KR0125122B1 - Flue gas desulfurization method and system - Google Patents

Abstract

According to one embodiment of the present invention, light magnesium is used as a desulfurization agent (MgO), and the desulfurization agent is directly supplied to an absorption liquid tank installed at the bottom of the desulfurization tower without any hydration treatment.

According to another embodiment of the present invention, the magnesium oxide powder is dispensed from the magnesium oxide storage hopper 61 into the flue 65 in which gas containing SOx flows. Magnesium oxide powder is introduced into the absorption tower 49 while absorbing SO ₃ present in the flue gas, and within the absorption tower 49, magnesium oxide is collected by contact with the circulating fluid from the spray line 47. . The circulating fluid falls through the absorption tower 49 to absorb and remove SO ₂ present in the flue gas. The circulating fluid is recycled to the bottom of the absorption tower 49 by the circulating pump 50, and the sulfite ion concentration therein is detected by the detector 78 with respect to the circulating fluid, and when the sulfite ion concentration is lowered, the oxidation blower ( 73) the oxidation to be carried out is inhibited so that the presence of sulfite ions in the liquid increases the activity of magnesium oxide. The flow rate of the supplied magnesium oxide is controlled by the control unit 74 based on the signals transmitted from the SOx concentration detector 76, the gas flow detector 77, and the PH meta 75.

Description

Flue gas desulfurization method and desulfurization device

1 is a schematic flowchart of a method for supplying an absorbent according to a first embodiment of the present invention.

2 is a schematic flowchart of supplying an absorbent to a desulfurization tower in one embodiment of the conventional method.

3 is a schematic flowchart illustrating one embodiment of a conventional flue gas desulfurization apparatus using magnesium.

4 is a schematic flowchart illustrating another embodiment of a conventional flue gas desulfurization apparatus using magnesium.

5 is a graph showing the relationship between the average particle diameter of MgO and the time required for dissolution.

6 is a graph showing the relationship between the amount of SO ₃ ²⁻ and the time required for the reaction of MgO.

7 is a graph showing the relationship between SO ₃ ^2- concentration and desulfurization efficiency of absorbent liquid.

8 is a graph showing SO ₂ gas absorption characteristics of MgO-containing liquid.

9 is a graph showing SO ₂ gas absorption characteristics of Mg (OH ₂ ) -containing liquid.

10 is a graph showing the particle size distribution measurement results of seawater magnesium.

FIG. 11 is a graph showing particle size distribution measurement results of light and small magnesia. FIG.

12 is a schematic partial cross-sectional view of a wet flue gas desulfurization apparatus structure according to a second embodiment of the present invention.

13 is a schematic cross-sectional view of a conventional flue gas desulfurization apparatus structure using magnesium hydroxide.

* Explanation of symbols for main parts of the drawings

1: MgO storage tank 2: water supply line

3: MgO dissolution tank 4, 9: stirrer

5: Absorbing liquid tank 6: Sedimentation tank

7: wet grinding machine 8: MgO hydration tank

10, 11, 12: piping 15, 16, 17: piping

21: desulfurization tower 22: entrance year part

23 absorber tank 24 absorber

25: boiler exhaust gas 26: mixed liquid

27 outlet 28 filled layer

29: blower 39: oxidation tower

31 waste liquid 40 cooling line

The present invention relates to a wet flue gas desulfurization method for removing SOx present in flue gas and the like and a desulfurization apparatus thereof. As an example of such a flue gas desulfurization method, a flue gas desulfurization method using magnesium is conventionally performed.

The flue gas desulfurization method using magnesium is described below, and above all, the technical terms used are clearly defined.

Magnesite; Ore based on MgCO ₃ .

Light burned magnesia; MgO obtained by firing magnesite at a relatively low temperature of about 800 ~ 1,100 ℃

Seawater Magnesium: Mg (CH) ₂ synthesized from seawater components

Hydromagnesium: Mg (OH) ₂ obtained by hydrating light magnesium

The SO ₂ absorption process of the flue gas desulfurization method using conventional magnesium will be described below. The conventional flue gas desulfurization method using magnesium is a suction desulfurization method using Mg (OH) ₂ as an absorbent, and the basic reaction of SO ₂ absorption is as follows.

The desulfurized waste liquid is sufficiently air oxidized as shown in equation (4), filtered and discharged.

