TW201806661A - Impurity removal method removing impurities such as dust contained in a gas such as exhaust gas with good efficiency and at low cost - Google Patents

Abstract

The present invention aims to provide an impurity removal method capable of efficiently and inexpensively removing dust, impurities contained in gases such as exhaust gas. An impurity removal method comprises: a step of forming a froth layer (A) in a tank (2) by blowing an exhaust gas via an exhaust gas dispersion pipe (7) into an absorbing liquid contained in the tank (2), if "gas retention" is defined as the ratio of gas in the froth layer (A), then the gas retention of the froth layer (A) is set as 0.4 to 0.9, and the height of the froth layer (A) is set 0.2 to 1.8 m, and the gas-liquid contact area per unit volume of the froth layer (A) is set 1,500 to 2,500 m2/m3, thereby removing the impurities such as dust contained in gases such as exhaust gas with good efficiency and at low cost.

Description

Impurity removal method

The present invention relates to an impurity removing method for removing impurities such as suspended particles contained in a gas such as exhaust gas.

Conventionally, in order to remove such impurities from exhaust gas containing environmental pollutants (impurities) such as SO ₂ or suspended particles, a wet exhaust gas treatment method has been known in which the exhaust gas is brought into contact with an absorption liquid.

For example, a desulfurization method is known, which contains an absorption liquid in the lowermost chamber of an enclosed tank divided into two or three chambers, and passes exhaust gas through a plurality of partition plates installed in the lower chamber and the upper chamber. The exhaust dispersion pipe is blown into the absorption liquid to desulfurize, and the purified exhaust gas is discharged from the lowermost chamber, or is discharged from the lowermost chamber to the uppermost chamber (see Patent Documents 1 to 4).

[Prior technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 3732291

[Patent Document 2] Japanese Patent No. 4616142

[Patent Document 3] Japanese Patent Publication No. 4-9570

[Patent Document 4] Japanese Patent Publication No. 3-70532

With regard to such a desulfurization method, there have been problems in operation of the device, such as prevention of scaling problems of the device, automatic control of the device, and improvement of the durability of the device, or upsizing of the device. Numerous studies have been carried out on problems and issues that have occurred at the time, and considerable technical progress has been made. However, it has not yet reached a sufficiently satisfactory stage in terms of economical aspects such as reduction in device cost or reduction in device operation cost, or in terms of stabilization of device operation.

In addition, in the aforementioned Patent Documents 1 to 4, the details of the bubble foam layer (froth layer) as a gas-liquid contact area are not described. In addition, for the submicron-level ones including PM2.5, Removal of fine particles of dust, etc., has not obtained sufficient performance.

The present invention has been made in view of the foregoing circumstances, and an object thereof is to provide an impurity removal method capable of efficiently and inexpensively removing impurities such as suspended particles contained in a gas such as exhaust gas.

In order to achieve the aforementioned object, the method for removing impurities according to the present invention includes the steps of blowing a gas containing impurities into a absorbing liquid contained in a tank through a gas dispersion tube, thereby forming a foam layer in the tank; Its characteristics are:

(i) Set the gas retention of the foam layer to 0.4 ~ 0.9

(ii) The height of the foam layer is set to 0.2 to 1.8 m. Furthermore, it is preferable to set the gas retention to 0.5 to 0.8, and to set the height of the foam layer to 0.4 to 1.2 m, respectively.

Here, the gas retention of the foam layer is set to 0.4 to 0.9 for the following reasons.

That is, if the gas retention is less than 0.4, a sufficient gas-liquid contact area cannot be obtained, the removal performance (impurity removal rate) is significantly lowered, and predetermined performance cannot be exhibited.

In addition, if the gas retention exceeds 0.9, a shortcut of gas will be generated in the foam layer, and a stable foam layer cannot be formed, which is not good. In addition, a large amount of gas will be blown in, and the energy input into the gas dispersion tube will be excessive .

Here, the height of the foam layer is set to 0.2 to 1.8 m for the following reasons.

