WO2007110983A1 - Method of emission gas treatment and facility therefor - Google Patents

Abstract

An emission gas treatment that realizes enhancement of a sulfuric acid mist trapping efficiency of wet electric dust collector. Removal of sulfuric acid mist is carried out by performing wet desulfurization of an emission gas to thereby remove any sulfur oxides, thereafter measuring the amount of sulfuric acid mist in the desulfurized emission gas, mixing ammonia gas with a concentration of 1 or less in terms of equivalent ratio to the amount of sulfuric acid mist, and causing the mixture to pass through a wet electric dust collector. This can be realized by emission gas treatment facilities including a wet desulfurization unit for removing of sulfur oxides from an emission gas and a wet electric dust collector for removing of sulfuric acid mist from the emission gas having been desulfurized by the wet desulfurization unit, and further including ammonia gas supply means for supply of ammonia gas to the emission gas to be introduced in the wet electric dust collector.

Description

 Specification

 Exhaust gas treatment method and equipment

 Technical field

 TECHNICAL FIELD [0001] The present invention relates to an exhaust gas treatment method and equipment, and more particularly to an exhaust gas treatment method and equipment for removing sulfuric acid mist in exhaust gas with a wet electrostatic precipitator.

 Background art

 [0002] Generally, in an exhaust gas treatment facility for treating exhaust gas from a boiler that uses petroleum, heavy oil, or the like as fuel, a dry electrostatic precipitator, a wet desulfurizer, and a wet electrostatic precipitator are arranged in order after the boiler. Yes. The exhaust gas discharged from the boiler boiler is first introduced into a dry electrostatic precipitator to remove dust, and then introduced into a wet desulfurizer. Then, by spraying a slurry such as slaked lime or magnesium hydroxide hydroxide inside the wet desulfurization apparatus, sulfur dioxide in the exhaust gas is mainly absorbed and removed. At this time, the temperature of the exhaust gas, which was a few hundred degrees with the dry electrostatic precipitator, decreases to about several tens of degrees. The desulfurized exhaust gas is introduced into a wet electrostatic precipitator, and after mist and solid components are removed, it is discharged to the outside.

 [0003] By the way, a part of sulfur dioxide in the exhaust gas reacts with oxygen and water to produce sulfuric acid.

. When the concentration of this sulfuric acid is several tens of ppm, the gaseous force also becomes liquid inside the wet desulfurization unit, generating mist. Since the mist containing sulfuric acid has a small particle size, it is difficult to remove it with a wet desulfurization apparatus having a low collision probability with the spray slurry.

[0004] Therefore, the sulfuric acid mist is removed by a wet-type electrostatic precipitator at the subsequent stage. However, the wet electrostatic precipitator has a space charge effect when the mist particle size force S is small, that is, when the total surface area of the mist occupying the unit volume of exhaust gas (hereinafter referred to as specific surface area) is large. The discharge current is suppressed and the collection effect is reduced. For this reason, it is necessary to increase the charging time. However, if the charging time is increased, the capacity of the wet electrostatic precipitator needs to be increased, which increases the overall size of the apparatus.

[0005] For these reasons, conventionally, a means for increasing the mist particle size by supplying particles into the exhaust gas at the inlet of the wet desulfurization apparatus is taken to improve the repair efficiency of the subsequent wet electrostatic precipitator. (Patent Document 1). Patent Document 1: JP 2001-170515 A

 Disclosure of the invention

 Problems to be solved by the invention

However, in the wet desulfurization apparatus, as described above, slurry such as slaked lime or hydroxide / magnesium is sprayed inside the apparatus, thereby mainly absorbing and removing diacid / sulfur sulfur in the exhaust gas. Therefore, it is impossible to avoid a decrease in exhaust gas temperature. This means that the sulfuric acid mist is contained in the outlet gas of the wet desulfurization unit as long as the residual sulfur content exists. In recent years, since regulations on discharged particulates have an impact on strict environmental problems, there is a further demand to reduce the number of discharged particulates while suppressing the increase in size of facilities.

[0007] The present invention has been made in view of such circumstances, and an object thereof is to provide an exhaust gas treatment facility capable of improving the collection efficiency of sulfuric acid mist in a wet electrostatic precipitator.

