JP2680603B2 - Method and apparatus for dry desulfurization and denitration of exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to sulfur oxides (SOx) and nitrogen oxides (NOx).
Method and apparatus for dry desulfurization and denitration using a fixed bed of carbonaceous material in exhaust gas containing NOx, particularly NOx accompanied with a small amount of SOx
It is suitable for desulfurization and denitration treatment of the contained exhaust gas.

[Conventional technology]

Many methods and apparatuses for dry desulfurization and denitration using carbonaceous substances in exhaust gas containing sulfur oxides (SOx) and nitrogen oxides (NOx) have been proposed. In these conventional methods, by adding ammonia to the exhaust gas and introducing it into a carbonaceous substance, SOx is changed to ammonium sulfate or ammonium hydrogensulfate, NOx is decomposed into nitrogen and water, and this is adsorbed by the carbonaceous substance. To remove.

Therefore, ammonium sulfate, ammonium hydrogen sulfate and the like adhere to the surface or inside of the carbonaceous material to increase the pressure loss and reduce the desulfurization and denitration rate, and in addition, the accumulation of dust accompanying exhaust gas accelerates this. In order to carry out desulfurization denitration within a range in which the increase in pressure loss and the reduction in desulfurization denitration rate are allowed, it is necessary to alternately operate the adsorption reaction step and the desorption regeneration step.

Therefore, when a fixed bed reactor is used, a complicated multi-series and multi-tower system is adopted, and a method of regenerating carbonaceous material is adopted by establishing a cycle of adsorption reaction step and desorption reaction step by switching valves. .

When a fluidized bed or moving bed reactor is used, a desorption / regeneration tower is provided separately, and the carbonaceous material that has undergone the adsorption reaction step is moved from that step to the desorption / regeneration tower outside the system, where desorption / regeneration is performed. Then, it is recycled to the fluidized bed or moving bed reactor.

[Problems to be solved by the invention]

The above-mentioned conventional dry desulfurization and denitration method using a carbonaceous material and the apparatus therefor have complicated and large-scale apparatus configurations, and the equipment cost and running cost are high, and therefore large-capacity and high-concentration SOx, NOx-containing exhaust gas treatment However, there is a disadvantage in that it is expensive to treat a small amount of exhaust gas or an NOx-containing exhaust gas accompanied by a small amount of SOx.

In recent years, environmental regulations have become stricter, and CO2 emission and other small-sized exhaust gas or NOx-containing exhaust gas accompanied with a small amount of SOx, for example, combustion exhaust gas of fossil fuel with low sulfur content, or wet desulfurization treatment using existing combustion equipment. There is a demand for an apparatus and method suitable for NOx-containing exhaust gas accompanied by a small amount of residual SOx after that.

The object of the present invention is to meet the above-mentioned demands, while being relatively small, it is possible to maintain a desulfurization and denitration rate for a long time, and it is possible to realize economical equipment cost and running cost, a small amount of SOx. The present invention provides a dry desulfurization denitration method and apparatus suitable for treating accompanying NOx-containing exhaust gas.

[Means for solving the problem]

The present invention provides a plurality of relatively small fixed bed reactors in series to the exhaust gas flow, regenerates the carbonaceous material by washing each reactor, and maximizes the washing and regeneration frequency of the uppermost fixed bed. By preventing the increase of pressure loss, efficient desulfurization /
A denitration method and an apparatus therefor.

That is, the present invention, after adding ammonia to the exhaust gas containing NOx accompanied by SOx, SOx, NOX, dust in the exhaust gas by sequentially passing this gas through a plurality of carbonaceous material fixed beds arranged in series. It is adsorbed and removed, and the fixed bed of carbonaceous material is intermittently washed with water or hot water to be regenerated so that the pressure loss increase of the fixed bed of carbonaceous material is within a predetermined value. The method for dry desulfurization and denitration of exhaust gas is characterized by maximizing the frequency of washing the fixed bed of carbonaceous material.

