JPH0714464B2 - Desulfurization denitration method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for desulfurizing and denitrifying exhaust gas. More specifically, the present invention relates to a desulfurization denitration method capable of using a catalyst that is inexpensive and has a high denitration performance, and thus can save space and reduce the cost of the entire apparatus.

[Prior Art] Exhaust gas from combustion of a boiler in a thermal power plant often contains sulfur oxides and nitrogen oxides, which are air pollutants. In recent years, it is urgently necessary to prevent air pollution. Therefore, desulfurization method and denitration method have been developed to remove both of them. The individual principles and technologies of desulfurization and denitration have been almost established at the practical level, and now the development focus is shifting to how to improve the efficiency of the entire system.

As a desulfurization method, a wet method, particularly a coal-gypsum method is mainly used. In this coal-gypsum method, a sulfur oxide such as SO ₂ is absorbed in an adsorbent containing calcium ions, and then this is oxidized and fixed as gypsum to be recovered. Inexpensive limestone is used for supplying calcium ions and neutralizing the liquid. Many variations of this lime-gypsum method have been developed, and among them, the method described in Japanese Patent Publication No. 60-4726 uses a specific reaction device called a jet bubbling reactor to save resources. To achieve energy saving and space saving.

As the denitration method, a dry method, particularly a selective catalytic reduction method is mainly used. This selective catalytic reduction method is a method of injecting ammonia gas into exhaust gas and decomposing nitrogen oxides into nitrogen and water in the presence of a catalyst. The catalyst used is one in which an active metal is supported on a carrier, and the activity is usually highest at 350 ° C or higher. The selection of the active ingredient and the carrier is the key to the efficient reaction.

When the coal-gypsum method is used as the desulfurization method and the denitrification method is used as the selective catalytic reduction method, the latter reaction is carried out at a higher temperature than the former, so the exhaust gas from the boiler economizer is first denitrified. Desulfurization and denitration are carried out in the order of passing through the device, and then passing through the air preheater the exhaust gas whose temperature has dropped to the desulfurization device.

[Problems to be Solved] However, the conventional method of performing desulfurization and denitration in the order as described above has the following problems.

First, since the exhaust gas of sulfur oxides directly contacts the denitration catalyst, usable denitration catalysts, especially usable carriers, are limited. That is, for example, if an alumina-based carrier is used, a catalyst with extremely high denitration performance itself can be obtained, but the alumina carrier is attacked by sulfur oxides,
With this catalyst, the NOx removal performance drops rapidly with use, making it useless. It is said that the cause is that alumina reacts with sulfur oxide to form a sulfate, and the surface area of the carrier is significantly reduced. Therefore, the denitration performance is not as high as that of the alumina carrier and the cost is high, but the fact is that a titania-based carrier must be used.

Secondly, when a large amount of dust (fly ash) is contained in the exhaust gas such as the exhaust gas from a coal combustion boiler, if this is passed through the granular catalyst packed tower type denitration equipment as it is, the catalyst packed bed will be clogged. Therefore, it is necessary to provide an electrostatic precipitator in the preceding stage of the denitration device, or to mold the catalyst into a dust-free type such as a honeycomb shape. In any case, the cost is high, and when the honeycomb is molded, the catalyst filling amount per unit volume cannot be large, so the contact efficiency between the exhaust gas and the catalyst is poor, and therefore it is high to increase the reaction rate. There is a problem that the residence time must be obtained by using the reaction temperature or by increasing the inner volume of the apparatus.

[Means for Solving Problems] The present invention reverses the conventional wisdom that denitration is performed after denitration when the coal-gypsum method is used as the desulfurization method and the selective catalytic reduction method is used as the denitration method. The above-mentioned problems are solved by adopting a configuration in which desulfurization is performed first and then denitration is performed.

When performing desulfurization by the coal-gypsum method first, and then performing denitration by the selective catalytic reduction method, it is necessary to raise the exhaust gas exiting the desulfurization apparatus to a temperature required for denitration, and in the conventional method, Since this point is the biggest problem, they did not adopt the structure of desulfurization first.

