JPH0866618A - Exhaust gas desulfurization method - Google Patents

Abstract

(57) [Abstract] [Purpose] In an exhaust gas desulfurization method in which the absorbent is brought into contact with the exhaust gas containing sulfurous acid gas while introducing air into the absorbent through the air inlet pipe, the absorbent against the inner wall surface of the air inlet pipe To prevent the precipitation of calcium compounds from the air and solve the problem of blockage of the air inlet pipe. [Composition] Oxidizing air is introduced into an absorbing liquid consisting of an aqueous slurry of a calcium compound that is reactive with sulfurous acid gas through a conduit having an air jet at its tip, and exhaust gas containing sulfurous acid gas is introduced. In an exhaust gas desulfurization method including a desulfurization step of contacting with the absorbing liquid, as the oxidizing air to be introduced into the absorbing liquid, cooling humidified air obtained by spraying a cooling liquid into air previously mixed with superheated steam. There is a temperature difference [T
(A) -T (L)] (T (A): temperature of oxidizing air introduced into the absorbent, T (L): temperature of the absorbent) are within the range of -7 to 7 ° C, and their relative values. A method for desulfurizing exhaust gas, characterized by using air having a humidity of 100%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for desulfurizing exhaust gas, which comprises contacting exhaust gas containing sulfurous acid gas with an aqueous slurry of a calcium compound.

[0002]

2. Description of the Related Art A slurry of calcium compound in water (hereinafter referred to as
Exhaust gas desulfurization method in which exhaust gas containing sulfurous acid gas is brought into contact with an absorbing liquid) in the presence of oxygen is widely practiced. In this method, the sulfurous acid gas in the exhaust gas is fixed as gypsum (CaSO ₄ ). In such an exhaust gas desulfurization method, oxygen for existing in the absorbing solution to oxidize the sulfite group (SO ₃ ) to the sulfuric acid group (SO ₄ ) is formed in the absorbing solution at the tip end to the air ejection portion. The air introducing pipe is arranged so that its tip is located at a predetermined depth in the absorbing liquid, and the oxidizing air is jetted into the absorbing liquid from the tip of the air introducing pipe through the air introducing pipe. Has been supplied. However, when the oxidizing air is introduced into the absorbing solution for a long period of time in this way, there is a problem that the calcium compound in the absorbing solution is deposited on the inner wall surface of the air introducing tube and the inside of the air introducing tube is blocked. Occurs. And when such a blocking trouble of the air introducing pipe occurs, in order to clean the air introducing pipe,
The equipment must be shut down, resulting in significant economic losses. Conventionally, in order to prevent such a clogging trouble of the oxidizing air introducing pipe, it is usually performed by spraying water into the oxidizing air to increase the humidity and then supplying the water to the air introducing pipe. There is. However, even with such a method, it is not possible to completely prevent the trouble of blocking the air introduction pipe. That is, since the air introducing pipe is heated by the absorbing liquid, the temperature of the air in the air introducing pipe becomes higher than the temperature supplied to the air introducing pipe, and the relative humidity of the air is 10%.
It will be lower than 0%. As a result, the absorption liquid adhering to the inner peripheral surface of the air introduction pipe is dried, and the calcium compound contained in the absorption liquid is precipitated. JP-A-62-25872
According to JP-B-9, water is allowed to pass through the air introducing pipe to form an inner peripheral wall surface of the air introducing pipe as a wetting wall, and an absorbing liquid or a calcium compound deposit adhered to the inner peripheral wall surface of the air introducing pipe. A method of washing the inner wall surface of the inner wall has been proposed. According to this method, the problem of blockage of the air introduction pipe can be almost completely solved, but since it is necessary to use a large amount of water, it cannot be said to be an economically advantageous method.

[0003]

DISCLOSURE OF THE INVENTION The present invention provides an exhaust gas desulfurization method in which air is introduced into an absorption liquid through an air introduction pipe while the absorption liquid and sulfur dioxide gas-containing exhaust gas are brought into contact with each other. The problem is to prevent the precipitation of calcium compounds from the absorbing liquid on the wall surface and solve the problem of the clogging of the air introduction pipe.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, the oxidizing air is introduced into the absorbing liquid consisting of the water slurry of the calcium compound which is reactive to sulfurous acid gas through the conduit formed with the air jet portion at the tip end, and the sulfurous acid is added. In an exhaust gas desulfurization method including a desulfurization step of contacting an exhaust gas containing gas with the absorbing liquid, as oxidizing air to be introduced into the absorbing liquid,
Cooling and humidifying air obtained by spraying a cooling liquid in the air previously mixed with superheated steam, the temperature difference [T (A) -T (L)] (T (A):
Exhaust gas characterized by using air having an oxidizing air temperature, T (L): absorbing liquid temperature, introduced into the absorbing liquid within a range of -7 to 7 ° C, and having a relative humidity of 100%. A method of desulfurization is provided.