The flue gas desulfurization method using magnesium can discharge the desulfurization liquid into the river or sea after air oxidation and filtration, thus eliminating the need for special after-treatment equipment, and compared to the flue gas desulfurization method using calcium. It has the advantage of being low. Moreover, there is almost no precipitation of CaCO ₃ , CaSO _4, etc. in the system and piping, and maintenance and operation can be easily performed, and high desulfurization efficiency is obtained. For this reason, it is widely used as a flue gas desulfurization apparatus for small and medium-sized self-powered boiler facilities. However, since seawater magnesium used as a desulfurization agent has a high cost, the small magnesium obtained by calcining magnesite is pulverized, classified and hydrated, and then the hydromagnesium thus formed is used to reduce the cost of the desulfurization agent (and further operating costs). It is the present situation.

Next, the apparatus for carrying out the flue gas desulfurization method using conventional magnesium will be described with reference to the schematic flowcharts of FIGS. 3 and 4. FIG. 3 shows a system in which gas and absorbent liquid are brought into countercurrent contact, and FIG. 4 shows a system in parallel contact with each other.

(1) gas cooling

A part of the absorbing liquid 24 in the absorbing liquid tank 23 is sprayed on the inlet flue 22 of the desulfurization tower 2 of the boiler exhaust gas to cool the boiler exhaust gas until the water is saturated. Numeral 25 denotes a boiler exhaust gas.

(2) Supply of absorbent liquid

The mixed liquid 26 of the desulfurizing agent and water is supplied to the absorbing liquid tank 23 provided at the bottom of the desulfurizing agent column under PH control.

(3) absorption of SO ₂ gas

The absorbing liquid 24 of the absorbing liquid tank 23 is sprayed into the boiler exhaust gas 25 introduced into the desulfurization tower, and the sprayed absorbing liquid absorbs SO ₂ in the gas and falls into the absorbing liquid tank 23.

(4) exhaust of desulfurization gas

The boiler exhaust gas 25 is brought into contact with the absorbing liquid while passing through the desulfurization tower 21, cooled and desulfurized, and then discharged through the outlet 27. Reference numeral 28 is a packed layer.

(5) Blowing air into the bottom of desulfurization tower

In order to prevent sedimentation and deposition of soot dust particles from the boiler exhaust gas, air is introduced by a blower 29 to adjust the concentration of sulfite ions (SO ₃ ^2- ) in the desulfurization column bottom absorption liquid 24.

(6) discharge of desulfurization liquid

Before the new absorbent liquid 26 is supplied to the absorbent liquid tank 23 provided at the bottom of the desulfurization column, the old absorbent liquid in the absorbent liquid tank 23 is discharged. The discharged absorbed liquid is air oxidized in the oxidation tower 30 to sufficiently reduce its chemical oxygen demand (COD), filtered and discharged as a waste liquid 31.

Next, a conventional absorption liquid supply system to a desulfurization tower will be described with reference to the schematic flow diagram of FIG.

(1) Underwater Degradation of Small Magnesia

The light magnesia in the MgO storage tank 1 and the water of the water supply line 2 are introduced into the MgO melting tank 3 via the pipes 10 and 11 and stirred with the stirrer 4.

(2) miniaturization of small and small magnesia particles

The small magnesia dispersion in the MgO melting tank 3 is transferred to the settling tank 6 via the pipe 14. In the sedimentation tank 6, small and small magnesia having a large particle diameter is sedimented and separated, and transferred to the wet grinder 7 via a pipe 15 for fineness.

(3) Hydromagnesium production by hydration reaction

MgO water was passed through a pipe (16) and (17), respectively, via a pipe (16) and (17), respectively, a liquid containing fine light small magnesia particles not separated in the sedimentation tank 6 and a liquid containing small light magnesia particles micronized by the wet mill. It introduces into flower tank 8. Hydrogen-magnesium-containing solution introduced into the MgO hydration tank (8) is heated and stirred continuously for several hours with a stirrer (9) to obtain hydromagnesium.

(4) Supply of hydromagnesium-containing liquid to the desulfurization tower

Hydromagnesium formed by completely hydrating the desulfurization agent in the MgO hydration tank 8 is introduced into the absorption liquid tank 23 provided at the bottom of the desulfurization column via a pipe 12.

