JPS59186633A - Treatment of waste gas - Google Patents

Abstract

PURPOSE:To prevent decrease in absorbing performance of SO2, sticking of gypsum scale and dissolving trouble of CaCO3 by adding an Mg compd. corresponding to the contents of HCl and HF or adding an Mg compd. corresponding to the contents of HCl to the absorbent so that Mn ions coexist therein. CONSTITUTION:The contents of HCl and HF in waste gas 1 are detected with a detector 3, and Mg(OH)2 of the amt. equiv. to the stoichiometric content at which MgCl2 and MgF2 are formed, or above is supplied through a line 8 into a treating column 2 for waste gas. CaCO3 of the amt. corresponding to the absorbing amt. of SO2 is supplied through a line 7. If an Mn compd. is further added to the absorbent liquid, a satisfactory result is obtd. by supplying the Mg compd. in the amt. corresponding to the content of HCl or above. Then the decrease in absorbing capacity of SO2 occurring in HF and HCl, the scale trouble owing to deposition of CaSO4.2H2O and the dissolution trouble of CaCO3 which is an SO2 absorbent are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating exhaust gas, and more particularly to a wet treatment method for exhaust gas containing SO, HCl, and HF, such as coal combustion exhaust gas.

When carrying out flue gas desulfurization using the generally known wet coal method, H
e/ and HF may be included.

An example of each component present in coal combustion exhaust gas is B
ox is about 10 D Oppff1%HOj? is about 60
pprn.

HF is approximately 40 ppHl.

When such exhaust gas is treated in a wet exhaust gas treatment tower using 0aOO, SO, and an absorbent, the following reaction occurs.

C! aco, 10 So, -+ 0aSO, + 001
(110aCO, +2HO1-)
0aOI! t + 00. +H,Of210aO
O, + 2HF −+ OaF, + 00. +
H,0131 However, the reaction of formula 12) is preferentially produced, and the C! produced by this reaction! O due to aof*
The presence of a"+ inhibits the dissolution of Ca0O, and as a result, it comes to interfere with the reaction of formula 11, resulting in a decrease in SO1 absorption performance and a decrease in OaSO4.2H20, which is generated along with the desulfurization reaction in the exhaust gas treatment tower. will stick to the surface pressure scale of the equipment material and interfere with the operation of the exhaust gas treatment equipment.

In order to prevent this problem, it is effective to add magnesium salt in proportion to 7t of HO and convert 0a (Vt) using the following reaction.CaO1t + MgX −+
Mg01t + C! aX f4) (herein, X represents an anion other than at) as disclosed in Japanese Patent Application Laid-Open No. 17565/1983.

Furthermore, HF is OaF with low solubility as shown in equation (3).

A77 contained in dust in exhaust gas without being fixed as
The dissolution of limestone is inhibited by the interaction of these A, J ions and F ions, so there is a method to prevent the problem by adding IJ Uno salt.
It is shown in the publication No. 167023.

Therefore, when treating exhaust gas containing So, H(J' and HF), it is possible to add magnesium salt in proportion to the amount of H(,
It can be seen that this method is effective as an exhaust gas treatment method that does not cause problems caused by O/4, AA ions, and F ions. However, while conducting experiments using this method, the present inventors discovered that it was possible to add an Mg compound corresponding to the amount of HF and HCV without adding the basic sulfur salt. For example, the following reactions proceed simultaneously, resulting in a decrease in SO1 absorption performance, scale sticking by 0a1304.2H,Oic, and 0.
It has been found that the problem of inhibiting the dissolution of aCO can be solved all at once.

The present invention was made based on the above findings, and includes SO,
When treating exhaust gas containing aCZ and HF, the amount of IC7 and HF in the exhaust gas is detected and at least MgCJ and MgF are treated in the exhaust gas treatment tower.

A method for treating exhaust gas containing SO, Hot and HF, characterized by supplying an amount of Mg compound and SO corresponding to the stoichiometric amount, and a Ca compound as an absorbent to an exhaust gas treatment tower. It is something.

The method of the present invention will be explained in detail below.

First, the reaction when Mg(OH,)t is used as the Mg compound is shown below.
Mg that produces EI04, MgIF, and MgO1t
As long as it is a compound, the effect is not much different.

Mg(OH)t+2HF −+ MgF, + 21(
,0(51Mg(OH)!+ 2HO1→MgO11+
2H10t6) MgCIt produced by formula (6)
has a large solubility and the Mg ion concentration is high, so (5
), MgF with low solubility is precipitated, and 0a
The dissolution of OO is restored.

