JPS61287423A - Treatment of exhaust gas - Google Patents

Abstract

PURPOSE:To prevent a combustion accident by adding NH3 to an exhaust gas contg. NOx, SOx and thereafter dividing the exhaust gas, introducing one part thereof into the first transfer layer and the other part into the second transfer layer to desulfurize and denitrate the exhaust gas and circulating activated carbon to the first transfer layer, the second transfer layer and a regenerator in order. CONSTITUTION:After introducing NH3 through a line 1 into an exhaust gas contg. NOx and SOx at 100-180 deg.C, the exhaust gas is divided into two gas glows and one part thereof is introduced into the first transfer layer reactor 3 packed with a carbonaceous catalyst 4 and the other part is introduced into the second transfer layer reactor 10 and the exhaust gas is subjected to the desulfurization and denitration treatments and discharged through the lines 5, 6 and joined and thereafter dust-removed with a dust collector 7 and discharged to the atmosphere. The carbonaceous catalyst discharged from the first reactor 3 is fed to the upper part of the second reactor 10 and discharged from the lower part, heated and regenerated in a regenerator 14 and returned to the first reactor 3. In such a way, the retention time of the catalyst is decreased to prevent the generation of a hot spot and the combustion accident is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for treating sulfur oxides (SOX) and nitrogen oxides (NO
Regarding the desulfurization and denitrification method for exhaust gas containing
The present invention relates to a method for desulfurizing and denitrating exhaust gas having a relatively low SOX concentration at a low temperature range of approximately 100 to 180°C.

As a treatment method for exhaust gas containing SOX and NOX, such as exhaust gas from coal-fired or heavy oil-fired Zeilers or exhaust gas from sintering furnaces at steel plants, ammonia gas is injected into these exhaust gases, and this gas is injected into a packed bed of carbonaceous catalyst. A method of processing by passing gas is known (Japanese Patent Application Laid-Open No. 50-92858).
. This method has the advantage that in addition to being able to simultaneously remove BOX and NOX from exhaust gas, the catalyst can be reused. However, in order to efficiently remove NOX with this method, it is necessary to maintain the reaction temperature at least 200°C or higher, preferably around 220 to 250°C; at temperatures lower than this, NOX cannot be removed sufficiently. I can't. However, when the reaction temperature exceeds 200"C, there is a problem that a part of the carbonaceous catalyst is consumed by the oxygen coexisting in the exhaust gas, as in the case of C+02 → CO1. Furthermore, there is a problem that the exhaust gas from Zei 2- etc. Since the temperature at the outlet of the air heater is generally around 150°C, there is the disadvantage that when treating this exhaust gas, it must be preheated to a temperature of 200°C or higher.

On the other hand, even at a temperature of about 150℃, SOX, of course,
Patent No. 12418 describes a method that can efficiently remove NOX
It is proposed in No. 99. This method uses two orthogonal moving bed reactors, and the exhaust gas injected with ammonia gas is first passed through the first moving bed reactor to remove most of the 5ox12
After removal, ammonia gas is mixed with the obtained treated gas again, and this mixed gas is introduced into the second moving bed reactor for reprocessing.

This two-stage treatment method is superior in that it can desulfurize and denitrate exhaust gas at low temperatures, but the SOX concentration is relatively low (approximately 3001).
When treating exhaust gas (below I) m), it tends to be too big a deal, and the use of more carbonaceous catalysts than necessary is not necessarily satisfactory.

Because the SOX concentration in the exhaust gas is low, if ammonia gas is mixed with the exhaust gas and introduced into the moving bed reaction of the carbonaceous catalyst, one reactor can be used instead of the two-stage treatment as in the above patent. This is because the exhaust gas can theoretically be sufficiently desulfurized and denitrated. However, when treating exhaust gas with a low SOX level of 6 degrees in a single stage, it is necessary to allow the residence time of the carbonaceous catalyst in the reactor to be somewhat longer than in the case of two-stage treatment. Even if the reaction temperature is as low as around 150° C., hot spots may occur in the catalyst layer due to the accumulation of heat of oxidation reaction in the carbonaceous catalyst, which may lead to catalyst combustion accidents.

