JPH0720534B2 - Flue gas desulfurization method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a flue gas desulfurization method based on the wet absorption method.

[Background of the Invention] Flue gas emitted from various fuel furnaces such as a thermal power plant boiler, an alchemy chemical plant, and a metal refining plant is usually sulfur dioxide (SO ₂ ) and sulfur trioxide (SO ₃ ). Since it contains sulfur oxides, from the perspective of pollution prevention,
Various proposals have been made for the flue gas desulfurization method for removing the sulfur oxides in the flue gas, and many have already been put to practical use.

Various methods are known as the flue gas desulfurization method as described above, and as one of the typical methods, the flue gas is contacted with an alkaline aqueous solution (absorption solution) such as lime slurry or an aqueous ammonia solution to obtain sulfur. A wet method for absorbing and removing oxides is known. When lime slurry is used as the absorbing liquid in this wet method, gypsum is obtained, and when an aqueous ammonia solution is used, salts such as ammonium sulfate and ammonium sulfite useful as raw materials for final products or other industrial chemicals. Therefore, various studies have been conducted from such a viewpoint. In order to efficiently absorb sulfur oxides into the absorbing solution and to increase the salt concentration in the sulfur oxide absorbing solution that is finally recovered, the flue gas is contacted with the salt-containing absorbing solution before recovery. A method is used in which the flue gas is cooled and then introduced into an absorption tower and brought into countercurrent contact with the absorbing liquid. Further, in this method, in order to increase the salt concentration of the salt-containing absorbing liquid generated in the absorption tower and to increase the absorption efficiency, countercurrent contact with the flue gas is performed while circulating the absorbing liquid.

On the other hand, it has been a problem that steam is accompanied by the treated gas discharged from the desulfurization apparatus using the wet flue gas desulfurization method. There is a problem that this steam is discharged in the state of white smoke and becomes stack rain, and that the steam is discharged in a state in which the smoke gas contains soot and dust. Therefore, the generation of acid rain due to these acidic water vapors is promoted.

Conventionally, as a method of preventing stack rain or preventing white smoke generated when exhaust gas is discharged from a chimney, a processing method described below has been used.

(B) Afterburning method This is a method in which the flue gas desulfurized by flue gas is heated to about 110 ° C using an afterburner and released into the atmosphere.

However, in the treatment by this method, there is a problem that the fuel cost increases and the increase reaches 3% of the main fuel. Further, although the emitted flue gas becomes transparent, there is a problem that the substance generated by this afterburning is additionally emitted.

(B) Swirling flow method and eliminator method This is to install a device such as a deflector plate inside the exhaust chimney to give a swirling flow to the discharged smoke gas and separate water droplets etc. from the smoke gas by centrifugal force. It is a method of collecting.

However, in this method, the equipment cost is high, and the particulate matter contained in the flue gas cannot be collected. Further, since the water droplet separation capacity changes depending on the amount of gas discharged, a certain separation capacity is not guaranteed. Further, there is a problem that it takes a long time to carry out the remodeling work inside the chimney, and it is necessary to stop the device for maintenance.

(C) Mist cotrel method This is a method of removing water vapor, soot dust, particulate matter, etc. using an electrostatic precipitator. It has excellent removal efficiency and removal capacity, but the equipment is very expensive and running. Costs and maintenance costs are also high. Furthermore, since the device is large, there is a problem that a large site is required.

The conventional method for removing steam contained in the desulfurized flue gas and preventing stack rain and white smoke from the chimney is insufficient in terms of efficiency or cost. It can be said that there was.

[Object of the Invention] The present invention provides a flue gas desulfurization method based on a wet absorption method,
A main object of the present invention is to provide a method capable of effectively collecting water vapor and particulate matter which are easily discharged together with a desulfurization gas by using a relatively simple device.

The present invention particularly cools the flue gas containing sulfur oxides in the cooling tower by bringing them into contact with the sulfur oxide absorbing liquid supplied from the absorption tower described later, and then introducing this into the absorption tower, To provide a method for improving the desulfurization method of flue gas, which comprises absorbing sulfur oxide into the absorption liquid by countercurrently contacting with the sulfur oxide absorption liquid introduced into the absorption tower under circulation. To aim.

SUMMARY OF THE INVENTION According to the present invention, flue gas containing sulfur oxide is cooled in a cooling tower by bringing it into contact with a sulfur oxide absorbing liquid supplied from an absorption tower described later, and then this is supplied to the absorption tower. A method for desulfurizing flue gas, which comprises introducing sulfur oxide into the absorption tower by countercurrently contacting with the sulfur oxide absorption solution to be introduced into the absorption tower under circulation, Characterized by including a step of forcibly cooling the sulfur oxide absorption liquid introduced into the absorption tower under circulation to a temperature in the range of 25 to 60 ° C. in the circulation process, and using an aqueous ammonia solution as the sulfur oxide absorption liquid. And the flue gas desulfurization method.