This fixation of F ions by MgP and precipitation is further promoted by the high concentration (yes, it is) of Mg0J produced by the reaction between HCI and the Mg compound supplied in proportion to the amount of HCjl in the absorption liquid. From the correlation equation of the solubility product of Mg ions and F ions (Mg") (Fi"=K), as the Mg ions, which are common ions, increase, the F ions become smaller.

If a Mg compound is added and the compound is ferrous (OaF, of course, which has a high solubility will be produced), OaF, which has a low solubility as the Oa ion concentration increases.

is precipitated and the F ion concentration decreases, but as mentioned above, 0a
07. SO, absorption performance decreases due to 0aSO4・
There is no escape from the problem of noticeable scale adhesion in 2H20.

On the other hand, when only basic salt +7um salt is added, F
The ions are neutralized as NaF, but the solubility of NaF is high and the concentration of the ions does not decrease. Therefore, h'! decreases in F ions! ,,80w absorbent Ca0O,
The reaction between NaF and F ions will be used to precipitate 0aFt, but since NaF is soluble, Mg(
Compared to the case where OH, 12 is added and precipitated and fixed as MgF, the decrease in F ion concentration is small.

If the concentration of F ions dissolved in the liquid without being fixed as a solid is high, the balance between acid and alkali will be temporarily disrupted, and the absorption liquid will become highly acidic. This immediately causes a problem in which the dissolution of Cocos is inhibited.Also, when draining a part of the absorption liquid, it is difficult to
In order to comply with wastewater regulations, it is necessary to treat wastewater with special F countermeasures, but there is a drawback that the equipment becomes complex in order to reduce 2 ions in wastewater.

In contrast to the above, according to the method of the present invention, HC! The Mg compound added in proportion to the amount will dissolve and accumulate as Mg04, so if the liquid obtained by separating the gypsum and calcium sulfite crystals produced by desulfurization is recycled and the waste liquid is reduced, the amount of Mg04 will be reduced. The ion concentration becomes higher, F ions are more easily fixed as MgF, and the F ion concentration in the absorption liquid can be lowered.

Mg compound UC1! If the amount corresponding to the amount of HF is not added, Oak/', or A/ion-F as described above.
Since ions are dissolved, SO using 0aOO as an absorbent
, the absorption performance becomes poor. That is, the generation of 0a04 is accompanied by an increase in dissolved Oa ions, which decreases the solubility of 0aSO, 2H, O (gypsum) generated with desulfurization and oxidation reactions, which promotes the growth of gypsum schools, and also increases Ca
The absorption liquid containing 1 liter is SO.

Because the partial pressure increases, the BO absorption performance decreases (that is, in the absorption liquid containing 0a04, the Oat + ion concentration increases, and (Oa") (80s"") =
As can be seen from the solubility equilibrium equation of Ksp, the solubility of 5Oj2- decreases. A decrease in so and t, which are dissolved components of SO and gas, means that the solubility of SO and gas decreases. In other words, the 5O2- produced by absorption of SO and gas immediately reaches a saturated concentration, resulting in a liquid that tends to have a high 801 partial pressure. On the other hand, if it is dissolved as Mg04, the saturation concentration of soj''- will be high, in other words, it will become an absorbing liquid with high solubility, and the dissolved amount of SO will increase, maintaining a low partial pressure of SO. The dissolution of caao is inhibited, preventing the normal operation of the desulfurization equipment, and the high concentration of ?
Measures to remove F are required to prevent further pollution.

As is clear from the above explanation, the amount of naz and HF in the exhaust gas are detected, and at least MgO
1, and an amount of Mg corresponding to the stoichiometric amount of MgF.
According to the method of the present invention, in which a compound is supplied to an exhaust gas treatment tower together with SO and an Oa compound as an absorbent, SO, a decrease in absorption performance, and 0a80.・2H,O
This provides an excellent effect in eliminating problems such as scale problems caused by precipitation, SO, and inhibition of dissolution of the absorbent.

Example The method of the present invention was carried out using the apparatus shown in FIG.

8 in Figure 1, exhaust gas from a coal-fired boiler passes through a denitrification device, an electrostatic precipitator, and a heat exchanger (all omitted in the drawing), and then is led to an exhaust gas treatment tower 2 as exhaust gas 1. .

A detection device 3 is installed at the entrance of the exhaust gas treatment tower 2, and the so
, approx. 1000 pl) III and HOj' approx. 6o ppm
and about 40 ppm of HF.
It was detected that OHm37/h was being introduced.

The inside of the exhaust gas treatment tower 2 is filled with a grid, and the absorption liquid is pumped from the top of the tower through an absorption liquid circulation pump 4 for 60 m/min.
The SO and HO in the exhaust gas are
7 and HF are absorbed and discharged as purified gas 6 through a mist eliminator 5.

