JP2008221100A - Nitrogen oxide removing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus where regeneration spacing is elongated so as to reduce regeneration frequency, and stable nitrogen oxide removing performance can be exhibited. <P>SOLUTION: The nitrogen oxide removing apparatus 10 for removing nitrogen oxide from a gas comprising nitrogen oxide and water vapor comprises an absorbent material obtained by carrying a hygroscopic salt to a carrier having a functional group and adsorbing nitrogen oxide. The absorbent material absorbs moisture in the air, and reduces the reduction speed of adsorbed nitrogen dioxide NO<SB>2</SB>to be reduced by the functional group into nitrogen monoxide NO. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus for adsorbing and removing nitrogen oxides contained in a gas.

In an apparatus that burns fuel such as a boiler, gas turbine, or combustion furnace and heats the fuel at a high temperature, carbon monoxide (CO), carbon dioxide (CO ₂ ), nitrogen monoxide (NO), nitrogen dioxide ( NO ₂ ) and the like are generated and discharged as exhaust gas. Nitrogen oxides such as NO and NO ₂ are air pollutants that cause photochemical smog and acid rain. NO reacts with oxygen (O ₂ ) or ozone (O ₃ ) by ultraviolet rays or the like and is easily oxidized to become NO ₂ . For this reason, environmental standards for NO ₂ are determined by the Air Pollution Control Law. NO ₂ shows a strong oxidative effect, damages cells, causes bronchitis, emphysema, and the like, and has an adverse effect on the human body.

Therefore, it is necessary to remove nitrogen oxides such as NO ₂ before the exhaust gas is diffused into the atmosphere. As a method of removing nitrogen oxides, for example, there are a method of absorbing using an alkali absorbing solution and a method of reducing with a reducing agent. In the method using an alkali absorbing liquid, it is possible to absorb nitrogen oxide at a low concentration, but CO ₂ coexisting in the exhaust gas is also absorbed at the same time, and nitrogen oxide cannot be efficiently absorbed. In the method of reducing with a reducing agent, even if it is reduced, it is oxidized again by O ₂ coexisting in the exhaust gas, so that it is also impossible to efficiently remove nitrogen oxides.

Then, in order to remove nitrogen oxide efficiently, the method of adsorbing and removing using an adsorbent is proposed (refer patent documents 1 and 2). Since the adsorbent selectively adsorbs nitrogen oxides, the above problem does not occur even if CO ₂ and O ₂ coexist. Therefore, nitrogen oxides contained in the gas can be efficiently removed.
JP 2004-121902 A JP 2006-37813 A

  In the method and apparatus of Patent Document 1, a pellet-like or honeycomb-like adsorbent made of activated carbon, zeolite, γ-alumina, etc. is filled, and exhaust gas is allowed to flow through the adsorbent, thereby adsorbing nitrogen oxides in the exhaust gas, It can be removed from the exhaust gas.

In these adsorbents, as the amount of NO ₂ adsorbed increases, the adsorbed NO ₂ is reduced to NO, desorbed from the adsorbent and released together with the exhaust gas. For this reason, when the amount of NO released increases, it is necessary to immerse the adsorbent in the regenerating solution and regenerate it. When the time interval for regenerating the adsorbent is short, there is a problem that the amount of regenerated liquid used and the amount of power used by the facility increase.

  Immediately after the regeneration, the adsorption performance of the adsorbent is remarkably lowered with the surface of the adsorbent covered with surface water. If the interval between regenerations is short, the removal failure state that does not temporarily adsorb frequently occurs. There is also a problem that occurs.

  On the other hand, in the system of Patent Document 2, a direct current voltage is applied to the adsorbent that adsorbs nitrogen oxides and moisture, and the nitrogen oxides are electrolyzed and reduced. Therefore, regeneration can be performed without using a regenerating solution, It can be adsorbed again.