 Means for solving the problem

 [0008] The present invention creates a state in which an equal amount of mist generated by the condensation of sulfuric acid contained in exhaust gas and ammonia gas is mixed due to a temperature drop in the wet desulfurization apparatus, and this is introduced until the wet electrostatic precipitator is introduced. This is based on the knowledge that if the residence time is kept above a certain level, harmless ammonium sulfate (acidic ammonium sulfate) can be produced while leaking ammonia gas can be reduced.

 [0009] That is, in order to achieve the above object, the exhaust gas treatment method according to the present invention performs wet desulfurization of exhaust gas to remove sulfur oxides, and then determines the amount of sulfuric acid mist in the desulfurized exhaust gas. It is characterized by removing the sulfuric acid mist by mixing ammonia gas with a concentration equal to or less than 1 with the amount of mist and passing it through a wet electrostatic precipitator.

[0010] Further, the present invention provides an exhaust gas treatment method in which exhaust gas is wet desulfurized to remove sulfur oxides, and then this desulfurized exhaust gas is introduced into a wet electrostatic precipitator to remove sulfuric acid mist! The ammonia gas is supplied into the desulfurization exhaust gas before the wet electrostatic precipitator, and the ammonia gas concentration at the outlet side of the wet electrostatic precipitator is obtained and supplied at the front of the electrostatic precipitator. The ammonia gas supply amount to be controlled is controlled to keep the concentration within a set range. [0011] In these cases, it is desirable to maintain a residence time of the mixed gas of the desulfurized exhaust gas and ammonia gas introduced into the wet electrostatic precipitator for 1 second or more.

 [0012] Further, the exhaust gas treatment facility according to the present invention includes a wet desulfurization device that removes sulfur oxides in the exhaust gas, and a wet electrostatic precipitator that removes sulfuric acid mist from the exhaust gas desulfurized by the wet desulfurization device. The exhaust gas treatment facility provided includes an ammonia gas supply means for supplying ammonia gas to the exhaust gas introduced into the wet electrostatic precipitator.

 [0013] According to such a configuration, since ammonia gas is supplied to the exhaust gas introduced into the wet electrostatic precipitator, the sulfuric acid mist in the exhaust gas reacts with the ammonia gas inside the wet electrostatic precipitator. As a result, acidic ammonium sulfate particles are formed, and the particle diameter is larger than that of the sulfuric acid mist. Thereby, the collection efficiency of sulfuric acid mist can be improved in a wet electrostatic precipitator.

 [0014] Further, when the exhaust gas treatment facility according to the present invention is applied, the higher the concentration of ammonia gas to be supplied, the higher the production efficiency of acidic ammonium sulfate. The surplus ammonia gas remains unreacted and the exhaust gas treatment facility Because it is released, it has a negative impact on the environment. Therefore, from the concentration of sulfuric acid mist (20 to 80 ppm) flowing into the wet electrostatic precipitator and the reaction efficiency at the exhaust gas temperature, the ammonia gas concentration is preferably an equivalence ratio of 1 or less with respect to the sulfuric acid mist concentration.

 [0015] Further, the ammonia supply gas supply means sets the reaction time by setting the residence time in the upstream exhaust gas of the ammonia gas introduced into the wet electrostatic precipitator to 1 second or longer. And the leakage ammonia gas concentration can be reduced.

[0016] In addition, in the wet electrostatic precipitator, the solid component and the liquid component contained in the waste liquid recovered by the wet electrostatic precipitator are separated, and the liquid component ammonia gas is separated to the inlet. It may be configured to have piping equipment that mixes with gas. By adopting this configuration, it is possible to reduce the amount of gas supplied by the original ammonia gas supply means while reusing the ammonia gas.

