JPS60153924A - Treatment of exhaust gas - Google Patents

Abstract

PURPOSE:To prevent the lowering in desulfurization capacity, in treating exhaust gas containing SO2, HCl and HF, by attaining the coexistence of a Ca-compound as a SO2-absorbent, a Mg-compound in an amount corresponding to the stoichiometric amount of HCl and a specific concn. of a Mn-ion. CONSTITUTION:After the amounts of SO2, HCl and HF in exhaust gas 1 from a coal burning boiler are detected by a detection apparatus 3, said exhaust gas 1 is guided to an exhaust gas treatment tower 2 where an absorbing solution is sprinkled to absorb SO2, HCl and HF while the treated gas is exhausted as purified gas 6. CaCO3 is supplied from a line 7 in correspondence with the SO2-absorbing amount and Mg(OH)2 corresponding to the stoichiometric amount of HCl is supplied from a line 8. In addition, MgSO2 is added so as to adjust the Mn-ion concn. in the absorbing solution to 10-400mg/l. By allowing the Mn-ion to coexist, the dissolution of CaCO3 is not inhibited even if the additional amount of the Mg-compound is made smaller than stoichiometric amounts of HCl and HF, and desulfurization capacity is not lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a method for treating exhaust gas, and particularly to a wet treatment method for exhaust gas containing SO2, HCl, and HF, such as coal combustion exhaust gas.

(Description of the prior art) When carrying out the flue gas desulfurization method using the generally known wet coal method, H
Ct and IF may be included. To give an example of each component present in coal combustion exhaust gas, Box is approximately I O0
0ppm, HCL about 60ppm, HF about 40
ppm is 0 such exhaust gas as CacO3
2 When treated as an absorbent in a wet exhaust gas treatment tower, the following reactions occur.

CaCO3+ 802 →Ca803 + CO2'
(1) CaCO3+ 2 HCl4 CaC42+ C
O2+ H2O(2)CaCO3+2HF −+CaF
2 + CO2 + H20 (3) However, the reaction of formula (2) is preferentially produced, and CaCl2 produced by this reaction
The presence of Ca2+ caused by oxidation inhibits the dissolution of Ca and CO3, and as a result, the reaction of equation (1) is hindered, resulting in a decrease in BO2 absorption performance and the formation of BO2 in the exhaust gas treatment tower as a result of the desulfurization reaction. Ca 804.2H20 adheres to the surface of the equipment material as scale and interferes 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 the amount of BO1 and convert CaC42 using the following reaction.CaC62+ M, pX -+
MyCL2 + CaX (4) (here, X represents an anion other than the Ct group).
No. 7.565.

Furthermore, HF is CaF2 with low solubility as shown in equation (6).
An, which is not fixed as
Since the dissolution of limestone is inhibited by the interaction between Aε ions and F ions, a method of adding a basic sodium salt to prevent the problem is disclosed in Japanese Patent Application Laid-Open No. 55-167.
Jl is shown in Japanese Patent No. 0'23.

(Explanation of the prior invention) Therefore, when treating exhaust gas containing SO2, Hct, and HF, magnesium salt is added in proportion to the amount of BO1, and basic sodium salt is further added to CaCl2.
It can be seen that this method is effective as an exhaust gas treatment method that does not cause problems caused by F ions, M ions, and F ions. However,
While conducting experiments on this method, the present inventors discovered that HFm and HC could be combined without adding basic sodium salt.
If M and the compound are added in an amount corresponding to 1, it will be described later (
The reactions of 5) and (6) proceed simultaneously, resulting in a decrease in SO2 absorption performance and school adhesion due to CaSO4/2H20.
We first discovered a method that can solve the problem of dissolution inhibition of CaCO3 at once, and when treating exhaust gas containing SO2, HC/=, and sweet, we detected the amount of HCl and HF in the exhaust gas and installed it in the exhaust gas treatment tower. at least MyCL2 and Mg
We proposed a method for treating exhaust gas containing SO2, HCl, and HF, which is characterized by supplying an amount of Ml compound corresponding to the stoichiometric amount of F2 and a Ca compound as an SO2 absorbent to an exhaust gas treatment tower. (% Gansho 58-358
No. 61).

