JPH0557139A - Lime blowing desulfurization - Google Patents

Abstract

PURPOSE:To suppress the reaction of acidic gases except SO2 in a combustion waste gas with a desulfurizing agent of a calcium-containing compound to improve the desulfurization function by using a calcium-containing compound wich which a chlorine compound is mixed as the desulfurizing agent and blowing the desulfurizing agent to a combustion waste gas flowing route. CONSTITUTION:A mixture of a calcium-containing compound with a chlorine compound is used as a desulfurizing agent and the desulfurizing agent is blown to a combustion waste gas flowing route in a boiler furnace 1 or a chimney 5. For example, using a mixture of a slurry or powder of calcium chloride with limestone as a desulfurizing agent, it is blown to the high temperature part in the boiler furnace 1 or the chimney 5. As a result, calcium carbonate production due to the reaction of carbondioxide gas in the combustion waste gas is suppressed, so that the desulfurization efficiency at the low temperature part is heightened and the desulfurizing agent is used efficiently. Also, owing to the addition of the chlorine compound such as calcium chloride to the desulfurizing agent and to the use of it, water in the combustion waste gas becomes easy to be adsorbed and the desulfurizing function of desulfurization at low temperature is heightened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a desulfurization method for removing sulfur oxides (hereinafter referred to as SO ₂ ) from combustion exhaust gas, and more particularly to a desulfurization method in which a fine particle desulfurizing agent is used in a boiler furnace and a flue.

[0002]

2. Description of the Related Art Desulfurization equipment for power generation boilers is
The wet desulfurization method called the limestone-gypsum method is the mainstream. This limestone-gypsum method mixes finely powdered limestone and water to form a slurry, and by contacting this slurry with the exhaust gas, the sulfur oxides in the exhaust gas are absorbed by the slurry to perform desulfurization, and the sulfur in the exhaust gas is removed. It is a high-performance desulfurization method that recovers oxides as gypsum.

On the other hand, a typical example of the dry method is an activated carbon desulfurization method. In either case, the desulfurization performance is high, but there is a problem in that the equipment is heavy equipment and the initial cost is high. Further, in the former limestone-gypsum method, wastewater treatment and reheating of exhaust gas are required.

On the other hand, a simple desulfurization method of spraying a fine-particle desulfurizing agent into a boiler furnace has been proposed.

[0005]

However, this simple desulfurization method has a problem that the desulfurization performance is low. In order to improve the desulfurization performance of the simple desulfurization method, it is necessary to increase the amount of desulfurization agent sprayed into the boiler furnace or to make the particle size of the desulfurization agent finer. However, when a large amount of desulfurizing agent is sprayed into the furnace, there is a problem that unreacted desulfurizing agent is mixed in the coal ash collected by the electrostatic precipitator and new secondary pollution is generated during the dumping process. On the other hand, the method of pulverizing the desulfurizing agent has a problem that the cost of pulverizing the desulfurizing agent becomes high.

Another problem in using the simple desulfurization method is that the combustion exhaust gas contains an acidic gas other than SO ₂ which reacts with the desulfurizing agent. For example, carbon dioxide gas (hereinafter sometimes referred to as CO ₂ ) is contained in the combustion exhaust gas at a concentration of 50 to 200 times that of SO ₂ . Therefore, the desulfurizing agent composed of a calcium-based compound such as limestone or slaked lime once sprayed in the boiler furnace reacts with an acidic gas such as SO ₂ and at the same time reacts with CO ₂ to produce calcium carbonate. However, calcium carbonate itself is C
The reactivity with SO ₂ is lower than that of aO, etc., which causes a decrease in desulfurization performance.

Therefore, in order to carry out a desulfurization reaction in a boiler furnace by spraying a desulfurizing agent composed of a calcium-based compound into the furnace and the flue gas, the reactivity with SO ₂ is selectively increased in the flue gas passage and carbon dioxide is added. To reduce the production of calcium,
It is important for improving desulfurization performance.

An object of the present invention is to provide a simple desulfurization process of improving the desulfurization performance by suppressing the reaction between the desulfurizing agent comprising S0 ₂ other acid gases with the calcium compound in the combustion exhaust gas.

