JPS61185318A - Desulfurization and denitration apparatus - Google Patents

Abstract

PURPOSE:To miniaturize the title apparatus while eliminating leaked NH3 and preventing the generation of desulfurization waste water, by arranging machineries in the order of a dust collector, a dry denitration apparatus, an air preheater and a dry desulfurization apparatus. CONSTITUTION:Exhaust gas from a boiler 1 is supplied to a dust collector 2 to remove dust therein and the treated exhaust gas 9 is supplied to a dry denitration apparatus 3 while receives the injection of NH3 8 to perform denitration and preheated by an air preheater 4 to enter a dry desulfurization apparatus 5. The dry desulfurization apparatus 5 is packed with an adsorbent, and SOX and NH3 discharged from the denitration apparatus 3 in an unreacted stat are simultaneously adsorbed and removed herein. Adsorbed SOX and NH3 are heated in a desorbing tower to be decompsed into SO2 and innoxious N. By this method, the leakage of NH3 is prevented and, because of no wet type, waste water is not also generated.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a desulfurization and denitrification equipment, and particularly to a desulfurization and denitrification equipment that prevents ammonia from flowing out of the system when a dry denitrification equipment using ammonia catalytic reduction is incorporated. It is.

(Prior art) Nitrogen monoxide, nitrogen dioxide, etc. (hereinafter referred to as NOx) and sulfur dioxide gas (hereinafter referred to as SOx) contained in exhaust gas from boilers, etc.
It is common to use a combination of dry denitrification equipment and wet desulfurization equipment for the treatment of Dry-type denitrification equipment generally uses the ammonia catalytic reduction method in which ammonia gas is added using a catalyst, while wet-type desulfurization equipment generally uses a method to remove SOx using an absorption liquid made by dissolving limestone or other alkaline substances in water. It is being done. In order to increase the denitrification rate in this dry denitrification equipment, it is necessary to increase the amount of added NH3 to NOx in the exhaust gas.
When the amount of ammonia is increased, the amount of ammonia leaking from the dry denitrification equipment also tends to increase, and for this reason, there is a limit to the amount of ammonia that can be added. Note that this leaked ammonia is usually suppressed to 5 pp'm or less, and is collected by equipment installed downstream of the dry denitration equipment. This will be explained in detail below with reference to the drawings.

FIG. 5 is a diagram showing a flow sheet of a conventional desulfurization and denitrification method. In FIG. reaction (i.e. 4NH3+4NO+O□
-'4N2+6H20) required ammonia gas (NH
3) is added through conduit 8 (this denitrification method is generally referred to as "high dust denitrification method"). The gas after denitrification is introduced into the air preheater 4 through the conduit 9, where the gas temperature is 300~
The exhaust gas is cooled from 400°C to about 130 to 150°C, and then dust in the exhaust gas is removed by a dust collector 2. On this occasion,
A part of the leaked ammonia from the dry denitrification device 3 will be mixed into the dust collected by the dust collector 2. The exhaust gas after dust collection is treated in a wet desulfurization device 13 and discharged from a chimney 6 through a conduit 12. In the wet desulfurization device 13, for example, about 95% of the ammonia gas in the inflowing gas is absorbed, mixed with the desulfurization wastewater, and discharged outside the system.

FIG. 7 is a diagram showing a flow sheet when the limestone-gypsum method is used as a wet desulfurization device.
The denitrified boiler exhaust gas is transferred from the conduit 24 to the absorption tower 2.
1 and, after desulfurization treatment, is discharged through the conduit 25 into the chimney. In the absorption tower 21, the absorption liquid supplied from the conduit 26 and the boiler exhaust gas come into gas-liquid contact, so that SO
While x is absorbed, ammonia content is also removed from the exhaust gas and collected in the absorption liquid. The absorption liquid that has absorbed these SOX and ammonia components passes through a conduit 27, and the calcium sulfite in the absorption liquid is oxidized in the gypsum production equipment (pH adjustment equipment, oxidation tower, etc.) 22, and the solidified gypsum slurry is discharged from the conduit 28. The liquid is sent to the liquid separator 23 and powdered gypsum is recovered from the conduit 29. The filtered water separated by the solid-liquid separator 23 is recycled through the conduits 30 and 32, but in wet desulfurization equipment, the filtered water is A part of the water is extracted from the conduit 3 and treated by the discharge treatment device 33. For example, in a 250 MW plant, the amount of water discharged from such a desulfurization equipment is 9) where the NH in the inlet gas is 51) Pm.
Assuming that 5% is absorbed and the amount of wastewater from the absorption system is 10t/h, the amount of NH3 in the absorption liquid and wastewater is approximately 300mg.
It is said that it will be /l. Furthermore, since NH3 is mixed into the wastewater, biochemical treatment or ammonia stripping treatment may be performed.