[0017] Power! Ammonia gas concentration meter is installed after the wet electrostatic precipitator to measure the concentration of unreacted ammonia gas from the wet electrostatic precipitator and supplied to the upstream of the wet electrostatic precipitator An adjusting means for limiting the amount of gas may be provided. The invention's effect

 [0018] According to the present invention, ammonia gas is supplied into the exhaust gas supplied to the wet electrostatic precipitator, and the sulfuric acid mist is made acidic ammonium sulfate particles to increase the particle size. The obtained sulfuric acid mist can be efficiently collected by a subsequent wet electrostatic precipitator. Brief Description of Drawings

FIG. 1 is an overall configuration diagram of an exhaust gas treatment facility according to an embodiment of the present invention.

 FIG. 2 is a graph showing the relationship between sulfuric acid mist concentration and ammonia gas concentration.

 FIG. 3 is a graph showing the relationship between the residence time of ammonia gas and sulfuric acid mist and the concentration of leaked ammonia gas.

 FIG. 4 is a configuration diagram of a waste liquid treatment apparatus using an ammonia tripping method of a wet electrostatic precipitator.

 FIG. 5 is a configuration diagram of a waste liquid treatment apparatus using a biological treatment method of a wet electrostatic precipitator. Explanation of symbols

 [0020] 10 Exhaust gas treatment equipment, 12 boiler, 14 denitration equipment, 16 air heater, 18 dry electrostatic precipitator, 20 wet desulfurization equipment, 22 wet electrical precipitator, 23 waste liquid treatment equipment, 24 heat exchanger, 26 Chimney, 28 ……

... Exhaust gas duct, 30 Ammonia gas supply device, 32 Ammonia gas supply duct, 34 SO concentration measuring device, 36 Control means, 38 Recording means, 40 ...

 2

 …… Ammonia gas concentration meter, 42 Waste liquid, 44 Neutralization tank, 46 Caustic soda solution, 48 Air, 50 First stripping tower, 52 Second stripping tower, 54 Stripping air, 56 Steam, 58 Stripped gas, 60 Regenerating liquid, 62 return piping, 64 replenishment piping, 66 ammonia oxidation tower, 68 gas distributor

70 Ammonia oxidation catalyst layer, 72 Denitration catalyst layer, 74 Ammonia gas mixer.

 BEST MODE FOR CARRYING OUT THE INVENTION

[0021] Preferred embodiments of an exhaust gas treatment method and equipment according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a flowchart of the exhaust gas treatment facility 10 according to the present embodiment.

 The exhaust gas treatment facility 10 according to the embodiment shown in the figure is for detoxifying and treating exhaust gas discharged from a boiler 12 that uses petroleum, heavy oil or the like as fuel.

 [0022] First, the basic configuration of the exhaust gas treatment facility 10 is as follows. Immediately after the boiler 12, a denitration device 14 is arranged, where nitrogen oxides are removed. An air heater 16 is provided for preheating boiler combustion air using the heat of the gas discharged from the denitration device 14. Exhaust gas whose temperature has dropped to a few hundred degrees by heat exchange with air such as combustion air in this air heater 16 is introduced into the dry electrostatic precipitator 18, where dust contained in the exhaust gas Is collected and then introduced into the wet desulfurization apparatus 20. In the wet desulfurization apparatus 20, a slurry such as slaked lime or magnesium hydroxide is sprayed inside to mainly absorb and remove sulfur oxides such as diacid and sulfur in the exhaust gas. Next, the exhaust gas that has passed through the wet desulfurization apparatus 20 is introduced into a wet electrostatic precipitator 22, where sulfuric acid mist and dust are removed, and then exhausted from the chimney 26 through heat exchange. A series of these processing apparatuses are connected by an exhaust gas duct 28, and the exhaust gas is circulated. Therefore, the exhaust gas discharged from the boiler 12 is dedusted by the dry electrostatic precipitator 18, desulfurized by the wet desulfurizer 20, and the sulfuric acid mist and dust are removed by the wet electrostatic precipitator 22 and released to the atmosphere. .

 [0023] Further, the wet electrostatic precipitator 22 is provided with a waste liquid treatment device 23 for separating acid ammonium sulfate dust generated by supplying ammonia gas and washing water, and waste liquid after dust separation. Is circulated and reused as cleaning water. The acidic ammonium sulfate dust after separation is reused as fertilizer.

