JPH0549853A - Method for stack gas desulfurization method and device therefor - Google Patents

Abstract

PURPOSE:To obtain a high desulfurization rate with a simple system by lowering the reactivity of a desulfurizer and CO2 in a desulfurizer storage device and dust collector. CONSTITUTION:The humidity and/or CO2 concn. in the atmosphere of the desulfurizer storage device 4 for supplying the desulfurizer A consisting of >=1 kinds of compds. among alkaline metals or alkaline earth metals to a desulfurization column 3 or exhaust gas flue 6 and/or the dust collector 7 for capturing particles contg. the unreacted desulfurizer (the particles recovered in the dust collector 7 are partly supplied as the desulfurizer again to the desulfurization column 3 or the exhaust gas flue 6) is previously removed. The humidity and the CO2 can both be decreased simply by supplying the dry air and the desulfurization performance is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flue gas desulfurization method and apparatus using at least one oxide or hydroxide of an alkali metal or alkaline earth metal as a desulfurizing agent,
In particular, the present invention relates to a flue gas desulfurization method and apparatus having improved desulfurization performance.

[0002]

2. Description of the Related Art Sulfur compounds (SOx) are contained in exhaust gas discharged from heavy oil-fired and coal-fired boilers in thermal power plants.
Acidic hazardous substances such as HCl and HCl are usually 100 to 3000
Since it is contained in the proportion of ppm and is a causative substance of acid rain and photochemical smog, its effective treatment means is desired. Conventionally, a wet method (for example, limestone-gypsum method) or a dry method (activated carbon method) has been carried out, but the wet method has a high removal rate of harmful substances, but it is difficult to treat wastewater and it is necessary to reheat exhaust gas. However, there is a problem that a high removal rate cannot be obtained by the dry method because of high equipment cost and operation cost.
Therefore, it is desired to develop a desulfurization method capable of obtaining a high removal rate in a low-cost process without drainage.

As a desulfurization method for exhaust gas from a boiler or the like, in addition to the above-mentioned method, a semi-dry method in which slaked lime or its slurry is sprayed into the exhaust gas or limestone is directly dispersed in high temperature gas in a furnace or a flue to produce an acid A dry method for removing harmful substances has been proposed. These desulfurization methods are characterized by low equipment costs and operating costs, but all of them have a problem of low sulfur oxide removal rate.

FIG. 5 shows a typical flow sheet of a method of spraying slaked lime or quick lime into exhaust gas to react with SO ₂ in the exhaust gas and removing it with a dust collector. The temperature of the exhaust gas from the boiler 1 is lowered by the air heater 2 and guided to the desulfurization tower 3. The desulfurization agent A such as slaked lime in the desulfurization agent tank 4 is sprayed and supplied from the desulfurization agent supply line 5 into the flue 6 or the desulfurization tower 3, and reacts with acidic harmful substances such as SO ₂ in the exhaust gas. At this time, the water B is also supplied from the water supply line 8 into the flue 6 or the desulfurization tower 3 to lower the temperature of the exhaust gas and raise the humidity. At this time, even if the water B is supplied separately from the desulfurizing agent A,
The desulfurization agent A may be simultaneously supplied as a slurry. Particles C containing unreacted and reacted desulfurization agent and ash (hereinafter referred to as collected particles C) are collected together with the ash in the exhaust gas by the dust collector 7, and a part of them is collected in the desulfurization agent recycling line 9
Further, it is supplied to the desulfurization tower 3 again and reacts with acidic harmful substances such as SO ₂ in the exhaust gas. The remaining collected particles C are discarded. In such a method, the removal rate of acidic harmful substances (hereinafter referred to as desulfurization rate) is naturally influenced by the ratio of the desulfurization agent A supplied to the desulfurization tower 3 and SO _{2 in} the exhaust gas, and the ratio is The higher the value, the higher the desulfurization rate. When the desulfurization agent A such as slaked lime newly supplied into the flue 6 or the desulfurization tower 3 is constant, the recycling ratio of the particles containing the unreacted desulfurization agent collected by the dust collection device 7 (in the dust collection device It is also effective to increase the ratio of the collected particles to be supplied to the desulfurization tower, etc., and the same shall apply hereinafter), but if this is done, the amount of particles that must be processed by the dust collector 7 will increase, and the dust collector 7
There was a problem that the reacted desulfurization agent C collected in 1. had low reactivity with SO ₂ .

