JP2012125698A - Method and device of treating exhaust gas, and boiler system including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device capable of automatically, continuously, and efficiently purifying nitrogen oxide included in exhaust gas stably for a long period of time, and to provide a boiler system including the same.SOLUTION: The method of treating exhaust gas includes: a step of mixing an oxidizing agent to the exhaust gas of a combustor for burning supplied fuel and discharging the exhaust gas containing nitrogen oxide and thereby oxidizing nitrogen oxide in the exhaust gas to thereby convert the exhaust gas into NO-containing oxidized gas; and a step of reducing the NOin the NO-containing oxidized gas by mixing a reducing agent to the NO-containing oxidized gas to thereby convert the NO-containing oxidized gas into nitrogen gas. The supply amount of the oxidizing agent to the exhaust gas and the supply amount of the reducing agent to the NO-containing oxidized gas are adjusted in response to the amount of fuel supplied to the combustor.

Description

  The present invention relates to an exhaust gas processing method, a processing apparatus used in the exhaust gas processing method, and a boiler system equipped with the processing method, and a processing method, a processing apparatus, and the same that can efficiently purify nitrogen oxides contained in exhaust gas. It relates to boiler systems.

Nitrogen oxides such as nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) are discharged along with the supply and consumption of energy typified by power plants, diesel engines and boilers.
Nitrogen oxides discharged into the environment cause photochemical smog, and countermeasures are being considered as an important issue for environmental problems in large cities. Attention has been paid.

  As a method for reducing nitrogen oxide, a combustion method, a catalyst method, a selective catalyst reduction method (SCR), an ammonia injection method, and the like are known. In recent years, nitrogen oxides are reduced by combining the catalyst method, non-thermal plasma, and electron beam technologies, and other chemical substances such as plasma, electron beam method, ammonia, hydrogen peroxide, and calcium chloride. There is known a method for reducing nitrogen oxides in combination with a method using a catalyst or a catalyst.

Among such methods, the plasma-chemical hybrid method is attracting attention. This method purifies exhaust gas containing nitrogen oxides, supplying air to a discharge plasma reactor to generate radical gas, supplying the radical gas to an oxidation reaction region, and removing the exhaust gas. The oxidation reaction region is supplied from a line different from the radical gas generation line. Thereby, nitrogen oxides in the exhaust gas are oxidized to an oxidizing gas containing NO ₂ by the radical gas, and then the oxidizing gas is converted to a compound such as Na ₂ SO ₃ , Na ₂ S and Na ₂ S ₂ O _3. NO ₂ is reduced to nitrogen gas and purified by bringing it into contact with the reducing agent aqueous solution contained in the 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, there is a method in which the pH is maintained at 11, the oxidation-reduction potential (ORP) is controlled to −50 to −250 mV, and an additional reducing agent aqueous solution and alkaline aqueous solution are replenished to the circulating treatment solution immediately before introduction into the reduction reaction region. It has been proposed (Non-Patent Document 1).

ORP is an index indicating whether the aqueous solution is an oxidizing atmosphere or a reducing atmosphere. The lower this value (0 mV or less), the stronger the reducing atmosphere, and the larger the value, the transition from the reducing atmosphere to the oxidizing atmosphere, Above 100 mV, the reduction reaction hardly occurs.
Further, in an acidic atmosphere at pH 6 or lower, Na ₂ SO ₃ as a reducing agent reacts with the acid and is wasted, and harmful SO ₂ is generated. Therefore, it is necessary to maintain the aqueous solution at a pH higher than pH 6.

International Publication No. 05/0665805 Pamphlet Japanese Patent Application Laid-Open No. 2004-068684 Japanese Patent Application Laid-Open No. 2000-117049 JP 2000-016553 A 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)

Although the method of Non-Patent Document 1 is excellent, it is a method performed in a laboratory. In this experiment, 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 present inventors performed a test on the method of Non-Patent Document 1 using a boiler combustor to replenish an additional reducing agent aqueous solution and an alkaline aqueous solution to the circulating treatment liquid immediately before introduction into the reduction reaction region. Since several percent of CO ₂ was contained in the exhaust gas, the pH of the aqueous solution immediately dropped, and it was difficult to maintain the condition of pH = 11 as described in Non-Patent Document 1. In addition, since ORP also increases, it was 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. Since it deteriorates in a short time, it seems that the additionally replenished aqueous solution did not contribute to the activity recovery of the circulating mixed aqueous solution.
For this reason, it has been difficult to continuously treat the exhaust gas for a long time while maintaining the nitrogen oxide removal performance.

The present invention has been made in view of such circumstances, and automatically and continuously purifies nitrogen oxides contained in exhaust gas stably over a long period of time. The present invention provides a processing method, a processing apparatus, and a boiler system equipped with the processing method capable of suppressing the generation of, for example, N ₂ O, HNO ₂ , HNO ₃ , NO ₃ ⁻ , CO, etc. that are by-produced during processing.

Thus, according to the present invention, an oxidant is mixed in the exhaust gas of the combustor that combusts the supplied fuel and exhausts exhaust gas containing nitrogen oxides, so that the nitrogen oxides in the exhaust gas are mixed. Converting the exhaust gas into a NO ₂ -containing oxidizing gas by oxidizing;
By mixing a reducing agent to the NO ₂ containing oxidizing gas, by reducing the NO ₂ of the NO ₂ containing oxidizing gas, and a step of converting the NO ₂ containing oxidizing gas to the nitrogen gas,
Provided is an exhaust gas processing method for adjusting the supply amount of an oxidant into the exhaust gas and the supply amount of a reducing agent into the NO ₂ -containing oxidation gas according to the amount of fuel supplied to the combustor. Is done.