Further, the present invention comprises, as means for realizing the above method, a fixed bed filled with a carbonaceous material, a washing means for the upper part of the fixed bed, a washing liquid removing means for the lower part of the fixed bed, an exhaust gas inlet and an exhaust gas outlet. An exhaust gas dry desulfurization and denitration apparatus is provided in which a plurality of fixed bed reactors are provided in series with an exhaust gas flow, and an ammonia addition unit is provided in an exhaust gas inlet conduit of at least a first reactor of the fixed bed reactors. .

Furthermore, in a particularly preferred embodiment of the present invention, the carbonaceous material fixed bed of at least the first reactor is a removable cartridge type bed, and the carbonaceous material fixed bed exchange means is provided. A device is used to ensure that the pressure drop increase is within a predetermined value by exchanging with a fresh or regenerated fixed bed of carbonaceous material before the pressure drop increase of the cartridge type fixed bed exceeds a predetermined value.
The above-mentioned method in which the removed fixed bed of carbonaceous material is washed and regenerated outside the system can be mentioned.

[Action]

The present invention is characterized in that the desulfurization and denitration reactor is a plurality of fixed bed reactors, and these are installed in series with respect to the flow of exhaust gas. With this arrangement, most of the SOx is adsorbed in the first reactor and dust contained in the exhaust gas is deposited, so that the pressure loss in the first reactor is significantly increased. Therefore, by increasing the regeneration frequency of the 1st reactor and maintaining a state where sufficient SOx can be removed at all times, a small amount of residual SOx and NOx can be supplied to the 2nd and subsequent reactors.
Since exhaust gas containing ammonia and ammonia is supplied, the increase in pressure loss is extremely small and the denitration activity can be maintained over a long period of time, so the regeneration frequency of the second and subsequent reactors is extremely low. I'm sorry. In the presence of ammonia
A carbonaceous substance having an increased pressure loss by treating SOx-containing exhaust gas and adsorbing and depositing ammonium sulfate, ammonium hydrogensulfate, dust or the like can be easily regenerated by washing with water (water or hot water). The method and apparatus of the present invention are particularly advantageous for treating exhaust gas containing SOx and NOx and having a small amount of SOx.

 The present invention will be specifically described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.
In FIG. 1, the exhaust gas containing NOx accompanied by a small amount of SOx is fed along the exhaust gas inlet conduit 4 with the ammonia addition conduit 5
A plurality of fixed bed reactors 1a, 41b, --- filled with carbonaceous material after the addition of ammonia gas from the gas stream Is introduced into the fixed bed reaction step 1 provided in the above. First, in the first fixed bed reactor 1a, ammonium sulfate and ammonium hydrogen sulfate are produced by the adsorption reaction of SOx and ammonia in the exhaust gas with the carbonaceous material. Dust is also adsorbed and deposited on the carbonaceous material together with these ammonium salts. As a result, the small amount of SOx contained in the exhaust gas
Gas and dust are removed virtually virtually entirely. Next, the gas is introduced into the fixed bed reactor 1b, and NOx is decomposed into nitrogen gas and water by the residual ammonia and removed.
After the exhaust gas is sequentially treated by the fixed bed reactors 1a, 1b, ---, the treated gas is discharged from the chimney 2 to the atmosphere through the outlet conduit 6.

In the fixed bed of the fixed bed reactors 1a and 1b, with the passage of time,
Products such as ammonium sulphate and ammonium hydrogen sulphate and dust adhere and deposit to increase the pressure loss and reduce the activity. When the increase in this pressure loss exceeds a predetermined value, the activity declines rapidly. Therefore, water is intermittently supplied from the regeneration washing water conduit 7 provided above the fixed bed reactors 1a, 1b so as not to exceed the predetermined value. Alternatively, hot and warm water of 100 ° C. or lower is sprayed and dropped onto the fixed bed, and ammonium sulfate, ammonium hydrogen sulfate and dust are washed away from the carbonaceous material of the fixed bed to regenerate the fixed bed. The washing liquid is sent to the product treatment tank 3 via the washing liquid discharge conduits 8 and 9. As a result, the carbonaceous material can be regenerated and the increase in pressure loss is eliminated.

