JP2007326079A - Flue gas treatment system and method of coal burning boiler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flue gas treatment system and a method of a coal burning boiler having an electrostatic precipitator, wherein electrostatic precipitation efficiency is constantly stable without generating back discharge at all times. <P>SOLUTION: This flue gas treatment system of the coal burning boiler is provided with: a GGH heat recovery part 3a, a heat recovering device recovering heat of exhaust gas of the coal burning boiler 1; and the dry type electrostatic precipitator (dry type EP) 4 provided at the rear stream side of the GGH heat recovery part 3a and collecting soot and dust in the exhaust gas. A steam or water injection device 20, as a relative humidity increasing device for increasing relative humidity by injecting any one of or both of steam and water into exhaust gas G2, is provided on the upstream side of the GGH heat recovery part 3a. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flue gas treatment system and method for a coal fired boiler.

  As a technique for effectively using waste heat in exhaust gas from a coal fired boiler, proposals have been made to recover the heat of the boiler exhaust gas and to heat the exhaust gas discharged to the outside. FIG. 28 shows an example of a coal fired boiler flue gas treatment system. As shown in FIG. 28, in the conventional exhaust gas treatment facility, the untreated exhaust gas A1 emitted from the coal fired boiler 1 is first led to the heat recovery device of the air heater (AH) 2, and the boiler 1 is heated by the heat of the untreated exhaust gas A1. The supplied air B is heated. Here, the untreated exhaust gas A1 is cooled to 120 ° C to 160 ° C.

  Next, the untreated exhaust gas A1 is introduced into a gas gas heater (GGH) heat recovery section 3a, recovered by heat, cooled to about 80 ° C. to 110 ° C., and then supplied to a low-temperature dry electrostatic precipitator (dry EP) 4. Led. In the dry EP4, a considerable amount of soot is removed from the untreated exhaust gas A1, the soot concentration is reduced, and the exhaust gas A2 is discharged.

  The exhaust gas A2 exiting the dry EP4 is introduced into the desulfurization apparatus 5 and mainly absorbs and removes sulfurous acid gas, and again, after collecting and removing soot dust, it is discharged as a treated exhaust gas A3.

  The treated exhaust gas A3 exiting the desulfurization unit 5 has a water saturation temperature (about 50 ° C.), and is reheated by the heat recovery heat medium 6 in the GGH reheating unit 3b, which is preferable for release into the atmosphere to prevent white smoke. The temperature (about 90 ° C. to 100 ° C.) is released from the chimney 7 to the atmosphere (Patent Document 1).

Japanese Patent Laid-Open No. 11-179147

  However, in the electric dust collector used in the conventional exhaust gas treatment system, when the specific electrical resistance of the collected dust becomes high, the voltage (electric field strength) applied to the dust layer is low when the same corona current flows. There is a problem called reverse ionization in which the dust layer formed in the electrostatic precipitator breaks down, and the charged state becomes unstable, resulting in a decrease in dust collection performance.

FIG. 26A is a relationship diagram between the exhaust gas temperature and the dust electric resistivity, and FIG. 26B is a schematic diagram of the surface conduction 11 and the volume conduction 12 in the dust particles 10.
As shown in these drawings, the electrical resistivity of the dust particles 10 is determined and modeled by a parallel circuit of the surface conduction 11 and the volume conduction 12. In the high temperature region, the volume conduction 12 is dominant, mainly affected by the alkali metal component in the ash, while in the low temperature region, the surface conduction 11 is dominant, and the SO is caused by the sulfur component in the coal. ₃ is affected by the fact that ₃ binds to moisture and aggregates as sulfuric acid on the dust surface.

  In ash having a low volume conduction 12 and a high electrical resistance in the high temperature region due to this, as shown in FIG. 27 showing the relationship between the exhaust gas temperature and the electrical resistivity of the ash, a relatively high temperature region ( (95-110 ° C.), the electrical resistivity of ash exceeds the reverse ionization threshold, and reverse ionization may occur, resulting in a decrease in electrostatic dust collection performance.

  In view of the above problems, the present invention is directed to a coal flue boiler flue gas treatment system and method in which the electric dust collection efficiency is always stable without always causing reverse ionization in the treatment of the coal flue boiler exhaust gas having the electric dust collector. It is an issue to provide.

