JPS6161855B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes a reactor having a moving bed of carbonaceous adsorbent particles and a moving bed regenerator for regenerating the adsorbent particles to produce sulfur oxides or sulfur oxides. This invention relates to improvements in methods for treating exhaust gas containing nitrogen oxides and nitrogen oxides.

For example, a sulfur oxide-containing exhaust gas is supplied to a reactor containing carbonaceous adsorbent particles such as activated carbon as a moving bed, and the exhaust gas and carbonaceous adsorbent particles are brought into contact with each other in countercurrent or cross-current flow. A method of desulfurizing exhaust gas by adsorbing sulfur oxides in the exhaust gas onto carbonaceous adsorbent particles is known as a dry flue gas desulfurization method. In this desulfurization method, metal oxides such as vanadium pentoxide are sometimes supported on carbonaceous adsorbent particles, but regardless of whether metal oxides are supported or not, sulfur oxides are adsorbed and reacted. The carbonaceous adsorbent particles discharged from the bottom of the vessel are usually transferred to a moving bed type regenerator where they are heated and regenerated, and the regenerated carbonaceous adsorbent particles are circulated back to the above-mentioned reactor. be.

This type of flue gas desulfurization method that uses a moving bed not only can treat flue gas containing dust, but also has the advantage that it does not involve the troublesome wastewater treatment that is seen in wet flue gas desulfurization methods. Showa 50-
As proposed in Publication No. 92858, if ammonia is mixed into the exhaust gas supplied to the reactor,
It has the advantage that the removal rate of sulfur oxides can be further improved and nitrogen oxides can also be removed at the same time.

However, since this method uses a moving bed, it is impossible to avoid pulverization of the carbonaceous adsorbent particles.
There are problems that new carbonaceous adsorbents must compensate for. However, the carbonaceous adsorbent powdered by the dry desulfurization method can be re-granulated into carbonaceous adsorbent granules using the same method as when granulating activated carbon, but the granulation cost is higher than that of new activated carbon. It is almost the same as granulation, and there is not much advantage, so conventionally it was common to incinerate it in a boiler etc.

The present invention aims to effectively utilize powdered carbonaceous adsorbent, and when treating exhaust gas mixed with ammonia by the above-mentioned dry desulfurization method, the powdered carbonaceous adsorbent particles contain nitrogen. However, it is based on the knowledge that when this powdered product is granulated, adsorbent granules with superior performance can be obtained compared to unused carbonaceous adsorbent granules of the same type.

In other words, 145℃ coal-fired boiler exhaust gas (SO ₂ 900-1400ppm, NOx 150-300ppm, dust
100 to 300 mg/Nm ³ ) is mixed with 300 to 600 ppm ammonia and passed through a granular activated carbon moving bed reactor in a cross flow to treat the above exhaust gas, while the granular particles discharged from the bottom of the reactor are If activated carbon is sent to a moving bed regenerator, heated gas at 370-450°C is passed through it to regenerate the granular activated carbon, and the regenerated granular activated carbon is circulated to the reactor, the operating time of the reactor and regenerator , and the nitrogen content of the powdered material collected at the bottom of the regenerator is shown in FIG.
As is clear from Figure 1, the nitrogen content in the powder increases with the passage of operating time, and it increases significantly from the start of operation to about 2,000 hours, but after that it gradually increases to about 8000 hours. % equilibrium value is reached.
Such a tendency is also observed in the nitrogen content of the granular activated carbon circulating in the reactor and regenerator.

In addition, when the carbonaceous adsorbent particles used for dry desulfurization of exhaust gas mixed with ammonia are powdered, the carbonaceous adsorbent obtained by granulating the powdered material is a common carbonaceous adsorbent for exhaust gas treatment. The following experimental example shows that the performance is higher than that of grains.

