JPS59196719A - Treatment of exhaust gas - Google Patents

Abstract

PURPOSE:To prevent an NH3 leak while high denitration ratio is kept, in a desulfurizing and denitrating method for passing exhaust gas through two reactors each filled with a carbonaceous catalyst while mixing NH3 in said gas, by adding SO3 or H2SO4 to the outlet gas of the second reactor before dust collection. CONSTITUTION:NH3 is added to NOx and SOx-containing exhaust gas from a line 2 while the NH3 added gas is introduced into a moving bed reactor 3 receiving a carbonaceous catalyst 4 to perform desulfurization and denitration. NH3 is again injected into the gas exhausted from the reactor 3 from a line 6 while the NH3 added gas is passed through a moving bed reactor 7 receiving a carbonaceous catalyst 8 to perform denitration and desulfurization and, thereafter, SO3 or H2SO4-containing gas is introduced into a line 9 to convert leaked NH3 in the gas to (NH4)2SO4 or NH4HSO4 which is, in turn, collected along with fly ash by a dust collector 10. The catalysts discharged from the reactors 3, 7 are regenerated under heating in a regenerator 12 to be recirculated. The high concn. SO2 gas recovered from the regenerator 12 is used as a stock material of SO3 or H2SO4 to be added to the outlet gas of the reactor 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating exhaust gas containing sulfur oxides and nitrogen dispersions, and more particularly to a method for solving the problem of leakage of ammonia mixed in during exhaust gas treatment.

Sulfur oxides (SOxJ and nitrogen oxides (NOxJ) are
A known method for treating exhaust gas containing a high concentration of is to mix ammonia into the exhaust gas and then pass the exhaust gas through a packed bed of carbonaceous catalyst. With this method, SOx and NOx f can be removed simultaneously, and
Advantages such as the ability to reuse the catalyst are significant.

However, in order to efficiently remove NOx f with this method, the temperature must be at least 200°C or higher, preferably 220°C or higher.
A reaction temperature of about 250° C. is required, and NOx f cannot be removed sufficiently at lower temperatures. However, at a reaction temperature of 200[deg.] C., there is a problem in that part of the carbonaceous catalyst is consumed as c-1-ot-+co due to acid accumulation in the exhaust gas. Further, since the temperature of exhaust gas from a boiler or the like is approximately 150° C. at the outlet of an air heater or the like, it is also disadvantageous in that the exhaust gas must be preheated to a temperature of 200° C. or higher.

In contrast, a method has been proposed that can remove not only SOx but also NOx at a high removal rate even at temperatures of about 150°C. In this method, ammonia is mixed into the exhaust gas, this mixed gas is introduced into the first reactor to remove most of the SOX, and then ammonia is mixed into the treated gas again, and this mixed gas is introduced into the second reactor. It is introduced into a reactor and reprocessed.

However, in this method, although a high denitrification rate can be obtained in the second reactor, there is a risk of secondary pollution due to large amounts of ammonia leaking into the treated gas. What if we reduce the amount of ammonia mixed into the outlet gas of the vessel? IJH, IJ-reduction will be reduced, but the denitrification rate will be reduced (result) □ It is an object of the present invention to provide an exhaust gas treatment method that maintains a high denitrification rate and solves the problem of ammonia leakage by VPf. [6] In the above method, the present inventors added SO, or )]2So4 to the second reactor outlet gas. When IJ is appointed, he gives birth to seven children and uses the invention as a trap.

An example of a process for treating exhaust gas containing NOx and SOx will be shown and the present invention will be explained in detail in the fc first diagram. 10
The exhaust gas, whose temperature is controlled to about 0-170°C, is introduced into the direct firing type moving bed reactor 3 via line 1. Ammonia is added to the exhaust gas via this gap line 2. The exhaust gas descends in the reactor 3 and comes in contact with the carbonaceous catalyst bed 4.
After being subjected to desulfurization and denitrification treatment, it is discharged from the reactor 3.

This discharged waste gas is sent to the second cross-flow moving bed reactor 7 via line 5. At this time, ammonia is injected again via line 6. The exhaust gas comes into contact with the carbonaceous catalyst bed 8 descending in the reactor 7 and is subjected to denitrification and desulfurization treatment, and then is introduced into the dust collector IO via the line 9.

At this time, SO3 or H, f90. The glue NH in the gas is mainly collected together with fly ash as (NH4J, SO4 or NH,H3O4). It is released into the atmosphere.The fly ash containing ammonium salts collected by the dust multiplier 10 is incinerated by Zeiler, etc.The dust collector may be an electrostatic precipitator, a bag filter, or a multi-cyclone, etc. You can use either one.