First, the method of the invention of the prior application will be explained in detail.

First, the reaction when My (OH)2 is used as the My compound is shown below.
OMy (O
H) 2 + 2 HF -) M, F2 + 2H20 (
5) M, (OH)2 + 2 Hosi → M≦C
12+ 2H20 (6n (6) Equation V
y C10 has a large solubility and Mf ion concentration is small, so M and F'2 with small solubility are generated by equation (5).
(: The dissolution of aCO3 is restored.

The fixation of F ions by this MgF2 precipitation increases as the concentration of MyCL2, which is generated by the reaction between Hct and the My compound supplied in proportion to the amount of HCl, in the absorption liquid increases.
This will be further promoted. In other words, from the correlation equation of the solubility product of Mf ion and F ion CMt'') CF-]2=K, as the common ion Ml ion increases, the F ion becomes smaller. However, since CaC22 with high solubility is generated, as the Ca ion concentration increases, CaFz with low solubility precipitates and the F ion concentration decreases, or as mentioned above, the absorption performance of gate 2 decreases due to CaCLz K and C
On the other hand, when only basic sodium salt is added, F ions are neutralized as NaF, or the solubility of NaF is high, and the concentration of F ions is Therefore, in order to reduce F ions, it is necessary to utilize the action of CaCO3, which is an S02 absorbent, and F ions reacting to precipitate CaF2.
/C, but since NaF has a solubility of 1, My (OH)
Compared to the case where F2 is added and precipitated and fixed as MgF2, the decrease in F ion concentration is small.

If the concentration of F ions dissolved in VC in the liquid without being fixed as a solid is high, the balance between acid and alkali will be temporarily disrupted and the acidity of the absorption liquid will become stronger. This causes a problem in which the dissolution of Cog is inhibited. Additionally, when discharging a portion of the absorption liquid, wastewater treatment with special F countermeasures is required in order to comply with strict F wastewater regulations, but the equipment becomes complex in order to reduce F ions in the wastewater. There are drawbacks.

In contrast to the above, according to the method of the prior invention, the My compound added in proportion to the amount of HCl dissolves and accumulates as MgCl2, so stones, fields, and calcium suboxide crystals produced by desulfurization can be separated. By circulating and using the liquid obtained in the absorption liquid to reduce the waste liquid, the My ion concentration will be higher, F ions will be more easily fixed as MyFz, and the F ion loss in the absorption liquid can be lowered. .

If My compound is not added in an amount corresponding to the amount of act Ifz and HF', as described above,! Since 1lCaCθ, waste ions, and F ions are dissolved, the SO2 absorption performance using CaC0a as an absorbent becomes poor. That is, CaCl
The production of 2 is accompanied by an increase in dissolved Ca ions, which reduces the solubility of CaSO4.2H2O (gypsum) produced with desulfurization and oxidation reactions, which promotes the growth of gypsum scale, and also increases the absorption liquid containing CaC62. Because the SO2 partial pressure increases, the BO2 absorption performance decreases (i.e. (
:'a In the absorption liquid containing C12, the concentration of Ca2+ ions increases, and as can be seen from the dissolution equilibrium equation of [Ca'') [SO32-]=KsP, the solubility of 5032- decreases.It is a dissolved component of 0so2 gas. A decrease in BO32- means a decrease in the solubility of S02 gas.In other words, 5 produced by absorption of SO2 gas
Since 032- immediately reaches the saturation concentration, the S02 partial pressure is high and the liquid becomes easy to move.On the other hand, if it is dissolved as MgCl2, the saturation concentration of 5Oa2- is also high.In other words, it becomes an absorbent with high solubility. (The liquid becomes a liquid, and the liquid with a low S02 partial pressure is maintained.) Furthermore, when the amount of dissolved M ions and F ions increases, the caco3 (QA) solution is inhibited and the normal operation of the desulfurization equipment is hindered. F removal measures are required to prevent pollution.

