JP5441029B2 - Exhaust gas treatment method and treatment apparatus - Google Patents

Description

  The present invention relates to an exhaust gas processing method and a processing apparatus used in the exhaust gas processing method, and more specifically, a processing method for efficiently purifying nitrogen oxides in exhaust gas by controlling the temperature of the exhaust gas, and the method The present invention relates to a processing apparatus used in the method.

Nitrogen oxides such as nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) are discharged with the supply and consumption of energy typified by power plants, diesel engines, and boilers.

  These nitrogen oxides discharged into the environment cause photochemical smog, and countermeasures are being considered as important environmental problems in large cities. Nitrogen oxide is also attracting attention as one of the causes of global warming, which has become a problem in recent years.

  As a method for reducing nitrogen oxides, a combustion method, a catalyst method, a selective catalytic reduction method (SCR), an ammonia injection method, and the like are known. In recent years, the catalyst method, non-thermal plasma, electron beam, etc. Nitrogen oxides can be reduced by combining technologies to reduce nitrogen oxides and other methods using plasma and electron beam methods and chemicals and catalysts such as ammonia, hydrogen peroxide, and calcium chloride. A method of reducing is known.

Among them, the plasma-chemical hybrid method is attracting attention. This method is a method of purifying exhaust gas containing nitrogen oxides, supplying air to a discharge plasma reactor to generate radical gas, supplying the radical gas and exhaust gas to an oxidation reaction region, Nitrogen oxides in the exhaust gas are oxidized with radical gas to be converted into an oxidizing gas containing NO _2, and the oxidizing gas contains compounds such as Na ₂ SO ₃ , Na ₂ S, and Na ₂ S ₂ O _3. This is a method of reducing and purifying NO ₂ to nitrogen gas (N ₂ ) by bringing it into contact with a reducing agent aqueous solution in a reduction reaction region (see, for example, Patent Documents 1 to 4).

  In putting the plasma-chemical hybrid method into practical use, it is necessary to continuously replenish the chemical scrubber with a chemical solution in order to maintain nitrogen oxide removal performance even under continuous processing conditions. For example, the pH is maintained at 11 and the redox potential (ORP) is controlled to −50 to −250 mV, and an additional reducing agent aqueous solution and alkaline aqueous solution are injected into the circulating treatment solution immediately before introduction into the reduction reaction region. A method of replenishment has been proposed (Non-Patent Document 1).

Although this method is excellent, it is performed in a laboratory, and synthetic exhaust gas containing almost no carbon dioxide (CO ₂ ) is used. In other words, this method does not consider the presence of CO ₂ that is necessarily contained in the combustion gas at a concentration of several percent.

The inventors tested this method using a boiler combustor to replenish an additional reducing agent aqueous solution and an aqueous alkali solution to the circulating treatment liquid immediately before introduction into the reduction reaction region. However, in this test, since the exhaust gas contained several percent of CO ₂ , the pH of the aqueous solution immediately decreased, and it was difficult to maintain the condition of pH = 11 as described in Non-Patent Document 1. .
In addition, since the oxidation-reduction potential (ORP) increases, it is difficult to operate at −50 mV or less as described in Non-Patent Document 1.

This is because the reducing agent aqueous solution and the alkaline aqueous solution additionally supplemented come into contact with the exhaust gas containing CO ₂ to cause an oxidation reaction of the reducing agent aqueous solution and a reaction between the alkaline aqueous solution and CO _2. It seems that the aqueous solution supplemented additionally did not contribute to the activity recovery of the circulating mixed aqueous solution because it deteriorated in a short time.

For this reason, it has been difficult to continuously treat exhaust gas for a long time while maintaining the nitrogen oxide removal performance, but the present inventors have proposed a wet reactor in which an oxidation reaction and a reduction reaction are performed. Replenishment of the aqueous solution containing the reducing agent and the alkaline aqueous solution to the reservoir of the mixed aqueous solution provided in the lower part of the basin prevents the additional aqueous solution from coming into contact with exhaust gas containing CO ₂ and immediately deteriorating. It was found that this can be done (Patent Document 5).