  The first invention of the present invention for solving the above-mentioned problems is a heat recovery device that recovers heat of exhaust gas from a boiler, and is provided on the downstream side of the heat recovery device to collect dust in the exhaust gas. A coal-fired boiler flue gas treatment system comprising a dry electrostatic precipitator, having a relative humidity increasing device for injecting either or both of water vapor and moisture into exhaust gas to improve relative humidity The present invention is in a flue gas treatment system for coal fired boilers.

  A second invention is characterized in that, in the first invention, the relative humidity increasing device is a water vapor or water injection device for injecting water vapor or moisture into an exhaust gas flue upstream of a heat exchanger.に In boiler flue gas treatment system.

  A third invention is characterized in that, in the first or second invention, the relative humidity increasing device improves the relative humidity of the exhaust gas by 3% or more as compared with a case where the relative humidity increasing device in the previous period is not used. It is in the flue gas treatment system of a coal fired boiler.

A fourth invention is a coal comprising: a heat recovery device that recovers heat of exhaust gas from a coal fired boiler; and a dry electric dust collector that is provided on the downstream side of the heat recovery device and replenishes soot in the exhaust gas. A flue gas treatment system for a coal fired boiler, comprising an SO ₃ supply device for improving SO ₃ concentration by injecting SO ₃ into exhaust gas. is there.

A fifth invention is the flue gas treatment system for a coal fired boiler according to the fourth invention, wherein the injection amount of SO ₃ is 3 ppm or more.

  A sixth invention is a flue gas treatment method for a coal fired boiler that collects the dust in the exhaust gas by a dry electrostatic precipitator after performing heat recovery of the exhaust gas of the boiler, and includes steam or moisture in the exhaust gas. One or both of them are injected to improve the relative humidity.

  A seventh invention is characterized in that, in the sixth invention, the relative humidity increasing device improves the relative humidity of the exhaust gas by 3% or more compared to the case where the previous relative humidity increasing device is not used. It is in the flue gas treatment method of coal fired boiler.

An eighth aspect of the present invention, after performing the heat recovery of the exhaust gas coal fired boiler, a flue gas treating process of coal combustion boiler for collecting dust in exhaust gas by dry electrostatic precipitator, SO ₃ in the exhaust gas In a flue gas treatment method for a coal fired boiler, characterized by improving the SO ₃ concentration by injecting NO.

According to a ninth aspect of the present invention, in the eighth aspect of the invention, there is provided a flue gas treatment method for a coal fired boiler, wherein the injection amount of SO ₃ is 3 ppm or more.

According to the present invention, by improving the relative humidity or SO ₃ concentration in the exhaust gas, the surface conduction of the dust in the low temperature region is sufficiently improved, and in the treatment of the coal fired boiler exhaust gas having the electric dust collector, always It is possible to perform a flue gas treatment of a coal fired boiler that does not cause reverse ionization and the electric dust collection efficiency is always stable.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

A flue gas treatment system for a coal fired boiler according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a conceptual diagram illustrating a flue gas treatment system for a coal fired boiler according to an embodiment. Note that the same members as those in the system of FIG. 27 described above are denoted by the same reference numerals, and redundant description is omitted.
As shown in FIG. 1, the flue gas treatment system for a coal fired boiler according to the present embodiment includes a GGH heat recovery unit 3a that is a heat recovery device that performs heat recovery of exhaust gas from the coal fired boiler 1, and the GGH heat recovery unit. 3a, a coal-fired boiler flue gas treatment system provided with a dry electrostatic precipitator (dry EP) 4 that collects the dust in the exhaust gas, provided on the downstream side of the exhaust gas G2, The water vapor or moisture injecting device 20 which is a relative humidity increasing device for injecting either or both of these to improve the relative humidity is provided upstream of the GGH heat recovery unit 3a.

  In the system of the present embodiment, the untreated exhaust gas G1 emitted from the coal fired boiler 1 is first guided to the heat recovery device of the air heater (AH) 2 and the air B supplied to the coal fired boiler 1 with the heat of the untreated exhaust gas G1. Heat. Here, the untreated exhaust gas G1 is cooled to 120 ° C to 160 ° C.