As is clear from the above description of the prior invention, the amount of HCl and HF f in the exhaust gas is detected, and the amount of My compound corresponding to the stoichiometric cap, which is at least MfC12 and MpF2, is generated in the exhaust gas treatment tower. Ca as an absorbent
According to the method of the present invention, which is supplied to the exhaust gas treatment tower together with the compound, it is possible to eliminate the problems of a decline in SO2 absorption performance caused by HCt and HF', scale troubles due to CaSO4#2'H20 precipitation, and inhibition of dissolution of the SO2 absorbent. This will give you excellent results).

(Example of the invention of the prior application) The method of the invention of the prior application was carried out using the apparatus shown in FIG.

In FIG. 1, exhaust gas from a coal-fired boiler passes through an electrostatic precipitator and a heat exchanger (both omitted in the drawing) during the denitrification process, 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 ppm and HCt approx. 60 ppm and HF
Exhaust gas containing about 4 Q ppm is about 400ON? ? ?
/h was detected to be installed.

The inside of the exhaust gas treatment tower 2 is filled with a grid, and the absorption liquid is supplied from the top of the tower via the absorption liquid circulation pump 4 to the bowl/
b, but here S02 and H in the exhaust gas
Cl and HF are absorbed and discharged as purified gas 6 through the mist eliminator 5.

Approximately 50 ppm of Id 802 was detected in the purified gas 6, but both HCL and HF were below the lower detection limit of 1 ppm.

CaCO3 is supplied from line 7 at a rate of approximately 17 kg/h commensurate with the absorption amount of S02, and at the same time My is supplied from line 8.
(OH)2 was supplied so as not to exceed 0.4 alcy/h, which corresponds to the stoichiometric amount of the HC/S absorption amount and the HF absorption amount.

Air was blown into the tank 9 at the lower part of the exhaust gas treatment tower 2 at a rate of about 2 ON-/h through an air nozzle 10 in order to oxidize the sulfite produced by absorbing 802 into sulfate.

The absorption liquid in the tank 9 was a suspension containing Ca5Oi.2H20 crystals and some CaCO3 powder, and water was replenished to adjust the water balance so that the slurry concentration was about 18% by weight.

SO-! In order to balance the absorption of CaSO3 and 2H20 crystals (gypsum) and remove them from the system, a part of the absorbed liquid is guided to the separator 12 via the pump 11, and the gypsum 13 is recovered as a by-product. A part of the lachrymal fluid was drained through the line 14, and the remainder was returned to the exhaust gas treatment tower 2.

Approximately 280 mmol/l of ct ions are dissolved in the absorption liquid when the operation is continued in steady state, whereas Mt ions are equivalent to 140 mmol/l of Ct ions.
It was never detected below mmot/l.

Further, dissolved F ions in the absorption liquid were not detected in excess of 2 mmoz/t, and were discharged from the system as solid MgF2.

My within the range of HC4 absorption and HF absorption
When (OH)2 was supplied, a decrease in desulfurization performance and a decrease in the pH of the absorption liquid were observed.
J! O3 supply protein! However, the performance did not recover. Furthermore, if the supply of My(OH)2 is stopped, the desulfurization performance will be significantly reduced and the dissolution of CaCO3 will be hindered, causing the stone 'F
1 scale became prominent.

In addition, in the method of the prior invention, the Mf compound to be added is M
HCt, limited to t(OH)2, reacts with HF to form MgC
Any chemical that produces l2, M, or F2 may be used, and any commonly available chemicals can be used.

Furthermore, when Mt(On)2, calcined dolomite, or Myo was used as the My compound, the reaction rate with halogen was fast, so it was easy to adjust the addition while detecting the pH of the absorption liquid.