[Detailed Description of the Invention] The flue gas to be treated by the flue gas desulfurization method of the present invention is a sulfur oxide discharged from a thermal power plant boiler or various fuel furnaces such as chemical plants and metal smelting plants. It is a high temperature flue gas containing. Usually, the flue gas contains sulfur oxide (SOx) in the concentration range of 500 to 5000 ppm. Further, such a flue gas usually contains water vapor in the range of 3 to 20% by weight, and further contains soot dust or fume (particulate matter).

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 is a flow sheet showing an example of arrangement of a cooling tower and an absorption tower suitable for carrying out the method of the present invention.

In FIG. 1, A is a cooling tower, B is a first absorption tower, and C is a second absorption tower. Usually, the first absorption tower B and the second absorption tower C are each filled with a filler such as Raschig rings or ball rings.

Below the cooling tower A, a conduit 1 for introducing the flue gas to be treated is provided. Cooling tower A near the top of cooling tower A
A conduit 2 for introducing the flue gas discharged from the first absorption tower B to the first absorption tower B is provided. The conduit 2 is connected to the lower part of the first absorption tower B so as to connect the cooling tower A and the first absorption tower B in series. Near the top of the first absorption tower B, a conduit 3 for introducing the flue gas discharged from this absorption tower to the second absorption tower C is provided. The conduit 3 includes a first absorption tower B and a second absorption tower C.
Are connected to the lower part of the second absorption tower C so that and are connected in series. A conduit 4 is provided near the top of the second absorption tower C to guide the flue gas discharged from the second absorption tower C to a chimney or the like.

On the other hand, a conduit for introducing the absorbing liquid (aqueous ammonia solution) to the second absorption tower C, the first absorption tower B, and the cooling tower is arranged separately from the above-mentioned flue gas conduit. I.e. conduit 11
A conduit 12 extending from the upper part of the second absorption tower C
Conduits 13 extending from 11 are connected to the upper part of the first absorption tower B, respectively. The conduit 14 from the lower part of the second absorption tower C is connected to the upper part of the first absorption tower B, and the conduit 15 from the lower part of the first absorption tower B is connected to the upper part of the cooling tower A. The cooling tower A is provided with a conduit 16 for discharging the absorbing liquid.

Further, in the second absorption tower C, a forced cooling means D ₂ such as a water cooling device is attached to the conduit 17 extending from the lower portion thereof, and the conduit 18 discharged from the forced cooling means D ₂ is connected to the upper portion of the second absorption tower C. The piping is arranged so that the absorbing liquid inside the second absorption tower C can be circulated while being cooled. Further, in the first absorption tower B as in the second absorption tower, a forced cooling means D ₁ is attached to the conduit 19 extending from the lower part thereof, and further the cooling means D ₁
The conduit 20 exiting from the above is connected to the upper part of the first absorption tower B, and piping is provided so that the absorption liquid inside the first absorption tower B can be circulated while being cooled.

A conduit 21 normally exits from the lower part of the cooling tower A, and its tip is connected to the upper part of the cooling tower A so that the cooling liquid inside the cooling tower can be circulated.

The forced cooling means D ₁ is provided with a conduit 31 for supplying and discharging the cooling liquid, and the forced cooling means D ₂ is provided with a similar conduit 32.

The flue gas desulfurization method of the present invention is carried out as follows using the cooling tower, the first absorption tower and the second absorption tower arranged in this way.

In the cooling tower A, the flue gas to be treated introduced through the conduit 1 is brought into contact with the absorbing liquid introduced from the first absorption tower through the conduit 15, and the temperature of the flue gas when leaving the cooling tower is usually The flue gas is cooled to a temperature of 80 ° C or lower (preferably 50 to 60 ° C).

Normally, the absorbent inside the cooling tower A is repeatedly contacted with the flue gas while circulating through the conduit 21. Contact is usually made in countercurrent.

In this way, when the flue gas is cooled in the cooling tower, a considerable amount of water contained in the absorbing liquid evaporates.

The cooled flue gas is sent from the cooling tower A to the first absorption tower B through the conduit 2 together with the steam generated by evaporation in the cooling tower.