  Further, according to another aspect of the present invention, a processing unit in which the exhaust gas of a combustor that combusts supplied fuel and exhausts exhaust gas containing nitrogen oxide is introduced, and the exhaust gas is introduced. An oxidant supply unit for supplying an oxidant into the processing unit, a reductant supply unit for supplying a reductant into the processing unit supplied with the oxidant, and a fuel for measuring the amount of fuel supplied to the combustor And a control unit that controls the oxidant supply unit and the reducing agent supply unit based on the measurement result from the fuel amount measurement unit to adjust the supply amount of the oxidant and the reducing agent into the processing unit. And an exhaust gas treatment apparatus.

  According to still another aspect of the present invention, there is provided a boiler system including a furnace flue type boiler and the processing device for processing exhaust gas from the furnace flue type boiler.

According to the present invention, the supply amount of the oxidizing agent into the exhaust gas and the supply amount of the reducing agent into the NO ₂ -containing oxidation gas are adjusted according to the amount of fuel supplied to the combustor. That is, the oxidizing agent and the reducing agent are supplied at appropriate supply amounts in accordance with the NOx generation amount that varies depending on the amount of fuel supplied to the combustor.
Therefore, even if the amount of fuel fluctuates during operation of the combustor, the nitrogen oxide in the exhaust gas can be purified to nitrogen gas in the most efficient state, and stable even in long-term continuous operation. The exhaust gas can be processed automatically.
The present invention is suitable for treatment of exhaust gas discharged from a flue-tube type boiler or exhaust gas discharged from a diesel engine.

FIG. 1 is an explanatory diagram showing the overall configuration of Embodiment 1 of the exhaust gas treatment apparatus of the present invention. FIG. 2 is a block diagram showing a control system in the exhaust gas processing apparatus of the first embodiment. FIG. 3A is a graph showing the relationship between the amount of city gas fuel and the amount of exhaust gas in Example 1, and FIG. 3B is a graph showing the relationship between the amount of city gas fuel and the generated NOx weight in Example 1. It is. FIG. 4 is a graph showing the relationship between the amount of city gas fuel, the required equivalent ratio of the reducing agent aqueous solution, and the required equivalent in Example 1. FIG. 5 is a graph showing the relationship between the elapsed time, the NOx amount before and after the exhaust gas treatment device, and the city gas fuel amount in Example 1. FIG. 6A is a graph showing the relationship between the heavy oil fuel amount and the exhaust gas amount in Example 2, and FIG. 6B is a graph showing the relationship between the heavy oil fuel amount and the generated NOx weight in Example 2. . FIG. 7 is a graph showing the relationship between the amount of heavy oil fuel, the required equivalent ratio of the reducing agent aqueous solution, and the required equivalent in Example 2. FIG. 8 is a graph showing the relationship between the elapsed time and the amount of NOx and the amount of heavy oil fuel before and after the exhaust gas treatment device in Example 2.

In the exhaust gas processing method according to the present invention, an oxidant is mixed in the exhaust gas of a combustor that burns supplied fuel and exhausts exhaust gas containing nitrogen oxides, thereby oxidizing nitrogen in the exhaust gas. Converting the exhaust gas into a NO ₂ -containing oxidizing gas by oxidizing a substance (converting NO into NO ₂ );
By mixing a reducing agent to the NO ₂ containing oxidizing gas, by reducing the NO ₂ of the NO ₂ containing oxidizing gas, and a step of converting the NO ₂ containing oxidizing gas to the nitrogen gas,
The supply amount of the oxidizing agent into the exhaust gas and the supply amount of the reducing agent into the NO ₂ -containing oxidation gas are adjusted according to the amount of fuel supplied to the combustor.
That is, according to the amount of NOx generated that varies depending on the amount (flow rate) of fuel supplied to the combustor, the oxidizing agent and the reducing agent are supplied at appropriate supply amounts, thereby realizing highly efficient exhaust gas processing.

  In this exhaust gas processing method, the exhaust gas is introduced into a combustor that combusts supplied fuel and exhausts exhaust gas containing nitrogen oxides, and the processing unit into which the exhaust gas is introduced. An oxidant supply unit that supplies an oxidant, a reductant supply unit that supplies a reductant into the processing unit that is supplied with the oxidant, and a fuel amount measurement unit that measures the amount of fuel supplied to the combustor. A control unit that controls the oxidant supply unit and the reductant supply unit based on the measurement result from the fuel amount measurement unit to adjust the supply amounts of the oxidant and the reductant into the processing unit. This can be done using an exhaust gas treatment device.

In the exhaust gas treatment method of the present invention, ozone gas (O ₃ ), chlorine dioxide (ClO ₂ ), chlorine (Cl ₂ ), or the like can be used as the oxidant mixed in the exhaust gas. Ozone gas is preferable from the viewpoint that it can be stably supplied at low cost.
Ozone gas can be generated from air, for example, by a low temperature non-equilibrium plasma reaction.
Here, in the present invention, the low temperature non-equilibrium plasma means an ionized plasma whose gas temperature is considerably lower than a normal gas combustion temperature (about 700 to 1000 ° C.), usually means 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.

In addition, the low-temperature non-equilibrium plasma reaction can generate a radical gas containing ozone stably from air, which is suitable for realizing an exhaust gas treatment method in which the efficiency is not lowered even when the steady operation is performed. The radical gas contains O, OH, HO ₂ radicals and the like in addition to ozone.

Most (90% or more) of nitrogen oxides (NOx) generated by combustion of fuel is nitric oxide (NO). The amount of NOx varies depending on the amount of fuel supplied to the combustor. Furthermore, the amount of NOx generated varies depending on the type of fuel. Furthermore, it varies depending on the type of combustor.
For example, when city gas, heavy oil, waste gas, waste oil, or a mixture thereof is supplied as a fuel to the combustor provided in the furnace tube type boiler, the amount of NOx generated naturally increases as the fuel supply amount increases. Furthermore, in the comparison of city gas and heavy oil, the amount of NOx generated in heavy oil is larger than that in city gas even with the same fuel supply amount. Furthermore, the amount of NOx generated increases as the combustor has lower combustion efficiency.