 With such a basic configuration, particularly in this embodiment, the ammonia gas of the ammonia gas supply device 30 is connected to the exhaust gas duct 28 that connects the wet desulfurization device 20 and the wet electrostatic precipitator 22. Supply duct 32 is connected and connected.

[0025] Inside the wet desulfurization apparatus 20, a slurry such as slaked lime or magnesium hydroxide is sprayed on the exhaust gas, and the sulfur dioxide in the exhaust gas is absorbed and removed. At this time, the temperature of the exhaust gas decreases to a saturation temperature of several tens of degrees, and in the process of this temperature decrease, first, sulfuric acid contained in the exhaust gas is condensed. Next, the temperature of the exhaust gas decreases to near the moisture saturation state. In this case, water is condensed in the mist, and a mist having a low sulfuric acid concentration is generated. The particle size of this sulfuric acid mist is in the submicron order of 1 micron or less, and it is difficult for the wet electrostatic precipitator 22 to collect.

[0026] When ammonia gas is supplied to the exhaust gas containing sulfuric acid mist by the ammonia gas supply device 30, acidic ammonium sulfate is generated, and its particle size becomes on the order of several microns or more, and the wet electrostatic precipitator 22 is used. Easy to collect.

[0027] Meanwhile, the concentration of ammonia gas supplied from the ammonia gas supply device 30 depends on the concentration and temperature of sulfuric acid mist and the reaction time. At an exhaust gas temperature of about 60 ° C at the outlet of the wet desulfurization device, the reaction time is 1 Experiments have shown that acidic ammonium sulfate can be produced at almost the same ammonia gas concentration as sulfuric acid mist concentration as shown in Figs.

 [0028] That is, when the sulfuric acid mist is 20 ppm, the ammonia gas power at a concentration of 20 ppm requires 80 ppm of ammonia gas at the concentration of 80 ppm. Normally, the concentration of sulfuric acid mist in the exhaust gas discharged from the wet desulfurizer 20 varies within the range of 20 to 80 ppm, and the ammonia gas concentration is preferably 20 to 80 ppm! /.

 [0029] In addition, when supplying ammonia gas, the time required for the reaction between sulfuric acid mist and ammonia gas is required, and it has been experimentally found that the relationship shown in Fig. 3 is dependent on the residence time of the exhaust gas. As a result of investigating the relationship between the residence time and leaked ammonia gas concentration by supplying 20 ppm ammonia gas to the inlet sulfuric acid mist concentration of 20 ppm, the residence time was 1.0 seconds or more, the leak ammonia was almost flat, and the reaction was sufficient Therefore, the residence time is preferably 1.0 seconds or more.

 Therefore, in the embodiment, the ammonia gas supply device 30 has a nozzle (not shown) arranged so that the supplied ammonia gas is uniformly dispersed in the exhaust gas treatment facility 10, and sulfuric acid mist in the exhaust gas at that time The ammonia supply amount is controlled and managed so that the concentration ratio is 1 or less with respect to the concentration of 20 to 80 ppm. In this case, since it is practically difficult to directly measure the amount of sulfuric acid mist, the SO concentration in the wet desulfurizer 20 is measured, and this SO

2 2 The rate of conversion to mist can be obtained as an actual value, and the amount of sulfuric acid mist can be obtained indirectly. For this reason, the SO concentration meter 34 uses S The O concentration is measured, and this measured value is output to the control means 36. Control hand

2

 Stage 36 controls the supply amount by the ammonia gas supply device 30. The data is read from the recording means 38 storing the actual mist conversion rate value according to the measurement result, the sulfuric acid mist concentration is converted, and the ammonia gas equivalent to this is read. Is introduced into the exhaust gas through the ammonia gas supply duct 32.

 [0031] Further, a densitometer 40 for detecting the ammonia gas concentration in the exhaust gas from which the outlet force of the wet electrostatic precipitator 22 is also discharged can be provided. Then, it is determined whether or not the ammonia gas concentration measured by the densitometer 40 is within the set value, and thereby whether or not the ammonia gas is supplied in an equal amount to the sulfuric acid mist in the exhaust gas. Can be determined. If the ammonia gas concentration is higher than the specified concentration, the supply of ammonia gas may be reduced by the control means 36 because it is oversupplied. At the same time, the supply amount of ammonia gas can be adjusted through the control means 36 so that the concentration of fine particles emitted by the ammonia gas into the atmospheric emission gas does not exceed the regulation value. As a result, it is possible to keep the emission fine particle regulation within the set range.