In the present invention, the structure of performing denitration after desulfurization is adopted because a catalyst support such as alumina-based catalyst having a high denitration performance can be used by performing desulfurization first, and especially the dust removing effect in the lime-gypsum method. If a method using a liquid phase continuous type device with a large size can be used, a granular catalyst filling type denitration device with high catalyst filling efficiency can be used, and as a result, the same degree of denitration ratio as the conventional method can be obtained. It was found that it does not necessarily require a high reaction temperature. That is, in the present invention, it is sufficient to raise the temperature of the exhaust gas that has exited the desulfurization device to about 200 to 330 ° C. at most, and if the temperature rises to this extent, it is practically used by appropriately using indirect heat exchange and the like. Almost no disadvantage,
Rather, the cost reduction effect is much greater because the titania-based catalyst does not have to be used and the honeycomb-shaped catalyst does not have to be used.

[Operation] The method of the present invention comprises a desulfurization step and a denitration step. Desulfurization is performed by the lime-gypsum method. The reason why the lime-gypsum method is used is that the desulfurization performance is stable, that it is economical, that it is the most widely adopted at present, and that this is a wet method that removes dust. This is because the excellent requirement satisfies the essential requirements of the present invention. On the other hand, denitration is performed by the selective catalytic reduction method. The reason why we chose to use the selective catalytic reduction method is that the operation is simple, it is resistant to load fluctuations, it does not generate wastewater or waste, and it has the excellent features of selectively decomposing and removing only nitrogen oxides. is there.

Lime - gypsum method lime - gypsum method is SO ₂ absorption, oxidation, consists stages of neutralization and gypsum crystallization. That is, when the exhaust gas comes into contact with the absorbing liquid, the sulfur oxides (mainly SO ₂
Of the form) dissolves in the absorption liquid to produce an acid such as sulfurous acid. They are converted to sulfuric acid by oxidizing the acids thus produced. Since the pH of the liquid drops due to the production of sulfuric acid, limestone is added to this to neutralize it. Then, calcium ion Ca ^{2 + of} limestone reacts with SO ₄ ^{2 − of} sulfuric acid to produce gypsum CaSO ₄ , which is separated and separated from the liquid. After all, the whole reaction is expressed by the following equation.

_{SO 2 + (O) + CaCO} 3 + 2H 2 O -> CaSO 4 · 2H 2 O + CO 2 SO 2 absorption and subsequent to the liquid phase from the gas phase of SO _2, and sulfurous acid H ₂ SO
_Since it is the stage of formation of ₃ , it essentially proceeds in a gas-liquid two-phase system. Oxidation is the step of conversion of H ₂ SO ₃ to H ₂ SO ₄ ,
Although it is a process that proceeds essentially in the liquid phase, it involves the process of dissolving oxygen in order to use oxygen in the air for oxidation.
Eventually, it will proceed in a gas-liquid two-phase system. Neutralization is also a process that essentially progresses in a liquid phase, but since limestone is used for neutralization, it involves a process of dissolving limestone, and eventually proceeds in a solid-liquid two-phase system. Since gypsum precipitation is the stage of CaSO ₄ formation and its transition from liquid phase to solid phase, it essentially proceeds in a solid-liquid two-phase system.

From the above, two gas-liquid system operations (gas absorption) and two solid-liquid system operations (dissolution and precipitation) are required to carry out the lime-gypsum method. However, if these operations are performed using different devices, the size of the entire device becomes large. Therefore, various methods have been devised to perform these operations in one device. Among them, the special public Sho 60-
The method described in Japanese Patent No. 4726 can be said to be the most preferable because it can perform all the steps of the lime-gypsum method extremely efficiently and the apparatus can be compactly integrated. A device for carrying out the method of Japanese Patent Publication No. 60-4726 is generally a jet bubbling reactor (JBR).
Is called.