As described above, the transition from the seawater magnesium, which has been conventionally used for the purpose of reducing the desulfurization agent cost, which constitutes the most of the operating cost, to the cheaper light magnesium is in progress. However, when light magnesium is used as the desulfurization agent, it is necessary to satisfy the following two prerequisites before supplying the desulfurization agent to the absorption liquid tank installed at the bottom of the desulfurization tower.

(i) The particle size of the light magnesia is made small.

(ii) convert small magnesium to hydromagnesium [Mg (OH) ₂ ].

In order to satisfy these prerequisites, the sedimentation tank 6, the crushing mill 7, the MgO hydration tank 8 (including a large capacity tank, a heating thermostat and a stirrer) are compared with a system using seawater magnesium as a desulfurization agent. And a pipe pump between these sensors, etc., which leads to an increase in initial cost and facility space. For reference, the particle size distribution measurement results of seawater magnesium containing Mg (OH) ₂ as the main component are shown in FIG. 10, and the particle size distribution measurement results of commercially available small magnesium products having MgO as the main component are shown in FIG.

Among conventional flue gas desulfurization apparatus using magnesium, it is well known to use magnesium hydroxide as an absorbent, and the structure of such an apparatus is shown in FIG. In this apparatus, the flue gas is moistly cooled to near the dew point by the cooling line 40 and then directed to the absorption tower 49 to the spray and packed bed 48 of the absorption liquid supplied from the absorption liquid circulation line 47. SOx is absorbed by gas-liquid reaction efficiently.

In the case that the exhaust gas containing SO _3, in the conventional priming type desulfurization system because of the conversion of the cooling stage when SO ₃ with a fine mist, SO ₃ can not be removed except for the contact between the liquid and mist of SO ₃ removal The efficiency is low, and therefore, SO ₃ fog generated in the flue gas desulfurization apparatus is removed instead of being discharged. Therefore, in some cases, a wet electric contactor 43 for removing SO ₃ is also provided at the outlet of the flue gas desulfurization apparatus.

In Fig. 13, reference numeral 41 denotes a magnesium hydroxide supply tank, and in this tank 14, magnesium hydroxide is supplied into the absorption tower 49 by the magnesium hydroxide supply pump 42. Reference numeral 50 denotes a pump for feeding the circulating fluid to the circulating fluid spray line 47 and the cooling line 40, and 51, 44, and 53 are wastewater treatment units, chimneys, and oxidation blowers, respectively.

In addition, although magnesium oxide is used as an absorbent in some cases, magnesium oxide is also converted to magnesium hydroxide and the latter is used as an absorbent.

Therefore, in the case of using magnesium oxide as an absorbent, the conventional apparatus requires a facility for hydrating magnesium oxide into magnesium hydroxide, and the operating cost can be reduced compared to the case of using magnesium hydroxide as an absorbent, but the equipment cost for hydration Is needed.

The present invention was completed in order to solve the above problems, and an object of the present invention is to use light small magnesia (MgO) as a desulfurization agent, which can omit equipment such as sedimentation tank, wet mill, MgO hydration tank, etc. It is to provide a simple flue gas desulfurization method.

In order to achieve the above object, the present invention provides a flue gas desulfurization method comprising using a light magnesia as a desulfurizing agent, and introducing the supply of desulfurizing agent as MgO directly without any hydration treatment to an absorption liquid tank installed at the bottom of the desulfurization tower.

As described above, in the conventional method, it is necessary to satisfy the following two points as a prerequisite for the use of light magnesium. In other words,

(i) The particle size of the light magnesia is made small.

(ii) convert small magnesium to hydromagnesium [Mg (OH) ₂ ].

The basis of these preconditions is that the conditions for supplying the desulfurization agent to the absorption liquid tank at the bottom of the desulfurization tower are the same as that of magnesium used widely.

As shown in FIG. 11, the average particle diameter of commercially available small-magnesia products is about 20 µm, which is considerably larger than seawater magnesium (ie several µm), and the particle size distribution is also broad (smaller particle diameter, more uniform, small-magnesia commercially available products). Silver is expensive and has no advantage as a substitute for seawater magnesium). Thus, wet grinder values require expensive equipment.

The present inventors found a method of chemically minimizing light magnesium, not mechanically, and conducted various experiments to confirm that it is not necessary to convert light magnesium to hydromagnesium.