WO05 / 0665805 Japanese Patent Application Laid-Open No. 2004-068684 Japanese Patent Application Laid-Open No. 2000-117049 JP 2000-016553 A WO2008 / 102708 Luke Chen, Jin-Wei Lin and Chen-Lu Yang, "Absorption of NO2 in a Packed Tower with Na2SO3 Aqueous Solution", Environmental Progress, vol.21, No.4, pp.225-230 (2002)

  However, even in this method, if the temperature of the exhaust gas containing nitrogen oxides increases, the removal performance of nitrogen oxides tends to decrease. Therefore, development of a treatment method that can cope with such cases has been desired. .

  As a result of intensive studies to develop a treatment method capable of efficiently removing nitrogen oxides even when the temperature of exhaust gas containing nitrogen oxides becomes high, the present inventors have found that the exhaust gas temperature is about 150 ° C. If it exceeds 1, the oxidation reaction of nitrogen oxides with ozone gas will be reduced, and as a result, the nitrogen oxide removal performance will be reduced, and the present invention has been completed.

Thus, according to the present invention, exhaust gas containing nitrogen oxides and ozone gas are introduced into the oxidation reaction region, and nitrogen oxides in the exhaust gas are reacted with ozone gas to oxidize the nitrogen oxides and contain NO _2. In the exhaust gas processing method including the step of converting to an oxidizing gas, the exhaust gas cooling device is operated when the temperature of the exhaust gas introduced into the oxidation reaction region exceeds a predetermined temperature, for example, about 150 ° C. An exhaust gas treatment method characterized by promoting the oxidation reaction of nitrogen oxides in the exhaust gas by lowering the temperature of the exhaust gas introduced into the reaction region to a predetermined temperature, for example, about 130 ° C. or lower; And a processing apparatus for use in the method.

  According to the present invention, when the temperature of the exhaust gas introduced into the oxidation reaction region exceeds about 150 ° C., the exhaust gas is cooled to a predetermined temperature, for example, about 130 ° C. or less. Therefore, it is possible to avoid a decrease in the oxidation reaction of nitrogen oxides by ozone gas, and as a result, even when the temperature of the exhaust gas exceeds a predetermined temperature, for example, about 150 ° C., the nitrogen oxide removal performance is not deteriorated. Thus, the operation of the processing apparatus can be continued.

It is explanatory drawing which shows the whole structure of one Embodiment of the processing apparatus of this invention. It is explanatory drawing which shows the whole structure of the conventional processing apparatus. In Experiment 1, it is a graph which shows the change with respect to the process elapsed time of the temperature of the exhaust gas in a boiler exit and an oxidation reaction area | region when the processing apparatus of this invention is used. It is a graph which shows the change with respect to the process elapsed time of the temperature of the exhaust gas in a boiler exit and an oxidation reaction area | region when the conventional processing apparatus is used in Test Example 1. FIG. It is a graph which shows the change with respect to the process elapsed time of the density | concentration of NO and NOx in a boiler exit and an oxidation reaction area | region when the processing apparatus of this invention is used in Test Example 2. FIG. It is a graph which shows the change with respect to process elapsed time of the density | concentration of NO and NOx in a boiler exit and an oxidation reaction area | region when the conventional processing apparatus is used in Test Example 2. FIG. In Test Example 3, the graph shows the relationship between the exhaust gas temperature in the oxidation reaction region and the molar ratio (ΔNO / O ₃ ) between the NO oxidation amount and the ozone supply amount.

  In the treatment method according to the present invention, when the exhaust gas generated from a boiler or the like is introduced into the oxidation reaction region of the wet reactor, the temperature of the exhaust gas is measured by the exhaust gas temperature measuring unit. The measurement location of the exhaust gas temperature is not particularly limited, but it is preferable to measure the exhaust gas temperature in the vicinity of the introduction into the oxidation reaction region because the temperature can be ascertained substantially the same as the exhaust gas temperature in the oxidation reaction region.

  The exhaust gas temperature thus measured is converted into an electrical signal and sent to the exhaust gas temperature control unit. When the temperature of the exhaust gas exceeds a predetermined temperature, for example, 150 ° C., the temperature control unit The exhaust gas cooling device is turned on based on the electrical signal.

  When the operation of the cooling device continues and the exhaust gas temperature falls below a predetermined temperature, for example, about 130 ° C., the exhaust gas temperature is converted into an electrical signal and sent to the exhaust gas temperature control unit, and the electrical signal from the temperature control unit Based on this, the exhaust gas cooling device is turned off.