(Basic knowledge of the present invention) In the above-mentioned embodiment of the prior invention, the present inventors conducted an experiment in which Mn S04 was added to the absorption liquid and Mn ions in the absorption liquid were gradually increased. As a result, very interesting results were obtained. That is, when the Mn ion concentration in the absorption liquid increases, the amount of Ml compound added is reduced by the amount of HCt and HF.
Even if the amount was reduced from the theoretical amount, no interference with the dissolution of CaCO3 was observed and the desulfurization performance was improved (Constitution of the present invention) The present invention was completed based on the above findings. , the present invention detects the amount of HCt in the exhaust gas to treat exhaust gas containing SO, HCl, and HF, and detects the amount of Mt compound in the exhaust gas treatment tower in an amount equivalent to the stoichiometric amount of at least MgCl2. A method containing SO2, HCl, and HF, characterized in that a Ca compound as an SO2 absorbent is supplied to an exhaust gas treatment tower, and Mn ions are made to coexist at 10 to 400 ri/l in the absorption liquid that comes into contact with the exhaust gas. The present invention relates to a method for treating exhaust gas.

Furthermore, when carrying out the above method, air is blown into the absorption liquid, in particular, the sulfite concentration in the absorption liquid is detected, and the amount of air is adjusted so that the concentration is 10 mmot/or less. Blowing air is a preferred embodiment.

(Detailed description of the present invention) In the flow shown in Fig. 1, the Mn ion concentration in the absorption liquid is gradually increased from 0 to about 400 my/l.
802 contained in purified gas 6 when adjusting the addition of 5O<
The change in F1 degree is shown in the M2 diagram. The experiment in Figure 2 is Mt
This shows the result when the supply of the compound was reduced and only a stoichiometric amount equivalent to 1% V of HC was supplied, and F ions were dissolved in the absorption liquid up to about 200 mol/l. Even though F ions are dissolved in the absorption liquid, as the Mn ion concentration in the absorption liquid increases, CaC
It became clear that no interference with O3 dissolution was observed and that the desulfurization performance was improved.

The experiment shown in Figure 2 was conducted using the air nozzle 10 with the flow shown in Figure 1.
This was done without blowing air. It is clear from FIG. 2 that the My ion concentration exerts its effect even at a very small amount (approximately 10 q/l), and that the effect is saturated when it reaches 400 q/l.

Next, air was blown, and the experimental data obtained when the amount of air blown was gradually reduced is shown in FIG. In Figure 3, M
The table shows the presence or absence of n ions and the amount of 1 and My(OH)2 added as parameters. That is, the third
In the figure, the mark indicates Mn ion addition of 601 da/l, M
When y(OH)2 is added in the stoichiometric amount of HCt (in the present invention), ○ indicates no addition of Mn ions, My(OH)
) 2 is added in stoichiometric amounts of Hct and HF (prior invention) and Δ indicates no addition of Mn ions, M9(OH)2
This is the data when a stoichiometric amount of HCl ft is added.

As the air blowing amount is reduced (which has the advantage of reducing the blowing power consumed for air blowing), the SO2 concentration in the purified gas tends to increase in any case, but as in the present invention, the Mn When ions are allowed to coexist, even if air blowing is stopped, if Mr(OH)2 is added in a stoichiometric amount to 1 HC, the tendency for the increase in the amount to increase ('acO3) is almost negligible. No dissolution interference was observed, indicating that high desulfurization performance was maintained.

In this way, the amount of M) compound corresponding to HCl M is supplied so that Ct ions are dissolved as MyC10, and Mn ions are added, or Mn ions are added and air is further blown. It was confirmed that the desulfurization performance does not deteriorate even if F ions are dissolved, in other words, even if they are not precipitated and fixed as My F2. This is thought to be due to the fact that the absorbed SO2 is immediately oxidized to sulfuric acid by Mn ions and air blowing, resulting in a reaction between the strongly acidic sulfuric acid and the absorbent CaCO3. That is, the apparent inhibition of CaCOs dissolution due to the interaction between M ions and F ions is due to
This is because sulfite is a weaker acid than sulfuric acid, and when Mn ions are added to the solution, even if F ions are dissolved, Ca
The dissolution reactivity of CO3 becomes easier to recover. As a result, desulfurization performance was improved.

