JPS5948133B2 - Wet flue gas desulfurization method using slag - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving economic efficiency in a wet flue gas desulfurization method using slag.

Mining slag (blast furnace slag, converter slag, open hearth slag, electric furnace slag, etc.) is partially used as raw material for steelmaking, cement raw material, fertilizer, roadbed material, etc., but most of it is disposed of in landfills, etc., and its utility value is low. low.

However, slag contains 40 to 50% calcium oxide, and it is well known that this calcium oxide can be used to remove sulfur dioxide gas from flue gas.

That is, slag is pulverized into fine powder and suspended in water to form a slurry liquid, and the flue gas is washed with this slurry liquid, thereby removing sulfur dioxide gas in the flue gas according to Equation 0.

CaO (mine slag) +5O2=CaSOa""■ Calcium sulfite has limited uses, so it is usually oxidized to gypsum and recovered.

In the case of a wet flue gas desulfurization method using lime (lime-gypsum method), a slurry containing calcium sulfite is extracted from the absorption tower, air oxidized in an oxidizer, and recovered as gypsum.

In the case of slag, A1203,5iOz, FezOa, M
Contains nO, etc., and these components have oxidation catalytic properties, so under the conditions where this catalyst acts, the 0-type absorption reaction proceeds simultaneously with the 0-type absorption reaction, and calcium sulfite is converted to gypsum in the absorption tower. It is oxidized and recovered.

CaSO3+y202=CaSO4・・・■ In this way, the flue gas desulfurization method using slag absorbs sulfur dioxide gas and converts it into gypsum in the absorption tower, so there is no need for the oxidation equipment required for the normal lime-gypsum method. It has excellent advantages.

The following methods have been reported as practical operating methods for wet flue gas desulfurization using slag.

1 In the case of one absorption tower, the pH of the absorption slurry liquid is set to 1.5.
How to drive as ~4.

2 In the case of two absorption towers, as seen from the gas side, the pH of the slurry liquid in the first absorption tower is made acidic, and the pH of the slurry in the second absorption tower is made acidic.
How to operate in neutral or alkaline conditions.

All of the above methods are characterized in that the pH of the slurry in the absorption tower from which the slurry is extracted for gypsum recovery is limited to an acidic pH of about 3.

This is because, in general, the lower the pH, the faster the oxidation reaction rate of calcium sulfite to gypsum, and this is true even in the presence of an oxidation catalyst, and the absorption tower is operated as oxidation to convert it into gypsum.

The wet flue gas desulfurization method using slag can be said to be an economical method as it makes effective use of slag that has little utility value, but conventional methods usually operate only on the acidic side, around pH 3, and therefore have various problems. , a solution is desired.

1. Due to the low pH of the absorption slurry liquid, the corrosive environment for equipment materials related to the absorption tower is severe.

For this reason, high-quality equipment materials must be used, which increases installation costs and causes many problems due to corrosion.

2. As is well known, the absorption rate of sulfur dioxide gas decreases as the pH of the absorption slurry liquid decreases, so in order to maintain a high absorption rate at low pH, it is necessary to increase the performance of the absorption tower.
For example, it is necessary to build a large absorption tower by increasing the height of the tower.
This also increases equipment costs and operating costs.

The present invention aims to solve the above-mentioned problems and improve the economic efficiency of the wet flue gas desulfurization method using slag.

That is, by keeping the pH of the absorption slurry liquid at 5 or more and within the range shown by formula 0, without making the pH unnecessarily low,
The absorption reaction and oxidation reaction to gypsum proceed simultaneously.

log pH≦-7,6-S +0.90・・・・・■
pH: Absorption slurry liquid pH 8: Ratio of sulfur dioxide gas concentration (SO□ (%), ) to oxygen concentration (02 (%)) at the absorption tower inlet 5 = SO□ (%) 10□ (%) Aspects of the present invention will be explained in FIG.

Exhaust gas 13 containing sulfur dioxide gas enters absorption tower 1 and pump 5
After being cleaned by an absorption slurry 15 containing slag that is circulated by the slag and removing sulfur dioxide gas, it becomes clean gas 14 and is discharged into the chimney.

On the other hand, the flow of absorption slurry is made by supplying powder or slurry slag (blast furnace, converter slag, open hearth slag, electric furnace slag, etc.) 12 and water 11 to a raw material slurry mixing tank 2, stirring, mixing, and adjusting the concentration to form a raw material slurry. The absorption tower 1 is closed by the pump 4.
supplied to

In the absorption tower 1, the absorption slurry 15 is circulated by the pump 5 to wash and absorb sulfur dioxide gas from the exhaust gas.

In this case, the values detected by the sulfur dioxide gas and oxygen concentration detector 6 at the inlet of the absorption tower are input into the pH setting device 7, and the pH of the absorption slurry liquid is set to 5 or higher and according to the formula 0.