  On the other hand, the radical gas generated from the air by the low-temperature non-equilibrium plasma reaction is supplied to the oxidation reaction region together with the above-mentioned nitrogen oxide-containing exhaust gas, or is supplied to the oxidation reaction region through a line different from the exhaust gas. Is done.

Reducing nitrogen oxides in the exhaust gas introduced to the oxidation reaction zone is oxidized by ozone in the radical gas becomes an oxidizing gas containing NO _2, the oxidation gas containing the NO ₂ is then introduced into the reduction reaction area Contacted with the agent aqueous solution, reduced to nitrogen gas and released into the atmosphere.

  The low temperature non-equilibrium plasma used in the treatment method of the present invention refers to an ionized plasma whose gas temperature is considerably lower than a normal gas combustion temperature (about 700 to 1000 ° C.), and generally refers to a plasma of 300 ° C. or lower. The lower limit temperature is about -200 ° C.

The low-temperature non-equilibrium plasma reaction in the present invention is preferably performed using a silent discharge type ozonizer, and the operating conditions are as follows, for example.
The temperature is 100 ° C. or less, preferably room temperature (0 to 40 ° C.), the pressure is about atmospheric pressure, the relative humidity is 50% or less, the voltage is about 10 kV, and the frequency is 0.42 to 6. The range is 82 kHz. If the ozonizer is operated under such conditions, there is an advantage that NO oxidation with high energy efficiency can be performed.

Further, the low-temperature non-equilibrium plasma reaction can stably generate radical gas containing ozone from the air, which is suitable for realizing an exhaust gas treatment method that does not decrease the efficiency even if it is operated in a steady state. The radical gas contains O, OH, HO ₂ radicals and the like in addition to ozone.

The supply amount of ozone gas (O ₃ , ppm) is based on the temperature of the nitrogen oxide-containing exhaust gas (T ° C.) and the amount of NO contained in the exhaust gas oxidized by ozone (ΔNO, ppm). Although it is preferable from the viewpoint of processing efficiency that the amount is obtained by the equation, this amount may vary somewhat up and down, for example, about 10%.
O ₃ (ppm) = ΔNO (ppm) / [-exp [(T-175) / 40] /10+1.15]
This mathematical formula is obtained based on the result of Test Example 3 described later.
In this specification, the ozone supply amount (O ₃ , ppm) means the concentration of ozone when diluted with exhaust gas.

The ozone gas supply amount can be increased or decreased by a normal method, for example, by adjusting the frequency of the ozonizer and the air supply amount to the ozonizer.
The adjustment of the ozone gas supply amount can be automatically performed by calculating the amount of ozone gas to be supplied by a microcomputer based on the above formula and reflecting the result in the operating conditions of the ozonizer.

  The reducing agent aqueous solution used in the treatment method of the present invention contains at least one compound selected from inorganic sulfur-containing reducing agents, and the alkaline aqueous solution contains at least one compound selected from alkali metal or alkaline earth metal hydroxides. Including.

Examples of the inorganic sulfur-containing reducing agent include sodium sulfite (Na ₂ SO ₃ ), sodium sulfide (Na ₂ S), and sodium thiosulfate (Na ₂ S ₂ O ₃ ).
Examples of the alkali metal or alkaline earth metal hydroxide include sodium hydroxide (NaOH), calcium hydroxide (Ca (OH) ₂ ), and potassium hydroxide (KOH).

In the above processing method, the pH and ORP of the mixed aqueous solution are measured as needed, and based on the results, the reducing agent aqueous solution and the alkaline aqueous solution are appropriately supplemented from the reducing agent aqueous solution tank and the alkaline aqueous solution tank to the mixed aqueous solution storage unit.
6-10 are preferable and, as for pH of the mixed aqueous solution introduce | transduced into a reduction reaction area | region, 8-9 are more preferable. The ORP of the mixed aqueous solution is preferably −50 to 100 mV, more preferably −50 to 0 mV.

  When inspecting the gas before release, for example, NOx concentration measurement with a NOx meter, ozone concentration measurement with an ozone monitor, etc. are arbitrarily performed on the gas before release, and the operating conditions of the processing method are necessary based on the results Will be modified accordingly.