  Next, the heat exchanged exhaust gas G2 is injected with either or both of water vapor and moisture by the water vapor or moisture injection device 20 to improve the relative humidity.

  Next, the exhaust gas G3 having an improved relative humidity is introduced into the GGH heat recovery section 3a and recovered, and the exhaust gas G4 cooled to about 80 ° C. to 110 ° C. is introduced into the dry EP4. In dry EP4, a considerable amount of soot is removed from the exhaust gas G4, the soot concentration is reduced, and the exhaust gas G5 is discharged.

  The exhaust gas G5 exiting the dry EP4 is introduced into the desulfurization unit 5 and mainly absorbs and removes sulfurous acid gas, and again, after collecting and removing soot dust, it is discharged as a treated exhaust gas G6.

  The treated exhaust gas G6 leaving the desulfurization unit 5 has a water saturation temperature (about 50 ° C.) and is reheated by the heat medium 6 collected in the GGH reheating unit 3b to release air to prevent white smoke. The exhaust gas G7 having a preferable temperature (about 90 ° C. to 100 ° C.) is discharged from the chimney 7 to the atmosphere.

  Moreover, in the system shown in FIG. 1, although the GGH reheating part 3b of white smoke prevention is installed before the chimney 7, this invention is not limited to this, As shown in FIG. Instead of installing the GGH reheating unit 3b, the heat medium 6 recovered by the GGH heat recovery unit 3a may be used for boiler equipment or the like. In this case, when the heat recovery capacity in the GGH heat recovery section 3a is increased, the heat generation capacity may be increased and the temperature of the exhaust gas G4 after heat recovery may be further decreased.

Here, the relative humidity increased by the water vapor or water injected by the water vapor or water injection device 20 in the present invention refers to the value of the relative humidity improved by 3 to 6% from the relative humidity in the exhaust gas G2 before the humidification. That is, it means that the relative humidity is improved by 3 to 6% compared to the case where the water injection device 20 is not used.
This is because when the relative humidity is less than 3%, the effect of increasing the humidity is not expressed, whereas when the relative humidity exceeds 6%, the additional effect is not expressed.

  For example, in the case of a 700 MW coal fired boiler, the supply of water vapor is preferably 30 to 50 t / h. In addition, in the case of supplying moisture, a synergistic effect between the humidity increasing effect and the temperature lowering effect can be expressed by injecting 5 to 7 t / h.

  In particular, by supplying moisture to the exhaust gas, the temperature may be lowered by several degrees from the exhaust gas temperature during the operation, so that the relative humidity may be improved as the exhaust gas temperature decreases.

  Further, the operating temperature may be lowered by increasing the heat exchange amount of the heat exchange device. As an example, if the operating temperature is lowered to 70 ° C., it is possible to improve the relative humidity equivalent to improving the moisture in the exhaust gas with water or steam at a higher temperature. In the embodiment of FIG. 1, since the heat recovery amount is determined by the amount of reheat of the exhaust gas, there is a limitation in the range of reduction of the exhaust gas temperature by the gas gas heater (GGH), but especially in the case of the embodiment of FIG. Without limitation, the operating temperature can be reduced to a temperature of 70 ° C. as an example.

  In this embodiment, water vapor or moisture is injected into the exhaust gas G3 between the AH (air heater) 2 and the GGH heat recovery unit 3a. However, the present invention is not limited to this, and the AH2 A predetermined amount of water vapor or moisture may be supplied on the upstream side or in the boiler. For example, a furnace using a suit blower installed for the purpose of removing deposits on the surface of the evaporation pipe in the boiler furnace. The same effect can be obtained by injecting the above.

  In particular, when water vapor or the like is supplied on the upstream side of AH2, the exhaust gas temperature is higher than when water vapor or the like is supplied on the downstream side of AH2, so that the efficiency of evaporation of the supplied water vapor or moisture is increased, which is more preferable. Become.

Further, an SO ₃ supply device (not shown) may be provided instead of the water vapor or moisture injection device 20.
The supply amount of SO ₃ is preferably 3 ppm or more and about 10 ppm in order to eliminate the reverse ionization.