However, similarly to the method of reducing with the reducing agent, O ₂ is contained in the exhaust gas, and O ₃ is also generated when electrolyzed. Therefore, even if the nitrogen oxide is reduced to nitrogen, the adsorption part is Nitrogen in the exhaust gas that has passed may be oxidized by O ₂ or O ₃ to generate nitrogen oxides again.

  Therefore, it is desired to provide an apparatus capable of extending the regeneration interval as much as possible to reduce the number of regenerations and exhibit stable nitrogen oxide removal performance.

As a result of intensive studies, the inventors of the present invention supported the hygroscopic salt such as magnesium chloride and sodium chloride on the surface of activated carbon and absorbed water vapor in the gas, thereby reducing the adsorbed NO ₂ to NO. I found it difficult. The present invention has been made by finding that it is difficult to reduce to NO, that is, reduces the reduction rate to NO, and the above problem is solved by providing the nitrogen oxide removing apparatus of the present invention. be able to.

  That is, according to this invention, the apparatus which removes nitrogen oxide from the gas containing nitrogen oxide and water vapor | steam can be provided. This apparatus comprises an adsorbent that adsorbs a hygroscopic salt on a carrier having a functional group and adsorbs nitrogen oxide, and the adsorbent absorbs water vapor and is adsorbed nitrogen that is reduced by the functional group. It is characterized by reducing the reduction rate of the oxide.

  The carrier having a functional group is activated carbon, and the hygroscopic salt can be selected from sodium chloride, magnesium chloride, calcium chloride, sodium acetate, and sodium carbonate.

  Moreover, in order to increase the amount of water vapor in the gas, a humidifier for humidifying the gas can be included.

  The adsorbent can be produced by immersing an aqueous solution of a hygroscopic salt in a carrier having a functional group.

  By providing the nitrogen oxide removing apparatus of the present invention, the interval for regenerating the adsorbent can be extended.

  In addition, it is possible to reduce the amount of regeneration liquid used to regenerate the adsorbent, and to reduce the power consumption and maintenance cost of the regeneration-related equipment.

  By reducing the number of regenerations, maintenance management is facilitated, the number of occurrences of removal failure states that are not temporarily adsorbed after regeneration can be reduced, and more stable removal of nitrogen oxides can be achieved.

The nitrogen oxide removing apparatus of the present invention is an apparatus that adsorbs and removes nitrogen oxide from a gas containing nitrogen oxide and water vapor. Here, examples of the gas include air contaminated with nitrogen oxides in road tunnels, underground parking lots, and urban highway areas. Nitrogen oxides include NO, NO ₂ , N ₂ O ₃ , N ₂ O ₄ , and N ₂ O ₅ . NO is easily oxidized by ultraviolet rays or the like to become NO ₂ , and N ₂ O ₃ is dissociated into NO ₂ and NO. N ₂ O ₄ is in equilibrium with NO _2, lower pressure in the environment, at low concentrations are biased into NO _2. N ₂ O ₅ reacts with water to become nitric acid. In the above polluted air, nitrogen oxides mostly present as NO and NO _2. The NOx concentration is, for example, about 1 to 5 ppm in the air in the road tunnel.

  FIG. 1 is a diagram showing one embodiment of a nitrogen oxide removing apparatus. A nitrogen oxide removing apparatus 10 shown in FIG. 1 contains a receiving nozzle 11 that receives a gas containing nitrogen oxide and water vapor, an adsorbent 12 that adsorbs nitrogen oxide in the gas, and an adsorbent 12, and has a predetermined configuration. A container 13 disposed at a position and a discharge nozzle 14 for discharging a gas from which nitrogen oxides have been removed are provided.