Next, the present invention will be described with reference to the drawings. FIG.
Shows a flow sheet when desulfurizing exhaust gas according to the present invention. In FIG. 1, 1 is a desulfurization device, 2 is a spray device, 3 is a mist separator, 4 is an exhaust gas supply line, 5
Is a dry air line, 6 is a superheated steam line, 10 is a spray nozzle, 11 is a cooling and humidifying air line, 12 is an oxidizing air supply line, and 13 is a gypsum extraction line.

The desulfurization apparatus 1 may have any structure as long as it can contact the exhaust gas containing sulfurous acid gas with the water slurry (absorption liquid) of the calcium compound and introduce the oxidizing air into the absorption liquid. Various types are used.
The aqueous slurry of calcium compound contains calcium compound as an absorbent and gypsum in water in a total amount of 3 to 30% by weight, preferably 10 to 20% by weight. As the calcium compound, calcium carbonate,
There are calcium hydroxide, calcium oxide, etc., but it is preferable to use calcium carbonate (CaCO ₃ ).

According to the invention, the dry air, which has not been subjected to a humidification treatment, is fed to the spray device 2 via the line 5.
However, prior to introducing the spray device 2,
Superheated steam from the superheated steam line 6 is mixed.
That is, in the present invention, dry air is previously supplied to the spray device 2 in the form of a mixture with superheated steam.
In the spray device 2, makeup water is supplied as a cooling liquid from a line 18, and this cooling liquid L is supplied to a spray nozzle 10 arranged at an upper part in the spray device through a line 7, a pump 8 and a line 9. It has been sprayed from here. The steam-containing dry air supplied to the spray device 2 comes into contact with the cooling liquid particles sprayed from the spray nozzle.

The steam-containing air that has come into contact with the cooling liquid particles is cooled by the contact with the cooling liquid particles, and is also cooled by the heat of vaporization of the cooling liquid particles which is vaporized when the cooling liquid particles come into contact with the cooling liquid particles. At the same time, the steam-containing air contains steam (steam) generated by the vaporization of the cooling liquid particles, so that it becomes humidified.
The wet air thus cooled and humidified is introduced into the mist separator 3, where the cooling liquid particles contained in the wet air are separated. The wet air from which the cooling liquid particles have been separated is supplied to the desulfurization apparatus 1 via the oxidizing air supply line 12. The conduit for introducing the oxidizing air into the desulfurization apparatus 1 has a tip formed at the gas ejection portion and may be a conduit having an open tip, or the tip structure as shown in FIGS. 2 and 3. Can have

The spray device 2 can also be simplified. That is, the line 7, the pump 8 and the line 9 may be omitted, and makeup water may be directly supplied from the line 18 to the spray nozzle. Even if the cooling liquid particles are supplied to the desulfurization apparatus 1 together with the air, there is no problem as long as the amount thereof is not large, and therefore the mist separator 3 can be omitted.

The temperature of the air passing through the dry air line 5 is
Usually, it is 50 to 100 ° C, and the temperature of the steam passing through the superheated steam line 6 is usually 140 to 260 ° C. Further, the temperature of the cooling liquid L is preferably close to the temperature of the absorbing liquid in the desulfurization apparatus 1, and generally, the temperature difference from the absorbing liquid is within ± 7 ° C, preferably within ± 3 ° C. The temperature is preferably.