Therefore, the present invention proposes an exhaust gas treatment that can desulfurize and denitrate even exhaust gas with a relatively low SOX concentration in a single stage process, and does not necessarily involve the occurrence of combustion accidents as described above.

That is, the present invention uses about 100
In the method of desulfurizing and denitrating the exhaust gas by bringing it into contact with a carbonaceous catalyst in the coexistence of ammonia gas at ~180″C, after injecting ammonia gas into the exhaust gas, the exhaust gas is divided into gas streams, A first exhaust gas stream is introduced into a first moving bed reactor packed with a carbonaceous catalyst for desulfurization and denitrification;
The exhaust gas stream is introduced into a second moving bed reactor filled with a carbonaceous catalyst for desulfurization and denitrification, and the carbonaceous catalyst discharged from the first moving bed reactor outlet is transferred to the second moving bed reactor inlet. The carbonaceous catalyst discharged from the outlet of the second moving bed reactor is heated and regenerated and then supplied to the inlet of the first moving bed reactor.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. First, in the embodiment shown in FIG.
The exhaust gas is mixed with ammonia injected from line 1 and then split into two gas streams, one exhaust gas stream is sent through line 2 to the first cross-flow moving bed reaction packed with carbonaceous catalyst. It is introduced into vessel 3. The exhaust gas is discharged from the reactor 3 into a line 5 after coming into contact with the carbonaceous catalyst layer 4 descending in the reactor 3 and undergoing desulfurization and denitration treatment. The other exhaust gas stream divided into two is introduced into the second cross-flow moving bed reactor 10 via line 9, contacts the carbonaceous catalyst layer 11 descending in the reactor, and undergoes desulfurization and denitrification treatment, It is discharged to line 6. The gases discharged from each reactor into lines 5 and 6 are combined and sent to a dust collector 7, where they are removed from dust and then discharged into the atmosphere from a line 8.

Regarding the carbonaceous catalyst, the catalyst discharged from the lower outlet of the first reactor 3 is supplied to the upper inlet of the second reactor 10 via line 12, and is discharged from the lower outlet of the reactor 10. The catalyst is passed through line 13 to regenerator 14.
guided by. In this regenerator, the catalyst is about 300 to 600
The regenerated catalyst is returned to the upper inlet of the first reactor 3 from the line 15 and reused.The high-concentration SO generated in the regenerator 14,
The gas is taken out to the line 16, purified directly or by means such as washing with water, and then supplied to a by-product recovery process to obtain sulfuric acid, ammonium sulfate, sulfur, and the like.

In the embodiment of FIG. 1, ammonia is injected and then the exhaust gas is divided into two gas streams, but after the exhaust gas is divided, ammonia may be injected into each gas stream. t
In addition, line 12゜13.15 should be filled with dust,
Additional means for separating catalyst powder etc., such as a vibrating screen, may be provided.

In the embodiment shown in FIG. 2, after dividing the exhaust gas into two gas streams, ammonia is injected only into the exhaust gas supplied to the first reactor 3, and into the exhaust gas supplied to the second reactor 10. There is no difference from the embodiment in Fig. 1 except that ammonia is not injected, but in the embodiment in Fig. 2, the amount of ammonia in the high concentration S02 gas recovered during heating regeneration of the catalyst can be reduced. .

As the carbonaceous catalyst of the present invention, activated coke and activated carbon obtained by heat treating coal or activating it with steam are generally used. Of course, those supported can also be used.