On the other hand, the absorption liquid obtained by cooling the flue gas in the cooling tower is the ammonium salt of sulfur oxide (eg, acidic ammonium sulfite [NH ₄ HSO ₃ ],
Ammonium sulphate [(NH ₄ ) ₂ SO ₄ ] and ammonium sulfite [(NH ₄ ) ₂ SO ₃ ]) are contained at a high concentration, and are usually discharged from the conduit 16 and sent to a purification process or the like. The salt contained in this cooling liquid is
For example, it is used for the synthesis of ammonium hydroxylamine disulfonate.

Next, in the first absorption tower B, the flue gas introduced through the conduit 2 (including water vapor evaporated in the cooling tower) and the absorption liquid are brought into countercurrent contact. The absorption liquid is extracted from the lower part of the first absorption tower B and is circulated and introduced into the upper part of the absorption tower.
In the present invention, the circulating absorption liquid is forcibly cooled in the circulation process by using the cooling liquid. And
The absorbent thus cooled is repeatedly contacted with the flue gas.

The absorption liquid can be cooled using various methods using a cooling liquid, but it is advantageous to use the forced cooling means D ₁ attached to the circulation line for circulating the absorption liquid. . That is, from the lower part of the first absorption tower B to the conduit 19
Introduced into the forced cooling means D ₁ the absorption liquid extracted in, where the cooling liquid is used, the liquid temperature is 25 to 60 ° C., preferably 55 to
Cool to within 25 ° C. The cooled absorption liquid is introduced into the upper part of the absorption tower B by the conduit 20, and comes into countercurrent contact with the flue gas. Water, seawater or the like is usually used as the cooling liquid.

By the countercurrent contact between the flue gas and the cooled absorbing liquid, the water vapor contained in the flue gas, that is, the water content and the cooling contained in the flue gas introduced into the cooling tower A. At least a part of the water vapor that has been evaporated and contained in the flue gas during cooling in the tower A aggregates, for example, with soot and dust contained in the flue gas as the core. Then, since the liquid temperature of the absorbing liquid can be adjusted by adjusting the amount of the cooling liquid introduced into the forced cooling means D ₁ , it is possible to adjust the amount of condensed water by using this method.

Sulfur oxides contained in the flue gas are absorbed by forming an ammonium salt in the absorbing liquid as in the case of the conventional wet flue gas defluxing method.

A part of the absorbing liquid is sent to the cooling tower A through the conduit 15 and used for cooling the flue gas.

The absorption liquid used in the first absorption tower B is supplied from the conduit 13. Further, when the second absorption tower is arranged,
It is also supplied from the second absorption tower C through the conduit 14.

In the desulfurization flue gas method of the present invention, the flue gas treated in the first absorption tower can be discharged as it is, but as shown in FIG. 1, the second absorption tower C is used.
It is preferable to introduce and treat the above.

In this example, the flue gas treated in the first absorption tower B is introduced into the second absorption tower C through the conduit 3.

The flue gas introduced into the second absorption tower C makes countercurrent contact with the absorbing liquid. This absorption liquid is extracted from the lower part of the second absorption tower and introduced into the upper part of the absorption tower. In the present invention, also in the second absorption tower, it is preferable to forcibly cool the circulating absorption liquid by using the cooling liquid. Then, the cooled absorption liquid repeatedly makes countercurrent contact with the flue gas.

It is advantageous to cool the absorbing liquid by using the forced cooling means D ₂ attached to the circulation line for circulating the absorbing liquid, similar to the cooling in the first absorption tower. That is, the absorption liquid withdrawn from the lower part of the second absorption tower C through the conduit 17 is introduced into the forced cooling means D ₂ , where it is cooled using the cooling liquid. The cooled absorption liquid is introduced into the upper part of the absorption tower C by the conduit 18. As the cooling liquid, as in the above case, water,
Use seawater.

By this countercurrent contact, at least a part of the water vapor remaining in the flue gas is further aggregated with, for example, soot and the like as nuclei. Therefore, as in the case of the first absorption tower, the temperature of the absorbing liquid can be adjusted by adjusting the amount of the cooling liquid introduced into the forced cooling means D _2, and the amount of water that aggregates can be adjusted.

Also in this step, the sulfur oxide remaining in the flue gas is absorbed as an ammonium salt in the absorbing liquid.

After countercurrent contact with the absorbing liquid in the second absorption tower C, the flue gas is
It is discharged from a chimney (not shown) via the conduit 4. Since the content of water vapor in the flue gas discharged by desulfurization treatment using the method of the present invention as described above is remarkably reduced and the temperature of the flue gas is lowered, white smoke prevention treatment, etc. There is no need to apply. However, a known white smoke prevention treatment can be used in combination if desired.