That is, if the height of the foam layer is less than 0.2 m, sufficient gas-liquid contact time cannot be obtained, the removal performance (impurity removal rate) is significantly lowered, and predetermined performance cannot be exhibited.

In addition, if the height of the foam layer exceeds 1.8m, in order to prevent the exhaust gas from being discharged out of the system with the smoke containing solid particles in the purified exhaust gas, the distance from the upper end of the foam layer to the opening of the gas outlet is increased. The need to increase the height of the device does not have any economic benefits, and the energy required to blow the gas will be too large, so it is not good.

In the present invention, by setting the gas retention of the foam layer to 0.4 to 0.9 and the height of the foam layer to 0.2 to 1.8 m, dust contained in gas such as exhaust gas, or SO can be used. Impurities such as gaseous toxic substances represented by _x or hydrogen chloride are efficiently and inexpensively removed.

In particular, it is possible to capture and remove dust having submicron-level fine particles which are difficult to be captured by a general spray type liquid dispersion type removal device.

In the aforementioned configuration of the present invention, (iii) the gas-liquid contact area per unit volume of the foam layer is preferably set to 1000 to 3000 m ² / m ³ .

In addition, the gas-liquid contact area per unit volume of the foam layer is more preferably set to 1500 to 2500 m ² / m ³ .

The gas-liquid contact area per unit volume of the foam layer is preferably set to 1000 to 3000 m ² / m ³ for the following reasons.

That is, by making the gas-liquid contact area per unit volume of the gas-liquid mixed layer (foam layer) 1000 m ² / m ³ or more, and further ensuring a sufficient gas-liquid contact area, the removal performance (impurities) can be stably maintained (Removal rate); In addition, if the gas ejection speed from the gas discharge hole of the gas dispersion pipe is greater, the bubbles are finer, and the distribution of the bubble diameter can be reduced to improve the removal performance (impurity removal rate). As the ejection speed increases, the energy consumption of the gas dispersion tube (the pressure loss accompanying the ejection increases) also increases. Therefore, the removal performance can be stably maintained while the gas-liquid contact area is 3000 m ² / m ³ or less. (Impurity removal rate) Excessive energy consumption is suppressed.

With such a configuration, a sufficient gas-liquid contact area can be obtained, so that impurities can be removed efficiently and at low cost, and energy consumption by the gas dispersion tube can be suppressed.

In the aforementioned configuration of the present invention, the impurities may include dust in the gas, or the gas may contain impurities having a particle diameter of 0.1 to 10 μm.

According to such a structure, compared with the conventional technology, the purpose of removing especially dust or the impurity with a particle diameter of 0.1-10 micrometers from a gas can exhibit higher removal efficiency compared with the prior art.

According to the present invention, it is possible to continuously and efficiently remove dust contained in a gas such as exhaust gas or impurities such as a gaseous toxic substance represented by SO _x or hydrogen chloride at low cost.

1‧‧‧ impurity removal device

2‧‧‧closed tank (slot)

3‧‧‧ first partition

4‧‧‧The first room

5‧‧‧Second Room

6‧‧‧ exhaust inlet

7‧‧‧ exhaust dispersion pipe

8‧‧‧ exhaust outlet

9‧‧‧ exhaust outlet

10‧‧‧ Mixer

11‧‧‧ Absorbent supply tube

12‧‧‧ Oxidation air supply pipe

13‧‧‧ Absorption liquid extraction tube

14‧‧‧Second partition

15‧‧‧ Third Room

16‧‧‧Exhaust riser

17‧‧‧wash liquid supply pipe

18‧‧‧washing liquid discharge port

A‧‧‧Gas-liquid mixed layer (foam layer)

B‧‧‧Solid-liquid separation space

D‧‧‧ diameter of exhaust nozzle

L‧‧‧ Absorbent

W‧‧‧ static liquid level of absorption liquid

[Fig. 1] Fig. 1 is a schematic diagram showing an example of an impurity removing apparatus according to an embodiment of the present invention.

[Fig. 2] A graph for explaining an impurity removing method according to an embodiment of the present invention, and showing a relationship between the removal rate of impurities and gas retention.