Here, the removal of sulfur oxides in JBR will be outlined using drawings. Figure 2 is a schematic diagram of a typical JBR.
Exhaust gas is blown through the inlet plenum 13 and a large number of sparger pipes 14 extending below the liquid surface to 100 to 400 mm below the liquid surface to form a jet bubbling layer 11. In this layer, highly efficient gas-liquid contact is performed and SO ₂ is absorbed. The desulfurized gas is discharged to the outside through the gas riser 15. Under the jet bubbling layer 11, there is a continuous oxygen dissolution region 12. SO ₂ absorbed in the jet bubbling layer
The sulfate ions immediately on the spot ^- is oxidized to (SO ₄ ^2).
The absorbing liquid moves to the lower part of the apparatus after the bubbles are separated, and the limestone slurry is injected into the absorbing liquid for neutralization and supply of calcium ions. The absorption liquid then moves to the oxygen dissolution region. In this region, the oxygen-dissolved absorbing solution moves to the jet bubbling layer and functions again as a medium for SO ₂ absorption and oxidation. The generated gypsum crystals exist in a state of being suspended in the absorption liquid, but as part of the absorption liquid is withdrawn from the lower part of the tank, it is discharged out of the tank and subjected to solid-liquid decomposition. Thus, in JBR, since the operations of absorption, oxidation, neutralization and crystallization are performed in one tank, the device is extremely compact and efficient desulfurization can be performed.

A major feature of JBR is that SO ₂ absorption and oxidation in the liquid phase proceed at the same time one after another as described above. This is closely related to the low pH of the absorption liquid, which is about 3-5. Related to. In JBR, SO ₂ is almost absent in the liquid, so SO ₂ is absorbed efficiently even at low pH,
The causative dithionate ion chemical oxygen demand _{(COD) (S 2 O 6} 2 -) almost no generation of.

Carrying out the lime-gypsum process with JBR is a highly preferred embodiment of the invention. This is not only because JBR is compact and has high desulfurization performance and is easy to treat wastewater, but also because JBR has an extremely high dust removal rate in exhaust gas.

Generally, desulfurization by the wet method has an effect of removing dust in exhaust gas. This is because dust in the exhaust gas adheres to the gas-liquid interface when the exhaust gas comes into contact with the absorbing liquid, and is then taken into the liquid. Therefore, it can be said that the dust removal rate is high if the dust in the exhaust gas has a large opportunity to reach the gas-liquid interface in this gas-liquid contact operation. Gas-liquid contact operations include a gas phase continuous type in which a liquid is dispersed in a gas phase and a liquid phase continuous type in which a gas is dispersed in a liquid phase. The removal rate is high. In a liquid-phase continuous gas-liquid contactor, gas is dispersed as bubbles in the liquid. Although details of the dust removal mechanism in this case were not always clear, the present inventors performed a simulation based on the single bubble model and confirmed that the dust removal was performed by the following mechanism.

When the gas is blown into the liquid, the gas becomes bubbles and rises in the liquid, and eventually reaches the liquid surface. The process during this can be divided into two processes. That is, it is divided into a process of generating bubbles while rapidly reducing the velocity of the injected gas and a process of rising the generated bubbles in the liquid. At the time of bubble generation, the gas rapidly reduces its velocity, whereas the dust particles with a large particle size in the gas try to maintain the velocity at the time when the gas is blown due to inertia, so such particles Is the gas-liquid interface (bubble surface)
Is collided with and removed. When the bubbles rise, a swirling motion occurs in the bubbles due to the friction between the bubbles and the liquid due to the movement of the bubbles in the liquid. It collides with the liquid interface and is removed. On the other hand, those having a small particle diameter diffuse in the bubble while repeatedly colliding with the gas molecule due to the thermal motion of the gas molecule in the bubble, and eventually reach the gas-liquid interface, where they are captured and removed. In other words, the gas phase concentration of small-sized particles at the gas-liquid interface is considered to be zero, so a concentration gradient of small-sized particles from the center of the bubble toward the gas-liquid interface is formed, which becomes the driving force and the small particle size. It is considered that the particles are carried toward the outer circumference of the bubble. As described above, among the dust particles in the gas, those with a large particle size are mainly transported to the gas-liquid interface by inertia, while those with a small particle size are mainly transported to the gas-liquid interface by diffusion, both of which are gas-liquid interfaces. It is captured at the interface and taken into the liquid.

The mechanism for removing dust particles from gas in the liquid-phase continuous gas-liquid contactor is explained as described above. Therefore, it is considered that the following factors are involved in the removal rate of dust particles. First, the smaller the distance that the dust particles (particularly small particles) move in the bubbles, the easier the removal. Therefore, the diameter of the bubbles is preferably small. If the bubbles move irregularly and violently in the liquid, a large inertial force acts on the large particles in the bubbles to facilitate removal. Furthermore, the removal rate is naturally higher as the time the bubbles stay in the liquid is longer.

