JPH07100330A - Flue gas desulfurizing method - Google Patents

Abstract

PURPOSE:To provide a flue gas desulfurizing method by which a high effect of decreasing COD in waste water is obtd. and the device is simplified. CONSTITUTION:This flue gas desulfurizing method comprises absorbing the SOx in waste gases 11 in an absorbent liquid 32, circulating the absorbent liquid 32 in which this SOx is absorbed to reuse the liquid for absorption of the SOx, partly oxidizing the absorbent liquid 32 and draining the liquid outside the system. Air 34 for oxidation is brought into contact with the absorbent liquid 32 to oxidize the absorbent liquid 32 in the active carbon of an active carbon packed bed 23 at the time of oxidizing a part of the absorbent liquid 32. The absorbent liquid 32 is oxidized by bringing the absorbent liquid 32 into contact with the air 34 in the the absorbent liquid 32 into contact with the air 34 in the active carbon in the state of adjusting its pH to 4.0 to 7.0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a flue gas desulfurization method,
It can be used to treat exhaust gas containing sulfur oxides from heating furnaces that use coal, heavy oil, etc. as fuel, boilers, refuse incinerators, and the like.

[0002]

BACKGROUND OF THE INVENTION In a flue gas desulfurization method using an absorbent containing a magnesium compound such as magnesium hydroxide or magnesium oxide, when the absorbent absorbs sulfur oxides, Sulfite is formed. The effluent having a high sulfite concentration has a high COD, and if drained as it is, it has an adverse effect on the environment. Therefore, COD is reduced by subjecting the waste liquid containing such a sulfite to an oxidation treatment by air aeration (JP-A-51-16192).
JP-A-57-4213 and JP-A-62-33530).

In order to increase the contact efficiency between air and sulfite during air aeration, various measures such as improving the dispersibility of air and subdividing the bubble size have been conventionally made. In general, the air pressure corresponding to the liquid depth of the aeration tank and the amount of air that is 1.5 to 10 times the theoretical equivalent of the oxidizing air are required. As a result, a high discharge pressure of the oxidizing air is required, which causes the following problems. That is, when power is driven by a motor, the amount of power used increases and the operating cost increases. In addition, noise countermeasures associated with the use of air compressors,
It is necessary to take measures against vibrations, and there is equipment cost and space for that.

Since the apparatus related to such flue gas desulfurization is not an original production facility, such incidental equipment can be simplified as much as possible while maintaining a desired flue gas desulfurization effect in order to suppress the product price. There is a demand for this.
Therefore, an object of the present invention is to provide a flue gas desulfurization method capable of obtaining a high effect of reducing COD in wastewater and simplifying the apparatus.

[0005]

According to the present invention, the absorbing solution absorbs the sulfur oxides in the exhaust gas, and the absorbing solution which has absorbed the sulfur oxides is circulated to re-absorb the sulfur oxides. In addition to using, in the flue gas desulfurization method of oxidizing a part of the absorption liquid and discharging it to the outside of the system, when oxidizing a part of the absorption liquid, contact the absorption liquid and an oxygen-containing gas in activated carbon. It is characterized by being oxidized. The supply amount of the oxygen-containing gas is about 2 to 10 times the theoretical equivalent amount to the sulfur oxide to be oxidized.

In the activated carbon, the absorbing liquid and the oxygen-containing gas come into parallel flow contact while descending, so that the pressure loss becomes small, and the pressure of the oxygen-containing gas is 100 to 200 mmAq. Therefore, a powerful compressor is not required, and the oxygen-containing gas can be supplied by a normal fan. Thus, by simultaneously contacting the absorbing liquid and the oxygen-containing gas in activated carbon, the oxidation efficiency of sulfite is increased, which is because sulfite in the absorbing liquid is adsorbed by activated carbon,
It is presumed that this is because the sulfite is oxidized by oxygen in this state, and the sulfate that is generated thereafter is dissolved in water and desorbed from the activated carbon.