Therefore, the supply amount of an oxidant that oxidizes NO in the exhaust gas and converts it into NO ₂ , for example, O ₃ , is adjusted according to the fuel supply amount, and also corresponds to the type of fuel, and further the type of combustor It is also preferable that the O ₃ supply amount correspond to the above.
A specific O ₃ supply amount can be determined based on data obtained by collecting various data in advance by experiment for each combustor to be used.
For example, for a certain combustor, if the relationship between the fuel supply amount and the exhaust gas amount and the relationship between the fuel supply amount and the NOx generation amount are measured in advance, ozone at an exhaust gas temperature of about 150 ° C. or less Since the reaction molar ratio of NO is 1: 1, an optimum O ₃ supply amount corresponding to the fuel supply amount is derived.

When inspecting the exhaust gas before discharge, for example, NOx concentration measurement by a NOx meter, ozone concentration measurement by an ozone monitor, etc. are arbitrarily performed on the exhaust gas before discharge, and the operating conditions of the processing method are based on the results. Will be modified as necessary.
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 reducing agent used in the exhaust gas treatment method of the present invention includes, for example, at least one compound selected from inorganic sulfur-containing reducing agents.
Specifically, 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 ). Among these reducing agents, sodium sulfite (Na ₂ SO ₃ ) is preferably used from the viewpoint of easy handling.
In this embodiment, a reducing agent solution containing Na ₂ SO ₃ is used as the reducing agent.

The reducing agent to convert the exhaust gas (NO ₂ containing oxidizing gas) reduced to nitrogen gas NO ₂ in (N _2), for example, the supply amount of Na ₂ SO ₃ is performed supply optimum O ₃ amount The amount of NO ₂ generated by NOx oxidation and efficient Na ₂ SO ₃ supply by conducting an experiment to investigate the relationship between the fuel supply rate and the efficient Na ₂ SO ₃ supply rate It can be determined by conducting an experiment examining the relationship with the quantity.

More specifically, the exhaust gas treatment method includes introducing an exhaust gas into the oxidation reaction region of a wet reactor equipped with an oxidation reaction region and a reduction reaction region and a treatment liquid reservoir provided above and below the oxidation reaction region. In the reaction zone, ozone gas is contacted with exhaust gas to convert it to NO ₂ containing oxidizing gas, and in the reduction reaction zone, the reducing agent solution is brought into contact with NO ₂ containing oxidizing gas to convert it to nitrogen gas and reduced to NO ₂ containing oxidizing gas. The treatment liquid contacted with the agent solution is stored in the treatment liquid storage section, and the treatment liquid mixed with the reducing agent solution supplied into the treatment liquid storage section is circulated to the reduction reaction region, so that it can be performed continuously and efficiently.

In this case, regardless of the type of fuel and the type of combustor, further fine adjustment of the Na ₂ SO ₃ supply amount or pH adjustment may be performed as in (1) to (3) below, and these are combined. It is preferable.
(1) The SO ₃ ²⁻ concentration of the treatment liquid is measured, and the treatment is performed so that the SO ₃ ²⁻ concentration is maintained at 1.0 to 2.0%, preferably at 1.5%. Finely adjust the supply amount of the reducing agent solution to the liquid reservoir.
In this case, after the control unit performs the main control of the oxidant supply amount of the oxidant supply unit and the reductant supply amount of the reductant supply unit based on the measurement result from the fuel amount measurement unit, the SO ₃ ^2- The concentration is measured, and adjustment control of the reducing agent supply amount is performed based on the measurement result of SO ₃ ²⁻ so that the SO ₃ ²⁻ concentration falls within a predetermined range.

(2) The oxidation-reduction potential (ORP) of the treatment liquid is measured, and the supply amount of the reducing agent solution to the treatment liquid reservoir is finely adjusted based on the result.
In this case, the processing apparatus further includes an ORP meter that measures the ORP of the processing liquid and outputs the measurement result to the control unit, and the control unit includes an oxidant supply unit based on the measurement result from the fuel amount measurement unit. After performing the main control of the oxidizing agent supply amount and the reducing agent supply amount of the reducing agent supply unit, adjustment control of the reducing agent supply amount based on the measurement result from the ORP meter is performed so that the ORP is within a predetermined range. Configured.

(3) The pH value of the treatment liquid may be measured, and an alkaline component may be added to the treatment liquid reservoir based on the result.
In this case, the processing apparatus further includes a pH meter that measures the pH of the processing liquid and the measurement result is output to the control unit, and the control unit measures the amount of fuel. After the main control of the oxidizing agent supply amount of the oxidizing agent supply unit and the reducing agent supply amount of the reducing agent supply unit based on the measurement result from the unit, the measurement result from the pH meter so that the pH falls within the predetermined range Is configured to perform adjustment control of the reducing agent supply amount based on the above.
Alternatively, the reducing agent solution does not contain an alkali component, and as the alkali component, for example, a NaOH aqueous solution supply unit is separately provided, and the processing apparatus is configured to perform adjustment control of the NaOH aqueous solution based on the measurement result from the pH meter. May be.

In both (1) and (2), fine adjustment of the supply amount of the reducing agent solution is performed in order to maintain the optimum activity of Na ₂ SO ₃ as the reducing agent in the treatment liquid, ), The pH is finely adjusted to maintain the optimum pH of the treatment liquid.
In the case of (1) above, the SO ₃ ²⁻ concentration in the treatment liquid is directly measured, and the SO ₃ ²⁻ concentration is maintained at 1.0 to 2.0%. The optimum activity of ₂ SO ₃ is maintained. If the SO ₃ ²⁻ concentration is less than 1.0%, the reduction efficiency of NO ₂ is greatly reduced, which is not preferable. Further, there is no problem even if the SO ₃ ²⁻ concentration exceeds 2.0%, but since the efficiency of reducing NO ₂ is not significantly improved, it is not preferable because the reducing agent solution is wasted.