The absorbing liquid in the second absorption tower is usually introduced into the first absorption tower B through the conduit 14. In addition, directly as it is, the cooling tower A
Can also be introduced.

In the present invention, when the first and second absorption towers are arranged, both of the absorbing liquids can be cooled as described above, or one of the absorbing liquids can be cooled. Further, when three or more absorption towers are arranged, the absorption liquid of at least one (preferably the last one, more preferably the last two) of the absorption towers may be cooled.

EFFECTS OF THE INVENTION According to the flue gas desulfurization method of the present invention, it is possible to coagulate the vapor in the flue gas with high efficiency by countercurrently contacting the flue gas with the absorbent that has been forcibly cooled in the absorption tower. it can.

Since the water produced as described above is introduced into the absorbing solution, it can be used as water for adjusting the concentration of the ammonium salt of sulfur oxide produced in the absorbing solution. Therefore, there is also an advantage that the concentration of the salt-containing absorption liquid recovered from the cooling tower can be freely adjusted according to the request of the subsequent processing step. That is, by adjusting the cooling temperature of the absorbing liquid, an arbitrary amount of water can be condensed and collected in the absorption tower, so that it is not particularly necessary to add water for adjusting the salt concentration from outside the system.

In the flue gas desulfurization method of the present invention, the content of water vapor in the flue gas can be adjusted by cooling the flue gas in the absorption tower to coagulate and recover the water vapor in the flue gas. Therefore, not only the generation of stack rain can be effectively prevented, but also the generation of white smoke can be effectively prevented even if the exhaust gas is discharged without performing the white smoke prevention processing.

Further, as described above, when the water vapor agglomerates in the absorption tower, the soot dust becomes a nucleus and is collected, so that the content of the dust particles in the flue gas can be remarkably reduced. Therefore, the flue gas can be emitted without performing the dust removal process.

Despite this effect, the removal efficiency of sulfur oxides does not decrease, but rather the absorption liquid temperature in the absorption tower is low, so ammonia and SO ₂ are absorbed and formed in the absorption liquid. Since the equilibrium vapor pressure of the salt becomes low, the absorption is further promoted, and the removal efficiency tends to be improved.

Next, examples and comparative examples of the present invention will be shown.

[Example 1] The cooling tower A, the first absorption tower B, and the second absorption tower C were arranged as shown in Fig. 1 to desulfurize the flue gas.

148000 kg / of flue gas (160 ° C) of the following composition a in the cooling tower A
The absorption liquid having the following composition A introduced from the first absorption tower B is introduced into the cooling tower A at a speed of 8000 kg / hour, and the flue gas and the absorption liquid are countercurrently contacted with each other and discharged. The smoke gas was cooled. The flue gas of the following composition b cooled to 56 ° C. from the cooling tower A was led out at a rate of 154000 kg / hour, and the absorption liquid of the following composition B was recovered from the cooling tower A at a rate of 1800 kg / hour.

In the cooling tower A, 6200 kg of water in the absorbing solution was evaporated per hour in order to cool the flue gas at 160 ° C to 56 ° C.

Flue gas composition a CO ₂ 16.0 wt% H ₂ O 6.7 wt% O ₂ 5.4 wt% N ₂ 71.6 wt% SO ₂ 2500 ppm Flue gas composition b CO ₂ 15.5 wt% H ₂ O 10.5 wt% O ₂ 5.2 wt% N ₂ 69.1 wt% SO ₂ 2500 ppm Absorbent composition A NH ₄ HSO ₃ 4.4 wt% (NH ₄ ) ₂ SO ₃ 1.4 wt% (NH ₄ ) ₂ SO ₄ 2.4 wt% H ₂ O 91.8 wt% Absorbent composition B NH ₄ HSO ₃ 19.4 wt% (NH ₄ ) ₂ SO ₃ 6.3 wt% (NH ₄ ) ₂ SO ₄ 10.4 wt% H ₂ O 63.9 wt% Next, the flue gas extracted from the cooling tower A is transferred to the first absorption tower B.
Introduced. To the first absorption tower B, 25% by weight aqueous ammonia solution was charged from the top at a rate of 500 kg / hour, and further, the absorption liquid led out from the bottom of the second absorption tower C was introduced at a rate of 3100 kg / hour.

409000 from the bottom of the first absorption tower B
Withdrawal at a rate of kg / hour and 250 seawater as a cooling liquid
A forced cooling device D ₁ (spiral cooler, cooling capacity 3.0 × 10 ⁶ Kcal / hour) introduced at a rate of ton / hour was used to cool to 51 ° C. The cooled absorption liquid, the aqueous ammonia solution, and the absorption liquid from the second absorption tower were combined and brought into countercurrent contact with the flue gas.