  In the embodiment shown in FIG. 1, the receiving nozzle 11 is provided on the lower side wall of the container 13, the discharge nozzle 14 is provided on the upper side wall of the container 13, and above the receiving nozzle 11 in the container 13 and from the discharge nozzle 14. The adsorbent 12 is disposed at a lower position. A ring-shaped support is provided on the inner wall of the container 13, and a metal net such as a punching plate having many holes for circulating gas is placed on the support, and the adsorbent 12 is disposed thereon. Can do. The container 13 may have any shape and material as long as there is no gas leakage, and the shape can be a box shape or a cylindrical shape. The material is carbon steel, stainless steel, FRP, PVC, and the like. can do.

  A gas containing nitrogen oxides and water vapor is received from the receiving nozzle 11, circulates upward from the lower side of the container 13 through the wire mesh and the adsorbent 12 as indicated by the arrow, and is discharged from the discharge nozzle 14. The Nitrogen oxides in the gas are adsorbed on the adsorbent 12 and removed from the gas.

The adsorbent 12 is composed of a porous carrier. In order to reduce pressure loss, the carrier can be crushed particles or molded particles of several mm to several cm, or honeycomb structured particles. In order to efficiently adsorb nitrogen oxides, it is preferable that the specific surface area is large. Further, in order to efficiently adsorb nitrogen oxides and reduce the reduction rate of the adsorbed nitrogen oxides, the humidity in the gas is preferably about 40% or more, more preferably about 60% or more. preferable. Furthermore, the space velocity of the gas is preferably about 1000～200000H ^-1, and more preferably about 3000~100000h ^-1. The support is preferably activated carbon having good adsorption performance for nitrogen oxides. Examples of the activated carbon include coconut palm activated carbon and pitch-based activated carbon. Other examples include charcoal, carbon fiber, fullerene, and carbon nanotube. These carriers have functional groups exhibiting specific physical properties and chemical reactivity.

  The activated carbon surface is chemically non-polar as a whole, but there are functional groups that become polar portions in part. Examples of the functional group include a carboxyl group, a carbonyl group, a hydroxyl group, and a quinone group. In addition, a carrier made of a carbon-based material is superior to various polar heavy metal ions and a small amount of polar pollutants in the atmosphere by introducing oxygen functional groups on the surface and imparting ion exchange characteristics. Adsorption selectivity is provided.

When activated carbon is used as the adsorbent, NO _{2 in} the gas is adsorbed and removed by the activated carbon, but as the amount of adsorption increases, a part of the NO ₂ adsorbed by the functional group of the activated carbon is reduced to NO. NO is discharged from the discharge nozzle 14 together with the gas. Conventionally, in response to the fact that the NO emission concentration is appropriately measured and increased, the adsorbent is immersed in a regenerating solution to regenerate the adsorbent. As the regenerating solution, an aqueous solution containing a basic substance or a reducing substance is used.

  Here, examples of the basic substance include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide, sodium carbonate, potassium carbonate and the like. Mention may be made of alkali metal carbonates and alkaline earth metal carbonates such as calcium carbonate and magnesium carbonate. Examples of the reducing substance include sulfites, thiosulfates, hydrogen sulfide, and aldehydes.

In the present invention, it has been found that the reduction rate of NO ₂ increases as the humidity decreases, and the reduction rate can be reduced by moisturizing. Specifically, a hygroscopic salt is supported on a carrier such as activated carbon, and water vapor in the gas is absorbed to make the adsorbent 12 in a moisturized state.

  By immersing an aqueous solution of a hygroscopic salt in a carrier having a functional group, such as activated carbon, the hygroscopic salt can be carried on the carrier. The immersion time may be any time as long as it can be supported, but for example, it can be immersed for several tens of minutes to several hours.

  The hygroscopic salt may be any substance as long as it absorbs water vapor in the gas, and examples thereof include sodium chloride, magnesium chloride, calcium chloride, sodium acetate, and sodium carbonate. These are preferable because they dissolve in an aqueous solution of a basic substance or a reducing substance used as a regenerating liquid, do not lose basicity or reducing ability necessary for regeneration, and have hygroscopicity.