This is because when the supply amount is less than 3 ppm, the addition does not occur, and when the supply amount is 10 ppm or more, the further addition effect is not exhibited. Note that most of the added SO ₃ is combined with moisture in the exhaust gas and aggregated as sulfuric acid on the surface of the dust, and is collected together with the dust by dry EP. Moreover, even if there is something that can pass through the dry EP, it is extremely small, so it hardly affects the amount of total sulfur oxide combined with sulfurous acid gas.

Further, the steam or moisture injection device 20 and the SO ₃ supply device may be used in combination.

<Test Examples 1-3>
Hereinafter, test examples for confirming the effect of increasing the relative humidity will be described.
In the test, a simulated gas was generated using an LPG soot gas generator, and test ash was added to the generated simulated gas and circulated to obtain a predetermined superficial velocity.
A test was performed by injecting moisture into the exhaust gas of the circulation line from a water injection device to increase the relative humidity in the exhaust gas.
In addition, in order to measure whether or not there is a difference in the pitch of the electrodes of the electrostatic precipitator, the case of 300 mm pitch (gas amount: 2100 m ³ N / h) is a solid line, and the case of 400 mm pitch (gas amount: 2800 m ³ N / h) Is indicated by a broken line.
In addition, from the characteristics of the test ash, it was necessary that the water temperature was 2% or less (resistance threshold: 8 × 10 ¹² Ωcm) as a condition for causing reverse ionization in the body temperature region.

[Tests 1-1 to 1-4]
In Tests 1-1 to 1-4, the exhaust gas temperature was changed and the gas temperature, moisture, and relative humidity were measured, assuming that the moisture was 1.1%.
The test results are shown in FIGS. 3 to 6 are relationship diagrams between applied voltage and current density according to Test 1-1 to Test 1-4.

  In FIG. 3 showing the result of Test 1-1, the temperature was 42 ° C., the water content was 1.1 vol%, and the relative humidity was 13.9%. In this case, both the case where the applied voltage was gradually increased and the case where the applied voltage was gradually decreased became almost the same plot, and the reverse ionization phenomenon was not confirmed.

  FIG. 4 showing the result of Test 1-2 was a temperature of 51 ° C., a water content of 1.1 vol%, and a relative humidity of 8.6%. In this case, there was a slight opening in the plot when the applied voltage was gradually increased and when it was gradually decreased, confirming the start of the reverse ionization phenomenon.

  In FIG. 5 showing the results of Test 1-3, the temperature was 61 ° C., the water content was 1.1 vol%, and the relative humidity was 5.4%. In this case, when the applied voltage was gradually increased and gradually decreased, the opening in the plot was clearly confirmed, and the reverse ionization phenomenon was confirmed.

  In FIG. 6 showing the results of Test 1-4, the temperature was 71 ° C., the water content was 1.1 vol%, and the relative humidity was 3.5%. In this case, when the applied voltage was gradually increased and gradually decreased, the opening in the plot was clearly confirmed, and the reverse ionization phenomenon was confirmed.

[Tests 2-1 to 2-4]
In Tests 2-1 to 2-4, the water content was changed from 1.1 vol% to 2.0 vol%, the water concentration was constant, the exhaust gas temperature was changed, and the gas temperature, moisture, and relative humidity were measured. .
The test results are shown in FIGS.
In FIG. 7 showing the results of Test 2-1, the temperature was 79 ° C., the water content was 2.0 vol%, and the relative humidity was 4.5%. In this case, both the case where the applied voltage was gradually increased and the case where the applied voltage was gradually decreased became almost the same plot, and the reverse ionization phenomenon was not confirmed.

  FIG. 8 showing the results of Test 2-2 shows that the temperature was 84 ° C., the water content was 2.0 vol%, and the relative humidity was 3.7%. In this case, there was a slight opening in the plot when the applied voltage was gradually increased and when it was gradually decreased, confirming the start of the reverse ionization phenomenon.

  In FIG. 9 showing the results of Test 2-3, the temperature was 91 ° C., the water content was 2.0 vol%, and the relative humidity was 2.8%. In this case, when the applied voltage was gradually increased and gradually decreased, the opening in the plot was clearly confirmed, and the reverse ionization phenomenon was confirmed.