(1) Sulfite ions (SO ₃ ^2- ) are effective for miniaturization of small and medium magnesia.

(i) Experiment I: Check the relationship between the particle size of MSO and its dissolution rate.

Method for measuring the dissolution rate of light small magnesia is as follows. After 200 ml of pure water was maintained at 50 ° C., the mixture was continuously stirred at 180 rpm with a stirrer, and then 18 mmole (as Mg) of light and small magnesium having a known particle diameter and composition was added and refreshed.

Thereafter, 2N-H ₂ SO ₄ is added to maintain the pH of the liquid at 6.0 (alkali liquid becomes an alkaline liquid when light magnesium is dissolved in water, so that the amount of acid required for neutralization is indicative of the amount of light magnesia dissolved). The time required for the dissolution of 80% of MgO, the main component (80% or more) of light small magnesia, from the time when light small magnesia is added is recorded. As a result, the relationship between the particle size of light and small magnesia and its dissolution rate is obtained as shown in FIG. As can be seen from the fifth degree, the dissolution rate of light small magnesia increases as the particle diameter decreases.

(ii) Experiment 2: Confirmation of the dissolution promoting effect of light magnesia by the addition of sulfite ions (SO ₃ ^2- ).

The dissolution rate of light small magnesia is measured by the same method described in Experiment 1, but prior to adding light small magnesia, a known amount of Na ₂ SO ₃ (ie, SO ₃ ^2- ) is added to the pure water. Next, an average particle diameter of 17 mu m and a predetermined amount of light small magnesia having known composition are added, and the time required for dissolution is recorded. As a result, a relationship between the concentration of SO ₃ ^{2- in the} liquid and the dissolution rate of light magnesium is obtained as shown in FIG.

As can be seen from FIG. 6, the dissolution rate of light magnesia becomes higher as the concentration of SO ₃ ^2- increases in the liquid. In the absence of SO ₃ ^2- , the time required for dissolution is 34 minutes.

MgO dissolution conditions used in Figure 6 are as follows.

1) Liquid temperature: 50 ℃

2) pH of solution: 6.0

3) MgO dissolved amount: 90mmol / l

4) Stirring Speed: 180rpm

The light magnesium (MgO) used was as follows.

1) Name: MDB (trade name, Sobue clay co., Ltd)

2) Average particle size: 17㎛

Summarizing the above results, it was confirmed by Experiment 1 that the dissolution rate of light magnesium in water depends on the particle diameter, and the smaller the particle diameter, the larger the dissolution rate. In addition, it was confirmed by Experiment 2 that the dissolution promoting effect of small and small magnesia was obtained by the presence of sulfite ions (SO ₃ ^2- ) in water. Considering the results of Experiment 1, this effect can be said to promote the miniaturization of small and small magnesia particles. In this connection, as a result of providing seawater magnesium with an average particle diameter of 3.5 µm in Experiment 1, the time required for dissolving Mg (OH) ₂ as its main component (90% or more) was 1.5 to 2.0 minutes, and the same dissolution rate was obtained. In order to obtain light magnesium with an average particle diameter of 17 µm, as can be seen from FIG. 6, the concentration of SO ₃ ^2- in liquid should be 10 ml / l or more.

In general, light magnesia is considered to have a rhombohedral crystal structure, and the micronizing means is performed by a conventional mechanical method and by hydration requiring a large amount of thermal energy and a long reaction time. However, it was confirmed by experiments 1 and 2 that the sulfite ions (SO ₃ ^2- ) were present in the liquid used to dissolve the light small magnesia, and the particle size of the light small magnesia was miniaturized efficiently in a short time.

In the actual flue gas desulfurization apparatus using magnesium, as described above in connection with the SO ₂ absorption process, the absorption liquid tank at the bottom of the desulfurization column generates MgSO ₃ (i.e., SO ₃ ^2- ), which is an amount sufficient to refine the light magnesium. It exists. This MgSO ₃ is an indispensable substance in the absorbent liquid in order to achieve high desulfurization efficiency (see FIG. 7), and in an actual apparatus, the concentration of MgSO ₃ in the absorbent liquid is limited to 10 mmol / l or more. In addition, the absorbent liquid at the bottom of the desulfurization column has a temperature suitable for dissolution around 60 ° C because it comes into contact with the hot boiler exhaust gas. The operation (simulation calculation) conditions used in FIG. 7 are as follows.