Further, in the present invention, when a part of the absorbing solution is oxidized, the absorbing solution is adjusted to pH 4.0 to 7.0, preferably 5.0 to 7.0. Adjust the pH of the absorbent to 4.
By setting it in the range of 0 to 7.0, the oxidation reaction of sulfite mediated by activated carbon can be most efficiently carried out. On the other hand, the absorption liquid after the oxidation treatment can be drained as it is without adjusting the pH as long as the pH is in the range of 6.0 to 9.0. Therefore, when considering both the efficiency of the oxidation reaction and the pH of the waste water, the pH of the absorbing solution after the oxidation treatment is 6.0 to 7.
It means that it is preferable to adjust to the range of 0.

[0008]

First, the structure of a flue gas desulfurization apparatus used in a flue gas desulfurization method according to an embodiment of the present invention will be described. Figure 1
As shown in FIG. 3, this flue gas desulfurization apparatus is provided with an absorption tower 12 for sulfur oxides in the exhaust gas 11, an oxidation tower 13 for sulfite, and an alkali tank 14. The liquid storage part 12A of the absorption tower 12 and the top of the oxidation tower 13 are connected by a first pipe 15, and a pump 16 and a filter 17 are provided on the way. A branch pipe 18 is provided between the pump 16 and the filter 17, and the branch pipe 18 is a spray nozzle 19 above the absorption tower 12.
The first loop 21 is formed in communication with the first loop 21.

A pump 16 is installed in the liquid reservoir 13A of the oxidation tower 13.
A second pipe 22 for drainage is provided via the. A branch pipe 23 is provided in the middle of the second pipe 22, and the branch pipe 23 is connected to the top of the oxidation tower 13 to form a second loop 24. The alkali tank 14 and the first pipe 15
The branch pipe 18 is connected by a third pipe 25. A distributor 26 is provided in the middle of the third pipe 25, and a branch pipe 27 is provided from the distributor 26 to the second loop 24.

The absorption tower 12 has an inlet 28 for the exhaust gas 11 formed on its side surface and an outlet 28 for the exhaust gas 11 formed on its upper surface.
29, a spray nozzle 19 provided inside, and a gas-liquid contact layer 31 provided below the spray nozzle 19. In addition, water 45 between the spray nozzle 19 and the gas-liquid contact layer 31
Is provided. The alkali absorbing liquid 32 in the alkali tank 14 is a solution of hydroxides such as sodium hydroxide, ammonium hydroxide, magnesium hydroxide and calcium hydroxide, and oxides such as magnesium oxide and calcium oxide.

The oxidation tower 13 has an activated carbon packed bed inside thereof.
33 is provided, and a supply port for the oxidizing air 34 and a supply port for the oxidation treatment liquid 35 circulating in the second loop 24 are formed at the top of the column. The oxidizing air 34 is supplied from the blower 42 through the air supply pipe 43. A valve 38 and a flow meter for controlling opening / closing of the valve 38 are provided in the middle of the air supply pipe 43.
44 are provided. In addition, the activated carbon packed bed 33 of the oxidation tower 13
A gas exhaust pipe 46 is connected between the liquid reservoir 13A and the liquid reservoir 13A. Then, the first pH sensor 36 causes the first loop 21
And provided in the bypass 37 between the liquid reservoir 12A of the absorption tower 12,
The pH sensor 36 is connected to the valve 38 provided in the third pipe 25.

A second pH sensor 39 is provided in a bypass 41 between the second loop 24 and the liquid reservoir 13A of the oxidation tower 13, and the pH sensor 39 is a branch pipe of the third pipe 25. It is connected to a valve 38 provided at 27. Next, a flue gas desulfurization method using this flue gas desulfurization apparatus will be described. The exhaust gas 11 introduced from the inlet 28 of the absorption tower 12 comes into countercurrent contact with the alkaline absorbent 32 sprayed from the spray nozzle 19 in the gas-liquid contact layer 31, and the sulfur oxide in the exhaust gas 11 absorbs the absorbent 32.
Will be absorbed and removed.

The desulfurized exhaust gas 11 is discharged from the outlet 29 to the outside of the system. The absorption liquid 32 that has absorbed the sulfur oxides is the absorption tower.
Collect in 12 liquid reservoirs 12A. The absorbing liquid 32 accumulated in the liquid reservoir 12A circulates through the first loop 21 and is sprayed again from the spray nozzle 19. Based on the detection result of the first pH sensor 36, the first loop 21
The opening / closing of the valve 38 is adjusted so that the pH of 32 becomes 5.0 to 7.0, and the alkali absorbing liquid 32 is supplied from the alkali tank 14.