Reacted desulfurizing agent C collected by the dust collector 7
When the reactivity with SO ₂ is low, water or steam is added to the particles containing the unreacted desulfurizing agent to destroy the shell of the reaction product formed on the surface, and part of this is again used in the boiler 1 A method has also been proposed in which the removal rate is improved by spraying it into the exhaust gas or its exhaust gas (for example, US Pat. No. 3,481,28).
9, JP-A-60-19019, JP-A-61-358.
No. 27).

[0006]

In the above prior art, even if water or steam is added to the particles containing the unreacted desulfurizing agent collected by the dust collector, the desulfurization rate is not sufficiently recovered, and the particles are not collected. Even if the particles collected by the dust device are slurried and then spray-supplied again to the boiler, a high desulfurization rate cannot be obtained. That is,
In the above-mentioned conventional technique, there is a problem that the desulfurizing agent inside the desulfurizing agent storage device and the dust collecting device reacts with carbon dioxide (CO ₂ ) to deteriorate the desulfurizing agent performance. Therefore, an object of the present invention is to provide a flue gas desulfurization method for obtaining a high desulfurization rate with a simple system in consideration of the reactivity of the desulfurization agent and carbon dioxide (CO ₂ ) inside the desulfurization agent storage device and the dust collector. To provide a device.

[0007]

The above objects of the present invention can be achieved by the following constitutions. That is, in a flue gas desulfurization method of treating combustion exhaust gas by using one or more compounds as desulfurization agents among alkali metal or alkaline earth metal compounds, among desulfurization agents supplied to a desulfurization agent storage device and an exhaust gas treatment unit. , Collecting particles containing unreacted desulfurizing agent,
At least one of the humidity and the CO ₂ concentration in the atmosphere in at least one of the dust collectors for circulating and supplying a part thereof to the desulfurizing agent supply unit is adjusted to adjust the desulfurizing agent. Flue gas desulfurization method to supply in combustion exhaust gas,
Alternatively, in a flue gas desulfurization apparatus in which a desulfurizing agent supply unit composed of one or more compounds among alkali metal or alkaline earth metal compounds is provided in a combustion exhaust gas passage or a desulfurization tower,
Out of the desulfurizing agent supplied to the desulfurizing agent storage device for supplying the desulfurizing agent to the desulfurizing agent supply section and the exhaust gas treating section, particles containing unreacted desulfurizing agent are collected, and a part thereof is desulfurizing agent supply section. The flue gas desulfurization apparatus is provided with a means for adjusting at least one of the humidity and the CO ₂ concentration in the atmosphere in at least one of the dust collectors for circulating supply to the above.

Here, as means for adjusting at least one of the humidity and the CO ₂ concentration in the atmosphere in the desulfurizing agent storage device or the dust collecting device, water and CO ₂ in the air supplied to the device are adjusted. Can be provided in advance. Also, the humidity and / or CO ₂
As the concentration adjusting means, only means for supplying dry air may be provided in the apparatus.

[0009]

The [action] prior art, since the desulfurizing agent and CO ₂ are reacted within desulfurizing agent storage device and a dust collector, the flue gas desulfurization agent after reaction with CO ₂ when supplied to the exhaust gas flue or desulfurization tower It becomes difficult to react with SO ₂ . On the other hand, since the reaction between the desulfurizing agent and CO ₂ can be suppressed by lowering the humidity and the CO ₂ concentration inside the desulfurizing agent storage device or the dust collecting device, this C
It is possible to reduce the decrease in reactivity with SO _{2 in} the exhaust gas when the desulfurizing agent whose reaction with O ₂ is suppressed is supplied to the exhaust gas flue or the desulfurization tower.

The reason why the desulfurization performance is improved by previously removing water and CO ₂ in the air is not completely clear, but the following may be considered. That is, when the humidity or CO ₂ concentration inside the desulfurizing agent storage device or the dust collecting device is high, slaked lime (Ca (OH) ₂ ) or quick lime (CaO) used as a desulfurizing agent reacts with CO ₂ as shown in the following formula. To become calcium carbonate (CaCO ₃ ). Therefore, the reactivity with an acidic gas such as SO ₂ is lowered.

Ca (OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O CaO + CO ₂ → CaCO ₃ Furthermore, by supplying dry air to the dust collector, the trapped particles that have absorbed water are dried in the desulfurizer and the flue. At this time, the shell of the reaction product (calcium sulfite or calcium sulfate) on the surface of the desulfurizing agent particles is destroyed, so that the reactivity at the time of recycling is also considered to be one of the reasons.