The predetermined value for the increase in pressure loss, which causes a rapid decrease in activity, will vary depending on the design of the exhaust gas to be introduced, the properties of the carbonaceous material, and the exhaust gas treatment conditions. The optimum value is set in advance.

Here, the cleaning frequency of the first fixed bed reactor 1a is
More than that. By this, the first fixed bed
The increase in pressure loss that occurs intensively in 1a can be stopped within the desired limit and a high desulfurization rate can be maintained at all times, and substances and dust produced from SOx and ammonia can be almost completely removed. Since the influence on the reactor is substantially prevented, the carbonaceous material after the second fixed bed reactor 1b can be maintained highly active for a long period of time without being substantially polluted.

The frequency of washing regeneration can be set arbitrarily depending on the design and various conditions. For example, if the first fixed bed reactor 1a is set to once every 20 days to 2 months, the second fixed bed reactor 1b will be set for half a year. Approximately once a year, a sufficiently good denitration function can be achieved.

In addition, by neutralizing the washing liquid in the product treatment tank 3 by adding a neutralizing agent such as caustic soda, magnesium hydroxide or lime supplied from the neutralizing agent conduit 10,
Ammonia gas is generated, and the obtained ammonia-containing gas is supplied to the ammonia addition conduit via the conduit 12 and is recycled.

In the above description, the case where the total amount of the ammonia added for desulfurization and denitration is introduced upstream of the fixed bed reactor process 1 has been described, but it is dividedly introduced at each gas inlet of the fixed bed reactors 1a and 1b-. It can also depend on the method.

The washing and regeneration of the first fixed bed reactor 1a is carried out when the operation is stopped, or a bypass pipe is provided during the operation to bypass the temporary exhaust gas to carry out the fixed bed as a closed system.

Further, the second fixed bed reactor 1b may be not only one but two or more in series and in parallel. A demister may be provided between the first and second fixed-bed reactors, and both fixed-bed reactors may of course be incorporated vertically instead of being connected in series horizontally.

In the present invention, as the carbonaceous material used for the fixed bed, for example, a carbonaceous material generally called activated carbon or activated coke with a specific surface area of 30 to 1500 m ² / g, or titanium, vanadium, chromium, manganese , Iron, cobalt,
Examples thereof include those carrying one or more kinds of oxides or chlorides of metals selected from nickel, copper, molybdenum, tungsten and the like.

FIG. 2 is a block diagram showing another embodiment of the present invention. In the present embodiment, the first fixed bed reactor 1a is equipped with a detachable cartridge-type fixed bed 1a ', and a replacement means for the cartridge-type fixed bed 1a' is provided. It's different. As in the case of FIG. 1, the exhaust gas is supplied with ammonia gas and treated in the fixed bed reactors 1a and 1b, and the cartridge type fixed bed 1a ′ is removed from the system so that the increase in pressure loss does not exceed a predetermined value. Take out and recycle the washing water conduit 11
Recycle by washing with water or hot / humid water or immersing. If it is inconvenient to remove the cartridge type fixed bed for regeneration during operation and then to make it an empty tower, a method of separately preparing a new or regenerated cartridge and inserting it may be used.

Note that the fixed-bed reactor equipped with the cartridge type fixed bed does not require the regenerating water washing means and the washing liquid take-out means, and therefore FIG. 2 shows a case where these are omitted.

By using such a cartridge type fixed bed, it is possible to easily replace the fixed bed in a short time, so that the influence on the process can be reduced and the regeneration frequency of the first fixed bed with a large pressure loss increase can be further improved. Since the fixed bed can be thoroughly washed outside the system, the effect is greater than that of the example shown in FIG.

