JPS58153523A - Dry type stack gas desulfurization and denitration method - Google Patents

Abstract

PURPOSE:To reduce an amt. of NH3 to be used, and to execute desulfurization and denitration treatment at low cost, by removing SOx in a stack gas contg. SOx and NOx in advance by adsorption, and reducing NOx to N2 by addition of a specified amt. of NH3. CONSTITUTION:A combustion waste gas 4 exhausted from a boiler 100 is supplied through a dust collector 101 to an adsorber 102 to remove most of SOx using activated carbon 21 as an adsorbing agent, obtd. by treating coal in a low temp. dry distillation apparatus 110 at low temp., oxidizing, dry distilling, and activating it with water vapor. The waste gas 6 cleared of most of SOx is partly sent to a detector 105 to detect a residual SOx concn. A' and a NOx concn. B, and gaseous NH3 9 amounting to (2A'+B) molar equiv. is mixed with the gas 6 and the mixture is fed to an adsorber similar to the adsorber 102. The residual SOx is converted into acidic ammonium sulfate or ammonium sulfate, NOx is reduced to N2, thus removing the pollutants. Since the activated carbon adsorbing agent in the adsorber 103 has contained ammonium sulfate, etc., it is fed to a heat desorption regenerator 104 to heat desorb the ammonium sulfate, etc., and regenerate it as an adsorbing agent.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dry flue gas desulfurization/denitrification method for removing O-sulfur oxides and nitrogen oxides from flue gas.

As a method for effectively removing sulfur oxides from combustion flue gas, the present inventors manufactured inexpensive activated carbon from fuel coal and described a dry flue gas desulfurization method using activated carbon in JP-A-54-34.
No. 617 and Japanese Patent Application Laid-open No. 54-59161.

If a denitrification device is installed, it will be carried out at the pre-stage of this desulfurization method or on the desulfurization equipment 0iIR floor! It is known that in these dry-type smoke desulfurization and denitrification methods KTh, neutralized ammonia gas is mixed into the exhaust gas, and a portion of the nitrogen oxides are catalytically reduced to nitrogen gas using activated carbon in the desulfurization process as a catalyst. . Generally, the reduction reaction of nitrogen oxides to nitrogen gas is (1
), NHs and NO in the exhaust gas react, producing N and HsOt.

NO1NHs+ ”Os →Ns +3-Hm O・
” (1) 2 On the other hand, the sulfur leather in the exhaust gas (80m long) undergoes adsorption, oxidation reaction, and hydration reaction simultaneously due to activated carbon, and Hs 80a・nl (tO) is adsorbed in the pores. do.

80s+HsO+”Os→Hs80j ”-”・(2
)81804 +IIH1O→Hs 804 ・nHs
O...(3) When exhaust gas neutralization 50m coexists, Kl
i. When NHs is added, sulfuric acid and NHs react and form acidic ammonium sulfate and ammonium sulfate.

■MuSO4+NHI→(NH4)H804""(4)H
sSOa+2NHs→(NH4)m 80m”・
(5) Therefore, when ammonia gas is mixed into the exhaust gas and catalytic reduction is performed by the catalytic action of activated carbon, and desulfurization is performed by the activated carbon, the amount of NHs added is 1% of the nitrogen oxides originally contained in the exhaust gas. The total chemical equivalent of the molar equivalent and 2 molar equivalents of the sulfur oxide is required. Furthermore, when the amount of KNHs added increases, H1804.nruO becomes ammonium sulfate because it is adsorbed in the activated carbon pores by the reaction shown in equation (5). Since this ammonium sulfate is in a solid state, when used activated carbon is regenerated through a thermal desorption process, the activated carbon is subject to considerable wear and tear (therefore, in a system that reuses recycled activated carbon, the desulfurization and denitrification rates are reduced). 11 The object of the present invention is to reduce the amount of ammonia gas added, thereby reducing the cost of desulfurization and denitrification, and at the same time improving the desulfurization and denitrification rates. Our objective is to provide a dry flue gas desulfurization and denitrification method.