(Problems to be Solved by the Invention) In the above-mentioned prior art (Fig. 5), ammonia is mixed into the dust collected by the dust collector 2, but for example, in the case of fly ash from a coal-fired boiler, cement When the dust is used in a landfill or disposed of, it may smell like ammonia and be disliked, and if the dust is used in a landfill,
Ammonia in dust is carried by rainwater from landfills and flows into rivers, and as mentioned above, when wastewater containing ammonia from desulfurization equipment flows into rivers or lakes, these This will promote eutrophication of water quality and cause pollution problems.

In order to prevent ammonia from being mixed into the dust collected by the dust collector 2, the dust collector 2 is installed as shown in Figure 6.
It is conceivable to adopt a denitrification method (low dust denitrification method) in which the ammonia is installed in the front stage of the dry denitrification equipment 3 and ammonia is injected after the dust has been collected. Contamination of leaked ammonia into the wet desulfurization device 13 is unavoidable, and there are problems such as the need to reprocess wastewater containing ammonia. Furthermore, since the above-mentioned low-dust denitrification method includes a small amount of fine dust, there may be a problem of blockage in the downstream air preheater 4 due to the formation of acidic ammonium sulfate. This can be practically dealt with by employing a low oxidation rate catalyst that suppresses the conversion rate of SO2 to SO3, but there is a drawback that the catalyst must be selected.

As mentioned above, in the wet desulfurization equipment downstream of the conventional denitrification equipment using the low dust method and the high dust method, it is unavoidable that ammonia gets mixed into the wastewater, so depending on the installation location, such ammonia can be removed depending on the installation location. It becomes necessary to provide special equipment for treatment.

An object of the present invention is to provide a desulfurization and denitrification device that eliminates the drawbacks of the prior art described above, reduces the ammonia content in the exhaust gas after desulfurization treatment, and does not produce desulfurization wastewater containing ammonia content.

(Means for Solving the Problems) In summary, the present invention provides a desulfurization and denitrification device equipped with a dry flue gas denitrification device using ammonia catalytic reduction, a flue gas desulfurization device, and a dust collector, in which the dust collector is replaced with the dry flue gas denitrification device. It is characterized in that it is installed upstream of the denitrification device and uses a dry flue gas desulfurization device as the flue gas desulfurization device. That is, in the present invention, a dust collector, a dry denitrification device, an air preheater, and a dry desulfurization device are typically arranged in this order for the gas flow.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

The device shown in FIG. 1 is the same as the conventional example shown in FIG. 4 in that a dust collector 2, dry denitrification device 3, and air preheater 4 are installed for the exhaust gas flow from the boiler 1. The difference is that the final stage wet desulfurization device 13 is replaced with a dry desulfurization device 5.

An example of a dry desulfurization device used in the present invention is shown in FIG. 2. In this device, boiler exhaust gas is sent from a conduit 43 to an adsorption tower 41 filled with a carbonaceous adsorbent. SOx in the exhaust gas is adsorbed and removed. At this time, ammonia in the exhaust gas is also removed at the same time, and these are shown by the following reaction formula.

*C here represents a carbonaceous adsorbent. The gas from which SOx and ammonia have been removed is discharged from the chimney via conduit 4.

On the other hand, the carbonaceous adsorbent that has adsorbed SOx and ammonia is led from a conduit 45 to a desorption tower 42, and heated to 300 to 700°C by heated gas introduced from a conduit 47, and at the same time, the adsorbed material is converted into S62 and harmless N2. Decomposed. These are shown by the following reaction formula.

*C-H, so, -vc +so2+)I, o+vc
o2-(413C+f'J, +3SO,+6H,O-+
The desorbed gas containing a high concentration of S02 is extracted from the conduit 49, sent to a by-product recovery process, and reduced to elemental sulfur and the like. The heat-regenerated carbonaceous adsorbent is cooled by the cooling medium introduced from the conduit 48, returned to the adsorption tower 41 again from the conduit 46, and used for circulation. Conduit 50, the above (
4) This is a conduit for replenishing an amount commensurate with the amount of carbonaceous adsorbent consumed in formulas, etc.