Example Coal-fired boiler exhaust gas mixed with ammonia is treated in a reactor with a moving bed of granular activated carbon,
The granular activated carbon inactivated by this process is regenerated at a temperature of approximately 400°C in a moving bed type regenerator, and the regenerated granular activated carbon is collected at the bottom of the regenerator in the exhaust gas treatment equipment where it is circulated to the reactor. Powdered product with a nitrogen content of approximately 8% (industrial analysis composition: fixed carbon
76.7%, volatile content 16%, ash content 7.3%) was finely pulverized into 100 meshes, 20% pitch was added thereto, kneaded, and then pressure-molded into granules of approximately 4 mmφ x 5 mm.
This is called molded body A. Further, the above powdered material was mixed with the same amount of coal by weight and pulverized, 20% pitch was added thereto and kneaded, followed by pressure molding into granules of approximately 4 mmφ x 5 mm. This is called molded body B.

Molded bodies A and B were carbonized at 650°C, then activated with steam at a temperature of 850°C, and 1 liter of each was filled as a fixed bed into a reaction tube with an inner diameter of 5 cm.
Nitrogen gas containing 900 ppm SO ₂ , 200 ppm NO, 6% O ₂ , and 8% H ₂ is mixed with 800 ppm ammonia, and this mixed gas is added to each reactor at a temperature of 150°C at a rate of 0.6 Nm ³ per hour. was passed for 50 hours at a flow rate _of For comparison, fresh granular activated carbon (4 mmφ x 5 mm), which is supplied to the above-mentioned exhaust gas treatment equipment when it starts operating, was tested under the same conditions.
SO ₂ removal rate and NO removal rate were measured.

The results are as shown in Figure 2, and the SO ₂ removal rate and NO removal rate are higher when using molded body A than when using fresh, unused granular activated carbon (see the solid line in Figure 2). (See dashed line) and molded body B
(See the two-dot dashed line) is better. In other words, in the method of desulfurizing exhaust gas mixed with ammonia using a moving bed of carbonaceous adsorbent particles, it is advantageous to granulate and reuse the powdered carbonaceous adsorbent particles that inevitably occur.

According to the method for treating exhaust gas containing sulfur oxides according to the present invention, ammonia is mixed into the exhaust gas, and this mixed gas is supplied to a reactor containing carbonaceous adsorbent particles as a moving bed. The sulfur oxides are adsorbed onto carbonaceous adsorbent granules and the treated gas, which has a substantially reduced content of sulfur oxides, is discharged from said reactor, while the carbon which has been inactivated by the adsorption of sulfur oxides is discharged from said reactor. The deactivated adsorbent particles are removed from the reactor, the inactivated adsorbent particles are fed to a moving bed regenerator for regeneration, and the regenerated adsorbent particles taken out from the regenerator are fed to the moving bed reactor. In a method for treating circulating exhaust gas, the regenerated adsorbent particles are sieved to separate the powdered material prior to circulation to the moving bed reactor, and the powdered material is granulated and transferred to the moving bed reactor. It is characterized by supplying.

In the present invention, the exhaust gas supplied to the reactor may contain nitrogen oxides, and in that case, at the same time as sulfur oxides are adsorbed and removed, at least a part of the nitrogen oxides is decomposed into nitrogen. be done. Activated carbon obtained from raw materials such as coal, charcoal, and coconut shells is generally used as the carbonaceous adsorbent.
It is also possible to use the activated carbon adsorbent by supporting a metal oxide such as vanadium pentoxide. In addition, as a means for granulating a powdered product of carbonaceous adsorbent particles, the powdered product is kneaded with a binder such as pitch, then pressure molded into a desired shape and size, and then the molded product is A method of carbonization at a temperature of 900°C can be adopted. When kneading the powdered material and the binder, an activated carbon raw material such as coal may be added as necessary. In any case, the carbonized molded product is preferably activated with steam or carbon dioxide gas at a temperature of 700 to 1000°C prior to use.

To further explain the invention with reference to FIG. 3, exhaust gas containing sulfur oxides or sulfur oxides and nitrogen oxides passes through line 1 and is mixed with ammonia supplied from line 3 to reactor 2. will be introduced in The reactor 2 contains carbonaceous adsorbent particles of activated carbon as a moving bed. The mixed gas of flue gas and ammonia is brought into contact with a moving bed of carbonaceous adsorbent particles in cross flow, whereby the sulfur oxides in the flue gas are adsorbed by the said adsorbent grains, and if nitrogen oxides are present, they are This is decomposed into nitrogen. The desulfurized or denitrated gas is taken out of the system through line 4.