For example, when ozone is detected in the exhaust gas by 1 ppm or more, the ozone emission is suppressed by adjusting the ozone generation amount in the plasma reaction part.
The treatment method of the present invention is suitable for the treatment of exhaust gas discharged from a furnace tube type boiler or exhaust gas discharged from a diesel engine.

The present invention also provides an exhaust gas processing apparatus used in the above processing method.
The treatment apparatus of the present invention includes a wet reactor having an oxidation reaction region and a reduction reaction region, an atmospheric pressure low temperature non-equilibrium discharge plasma reaction unit that generates radical gas from air, and supplies the generated radical gas to the oxidation reaction region. An exhaust gas supply unit that supplies exhaust gas containing nitrogen oxide to the oxidation reaction region, and an aqueous solution supply circulation unit that supplies and circulates the reducing agent aqueous solution and the alkaline aqueous solution to the wet reactor. In the exhaust gas processing apparatus, an exhaust gas cooling device is provided between the exhaust gas generation source and the exhaust gas supply unit, and an exhaust gas temperature measurement unit is provided between the cooling device and the oxidation reaction region, and the measurement is performed. An exhaust gas temperature control unit for operating the exhaust gas cooling device based on the measurement result of the unit is provided.

  According to this processing apparatus, since the temperature of the exhaust gas introduced into the oxidation reaction region can be maintained within a predetermined range, the exhaust gas can be processed efficiently without reducing the oxidation reaction rate of nitrogen oxides by ozone gas. .

  Therefore, even if the temperature of the exhaust gas becomes high, the nitrogen oxide in the exhaust gas can be treated efficiently and stably without deteriorating the treatment performance of the exhaust gas containing nitrogen oxide.

The wet reactor in the treatment apparatus of the present invention is preferably a tower reactor or a column reactor having excellent reaction efficiency.
In order to promote the contact between the gas and the liquid in the reduction reaction region, polypropylene Terralet S- (II) (manufactured by Tsukishima Environmental Engineering Co., Ltd., trade name), SUS Rashihi Super Ring RSR ( Rashihi's product name) is filled.

Although it does not specifically limit as a cooling device in the exhaust-gas processing apparatus of this invention, For example, a water spray type cooler etc. are mentioned.
The mixed aqueous solution circulation section in the exhaust gas treatment apparatus according to the present invention is composed of a circulation line and a circulation pump for circulating the mixed aqueous solution in the mixed aqueous solution storage section provided in the lower part of the wet reactor to the reduction reaction region.

Hereinafter, the processing apparatus of this invention is demonstrated in detail based on drawing.
FIG. 1A is an explanatory diagram showing an overall configuration of a processing apparatus according to an embodiment of the present invention, and FIG. 1B is an explanatory diagram showing an overall configuration of a conventional processing apparatus to be compared.

First, the processing apparatus according to the embodiment of the present invention shown in FIG. 1A will be described.
The treatment apparatus of the present invention includes an ozonizer 1 as a low temperature non-equilibrium discharge plasma reaction section, a boiler 2 having an exhaust gas cooling device 2a, a wet reactor 3 having an oxidation reaction region 4 and a reduction reaction region 5, and a wet reactor. 3, a mixed aqueous solution storage unit 10 provided at a lower portion, an exhaust gas supply line 2 b connecting the boiler 2 and the oxidation reaction region 4, and an exhaust gas temperature measurement unit provided in the exhaust gas supply line 2 b immediately before the oxidation reaction region 4 2c, an exhaust gas temperature control unit 2d electrically connected via a signal line between the exhaust gas temperature measuring unit 2c and the exhaust gas cooling device, an ozone supply line 1a connecting the ozonizer 1 and the oxidation reaction region 4 The mixed aqueous solution circulation line 9 mainly connects the reservoir 10 and the upper part of the reduction reaction region 5 via the circulation pump 11.

  In more detail, the ozonizer 1 generates ozone by processing air with low-temperature non-equilibrium plasma, and the generated ozone gas passes from the upper part of the ozonizer 1 through the ozone supply line 1a. The gas is led to the middle of the exhaust gas supply line 2 b from the boiler 2, and is led to the oxidation reaction region 4 together with the exhaust gas from the boiler 2.