By the way, SOX in exhaust gas is adsorbed and removed as sulfuric acid through contact with a carbonaceous catalyst as follows.

so, +h to +I(,0 → H, 80, (1) 80, -4
- H, O-+ ) (, 80, (2) In this case, if ammonia is made to coexist in the exhaust gas in advance, the adsorbed sulfuric acid is converted to ammonium salt.

H,80,+NHs→NH,H8O,+31NH,[
804-4-NH, → (NI(4)tSO, (4) In other words, when the carbonaceous catalyst comes into contact with the exhaust gas, the adsorption amount of sulfuric acid and its ammonium salt increases, so it is gradually inactivated, but the speed is The higher the SOx concentration in the exhaust gas, the faster the rate of de-sulfurization. Therefore, when the SOx concentration is high, it is necessary to shorten the residence time of the catalyst in the moving bed reactor so that the desired desulfurization rate can be maintained. On the other hand, SOX in exhaust gas
When the concentration is low, the residence time of the catalyst can be increased to a certain extent; however, if the residence time is increased, hot spots will occur in the catalyst layer due to the accumulation of heat from the oxidation reaction of the catalyst even at temperatures of about 150°C. , there is a risk of catalyst combustion accident.

However, in the present invention, the exhaust gas is divided into two parts and each is introduced into a separate reactor, so the residence time of the catalyst in each reactor can be shortened, and the problem of hot spots can therefore be avoided. can. In addition, in the present invention, the catalyst used in the first reactor can be used in the second reactor without being regenerated, so there is an advantage that the catalyst can be used effectively.

In addition, when denitrating by injecting NH3 into the exhaust gas containing SOX and NOX, the denitrification reaction occurs at a reaction temperature of around 150"C (denoted by 51). In this case, most of the injected NH undergoes a neutralization reaction with SO adsorbed on the carbonaceous catalyst (actually, it is adsorbed as sulfuric acid) [above (31)].
(4)]. In particular, since reaction (3) is fast, N11 is required for denitrification reaction (5). The injection volume is determined by the reaction (
It must be added in addition to the t' consumed by 3). That is, there is a relationship between the denitrification rate and the injection amount as shown below.

(NH, injection amount, ppm) # (SOX concentration, ppmx desulfurization rate) - l - (NOX concentration, ppmx removal rate) + (NH
3, ppm) In other words, the ratio of NH adsorbed on the carbonaceous catalyst used for desulfurization and denitrification and discharged from the reactor to 802 (NH4
+/5O4t''') is close to about 1, and when the catalyst is heated and regenerated in such a state, the rate of decomposition of ammonium salt to nitrogen is low, and a large amount of NH8 is mixed into the recovered SO1, resulting in H!80
4. When recovering S and other by-products, problems such as blockage and reduction in product purity occur, and when purification is performed by combining or washing with water, NH and H8 are released into the wastewater.
Since a large amount of 03 etc. is dissolved, a loss occurs.

By the way, Figure 3 shows various types of NH in SO1-containing gas.

After passing the injected gas through the activated carbon layer, it is heated to 400℃.
This is a measurement of the decomposition rate of adsorbed NH, to N2 when heated and regenerated.As can be understood from this, NH
, When the injection amount is large and the amount of adsorbed NH on activated carbon increases,
The decomposition rate to N2 decreases. And the amount of N4 adsorption is large,
A decrease in the NH3 decomposition rate means that the NH3 concentration in the recovered SO and gas becomes significantly higher.

According to the method of the present invention shown in FIG. Almost the same amount of SO,
(actually H280,), so NH,/80
．． is approximately O15. It can be understood that the NH3 concentration in the desorbed gas is therefore significantly reduced.

In the present invention, the ratio when dividing the exhaust gas into two is approximately 1/2 because it is actually convenient to manufacture the same reactor.
Although it is suitable to divide it into two parts, in the embodiment shown in FIG. 2, it is generally NH.

The amount supplied to the first reactor where injection is performed can be about 1/4 to 2/3 of the total amount of exhaust gas.