A part of the absorption liquid 32 which has absorbed the sulfur oxides is sent to the oxidation tower 13 through the first pipe 15 and is sprayed from the top of the tower into the tower. The absorbing liquid 32 descends in the activated carbon packed bed 33 together with the oxidizing air 34 also supplied from the tower top and the oxidizing treatment liquid 35 circulating in the second loop 24. At this time, as the oxidizing air 34, the air 34 corresponding to 1.5 to 10 molar equivalents of oxygen with respect to the load of the sulfur oxide in the absorption tower 12 is supplied.

Then, in the activated carbon of the activated carbon packed bed 33, the absorbing liquid 32 and the oxidizing air 34 come into parallel flow contact with each other to oxidize the sulfite salt in the absorbing liquid 32 to generate a sulfate salt. The activated carbon packed bed
The gas that has passed down 33 is discharged from the system through the exhaust pipe 46. In this second loop 24, a second pH sensor 39
The pH of the oxidation treatment liquid 35 is 6.0 to 7.0 based on the detection result of
The opening / closing of the valve 38 is adjusted so that the alkali absorbing liquid 32 is supplied from the alkali tank 14. A part of the oxidation treatment liquid 35 is drained through the second pipe 22.

Experimental Example In the above-mentioned embodiment, when the supply amount of the oxidizing air 34 in the oxidation tower 13 is 2 Nm ² / H and the supply amount of the absorbing liquid 32 is 500 l / H (in FIG. 2, mark ●). In addition, the COD of the oxidation treatment liquid 35 was measured to confirm the oxidizing effect of sulfurous acid when the supply amount of the absorption liquid 32 was 250 l / H (indicated by ▲ in FIG. 2). The activated carbon in the activated carbon packed layer 33 is so-called activated activated carbon that has been subjected to a firing treatment at a temperature of approximately 200 ° C. or higher.

On the other hand, as a comparative example, the COD of the oxidation treatment liquid 35 was measured in the same manner as in the experimental example when direct aeration similar to the conventional one was performed (indicated by a circle in FIG. 2). As can be seen from this graph, when the absorbing solution 32 is oxidized using activated carbon (●, ▲), the COD value is lower than in the case of conventional direct aeration (○), and the absorbing solution 32 is absorbed by activated carbon.
It can be seen that the oxidizing effect of the sulfite in the inside was enhanced. Therefore, it is possible to increase the oxidation effect of sulfite in addition to the simplification of the apparatus that a conventional powerful compressor becomes unnecessary.

[0018]

According to the flue gas desulfurization method of the present invention, a high effect of reducing COD in waste water can be obtained, and the apparatus can be simplified.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a flue gas desulfurization apparatus used in a flue gas desulfurization method according to an embodiment of the present invention.

FIG. 2 is a graph in which COD of an oxidation treatment liquid according to an experimental example and a comparative example is measured.

[Explanation of symbols]

 11 Exhaust gas 12 Absorption tower 13 Oxidation tower 14 Alkaline tank 21 First loop 24 Second loop 31 Gas-liquid contact layer 32 Alkali absorption liquid 33 Activated carbon packed bed 34 Oxidation air 35 Oxidation treatment liquid

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location C02F 1/74 C B01D 53/34 125 R (72) Inventor Mikito Hayashi Chuo-ku, Chiba City, Chiba Prefecture 37-24 Nittacho Idemitsu Engineering Co., Ltd.

Claims (2)

[Claims] 1. An absorption liquid that absorbs sulfur oxides in exhaust gas, and the absorption liquid that has absorbed this sulfur oxide is circulated and reused for absorption of sulfur oxides, and a part of the absorption liquid. In the flue gas desulfurization method of oxidizing the wastewater and discharging it to the outside of the system, when oxidizing a part of the absorption liquid, the exhaust gas is characterized in that the absorption liquid and the oxygen-containing gas are brought into contact with each other in the activated carbon to oxidize. Desulfurization method. 2. The flue gas desulfurization according to claim 1, wherein the absorbent is brought into contact with the oxygen-containing gas to oxidize it in activated carbon in a state where the pH of the absorbent is adjusted to 4.0 to 7.0. Method.