  An exhaust gas cooling device 2a is provided above the boiler 2, and the nitrogen oxide-containing exhaust gas after being cooled to a predetermined temperature or less by the exhaust gas cooling device 2a passes through the exhaust gas supply line 2b. On the way, it is combined with the ozone gas and guided to the oxidation reaction region 4.

  Immediately before being introduced into the oxidation reaction region 4, the temperature of the nitrogen oxide-containing exhaust gas is measured by the exhaust gas temperature measurement unit 2 c, and the measurement result is converted into an electrical signal and sent to the exhaust gas temperature control unit.

When the measurement result received from the exhaust gas temperature measuring unit 2c exceeds a predetermined temperature, for example, 150 ° C., the exhaust gas temperature control unit 2d issues a signal for starting the exhaust gas cooling device 2a to the exhaust gas cooling device.
Conversely, the exhaust gas temperature control unit 2d sends a signal for stopping the exhaust gas cooling device 2a when the measurement result received from the exhaust gas temperature measurement unit 2c is below a predetermined temperature, for example, 130 ° C. Leave to.

  The wet reactor 3 is a column type reactor composed of a lower oxidation reaction region 4 and an upper reduction reaction region 5, and the oxidation reaction region 4 and the reduction reaction region 5 are in one wet reactor 3 (scrubber). Exists. A treated gas discharge port 15 is provided at the upper end of the wet reactor 3, and a reservoir 10 is provided under the oxidation reaction region 4.

A spray 6 is installed above the reduction reaction region 5, and a mixed aqueous solution of a reducing agent (for example, Na ₂ SO ₃ ) aqueous solution and an alkali (for example, NaOH) aqueous solution circulated from the storage unit 10 through the circulation line 9 is sprayed 6. To the reduction reaction region 5.
The inside of the reduction reaction region 5 is filled with a filler (not shown) for improving the degree of contact between gas and liquid and promoting the reduction reaction.

The boundary between the reduction reaction region 5 and the oxidation reaction region 4 allows the oxidation gas containing NO ₂ gas generated in the oxidation reaction region 4 to pass through the reduction reaction region 5 and the mixed aqueous solution from the reduction reaction region 5 to the oxidation reaction region 4. A partition wall having a plurality of passage holes for passing therethrough is provided.

  Further, the boundary between the oxidation reaction region 4 and the storage unit 10 may be provided with a partition wall having a plurality of passage holes for allowing the mixed aqueous solution that has passed through the oxidation reaction region 4 from the reduction reaction region 5 to pass therethrough. .

  An aqueous solution replenishment line 14 is connected to the upper part of the reservoir 10 and an overflow port (not shown) is provided in preparation for the reservoir 10 being filled with the mixed aqueous solution. In addition, a circulation line 9 of the mixed aqueous solution is connected to the lower part of the storage unit 10.

Nitrogen oxides in the exhaust gas introduced into the oxidation reaction region 4 are oxidized by the ozone introduced into the oxidation reaction region 4 to become NO ₂ .
The oxidizing gas containing NO ₂ thus generated in the oxidation reaction region enters the reduction reaction region 5 and is reduced by contacting with the mixed aqueous solution sprayed from the spray 6 to become nitrogen gas. It is discharged from the outlet 15 into the atmosphere.

The mixed aqueous solution after contacting the oxidizing gas containing NO ₂ in the reduction reaction region 5 enters the oxidation reaction region 4 from the reduction reaction region 5, and further enters the storage unit 10 from the oxidation reaction region 4 to be prepared for the next circulation. .

  The mixed aqueous solution circulation part is composed of a circulation line 9 and a circulation pump 11 provided in the middle thereof, the start end of the circulation line 9 is connected to the lower part of the storage part 10, and the end thereof is connected to the spray 6. ing.

  The mixed aqueous solution stored in the storage unit 10 returns to the storage unit 10 from the storage unit 10 through the circulation line 9, the reduction reaction region 5, and the oxidation reaction region 4 by driving the circulation pump 11. .

  A part of the circulated mixed aqueous solution enters a path branched from the circulation line 9, and ORP and pH are measured by the ORP meter 12 and the pH meter 13, respectively, and then returned to the storage unit 10 through the aqueous solution replenishment line 14. . In this embodiment, the ORP meter 12 is provided on the upstream side and the pH meter is provided on the downstream side, but the order of these is arbitrary.