  In FIG. 10 showing the results of Test 2-4, the temperature was 97 ° C., the water content was 2.0 vol%, and the relative humidity was 2.3%. In this case, when the applied voltage was gradually increased and when it was gradually decreased, an opening was clearly confirmed in the plot, and the reverse ionization phenomenon was confirmed.

[Tests 3-1 to 3-4]
In Test 3, unlike Test 1 and Test 2, the gas temperature was kept constant at approximately 90 degrees, the moisture was changed, and the gas temperature, moisture, and relative humidity were measured.
The results of the test are shown in FIGS.

  In FIG. 11 showing the results of Test 3-1, the temperature was 95 ° C., the water content was 1.3 vol%, and the relative humidity was 1.5%. In this case, when the applied voltage was gradually increased and gradually decreased, the opening in the plot was clearly confirmed, and the reverse ionization phenomenon was confirmed.

  In FIG. 12 showing the results of Test 3-2, the temperature was 91 ° C., the water content was 2.9 vol%, and the relative humidity was 4.0%. In this case, when the applied voltage was gradually increased and gradually decreased, the opening in the plot was clearly confirmed, and the reverse ionization phenomenon was confirmed.

  In FIG. 13 showing the results of Test 3-3, the temperature was 91 ° C., the water content was 3.4 vol%, and the relative humidity was 4.8%. In this case, when the applied voltage was gradually increased and gradually decreased, the plot was slightly opened, and the reverse ionization phenomenon was almost eliminated.

  In FIG. 14 showing the results of Test 3-3, the temperature was 91 ° C., the water content was 4.4 vol%, and the relative humidity was 6.2%. In this case, when the applied voltage was gradually increased and gradually decreased, the plot did not open and the reverse ionization phenomenon was completely eliminated.

The results of Test 1 to Test 3 are shown in FIGS. 15 to 17 are graphs showing the relationship between the relative humidity and the hysteresis (kV / cm) of the electric field strength at a current density of 0.2 mA / m ² . In the drawing, black circles indicate the case where the electrodes are 300 mm pitch, and white circles indicate the case where the pitch is 400 mm.

15 to 17, the hysteresis of the electric field strength (difference in electric field strength value when Vl increases and decreases) at the current density of 0.2 mA / m ² previously tested is used as an index of the degree (degree) of reverse ionization. . Further, the hysteresis of the electric field strength at a current density of 0.2 mA / m ² = 0.05 kV / cm was assumed as the threshold value for the occurrence of reverse ionization.

  As shown in FIGS. 15 to 17, it is found that the degree of reverse ionization has a linear relationship with the relative humidity in any case, and it is confirmed that the reverse ionization phenomenon is eliminated by improving the relative humidity. It was done. Moreover, it was confirmed that there is no difference in the pitch between electrodes.

18 to 20 are graphs showing the relationship between the relative humidity of FIGS. 15 to 17 and the hysteresis of the electric field strength (kV / cm) at a current density of 0.2 mA / m ² . .2 kV / cm, and when the index for eliminating this reverse ionization is 0.05 kV / cm or less, the starting point and the ending point are indicated by arrows.
As a result, it was confirmed that the reverse ionization was eliminated by improving the relative humidity by about 3 to 5%.
In the actual boiler, the hysteresis when reverse ionization occurred was 0.19 kV / cm, which was a value within the range of 0.2 kV / cm.

  In this test example, it is preferable to increase the relative humidity by 3 to 5%. However, in an actual boiler, the value of the hysteresis of the electric field strength may vary, so the upper limit of the relative humidity is further increased by 1%. It is preferable to make it 6% which increased to some extent.

<Test 4>
In an actual plant of 700 MW, in operation at 350 MW, a decrease in the soot concentration when steam was injected was confirmed.
The result is shown in FIG.
In FIG. 21, the horizontal axis represents time, the vertical axis represents the average voltage (kV) from the top, the presence or absence of water vapor input, the dust concentration (mg / m ³ N) at the outlet of the dry EP, and 14 t / h in the exhaust gas. Steam was injected to confirm that reverse ionization was eliminated. The presence or absence of reverse ionization was confirmed by an increase in voltage and a rapid decrease in dust concentration.