[0009]

The above object of the present invention can be achieved by the following main constitutions. That is, a mixture of a chlorine compound and a calcium compound is used as a desulfurizing agent, and the desulfurizing agent is blown into a combustion exhaust gas passage in a boiler furnace or a flue by a lime blowing desulfurization method, or a calcium compound is mixed with a chlorine compound. Further, it is a lime blowing desulfurization method in which a slurry obtained by adding water to this is used as a desulfurizing agent and is blown into a combustion exhaust gas passage in a boiler furnace or a flue.

When a desulfurizing agent composed of a calcium compound is blown into the boiler furnace, the desulfurizing agent becomes CaO and reacts with the acid gas in the combustion exhaust gas. Carbon dioxide is less reactive than SO _2, but since the exhaust gas contains several hundred times more than SO ₂ , the amount of calcium carbonate produced increases as the residence time increases, and the desulfurization performance decreases. The production reaction of calcium carbonate progresses as the temperature rises, but calcium carbonate itself undergoes a decomposition reaction at 800 ° C. or higher and decomposes into CaO and CO ₂ . Therefore, in the lime-blown desulfurization method, calcium carbonate produced by the reaction of CaO and CO ₂ occurs in a temperature range of 800 ° C or lower.

As a result of the investigation by the present inventors, it was found that the reactivity of CO ₂ with CaO is reduced when chlorine coexists on the side of CaO which is solid. It has been clarified that when a calcium compound and a chlorine compound coexist, a chlorine film is formed on the surface of the desulfurizing agent for the calcium compound, which lowers the reactivity with CO ₂ . Therefore, when a chlorine compound coexists with the calcium-based compound, the amount of calcium carbonate produced from CaO produced in the exhaust gas passage in the high temperature portion of the furnace or the flue can be reduced.

When a chlorine compound coexists with the calcium compound, calcium chloride (Ca) is formed on the surface of the desulfurizing agent.
Cl ₂ ) is produced. Therefore, when water is supplied in the low temperature portion of the exhaust gas passage to increase the water concentration in the combustion exhaust gas, the water is adsorbed by calcium chloride (CaCl ₂ ).

Thus, in low-temperature desulfurization, S in the combustion exhaust gas is
O ₂ is once adsorbed by the water adsorbed on the desulfurizing agent, and H ₂ SO
Collected as ₃ . The collected H ₂ SO ₃ is characterized in that it reacts with CaO in the desulfurizing agent to produce CaSO ₃ .

By including a chlorine-based compound in the desulfurizing agent sprayed in the furnace or the flue, the reaction between the desulfurizing agent and CO ₂ is suppressed in the high temperature part of the furnace, and CaCl 2 is contained in the low temperature part in the exhaust gas passage. _{By 2} , water can be adsorbed and desulfurization performance can be improved.

[0015]

[Function] Taking limestone as an example of the calcium-based desulfurizing agent,
The operation of the present invention will be described. When fine particles of about 10 μm obtained by crushing limestone are blown into the temperature range of 1000 to 1200 ° C., a decarboxylation reaction occurs and decomposes into CaO and CO ₂ .
The reaction is represented by the following equation. CaCO ₃ → CaO + CO ₂ (1)

In the present invention, a chlorine compound is added to the desulfurizing agent. As the chlorine compound, calcium chloride is shown here as an example. Calcium chloride is mixed with limestone in the form of slurry or powder and is blown into the high temperature part in the furnace or the flue. The reaction at this time is shown by the following equation. CaCO ₃ + CaCl ₂ → CaO ・ CaCl ₂ + CO ₂ (2)

CaO.CaCl ₂ is a boundary film of calcium chloride formed on the surface of CaO. CaO · CaCl ₂ produced by the equation (2) is an acidic gas (SO ₂ ,
HCl, F, etc.) to react with CaSO ₄ , CaSO ₃ , C
It produces aCl ₂ , CaF _2, etc. Further, since the combustion exhaust gas contains about 10% of CO ₂ , CaO.
CaCl ₂ has the property of reacting with CO ₂ and producing CaCO ₃ . Therefore, according to the present invention, unreacted CaO.CaCl ₂ supplied to the flue along with the furnace or the combustion exhaust gas is supplied.
Water is adsorbed by supplying water to CaO generated on the surface, and the reaction of CaO.CaCl ₂ and CO ₂ produces C
Generation of aCO ₃ can be suppressed.

