concentration is a second oxygen concentration higher than the first oxygen concentration. M3 is a line representing a change in conversion rate when the oxygen concentration is a third oxygen concentration higher than the second oxygen concentration. As shown in the graph of FIG. 3, it can be seen that M1, M2, and M3 change so that the conversion rate to sulfur trioxide increases as the operation period of the boiler 5 becomes longer. Then, when the oxygen concentration corresponding to the predetermined conversion rate in FIG. 3 is plotted along the horizontal axis and the vertical axis in FIG. 2 with reference to the operation period of the boiler, a correlation map M is obtained. As can be seen from the obtained correlation map M, the conversion rate to sulfur trioxide becomes constant by decreasing the oxygen concentration as the operation period of the boiler becomes longer.

The operation control device 9 sets the target oxygen concentration from the correlation map M as the target oxygen concentration based on the current operation period of the boiler 5 and the target conversion rate (for example, L1 or L2). Then, the operation control device 9 controls the air supply unit 16 so that the oxygen concentration detected from the O ₂ sensor 25 becomes the target oxygen concentration.

  Next, an exhaust gas treatment method for controlling the operation of the boiler 5 by the operation control device 9 of the exhaust gas treatment device 1 will be described with reference to FIG. First, the operation control device 9 acquires the current operation period of the boiler 5 (step S1: operation period acquisition step). Thereafter, the operation control device 9 acquires a target conversion rate to sulfur trioxide, which is a target conversion rate (step S2: target conversion rate acquisition step). The target conversion rate is preferably set as appropriate according to the quality of the fuel used in the boiler 5 and the like.

When acquiring the target conversion rate, the operation control device 9 acquires and sets the target oxygen concentration from the correlation map M based on the acquired operation period of the boiler 5 and the acquired target conversion rate (step S3: target oxygen). Density setting step). When the target oxygen concentration is set, the operation control device 9 detects the oxygen concentration in the exhaust gas E discharged from the operating boiler 5 by the O ₂ sensor 25 (step S4: oxygen concentration detection step), The air supply unit 16 is controlled so that the detected oxygen concentration becomes the target oxygen concentration (step S5: oxidant supply amount adjustment step).

  From the above, according to the configuration of the present embodiment, the operation control device 9 maintains a constant conversion rate for conversion to sulfur trioxide in the exhaust gas E discharged from the boiler 5 even when the operation period of the boiler 5 becomes longer. Rate. Thereby, when the electrostatic precipitator 7 with the ammonia injection equipment 21 is connected to the boiler 5, the increase in sulfur trioxide in the exhaust gas E flowing into the electrostatic precipitator 7 can be suppressed, and the exhaust gas E in the exhaust gas E flowing into the electrostatic precipitator 7 can be suppressed. The inflow of sulfur trioxide can be made constant. For this reason, the electrode of the electrostatic precipitator 7 can be made difficult to get dirty, and the operation of the electric precipitator 7 can be prolonged. Further, since the inflow amount of sulfur trioxide flowing into the electrostatic precipitator 7 can be made constant, the addition amount of ammonia added from the ammonia injection facility 21 can be made constant, thereby suppressing the addition of excess ammonia. can do.

  Moreover, according to the structure of a present Example, the correlation map M from which the conversion rate to sulfur trioxide becomes constant can be used by reducing oxygen concentration as the operation period of the boiler 5 becomes long. Thereby, when the operation control apparatus 9 makes the conversion rate of sulfur trioxide constant, the supply amount of air supplied from the air supply unit 16 as the operation period of the boiler 5 becomes longer so as to reduce the oxygen concentration. Should be reduced. For this reason, the operation control apparatus 9 can control the air supply part 16 based on the correlation map M, and can make the conversion rate of sulfur trioxide suitably constant.

1 exhaust gas treatment apparatus 5 boiler 6 denitrator 7 electrostatic precipitator 8 desulfurizer 9 operation control unit 15 the fuel supply unit 16 the air supply unit 17 heat transfer tube 21 ammonia injection equipment 22 the chimney 25 O ₂ sensor F Fuel A air E exhaust M correlation map

Claims (4)

A boiler that burns fuel;
An oxidant supply means for supplying an oxidant to the boiler;
Oxygen concentration detection means capable of detecting the oxygen concentration contained in the exhaust gas discharged from the boiler;
A correlation map representing a correlation between an operation period of the boiler, the oxygen concentration, and a conversion rate in which oxygen and sulfur contained in the exhaust gas are combined and converted to sulfur trioxide;
Control means capable of controlling the oxidant supply means and adjusting the supply amount of the oxidant supplied to the boiler,
The control means includes
A target oxygen concentration is acquired from the correlation map based on the conversion rate that is a target according to an operation period of the boiler, and the oxygen concentration detected by the oxygen concentration detection means becomes the target oxygen concentration. An exhaust gas treatment apparatus that adjusts a supply amount of the oxidizing agent to the boiler.   2. The exhaust gas treatment apparatus according to claim 1, wherein the correlation map makes the conversion rate constant by decreasing the oxygen concentration as the operation period of the boiler becomes longer.   The exhaust gas treatment apparatus according to claim 1, wherein the oxidant is air. The operation period of the boiler to which the oxidant is supplied, the oxygen concentration contained in the exhaust gas discharged from the boiler, the conversion rate at which oxygen and sulfur contained in the exhaust gas are combined and converted to sulfur trioxide, and An exhaust gas treatment method for treating exhaust gas discharged from the boiler using a correlation map representing the correlation of
An operation period acquisition step of acquiring an operation period of the boiler;
A target conversion rate acquisition step of acquiring a target conversion rate that is the conversion rate that is a target according to the operation period of the boiler;
A target oxygen concentration acquisition step of acquiring a target oxygen concentration from the correlation map based on an operation period of the boiler and the target conversion rate;
An oxygen concentration detection step for detecting the oxygen concentration;
An oxidant supply amount adjustment step of adjusting the supply amount of the oxidant to the boiler so that the oxygen concentration detected in the oxygen concentration detection step becomes the target oxygen concentration. Exhaust gas treatment method.

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