[0012]

The present invention will be explained in more detail by the following examples, but it should not be construed as being limited to the following examples. Example 1 A case in which slaked lime is used as a desulfurizing agent to desulfurize exhaust gas from a coal-fired boiler will be described with reference to an example in which an apparatus according to the present invention is applied. The desulfurization process of the present invention is shown in FIG. This process is the same as that shown in FIG.
However, the structures of the desulfurizing agent storage device 4 and the dust collector 7 are different from those of the conventional example shown in FIG.

2 (a) and 2 (b) show the structures of an embodiment of the desulfurizing agent storage device 4 and the dust collecting device (bag filter) 7 according to the present invention, respectively. In the desulfurization agent storage device 4, when the desulfurization agent A is put into and discharged from the hopper 10, the air from which moisture and CO ₂ have been previously removed by the pretreatment device 11 is supplied to the hopper 10 from the line 13 by using the pump 12. To be done. Similarly, in order to adjust the humidity and CO ₂ concentration inside the dust collector 7, water and C
Air from which O ₂ has been removed in advance is supplied from the nozzle 15 at the lower part of the dust collector 7 through the line 14, and the collected particles C dropped from the filter cloth 16 of the bag filter are sent to the lower part of the dust collector 7 while flowing. .. In these devices, zeolite as a method of removing water in the air to be supplied in advance,
A method using a deliquescent salt such as calcium chloride and a separation membrane can be considered, but any method can be used as long as it can reduce the water content in the air. On the other hand, any method may be used for removing CO ₂ in the air, such as a method using various alkalis or other absorbents.

The desulfurization performance when coal A (with a sulfur content of 0.8% in coal) was burned was measured using the apparatus shown in FIGS. However, slaked lime is used as the desulfurization agent A, and water B is supplied to the desulfurization tower 3.
It was sprayed with. SO containing slaked lime A in exhaust gas
2.0 times the molar ratio of ₂ (hereinafter, the desulfurizing agent supply amount Ca /
Call S = 2.0. ), And water B was added in an amount of 3% by weight of the exhaust gas. Of the particles C collected by the dust collector 7, 50% by weight was discarded, and the remaining 50% was again spray-supplied to the desulfurization tower 3 through the line 9. Further, the humidity in the atmosphere was 70% relative humidity (temperature 30 ° C.), and the CO ₂ concentration in the atmosphere was 310 ppm. Reduced to 15% (temperature 30 ° C.) and 10 ppm, respectively.

At the outlet of the boiler 1 and the outlet of the dust collector 7, after removing water in the gas, the SO ₂ concentration was measured to be 640 ppm and 85 ppm, respectively. That is, 87% of SO _{2 in} the exhaust gas was removed (hereinafter referred to as desulfurization rate 87%).

Example 2 Using the same apparatus as in Example 1, the desulfurization rate was measured under the same conditions. However, only water was removed without removing CO ₂ in the atmosphere. FIG. 3 (a) shows the relationship between the relative humidity and the desulfurization rate at that time. It is effective to improve the desulfurization rate by removing only water without removing CO ₂ in the atmosphere. Further, (b) in FIG. 3 shows slaked lime (Ca (OH) ₂ ) and calcium carbonate (CaCO ₃ ) in the collected particles C at that time.
The ratio (% by weight) of calcium carbonate to the total weight of is shown, and the lower the water content, the lower the ratio of CaCO ₃ .

Example 3 Using the same apparatus as in Example 1, the desulfurization rate was measured under the same conditions. However, the desulfurizing agent supply amount Ca / S is 1.0 to 3.
It was changed to 0, and the desulfurization rate at that time was measured. The results are shown in (a) of FIG. 4, and even if the desulfurizing agent supply amount Ca / S was 1.0, a desulfurization rate of about 70% was obtained.

Example 4 Using the same apparatus as in Example 1, the desulfurization rate was measured under the same conditions. However, 5 coal types having different sulfur contents were used. Table 1 shows the sulfur content and the SO ₂ concentration at the outlet of the boiler 1 and the outlet of the dust collector 7 for each coal.
Shown in.

[0019]

[Table 1]

Example 5 Using the same apparatus as in Example 1, the desulfurization rate was measured under the same conditions. However, quick lime (CaO) and dolomite hydroxide (Ca.Mg (OH) ₂ ) were used as the desulfurization agent A, and their desulfurization performances were examined. The results are shown in Table 2.