In the pH controller 9, the control valve 10 is operated based on the pH value set by the pH setting device 7 and the pH value of the absorption slurry liquid detected by the pH detector 8, and the raw material slurry 17 is supplied to the absorption tower 1.
By controlling the supply amount of
is controlled to the set value.

This allows the absorption reaction and the gypsum reaction to proceed simultaneously.

In addition, when the sulfur dioxide gas and oxygen concentrations at the absorption tower inlet are stable, the sulfur dioxide gas and oxygen concentration detector 6 and the pH setting device 7 are not provided, and the pH is set in advance to a value of 5 or higher using the 0 formula. and set this pH value to p
It is sufficient to input it into the H controller 9.

One part 16 of the circulating absorption slurry liquid is extracted to a gypsum recovery process 3, and after being subjected to neutralization treatment etc., gypsum 18 is recovered.

The water separated in the gypsum recovery process 3 is transferred to the raw material slurry mixing tank 2.
The water is recycled and used as feed water 11, etc.

Although FIG. 1 shows the case of one absorption tower, it is also possible to use a plurality of absorption towers if necessary.

In this case, the pH of all absorption towers should be 5 or higher and 0.
However, since detection of sulfur dioxide gas and oxygen concentrations, pH control, etc. are complicated, it is preferable to use the absorption tower at the final stage from the viewpoint of the slurry flow, that is, the absorption tower that extracts the gypsum slurry to the gypsum recovery process. The pH may be kept within the range of 5 or more and 0, and the pH of other absorption towers may be appropriately selected from the viewpoint of absorption rate, etc.

The advantage of having a plurality of absorption towers is that the height of the absorption tower can be lowered and the absorption tower can be made more compact.

When setting the pH of the slurry liquid in the absorption tower to a pH of 5 or more and according to the 0 formula, it is of course possible to detect the sulfur dioxide gas and oxygen concentration in the exhaust gas and manually set the pH to a pH of 5 or more and according to the 0 formula. However, it is preferable to detect the sulfur dioxide gas and oxygen concentrations, and automatically set the pH to 5 or more according to the 0 formula.

In this case, if the sulfur dioxide concentration or oxygen concentration is stable, detection of stable components is omitted, and the fixed value is p.
Of course, it is possible to input it into the H setting device 7.

After setting the pH, the pH of the absorption slurry may be controlled dynamically by a conventional method, for example, the method shown in FIG.

In addition, if a cooling tower is placed in front of the absorption tower, the detection position of the sulfur dioxide gas and oxygen concentrations at the absorption tower entrance can be moved to the cooling tower entrance, since sulfur dioxide gas absorption in the cooling tower is small.

Normally, the exhaust gas has a considerable temperature, so either a gas cooling tower that circulates water is placed in front of the absorption tower, or the exhaust gas is directly introduced into the absorption tower so that it also functions as a cooling tower.

When a cooling tower is installed, dust is removed by the cooling tower and dust accumulates in the circulating fluid of the cooling tower, so it is necessary to extract the fluid as appropriate.

According to an analysis example of the solid components in the liquid extracted from the cooling tower when the sintering exhaust gas after cyclone removal is introduced into the cooling tower, 54% of the solid content is found in gypsum (the concentration of calcium oxide in the sintering dust that does not dissolve in water is The quality of the gypsum recovered from the absorption tower shown in Table 3 below is not much different, and the quantity is also small. Therefore, the liquid extracted from the cooling tower is mixed with the gypsum slurry extracted from the absorption tower, and the gypsum slurry is extracted from the absorption tower. The quality of the gypsum is hardly affected even if it is recovered.

Furthermore, when the gas is directly introduced into the cooling/absorption tower, it is also removed in this tower and dust is mixed into the gypsum, but for the same reason as mentioned above, the quality of the gypsum is not impaired.

The concentration of the raw material slag slurry in carrying out the present invention is not particularly limited in terms of the absorption reaction of sulfur dioxide gas or the gypsum reaction, so it may be within a range that can be handled as a slurry, but it is preferably 3 to 15% in practice.

Next, the principle of the present invention will be explained based on experimental results.

The experimental conditions are as follows.

Experimental equipment: 1 plate tower, gas volume 1100ON'/H Exhaust gas: Sintering exhaust gas, combustion exhaust gas Desulfurization agent: Converter Slag type oxidation reaction rate is based on pH 1 temperature of absorption slurry when lime is used It is known that it is affected by the oxygen partial pressure in exhaust gas, but there are few reports regarding mine slag.

According to the experimental results of the present inventors, in the case of slag, the oxidation reaction rate of formula 0 is extremely fast compared to the case of lime due to the catalytic action, but under all conditions, it does not turn into gypsum in the absorption tower, and it turns into gypsum. It has been found that there is a certain range determined by two factors: absorption slurry liquid pH and absorption tower inlet 502 (%) and 102 (%).