- ten thousand, reactors 3 and 7] The catalyst discharged from the regenerator 12
V was guided here 't''^ under a warm inert gas atmosphere for 300 minutes.
After being heated and regenerated to ~600℃.

It is returned to the top of each of reactors 3 and 7 for reuse.

Alternatively, as a catalyst flow, the catalyst discharged from the second reactor 7 is supplied to the first reactor 3, and then supplied to the catalyst tray regenerator 12 from which it is discharged, and then regenerated and then transferred to the second reactor. It may be supplied to 7 and used for circulation ^ S OB or H, S added to the outlet gas of reactor 7
The raw material for O4 is usually municipal S02 gas recovered in the regenerator 12. This high school gas 5()2 gas is sulfuric acid, sulfur,
Sulfur is recovered as a by-product of gypsum, etc. Figure 1 shows that sulfur is recovered and the tail gas of this recovery process is leaked.
Highly saponified f131o2 gas generated in the regenerator 12 is supplied together with air to a moving bed type reduction reactor 14 filled with coal or coke, etc. A reduction reaction of S02 is carried out at a temperature of 950° C. S, H2S, COS from the reduction reactor 14
, Soy, etc. passes through a dust collector 15 and is cooled in a sulfur condenser 16 to recover sulfur. Furthermore, the gas exiting the condenser 6 is heated in a temperature controller (not shown), and then passes through a Claus reactor 17 and a sulfur condenser 18, where sulfur is recovered.The Claus reaction is usually carried out in two or more Claus reactors. Implemented by

The gas exiting the condenser 18 passes through a demister 19, is incinerated, and is returned to the inlet of the reactor 30. At this time, a part of the gas before or after the incineration process is passed through the catalytic reactor 20 to oxidize SO8 to SO3, and then injected into the inlet of the dust collector via the line 21 to collect and remove all leaked NH. do. The catalyst used in the catalytic reactor 20 is not particularly limited, and the purpose can be sufficiently achieved by using a commonly used vanadium oxide catalyst.

In addition, SO5 or H2SO4 injected from line 21
As a source, high concentration SO in the line 13 may be used by oxidizing a part of the gas, or when recovering sulfuric acid as a by-product, tail gas containing SOs may be used. Alternatively, the catalyst powder may be added through the nozzle line 21 which adsorbs sulfuric acid, which is discharged from the lower part of the reactor 3.

What is the amount of S03 or H, So added to the exhaust gas?

It is preferably about 0.2 to 1 mole per mole of NH in the gas, and more preferably 0.5 to 1 mole, which is the condition for producing ammonium sulfate.
It is on the order of moles.

In addition, in the first and second reactors in the invention, a carbonaceous catalyst such as activated coke grains obtained by heat treating coal or activating coal with steam etc. is generally used.
Metal oxides such as vanadium, iron, copper, etc. can also be supported on this catalyst. The case where the exhaust gas with a low sulfur oxide concentration (approx.
ppm or less], for example, when processing LNG combustion exhaust gas, garbage incinerator exhaust gas, or exhaust gas that has been pretreated with a wet desulfurization device.

The first reactor is omitted, and an example of its configuration is as shown in FIG. Since the SOx concentration of the exhaust gas to be treated is low, 1
Normally, the process for producing the S02 gas by-product is omitted.

The present inventors confirmed the effect of NH injection on the desulfurization rate and the denitrification rate through all experiments. 3rd white is So, 110
50pp, NOx 230ppm, H, 07, 8%
A predetermined amount of ammonia is injected into the exhaust gas containing 0.3.8, and the mixed gas is heated at 1145°C to the first cross-flow moving bed reactor filled with a carbonaceous catalyst at a space velocity of 600.
Nu, injection amount and N when passed at a speed of hr-1
It is a graph showing the relationship between Ox + 802 removal rate and NHs leakage amount. Note that the residence time of the catalyst in the reactor in this case was 33 hr.

From the results shown in Figure 3, the amount of NH3 leakage is several ppm.
There is no problem below, but it can be seen that the denitrification rate is low at about 20 to 4 degrees.

Figure 4 shows SO250ppm, NOx 160ppm
m.

A predetermined amount of ammonia was injected into the exhaust gas containing H, 07.8%, and 0.3.8%, and the mixed gas was transferred to a second moving bed reactor filled with carbonaceous reactor at 145°C. The results are obtained when the catalyst is passed through the reactor at a speed of 800 hr-''.The residence time of the catalyst in this reactor is 25
Chill in hr. Fruit set shown in Figure 4.