In the present invention, exhaust gas is once brought into contact with a Sakaki elemental adsorbent, most of the sulfur oxides in the exhaust gas are removed by t-adsorption, and then the amount of sulfur oxides and nitrogen oxides in the exhaust gas is detected, and the amount of sulfur oxides OA' is detected. The above object was achieved by contacting the carbonaceous adsorbent with a molar equivalent of nitrogen and then contacting the carbonaceous adsorbent.

In other words, the amount of sulfur oxide in the exhaust gas is t-A molar equivalent, and the desulfurization rate t9 in a double-stage adsorption machine 4MK that desulfurizes by contacting with a carbonaceous adsorbent without adding ammonia gas.
In the case of 0%, the sulfur oxide in the exhaust gas at the outlet of the adsorption process of the main stage is reduced to A1 molar equivalent (=1-α9m), so the reaction that produces acidic ammonium sulfate and ammonium sulfate is K714 Vh and the ammonia amount IA It is possible to reduce the amount of carbonaceous adsorbent in the thermal desorption process and INK.

Hereinafter, an embodiment of the dry flue gas desulfurization/denitrification method of the present invention will be described with reference to the flow sheet shown in FIG.

Fuel coal 1 is supplied to the boiler 100. Boirato 00
The flue gas 4Fi generated in the dehydrator 101 is first guided to the adsorption tower 102. Adsorption tower 10
2 is usually a moving bed type 1kIIR, in which most of the sulfur oxides in the combustion exhaust gas are removed. The combustion exhaust gas 6 from which most of the sulfur oxides have been adsorbed and removed is first detected by the detector 105 from the detection end 7 to the concentration of sulfur oxides and the amount of nitrogen oxides in the exhaust gas. The determined one ammonia is supplied from the stream 8 through the ammonia supply control valve 106, and is supplied from the stream 9 to the exhaust gas 6, where they are combined to form a stream 10. The exhaust gas 10Fi containing ammonia gas is then transferred to the adsorption tower 103, and the sulfur oxides in the exhaust gas are converted into acidic ammonium sulfate and ammonium sulfate according to the reaction acid, and the nitrogen oxides in the exhaust gas are reduced to nitrogen gas. Performs desulfurization and denitrification.

Next, the compressed exhaust gas 11 that has been desulfurized and denitrified is sent to the desulfurizer 107.
It is then released from stream 12 to the atmosphere. Adsorption tower 10
2.103 is usually carried out using a moving bed type, so Hs 80
The activated carbon adsorbing 4.nHa and O is removed from the stream 13, and further in the adsorption tower 103, the activated carbon has (NH4) adsorbed.
Since sulfur oxides are adsorbed as H804 or (NH4) snow 804, these adsorbents are removed from stream 14. Streams 13 and 14 are then led to thermal desorption regeneration tower 104 to regenerate activated carbon.

HaSOa, (NH4) H804-(NH4)
18041-The adsorbed activated carbon is thermally desorbed at a temperature of 350 to 5 ooc, and SO-rich, co,
co.

A gas containing Hlo, Nl, and some NHst is generated.

(NH4) Fable 804 → (NH4) H80a +NHs
(NH4)H804→NHs +80s +Hi 0N
Hs + SOs →SOs +HI O+ '
3 Nm The desorption gas containing these gases is led from stream 15 to a concentrated f80g gas treatment unit 108 for treatment.

Normally, the desorption gas in stream 15 is reacted with carbon, and a portion is recovered as sulfur, and further by Claus reaction etc. using 2H18/80z production control) bS, SO
Reduce z' to elemental sulfur. The tail gas of 10 g of the 80 m high-rise gas treatment device is supplied from the flow 16 to the inlet side of the electrostatic adsorption tower 1020 to prevent secondary pollution from occurring.

On the other hand, the recycled activated carbon 17 is mixed into the fuel of the Boitz 100 from the fine activated carbon Fi stream 4 in the classifier 109 for treatment. The regenerated activated carbon 18 that has classified the fine particles is divided into streams 19 and 20, and the streams 19 are sent to the ms and o adsorption towers 102, respectively.
Stream 20 is fed to a downstream adsorption column 103. Activated carbon is replenished from the activated carbon circulation 21.Replenishment activated carbon is usually extracted from the fuel coal 1 -mt*re 3, crushed and classified, and coal of an appropriate particle size is produced in the adsorbent production equipment 11 ( l send,
The coal t! 2! After drying at a low temperature of about 1J$ ~ 350c, carbonize it, then smoke it! active vcIII
! In order to reduce the
11.