In other words, the experimental results are shown in Figure 2, and gypsum formation in the absorption tower can only be achieved when the pH of the absorption rally liquid is within the range shown by the formula .

In previous reports, batch-type experiments (only the exhaust gas is continuously introduced into the absorption tower, and the slag slurry is supplied to and taken out from the absorption tower) The slag slurry is circulated and the exhaust gas is cleaned.

Therefore, the pH of the slurry gradually decreases due to absorption of sulfur dioxide gas.

) According to the results of SO2, 0,1% sintering exhaust gas (0
If it is 2-12%, SO□(%)102(%)-8,3
In the case of X1073), there is data that says that unless the pH of the absorption slurry liquid is 5 or less, it will not turn into gypsum in the absorption tower, which is different from the results shown in Figure 2.

This is because the results shown in Figure 2 are from a continuous experiment (exhaust gas is continuously introduced into the absorption tower, and the pH of the sulfur dioxide gas absorption slurry liquid decreases, but in order to compensate for this, the raw material slag slurry is supplied to the absorption tower). The pH of the absorption slurry liquid is maintained constant by withdrawing the absorption slurry corresponding to the amount supplied.

), which is due to the difference in the experimental method, and does not negate the results shown in Figure 2.

As is well known, when lime is used, the absorption rate of sulfur dioxide gas begins to decrease when the pH of the absorption slurry liquid drops to about 6 or below, so the normal lime-gypsum method is operated at a pH of about 6 or above. , the same results were obtained in experiments conducted by the present inventors.

In the case of slag, the present inventors conducted an experiment using an absorption tower with the same tower height and the same operating conditions as in the case of lime, and found that the absorption rate decreased at pH = 5 or less, which is slightly lower than in the case of lime.

It was also found that if the height of the absorption tower was made very high, the absorption rate could be maintained even at pH -5 or lower.

However, increasing the height of the absorption tower not only increases the equipment cost, but also increases the pressure loss of the tower, which increases the blowing power, that is, the electricity cost, which impairs economic efficiency.

Therefore, even in the case of slag, the p of the absorption slurry liquid is
H should be maintained at 5 or higher to increase the absorption rate, and the operation should be carried out within a range that takes advantage of the greatest advantage of using slag, which is that no oxidation equipment is required because it is turned into gypsum in the absorption tower.

According to Figure 2, 5O2 (%) 102 (%) ≦26 X
When it is 10-30210%, it becomes 802≦0.26%, which sufficiently covers the exhaust gas range of industrially implemented flue gas desulfurization equipment.

), even if the pH of the absorption slurry liquid is 5 or more, which allows a high absorption rate to be maintained, it can be turned into gypsum in the absorption tower, and the greatest advantage of using slag, which is that an oxidizer is not required, is not impaired.

The present invention has been described in detail based on the experimental results as described above, and as is clear from the above, it is possible to maximize the economic efficiency of the wet flue gas desulfurization method using slag by implementing the present invention. can.

According to the present invention, it is possible to operate with the pH of the slurry liquid as high as possible, so a high absorption rate can be obtained without unnecessarily increasing the absorption tower equipment, and it is possible to lower the quality of equipment materials due to high pH operation, and moreover, it is possible to avoid equipment troubles. is resolved.

Next, a detailed explanation will be given of the present invention, which was carried out generally through the steps shown in FIG.

Using a plate tower as an absorption tower and converter slag (Table 1) as a desulfurization agent, a desulfurization experiment was conducted on flue gas (100ONm3/H), and as shown in Table 2, a high desulfurization rate was obtained. Ta.

Further, the recovered reaction product was completely converted into gypsum as shown in Table 3.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining an embodiment of the present invention, and FIG. 2 is a diagram for explaining the present invention in detail (experimental results). 1 is an absorption tower, 2 is a raw material slurry mixing tank, 3 is a gypsum recovery process, 4 and 5 are pumps, and 6 is an SO2. o2 detector, 7 is p
H is a setting device, 8 is a pH detector, 9 is a pH controller, 10 is a control valve, 11 is water, 12 is slag, 13 is exhaust gas, 14 is clean gas, 15 to 17 are slurry paths, and 18 is plaster.

Claims (1)

[Claims] 1 [t' In a wet flue gas desulfurization method using slag, the pH of the absorption slurry liquid is kept at 5 or more and within the range shown by the formula 0, and within the pH range, desulfurization and gypsumization are performed at the same time. A wet flue gas desulfurization method characterized by carrying out the following. log; pH≦-7,6-S +0.90-...
- ■ pH: Absorption slurry liquid pH 8: Ratio of sulfur dioxide gas concentration (SO2 (%)) to oxygen concentration (02 (%)) at the inlet of absorption tower 5 = SO2 (%) 10□ (%)