Example 150 m) 11m sulfur oxide, 25011) l)
Exhaust gas at 120"C containing 1000 ONm3/h of nitrogen oxides, 10% moisture and 10% oxygen
0 Nm”/h, and one exhaust gas has NH,i
After injecting 350 ppm, it was passed through a first cross-flow moving bed reactor packed with 8.3 m" of granular activated carbon. In this case, the residence time of activated carbon in the reactor was set to 40 hours. This reaction The desulfurization rate of the vessel is 99.9cm, and the denitrification rate is 8.
0chi and leakage NU were 16 ppm.

On the other hand, the remaining exhaust gas of 500ONm'/h is directly 6.3
Passed through a second cross-flow moving bed reactor packed with m3 of activated carbon. The residence time of activated carbon in the reactor in this case is set to 40 hours.

The desulfurization rate of this reactor was 95%, and the denitrification rate was 6%.

When the gas discharged from the first and second reactors was combined, a denitrification rate of 43% and a desulfurization rate of 97.5% were obtained with respect to the original exhaust gas. Also, NH was 8 ppm.

On the other hand, the used activated carbon discharged from the second reactor via the first reactor was supplied to a regenerator and regenerated by heating at 400'C in an inert carrier gas atmosphere. By adjusting the amount of carrier gas to the regenerator, 15% high concentration SO□ gas was recovered. As a result of measuring the NH concentration in this SO gas, the NH concentration was 0.95%.

Comparative Example As a comparative example, 10000 N without dividing the exhaust gas
After injecting 175 Ppm of NH into the exhaust gas at m”/h,
16.6 m5f of granular activated carbon: introduced into a packed cross-flow moving bed reactor. In this case, the residence time of activated carbon is set at 80 hours. The desulfurization rate of the exhaust gas discharged from the reactor 1q- is 97%, and the denitrification rate is 20%.
%Met. Also, the leakage NH8 was sp ppm.

In this case, the high concentration SO and gas (15
%), the concentration of NH was 4.5%.

As another comparative example, in order to obtain the same denitration rate as in the example, the NH injection amount was changed to 250 pIl1m, and as a result, a desulfurization rate of 98.15% and a denitration rate of 43% were obtained.

Also, the leakage NH was 8 ppm. In this case, the NH3 concentration in the high-concentration SO gas (15%) obtained in the regenerator was extremely high at 5.2%.

[Brief explanation of the drawing]

FIGS. 1 and 2 are flow diagrams showing one embodiment of the present invention, and FIG. 3 shows NH adsorbed on activated raw carbon,
/80. It is a graph showing the relationship between the molar ratio and the decomposition rate of adsorbed NH3.

Claims (1)

[Claims] 1. About 100-18 containing sulfur oxides and nitrogen oxides
In the method of desulfurizing and denitrating the exhaust gas by bringing it into contact with a carbonaceous catalyst in the presence of ammonia gas,
After injecting ammonia gas into the exhaust gas, the exhaust gas is divided into gas streams, the first exhaust gas stream is introduced into a first moving bed reactor filled with a carbonaceous catalyst for desulfurization and denitrification, and the second exhaust gas stream is is introduced into a second moving bed reactor filled with a carbonaceous catalyst for desulfurization and denitrification, and the carbonaceous catalyst discharged from the outlet of the first moving bed reactor is supplied to the inlet of the second moving bed reactor. , second
A method for treating exhaust gas, comprising heating and regenerating a carbonaceous catalyst discharged from an outlet of a first moving bed reactor, and then supplying the carbonaceous catalyst to an inlet of a first moving bed reactor. 2. In the method described in claim 1, before the injection of ammonia gas, the exhaust gas is divided into two gas streams, and the ammonia gas is injected into one or both of the gas streams, and the ammonia gas is transferred to the first and second gas streams, respectively. A method for treating exhaust gas, characterized by introducing the exhaust gas into a bed reactor.