[Fig. 3] A graph showing the relationship between the impurity removal rate and the height of the foam layer as described above.

[Figure 4] Same as above, and shows the removal rate of impurities and the unit volume of the foam layer Graph showing the relationship between the accumulated gas-liquid contact area.

[Fig. 5] A graph showing the collection efficiency (impurity removal rate) of each particle diameter of dust particles in the exhaust gas, as described above.

[Fig. 6] Fig. 6 is a schematic diagram showing another example of the impurity removing device according to the embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of an impurity removing device having a three-chamber structure according to the present invention. In the figure, the symbols refer to: 1 series desulfurization device, 2 series closed tank, 3 series first partition, 4 series first chamber, 5 series second chamber, 6 series exhaust inlet, and 7 series exhaust Gas dispersion tube, 8 series exhaust outlet, 9 series exhaust outlet, 10 series mixer, 10 'series stirring shaft, 11 series absorbent supply tube, 12 series oxidation air supply tube, 13 series absorption liquid extraction tube, 14 series second partition, 15 series third chamber, 16 series exhaust riser, 17 series cleaning liquid supply pipe, 18 series cleaning liquid discharge pipe, L series absorption liquid, W series absorption liquid, A series gas-liquid mixed layer (foam layer), B series solid-liquid separation space.

The impurity removing device shown in FIG. 1 divides the inside of the closed tank 2 by the first partition plate 3 and the second partition plate 14 to form a first chamber 4, a second chamber 5, and a third chamber 15. Three-room construction. The first partition plate 3 and the second partition plate 14 may be any of a horizontal plate, a stepped plate, and an inclined plate. However, it is particularly preferable to use an inclined plate. In addition, the first room The 4th type is a chamber which accommodates the absorption liquid blown into the gas containing an impurity through the exhaust dispersion pipe 7, and is provided in the lower part of the closed tank 2.

An exhaust gas inlet 6 is arranged in the second chamber 5. The exhaust gas introduced from the exhaust gas inlet 6 is blown into the stationary liquid surface of the specific absorption liquid L through an exhaust gas dispersion pipe 7 from an exhaust gas discharge hole 8. W the lower part. A gas-liquid mixed layer (foam layer) A is formed above the exhaust gas ejection hole 8, and the dust or sulfurous acid gas system in the exhaust gas is absorbed therein. As the absorption liquid L, a gypsum slurry containing a calcium compound or a calcium compound-containing substance such as limestone and / or slaked lime is used as an absorbent.

The purified exhaust gas discharged above the gas-liquid mixed layer (foam layer) A in the first chamber 4 moves horizontally while rising to the upper space B (solid-liquid separation space) of the first chamber 4. During the flow of the purified exhaust gas, the smoke in the exhaust gas and the relatively large solid particles that cannot be removed by the gas-liquid mixed layer (foam layer) A are deposited in the solid-liquid separation space B by gravity settlement and The collision of the exhaust dispersion pipe 7 separates most of it from the purified exhaust gas. Purified exhaust gas subjected to solid-liquid separation is lifted by the exhaust riser 16 and is introduced into the third chamber 15. In the third chamber 15, the purified exhaust gas is switched from an upward flow direction to a substantially horizontal flow, and after the smoke and solid particles are separated from the purified exhaust gas, the purified exhaust gas is discharged from the exhaust discharge port 9. .

The solid particles deposited on the bottom surface (second partition plate 14) of the third chamber 15 are, for example, intermittent or continuous supply of a cleaning liquid from a cleaning liquid supply pipe 17, such as a gypsum-containing slurry, a Absorbs liquid, water, seawater, etc., and peels off from the surface of the second partition plate 14 together with The washing liquid is discharged together from the washing liquid discharge port 18 at one or more locations.

The inventors have found that the absorption liquid contained in the first chamber 4 of the closed tank 1 as described above is blown in by the exhaust gas dispersion pipe 7 to form a gas-liquid mixture in the first chamber 4 In the case of layer A (foam layer) A, the gas-liquid components of gas-liquid mixed layer (foam layer) A are set to the following (i) and (ii), thereby enabling the efficiency of impurities such as dust contained in the exhaust gas to be effectively reduced. Good and low cost continuous removal.