 [0032] Further, as described above, it is desirable that the residence time of the pipe after mixing ammonia gas in the exhaust gas by the ammonia gas supply device 30 and introducing the ammonia gas into the wet electrostatic precipitator 22 is 1 second or more. . For this reason, the connection point of the ammonia gas supply duct 32 is set so that the flow time until the mixed gas reaches the inlet of the wet electrostatic precipitator 22 is 1 second or longer. This is because the connection length to the wet electrostatic precipitator 22 can be adjusted by the internal flow velocity.

 Thus, the wet electric dust collector 22 is supplied with the exhaust gas mixed with ammonia gas and sulfuric acid mist having an appropriate concentration and ensuring an appropriate residence time.

In this embodiment, as described above, the wet electrostatic precipitator 22 has a waste liquid treatment device 23 that separates acid ammonium sulfate dust generated by supplying ammonia gas from washing water. Is provided. The waste liquid treatment apparatus 23 may be configured to use an ammonia stripping method as shown in FIG. 4, for example. That is, the solid-liquid separated waste liquid 42 is supplied to the neutralization tank 44, to which the caustic soda solution 46 is added, the generated ammonia gas is purged with air 48, and supplied to the top of the first stripping tower 50. The liquid is the top of the second stripping tower 52 To supply to the department. Dissipation air 54 and steam 56 are supplied to the bottom of the second diffusion tower 52. As a result, the tower top force of the first stripping tower 50 generates ammonia, steam, oxygen, and nitrogen stripping gas 58, and the regenerated liquid 60 from which ammonia nitrogen has been removed is extracted from the bottom of the tower. The regenerated liquid 60 can be reused as spray water, and is circulated through the return pipe 62 to the spray means (not shown) of the wet electrostatic precipitator 22. On the other hand, in this embodiment, a part of the diffused gas 58 including the separated ammonia gas is introduced into the ammonia gas supply device 30 through the supplementary pipe 64 so that the sulfuric acid mist is reused for the production of acidic ammonium sulfate. I have to. The remaining emitted gas is supplied to the ammonia acid tower 66 and converted to nitrogen. The ammonia oxidation tower 66 is arranged in the order of a gas distributor 68, an ammonia oxidation catalyst layer 70, and a denitration catalyst layer 72. In this example, the ammonia oxide catalyst layer 66 and the denitration catalyst layer 72 An ammonia gas mixer 74 having a throat portion is provided between them, the ammonia-containing gas to be introduced into the ammonia acid tower 66 is divided into two parts, one is introduced into the ammonia acid catalyst layer 70, and the other is introduced. The gas is introduced from the gas introduction pipe into the ammonia gas mixer 74.

[0035] Further, the waste liquid discharged from the wet electrostatic precipitator 22 can be regenerated and reused as spray water by a biological treatment method as well as the above ammonia tripping method. In this case, as shown in FIG. 5, waste water containing ammonia is passed through a membrane separation device 76 that performs dust separation treatment, and then supplied to an ammonia nitrification tank 78 having a nitrifying bacteria-fixing carrier. After that, supplying the denitrification tank 80 produces a regenerated liquid from which ammonia has been separated.

Next, the operation of the exhaust gas treatment facility 10 configured as described above will be described.

 The exhaust gas discharged from the boiler 12 passes through the denitration device 14, is cooled to hundreds of degrees by the air heater 16, is then introduced into the dry electrostatic precipitator 18, and dust in the exhaust gas is removed by static electricity.

