JP2994913B2 - Wet flue gas desulfurization apparatus using magnesium oxide and desulfurization method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wet type exhaust gas desulfurization apparatus for removing SO _x in the flue gases.

[0002]

2. Description of the Related Art Conventionally, as a flue gas desulfurization apparatus using magnesium, a method using magnesium hydroxide as an absorbent is known. FIG. 2 shows the flow. The flue gas is humidified and cooled by the cooling line 20 to near the water dew point, then guided to the absorption tower 9 and sprayed and filled with the absorbent supplied from the absorbent circulation line 7. The layer 8 efficiently absorbs SO _x by a gas-liquid reaction.

[0003] Also, since if in the exhaust gas containing SO _3, which SO ₃ because the SO ₃ in the cooling process results in a fine mist in the desulfurization apparatus of the conventional wet are not only removed at the contact of the liquid and mist, the removal There is a problem that the efficiency is low, and the mist of SO ₃ from the flue gas desulfurization device is discharged without being removed. Therefore, the wet electric dust collector 23 for removing SO ₃ is installed at the outlet of the removal device. There are also examples.

[0004] In FIG. 2, reference numeral 21 denotes a magnesium hydroxide supply tank.
Thus, magnesium hydroxide is supplied into the absorption tower 9. Reference numeral 10 denotes a pump for sending the circulating liquid to the circulating liquid spray line 7 and the cooling line 20. 11 is a wastewater treatment unit,
24 indicates a chimney. 13 is an oxidation blower.

In some cases, magnesium oxide is used as an absorbent. In that case, magnesium oxide is converted to magnesium hydroxide and used as an absorbent. Therefore, when using magnesium oxide as an absorbent, in the conventional example, equipment for hydrating magnesium oxide to magnesium hydroxide is required, and although running costs can be reduced as compared with using magnesium hydroxide as an absorbent, Equipment costs for hydration were required.

[0006]

DISCLOSURE OF THE INVENTION The present invention is directed to a wet flue gas system which uses magnesium oxide as an absorbent to efficiently remove SO ₃ contained in exhaust gas and does not require equipment for hydrating magnesium oxide. It is an object to provide a desulfurization device. Another object of the present invention is to provide a wet flue gas desulfurization apparatus having an absorption tower capable of increasing the reaction activity of magnesium oxide.

Furthermore, the present invention provides a more stable SO _x by the above-described apparatus without causing problems such as scaling.
It is an object of the present invention to provide a wet flue gas desulfurization method capable of maintaining the removal efficiency.

[0008]

According to the present invention, SO ₂ and SO ₂ are provided.
_In exhaust gas treatment of heavy oil-fired boilers including both
As a means for removing SO ₃ gas, powder of magnesium oxide (MgO) is directly sprayed on a flue, and the powder is collected by a circulating liquid of a later-stage wet-type absorption tower, and the SO 3 is collected in a slurry state. Used as _x gas absorber. The powder MgO
In order to efficiently utilize the compound for wet absorption of SO _x , MgO is not hydrated to magnesium hydroxide (Mg (OH) ₂ ), but is directly collected by a circulating liquid containing sulfite ions. As a result, M
The solubility of gO increases, and the activity as an absorbent increases.

Further, in another wet flue gas desulfurization apparatus according to the present invention, in addition to the above-mentioned means, a constitution having an oxidation suppressing means in the absorption tower is employed in order to secure a fixed amount of sulfite ions in the circulating liquid. . This oxidation suppressing means can be a device for suppressing the amount of oxidized air sent to the bottom of the absorption tower when the amount of sulfite ions in the circulating liquid decreases.

Further, according to the present invention, in the above-mentioned wet flue gas desulfurization apparatus, the wet-type flue gas desulfurization apparatus controls the injection amount of magnesium oxide based on the SO ₂ concentration and the gas flow rate in the exhaust gas and the PH value in the liquid in the absorption tower. Adopt flue gas desulfurization method.