It is thought that the reason why JBR achieves a high dust particle removal rate is that it is a liquid-phase continuous gas-liquid contactor, and that the bubbles produced are minute and the residence time in the liquid is long. . That is, in JBR, the exhaust gas is 100 to 400 mm below the liquid level.
It is jetted horizontally in a jet shape from the opening of the gas sparger located at, and vigorously mixes with the absorbing liquid, forming bubbles of several mm and forming a jet bubbling layer. Although SO ₂ absorption and oxidation proceed in this layer as described above, at the same time, dust particles in the exhaust gas are also efficiently removed.

Note that the exhaust gas may contain a small amount of SO _3, but this is difficult to remove by the lime-gypsum method. A part of SO ₃ is removed by JBR together with SO ₂ , but it is difficult to remove it sufficiently. However, this can be completely removed by adding ammonia to the exhaust gas in advance. That is, if ammonia is added to make SO ₃ ammonium sulfate or acidic ammonium sulfate, it is removed by a dust collector or is solubilized and separated in a wet desulfurization step. For example, by separately injecting ammonia into the exhaust gas upstream of the desulfurization step of the present invention,
SO ₃ is easily removed. By this method, S in exhaust gas
The amount of O ₃ is 10 mg / Nm ³ or less, the clogging of the desulfurization catalyst layer is prevented, and high activity can be maintained for a long period of time.

Selective catalytic reduction method The selective catalytic reduction method injects ammonia gas into the exhaust gas and brings the active metal such as molybdenum and vanadium into contact with a catalyst supported on a predetermined carrier to convert nitrogen oxides in the exhaust gas into nitrogen. It decomposes into water. It is said that the reaction mainly follows the following reaction formula.

_{4NO + 4NH 3 + O 2 -} > 4N 2 + 6H 2 O Conventionally, the reaction is carried out at 300 to 450 ° C., lime which is a wet process - for than the reaction temperature is higher gypsum method, lime from the viewpoint of thermal efficiency - gypsum method Has been placed in front of. However, as described above, such a method necessitates the use of a titania-based carrier catalyst and also necessitates molding the catalyst into a honeycomb shape.

The titania-based carrier certainly does not deteriorate due to sulfur oxides and exhibits stable performance over a long period of time, but when compared with, for example, an alumina-based carrier, it is unavoidable that the cost becomes high. Further, the original denitration performance is not necessarily excellent, and in general, the alumina-based carrier is often superior to the original initial denitration performance in many cases. In any case, it is not preferable that the catalyst carrier is limited to only the titania-based catalyst because it deprives the process designer of freedom.

In the method of the present invention, the exhaust gas desulfurized by the lime-gypsum method is denitrified by the selective catalytic reduction method. Therefore, various materials other than the tatinia-based material can be used as the carrier for the denitration catalyst. Although typical ones of those catalyst support materials are described below, it goes without saying that the method of the present invention is not limited to the use of those support materials.

As the carrier for the denitration catalyst that can be used in the present invention,
First of all, the alumina type is used. Alumina is a material that has been widely used as a catalyst carrier since it has a large mechanical strength and a relatively large specific surface area. In particular, r-alumina is said to be preferable because it is excellent in thermal stability and mechanical strength. In order to produce r-alumina satisfying the requirements that the specific surface area required as a catalyst carrier is large, the pore size distribution and the pore volume are appropriate, and the mechanical strength is large, many studies have been conducted conventionally. Has been done.

It is known that r-alumina is produced by firing boehmite gel (a hydrated gel of fibrous boehmite microcrystals, which is also called pseudo-boehmite), and r-alumina having controlled pore diameter distribution and pore volume is used. In order to obtain alumina, the crystal size and distribution of this boehmite gel must be adjusted to appropriate values. However, in the method of simply adjusting the size of each individual crystal particle, it is difficult to obtain a suitable catalyst carrier because the specific surface area becomes smaller if the pore size is increased.