<Test 5>
A test example for confirming the effect of eliminating the reverse ionization phenomenon by supplying SO ₃ will be described using the same apparatus as in Test 1.
In the test, SO ₃ was supplied to the generated simulated gas and circulated to obtain a predetermined superficial velocity.

The results of Tests 5-1 to 5-4 are shown in FIGS.
FIG. 22 showing the results of Test 5-1 shows that the temperature was 89 ° C., the water content was 1.2 vol%, and the SO ₃ concentration was 1.82 ppm. In this case, when the applied voltage was gradually increased and gradually decreased, the opening in the plot was clearly confirmed, and the reverse ionization phenomenon was confirmed.

FIG. 23 showing the results of Test 5-2 shows that the temperature was 90 ° C., the water content was 1.2 vol%, and the SO ₃ concentration was 3.64 ppm. In this case, when the applied voltage was gradually increased and gradually decreased, the opening in the plot was reduced, and the tendency to eliminate the reverse ionization phenomenon was confirmed.

In FIG. 24 showing the results of Test 5-3, the temperature was 90 ° C., the water content was 1.2 vol%, and the SO ₃ concentration was 6.06 ppm. In this case, when the applied voltage was gradually increased and gradually decreased, the plot did not open and the reverse ionization phenomenon was eliminated.

The results of Tests 5-1 to 5-3 are shown in FIG. FIG. 25 is a graph showing the relationship between the SO ₃ concentration and the hysteresis (kV / cm) of the electric field strength at a current density of 0.2 mA / m ² .
In FIG. 25, the hysteresis of the electric field strength at the current density of 0.2 mA / m ² (the difference between the electric field strength values when Vl increases and decreases) is used as an index of the degree (degree) of reverse ionization. Further, the hysteresis of the electric field strength at a current density of 0.2 mA / m ² = 0.05 kV / cm was assumed as the threshold value for the occurrence of reverse ionization.

As shown in FIG. 25, the degree of back corona is found that there is a correlation with the SO ₃ concentration, to improve the SO ₃ concentration, that back corona phenomenon is eliminated was confirmed. Moreover, it was confirmed that there is no difference in the pitch between electrodes.

In the graph showing the relationship between the SO ₃ concentration in FIG. 25 and the hysteresis (kV / cm) of the electric field strength at a current density of 0.2 mA / m ² , the reverse ionization hysteresis is 0.2 kV / cm. When the index to be eliminated and 0.05 kV / cm or less, the starting point and the ending point are indicated by arrows.
As a result, it was confirmed that the reverse ionization phenomenon was eliminated by increasing the SO ₃ concentration by about 3% or more.

In this test example, it is preferable to increase the SO ₃ concentration by 3% or more. However, in an actual boiler, the value of the hysteresis of the electric field strength may fluctuate, so the upper limit of the SO ₃ injection amount is further increased. It is preferable to make it 3-4% or more increased by about 1%.

  In the present embodiment, a coal fired boiler has been described as an example of the boiler, but the present invention is not limited to this.

  As described above, in the treatment of exhaust gas from a coal fired boiler having an electrostatic precipitator according to the present invention, it is suitable for use in exhaust gas treatment from a coal fired boiler in which reverse ionization is prevented and the electrostatic dust collection efficiency is always stable. Yes.