In the present invention, as described above, the oxidizing air introduced into the absorbing solution of the desulfurizer has a relative humidity of 100%, and at the same time, its temperature is It is necessary to satisfy the formula. −7 ≦ T (A) −T (L) ≦ 7 (In the formula, T (A) represents the temperature of the oxidizing air introduced into the absorbing liquid, and T (L) represents the absorbing liquid temperature.) Inventor According to these studies, if the temperature difference ΔT [T (A) -T (L)] between the oxidizing air and the absorbing liquid is in the range of −7 ° C. to 7 ° C., it is arranged in the desulfurization device. It has been found that it is possible to effectively prevent the occurrence of blockage troubles in the oxidizing air introduction pipe. When the temperature difference ΔT becomes smaller than −7 ° C., the oxidizing air passing through the air introduction pipe arranged in the desulfurization device is heated by the absorption liquid in the desulfurization device and rises in temperature.
The relative humidity of the air becomes considerably lower than 100%, and it becomes impossible to prevent the absorption liquid adhering to the inner peripheral wall surface of the air introduction pipe from drying. On the other hand, when ΔT is larger than 7 ° C., the amount of heating steam for obtaining the oxidizing air having a relative humidity of 100% is large and the economical efficiency is impaired. The temperature difference ΔT is preferably within ± 6 ° C, more preferably within ± 3 ° C. More preferable temperature difference Δ
T is in the range of 0 to 6 ° C, preferably 0 to 3 ° C.

In order to maintain the oxidizing air supplied to the desulfurization apparatus 1 at the above temperature and humidity conditions, as described above,
It is necessary that the dry air is mixed with superheated steam to prepare a dry air / superheated steam mixture in advance and then brought into contact with cooling liquid particles to be cooled. Simply spraying the cooling liquid into dry air cannot obtain the desired cooling air with a relative humidity of 100%. That is, when the cooling liquid is sprayed on the dry air to cool the air temperature to the absorption liquid temperature in the desulfurizer, the cooling of the dry air is performed by the cooling liquid particles formed by the spray as described above. And the vaporization of the cooling liquid particles at the time of contact, the cooling of the dry air does not require a spray amount of the cooling liquid such that the relative humidity of the dry air reaches 100%. The relative humidity of the cooling air taken will fall below 100%. On the other hand, if the superheated steam is mixed in the dry air in advance and then cooled by spraying the cooling liquid, the relative humidity of the dry air is increased in advance by mixing the superheated steam. By cooling with the spray of the cooling liquid, cooling air having a relative humidity of 100% can be obtained. As can be understood from the above description, in order to obtain cooling air having a relative humidity of 100% by spraying a cooling liquid, it is necessary to mix superheated steam with dry air in advance. Is appropriately selected according to the amount of water vapor in the dry air, the desired air cooling temperature, and the steam temperature used.

A dust removal tower for removing solid fine particles such as soot and dust contained in the exhaust gas is usually provided in the preceding stage of the desulfurization apparatus 1. This dust removal tower is provided with a liquid spraying device in the upper part of the tower, and while cooling the exhaust gas by spraying the cooling liquid into the exhaust gas introduced into the tower,
The solid fine particles contained in the exhaust gas are removed. In this dust removing tower, the sprayed cooling liquid stays in the lower part of the tower. In this case, water is usually used as the cooling liquid. The cooling water in the dust removing tower can be used for cooling and humidifying the oxidizing air according to the present invention. A flow sheet in this case is shown in FIG. In FIG. 4, 15 indicates a dust removing tower, 16 indicates an exhaust gas supply line, and 17 indicates a cooling makeup water supply line. In the dust removing tower 15, cooling water is circulated between the liquid reservoir at the bottom of the tower and the spray device at the top of the tower. In addition, in the code | symbol shown in FIG. 4, the code | symbol same as what was shown in FIG. 1 has the same meaning.

In the exhaust gas desulfurization method shown in the flow sheet of FIG. 4, makeup water for cooling is sprayed into the dust removing tower 15 through the line 17. On the other hand, exhaust gas is line 16
The exhaust gas is introduced into the dust removal tower 15 through and is contacted with the fine particles of cooling circulating water sprayed in the tower. The solid particulates are removed and the cooled exhaust gas is introduced into the desulfurization apparatus 1 through the line 4. The temperature of the exhaust gas passing through the line 4 is 40 to 70 ° C.

A part of the cooling water is extracted from the lower part of the dust removing tower 15 through a line 18 and introduced into the spray device 2 for cooling the oxidizing air. The temperature of the cooling water extracted from the dust removing tower 15 via the line 18 is the same as that of the desulfurization apparatus 1
The temperature is equal to or lower than the temperature of the absorbing liquid in the inside by about 0 to 7 ° C. The temperature difference between the temperature of the cooled and humidified air passing through the line 12 and the temperature of the absorbing liquid in the desulfurization device 1 is preferably 0 to 7 ° C, more preferably 0 to 3 ° C. Although a part of the cooling liquid is extracted from the spray device 2 through the line 14, this cooling liquid is preferably returned to the dust removing tower 15, but in some cases, it can be discharged to the outside of the system. As described above, by using the cooling liquid in the dust removing tower 15, cooling and humidification of the oxidizing air can be efficiently and economically performed, as in the case shown in FIG. 1. It is possible to prevent clogging trouble of the oxidizing air introduction pipe arranged in the desulfurization apparatus 1.