In order to adjust the average pore size without reducing the specific surface area of r-alumina, for example, it is conceivable to adjust the shrinkage of the gel structure in the drying and sintering process of boehmite gel. (J. Polymer Science, Vol. 34, p. 129), and a method of applying shearing force to concentrated boehmite gel (JP-A-49-3159).
No. 7), a method of adding a water-soluble polymer compound such as polyethylene glycol to boehmite gel (JP-A-52-1044).
98, JP-A-52-77891), a method in which a part or most of the boehmite gel is replaced with alcohol (JP-A-50-123588), and a part of the boehmite gel is previously made into xerogel. Furthermore, a method of mixing this with a slurry of boehmite gel (Japanese Patent Publication No. Sho 49-37517) is known. However, it is said that r-alumina produced by these methods has problems in mechanical strength and the like.

It is also known to overcome the difficulties of the above methods and to produce improved r-alumina. For example, Japanese Patent Publication Sho-57-44
In the method described in Japanese Patent No. 605, r-alumina having a remarkably large surface area and a controlled pore volume is produced by causing the crystal growth of boehmite to be carried out rapidly. This method keeps the aluminum hydroxide slurry as the crystal seeds at 50 ° C. or higher and alternately adds an aluminum salt and a neutralizing agent to this while stirring to generate active aluminum hydroxide, which is By occluding the seed aluminum hydroxide, its crystal growth is promoted, boehmite loose aggregates are formed by the binding of grown boehmite particles, and the degree of shrinkage of boehmite gel during drying is controlled by changing the aggregation state. To give an r-alumina carrier having a controlled pore volume and pore size and a large specific surface area. Or Japanese Examination 1-16
The method described in Japanese Patent No. 772 is a further improvement of this method, instead of alternately adding an aluminum salt and a neutralizing agent, while maintaining the system in the range of pH 8 to 11, which is the crystal growth region of boehmite, The aluminum salt and the neutralizing agent are continuously added, and at the time, the sulfate radical is substantially present in the system to keep the condition that the crystal seeds are hard to be generated, thereby avoiding the complicated operation. . Furthermore, the method described in JP-A-60-25545 aims to increase the mechanical strength by incorporating zirconia into alumina, and particularly to prevent the mechanical strength from decreasing in an alumina carrier having a large pore diameter and a large pore volume. It is a thing.

A denitration catalyst using a sepiolite-based carrier can also be suitably used in the method of the present invention. Sepiolite is a porous magnesium silicate also called sepiolite,
In addition to those naturally produced, those synthesized from magnesium compounds and silicon compounds are also known. Since sepiolite generally has an extremely large pore volume, it has a feature that when used as a catalyst, the pores are unlikely to be clogged, but the specific surface area or the ability to carry catalytically active species is not necessarily large, and the mechanical strength is not always required. There is a problem that it is not big. Therefore, various modified sepiolites for catalyst carriers have been developed that solve these problems.

For example, the method described in Japanese Examined Patent Publication No. 55-31085 discloses a method in which a raw material sepiolite is crushed, then tempered and kneaded, and then molded and fired, thereby increasing the specific surface area and increasing mechanical strength. It is manufactured. In this method, the bundle of sepiolite fibers is loosened by the above kneading step, and the structure is changed completely from that of the raw material sepiolite. The method described in Japanese Patent Publication No. 59-6697 is characterized by desorbing skeletal magnesium ions from natural sepiolite to increase the silica / magnesia molar ratio to 4 or more. This method focuses on the ion exchange ability of sepiolite, and increases the specific surface area and pore volume by chemical means rather than mechanical means. Incidentally, Japanese Patent Publication No. 59-6697 describes this modified sepiolite as a hydrogenation catalyst, but according to the study by the present inventors, it was found that it can be used as a catalyst for flue gas denitration. ing.

Also, as the same magnesium silicate as sepiolite, attapulgite, palygoskite, etc. show similar pore sizes, while amphibole-based asbestos minerals have been found to have larger pore sizes, and are also used as carriers for denitration catalysts. can do.

In general, alumina is composed of a collection of small needle-shaped crystals, whereas magnesium silicates such as sepiolite are composed of long fibrous crystals, so magnesium silicates with the same pore volume are used. Is characterized by higher strength and less pulverization.