(i) The gas retention of the foam layer is set to 0.4 to 0.9.

(ii) The height of the foam layer is set to 0.2 to 1.8 m.

The so-called gas retention refers to the proportion of gas in the gas-liquid mixed layer (foam layer) A. The relationship between the gas retention Φ, the height H of the gas-liquid mixed layer (foam layer) A, and the gas injection depth L, is It can be expressed by the following formula. The height H of the gas-liquid mixed layer (foam layer) A refers to the length in the vertical direction from the center of the exhaust gas discharge hole 8 to the upper end of the gas-liquid mixed layer (foam layer) A; the gas injection depth L, The length in the vertical direction from the center of the exhaust gas ejection hole 8 to the stationary liquid level W of the absorption liquid L before the gas is blown in.

H = L × 1 / (1-Φ)

Here, the reason for setting the gas-liquid constituents of the gas-liquid mixed layer (foam layer) A to (i) and (ii) below is as follows.

That is, if the gas retention is less than 0.4, a sufficient gas-liquid contact area cannot be obtained, the removal performance (impurity removal rate) is significantly lowered, and predetermined performance cannot be exhibited. On the other hand, if the gas retention exceeds 0.9, a gas shortcut is generated in the gas-liquid mixed layer (foam layer) A, and a stable gas cannot be formed. The liquid mixing layer (foam layer) A is not good. In addition, a large amount of gas is blown in, and the energy input to the exhaust dispersion pipe 7 becomes excessive. Therefore, the gas retention is set to 0.4 to 0.9.

In addition, as shown in FIG. 2, when the gas retention exceeds about 0.5, the increase rate of the removal performance (impurity removal rate) starts to decrease, and when it exceeds about 0.8, the removal performance (impurity removal rate) reaches the upper limit.

Therefore, from the viewpoint of Fig. 2 and energy consumption, the gas retention system is more preferably set to 0.5 to 0.8.

In addition, if the height of the gas-liquid mixed layer (foam layer) A is less than 0.2 m, sufficient gas-liquid contact time cannot be obtained, the removal performance (impurity removal rate) is significantly lowered, and predetermined performance cannot be exhibited. On the other hand, if the height of the gas-liquid mixed layer (foam layer) A exceeds 1.8 m, in order to prevent the smoke containing solid particles from being discharged out of the impurity removal device 1 along with the purified exhaust gas, the foam layer is generated. It is necessary to increase the distance from the upper end to the gas outlet opening (exhaust exhaust port 9), so that the height of the device is increased without any economic benefits, and the energy required to blow the gas becomes too large, So bad. Therefore, the height of the foam layer is set to 0.2 to 1.8 m.

In addition, as shown in FIG. 3, when the height of the foam layer exceeds about 0.4 m, the increase rate of removal performance (impurity removal rate) starts to decrease, and when it exceeds about 1.2 m, the removal performance (impurity removal rate) reaches Ceiling.

Therefore, from the viewpoint of FIG. 3 and energy consumption, the height of the gas-liquid mixed layer (foam layer) A is preferably set to 0.4 to 1.2 m.

In addition, the present inventors have discovered that (iii) by setting the gas-liquid contact area per unit volume of the foam layer to 1000 to 3000 m ² / m ³ , it is also possible to include impurities such as dust contained in the exhaust gas Continuous removal with good efficiency and low cost.

The reason why the gas-liquid contact area per unit volume of the foam layer is so limited is because the gas-liquid contact area per unit volume of the gas-liquid mixed layer (foam layer) A is 1000 m ² / m ³ or more, and further ensure sufficient The gas-liquid contact area can stably maintain the removal performance (impurity removal rate). In addition, the larger the gas ejection speed from the exhaust gas discharge holes 8 of the exhaust dispersion pipe 7, the finer the bubbles and the larger the bubbles The diameter distribution is reduced to improve the removal performance (impurity removal rate). However, if the gas ejection speed is to be increased, the energy consumption (increased by the ejection pressure loss) carried by the exhaust dispersion pipe 7 is also increased. When the gas-liquid contact area is 3000 m ² / m ³ or less, it is possible to suppress excessive energy consumption while stably maintaining removal performance (impurity removal rate).