The water adsorption reaction formula of CaO.CaCl ₂ is shown in the following formula. CaO ・ CaCl ₂ + nH ₂ 0 → CaO ・ CaCl ₂・ nH ₂ O (3) CaO ・ CaCl ₂・ nH ₂ O in the formula (3) is CaO ・ Ca
A state in which n molecules of water are adsorbed on the surface of Cl ₂ is shown, but the amount of adsorbed water largely depends on the water concentration of the combustion exhaust gas.

In the desulfurization reaction in the flue, particularly at 150 ° C. or lower, H ₂ SO ₃ is produced through the reaction of SO ₂ absorbed by the adsorbed water represented by the formula (3). The reaction formula is represented by the following formula. SO ₂ + H ₂ O → H ₂ SO ₃ (4)

H ₂ SO ₃ is fixed as CaSO ₃ by the reaction shown by the following formula with CaO of the formula (1). H ₂ SO ₃ + CaO → CaSO ₃ · H ₂ O (5)

The desulfurization reaction in the furnace or the flue of the present invention has been described above. By suppressing the reaction between CaO generated in the high temperature part in the furnace or the flue and CO ₂ in the combustion exhaust gas as much as possible, the flue Highly active C required for desulfurization reaction performed in
Since aO can be supplied, desulfurization performance can be improved.

[0022]

EXAMPLE An example of the present invention will be described below. In FIG. 1, pulverized coal 3 and air 4 are supplied to and burned in a coal-fired power generation boiler furnace 1. The combustion exhaust gas in the boiler furnace 1 is introduced into the low temperature desulfurization tower 8 through the flue 5. The outlet combustion exhaust gas 9 of the low temperature desulfurization tower 8 is introduced into the dust collector 10, the solid matter in the combustion exhaust gas is recovered from the flow passage 11, and the processing gas 12 that has exited the dust collector 10 is exhausted from the chimney 13.

The desulfurizing agent 2 composed of the calcium compound and the chlorine compound of this embodiment is blown into the boiler furnace 1. Further, the desulfurizing agent 6 can be blown into the flue 5.
Further, in order to enhance the desulfurization performance in the flue 5, it is effective to spray water 7 on the flue 5 to lower the temperature of the combustion exhaust gas. The low temperature desulfurization tower 8 is installed in the combustion exhaust gas line of the flue 5.

As shown in FIG. 2, the thermal decomposition characteristics of slaked lime and limestone as calcium compounds, the dehydration reaction of slaked lime begins at around 300 ° C., and the thermal decomposition reaction is completed at around 500 ° C. Then, this reaction produces CaO. For limestone, 6
The decarboxylation reaction starts at around 00 ° C, and the thermal decomposition is completed at around 870 ° C. Therefore, in order to blow the calcium-based compound into the furnace or the flue, the decomposition temperature for producing CaO differs depending on the calcium-based compound,
It is necessary to spray in the optimum temperature range in the boiler.

FIG. 3 is an embodiment showing the effect of the present invention.
C of desulfurization agent in which slaked lime is used as a calcium compound and 5% of calcium chloride is mixed as a chlorine compound
Shows the results of examining the reactivity with O _2. Slaked lime alone and calcium chloride (CaCl ₂ · 2H ₂ O) in slaked lime
For two kinds of desulfurization agents mixed with
° C., is contacted with a gas containing CO ₂ 10% After 30 minutes of thermal decomposition was determined increase in weight due to the adsorption of CO _2. Compared with CaO, which is obtained by thermally decomposing slaked lime at 700 ° C, the substance obtained by thermally decomposing a mixture of slaked lime and calcium chloride at 700 ° C clearly has a different reactivity with CO ₂ ,
The amount of CO ₃ produced is different. The slaked lime added with calcium chloride has an effect of reducing the amount of calcium carbonate produced to about 1/5 as compared with the one not containing calcium chloride.

Therefore, the production of calcium carbonate can be suppressed by mixing the chlorine-based compound with the desulfurizing agent composed of the calcium-based compound of the present embodiment and blowing the mixture into the furnace or the flue.