  In the case of (2), it is preferable to maintain ORP at −50 to 100 mV, and more preferably at −50 to 0 mV. When the ORP is less than −50 mV, the reducing agent solution is supplied more than necessary, which is not preferable because the reducing agent solution is wasted. On the other hand, if it exceeds 100 mV, it becomes an oxidation reaction atmosphere, and a reduction reaction is not performed.

In the case of (3), the pH is preferably maintained at 6 to 10, more preferably 8 to 9. When the pH is lower than 6, SO ₃ ^2- reacts with the acid and is wasted, and harmful SO ₂ is generated. On the other hand, if it exceeds 10, it becomes a strong alkaline solution and it becomes difficult to handle it, which is not preferable.
Examples of the alkali component include compounds selected from alkali metal or alkaline earth metal hydroxides.
Examples of the alkali metal or alkaline earth metal hydroxide include sodium hydroxide (NaOH), calcium hydroxide (Ca (OH) ₂ ), and potassium hydroxide (KOH). Used.

As described above, since the reducing agent (and alkali component) is temporarily stored in the treatment liquid storage part and does not come into contact with the ozone gas and the exhaust gas, rapid oxidation (deterioration) of the reducing agent by the ozone gas and in the exhaust gas. Rapid deterioration of the alkali component due to CO ₂ contained can be avoided.
As a result, a decrease in pH and an increase in ORP of the processing solution that circulates during continuous processing are suppressed, contributing to recovery of the activity of the processing solution that is circulated. Therefore, the exhaust gas treatment can be continuously performed efficiently over a long time while maintaining the nitrogen oxide removal performance.

In this case, the reducing agent solution and the alkaline aqueous solution may be individually supplied into the processing liquid storage unit, or a reducing agent solution containing an alkali component may be supplied into the processing liquid storage unit. In the latter case, only one supply path is required, and industrial waste liquid (Na ₂ SO ₃ concentration of about 8 to 12%, NaOH concentration of about 0.4 to 0.6%) is used as a reducing agent solution containing an alkali component. There are advantages you can do.
In addition, this industrial waste liquid is a by-product at the time of sulfuric acid manufacture, for example, can be obtained from Teika Co., Ltd.

  Hereinafter, embodiments of an exhaust gas processing method and a processing apparatus of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is an explanatory diagram showing the overall configuration of Embodiment 1 of the exhaust gas processing apparatus of the present invention, and FIG. 2 is a block diagram showing a control system in the exhaust gas processing apparatus of Embodiment 1.
The processing apparatus combusts the supplied fuel and discharges exhaust gas containing nitrogen oxides. The processing unit in which the exhaust gas is introduced into the combustor, and the processing unit into which the exhaust gas is introduced has an oxidant. An oxidant supply unit for supplying, a reductant supply unit for supplying a reductant into the processing unit supplied with the oxidant, a fuel amount measuring unit for measuring the amount of fuel supplied to the combustor, and the fuel A control unit that controls the oxidant supply unit and the reducing agent supply unit based on the measurement result from the amount measurement unit to adjust the supply amount of the oxidant and the reducing agent into the processing unit.

  More specifically, this processing apparatus is a wet type equipped with an ozonizer (oxidant supply unit) P1 as a low-temperature non-equilibrium discharge plasma reaction unit, and a reduction reaction region P5, an oxidation reaction region P4, and a processing liquid storage unit P10 from the top. Reactor (treatment unit) P3, reducing agent aqueous solution tank P7 and pump P7b (reducing agent supply unit), exhaust gas supply line 2b connecting boiler (combustor) 2 and oxidation reaction region P4 of wet reactor P3, exhaust An ozone supply line P1a that connects the ozonizer P1 and the oxidation reaction region P4 via the gas supply line 2b, and a treatment liquid circulation line that connects the reservoir P10 and the upper part of the reduction reaction region P5 via the treatment liquid circulation pump P11. P9 branches from the circulation line P9, passes through the ORP meter P12 and pH meter P13, and downstream from the reducing agent aqueous solution tank P7. From the aqueous solution replenishment line P14 that joins the original agent aqueous solution replenishment line P7a and reaches the reservoir P10, the fuel flow meter (fuel amount measuring unit) P20 that measures the flow rate of fuel supplied to the boiler 2, and the fuel flow meter P20 From the control unit P30 (see FIG. 2) that controls the ozonizer P1 and the pump P7b of the reducing agent aqueous solution tank P7 on the basis of the measurement results to adjust the supply amount of the oxidizing agent and the reducing agent to the wet reactor P3. It is configured.

  The ozonizer P1 treats air with low-temperature non-equilibrium plasma to generate ozone, which is a kind of radical gas. The gas is led to the middle of the gas supply line 2b and led to the oxidation reaction region P4 together with the exhaust gas from the boiler 2.

  An exhaust heat recovery device 2a is provided in the upper part of the boiler 2, and the nitrogen oxide-containing exhaust gas after the heat is recovered by the exhaust heat recovery device 2a passes through the exhaust gas supply line 2b, and in the middle Together with the ozone gas, it is led to the oxidation reaction region P4.

The wet reactor P3 is a tower reactor composed of a lower oxidation reaction region P4 and an upper reduction reaction region P5. The oxidation reaction region P4 and the reduction reaction region P5 are in one wet reactor P3 (scrubber). Exists. In addition, a column type reactor can also be used as a wet reactor.
A treated gas discharge port P15 is provided at the upper end of the wet reactor P3, and a reservoir P10 is provided below the oxidation reaction region P4.