FIG. 3 shows an example of application of the dry desulfurization and denitration method of the present invention shown in FIG. 1 or 2 above, with a small amount of residual SOx obtained after subjecting combustion waste gas to wet desulfurization and NOx
By applying the present invention to the treatment of the exhaust gas containing, it is possible to carry out substantially complete desulfurization and denitration. In the drawing, an example in which the method of the fixed bed of the cartridge type shown in FIG. 2 is adopted will be described. The combustion waste gas is introduced into the wet desulfurization device 20 from the combustion waste gas conduit 22 through the heat exchanger 23. Here, most of SOx in the combustion waste gas is washed and removed by the absorption liquid from the absorption liquid pipe 25, and the desulfurization effluent is introduced into the desulfurization circulation liquid tank 21 by the desulfurization circulation liquid pipe 26. While most of
In the exhaust gas from which SOx has been removed, about 50 to 150 ppm of SOx usually remains, so the heat exchanger 23 exchanges heat with the combustion waste gas to raise the temperature to a temperature suitable for dry denitration by carbonaceous material, and then the exhaust gas inlet conduit It is introduced into the first fixed bed reactor 1a of the dry desulfurization and denitration apparatus using a carbonaceous material via No.4. An ammonia addition conduit 5 (optionally with the recovered ammonia-containing gas from the recovered ammonia-containing gas conduit 12) is connected to the exhaust gas inlet conduit 4 to add ammonia to the exhaust gas. Hereinafter, the gas desulfurized and denitrated as described with reference to FIG. 2 is released to the atmosphere through the outlet conduit 6 and the chimney 2.

Cartridge-type fixed bed 1a 'is taken out of the system as indicated by the dotted line so that the increase in pressure loss does not exceed a predetermined value, and is washed and regenerated with water or hot water from the washing water conduit 11 for regeneration. It is introduced into the product treatment tank 3 via 8 and the washing liquid from the second fixed bed reactor 1b is also introduced into the product treatment tank 3 via the washing liquid discharge conduit 9.

In the product treatment tank 3, an ammonia-containing gas generated by adding a neutralizing agent such as caustic soda, magnesium hydroxide, and lime to the washing liquid from the neutralizing agent conduit 10 is collected from the ammonia-containing gas conduit 12 and removed from the ammonia-adding conduit 5. Combine with ammonia and add to the exhaust gas. On the other hand, the wastewater after the treatment is sent from the wastewater extraction conduit 13 to the desulfurization circulation liquid tank 21 of the wet desulfurization device, and is introduced together with the desulfurization circulation liquid from the desulfurization circulation liquid pipe 26 through the desulfurization absorbent pipe 27, caustic soda It is processed by adding desulfurization absorbents such as magnesium and slaked lime. A part of the processing liquid is circulated to the wet desulfurization device 20 through the absorption liquid conduit 25 as the absorption liquid for wet desulfurization, and the rest is desulfurized through the waste liquid discharge pipe 28. It is sent to a waste liquid treatment device (not shown).

In the above description, the waste water from the waste water take-out conduit 13 is explained to be sent to the desulfurization circulation liquid tank 21, but as shown by the dotted line, it is joined to the waste liquid discharge pipe 28 to a desulfurization waste liquid treatment device (not shown). You may send it.

In this way, the ammonia gas is collected and the remaining wastewater is combined with the desulfurization waste liquid of wet desulfurization to be processed, so that the amount of ammonia consumed can be reduced and the equipment associated with dry desulfurization denitration can be rationalized, and equipment costs and running costs can be reduced. The cost can be further reduced.

〔Example〕

The exhaust gas was treated with the configuration shown in FIG. The main conditions are as follows.