In addition, as shown in Figure 4, when the gas-liquid contact area per unit volume of the foam layer exceeds about 1500 m ² / m ³ , the rate of increase in removal performance (impurity removal rate) starts to decrease, and when it exceeds 2500 m ² / m ³ At the left and right, the removal performance (impurity removal rate) reaches the upper limit.

Therefore, from the viewpoint of FIG. 4 and energy consumption, the gas-liquid contact area per unit volume of the foam layer is more preferably set to 1500 to 2500 m ² / m ³ .

The gas-liquid contact area SA per unit volume of the foam layer is calculated as follows.

SA = Sb. N / Vf

Sb: average surface area of a single bubble forming a foam layer

Sb = π. db ²

db: bubble diameter

N: Number of bubbles in the foam layer

Vf: volume of foam layer

Vf = L. 1 / (1-Φ). S

N = Vf. Φ / Vb

Vb = 1/6. π. db ³ (volume of a single bubble)

L: gas injection depth (depth from the center of the gas injection hole of the gas dispersion tube to the stationary liquid surface before the gas is injected)

Φ: gas retention

S: The cross-sectional area of the foam layer (from the horizontal cross-sectional area of the gas-liquid mixed layer (foam layer) A minus the horizontal cross-sectional area of the exhaust dispersion pipe 7 and the horizontal cross-sectional area of the structure such that the purified exhaust cannot pass through. (Cross-sectional area)

In addition, the gas-liquid components of the gas-liquid mixed layer (foam layer) A are to be set as described in (i) to (iii) above. 8 equivalent diameter, the ejection speed from the exhaust ejection hole 8, the distance from the average position of the center points of the exhaust ejection holes 8 to the lower end of the exhaust dispersion pipe 7, and the purification of the first chamber 4 The average rising speed of the exhaust gas, the average horizontal speed of the purified exhaust gas in the first chamber 4, the speed of the purified exhaust gas rising from the exhaust rising cylinder 16, and the like are set as appropriate.

The equivalent internal diameter of the exhaust dispersion pipe and the equivalent diameter of the exhaust nozzle Represented by the equation.

Equivalent inner diameter of exhaust dispersion pipe = (4 × A) / B

A: Horizontal cross-sectional area of the internal space of the arrangement position of the exhaust gas discharge holes of the exhaust dispersion pipe

B: Length of the periphery of the horizontal cross section of the internal space surrounding the arrangement position of the exhaust gas discharge holes of the exhaust dispersion pipe

Equivalent diameter of exhaust nozzle = (4 × C) / D

C: The area of the exhaust nozzle

D: Length of the periphery of the exhaust gas ejection hole

The average rising speed of the purified exhaust gas in the first chamber 4 is based on the horizontal cross-sectional area of the space B above the gas-liquid mixed layer (foam layer) A minus the horizontal cross-sectional area of the exhaust dispersion pipe 7. The speed of the horizontal cross-sectional area of the total of the horizontal cross-sectional area of the structure through which the purge exhaust cannot pass.

The average horizontal velocity of the purified exhaust gas in the first chamber 4 is a velocity based on the vertical cross-sectional area around the opening of the lower end portion of the exhaust gas riser 16 from the space B above the gas-liquid mixed layer A.

The exhaust dispersion pipe 7 can have a polygonal shape such as a circle, a triangle, a quadrangle, or a hexagon, or an arbitrary cross-sectional shape such as a trough. In addition, a plurality of exhaust gas ejection holes 8 are formed on the side wall of the exhaust gas dispersion pipe 7 at a certain height from the horizontal plane. The shape of the exhaust gas ejection holes can be circular, triangular, quadrangular, hexagonal, or star. Any shape, such as a pattern, can also be a slit shape. The exhaust gas ejection holes may be arranged in a row at a certain height for the exhaust dispersion pipe, and arranged in two rows at different heights. Or three or more columns are also acceptable.