A spray P6 is installed above the reduction reaction region P5, and a treatment liquid containing a reducing agent (for example, Na ₂ SO ₃ ) aqueous solution and an alkali (for example, NaOH) aqueous solution circulated from the reservoir P10 through the circulation line P9 is sprayed. Sprayed from P6 into the reduction reaction region P5.
The inside of the reduction reaction region P5 is filled with a filler (not shown) for improving the degree of contact between gas and liquid and promoting the reduction reaction. As this filler, for example, Terralet S- (II) made of polypropylene (trade name, manufactured by Tsukishima Environmental Engineering Co., Ltd.), Rashihi Super Ring RSR made by SUS (trade name, manufactured by Rashihi Co., Ltd.) can be used. .

The boundary between the reduction reaction region P5 and the oxidation reaction region P4 allows the oxidation gas containing NO ₂ gas generated in the oxidation reaction region P4 to pass through the reduction reaction region P5, and the treatment liquid from the reduction reaction region P5 to the oxidation reaction region P4. A partition wall having a plurality of passage holes for passing therethrough is provided.
In addition, the boundary between the oxidation reaction region P4 and the storage portion P10 may be provided with a partition wall having a plurality of passage holes for allowing the treatment liquid that has passed through the oxidation reaction region P4 from the reduction reaction region P5 to pass therethrough. .

  A processing liquid replenishment line P14 is connected to the upper part of the storage part P10, and an overflow port (not shown) is provided in preparation for the storage part P10 being full of processing liquid. A processing liquid circulation line P9 is connected to the lower portion of the reservoir P10.

The nitrogen oxides in the exhaust gas introduced into the oxidation reaction region P4 are oxidized by the ozone introduced into the oxidation reaction region P4 to become NO ₂ .
The oxidizing gas containing NO ₂ thus generated in the oxidation reaction region enters the reduction reaction region P5, is reduced by contact with the treatment liquid sprayed from the spray P6, and becomes nitrogen gas. It is discharged into the atmosphere from the outlet P15.

The treatment liquid that has come into contact with the oxidizing gas containing NO ₂ in the reduction reaction region P5 enters the oxidation reaction region P4 from the reduction reaction region P5, and further enters the storage unit P10 from the oxidation reaction region P4, and is prepared for the next circulation. .

  The treatment liquid circulation part is composed of a circulation line P9 and a circulation pump P11 provided in the middle thereof, the start end of the circulation line P9 is connected to the lower part of the storage part P10, and the end thereof is connected to the spray P6. ing.

The processing liquid stored in the storage part P10 returns to the storage part P10 from the storage part P10 via the circulation line P9, the reduction reaction region P5, and the oxidation reaction region P4 by driving the circulation pump P11. .
In addition, when it is necessary to dilute the processing liquid in the reservoir P10, a water supply pipe P16 of the makeup water supply means is connected to the upper portion of the reservoir P10 so that makeup water is supplied to the reservoir P10. The makeup water supply means includes, for example, industrial water as a water source, the water supply pipe P16 connecting the industrial water and the storage part P10, a flow meter provided in the water supply pipe P16, and an electric valve (not shown).

  A part of the circulating processing liquid enters the path branched from the circulation line P9, and the ORP and pH are measured by the ORP meter P12 and the pH meter P13, respectively, and then returned to the storage part P10 again through the processing liquid replenishment line P14. It is. In this embodiment, the ORP meter P12 is provided on the upstream side and the pH meter is provided on the downstream side, but the order of these is arbitrary.

A reducing agent aqueous solution replenishment line P7a is connected to the treatment liquid replenishment line P14 on the downstream side of the ORP meter P12 and the pH meter P13.
The upstream end of the reducing agent aqueous solution replenishment line P7a is a reduction containing a reducing agent aqueous solution in which NaOH (concentration of about 1%) is mixed as an alkaline component in an aqueous solution of Na ₂ SO ₃ (concentration of about 20%) via a pump P7b. It is connected to the agent aqueous solution tank P7. The downstream end of the reducing agent aqueous solution replenishment line P7a is connected to the processing liquid replenishment line P14 via a flow meter.

As shown in FIGS. 1 and 2, the fuel flow meter P20 is provided in a fuel supply pipe P21 that supplies fuel to the combustor of the boiler 2, measures the fuel flow rate, and transmits the measurement value signal to the control unit P30. To do.
The ORP meter P12 measures the ORP of the processing liquid from the storage unit P10 and transmits the measurement value signal to the control unit P30. The pH meter P13 measures the pH of the treatment liquid from the storage unit P10 and transmits the measurement value signal to the control unit P30.
The control unit P30 receives the measurement value signals from the fuel flow meter P20, the ORP meter P12, and the pH meter P13, and the measurement value signals from the fuel flow meter P20, the ORP meter P12, and the pH meter P13. And an output unit that outputs the corresponding output signals to the ozonizer P1, the reducing agent aqueous solution pump P7b, and the electric valve of the water supply pipe P16.

For example, during the continuous operation of the boiler 2 using fuel as city gas, the control unit P30 controls the ozonizer P1 and the reducing agent aqueous solution pump P7b as follows.
For example, when the fuel flow rate of the city gas supplied to the boiler 2 is determined, the control unit P30 outputs an output signal (command signal) for supplying ozone gas at an optimum supply amount to the oxidation reaction region P4 of the processing apparatus to the ozonizer P1. ) And an output signal (command signal) for supplying the reducing agent aqueous solution at an optimum supply amount to the storage unit P10 of the processing apparatus to the pump P7b.
In addition to the control of the pump P7b by the control unit P30, the control unit P30 outputs an output signal to the circulation pump P11 in order to adjust the ejection amount of the processing liquid from the spray P6 according to the fuel flow rate. You may make it do.