Exhaust gas: Exhaust gas from a boiler using gas as fuel (with almost no dust and containing 20% H ₂ O) Same composition (dry base): O ₂ 4.7%, CO ₂ 7.7%, N ₂ 87.6
%, NOx85-95PPM, SOx10-20PPM.

Exhaust gas flow rate: 200 Nm ³ / Hr NH ₃ addition amount: 20 to 24 Nl / Hr Reaction temperature: 150 ° C Carbonaceous material used for fixed bed: activated coke 50/1 fixed bed Number and type of fixed beds: Cartridge type 4 units ( Total amount of active coke 200) First, as a comparative example, when the treatment was performed without washing, as shown in the following table, an increase in pressure loss and a decrease in the denitration rate after 31 days were remarkable. The pressure loss and the denitrification rate were measured with the total of four fixed beds. Most of the increase in pressure loss was in the first fixed bed.

In view of the results of the comparative example, as an example of the present invention, first, as a result of washing only the first fixed bed, a pressure loss of 25 to
The NOx removal rate returned to 30 mmAq and 49 to 53%. As a result, the set value for cleaning the first fixed bed is 100 mmA for pressure loss.
q Denitrification rate was 36%.

As a result, only the first fixed bed was washed once at a frequency of 30 to 31 days, and it was possible to maintain the denitration rate of 49 to 35% and the exhaust gas outlet without SOx, thus confirming the effect of the present invention.

 The neutralizer used was caustic soda.

〔The invention's effect〕

As described above, in the method and apparatus of the present invention, a plurality of relatively small fixed bed reactors with water washing means are provided in series, and at least the required amount is provided upstream of the first fixed bed reactor. Ammonia is added, and it can be washed and regenerated by washing with water so that the increase in pressure loss of each fixed bed reactor does not exceed a predetermined value. Especially, by maximizing the number of washings of the first fixed bed reactor, The desulfurization rate can always be maintained at a high level to prevent contamination of the second fixed bed reactor and thereafter, and maintain a good activity for a long period of time.

Therefore, according to the present invention, it is not necessary to regenerate the carbonaceous material by a complicated multi-series and multi-tower system in order to maintain the activity, or the carbonaceous material having a reduced activity is moved to separate a large scale. Since it does not need to be regenerated by a simple desorption / regeneration device and a combination of relatively small fixed bed reactors based on a rational design corresponding to the exhaust gas capacity and SOx and NOx contained, a simple and economical equipment cost can be achieved. In addition, desulfurization and denitration can be performed at a running cost.

Moreover, the present invention in which at least the first fixed bed reactor is a cartridge type is a simple replacement work, but the denitrification rate of the fixed bed reactor can always be kept high without time loss, and the used cartridge can be sufficiently washed out of the system. Because it can be played
Workability, efficiency, and economic efficiency can be improved.

Further, in the method and production of the present invention, complete desulfurization and denitration steps can be realized by recovering used ammonia and combining with wet desulfurization step.

[Brief description of the drawings]

1 to 3 are views for explaining the embodiment of the present invention, FIG. 1 shows the basic constitution of the present invention, and FIG. 2 is the first carbonaceous material fixed bed. Is shown as a removable cartridge type, and FIG. 3 shows an example in which the structure of the present invention of the type shown in FIG. 2 is applied to the treatment of exhaust gas from a wet desulfurization process. 1 ... Fixed bed reaction process, 1a ... 1st fixed bed reactor, 1b ... 2nd fixed bed reactor, 1a '... Cartridge type 1st fixed bed, 2 ... Chimney 3 ... Product treatment tank, 4 ... Exhaust gas inlet conduit, 5 ... Ammonia addition conduit, 6 ... Treated exhaust gas outlet conduit, 7,11 ... Regeneration cleaning water conduit, 8,9 ... Cleaning liquid Extraction conduit, 10 ... Neutralizer conduit, 12 ... Recovered ammonia-containing gas conduit, 13 ... Wastewater extraction conduit, 20 ... Wet desulfurization device, 21 ... Desulfurization circulation tank, 22 ... Combustion waste gas conduit, 23 ... Heat exchanger, 25 ... Absorption liquid conduit, 26 ... Desulfurization circulation liquid conduit, 27 ... Desulfurization absorbent conduit, 28 ... Waste liquid outlet pipe.