[0011]

The magnesium oxide obtained by calcining magnesium carbonate is commercially available at a relatively low cost, and the fine powder having a particle size of 10 to several tens μm is commercially available. By spraying this powder into a boiler exhaust gas containing SO _x , it is possible to react with SO _{3 in} the gas. Here, the place where the powder is sprayed is the exit flue of the air heater in the case of a boiler, and a temperature range of an acid dew point of 150 to 200 ° C. or higher is desirable. It is desirable to be as far upstream as possible.

Generally, the velocity in the flue gas is 15 m / s or more, and commercially available magnesium oxide is guided to the downstream wet absorption tower without sedimentation in the gas. On the other hand, by setting the input amount of magnesium oxide close to the equivalent of SO ₂ , it is possible to secure a sufficient equivalent ratio to SO ₃ . (Assuming that the molar ratio of MgO and SO ₂ is 1, SO ₃ is about 1 to 2% of SO ₂ , so SO ₃
Is close to 50. ) Thus although SO ₃ and MgO is in solid-gas reactions, by increasing the MgO ratio SO _3, sufficient SO ₃ removal efficiency can be expected. SO ₃ reacts with MgO to form MgSO ₄ (magnesium sulfate).

Next, the unreacted MgO powder and the powder partially converted to magnesium sulfate are led to a wet absorption tower, and brought into contact with the circulating liquid to be taken into the liquid to form a thin slurry. . Here, since MgSO ₄ has high solubility, it is dissolved in a liquid, and the scaling problem does not occur. After the wet absorption tower, it is basically the same as the conventional water mug method, except that the absorption tower must be downflowed and have a sufficient gas-liquid ratio to prevent clogging with magnesium oxide powder. Is desirable.

Next, in the apparatus according to the present invention provided with an oxidation control means in the absorption tower, a certain amount of sulfite ions in the circulating liquid is secured to increase the reaction activity of magnesium oxide. Thereby, dissolution of magnesium oxide is promoted, and as a result, stable absorption of SO ₂ becomes possible.

Further, in the apparatus according to the present invention, while controlling the pH in the liquid in the absorption tower within a certain range, the S in the gas is controlled.
By adopting a desulfurization method in which an amount of magnesium oxide corresponding to O _x and a gas flow rate is adopted, it is possible to maintain a stable removal efficiency without causing a problem such as scaling with respect to fluctuations of SO ₂ and SO _3. It is possible.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a flue gas desulfurization apparatus using magnesium oxide according to the present invention will be described in detail with reference to an embodiment shown in FIG. In FIG. 1, the same parts as those in FIG. 2 are denoted by the same reference numerals, and a duplicate description thereof will be omitted. In FIG. 1, a gas containing SO _x (SO ₂ and SO ₃ ) flows through the flue, and a nozzle 6 supplies magnesium oxide powder of 10 to several tens μm into the flue. The magnesium oxide powder is quantitatively cut out from the feeder 2 from the storage hopper 1, pressurized by means such as a jet conveyor 3, and supplied to the flue gas. 4 is a blower.

It is needless to say that it is desirable to spray the magnesium oxide uniformly into the flue gas.
The sprayed magnesium oxide is directly guided to the wet absorption tower 9 while absorbing SO ₃ while floating in the flue gas. The magnesium oxide guided into the absorption tower 9 is contacted and collected by a large amount of circulating water sprayed by the circulating liquid spray line 7. Here, magnesium oxide has a particle size of 10
Since it is at least μm, wet spray collection can be easily performed.

The circulating water falls in the absorption tower 9 while
Drops downward while in gas-liquid contact with ₂ . In order to increase the gas-liquid contact efficiency at this time, it is effective to provide the packed layer 8. However, it is needless to say that the filled layer 8 has a structure in which no deposit occurs, for example, a grid. The circulating liquid is recycled from the bottom of the tower by the circulating pump 10 and used. The method of introducing water from the outside so that the salt concentration in the liquid does not rise excessively, extracting a part of the liquor, and transferring it to the wastewater treatment facility 11 is as follows. It is the same as the conventional water mug method discharge device.