Although the alumina system centered on r-alumina and the magnesium silicate system centered on sepiolite have been described above, the present invention is characterized in that the material of the catalyst carrier is not particularly selected as described above. It goes without saying that it is also possible to use a titania-based material, a zeolite-based aluminosilicate-based material, etc.

As the active metal supported on the carrier, those conventionally used for the denitration catalyst can be used in the same manner, but particularly preferable ones are vanadium, tungsten, molybdenum, chromium, manganese, iron, cobalt and nickel. is there.

As a method of injecting ammonia into the exhaust gas, it is common to vaporize liquid ammonia with a vaporizer by steam heating, electric heating, etc. and inject the produced ammonia gas into the exhaust gas, but liquid ammonia is an aqueous ammonia solution. Alternatively, a method using an aqueous ammonia solution or an aqueous urea solution is preferable because it requires considerable care and is more expensive than an aqueous urea solution. One of such methods is LP for raising the temperature of exhaust gas after flue gas desulfurization.
There is a method of injecting an aqueous ammonia solution or an aqueous urea solution into the hot gas generated by burning G, LNG, etc., and injecting the ammonia-containing gas thus generated into the exhaust gas. In the case of the aqueous urea solution, urea injected into the high temperature combustion exhaust gas is decomposed to produce ammonia. With this method,
Steam heating as when vaporizing liquid ammonia is not required. Liquid ammonia may be injected into the hot gas produced by LPG combustion instead of the aqueous ammonia solution. In this case, the drawback of using liquid ammonia remains,
After all, heating by steam etc. is unnecessary. Further, in any of these cases, the air for diluting ammonia as in the conventional method is unnecessary.

When the denitration temperature is 120 ° C. or lower, the ammonium sulfate crystals are precipitated without being decomposed so that the reaction progress may be hindered, but if it is 120 ° C. or higher, it can be said in principle that it is possible. However, it has hitherto been considered that a temperature of 300 ° C. or higher, preferably 350 to 400 ° C. is required to obtain a practical reaction rate. This is because the conventional denitration catalyst uses a titania-based catalyst carrier and is not necessarily advantageous in terms of reaction rate, and therefore a considerably high temperature is required to obtain a sufficient reaction rate. On the other hand, if a catalyst having r-alumina having a very large specific surface area as a carrier is used in the method of the present invention, a sufficiently practical reaction rate can be obtained at 200 to 330 ° C, and in some cases 200 ° C or less. .

Therefore, in the present invention, before the exhaust gas from the desulfurization apparatus by the lime-gypsum method is put into the denitration apparatus by the selective catalytic reduction method, the running cost is not increased so much by simply blowing steam and heating, By using an indirect heat exchange device that uses steam as the heat medium, if necessary,
Heat exchange may be performed between the temperature decreasing process when introducing into the desulfurization device and the temperature increasing process when introducing into the denitration device.

In the present invention, since the amount of dust particles in the exhaust gas flowing into the denitration device is small, even if a granular catalyst is used, there is almost no blockage of the device due to dust accumulation. Especially when JBR is used, the amount of dust in the desulfurized exhaust gas is generally 10
It is less than mg / Nm ³ , and in this case, the problem of clogging due to the use of the granular catalyst does not substantially occur.

[Example] (Example 1) An example of an apparatus for carrying out the method of the present invention is schematically shown in a block diagram in FIG. Exhaust gas from the boiler flows into JBR2 after it has been cooled to 130 ° C by heat exchanger 1. The composition of the exhaust gas flowing into the JBR is as follows.

SO ₂ 1600ppm (dry) NO _X 300ppm H ₂ O 10% by volume Dust 200mg / Nm ³ On the other hand, the characteristics of the exhaust gas flowing out from JBR are as follows.

SO ₂ 32ppm Dust 5mg / Nm ³ Exhaust gas desulfurized with JBR is 50 ℃ in heat exchanger (GGH) 3.
To 190 ° C, and then steam heater 4 to 250 ° C
After the temperature is raised to 1, it passes through the reactor 5 filled with the denitration catalyst layer. As the denitration catalyst, a r-alumina produced according to the method of Japanese Examined Patent Publication No. 1-16772, on which vanadium is supported, and formed into a pellet, is used. Ammonia gas is injected into the exhaust gas before it enters the denitration catalyst layer.
The composition of the exhaust gas subjected to the denitration treatment is as follows.