In the purified gas 6, SO, was detected at approximately 50 pI)m, but H, (3j' and HF were both at the lower detection limit i pp
It was less than m.

C from line 7 commensurate with the absorption amount of SO2! aoo.

is supplied at a rate of approximately 17 kg/h, and at the same time from line 8
It was supplied so as not to exceed 0.48 kg/h, which corresponds to the stoichiometric amount of g(OIl)t, HO7 absorption amount, and HF absorption amount.

The tank 9 at the bottom of the exhaust gas treatment tower 2 contains BO.

Air was blown through the air nozzle 10 at a rate of about 2 ONm''/h in order to oxidize the sulfite produced by absorbing the sulfite into sulfate.

The absorption liquid in tank 9 becomes a suspension containing Ca5O,.2n,o crystals and some OaOO, powder. Water is replenished so that the concentration is about 18% by weight. Adjusted water balance.

In order to balance the absorption of SO3 and take out the 0aSO4.2H10 crystals (gypsum) from the system, a part of the absorption liquid is guided to the separator 12 via the pump 11, and the gypsum 13 is recovered as a by-product. Part of the liquid F was drained through the line 14, and the remainder was returned to the exhaust gas treatment tower 2.

When the operation is continued in steady state, aZ ions are dissolved in the absorption liquid at approximately 280 m mol/l, whereas Mg ions are dissolved in an amount equivalent to 140 m mol/l of O/ion.
It was never detected below mol/1. Further, dissolved F ions in the absorption liquid were not detected at a concentration exceeding 2 m mop/z, and were discharged from the system as solid Mg'x.

Mg(o
n), a decrease in desulfurization performance and a decrease in the pH of the absorbent solution were observed, and the performance did not recover even if the amount of SO absorbent 0aOOj supplied was increased. Furthermore, 'g(O
H) When the supply of w was stopped, the desulfurization performance significantly decreased and the dissolution of 0aOO3 was hindered, resulting in noticeable gypsum school.

What? , in the method of the present invention, the Mg compound added is Mg
(OH), limited to HO7, reacts with HD' and MgC1
Any chemical agent that generates t s ''gFs can be used, and commonly available chemicals can be used.

Furthermore, when Mg(OH)t, calcined dolomite, or MgO is used as the Mg compound, the reaction rate with nitrogen is fast, so it is easy to adjust the addition while detecting the pH of the absorption liquid.

Furthermore, in the above-mentioned embodiment, when the Mn compound was added to the absorption liquid, even if the air blowing from the air nozzle 10 was stopped, sulfite was not generated in the absorption liquid and was contained in the exhaust gas. Results were obtained in which the total amount of SO absorbed by oxygen gas in the gas-liquid contact area of the grid filling part turned into sulfate. At this time, even when the amount of Mg compound added was less than the stoichiometric amount of Hot # and I(F amount), no interference with the dissolution of OaC!O was observed, and the desulfurization performance was improved.

When the Mn compound was gradually added until the Mn ions in the absorption liquid reached about 400 mt/l, the SO contained in the purified gas 6 was maintained at 50 ppm or less, and during this time the supply of the Mg compound was reduced. ,HCI! Since the stoichiometric amount corresponding to the amount of F ions was supplied, the amount of F ions was 200 my/l.
It was dissolved to some extent.

In this way, by supplying the Mg compound in an amount that matches Ic and HCjJl, the aZ ion becomes Mg07. If K is dissolved as K and Mn ions are added, ? It was confirmed that even if ions were dissolved, in other words, the desulfurization performance did not deteriorate even if the ions were not precipitated and fixed as MgF. This is because the absorbed SOl is immediately oxidized to sulfuric acid by Mn ions, so strong acidic sulfuric acid and absorbent 0aOO,
This is thought to be due to the reaction. That is, A
The reason why the dissolution of 0aOO Hatake is inhibited by the interaction between j ions and F ions is because sulfurous acid is apparently a weaker acid than sulfuric acid, and if Mn ions are added to oxidize sulfurous acid to sulfuric acid, 0aOOjl Even if F ions are dissolved, the reaction begins. As a result, desulfurization performance was improved.