Further, in order to secure a certain amount or more of sulfite ions in the circulating fluid, the sulfite ions in the circulating fluid are detected by a sulfite ion concentration detecting device 18. The control valve 19 suppresses the amount of oxidizing air from the oxidizing nozzle 12. Due to the presence of sulfite ions in the liquid, the activity of MgO can be improved to the level of a conventional slurry of magnesium hydroxide (Mg (OH) ₂ ).

Although the amount of oxidizing air is automatically controlled in FIG. 1, it is possible to manually adjust the amount of oxidizing air in an example in which an operation in which the load condition is clear is performed in advance.

The supply amount of the MgO powder is controlled by the amount of SO in the gas.
It is controlled to provide the amount corresponding to the SO _x loading at _x concentration detector 16 and a gas flow detector 17 on the basis of a signal supplied from the control unit 14. Further, the signal of the PH detector 15 is sent to the control unit 14 to control the supply amount so as to enter a certain area so that a problem such as scaling in the tower does not occur.

[0022]

As it has been specifically described according to the present invention, in the wet flue gas desulfurization apparatus using the magnesium oxide of the present invention, a powder blowing to flue magnesium oxide in accordance with the SO _x concentration in the gas This makes it possible to remove SO _x in a gaseous state. In addition, by collecting the magnesium oxide powder scattered in the flue with a circulating water spray in a conventional wet-type absorption tower configuration, both replenishment of the absorbent and recovery of the powder can be performed.

In particular, in the case of adopting a structure in which a certain amount of sulfite ions in the circulating fluid is secured by providing an oxidation suppressing means, the activity of magnesium oxide is increased.
No special equipment for hydrating Mg to Mg (OH) ₂ is required, and in addition to the above-mentioned SO ₃ removal effect, the function of eliminating the magnesium method is improved, the construction cost is significantly reduced, and the inexpensive oxidation is also performed. The running cost can be reduced by using the magnesium absorbent.

Further, by adopting the operation method according to the present invention, the SO method can be realized without causing a problem such as scaling.
_x Stable operation of the flue gas desulfurization apparatus of the present invention suitable for the load is performed.

[Brief description of the drawings]

FIG. 1 is a layout view showing a partial cross section of a device configuration of a wet flue gas desulfurization apparatus according to an embodiment of the present invention.

FIG. 2 is a layout diagram showing a partial cross-sectional view of a device configuration of a conventional water mug method flue gas desulfurization apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Magnesium oxide storage hopper 2 Quantitative feeder 3 Jet conveyor 4 Blower 5 Flue 6 Blow nozzle 7 Circulating fluid spray line 8 Packing layer 9 Absorption tower 10 Pump 11 Wastewater treatment unit 12 Oxidation nozzle 13 Oxidation blower 14 Control unit 15 PH meter 16 SO _x Total 17 Flow meter 18 Sulfurous acid concentration meter 19 Control valve 20 Cooling line 21 Magnesium hydroxide supply tank 22 Water mag supply pump 23 Wet electric dust collector 24 Chimney

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-167431 (JP, A) JP-A-6-304442 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 53/50 B01D 53/34 B01D 53/77 B01D 53/81

Claims (3)

(57) [Claims] In a flue gas desulfurization apparatus using magnesium oxide as an absorbent, a powder of magnesium oxide is directly sprayed into a flue gas, and SO ₃ gas contained in the flue gas by a part of the magnesium oxide is used. Spraying means for causing a solid-gas reaction of the magnesium oxide powder, and a circulating liquid for collecting the magnesium oxide powder and a reaction product of the magnesium oxide and SO ₃ and being disposed downstream of the spraying means. A wet flue gas desulfurization apparatus using magnesium oxide, comprising a wet absorption tower for absorbing SO ₂ gas by a gas-liquid reaction. 2. The wet flue gas desulfurization using magnesium oxide according to claim 1, further comprising oxidation suppression means for suppressing oxidation in the absorption tower and securing a certain amount or more of sulfite ions in the circulating liquid. apparatus. 3. The method according to claim 1, wherein the injection amount of the magnesium oxide is controlled based on the SO ₂ concentration in the exhaust gas, the flow rate of the flue gas, and the PH value of the liquid in the absorption tower.
A wet flue gas desulfurization method using the apparatus described in the above.