The adsorbent 12 having a carrier carrying a hygroscopic salt absorbs water vapor in the gas and puts it in a moisturized state, making it difficult for the adsorbed NO ₂ to be reduced to NO. Thereby, the regeneration interval by the regeneration solution can be extended and the number of regenerations can be reduced.

  FIG. 2 is a view showing another embodiment of the nitrogen oxide removing apparatus. Although the configuration including the receiving nozzle 11, the adsorbent 12, the container 13, and the discharge nozzle 14 is the same, a humidifier 21 is connected to the receiving nozzle 11 via a line 20.

  The humidifying device 21 is, for example, a device provided with a shower nozzle that sprays water on a gas and a pump for supplying water to the shower nozzle, or a container filled with water-damped filler, from the lower part or the upper part. An apparatus for flowing a gas and flowing between fillers can be mentioned. In addition, it is also possible to use a device that circulates gas and humidifies the water surface.

By humidifying the gas in this way, the amount of water vapor absorbed by the adsorbent 12 can be increased, and the reduction rate of NO ₂ can be further reduced by increasing the humidity.

Next, tests carried out to verify the effect of improving the ability to remove nitrogen oxides by supporting a hygroscopic salt and the test results are shown below. Activated carbon was used as the carrier having a functional group, and magnesium chloride (MgCl ₂ .6H ₂ O) was used as the hygroscopic salt.

The following method was adopted as a method of supporting activated carbon with magnesium chloride.
(1) A predetermined amount of magnesium chloride is weighed and dissolved in 10 ml of water.
(2) Weigh 5 g of activated carbon and put into the aqueous solution prepared in (1).
(3) Let stand for 2 hours.
(4) Put in a thermostatic bath and dry at 120 ° C. for 5 hours.
Magnesium chloride was weighed and supported so that the supported rate of magnesium chloride on activated carbon was 10% by mass.

In FIG. 3, the outline of the evaluation apparatus for evaluating nitrogen oxide removal performance is shown. This evaluation apparatus includes a thermostat and the like, and a thermostat 30 that automatically keeps the temperature of the experimental system constant, a humidifier 31 that humidifies gas, and a U-shaped reaction filled with activated carbon supporting magnesium chloride. A tube 32 and a NOx meter 33 for measuring the nitrogen oxide concentration are provided. Here, the nitrogen oxide is NO ₂ , and the NOx meter 33 is a device that measures the NO ₂ concentration.

  The humidifier 31 and the reaction tube 32 are installed in the thermostat 30 and the temperature is kept constant. The gas containing nitrogen oxides is sent to the humidifier 31, humidified, and then sent to the reaction tube 32. The humidifier 31 can be adjusted to have a predetermined humidity. For example, the humidifier 31 can be a device that contains water and humidifies the gas by passing it into the water. The gas from which nitrogen oxides are adsorbed and removed in the reaction tube 32 is sent to the NOx meter 33, and the nitrogen oxide concentration in the gas is measured. In FIG. 3, air lines 34 and 35 for purging nitrogen oxides remaining in the humidifier 31 and the reaction tube 32 after the test are provided. The gas sent to the reaction tube 32 contains water vapor, and the nitrogen oxide concentration is measured after removing the water vapor. This is because condensation in the NOx meter 33 causes measurement errors. For this reason, in order to separate the water vapor in the gas, a separator 36 is provided that is cooled and condensed with ice or the like and separated as condensed water. Table 1 shows the test conditions of a test performed using this evaluation apparatus.

The test is performed using the evaluation apparatus shown in FIG. 3 under the conditions shown in Table 1 above, and the time until the NO ₂ concentration measured by the NOx meter 33 is less than 90% and less than 70% of the inlet concentration (removal life). ) Was measured. The temperature in the evaluation apparatus was kept constant at about 25 ° C.

