JPS5849422A - Desulfurizing method for waste gas - Google Patents

Abstract

PURPOSE:To prevent the degradation in desulfurization performance occuring in the Al compds. contained in the slurry in an absorption stage in a wet type lime gypsum desulfurization method for waste gases by supplying phosphoric acid or phosphoric acid compds. into the absorption stage. CONSTITUTION:The waste gas from a coal firing installation 1 is conducted to an absorption tower 3, where SO2, HF, and dust are absorbed away from the waste gas by the slurry from a spray nozzle 6. A purified gas 4 is discharged from said tower. The slurry contg. the Ca compds. such as the CaSO3 and CaSO4 formed by absorption of SO2, the CaCO3, etc. in the absorbents, and the Al-F complex ions, etc. formed by the reaction of the Al compds. and HF dissolved in the slurry in the absorption stage originating in the dust, the absorbents, and makeup water is circulated in the tower 3 by a pump 5. Here, the concn. of the fluorine in the waste gas 2 and the flow rate of the waste gas are detected, and the inflow rate of the F compd. is determined. A phosphoric acid compd. 13 of the amt. conforming to said rate is added to decompose the Al-F complex ions, whereby the desulfurization performance is recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flue gas desulfurization method, and more particularly to an improved R' of the so-called wet lime-gypsum flue gas desulfurization method that removes SO from combustion flue gas using limestone or slaked lime as an absorbent raw material. It is something.

In the absorption process in wet lime plaster method flue gas desulfurization equipment, s
o, 'ta: Containing combustion exhaust gas, Ca(OR)*.

CaC0, *Ca80. al12H20, CaSO
4@2)! So, y is removed from the exhaust gas by contacting it with two rallies containing calcium compounds with low solubility such as ,
Although SO is absorbed, the absorption reaction can be expressed as a general reaction equation.

So, +Ca(OH)*→CaSO3aunt O+%
Ht O(1)SO2+CaC0,+%BHy O-*
Ca5O, .'72H1O+CO, (21), and the #R element in the exhaust gas causes the following oxidation reaction.

CaSO3・% H20+'J O! +5/2H
20 → CaSO4.2 H, O (3) Although this general reaction formula is simple, the actual reaction mechanism is not so simple (1) It is said that various iodines are involved in an extremely complicated manner. However, there are a wide variety of chemical factors that affect the desulfurization performance in the absorption process. Even now, various analyzes have been conducted based on various studies, and various desulfurization processes have been investigated. It is clear from the fact that SO gas has been proposed, and in addition to the complexity of the SO absorption reaction in a three-phase gas-liquid-solid system.

Research and research into the effects of a wide variety of trace elements is endless.

In addition to KG'lo in the combustion exhaust gas, many other compounds such as A:Jr:nia compound, H0Geco compound, and Tast are included as trace components, and the composition of dust varies depending on the exhaust gas source. It is difficult for anyone in the field of chemistry to imagine that the field is multi-layered.

In particular, due to recent changes in the energy situation, coal is being used extensively as boiler fuel in IA power stations and factories, and this coal combustion exhaust gas has an order of magnitude higher concentration of tasto and hexene compounds than heavy oil combustion exhaust gas. It exists in

These dusts, bald compounds, etc. are absorbed into the slurry of the absorption process in the same way as SO.

The present inventors were faced with the dust phenomenon in which the desulfurization performance deteriorates when low-strength and 8-°0 Gesi compounds are mixed into the slurry of the absorption process, and as a result of various studies on the causes of this, the inventors found that when the slurry of the absorption process It was discovered that the sulfur sulfur performance deteriorates due to the presence of dissolved Al:Nium compounds.

The mechanism of the reaction that Al:Nium compounds have on desulfurization performance is currently not fully understood, but as shown in Figure 1, as the concentration of dissolved aluminum increases, the desulfurization performance significantly decreases, causing the construction work to be carried out by the inventors. has been confirmed.

The origin of this molten aluminum is dust in the exhaust gas, absorbent, make-up water, etc., and the exhaust gas, absorbent, and make-up water that flow into the absorption process each contain real aluminum compounds in varying concentrations. . Whether the aluminum compounds that flow into the absorption process exist as dissolved aluminum or partially dissolved and the remainder as solid aluminum compounds depends on the history of the aluminum compounds and the atmosphere at the time.・Varies depending on conditions.

For example, even if an aluminum compound is eluted in the absorption process, J(OH), t' influence will be affected by the reaction of formula (1) in a liquid slurry of 5 or more as in the absorption process of a normal wet flue gas desulfurization equipment. form f, -me, melt j51
L! :')'Mu concentration is 10 I! 1t/l
It is known that the concentration is as low as (am AJ) or less.

Al1”+30H-→AJ? (0H)i↓
(4) However, when the present inventors absorbed 6-membered combustion exhaust gas, even when the absorption tower slurry was 5 to 6, it was 11th! ! ! As shown in I (aluminum is 5 x
It has been confirmed that t O-3 mol/l (as AI) is also stably dissolved.