The desulfurization performance when a desulfurizing agent mixed with a chlorine-based compound was supplied to a reaction field simulating the inside of a furnace or a flue was examined. The experimental apparatus was examined with a reaction tube simulating the inside of the furnace shown in FIG. The reaction tube is made of ceramic and is 2 m long
The inner diameter is 13 mm. It was heated with a Kanthal wire from the outside of the reaction tube. The desulfurizing agent was atomized and supplied from the upper part of the reaction tube, and brought into contact with the simulated combustion exhaust gas in a cocurrent flow. Simulated combustion exhaust gas composition is SO ₂ 1500 ppm, NO 500 pp
m, CO ₂ 10%, O ₂ 6%, water content 10%, balance N ₂ .

In the embodiment of FIG. 5, slaked lime and limestone are used as a desulfurizing agent as a calcium compound, and calcium chloride is added to 5
% Added to each. In FIG. 5, white circles are slaked lime alone, and black circles are desulfurization agents obtained by adding 5% of calcium chloride to slaked lime. The Ca / S and the desulfurization rate when the reaction temperature is set to 650 ° C are shown. Further, the white triangles in FIG. 5 are the results when limestone alone was used, and the black triangles are the experimental results when the reaction temperature of the desulfurizing agent in which 5% of calcium chloride was added to limestone was set to 1000 ° C.

Desulfurization agents to which calcium chloride has been added have a tendency that the desulfurization rate decreases by several% in a high temperature range. Here, when the carbon content of each desulfurizing agent after being brought into contact with the simulated combustion exhaust gas was measured, it was 1/3 to 1/1 in the sample to which calcium chloride was added, as compared with that of slaked lime alone.
There is an effect that can be reduced to 6. Therefore, it was confirmed that the desulfurizing agent containing calcium chloride has an effect of suppressing the production of calcium carbonate.

Here, the desulfurization performance at 150 ° C. or lower was investigated using the sample obtained in the experiment of FIG. Experiment 50 inner diameter
0 mm × supplying combustion exhaust gas into a reaction tube length 2500 mm, by adjusting the SO ₂ concentration 950 ppm, was bubbled through the sample thereto. A nozzle was attached to the reaction tube so that water could be sprayed so that the temperature of the reaction tube outlet could be changed.

The example of FIG. 6 is a result obtained by using the sample obtained in the experiment of slaked lime alone shown in FIG. 5, and Ca / S was changed to 1, 2 and 3 as parameters. The desulfurization rate increases as the water supply increases and increases as Ca / S increases. At this time, the amount of water supplied and the temperature at the outlet of the reaction tube had a relationship as shown in FIG.

On the other hand, the result obtained by using the sample obtained by the experiment in which calcium chloride was added to slaked lime is shown in FIG.
Shown in. Compared with the sample of slaked lime alone in Fig. 6, the same Ca / S
Even with a molar ratio (adjusted to the same supply amount as in the case of slaked lime alone), the sample obtained in the experiment in which calcium chloride was added is effective in increasing desulfurization performance by 7 to 16%.

This effect is that by adding calcium chloride to the desulfurizing agent, the reaction between CaO and CO ₂ can be suppressed and the production of calcium carbonate can be reduced, and in the desulfurization reaction at 150 ° C. or less, the chloride formed on the surface of the particles can be reduced. It is considered that water is easily adsorbed by calcium.

In this embodiment, a chlorine compound is added to a calcium compound, but in order to exert the effect of the chlorine compound, it may be mixed as a powder, but it is mixed in a slurry form and evaporated. It is also possible to dry it and blow it into the furnace or flue, or spray the slurry directly into the furnace or flue.

In addition to SO ₂ gas, the combustion exhaust gas contains N
_{Ox and the} like are contained, and nitrogen oxides can be reduced to N ₂ at the same time as desulfurization by the calcium compound.
For this purpose, a desulfurizing agent to which urea, cyanuric acid or the like is added as a reducing agent can be used as a desulfurizing and denitrifying agent. At this time, it is particularly effective to make calcium compounds, chlorine compounds, urea and cyanuric acid into slurry and add iron oxide to the slurry to enhance the denitration performance.