[0016]

EFFECTS OF THE INVENTION According to the present invention, since the air humidified by cooling is introduced into the oxidizing air introducing pipe arranged in the desulfurization device, the temperature of the absorbing liquid in the desulfurizing device is substantially the same as that of the absorbing liquid in the desulfurization device. It is possible to prevent clogging troubles of the air introduction pipe due to precipitation of calcium compounds on the inner peripheral wall surface of the air introduction pipe.
Moreover, in the case of the present invention, for the cooling and humidification of the oxidizing air, it is possible to use the desulfurization device absorption liquid already present in the desulfurization system, or the cooling water in the dust removing tower, so that the special cooling liquid Since no use is required and the amount of drainage from the desulfurization system does not increase, cooling and humidification of the oxidizing air can be performed very economically and efficiently.

[0017]

Next, the present invention will be described in more detail with reference to examples. Example 1 According to the flow sheet shown in FIG. 1, desulfurization treatment of flue gas from a heavy oil combustion device in a thermal power generation facility was performed.
The main operating conditions for desulfurization in this case are shown below. (1) Line 4 Sulfurous acid gas concentration: 1300 volppm (2) Line 18 Make-up water temperature: 20 ° C (3) Line 5 Air supply: 10000 Nm ³ / h Air temperature: 82 ° C (4) Line 6 Steam temperature: 253 ° C Steam Supply rate: 0.08 kg / h for 1 Nm ³ / h of air passing through line 5 (5) Line 12 Air temperature: 50 ° C Air relative humidity: 100% (6) Line 14 Absorbing liquid temperature: 50 ° C

Even after continuous operation for one year under the above conditions, no clogging trouble of the air introduction pipe arranged in the desulfurization apparatus occurred. On the other hand, when desulfurization treatment was performed in the same manner except that the amount of the absorbing liquid sprayed in the spray device 2 was changed and the temperature of the oxidizing air passing through the line 12 was changed, the temperature difference between the oxidizing air temperature and the absorbing liquid temperature was obtained. Is -1
In the case of 0 ° C., when the air introduction pipe was inspected after one month of operation, the air introduction pipe was found to be clogged with precipitates, but the difference between the oxidizing air temperature and the absorbing solution temperature was − 7 to 7
In the case of ℃, after the operation for 1 month, the air inlet pipe was not clogged with precipitates. From the above, it is understood that the clogging trouble of the oxidizing air introducing pipe can be prevented for a long period of time by keeping the temperature difference between the oxidizing air and the absorbing liquid at ± 7 ° C. or less.

[Brief description of drawings]

FIG. 1 shows an example of a flow sheet of an exhaust gas desulfurization method of the present invention.

FIG. 2 is a perspective view of a tip end portion of an example of an air introduction pipe arranged in the desulfurization apparatus shown in FIG.

FIG. 3 is a perspective view of a tip end portion of another example of the air introduction pipe arranged in the desulfurization apparatus shown in FIG.

FIG. 4 shows another example of the flow sheet of the exhaust gas desulfurization method of the present invention.

[Explanation of symbols]

 1 Desulfurization Device 2 Spray Device 3 Mist Separator 15 Dust Tower 22 Air Jet Hole 23 Air Jet Notch Hole

Claims (1)

[Claims] 1. An oxidizing air is introduced into an absorbing liquid composed of an aqueous slurry of a calcium compound having reactivity with sulfurous acid gas, through a conduit having a tip portion formed in an air jetting portion, and contains sulfurous acid gas. In an exhaust gas desulfurization method including a desulfurization step of contacting exhaust gas with the absorbing liquid, as a oxidizing air to be introduced into the absorbing liquid, a cooling and humidifying method obtained by spraying a cooling liquid into air premixed with superheated steam. Air is a temperature difference [T (A) -T (L)] [T (A): oxidizing air temperature to be introduced into the absorbing liquid, T (L): absorbing liquid temperature] with the absorbing liquid. -7 to 7
A method for desulfurizing exhaust gas, characterized by using air having a relative humidity of 100% within a range of ° C.