As a result of various studies on this phenomenon, it was found that molten aluminum reacts with fluorine compounds brought by exhaust gas, resulting in stable Al1.F and MyuFt-An.F.

M * F4-I A, "Fnee e M * Ru'. A,
It was discovered that it exists in the form of AE'Jlh-79 elementary complex Ioko. Figure 2 shows the absorption process gas at 5 lees.
This shows an example of the relationship between the dissolved fluorine concentration and the dissolved aluminum concentration.
/mol). This means that the generally understood aluminum concentration is determined by the dissolved fluorine concentration.

The source of this dissolved fusilicium is fu! in exhaust gas. I
There are elementary compounds, absorbents, etc., but especially in coal combustion exhaust gas, which has been frequently used due to recent changes in the energy situation, SO, which is equivalent to 1/10 to 1/100 of gas, contains several tens of SO, which is equivalent to 1/10 to 1/100 of gas
Several p fluorine compounds are present, and when such exhaust gas is treated with a wet flue gas treatment device, the absorption step Ct
) The concentration of aluminum iodine dissolved in the bath increases.

Is the desulfurization performance decreasing due to this aluminum compound? One of the preventive measures is to promote the discharge of aluminum compounds from the system.

This can be achieved by adding alkali metal or alkaline earth metal hydroxide to the circulating fluid in the desulfurization equipment system.
By maintaining the liquid at a high pH, the dissolved aluminum in the slurry in the absorption process can be separated as a precipitate by neutralizing it with a ClW-decomposed alkali and separating it as a precipitate. This is to keep the degree of desulfurization low and reduce the decrease in desulfurization performance.

However, the precipitation separation treatment operation by neutralizing the aluminum compound is troublesome, impairs economic efficiency, and increases the burden of wastewater, which does not meet the needs of the times from the viewpoint of preventing secondary official documents due to wastewater.

The present invention uses limestone and slaked lime as absorbent raw materials to improve the desulfurization performance brought about by the aluminum compound contained in the slurry of one ton of absorption in the wet lime-gypsum flue gas desulfurization method for removing SO from the flue gas. In order to prevent deterioration, 1 fl. of phosphoric acid compound is supplied to the absorption step.

According to the present invention, there is no need for an operator to remove dissolved aluminum compounds, ie, precipitation separation by neutralization treatment or an increase in the amount of water discharged, and it is possible to prevent deterioration in the desulfurization performance.

That is, the present invention mimics the deterioration of desulfurization performance in the absorption process (
This relates to a method for decomposing and removing the main cause of the bath decomposition, Al-320, and the details will be described below. − In the absorption process, aluminum compounds are commonly
As mentioned above, it exists as an aluminum-fluorine complex. It was discovered that when GO2Y in the combustion exhaust gas is absorbed by a slurry containing Ni-F-Si complex sulfur, the desulfurization performance recovers depending on the amount of phosphoric acid added, as shown in Figure 6, when the phosphoric acid compound is added. The present invention was made possible by this.

Aluminum-fu caused by phosphoric acid compounds! The J-vote complex iocolli decomposition reaction is as follows.

When a phosphoric acid compound is added to the slurry in the absorption step, the phosphoric acid compound reacts with Ca5O and a 2 H2O contained in the slurry to produce JNR calcium.

2M", -PO, +3CaS04・2H10-+Ca5
(PO4)+3-・SO4+2H10(51(here M
: Indicates a monovalent cation. ) Konosu:/+1! When calcium coexists with fluorine, fluoroapatite is produced by the trap of formula (6). Since this fluoroapatite is an extremely aS-decomposable compound, aluminum-hu! The IX complex iodine is decomposed by the following reaction, and the fluorine iodine is fixed in the solid and at the same time reed! Nium iosi is (4)
According to the formula, it was found that L/(OH) was precipitated and removed.

! (1-Fn)”-”-? 6Ca3PQ)t+ca"-
+2Caa(POa"F+"AA"" (615+ AJ + 5 H, O→ kl(0■), ↓+3B
(4) Therefore, it is considered that the desulfurization performance was restored because the aluminum-fluorine complex was decomposed and removed by the above reaction.

The phosphoric acid compound supplied to the absorption process may be a reactive component:
In addition to calcium phosphate, soluble compounds including phosphoric acids such as potassium phosphate, sodium phosphate, and acinium phosphate, and phosphoric acid are also effective. Note: / The supply of acid compounds is not limited to the absorption process, but also to liquids containing aluminum complexes and iodine complexes, for example * s
Q.

An oxidation process in which Ca 803.17H20Y produced by absorbing oxidizes to Ca Boa.2H20 by air,
Supernatant liquid from solid-liquid separation process, supernatant liquid and absorbent C
It is also effective in the raw material preparation process where aC0, is mixed.