Although it is possible to obtain a high denitration rate due to the low SO concentration in the second reactor, the total denitrification rate (the amount of NH,jJ- increases as much as It can be seen that the same level of denitrification rate is difficult.
1 In the present invention, since SO or H2So4f is added to the second reactor outlet gas, it quickly reacts with NH3 in the gas to form an ammonium salt.
Collect it with a dust collector together with the light. For this reason,
The N1 (3) in the gas after the multiplication treatment is reduced.This can solve the problem of NH3 leakage.
The amount of NH8 injected at the inlet of the reactor can be increased, and the denitrification rate can be improved. Furthermore, since the tail gas can be fully utilized for sulfur recovery or sulfuric acid recovery, the load on tail gas treatment can be reduced by 1-1.

However, the effect of treating exhaust gas with a low SOx concentration using the bulb shown in FIG. 2 is clear from the above explanation. [Example 1] After 500 pprn of ammonia gas was mixed into exhaust gas containing 1050 ppm SOx and 230 ppm NOx, this mixed gas was heated to 145°C in a cross-flow system filled with granular carbonaceous catalyst. was passed through the moving bed reactor at a space velocity of 600 hr-''. In this case 1
The residence time 1fa of the catalyst in the reactor is set to 33 hours. The desulfurization rate in this reactor was 95.2 qb, and the denitrification rate was 30%.

Also, NH and leak h[are good friends at 0.5 ppm.

Next, 170 ppm of ammonia gas was again mixed into the outlet gas of the reactor, and a carbonaceous catalyst different from the above was filled into the vertical flow moving bed reactor at a space velocity of 800 hr.
Let your friend pass at the speed of.

In this case, the residence time of the catalyst in one reactor was set at 25 hours. In this reactor, the desulfurization rate with respect to the gas introduced into the second reactor was 1001, and the denitration rate was 86. Therefore, the total desulfurization rate in the first and second reactors is 100%.
The denitrification rate was 90%. The leakage amount was 19 ppm, and the amount of sulfur was 70 μ/Nd.Furthermore, a total of 9 ppm of So was added to the exit sludge of the second reactor, and the results were introduced into the electrostatic precipitator. .

The amount of NH from the dust collector is 'Ppmh, and the amount of dust is 1.
It was 019/Nnl. Also, SO8 was hardly detected ◎ Example 2 SO ppm of 80 x and 170 [NOx of 1 m]
After mixing iso ppm of ammonia gas into the exhaust gas containing je, this mixed gas (at a temperature of 7145'C) was transferred to a cross-flow moving bed reactor packed with granular carbonaceous catalyst at a space velocity of 80 U hr. ” I was able to pass at a speed of .

In this case, the residence time of the catalyst in one reactor is set to 25 hours. The desulfurization rate in this reactor was 100%, and the denitrification rate was 85 cycles. Ma1ko NH.

The leakage amount was 20 ppm, and the dust content was 50Q/Nr%.

Next, 1θppm of SO8 was added to the outlet scum of the reactor, and then introduced into the baggage filter.
It was TR9/Ni. Also, SO3 was hardly detected.

[Brief explanation of the drawing]

FIG. 1 shows an example of a treatment process for a gas containing NOx and SOx. Figure 2 shows low @ degree S
Figures 3 and 4, which show an example of the treatment of exhaust gas containing OX, show the relationship between the NH8 injection amount and the N
It is a graph showing the relationship between the removal rate of Ox, 80214, and NHs leak rate. 3.7...Cross-flow type moving bed reactor] 0... Dust collector 12... Container 20
Catalyst reactor whistle 3 figure agent 4 flash

Claims (1)

[Claims] 1. Ammonia is mixed into the exhaust gas containing nitrogen oxides and sulfur oxides, and this mixed gas is filled with a carbonaceous catalyst and introduced into the FC first reactor to undergo desulfurization and denitrification treatment. This treated gas is then completely mixed with ammonia, and this mixed gas is introduced into a second reactor filled with a fully carbonaceous catalyst for denitration and denitrification.
After completing the desulfurization process, add SO3 or H to the second reactor outlet gas.
An exhaust gas treatment method that performs dust collection treatment after adding 2SO,'i. 2. Mix ammonia into nitrogen oxide-containing exhaust gas with a low sulfur oxide content, introduce this mixed gas into a reactor filled with a carbonaceous catalyst to perform denitrification and desulfurization treatment, and add SO8 or H to this treated gas. , SO4 is added, followed by dust collection treatment.