1) SO ₂ concentration in exhaust gas: 1,200ppm

2) Exhaust gas flow rate: 2 * 10 ⁵ Nm ³ / h

3) Absorption liquid circulation rate: 2,000m ³ / h

4) Absorbent PH: 6.5

5) Internal temperature of absorption tower: 60 ℃

6) Filling: HEILEX-500

7) Filling layer diameter: 7.4mø

8) Filling layer height: 2.4m ^H

(2) SO ₂ absorption does not necessarily require conversion of light magnesium to hydromagnesium.

Experiment 3: Compare the SO ₂ gas absorption capacity of seawater magnesium and light magnesium.

The test method was as follows: A glass absorbent bottle (at room temperature) containing 10 ml of pure water was secreted and continuously stirred at 180 rpm using a stirrer. To this, seawater magnesium or light magnesium is weighed out to 41.15 mmol (as Mg) and added. A standard gas containing 4,800 ppm SO _{2 in} N ₂ is bubbled through the liquid into the absorption bottle at a rate of 1.48 N ₁ / min, and the change in pH of the liquid and SO ₂ concentration of the liquid after bubbling is recorded.

The test results for light magnesium are shown in FIG. 8 and the results of sea magnesium are shown in FIG. Comparing both, the SO ₂ gas absorption power is almost similar, that is, approximately 2 mol of SO ₂ is absorbed by 1 mol of Mg in each dehydrating agent. As a result, it was found that it is not necessary to convert light magnesium to hydromagnesium for SO ₂ gas absorption.

It is another object of the present invention to provide a wet type flue gas desulfurization apparatus that uses magnesium oxide as an absorbent to efficiently remove SO ₃ present in exhaust gas and does not require equipment for hydrating magnesium oxide. .

Still 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.

It is also an object of the present invention to provide a wet flue gas desulfurization method that can maintain a safe SOx removal efficiency using the above-described device without causing problems such as scaling.

In order to achieve the above object, the present invention provides magnesium oxide (MgO) powder directly to the flue as a means for removing SO ₃ gas in the treatment of exhaust gas (containing both SO ₂ and SO ₃ ) in a heavy oil combustion boiler or the like. It sprays and collects this powder with the circulating fluid of the following wet absorption tower, and provides the wet type flue gas desulfurization apparatus which uses it as an absorbent of SOx gas in slurry form. Furthermore, in order to efficiently use MgO powders for the wet absorption of SOx, instead of hydrating MgO with magnesium hydroxide [Mg (OH) ₂ ], it is directly collected into a circulating fluid containing disulfide ions.

As a result, the solubility of MgO improves and activity as an absorbent increases. In addition, in the wet type flue gas desulfurization apparatus according to another embodiment of the present invention, in addition to the above means, oxidation inhibiting means is attached to the absorption tower in order to secure a predetermined amount of sulfite ions in the circulating fluid. The oxidation inhibiting means may comprise a device for reducing the supply rate of the oxidized air supplied to the bottom of the absorption tower when the concentration of sulfite ions in the circulating fluid is lowered.

In the wet flue gas desulfurization apparatus according to the present invention, the wet flue gas desulfurization method of controlling the injection amount of magnesium oxide on the basis of the concentration of SO ₂ in the exhaust gas, the gas flow rate, and the pH of the liquid in the absorption column. It is adopted.

Magnesium oxide is marketed relatively cheaply by reducing magnesium carbonate. In addition, fine powders having a particle diameter of 10 to several tens of micrometers are also commercially available. Sikimeuroseo powder sprayed in the boiler exhaust gas containing SOx, are magnesium oxide can be reacted with SO ₃ present in the gas.

In the case of the boiler, the place where the powder is sprayed is the outlet year of the air heater, and the temperature range of the acid dew point of 150 to 200 ° C or higher is preferable. In order to ensure sufficient time for the solid-gas reaction, the spray site is preferably located as far upstream as possible from the absorption tower. In general, the gas flow rate in the year is 15 m / s or more, and commercial magnesium oxide is led into a wet absorption tower located downstream without sedimentation in the gas.