FIG. 3 is a diagram showing the NH3 concentration in the exhaust gas at the inlet and outlet of the adsorption tower of the dry desulfurization apparatus used in the present invention. As a result of testing in the range of adsorption tower population NH3 concentration from 0.5 to 250 ppm, the adsorption tower outlet NH3 concentration was approximately 0.061)
It was found that the temperature could be kept below pm. It is clear that this can prevent NH3 leakage from the treated exhaust gas. In addition, when the ammonia content in the highly concentrated S02-containing snack gas generated from the desorption tower was measured using the adsorption tower population NH3 concentration as zooppm, it was found to be less than o, e ppm. In addition, the S02 concentration in the boiler exhaust gas is 500p.
pm (dry basis), the So2 concentration in the highly concentrated SO□ gas recovered from the desorption tower was 4Qvo 1% (dry basis), which means that the S02 in the boiler exhaust gas was approximately
It shows that it was concentrated by a factor of (4010,05). Therefore, ammonia should be decomposed in the desorption column to -15vo 1%, but in reality it is 0.6 ppm, so it can be seen that in this case, 99.9996% of NH3 has been decomposed. In this way, the ammonia that flows into the dry desulfurization equipment is mostly decomposed into harmless N2, so the leak ammonia from the dry desulfurization equipment does not need to be limited as in the past, and there is no need to limit the amount of ammonia necessary for denitrification. This makes it possible to supply ammonia.

Figure 4 shows the denitrification rate, leak ammonia and NH:i/
3 shows a relationship diagram of NOx ratio. Conventionally, the denitrification rate was 80
% and to suppress the discharge of ammonia to the outside of the system, it was necessary to set the SV of the dry denitrification equipment to about 5000 h. However, according to the present invention, there are no restrictions on leakage ammonia from the dry denitrification equipment. Instead, SV is 10,0OO
Since it becomes possible to set it to about h-, the capacity of the dry denitrification device can be reduced to 172 compared to the conventional one.

According to the above-mentioned embodiment, by installing the dust collector before the dry denitrification equipment and installing the dry desulfurization equipment at the last stage, there is no ammonia mixed into the collected dust, and the dry denitrification equipment has low Since it can be operated with dust and desulfurization is carried out by a dry method, it does not generate desulfurization wastewater unlike wet desulfurization equipment, and therefore no ammonia-containing wastewater is generated. Furthermore, the economic efficiency of dry denitrification equipment depends on the amount of catalyst and its lifespan, but in the present invention, since exhaust gas with low dust is treated, there is no problem of catalyst wear, and it can be used in both coal-fired boilers and oil-fired boilers. It becomes possible to design according to exhaust gas. Furthermore, due to the low dust exhaust gas, the gas flow rate can be increased, and therefore the denitrification device can be made more compact, allowing for economical design.

The dry desulfurization equipment used in the desulfurization and denitrification equipment of the present invention includes:
In addition to the moving bed type equipment shown in Fig. 2, fixed bed type desulfurization equipment similarly uses a carbonaceous adsorbent and regenerates the carbonaceous adsorbent by heating regeneration (for example, JP-A-56-1
52721) can also be used.

(Effects of the Invention) According to the present invention, by arranging the equipment in the order of the dust collector, dry denitrification device, air preheater, and dry desulfurization device, the exhaust gas containing ammonia is removed by the dry desulfurization device using harmless N2.
Since the dry process does not produce desulfurization wastewater, the discharge of ammonia to the outside of the system is essentially eliminated.
Furthermore, since there are no restrictions on the equipment due to leaked ammonia, it is possible to make the dry denitrification equipment more compact.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a flow sheet of a flue gas desulfurization and denitrification device showing one embodiment of the present invention, FIG. 2 is an explanatory diagram of a dry desulfurization device used in the present invention, and FIG. A diagram showing the relationship between the NH3 concentration at the inlet and outlet of the adsorption tower of the dry desulfurization equipment,
Figure 4 shows the estimated nitrification rate, leak ammonia and NH3/N of the dry denitrification equipment. Figures 5 and 6 are diagrams showing the relationship between the molar ratio of FIG. 2 is an explanatory diagram of a wet desulfurization device used in the processing device. 1... Boiler, 2... Dust collector, 3... Dry denitrification device, 4... Air preheater, 5... Dry desulfurization device, 6
...Chimney, 13...Wet desulfurization equipment. Agent Patent Attorney Takeshi Kawakita Figure 1 Figure 2 Figure 3 = ssts entered oN83JK (ppm) Figure 4 NH3/NOX (zLW Figure 5 Figure 7

Claims (1)

[Claims] (1) In a desulfurization and denitrification device equipped with a dry flue gas denitrification device using ammonia catalytic reduction, a flue gas desulfurization device, and a dust collector, the dust collector is provided on the upstream side of the dry flue gas denitrification device, and the flue gas A desulfurization and denitrification device characterized in that a dry flue gas desulfurization device is used as the desulfurization device.