Reducing agent aqueous solution replenishment line 7a and alkaline aqueous solution replenishment line 8a are connected to aqueous solution replenishment line 14 on the downstream side of ORP meter 12 and pH meter 13, respectively.
The leading end of the reducing agent aqueous solution replenishment line 7 a is connected to a reducing agent (Na ₂ SO ₃ ) aqueous solution tank 7, and the tip of the alkaline aqueous solution supplementing line 8 a is connected to the alkaline (NaOH) aqueous solution tank 8.

  When the measured ORP value of the mixed aqueous solution is higher than a predetermined value, a reducing agent aqueous solution is supplied to the reservoir 10 by turning on a liquid feed pump (not shown) provided in the middle of the reducing agent aqueous solution replenishment line 7a. To be replenished.

  Similarly, when the measured pH of the mixed aqueous solution is lower than a predetermined value, an alkaline aqueous solution is replenished to the reservoir by turning on a liquid feed pump (not shown) provided in the middle of the alkaline aqueous solution replenishment line 8a. The

  Thus, the ORP and pH of the mixed aqueous solution are measured as needed, and the ORP and pH of the mixed aqueous solution stored in the storage unit 10 are appropriately supplemented with the reducing agent aqueous solution and the alkaline aqueous solution based on the results. The predetermined range is maintained.

  Therefore, the activity of the mixed aqueous solution in the storage unit 10 is maintained within a predetermined range even though the mixed aqueous solution that has been circulated through the wet reactor 3 and the activity has decreased is returned to the storage unit 10.

In this embodiment, the reducing agent aqueous solution and the alkaline aqueous solution is replenished is temporarily stored in the storage unit 10, because that is not in contact with the ozone gas and exhaust gas, CO ₂ contained rapid oxidation of the reducing agent by the ozone gas, and in the exhaust gas It is possible to avoid the rapid deterioration of the alkaline aqueous solution due to.

FIG. 1B is an explanatory diagram showing the entire configuration of a processing apparatus of a conventional example described in Patent Document 5 and used as a comparison target in a test example described later.
In this conventional example, the exhaust gas temperature measuring unit 2c, the exhaust gas temperature control unit 2d, and the exhaust gas cooling device 2a in the embodiment of the present invention shown in FIG. 1A are not provided. It is different from the processing device.

  In this conventional example, since the temperature of the exhaust gas is not controlled within a predetermined range, if the temperature of the exhaust gas exceeds, for example, 150 ° C., the oxidation reaction rate of nitrogen oxides by ozone gas in the oxidation reaction region decreases, and as a result As a result, the exhaust gas processing performance is lowered.

  On the other hand, in the processing apparatus according to the present invention, the exhaust gas temperature is maintained in a predetermined range, so that the oxidation reaction rate of nitrogen oxides by ozone gas does not decrease, and the exhaust gas processing performance can be maintained at a high level. .

  Therefore, according to the processing apparatus of the present invention, even if the load on the boiler increases and the temperature of the exhaust gas increases, the processing apparatus can be efficiently operated without degrading the processing performance of the processing apparatus. .

In the processing apparatus of the present invention, the reducing agent aqueous solution is branched from the circulation line 9 and passes through the ORP meter 12 and the pH meter 13 in FIG. 1A representing one embodiment of the processing apparatus of the present invention and downstream thereof. The aqueous solution replenishment line 14 that joins the reducing agent aqueous solution replenishment line 7a from the tank 7 and the alkaline aqueous solution replenishment line 8a from the alkaline aqueous solution tank 8 to reach the storage unit 10 is not essential and is optional and can be omitted.
Next, the effects of the present invention are illustrated by giving test examples.

Test example 1
Using the treatment apparatus of the present invention shown in FIG. 1A and the conventional treatment apparatus to be compared shown in FIG. 1B, a treatment test for exhaust gas from a pilot plant boiler was conducted using city gas as fuel under the following conditions. It was.
Exhaust gas flow rate: 1390 Nm ³ / hour Ozone supply amount: 86 g / hour NO concentration in exhaust gas: 28-29 ppm
Flow rate of mixed aqueous solution: 4.5 m ³ / hour ORP of mixed aqueous solution: −72 to −57 mV
PH of mixed aqueous solution: 8.3-8.4

The temperature of the exhaust gas at the exhaust gas outlet from the boiler 2 and the temperature of the exhaust gas immediately before introduction into the oxidation reaction region 4 were measured over time using a thermocouple.
FIG. 2A shows the measurement results when the processing apparatus of the present invention is used, and FIG. 2B shows the measurement results when the conventional processing apparatus is used.