4, if not carrying MgCl ₂ and (loading of 0 mass%) is a diagram showing a nitrogen oxide removal lifetime of case of carrying MgCl ₂ (loading of 10% by weight). The vertical axis represents the removal life (time), and the horizontal axis represents the MgCl ₂ loading (mass%). FIG. 4 shows a lifetime in which 90% of nitrogen oxides can be adsorbed and removed and a lifetime in which 70% can be adsorbed and removed.

Referring to FIG. 4, by loading MgCl ₂ which is a hygroscopic salt, the nitrogen oxide removal life was extended about 3 to 4 times. Thus, it has been found that the interval for regenerating the adsorbent with the regenerating liquid can be extended by supporting the hygroscopic salt. Here, as shown in Table 1, the humidity of the gas was set to 40%. However, when the humidity was increased, the removal life (time) could be further extended. Incidentally, when the humidity was 70%, the 90% NOx removal life could be extended about three times as compared with the case where the humidity was 40%.

FIG. 5 is a diagram showing the results when NaCl is used as the hygroscopic salt instead of MgCl ₂ . The loading method and test conditions are the same as those in the above (1) to (4) and Table 1. For NaCl, tests were conducted on three patterns with a loading rate of 0 mass%, 10 mass%, and 15 mass%.

  Referring to FIG. 5, by supporting 10% by mass of NaCl, which is a hygroscopic salt, this also extended the nitrogen oxide removal life by about 3 to 4 times. Thereby, it was confirmed that the interval for regenerating the adsorbent with the regenerating liquid can be extended by supporting the hygroscopic salt. It has also been found that the lifetime can be further increased by increasing the loading rate.

  From these facts, the higher the loading of the hygroscopic salt and the higher the humidity, the longer the life of the adsorbent. As described above, the number of times of regeneration with the regenerating liquid is reduced to 1/3 to 1/4 by being extended by about 3 to 4 times compared with the conventional activated carbon alone, Electricity consumption can be greatly reduced.

  Although the present invention has been described with the embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, etc. It can be changed within the range that can be conceived by a trader, and any embodiment is included in the scope of the present invention as long as the effects and effects of the present invention are exhibited.

The figure which showed 1st Embodiment of the nitrogen oxide removal apparatus. The figure which showed 2nd Embodiment of the nitrogen oxide removal apparatus. Schematic of the evaluation apparatus used in order to evaluate nitrogen oxide removal performance. The figure which showed the relationship between the loading rate of a hygroscopic salt, and the removal lifetime of a nitrogen oxide. The figure which showed the relationship between the loading rate of a hygroscopic salt, and the removal lifetime of a nitrogen oxide.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Nitrogen oxide removal apparatus, 11 ... Acceptance nozzle, 12 ... Adsorbent, 13 ... Container, 14 ... Discharge nozzle, 20 ... Line, 21 ... Humidifier, 30 ... Constant temperature bath, 31 ... Humidifier, 32 ... Reaction tube 33 ... NOx meter, 34, 35 ... Air line, 36 ... Separator

Claims (4)

An apparatus for removing nitrogen oxides from a gas containing nitrogen oxides and water vapor,
A carrier having a functional group is loaded with a hygroscopic salt, and includes an adsorbent that adsorbs the nitrogen oxides,
The adsorbent absorbs the water vapor and reduces the reduction rate of the adsorbed nitrogen oxide reduced by the functional group.   The nitrogen oxide removing apparatus according to claim 1, wherein the carrier having the functional group is activated carbon, and the hygroscopic salt is selected from sodium chloride, magnesium chloride, calcium chloride, sodium acetate, and sodium carbonate.   The nitrogen oxide removing device according to claim 1, further comprising a humidifying device for humidifying the gas.   The said adsorbent is a nitrogen oxide removal apparatus of any one of Claims 1-3 manufactured by immersing the aqueous solution of the said hygroscopic salt in the support | carrier which has the said functional group.

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