Thus, the control unit P30 controls the ozonizer P1 and the reducing agent aqueous solution pump P7b according to the fuel flow rate of the city gas supplied to the boiler 2, so that the ozone gas can be supplied at the optimum supply amount most efficient for the oxidation reaction. While being supplied, the reducing agent aqueous solution is supplied at an optimum supply amount that is most efficient for the reduction reaction.
At this time, the optimal supply amount of ozone gas and the optimal supply amount of the reducing agent aqueous solution differ depending on the type of fuel and the type of combustor of the boiler 2.
Therefore, the optimal supply amount of ozone gas and the optimal supply amount of reducing agent aqueous solution according to the type of fuel, the type of combustor, and the fuel flow rate are preset and input to the control unit P30.
Moreover, since the control part P30 is provided with the operation part which selects the kind of fuel and the kind of combustor which are the use conditions of the boiler 2 to be used, an operator uses a use condition in an operation part before the boiler 2 driving | operation. Can be entered.
Note that the optimum supply amount of ozone gas and the optimum supply amount of the reducing agent aqueous solution according to the type of fuel, the type of combustor, and the fuel flow rate are set in advance by collecting various experimental data.

During such continuous operation of the boiler 2, the treatment liquid that has circulated through the wet reactor P <b> 3 and has decreased in activity is returned to the reservoir P <b> 10, so that the activity of the treatment liquid in the reservoir P <b> 10 deviates from a predetermined range. However, it is preferable to maintain the SO ₃ ²⁻ concentration, ORP, and pH of the treatment liquid in the optimum ranges in order to perform more efficient exhaust gas treatment.
The SO ₃ ²⁻ concentration is preferably maintained at 1.0 to 2.0%, and particularly preferably 1.5%, for the above reasons.
The ORP is preferably maintained at −50 to 100 mV for the reasons described above, and is usually particularly preferably maintained at −50 to 0 mV.
For the above reason, the pH is preferably maintained at 6 to 10, and particularly preferably 8 to 9.

Therefore, during the operation of the boiler 2, each measured value signal from the ORP meter P12 and the pH meter P13 is input to the control unit P30.
The control unit P30 performs the main control of the ozonizer P1 and the reducing agent aqueous solution pump P7b based on the measurement value signal from the fuel flow meter P20, and then the ORP meter P12 and the ORP meter P12 so that the ORP and pH are within the above range. Adjustment control of the electric valve of the ozonizer P1, the pump P7b of the reducing agent aqueous solution P7, and the water supply pipe P16 based on each measurement value signal from the pH meter P13 is also performed.
By such main control and adjustment control, the supply amount of ozone gas and the supply amount of the reducing agent aqueous solution can be adjusted with high accuracy, and thereby more efficient exhaust gas treatment can be performed.
Since the reducing agent aqueous solution contains an alkali component (NaOH), the pH can be adjusted.

The adjustment control for maintaining the SO ₃ ²⁻ concentration, ORP and pH of the treatment liquid within the above ranges is performed, for example, as follows.
When the SO ₃ ²⁻ concentration of the treatment liquid is less than 1.4%, the reducing agent aqueous solution is replenished to the reservoir P10 by turning on the reducing agent aqueous solution pump P7b, and the SO ₃ ²⁻ concentration is 1.5. The pump P7b is turned OFF when it is within the range of ˜1.6%.
When the ORP of the treatment liquid exceeds 100 mV, the reducing agent aqueous solution pump P7b is turned on to replenish the reducing agent aqueous solution in the reservoir P10, and the ORP is in the range of −50 to 100 mV. P7b is turned off.
Further, when the pH of the treatment liquid is less than 6, the reducing agent aqueous solution pump P7b is turned on, so that the reducing agent aqueous solution is replenished to the storage portion P10, and when the pH falls within the range of 6 to 10, the pump P7b. Set to OFF.

As described above, in this embodiment, ozone gas and the reducing agent aqueous solution are supplied to the wet reactor P3 at a supply amount corresponding to at least the fuel supply amount of the boiler 2, so that the exhaust gas treatment (NOx oxidation and NO ₂ oxidation) can be performed efficiently. In addition, the exhaust gas treatment can be performed more efficiently by maintaining the SO ₃ ²⁻ concentration, ORP and pH of the treatment liquid within predetermined ranges.
In addition, since the reducing agent aqueous solution containing the alkali component to be replenished is temporarily stored in the storage part P10 and does not come into contact with the ozone gas and the exhaust gas, the oxidizing agent is rapidly oxidized by the ozone gas, and the CO ₂ contained in the exhaust gas. Rapid deterioration of the alkali component can be avoided.

(Embodiment 2)
In the first embodiment, the case where the reducing agent aqueous solution containing an alkali component is accommodated in one tank P7 to supply the reducing agent aqueous solution into the storage unit P10 using one supply path is exemplified. And a reducing agent aqueous solution that does not contain an alkali component may be housed in a separate tank, and the alkaline aqueous solution and the reducing agent aqueous solution may be independently supplied into the storage portion P10 using different supply paths.

(Embodiment 3)
In the first embodiment, the case where the ozone supply line P1a is connected to the exhaust gas supply line 2b is illustrated, but the ozone supply line P1a may be directly connected to the oxidation reaction region P4.
If it does in this way, the activity fall of ozone by the heat of exhaust gas can be controlled.

(Embodiment 4)
ADVANTAGE OF THE INVENTION According to this invention, the boiler system provided with combining the processing apparatus of the exhaust gas demonstrated in Embodiment 1-3 and the boiler 2 can be provided.

<Example 1>
Using the treatment apparatus of the second embodiment, a treatment test of exhaust gas discharged from a furnace tube type pilot plant boiler was performed. This boiler is equipped with a general oil / gas switching rotary burner as a combustor. The following description will be given with reference to FIGS.
The exhaust gas containing nitrogen oxides discharged from the boiler 2 passed through the exhaust heat recovery device 2a, and then was introduced into the oxidation reaction region P4 of the wet reactor P3 through the exhaust gas supply line 2b.
On the other hand, the radical gas containing ozone generated by the ozonizer P1 was led from the ozone supply line P1a to the exhaust gas supply line 2b and introduced into the oxidation reaction region P4 together with the exhaust gas.
The initial concentration of sodium sulfite in the reservoir P10 was 1.6% (16 g / L).