  In the processing apparatus of the present invention in which the temperature of the exhaust gas is controlled, the exhaust gas temperature near the exhaust gas outlet of the boiler is about 320 ° C., but the cooling device 2a is activated by the action of the exhaust gas temperature control unit 2d and the exhaust gas is discharged. As a result of the cooling of the gas, the temperature of the exhaust gas introduced into the oxidation reaction region 4 was maintained at about 160 ° C. (see FIG. 2A).

  On the other hand, in a conventional processing apparatus that does not include an exhaust gas cooling device, the exhaust gas temperature near the exhaust gas outlet of the boiler is about 320 ° C., and the temperature of the exhaust gas introduced into the oxidation reaction region 4 is slightly lowered. Maintained at about 275 ° C. (see FIG. 2B).

Test example 2
In parallel with Test Example 1 above, the concentration of NO and NOx in the exhaust gas at the exhaust gas outlet from the boiler 2 and the concentration of NO and NOx in the exhaust gas that passed through the oxidation reaction region 4 were measured using a gas analyzer. Using a Horiba Seisakusho Co., Ltd., PG-240, each was measured over time.
FIG. 3A shows a measurement result when the processing apparatus of the present invention is used, and FIG. 3B shows a measurement result when the conventional processing apparatus is used.

  In the treatment apparatus of the present invention in which the temperature of the exhaust gas is controlled, the NO concentration of about 28 ppm at the boiler outlet is oxidized in the oxidation reaction region to be reduced to about 0 ppm, and the NOx concentration of about 34 ppm at the boiler outlet is reduced to about 12 ppm. (See FIG. 3A).

  On the other hand, in a conventional processing apparatus that does not control the exhaust gas temperature, the NO concentration of about 29 ppm at the boiler outlet is reduced to about 26 ppm in the oxidation reaction region, and the NOx concentration of about 34 ppm at the boiler outlet is reduced to about 31 ppm. (See FIG. 3B).

Test example 3
Using the treatment apparatus of the present invention shown in FIG. 1A, a treatment test of exhaust gas from a pilot plant boiler was performed under the following conditions.
Flow rate of exhaust gas: 415 to 1390 Nm ³ / hour Supply amount of ozone: 25 to 175 g / hour Flow rate of mixed aqueous solution: 2.5 to 4.5 m ³ / hour ORP of mixed aqueous solution: −73 to 37 mV
PH of mixed aqueous solution: 7.7 to 8.4

In this test, using heavy oil or city gas as fuel, the temperature of exhaust gas in the oxidation reaction region and the molar amount of NO oxidation and ozone supply when the boiler is subjected to low, medium or high load. The relationship of the ratio (ΔNO / O ₃ ) was examined. The results are shown in FIG.
The operating conditions at low load, medium load and high load are as follows.
Low load: City gas combustion amount: 30 m ³ / hour; Heavy oil combustion amount: 50 L / hour Medium load: City gas combustion amount: 70 m ³ / hour High load: City gas combustion amount: 100 m ³ / hour; Heavy oil combustion amount: 89 L /time

As is apparent from FIG. 4, the molar ratio (ΔNO / O ₃ ) between the NO oxidation amount and the ozone supply amount is stable until the exhaust gas temperature is around 150 ° C., but from around 150 ° C. The molar ratio rapidly decreases, and when the exhaust gas temperature is around 260 ° C., the molar ratio becomes about 0.2, indicating that NO and ozone are hardly reacted.

From the results obtained in this test, the relationship between the exhaust gas temperature and the molar ratio (ΔNO / O ₃ ) can be expressed by the following equation.
ΔNO / O ₃ = −exp [(T-175) / 40] /10+1.15

The molar ratio (ΔNO / O ₃ ) is equal to the concentration ratio [ΔNO (ppm) / O ₃ (ppm)] in the exhaust gas between the NO oxidation amount and the ozone supply amount.
From this test result, if the temperature of the exhaust gas is controlled to about 150 ° C. or less by using a cooling device, it is possible to suppress a decrease in the reaction rate between nitrogen oxides and ozone gas, and therefore, the NOx removal performance can be maintained at a high level. I understand.