Next, the exhaust gas from which the dust has been removed is introduced into the wet desulfurization apparatus 20. Inside the wet desulfurization device 20, a slurry such as slaked lime or magnesium hydroxide is sprayed on the exhaust gas, and the sulfur dioxide in the exhaust gas is absorbed and removed. At this time, the temperature of the exhaust gas decreases to a saturation temperature of several tens of degrees, and in the process of this temperature decrease, first, sulfuric acid contained in the exhaust gas is condensed. Shrink. Next, when the temperature of the exhaust gas is lowered to near the saturated state of water, water is condensed in the mist, and mist having a low sulfuric acid concentration is generated. The particle size of this sulfuric acid mist is in the submicron order of 1 micron or less, and it is difficult for the wet electrostatic precipitator 22 to collect.

 In the exhaust gas containing sulfuric acid mist, ammonia gas is supplied from the ammonia gas supply device 30 to produce acidic ammonium sulfate, the particle diameter of which is on the order of several microns or more, and is collected by the wet electrostatic precipitator 22. Since it becomes easy, it is removed with high collection efficiency. Further, the position where the ammonia gas is supplied is set so that the residence time until it is introduced into the wet electrostatic precipitator 22 is 1.0 second or longer. Therefore, as shown in FIG. The acid mist and ammonia gas can be sufficiently reacted, thereby greatly reducing the amount of leaked ammonia gas generated.

Claims

The scope of the claims  [1] After the exhaust gas is wet desulfurized to remove sulfur oxides, the amount of sulfuric acid mist in the desulfurized exhaust gas is determined, and ammonia gas having a concentration ratio of 1 or less is mixed with the sulfuric acid mist amount. An exhaust gas treatment method characterized by removing sulfuric acid mist by passing through an electric dust collector.  [2] Measure the SO concentration in the wet desulfurization unit and realize the rate of conversion from this SO to sulfuric acid mist.  twenty two  2. The exhaust gas treatment method according to claim 1, wherein the exhaust gas treatment method is obtained as a result value, and the amount of sulfuric acid mist is indirectly obtained therefrom.  [3] The exhaust gas treatment method according to claim 1, wherein the retention time of the mixed gas of the desulfurized exhaust gas and ammonia gas introduced into the wet electrostatic precipitator is maintained at 1 second or longer.  [4] An exhaust gas treatment method in which exhaust gas is wet desulfurized to remove sulfur oxides and then the desulfurized exhaust gas is introduced into a wet electrostatic precipitator to remove sulfuric acid mist. Ammonia gas is supplied into the desulfurization exhaust gas at the front stage of the dust collector, the ammonia gas concentration at the outlet side of the wet electrostatic precipitator is obtained, and the ammonia gas supply amount supplied at the front stage of the electrostatic dust collector is controlled. And maintaining the concentration within a set range.  5. The exhaust gas treatment method according to claim 4, wherein the retention time of the mixed gas of the desulfurized exhaust gas and ammonia gas introduced into the wet electrostatic precipitator is maintained at 1 second or longer.  [6] An exhaust gas treatment facility equipped with a wet desulfurization device that removes sulfur oxides in exhaust gas and a wet electric dust collector that removes sulfuric acid mist from the exhaust gas power desulfurized by the wet desulfurization device. An exhaust gas treatment facility comprising ammonia gas supply means for supplying ammonia gas to the exhaust gas introduced into the wet electrostatic precipitator.  7. The exhaust gas treatment facility according to claim 6, wherein the ammonia gas supply means is provided with a control means for setting the ammonia gas concentration to an equivalent ratio of 1 or less with respect to the sulfuric acid mist concentration.  [8] The ammonia supply gas supply means is characterized in that the residence time in the upstream exhaust gas of the ammonia gas introduced into the wet electrostatic precipitator is set at a position where it is 1 second or longer. The exhaust gas treatment facility according to claim 6. [9] In the wet electrostatic precipitator! Included in the waste liquid collected by the wet electrostatic precipitator 7. The exhaust gas treatment facility according to claim 6, further comprising a piping facility that separates the solid component and the liquid component, separates the liquid component ammonia gas, and mixes it with the inlet gas.  An ammonia gas concentration meter is installed after the wet electrostatic precipitator, the concentration of unreacted ammonia gas from the wet electrostatic precipitator is measured, and the amount of ammonia gas supplied to the front of the wet electrostatic precipitator is determined. 7. The exhaust gas treatment facility according to claim 6, further comprising an adjusting means for limiting.