[0021]

[Table 2]

Comparative Example 1 The desulfurization rate was measured under the same conditions as in Examples 1 and 4 for six types of coals, A to F, using the apparatus according to the prior art shown in FIG. However, water B is added by spraying 3% by weight of the exhaust gas into the flue, 50% of the internal weight ratio of the particles C collected by the dust collector 7 is discarded, and the remaining 50% is passed through the line 9. It was again spray-supplied to the desulfurization tower 3. The results are shown in Table 3. The desulfurization rate is lower than that of the flue gas desulfurization apparatus according to the present invention.

[0023]

[Table 3]

Comparative Example 2 Using the apparatus based on the prior art shown in FIG. 5, the desulfurizing agent supply amount Ca / S was 1.
The desulfurization rate was measured by changing from 0 to 3.0. The results are shown in (b) of FIG. The desulfurization rate is lower than that of the flue gas desulfurization apparatus according to the present invention.

Comparative Example 3 Example 5 was carried out using the apparatus according to the prior art shown in FIG.
In the same manner as above, quick lime (CaO) and dolomite hydroxide (Ca.Mg (OH) ₂ ) were used as the desulfurizing agent A,
Each desulfurization performance was investigated. The results are shown in Table 4.
The desulfurization rate is low (the SO ₂ concentration at the outlet of the dust collector 7 is high) as compared with the flue gas desulfurization device according to the present invention.

[0026]

[Table 4]

[0027]

According to the present invention, since the reaction between the desulfurizing agent and CO ₂ can be suppressed by lowering the humidity and the CO ₂ concentration inside the desulfurizing agent storage device and the dust collecting device, the desulfurizing performance in the desulfurizing tower can be improved. improves. Also, in the dust collector, the collected particles that have absorbed water are dried, and at this time, the shell of the reaction product (calcium sulfite or calcium sulfate) on the surface of the desulfurization agent particles is destroyed, so the reactivity when recycled to the desulfurization tower is high. Is improved.

[Brief description of drawings]

FIG. 1 is a flow sheet of a flue gas desulfurization apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic view of a desulfurizing agent storage device and a dust collecting device in FIG.

[Fig. 3] Relative humidity, desulfurization rate, and Ca of an example of the present invention
It is a relationship diagram of the ratio of CO ₃ .

FIG. 4 is a desulfurizing agent supply amount Ca / of an example of the present invention and a comparative example.
It is the experimental data which showed the relationship between S and the desulfurization rate.

FIG. 5 is a flow sheet of a conventional flue gas desulfurization apparatus.

[Explanation of symbols]

1 Boiler 3 Desulfurization Tower 4 Desulfurization Agent Storage Device 7 Dust Collection Device 13, 14 Dry Air Supply Line A Desulfurization Agent B Water C Captured Particles (particles containing unreacted and reacted desulfurization agent and ash)

Claims (4)

[Claims] 1. A flue gas desulfurization method for treating combustion exhaust gas by using one or more compounds of an alkali metal or alkaline earth metal compound as a desulfurizing agent, wherein the desulfurization is supplied to a desulfurizing agent storage device and an exhaust gas treating section. Humidity and CO ₂ concentration in the atmosphere of at least one of the dust collectors for collecting particles containing an unreacted desulfurizing agent and circulatingly supplying a part of them to the desulfurizing agent supply unit. Among these, at least any one is adjusted and the adjusted desulfurizing agent is supplied to combustion exhaust gas, The flue gas desulfurization method characterized by the above-mentioned. 2. In a flue gas desulfurization apparatus in which a desulfurizing agent supply section comprising one or more compounds of alkali metal or alkaline earth metal compounds is provided in a combustion exhaust gas passage or a desulfurization tower, the desulfurizing agent is supplied to the desulfurizing agent supply section. Of the desulfurizing agent supplied to the desulfurizing agent storage device and the exhaust gas treating section for supplying the desulfurizing agent, particles for collecting unreacted desulfurizing agent are collected and a part thereof is circulated and supplied to the desulfurizing agent supplying section. A flue gas desulfurization apparatus comprising means for adjusting at least one of humidity and CO ₂ concentration in the atmosphere in at least one of the dust apparatuses. 3. As means for adjusting at least one of humidity and CO ₂ concentration in the atmosphere inside the desulfurizing agent storage device or the dust collecting device, water and CO ₂ in the air supplied into the device are adjusted. The flue gas desulfurization apparatus according to claim 2, further comprising means for removing in advance. 4. As a means for adjusting at least one of humidity and CO ₂ concentration in the atmosphere in the desulfurizing agent storage device or the dust collecting device, a device for supplying dry air is provided in the device. The flue gas desulfurization apparatus according to claim 2, wherein