On the other hand, the addition amount of magnesium oxide, it is possible to ensure a sufficiently high equivalent ratio for the SO ₃ by eq close set and SO ₂ (when the molar ratio of MgO and SO ₂ to 1, SO ₃ is SO ₂ is about 1-2% The molar ratio of MgO to SO ₃ is close to 50).

Therefore, although the reaction between MgO and SO ₃ is a solid-gas reaction, a sufficiently high SO ₃ removal efficiency can be expected by increasing the ratio of MgO to SO ₃ .

SO ₃ reacts with MgO to magnesium sulfate (MgSO ₄ ).

Thereafter, the unreacted MgO powder and the powder partially converted to magnesium sulfate are introduced into the wet absorption tower to form a thin slurry by contacting the circulating liquid and entering the liquid. Since MgSO ₄ is highly soluble, it does not dissolve in the circulating fluid and does not cause scaling problems.

After the wet absorption tower, it is basically the same as the conventional apparatus using magnesium hydroxide, but in order to prevent the blockage by the magnesium oxide powder, the absorption tower is preferably downflow type, and the gas-liquid ratio is preferably high enough.

In addition, in the case where the oxidation inhibiting means is provided in the absorption tank according to the present invention, in order to increase the reaction activity of magnesium oxide, by operating a predetermined amount of sulfite ions in the circulating fluid, dissolution of magnesium oxide is promoted to stabilize SO ₂ . Will be absorbed.

Further, in the apparatus according to the present invention, when the desulfurization method in which the amount of magnesium oxide in correspondence with the SOx concentration and the gas flow rate in the gas is used while adjusting the pH in the liquid of the absorption tower within a certain range, SO ₂ , SO ₃ Despite the change in concentration, stable removal efficiency can be maintained without causing problems such as scaling.

A first embodiment of the present invention will be described with reference to FIG.

(1) Underwater dispersion of light and small magnesia.

Into the MgO dissolution tank 3, light magnesium and the water of the water supply line 2 in the MgO storage tank 1 are introduced via the pipes 10 and 11, respectively, and stirred by the stirrer 4.

(2) Supply of the light and small magnesia dispersion to the desulfurization tower.

The liquid in the MgO dissolution tank 3 is introduced into the absorption liquid tank 5 at the bottom of the desulfurization column via the pipe 12 (typically, the absorption liquid tank 5 contains dozens of mmol / l sulfite ions (SO ₃ ^2- ). It is present and the light magnesium is finely dissolved in a particle diameter equivalent to that of seawater magnesium, which is conventionally used as a dehydrating agent).

(3) The SO ₃ ^2- concentration in the absorbing liquid tank 5 is lowered.

When the concentration of SO ₃ ^2- in the absorbent liquid tank 5 is lowered, the rate of miniaturization (or dissolution) of the light and small magnesia particles introduced into the absorbent liquid tank 5 through the pipe 12 in the MgO melting tank 3 is slow. In addition, the residence time in the absorbing liquid tank 5 must be lengthened. In this case, it is necessary to circulate the liquid in the absorbing liquid tank 5 back to the MgO dissolution tank 3 via the pipe 13.

When light magnesium is used as the desulfurization agent according to the present invention, by supplying light magnesium to the absorption tank at the bottom of the desulfurization column, it is not necessary to install facilities such as sedimentation tank, wet mill and MgO hydration tank, and the system uses seawater magnesium as the desulfurization agent. As in the case, the configuration is very simple. As a result, the installation area of the desulfurization facility and the initial cost can be reduced, and power consumption due to the removal of the heater and the pump is also saved. In addition, the operation, maintenance and inspection of the device becomes easy.

Next, another flue gas desulfurization apparatus using magnesium oxide constructed in accordance with the second embodiment of the present invention will be described in detail with reference to FIG. In FIG. 12, the same parts as those in FIG. 13 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 12, gas containing SOx (that is, SO ₂ and SO ₃ ) flows through the flue 65, and magnesium oxide powder having a diameter of 10 to several 10 μm is supplied by the nozzle 66 therein. More specifically, the magnesium oxide powder is quantitatively taken out of the storage hopper 61 through the feeder 62, pressurized by means such as a jet conveyor 63, and supplied into the flue gas in the flue 65. 64 is a blower.