DESCRIPTION OF SYMBOLS 1 Ozonizer 1a Ozone supply line 2 Boiler 2a Exhaust gas cooling device 2b Exhaust gas supply line 2c Exhaust gas temperature measurement part 2d Exhaust gas temperature control part

3 Wet reactor 4 Oxidation reaction zone 5 Reduction reaction zone 6 Spray 7 Reducing agent aqueous solution tank 7a Reducing agent aqueous solution replenishment line 8 Alkaline aqueous solution tank 8a Alkaline aqueous solution replenishment line 9 Mixed aqueous solution circulation line

DESCRIPTION OF SYMBOLS 10 Mixed aqueous solution storage part 11 Circulation pump 12 ORP meter 13 pH meter 14 Aqueous solution replenishment line 15 Gas discharge port

Claims (6)

Introducing exhaust gas containing nitrogen oxides and ozone gas into the oxidation reaction region, reacting nitrogen oxides in the exhaust gas with ozone gas, oxidizing the nitrogen oxides and converting them into NO ₂ -containing oxidizing gas In the exhaust gas treatment method, the temperature of the exhaust gas introduced into the oxidation reaction region by operating the exhaust gas cooling device when the temperature of the exhaust gas introduced into the oxidation reaction region exceeds a predetermined temperature (A) Is reduced below a predetermined temperature (B) to promote the oxidation reaction of nitrogen oxides in the exhaust gas,
The predetermined temperature (A) is 150 ° C., the predetermined temperature (B) is 130 ° C.,
The relationship between the amount of ozone to be introduced (O ₃ , ppm) and the required oxidation amount of NO (ΔNO, ppm) and the exhaust gas temperature (T ° C.):
ΔNO / O ₃ = −exp [(T-175) / 40] /10+1.15
A method for treating exhaust gas, characterized in that the amount is determined by the above. The processing method according to claim 1, wherein the ozone gas is a radical gas generated from air by an atmospheric pressure low temperature non-equilibrium discharge plasma reaction. Wherein the NO ₂ containing oxidizing gas is reduction treatment with a reducing agent aqueous solution, the processing method according to claim 1 or 2. The processing method according to any one of claims 1 to 3 , wherein the exhaust gas is exhaust gas from a furnace flue boiler or a diesel engine. A wet reactor equipped with an oxidation reaction region and a reduction reaction region; an atmospheric pressure low-temperature nonequilibrium discharge plasma reaction unit that generates radical gas from air; a radical gas supply unit that supplies the generated radical gas to the oxidation reaction region; In an exhaust gas processing apparatus comprising an exhaust gas supply unit that supplies exhaust gas containing nitrogen oxides to an oxidation reaction region, and an aqueous solution supply circulation unit that supplies and circulates a reducing agent aqueous solution and an alkaline aqueous solution to a wet reaction unit, An exhaust gas cooling device is provided between the exhaust gas generation source and the exhaust gas supply unit, an exhaust gas temperature measurement unit is provided between the cooling device and the oxidation reaction region, and based on the measurement result of the measurement unit An exhaust gas temperature control unit for operating the exhaust gas cooling device is provided,
The exhaust gas temperature control unit operates the exhaust gas cooling device when the temperature measured by the exhaust gas temperature measurement unit exceeds 150 ° C., and the temperature measured by the exhaust gas temperature measurement unit is 130 ° C. or less. Provided to lower,
The atmospheric pressure low temperature non-equilibrium discharge plasma reaction part is an ozonizer,
Based on the required amount of oxidation of NO (ΔNO, ppm) and exhaust gas temperature (T ° C.), the amount of ozone (O ₃ , ppm) required for oxidation of NO is expressed by (formula) ΔNO / O _3. = -Exp [(T-175) / 40] /10+1.15, and further includes a computer that controls the adjustment of the frequency of the ozonizer and the adjustment of the air supply amount to the ozonizer based on the calculation result. An exhaust gas processing apparatus characterized by the above. The exhaust gas processing device according to claim 5 , wherein the exhaust gas cooling device is a water spray type cooler.

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