It is a flue gas processing system figure of a coal fired boiler concerning an example. It is a flue gas processing system figure of the other coal fired boiler concerning an example. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 1-1, and current density. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 1-2, and current density. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 1-3, and current density. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 1-4, and current density. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 2-1, and current density. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 2-2, and current density. It is a related figure of the applied voltage at the time of changing the relative humidity which concerns on the test 2-3, and a current density. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 2-4, and current density. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 3-1, and current density. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 3-2, and current density. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 3-3, and current density. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 3-4, and current density. It is a graph which shows the relationship between the relative humidity which concerns on the test example 1, and the hysteresis (kV / cm) of the electric field strength in current density 0.2mA / m < ² >. It is a graph which shows the relationship between the relative humidity which concerns on Test Example 2, and the hysteresis (kV / cm) of the electric field strength in current density 0.2mA / m < ² >. It is a graph which shows the relationship between the relative humidity which concerns on the test example 3, and the hysteresis (kV / cm) of the electric field strength in the current density of 0.2 mA / m < ² >. In the graph which shows the relationship between the relative humidity which concerns on the test example 1, and the hysteresis (kV / cm) of the electric field strength in the current density of 0.2 mA / m < ² >, it is the graph which showed the range where reverse ionization is eliminated. In the graph which shows the relationship between the relative humidity which concerns on Test Example 2, and the hysteresis (kV / cm) of the electric field strength in the current density of 0.2 mA / m < ² >, it is the graph which showed the range by which reverse ionization is eliminated. In the graph which shows the relationship between the relative humidity which concerns on the test example 3, and the hysteresis (kV / cm) of the electric field strength in the current density of 0.2 mA / m < ² >, it is the graph which showed the range where reverse ionization is eliminated. 6 is a graph showing the effect of eliminating the reverse ionization phenomenon in an actual plant according to Test Example 4. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 5-1, and current density. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 5-2, and current density. It is a related figure of an applied voltage at the time of changing relative humidity concerning test 5-3, and current density. It is a graph which shows the relationship between the relative humidity which concerns on Test Example 5, and the hysteresis (kV / cm) of the electric field strength in the current density of 0.2 mA / m < ² >. It is a related figure of exhaust gas temperature and dust electrical resistivity. It is a schematic diagram of the state of surface conduction and volume conduction in dust particles. It is a related figure of exhaust gas temperature and the electrical resistivity of ash. It is a flue gas processing system figure of a coal fired boiler.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coal fired boiler 2 Air heater 3a GGH heat recovery part 3b GGH reheating part 4 Dry EP
5 Desulfurizer 7 Chimney 20 Steam or water injection device

Claims (9)

A coal-fired boiler flue gas treatment system comprising: a heat recovery device that recovers heat of exhaust gas from a boiler; and a dry electric dust collector that is provided on a downstream side of the heat recovery device and collects dust in the exhaust gas. Because
A coal flue boiler flue gas treatment system comprising a relative humidity increasing device that injects one or both of water vapor and moisture into exhaust gas to improve relative humidity. In claim 1,
A flue gas treatment system for a coal fired boiler, wherein the relative humidity increasing device is a water vapor or moisture injection device for injecting water vapor or moisture into an exhaust gas flue upstream of a heat exchanger. In claim 1 or 2,
The flue gas treatment system for a coal fired boiler, wherein the relative humidity increasing device improves the relative humidity of the exhaust gas by 3% or more compared to the case where the relative humidity increasing device is not used in the previous period. Smoke treatment of coal fired boiler comprising heat recovery device for recovering heat of exhaust gas from coal fired boiler, and dry electric dust collector provided on the downstream side of the heat recovery device to replenish dust in exhaust gas A system,
An exhaust gas treatment system for a coal fired boiler, comprising an SO ₃ supply device for injecting SO ₃ into exhaust gas to improve the SO ₃ concentration. In claim 4,
A flue gas treatment system for a coal fired boiler, wherein the injection amount of SO ₃ is 3 ppm or more. A method for exhausting smoke from a coal fired boiler that collects dust in the exhaust gas by a dry electrostatic precipitator after heat recovery of the exhaust gas from the boiler,
A method for flue gas treatment of a coal fired boiler, characterized by injecting either or both of water vapor and moisture into exhaust gas to improve relative humidity. In claim 6,
The flue gas treatment method for a coal fired boiler, wherein the relative humidity increasing device improves the relative humidity of the exhaust gas by 3% or more compared to the case where the relative humidity increasing device in the previous period is not used. A flue gas treatment method for a coal fired boiler that collects dust in the exhaust gas by a dry electrostatic precipitator after heat recovery of the exhaust gas of the coal fired boiler,
A method for treating flue gas from a coal fired boiler, wherein SO ₃ concentration is improved by injecting SO ₃ into exhaust gas. In claim 8,
A flue gas treatment method for a coal fired boiler, wherein the injection amount of SO ₃ is 3 ppm or more.

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