Next, the desulfurization and denitrification effects of the above flow sheet will be explained based on experimental examples.

Figure 2 shows the results of a desulfurization and denitrification test using activated carbon produced from coal-based materials. The combustion exhaust gas was conducted with the following simulated exhaust gas composition: 11801700 ppm.

The balance gas was 300pp of NNO, 025%, 1G% of Hm, and N dew. The temperature is constant at 130C, and the space n
xm'F18Valk5000h-' and IJ, the horizontal axis d is the reaction contact time, and the vertical axis is the desulfurization rate and the denitrification rate. The amount of NHs added is 1.0% of the theoretical reaction amount. o5 no 2
In Fig. 2, ηSO richness represents the desulfurization rate t, and vNO represents the denitrification rate.

Here, the effect of exemption will be shown assuming that most of 80 g is adsorbed and removed in the adsorption tower 102 in the above flow sheet.

If the adsorption tower is 1020 people 080*t-700 ppm, and the desulfurization rate is 928%, the majority of the 80 m will be adsorbed and removed (9), then the S (h) detected at stream 6 in Figure 1 will be 50 ppm. Simulated exhaust gas composition ksO*50 ppm-N
O500pprn, Os 5%, HmO1O%,
@[1:10C, 8V=5000h' constant, Ni
1s addition amount t - Approximately 1.1 times the field theory warpage amount 660 pp
Figure 3 shows the results of a desulfurization and denitrification test conducted with m.

As is clear from FIG. 2 and the TSS diagram, FIG. 3 shows a higher desulfurization rate and higher denitrification rate over a longer period of time.

Therefore, it is possible to improve the denitrification rate by removing most of the sulfur oxides in the exhaust gas in advance in the #i stage adsorption process, and then adding KNHI to perform denitrification. Compared to the case where desulfurization and denitrification are performed at the same time, the amount of NHs added can be reduced by about 33%.

In addition, in the example based on the above flow sheet, the activated carbon used can be manufactured from fuel coal used in boilers, etc.
Compared to using conventional O#A carbon, gas and tar by-produced from the activated carbon manufacturing process can be recovered as heat, making it much cheaper and effective in reducing desulfurization costs.

As described above, according to the present invention, the adsorption process is divided into two stages,
#After removing most of the sulfur oxides from the exhaust gas in the crotch adsorption step, ammonia [which is equivalent to the theoretical chemical equivalent of 080s and NO] is added to the exhaust gas that has gone through this step, and then the latter adsorption step is performed. Therefore, the weight of N H can be reduced by twice the chemical equivalent of the amount of sulfur oxides removed in the adsorption step of the spinning stage. Furthermore, by reducing the amount of VcN Hs added, the amount of ammonium sulfate produced by reaction with ammonia can be reduced, so the loss i* of the carbonaceous adsorbent in the thermal desorption process can be reduced.

The denitrification effect can be improved.

[Brief explanation of the drawing]

Fig. 1 is a flow sheet showing one embodiment of the present invention, Fig. 2 shows the results of desulfurization and denitrification tests in the conventional dry desulfurization and denitrification method, and Fig. 3 shows the desulfurization and denitrification test results in the example shown in Fig. 1.
It is a figure showing the I test result.

Claims (1)

[Claims] 1. When removing sulfur oxides and nitrogen oxides contained in exhaust gas, the exhaust gas, carbonaceous adsorbent and tI! Most of the sulfur oxides in the exhaust gas are adsorbed and removed.
The sulfur oxide concentration A' in the exhaust gas and the nitrogen oxide layer 1 [
A dry flue gas desulfurization and denitrification method that detects Bt, 2A' + BO chemically, and ammonia gas [is supplied to the flue gas and mixed, and then brought into contact with the flue gas and a carbonaceous adsorbent to form mold. 2. In claim 1, the carbonaceous adsorbent is
A dry flue gas desulfurization/denitrification method using activated carbon produced by subjecting fuel coal to low-temperature oxidation, carbonization, and activation.