  The treatment liquid introduced into the reduction reaction region P5 of the wet reactor P3 is sprayed from the upper spray P6 of the reduction reaction region P5, returns to the lower reservoir P10 through the reduction reaction region P5 and the oxidation reaction region P4, Subsequently, it was sent again to the upper spray P6 via the circulation line P9 by the circulation pump P11.

The SO ₃ ²⁻ concentration, pH, and ORP of the processing liquid circulating in the processing apparatus were measured on a path branched from the circulation line P9 to the storage section P10 on the downstream side of the circulation pump P11.
The circulating treatment liquid is a mixed aqueous solution of a reducing agent aqueous solution containing sodium sulfite (Na ₂ SO ₃ ) for reducing NO ₂ to N ₂ and an alkaline aqueous solution containing sodium hydroxide (NaOH) for pH adjustment. In order to control the pH and ORP of this mixed aqueous solution, the reducing agent aqueous solution (concentration: 126 g / L) was replenished at a rate of 1 L / min from the reducing agent aqueous solution tank and the alkaline aqueous solution tank.
In addition, although the liquid level of the storage part P10 rises by replenishment of said aqueous solution, this liquid level is maintained constant by the waste_water | drain from the overflow port (illustration omitted) provided in the upper part of the storage part P10. It was.

In the first embodiment, city gas is supplied to the combustor of the flue-tube type boiler, and the exhaust gas of the flue-tube-type boiler generated in large quantities, that is, exhaust gas containing CO ₂ is used as the gas to be processed. It was.
In Example 1, the amount of city gas fuel (flow rate) was changed in the range of 40 to 160 Nm ³ / hour, and the exhaust gas amount relative to the fuel amount, the generated NOx weight, and the required equivalent ratio of the reducing agent aqueous solution were examined.
FIG. 3A is a graph showing the relationship between the fuel amount and the exhaust gas amount in the first embodiment, and FIG. 3B is a graph showing the relationship between the fuel amount and the generated NOx weight in the first embodiment. FIG. 4 is a graph showing the relationship between the amount of fuel, the required equivalent ratio of the reducing agent aqueous solution, and the required equivalent in Example 1. FIG. 5 is a graph showing the relationship between the elapsed time, the NOx amount before and after the exhaust gas treatment device, and the city gas fuel amount in Example 1.

The exhaust gas amount in FIG. 3 (A) is a value calculated from the fuel amount and the oxygen concentration in the exhaust gas, and the generated NOx weight in FIG. 3 (B) is the exhaust gas collected from the sampling port MP1 of the boiler 2 to the analyzer A. It is a value obtained from the product of the NOx concentration and the amount of exhaust gas measured after introduction. Further, in FIG. 5, ● represents the value measured by introducing the exhaust gas collected from the sampling port MP1 of the exhaust gas supply line 2b into the analyzer A, and ○ represents the sampling port near the gas discharge port P15 of the wet reactor P3. This is a value measured by introducing the exhaust gas collected from MP3 into the analyzer A. The solid line represents the change over time in the amount of city gas fuel.
FIG. 3 shows that the fuel amount and the exhaust gas amount are in a proportional relationship, and the fuel amount and the generated NOx weight are in a proportional relationship.

From FIG. 4, when the fuel amount is 50 to 150 Nm ³ / h, the required equivalent of the reducing agent aqueous solution increases to 0.38 to 1.06 kg / h, but the required equivalent ratio is 20.9 to 9 on the contrary. .9. This is thought to be because the required equivalent ratio increases when the amount of fuel is small, that is, when the amount of generated NOx is small, because the reducing agent also reacts with oxygen in the exhaust gas. This shows that the required equivalent ratio of the reducing agent aqueous solution can be reduced when the amount of fuel is large.
Further, from FIG. 5, during 330 minutes from the start of operation, the NOx amount in the exhaust gas before being introduced into the wet reactor P3 was stable at 65 to 80 ppm and was processed in the wet reactor P3. The amount of NOx in the exhaust gas was reduced to 5 to 35 ppm. Note that when the amount of fuel is large, the amount of NOx after treatment is higher than when the amount of fuel is small because the amount of ozone supply is insufficient.
From this, it turned out that the processing method of the exhaust gas of this invention is effective in the removal of the nitrogen oxide in the exhaust gas discharged | emitted from the boiler 2 which uses city gas as a fuel.

<Example 2>
The second embodiment is substantially the same as the first embodiment except that heavy oil is supplied to the combustor of the furnace tube type boiler and burned.
In Example 2, the fuel amount (flow rate) was changed in the range of 65 to 145 Nm ³ / hour, and the exhaust gas amount, generated NOx weight, and reducing agent aqueous solution supply amount with respect to the fuel amount were examined.
FIG. 6A is a graph showing the relationship between the fuel amount and the exhaust gas amount in Example 2, and FIG. 6B is a graph showing the relationship between the fuel amount and generated NOx weight in Example 2. FIG. 7 is a graph showing the relationship between the amount of fuel, the required equivalent ratio of the reducing agent aqueous solution, and the required equivalent in Example 2. FIG. 8 is a graph showing the relationship between the elapsed time and the amount of NOx and the amount of heavy oil fuel before and after the exhaust gas treatment device in Example 2.