Claims (5)

(57) [Claims] 1. SOx in exhaust gas is obtained by adding ammonia to exhaust gas containing NO _X accompanied by SO _X , and sequentially passing the gas through a plurality of fixed beds of carbonaceous material arranged in series. _X , NO _X , and dust are adsorbed and removed, and the fixed bed of carbonaceous material is intermittently washed with water or hot water so that the pressure loss increase of the fixed bed of carbonaceous material is within a predetermined value. Of the plurality of carbonaceous material fixed beds arranged in series in the exhaust gas dry desulfurization denitration method in which the cleaning frequency of the first carbonaceous material fixed bed is maximized. The fixed bed of carbonaceous material is removable and replaced with a new or regenerated fixed bed of carbonaceous material so that the increase in pressure loss is within a predetermined value, and the removed fixed bed of carbonaceous material is washed outside the system. Exhaust gas characterized by regeneration Dry desulfurization and denitration method. 2. SOx in exhaust gas is obtained by adding ammonia to exhaust gas containing NO _X accompanied by SO _X , and then sequentially passing the gas through a plurality of fixed beds of carbonaceous material arranged in series. _X , NO _X , and dust are adsorbed and removed, and the fixed bed of carbonaceous material is intermittently washed with water or hot water so that the pressure loss increase of the fixed bed of carbonaceous material is within a predetermined value. In the method for dry desulfurization and denitration of exhaust gas, where the first fixed bed of carbonaceous material is washed most frequently, the fixed bed of carbonaceous material is washed with water or hot water to remove the washing water. A method for dry desulfurization and denitration of exhaust gas, which comprises adding a solvating agent and recovering the ammonia-containing gas generated thereby to circulate and use as ammonia to be added to the exhaust gas. 3. SOx in exhaust gas is obtained by adding ammonia to exhaust gas containing NO _X accompanied by SO _X , and then sequentially passing this gas through a plurality of fixed beds of carbonaceous material arranged in series. _X , NO _X , and dust are adsorbed and removed, and the fixed bed of carbonaceous material is intermittently washed with water or hot water so that the pressure loss increase of the fixed bed of carbonaceous material is within a predetermined value. Of the plurality of carbonaceous material fixed beds arranged in series in the exhaust gas dry desulfurization denitration method in which the cleaning frequency of the first carbonaceous material fixed bed is maximized. The fixed bed of carbonaceous material is removable and replaced with a new or regenerated fixed bed of carbonaceous material so that the increase in pressure loss is within a predetermined value, and the removed fixed bed of carbonaceous material is washed outside the system. Regenerate the carbonaceous material fixed bed with water or A method for dry desulfurization and denitration of exhaust gas, characterized by adding a neutralizing agent to the wash water extracted after washing with hot hot water, recovering the ammonia-containing gas generated by this, and circulatingly using it as ammonia added to the exhaust gas. . 4. A fixed bed reactor comprising a fixed bed filled with a carbonaceous material, a washing means at the upper part of the fixed bed, a washing solution taking-out means at the lower part of the fixed bed, an exhaust gas inlet and an exhaust gas outlet, On the other hand, a dry desulfurization and denitration apparatus for exhaust gas, which is provided in series with a plurality of units and has an ammonia addition means in the exhaust gas inlet conduit of at least the first reactor of the fixed bed reactor. 5. The carbonaceous material fixed bed of at least the first reactor is a detachable cartridge type, and the cartridge type carbonaceous material fixed bed exchange means is provided. The dry desulfurization and denitration device described.