The amount of phosphoric acid compound supplied to the absorption process P (moA!/Hr
) is the inflow amount F (mo
A'41F) ratio P/F (mol/mol) is 6
In the above range, the adverse effect of aluminum compounds on desulfurization performance can be completely prevented, but in the range where P/F is 6 or less, desulfurization performance recovers in proportion to the amount of helicate compound added. The fluorinated compounds that flow into the absorption process are mainly from the exhaust gas, so if the cumulative concentration of feces in the exhaust gas and the flow rate of the exhaust gas are detected at the same time, the amount of fluorinated compounds transported can be determined from that amount. It is sufficient to determine the supply amount Y.

The present invention will be specifically explained below using Examples.

Example 1 An embodiment of the present invention will be explained with reference to FIG. 5'.

The exhaust gas 2 leaving the coal combustion equipment 1, which is composed of a coal combustion furnace and a Gascoo 5-0 dry dust collector, is So, 120
0ppm, dust 10~200019/m”N.

It is a gas at about 70°C containing HF 5-25 ppm' and about 2000 W? It is guided to the absorption tower 3 with N/Hr.

In the absorption tower 3, the exhaust gas is brought into contact with the exhaust gas injected from the spray nozzle 6, and is discharged from the absorption tower 6 as the exhaust gas 4 from which SOI and dust IF have been removed. In absorption tower 3, S
o, Ca8G1.In produced by Y absorption.

and the oxidized Ca5O6・iuma0, as well as the absorbent CaC0, which is a galsium compound, and the aluminum two-moof 9 complex sulfide produced by absorbing HF, -! A slurry containing two strokes is circulated from the absorption tower tfI ring positive 5 through the spray nozzle 6.

The circulation flow rate was 30 rrl/Hr.

The slurry containing the /rim compound and the aluenium-fluorine complex is circulated by the absorption tower circulation pump 5K, while being sent to the solid-liquid separation machine 8 from a portion of the lifecycle at a rate of about 1001/Hr.Ca5O1*2 It was divided into a solid substance 14 mainly composed of H and O and a supernatant liquid 9. The supernatant liquid 9 is sent to the absorbent takoku 10 and mixed with the charcoal slurry 11.
It was supplied as a wt% carbon slurry to the absorption tower 3 from the pipe J12 at a rate of about 125 l/H.

Dissolution a in the absorption tower circulation slurry when the dust concentration and HF concentration contained in the exhaust gas 2 are varied! Correlation data between the nium iococoncentration and the concentration of absorption and derivation So in the exhaust gas 4 is shown in FIG.

fI! It can be seen that as the IPfl aluminum ion concentration increases, the absorption and extraction So concentration also increases and the desulfurization performance decreases.

Some dissolution of the absorption circulation system! Correlation data between the concentration of two sulfur sulfur and the concentration of dissolved 71 element sulfur are shown in Figure 2.

Dissolved aluminum iodine: JI 11 degrees and the rate of increase in dissolved fluorine iodine concentration are almost constant ratio F/AJ = 3 to 4
It can be seen that (mol/mol).

Next, Fig. 3 shows how the desulfurization performance recovered when a phosphoric acid compound was supplied from Ico 13 to the absorption tower at various concentrations. A remarkable recovery effect on desulfurization performance was obtained. Nao Rai:
The phosphoric acid compound supplied to the absorption tower from J13 was acunium ricinate.

Both phosphoric acids showed similar effects.

Implementation 9112 In this example, SO was produced using the desulfurization apparatus shown in FIG.

1200ppm, HF7ppm, Tast 150W
/dN v was desulfurized from the coal combustion furnace exhaust gas and analyzed the composition of the upper liquid 9. A/11 degrees is t 7 mm.
The F-quality was 5.2 mrnol/l in ol/l. This supernatant was treated with licorice and rheum Ca3 (PO
4) Figure 4 shows the correlation between the AA' concentration and F-1 and the amount of licic acid and jJ lucium added when various concentrations of * were added.

Pdr/F'E L ratio 6.0 TeA7?5+1111
The degree is all A, and you can see that there is no L7.

[Brief explanation of the drawing]

FIG. 1 is a correlation diagram of experimental results in which desulfurization performance decreased as the concentration of Ae3+ ions increased in the circulating slurry of the absorption tower. FIG. 2 is a correlation diagram of liquid composition analysis results showing the Al ion concentration in the absorption tower circulation slurry and the ratio of F-io:J# degree. Figure 3 shows the absorption tower circulation stream containing A15+ioco.
Garlic: Correlation diagram of experimental results in which desulfurization performance was recovered when J acid oxide was added. Figure 4 is a correlation diagram of experimental results showing IIY that AlS + lS + ions - ions are removed when calcium phosphate is added to the supernatant containing Al ions and F'' ions. Figure 5 is an embodiment of the present invention. This is a diagram. 0/2345

Claims (1)

[Claims] In order to absorb the SO in the combustion exhaust gas by contacting the combustion exhaust gas containing aluminum-containing dust, SO, gas and HP gas with a slurry containing a calcium compound and an aluminum compound', the SO in the combustion exhaust gas is absorbed into the absorbent. A flue gas desulfurization method characterized by supplying a heavy licic acid or ricic acid compound in proportion to the amount of inflowing sucrose compounds.