In other words, when treating exhaust gas containing HF, HCl, and SO2, an amount of M and compound corresponding to the amount of HC6 is supplied, an amount of C(L) compound corresponding to the amount of SOX is supplied as an absorbent, and further absorption The ICMn ion content in the liquid is present in the range of vc to ~400 ~/l as can be determined from Figure 2, and when air is blown into the absorption liquid to oxidize sulfurous acid to sulfuric acid, desulfurization is achieved even if F ions are dissolved. It was confirmed that the performance did not deteriorate.

The amount of air blown is approximately 4 o o o Nyy/
/h, In the experimental example where the inlet S02 was about 1000 ppm, an air amount in the range of 5 to 110 yi/b, that is, equivalent to about 0.125 to 2.75% based on the exhaust gas amount standard, was blown, but the population was 502 g. As the temperature increases, the amount of sulfite to be oxidized increases, so the amount of air blown should be adjusted in accordance with the amount of sulfite.

The most convenient way to adjust the amount of air blowing in the present invention is to continuously measure the sulfite concentration in the absorption liquid, and check that the concentration is 10 mm
t/ is oxidized until the following is maintained. It was confirmed that by doing this, the solubility of CaC,03 was recovered. That is, in Figures 2 and 3, in experiments where the 802 fA degree in the purified gas was in the range of 50 ppm or less, the sulfite concentration in the absorption liquid was 10 mmoz.
Therefore, the amount of air blown should be increased by detecting the sulfite concentration in the absorption liquid until the concentration becomes preferably 1Q mmol/ or less. Of course, when there is no air blowing and the sulfite concentration in the absorption liquid is below 1 (I mmoz/z) due to the action of Mn ions, the solubility of C'aCO3 is good even with air blowing stopped. It is the same as stated above that this is maintained.

In addition, the Mn compounds to be added are MnSO4, Mn0O
It has been found that H, MnO2, and MnCl2 are effective, and that the effects of the present invention can be obtained at concentrations dissolved as KMn in the absorption liquid accompanied by a redox reaction. You don't have to.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention. 1...Exhaust gas 2...Exhaust gas treatment tower 3...Detection device 4...Absorption liquid circulation pump 5...Mist eliminator 6...Purification Gas 7... Ca compound supply line 8...
M2 compound supply line 9... Tank 10... Air nozzle 11... Pump 12... Separator 13... Gypsum 14 ・11-1 Offshore The liquid line in Figure 2 is experimental data obtained in an example of the present invention.
The SO2 concentration contained in the purified gas 6 is shown when My(oH)2 is added in a stoichiometric amount with the amount of HCl until the Mn ion concentration in the absorption liquid reaches about 400 q/L. FIG. 3 shows experimental data obtained in an example of the present invention.
The correlation between the change in the amount of air blown into the absorption liquid until it is stopped and #t7) SO26 degrees contained in the purified gas 6 is shown. Sub-agent 1) Mei-Fu agent Ryo Hagiwara - Fan 1 figure, 3 M-ion ion in the blotting liquid in flood 2 area (Hiroshike), tail 3 figure air blown U amount (mjA//f, ) Continued from page 1 0 Inventor Susumu Okino 4-6-n, Kannon Shinmachi Hiroshima Research Institute, Nishi-ku, Hiroshima Mitsubishi Heavy Industries, Ltd.

Claims (1)

[Claims] (i) When treating exhaust gas containing SO2, HCt, and HF, the amount of HC'4 in the exhaust gas is detected and the amount of HC'4 is reduced to a stoichiometric amount of at least MgCl2 in the exhaust gas treatment tower. Equivalent amount of M? A method containing S02, HCl, and HF characterized in that the compound and a Ca compound as an SO2 absorbent are supplied to an exhaust gas treatment tower, and 10 to 4 QOmy/l of Mn ions are allowed to coexist in the absorption liquid that comes into contact with the exhaust gas. Exhaust gas treatment method (2) Exhaust gas treatment method according to claim (1), characterized by blowing air into the absorption liquid (3) Detecting the concentration of sulfite in the absorption liquid, and detecting that the concentration is 1
The exhaust gas processing power method according to claim (2), wherein the total percentage is to adjust the air amount so that 0 mmot/ is below.