The temperature of the flue gas discharged from the first absorption tower B is 51 ° C., and 24.7% by weight of water vapor contained in the flue gas introduced from the cooling tower A is condensed in the first absorption tower B. It was possible (water content 8.1% by weight in the flue gas discharged from the first absorption tower).

Next, the flue gas extracted from the top of the first absorption tower B was introduced into the second absorption tower C. On the other hand, 25% by weight aqueous ammonia solution was charged from the top of the second absorption tower C at a rate of 70 kg / hour.

Furthermore, the absorption liquid is circulated from the bottom of the second absorption tower C.
With the forced cooling device D ₂ (model and cooling capacity are the same as above) in which seawater was introduced at a speed of 394,000 kg / hour and seawater was introduced as a cooling liquid at a rate of 150 tons / hour, the extracted absorption liquid was brought to 46 ° C. Cooled.

The cooled absorbing liquid and the aqueous ammonia solution were combined and brought into countercurrent contact with the flue gas.

The temperature of the flue gas discharged from the second absorption tower C is 46 ° C, and at this stage, 24.7% by weight of the steam introduced into the second absorption tower C via the first absorption tower B can be condensed. (The total steam aggregation rate of the first absorption tower and the second absorption tower was 43.3% by weight). The amount of flue gas discharged from the second absorption tower C is 147 tons / hour.

The composition of the discharged flue gas is shown below (flue gas composition c).

Flue gas composition c CO ₂ 16.2% by weight H ₂ O 6.2% by weight O ₂ 5.5% by weight N ₂ 72.2% by weight SO ₂ 10 ppm In this example, precipitation of ammonium salt of sulfur oxide was not observed, Therefore, it was not necessary to add water for adjusting the salt concentration from outside the system.

In addition, the desulfurization rate was 99% by weight or more, and when observed with the naked eye, almost no white smoke was generated from the chimney. The dust reduction rate (measured according to JIS-Z-8808) was 30%.

[Comparative Example 1] In Example 1, the flue gas desulfurization treatment was performed without operating the forced cooling devices of the first absorption tower B and the second absorption tower C.

In this flue gas desalination process, 2500 kg /
It was necessary to feed water for salt concentration adjustment from the outside of the system at a rate of 4350 kg / hour in the second absorption tower C for a certain time.

The H ₂ O concentration in the flue gas discharged from the second absorption tower C was 10.
It was 5% by weight, and generation of white smoke was observed from the chimney. The desulfurization rate was 95% by weight.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an example of an arrangement of a cooling tower and an absorption tower suitable for carrying out the method of the present invention. A: cooling towers, B: the first absorption tower, C: second absorption tower, D _1, D _2: forced cooling means (water cooler) 4: flue gas conduit, 11-16: absorbing liquid conduit , 17 ~ 21:
Absorption liquid circulation conduit, 31, 32: Cooling liquid conduit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location B01D 53/34 ZAB (72) Inventor Toshimi Furukawa 3-1, 1 Tsukikoshinmachi, Sakai City, Osaka Prefecture Sakai Factory (56) References JP-A-60-58230 (JP, A)

Claims (5)

[Claims] 1. A flue gas containing ionic oxides is cooled in a cooling tower by bringing it into contact with a sulfur oxide absorbing liquid supplied from an absorption tower, which is then introduced into the absorption tower. A method for desulfurizing flue gas, which comprises causing sulfur oxide to be absorbed by the absorbing solution by countercurrently contacting with the sulfur oxide absorbing solution introduced into the absorbing tower, which is circulated to the absorbing tower. A flue gas characterized by including a step of forcibly cooling the sulfur oxide absorption liquid introduced below to a temperature in the range of 25 to 60 ° C. in the circulation process, and using an aqueous ammonia solution as the sulfur oxide absorption liquid. Desulfurization method. 2. The flue gas desulfurization method according to claim 1, wherein the sulfur oxide absorption liquid introduced into the absorption tower under circulation is forcibly cooled to a temperature range of 25 to 55 ° C. during the circulation process. 3. An apparatus for using two or more absorption towers connected in series and forcibly cooling the sulfur oxide absorption liquid in at least the last of the absorption towers. Flue gas desulfurization method according to item 1. 4. A patent using two or more absorption towers connected in series, wherein at least the last two of the absorption towers are each equipped with a device for forcibly cooling the sulfur oxide absorption liquid. The flue gas desulfurization method according to claim 1. 5. The flue gas desulfurization method according to claim 1, wherein the flue gas is cooled in a cooling tower to a temperature of 80 ° C. or lower.