The carbonaceous adsorbent particles adsorbing sulfur oxides are taken out from the bottom of the reactor 2 and sent to a vibrating screen 5, where powdered carbonaceous adsorbent particles and dust are sieved from the adsorbent particles. Generally, the dust in the exhaust gas collects under the sieve, so it is possible to incinerate the dust under the sieve of the vibrating screen 5.
When processing exhaust gas with a relatively low dust content, for example, when processing heavy oil-fired boiler exhaust gas with a dust content of about 10 to 30 mg/ ^Nm3 , the bottom of the vibrating screen 5 is also It is also possible to reuse it by supplying it to a granulating device 14, which will be described later.

The carbonaceous adsorbent particles separated from the powdered material etc. by the vibrating screen 5 are supplied to the upper part of the moving bed type regenerator 8 via a line 6 and a conveyor 7. In the regenerator 8, the inactivated carbonaceous adsorbent particles are heated to 350 to 600°C in an inert gas or reducing gas atmosphere to be regenerated. At this time, a gas containing a high concentration of SO ₂ is generated, which is taken out through line 9 and supplied to a sulfur or sulfuric acid production device (not shown). The regenerated adsorbent particles are sent from the bottom of the regenerator 8 to the vibrating screen 10, where the powdered adsorbent particles are separated under the sieve, and then passed through the line 11 and conveyor 12 to the moving bed reactor 2. Circulated to the top.

The under sieve of the vibrating screen 10 is substantially free of dust, and all of the dust is powdered carbonaceous adsorbent particles generated in the regenerator 8, but this powdered material is supplied from the line 13 to the granulation device 14. After being molded into the desired size and shape here, it is preferably activated and fed to the moving bed reactor 2 via line 15.

As described above, the exhaust gas treatment method of the present invention not only enables the effective reuse of the powdered carbonaceous adsorbent that was conventionally incinerated, but also can be expected to reliably improve the efficiency of desulfurization or denitrification through its reuse. It has the effect that it can do.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the nitrogen content of the powdered material collected at the bottom of the regenerator of the exhaust gas treatment equipment and the equipment operating time, and Figure 2 is a graph showing the relationship between the nitrogen content of the powdered material collected at the bottom of the regenerator of the exhaust gas treatment equipment and the equipment operating time. It is a graph showing the relationship between NO removal rate, SO ₂ removal rate, and gas passage time. Third
The figure is a flow sheet showing one embodiment of the method of the present invention. 2: moving bed reactor, 5, 10: vibrating screen, 7, 12: conveyor, 8: moving bed regenerator,
14: Granulation device.

Claims (1)

[Claims] 1. Ammonia is mixed into exhaust gas containing sulfur oxides or sulfur oxides and nitrogen oxides, and this mixed gas is supplied to a reactor containing carbonaceous adsorbent particles as a moving bed, The sulfur oxides in the flue gas are adsorbed onto the carbonaceous adsorbent granules, and the treated gas whose sulfur oxide content is substantially reduced is discharged from the reactor, while the sulfur oxides are absorbed by the adsorption of the sulfur oxides. The activated carbonaceous adsorbent particles are taken out from the above-mentioned reactor, the inactivated adsorbent particles are supplied to the moving bed type regenerator for regeneration, and the regenerated adsorbent particles taken out from this regenerator are transferred to the above-mentioned moving bed type regenerator. In a method for treating exhaust gas circulating to a reactor, the powdered material generated as the carbonaceous adsorbent moves is collected, regenerated into granular carbonaceous adsorbent, and supplied to the above-mentioned moving bed reactor. A method for treating exhaust gas containing sulfur oxides. 2. In the method described in claim 1,
A method for treating exhaust gas containing sulfur oxides, which comprises collecting the generated powder, mixing it with coal, etc., which is a raw material for the carbonaceous adsorbent, and regenerating the carbonaceous adsorbent after granulation.