In other words, when treating exhaust gas containing HF, H(d, and SOI), an amount of Mg compound corresponding to the amount of HOJ is supplied, an amount of Oa compound corresponding to %Roti is supplied as an absorbent, and further absorption is achieved. If Mn ions are added to the solution, F
It was confirmed that the desulfurization performance did not deteriorate even if ions were dissolved. This phenomenon is caused by the fact that when Mg compounds are supplied in proportion to the amount of HO7 and HF, even if there is a temporary shortage of Mg compounds, if Mn ions are added, the desulfurization performance will decrease. Show that the problems that occur can be prevented.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention. 1-111 Exhaust gas 2-111 Exhaust gas treatment tower 5-111 Detection device 4-111 Absorbing liquid circulation pump 5-111 Mist eliminator 6----Purified gas 7---- Oa compound supply line 8 ---- Mg compound supply line 9 - 11 Tank 10 - 1 Air nozzle 11 ---- Pump 12 - 1 Separator 13 - 1 Gypsum 14 - 1 Filtrate line sub-agent 1) Clearance agent Ryo Hagiwara - Figure 1 Procedural amendment 1982 1 I] 2J 1 (Mr. Kazuo Wakasugi, Commissioner of the Japan Patent Office 1 Indication of matter A'1 Showa 11158 in hand) i'i1.91"ith s s 86
1. Name of the invention. Method for treating exhaust gas. 3. Relationship with the person who extracts the pressure. 1. Name of the invention
Mr. 2-5-1 Marunouchi, Chiyoda-ku, Tokyo 8
(620) Mitsubishi Heavy Industries, Ltd. (name: V), ) 4 voices, 6 people, the teaching of inventions that increase the correction beam Hj'+
-"A'--Object of the 8th amendment (1) "Claims" column of the specification (2)
Contents of amendment in column a of “Detailed Description of the Invention” of the specification (1) The scope of claims on page 1 of the specification is corrected as shown in the attached sheet. (2) On page 1, line 15, "wet coal method" is corrected to "wet lime method." (3) On page 3, lines 17-18, "first-order reaction" is corrected to "reactions such as (5), (6), etc., which will be described later." (4) On page 4, lines 2 to 9, "The present invention relates to..." is corrected as follows. The present invention has been made based on the above findings. (1) When treating exhaust gas containing so□, HCl, and HF, the amount of HCl and HF in the exhaust gas is detected and and supplying an amount of Mg compound corresponding to the stoichiometric amount of at least Mg, Cum and MgF, and an O, a compound as an SO2 absorbent to an exhaust gas treatment tower. (2) In treating an exhaust gas containing so, HOt, and I(F, the amount of HCl in the exhaust gas is detected and at least M g Ot2 and A BOI characterized in that an Mg compound, BO, and an Oa compound as an absorbent are supplied to an exhaust gas treatment tower in an amount corresponding to a stoichiometric amount of (5) Insert the following sentence between line 4 and line 10 of the same page. A preferred embodiment is to blow air into the absorption liquid of "Mg(OH)z and" in the line (-Mg
(OH) Correct 2 to 7, (8) [soUg! on page 11, line 2] l! Matashii 11]
80. "Absorbent" is corrected. Claims (1) In treating exhaust gas containing SO2, HCl and HF, the amount of HCl and HF-ff1 in the exhaust gas is detected and at least tAgc t2 and M
SC2 and HCt whose 1F4j characteristic is to supply the lunar Mg compound corresponding to the stoichiometric amount of gF2 and the Oa compound as EIO2 absorbent to the exhaust gas treatment tower.
and HF. Commissioner of the Japan Patent Office Kazuo Wakasugi 1 Display of small bones Showa 581 Kushi'+14+1 No. 35861; 32,
Name of the invention: Exhaust gas treatment method 3, Relationship with person who performs God-11 4' + Applicant 11 4 5-1-4, Maruno Potter-chome, Chiyoda-ku, Tokyo
116, 2nd Offender 5, 116, 2nd Offender, 1, 1, Toramon, Minato-ku, Tokyo The 1F ion in lines 4 to 8 on page 6 of the specification of correction causes a problem. ” is corrected as follows. [If the absorption liquid becomes acidic while the F ions do not become solid and remain dissolved in the liquid at a high concentration, they will immediately form a complex that inhibits the dissolution of aCO3. It is thought to be generated by the interaction between F ions and F ions.The absorption liquid becomes acidic when the balance between acid and alkali is disrupted, such as by temporarily stopping the supply of the absorbent C!aoQJ. Once the absorption liquid has become acidic, C!aC!03 is applied from the outside.
Even if you supply additional CaC! Since there is a complex that inhibits the dissolution of 0.03, we are faced with the problem that it is almost impossible to transfer the absorption liquid to the desired alkaline side. ”

Claims (1)

[Claims] It is roaring to treat exhaust gas containing SO, HO7 and HF, and HOj? After detecting the amount of Mg and HF', a small amount of Mg compound (both Mg, Olt, and MgF) corresponding to the stoichiometric amount, SO, and Ca compound as an absorbent are added to the exhaust gas treatment tower. A method for treating exhaust gas containing SO, Hα, and HF.