The magnesium oxide is preferably sprayed uniformly in the flue gas, and the sprayed magnesium oxide is directly led to the absorption type absorption tower 49 while absorbing SO ₃ while floating in the flue gas. Magnesium oxide introduced into the absorption tower 49 is collected by contact with a large amount of circulating fluid sprayed through the spray line 47. Since magnesium oxide has a particle diameter of 10 µm or more, it can be easily collected by wet spraying.

The circulating water drops while being gas-liquid contacted with SO ₂ through the absorption tower 49. At this time, in order to increase the gas-liquid contacting efficiency, the installation of the packed layer 48 is efficient, but the packed layer 48 has no accumulation of deposits. In order not to occur, for example, it should be configured as a grid. The circulating fluid is recycled by the circulating pump 50 at the bottom of the absorption tower, but water is introduced from the outside so that the salt concentration in the liquid is not excessively increased, and some of the liquid is discharged and transferred to the wastewater treatment unit 51. The method is the same as that of a flue gas desulfurization apparatus using conventional magnesium hydroxide.

In addition, in order to secure a predetermined amount or more of sulfite ions in the circulating fluid, the sulfite ion concentration in the circulating fluid is detected by the sulfite ion concentration detector 78, and when the sulfite ion concentration is small, the absorption tower through the oxidation nozzle 72. The control by the control valve 79 of the flow rate of the oxidized air supplied to the bottom part suppresses the oxidation by the oxidizing blower 73.

The presence of sulfite ions in the liquid improves the activity of MgO to the same extent as conventional magnesium hydroxide [Mg (OH) ₂ ] slurries.

In FIG. 12, the flow rate of oxidizing air is automatically controlled. However, when the system is operated by knowing the load condition in advance, it may be manually adjusted. The supply amount of the MgO powder is controlled to be supplied at a supply rate corresponding to the SOx load in the control unit 74 based on the signals transmitted from the SOx concentration detector 76 and the gas flow detector 77 in the gas. In addition, the supply amount of the MgO powder is controlled so that a signal is transmitted from the PH meta 75 to the control unit 74 so as to be within the fixed region so that problems such as scaling in the absorption tower 49 do not occur.

As specifically described above, in the wet type flue gas desulfurization apparatus using magnesium oxide according to the present invention, the SOx gas can be removed as it is by blowing the magnesium oxide powder corresponding to the SOx concentration in the gas into the flue. In addition, by spraying the circulating liquid with magnesium oxide powder scattered within the flue in the same manner as in the conventional wet absorption tower, both the diffusion of the absorbent and the recovery of the powder can be performed.

In particular, in the case of adopting a configuration in which a predetermined amount of disulfate ions is secured by providing an oxidation inhibiting means, since the activity of MgO increases, no special facility for hydrating MgO to Mg (OH ₂ ) is required. Along with the SO ₃ removal effect, the function of the flue gas desulfurization apparatus using magnesium and the construction cost can be greatly reduced, and the operation cost can be reduced by using a cheap magnesium oxide absorbent.

Further, by employing the operation method according to the present invention, it is possible to safely operate the flue gas desulfurization apparatus of the present invention in response to SOx load without causing problems such as scaling.

Claims (4)

A flue gas desulfurization method comprising using a small gas magnesia as a desulfurizing agent and directly supplying it as MgO without hydrating the desulfurizing agent installed in the bottom of the desulfurization tower. In a flue gas desulfurization apparatus using magnesium oxide as an absorbent, magnesium oxide spray means and magnesium oxide spray means for spraying magnesium oxide powder directly into flue gas to solid-liquid react a portion of magnesium oxide with SO ₃ gas present in the flue gas. And a wet absorption tower disposed downstream of the means to collect magnesium oxide powder and reaction product of magnesium oxide and SO ₃ into a circulating fluid, and to absorb SO ₂ gas through the gas-liquid reaction in the circulating fluid. Wet type flue gas desulfurization apparatus. The wet type flue gas desulfurization apparatus according to claim 2, further comprising an oxidation inhibiting means for inhibiting oxidation in the absorption tower to secure a predetermined amount or more of sulfite ions in the circulating fluid. The wet type flue gas desulfurization apparatus according to claim 2 or 3, wherein the injection amount of magnesium oxide is controlled according to the concentration of SO ₂ in the flue gas, the flow rate of the flue gas, and the pH of the liquid in the absorption tower.