FIG. 6 shows that the fuel amount and the exhaust gas amount are in a proportional relationship, and the fuel amount and the generated NOx weight are in a proportional relationship.
Further, from FIG. 7, when the fuel amount is 65 to 145 L / h, the necessary equivalent of the reducing agent aqueous solution increases to 0.90 to 1.97 kg / h, but the necessary equivalent ratio is 11.1 to 1.1. It decreased to 5.09. From this, it can be seen that the required equivalence ratio of the reducing agent aqueous solution can be reduced when the amount of fuel is large when using heavy oil fuel as well as when using city gas fuel.
Further, from FIG. 8, during 300 minutes from the start of operation, the NOx amount in the exhaust gas before being introduced into the wet reactor P3 was stable at 90 to 110 ppm, and was processed in the wet reactor P3. The amount of NOx in the exhaust gas was reduced to 5 to 60 ppm. Note that when the amount of fuel is large, the amount of NOx after treatment is higher than when the amount of fuel is small because the amount of ozone supply is insufficient.
From this, it was found that the exhaust gas treatment method of the present invention is effective for removing nitrogen oxides in the exhaust gas discharged from the boiler 2 using heavy oil as fuel.

  INDUSTRIAL APPLICABILITY The present invention can be applied to a processing method and a processing apparatus for reducing nitrogen oxides in exhaust gas generated when fuel is combusted in a combustor, and in particular, a flue-tube type boiler using city gas or heavy oil as fuel. It is suitable for the treatment of exhaust gas discharged from.

P1 Ozonizer P1a Ozone supply line 2 Boiler 2a Waste heat recovery device 2b Exhaust gas supply line P3 Wet reactor P4 Oxidation reaction region P5 Reduction reaction region P6 Spray P7 Reducing agent aqueous solution tank P7a Reducing agent aqueous solution replenishment line P9 Mixed aqueous solution circulation line P10 Mixing Aqueous solution reservoir P11 Circulation pump P12 ORP meter P13 pH meter P14 Aqueous solution replenishment line P15 Gas outlet

Claims (11)

The exhaust gas is burned by mixing an oxidant in the exhaust gas of the combustor that burns the supplied fuel and exhausts the exhaust gas containing nitrogen oxide, and oxidizes the nitrogen oxide in the exhaust gas. Converting the NO ₂ into an oxidizing gas containing NO ₂ ;
By mixing a reducing agent to the NO ₂ containing oxidizing gas, by reducing the NO ₂ of the NO ₂ containing oxidizing gas, and a step of converting the NO ₂ containing oxidizing gas to the nitrogen gas,
An exhaust gas characterized by adjusting the supply amount of the oxidant into the exhaust gas and the supply amount of the reducing agent into the NO ₂ -containing oxidation gas in accordance with the amount of fuel supplied to the combustor. Processing method. The exhaust gas processing method according to claim 1, wherein the oxidizing agent is ozone gas, and the reducing agent is a reducing agent solution containing Na ₂ SO ₃ . The exhaust gas is introduced into the oxidation reaction region and the oxidation reaction region of a wet reactor equipped with a reduction reaction region and a treatment liquid reservoir provided above and below the oxidation reaction region, and the ozone gas is brought into contact with the exhaust gas in the oxidation reaction region. converted to NO ₂ containing oxidizing gas, said the reducing agent solution in the reduction reaction area in contact with the NO ₂ containing oxidizing gas is converted to nitrogen gas, the reducing agent solution is in contact with the NO ₂ containing oxidizing gas treatment The exhaust gas processing method according to claim 2, wherein a liquid is stored in the processing liquid storage section, and a processing liquid mixed with the reducing agent solution supplied in the processing liquid storage section is circulated in the reduction reaction region. The SO ₃ ²⁻ concentration of the treatment liquid is measured, and the supply amount of the reducing agent solution into the treatment liquid reservoir is finely adjusted so that the SO ₃ ²⁻ concentration is maintained at 1.0 to 2.0%. Item 4. An exhaust gas treatment method according to Item 3.   The exhaust gas treatment method according to claim 3 or 4, wherein an oxidation-reduction potential (ORP) of the treatment liquid is measured, and a supply amount of the reducing agent solution into the treatment liquid reservoir is finely adjusted based on the result. The reducing agent solution contains an alkaline component;
The exhaust gas treatment method according to any one of claims 3 to 5, wherein the pH of the treatment liquid is measured, and the amount of the reducing agent solution supplied into the treatment liquid reservoir is finely adjusted based on the result.   The exhaust gas processing method according to any one of claims 1 to 6, wherein the combustor is a furnace flue-tube boiler using city gas, heavy oil, waste gas, waste oil, or a mixture thereof as fuel.   A processing unit in which the exhaust gas of the combustor that burns the supplied fuel and exhausts exhaust gas containing nitrogen oxides is introduced, and an oxidant supply that supplies oxidant into the processing unit into which the exhaust gas is introduced A reductant supply unit for supplying a reductant into the processing unit supplied with the oxidant, a fuel amount measurement unit for measuring the amount of fuel supplied to the combustor, and a fuel amount measurement unit A control unit that controls the oxidant supply unit and the reductant supply unit based on a measurement result to adjust a supply amount of the oxidant and the reductant into the processing unit. Processing equipment. Further comprising an ORP meter that measures the oxidation-reduction potential (ORP) of the treatment liquid and outputs the measurement result to the control unit;
The control unit performs main control of the oxidant supply amount of the oxidant supply unit and the reductant supply amount of the reductant supply unit based on the measurement result from the fuel amount measurement unit, and then the ORP is within a predetermined range. The exhaust gas processing apparatus according to claim 8, configured to perform adjustment control of the oxidant supply amount and the reducing agent supply amount based on a measurement result from the ORP meter so as to be within a range. The reducing agent solution contains an alkaline component;
A pH meter that measures the pH of the treatment liquid and outputs the measurement result to the control unit;
The control unit performs a main control of the oxidant supply amount of the oxidant supply unit and the reductant supply amount of the reductant supply unit based on the measurement result from the fuel amount measurement unit, and then the pH is within a predetermined range. The exhaust gas processing apparatus according to claim 8 or 9, wherein the control device controls the reducing agent supply amount based on a measurement result from the pH meter so as to be within a range.   The boiler system provided with the furnace flue-tube type boiler and the exhaust-gas processing apparatus as described in any one of Claims 8-10 which processes the exhaust gas from this furnace-tube smoke tube type boiler.

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