SO ₂ 32ppm NO _X 80ppm Dust 5mg / Nm ³ NH ₃ 3ppm The temperature of the treated exhaust gas is lowered by the heat exchanger (GGH) 6 and discharged from the stack at 110 ° C.

The heat recovered in GGH6 is used to raise the temperature of exhaust gas in GGH3 by indirect heat exchange using water as a heat medium. This reduces the consumption of steam for raising the temperature of exhaust gas.

(Example 2) Instead of the above-mentioned r-alumina as a denitration catalyst carrier, Japanese Patent Publication No.
In the case of using the modified sepiolite manufactured by the method of Japanese Patent No. 6697, the properties of the exhaust gas subjected to the denitration treatment are as follows.

SO ₂ 32ppm NO _X 120ppm Dust 5mg / Nm ³ NH ₃ 3ppm (Example 3) Except for denitration at 190 ° C and omitting the temperature rise by steam, the properties of the denitration treated exhaust gas were the same as in Example 1. Is as follows.

SO ₂ 32ppm NO _X 150ppm Dust 5mg / Nm ³ NH ₃ 5ppm

[Brief description of drawings]

FIG. 1 is a flow sheet showing an embodiment of the present invention. FIG. 2 is a schematic diagram showing an example of JBR that is preferably used in the method of the present invention. 1 ... Heat exchanger (GGH) 2 ... Desulfurization device (JBR) 3 ... Heat exchanger (GGH) 4 ... Steam heater 5 ... Denitration device (selective catalytic reduction method) 11 ... Jet bubbling layer 12 ... … Oxygen dissolution region

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01D 53/77 53/86 ZAB B01J 21/16 ZAB A 8017-4G 23/22 ZAB A 8017-4G 23/24 ZAB A 8017-4G 23/34 ZAB A 8017-4G 23/74 ZAB A 8017-4G 29/16 ZAB A 9343-4G B01D 53/36 ZAB 53/34 125 E ZAB (72) Inventor Taketa Ito 6-35-36 Yokodai, Isogo-ku, Yokohama-shi, Kanagawa (56) References JP-A-62-129128 (JP, A) JP-A-56-105732 (JP, A) JP-A-51-37077 (JP, A) JP-A-51-54073 (JP, A) JP-A-59-4422 (JP, A)

Claims (10)

[Claims] 1. A desulfurization and denitration method for removing sulfur oxides and nitrogen oxides from exhaust gas containing sulfur oxides and nitrogen oxides, wherein the exhaust gas is lime-gypsum using a liquid phase continuous gas absorption device. After desulfurization treatment by the method, a denitration treatment is performed by a selective catalytic reduction method using a denitration catalyst in which an active metal is supported on a magnesium silicate-based catalyst carrier. 2. The method according to claim 1, wherein heat is recovered from the exhaust gas after the denitration treatment by the selective catalytic reduction method and is used for raising the temperature of the exhaust gas after the desulfurization treatment by the lime-gypsum method. 3. The method according to claim 1, wherein the amount of dust in the exhaust gas after desulfurization by the lime-gypsum method is 10 mg / Nm ³ or less. 4. The method according to claim 1, wherein the desulfurization treatment is carried out in a jet bubbling reactor. 5. The method according to claim 1, wherein the catalyst carrier is sepiolite. 6. The method according to claim 1, wherein the active metal is vanadium, tungsten, molybdenum, chromium, manganese, iron, cobalt or nickel. 7. The method according to claim 1, wherein the denitration temperature is 200 to 330 ° C. 8. A denitrification treatment by injecting an ammonia-containing gas produced by injecting one or more selected from liquid ammonia, an aqueous ammonia solution and an aqueous urea solution into the combustion exhaust gas into the exhaust gas after desulfurization treatment. The method according to any one of 1 to 7. 9. The method according to claim 1, wherein ammonia is separately injected into the exhaust gas before desulfurization treatment. 10. The amount of SO ₃ in the exhaust gas after desulfurization treatment is 1
The method according to claim 9, wherein the amount is 0 mg / Nm ³ or less.