Further, the solid matter recovered by the dust collector 10 (FIG. 1) contains unreacted CaO and substances effective for the desulfurization reaction, and the dust is collected when the desulfurizing agent is adjusted. Bowl 10
It is also possible to add some of the material recovered from the.

Further, it is preferable to add a chlorine compound to the desulfurizing agent of this embodiment, but seawater or the like can be used instead of water at the time of adjusting the slurry as an alternative to the addition of the chlorine compound.

[0038]

EFFECTS OF THE INVENTION According to the present invention, by using a desulfurizing agent in which a chlorine compound is mixed with a calcium compound, generation of calcium carbonate due to a reaction of carbon dioxide gas in combustion exhaust gas is suppressed, so that desulfurization performance is improved in a low temperature portion. Therefore, the desulfurizing agent can be effectively used.

Further, by adding a chlorine compound such as calcium chloride to the desulfurizing agent and using it, water in the combustion exhaust gas is more easily adsorbed, and the desulfurization performance in low temperature desulfurization is enhanced. Furthermore, when a denitrifying agent is added to a desulfurizing agent containing a chlorine compound, a denitrifying effect is also obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a process in which the present invention is applied to exhaust gas of thermal power generation.

FIG. 2 is a diagram showing thermal decomposition characteristics of slaked lime and limestone used as a desulfurizing agent.

FIG. 3 is a diagram showing the reactivity with carbon dioxide when calcium chloride is added to slaked lime.

FIG. 4 is a diagram showing a reaction tube simulating the inside of a boiler furnace.

FIG. 5 is a diagram showing high-temperature desulfurization characteristics of slaked lime and a desulfurizing agent obtained by adding calcium chloride to slaked lime.

FIG. 6 is a diagram showing low-temperature desulfurization characteristics using a sample after high-temperature desulfurization with slaked lime.

FIG. 7 is a diagram showing a relationship between a water supply amount and a temperature of a combustion exhaust gas in low temperature desulfurization.

FIG. 8 is a diagram showing low temperature desulfurization characteristics using a sample after a desulfurizing agent obtained by adding calcium chloride to slaked lime was used in high temperature desulfurization.

[Explanation of symbols]

 1 Boiler furnace 2 Desulfurization agent 3 Fine coal 4 Air 5 Flue 6 Desulfurization agent 7 Water 8 Low temperature desulfurization tower 9 Combustion exhaust gas passage 10 Dust collector 11 Solid matter 12 Treatment exhaust gas 13 Chimney

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Miyadera 4026 Kujimachi, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Ltd. Company Kure Institute

Claims (7)

[Claims] 1. A lime-blown desulfurization method, characterized in that a mixture of a calcium compound and a chlorine compound is used as a desulfurizing agent, and the desulfurizing agent is blown into a combustion exhaust gas passage in a boiler furnace or a flue. 2. A calcium compound is mixed with a chlorine compound, and water is added to the mixture to make a slurry, which is used as a desulfurizing agent and is blown into a combustion exhaust gas passage in a boiler furnace or a flue. A method for desulfurization by blowing lime. 3. The desulfurizing agent is sprayed into a high temperature area in a furnace or a flue, and water is supplied to a combustion exhaust gas path in the flue,
The lime blowing desulfurization method according to claim 1 or 2, wherein the temperature of the combustion exhaust gas is lowered. 4. A method in which slurry obtained by evaporating to dryness and atomizing is sprayed as a desulfurizing agent into a high temperature region in a furnace or a flue, and water is supplied to a combustion exhaust gas passage to lower the temperature of the combustion exhaust gas. The lime blown desulfurization method according to claim 2. 5. The lime-blown desulfurization method according to claim 1 or 2, wherein the solid matter in the desulfurized combustion exhaust gas is recovered. 6. The desulfurizing agent according to claim 1 or 2, wherein a substance capable of supplying silica and alumina is added to the calcium compound in the lime-blown desulfurization method, and a chlorine compound is added to the calcium compound. And lime blowing desulfurization method. 7. The lime-blown desulfurization method according to claim 6, wherein coal ash is used as the substance for supplying silica and alumina.