The shape of the opening at the lower end of the exhaust dispersion pipe 7 may be any of a simple one having a horizontal end surface, an arbitrary inclined end surface, a blade shape of a saw, or a shape having a plurality of cutouts.

The cross-sectional shape of the exhaust rising cylinder 16 may be various shapes such as a circle, a square, and a rectangle.

Next, experimental examples will be described.

The gas-liquid constituents of the foam layer A are set as described in (i) to (ii) above.

Other conditions such as the size of the exhaust gas dispersion pipe (sparger) and the diameter (hole diameter) of the exhaust gas discharge hole are as described in Table 1 below.

In addition, the so-called inlet in Table 1 is an introduction port for introducing exhaust gas to the experimental device in this experiment, and the so-called outlet is a discharge port for exhaust gas from which the impurities and the like are removed from the experimental device.

The hole diameter is the equivalent diameter of the exhaust gas ejection hole, the number of holes is the number of exhaust gas ejection holes of each exhaust dispersion pipe, and the ejection velocity of the hole is the flow velocity of the exhaust gas ejected from the exhaust gas ejection hole.

The depth of the immersion liquid refers to the depth of the gas injection, and the length in the vertical direction from the center of the exhaust gas ejection hole to the stationary liquid surface of the absorption liquid before the gas is injected. The height of the foam layer is the length in the vertical direction from the center of the exhaust gas discharge hole to the upper end of the foam layer.

The superficial tower velocity of the foam layer gas is the average rising speed of the purified exhaust gas in the first chamber 4 shown in FIG. 1.

The results are shown in FIG. 5.

As shown in FIG. 5, from this experiment, it can be seen that dust having submicron-level fine particles that are difficult to be captured by a general liquid dispersion type removal device can be captured and removed.

As described above, according to this embodiment, the gas retention of the gas-liquid mixed layer (foam layer) A is set to 0.4 to 0.9, and the height of the gas-liquid mixed layer (foam layer) A is set to 0.2 to 1.8 m. It is possible to continuously and efficiently remove dust contained in a gas such as exhaust gas or impurities such as a gaseous toxic substance represented by SO _x or hydrogen chloride at low cost.

Fig. 6 is a schematic diagram showing an example of an impurity removing device having a two-chamber structure according to the present invention. In this figure, the same symbols as those shown in Figure 1 have the same meaning.

In the impurity removal device shown in Fig. 6, the exhaust gas purified by contact with the absorption liquid in the first chamber 4 is maintained at an average rising speed of 0.5 to 5 m / s, preferably 0.7 to 4 m / s. The average horizontal velocity is 8 m / s or less, preferably 6 m / s or less, and moves in the horizontal direction while rising in the upper space B of the first chamber 4. During the flow of the purified exhaust gas, the smoke and solid particles in the exhaust gas are separated from the exhaust gas in the solid-liquid separation space B by gravity settlement and collision separation with the exhaust dispersion pipe 7, and the smoke is separated. The purified exhaust gas and solids are discharged from the exhaust discharge port 9.

In such an impurity removal device, as in the above-mentioned case, by setting the gas-liquid constituent elements of the gas-liquid mixed layer (foam layer) A as described in (i) to (iii), the exhaust gas can be removed. The contained dust or impurities such as SO _x are efficiently and continuously removed at low cost.

1‧‧‧ impurity removal device

2‧‧‧closed tank (slot)

3‧‧‧ first partition

4‧‧‧The first room

5‧‧‧Second Room

6‧‧‧ exhaust inlet

7‧‧‧ exhaust dispersion pipe

8‧‧‧ exhaust outlet

9‧‧‧ exhaust outlet

10‧‧‧ Mixer

10’‧‧‧ mixing shaft

11‧‧‧ Absorbent supply tube

12‧‧‧ Oxidation air supply pipe

13‧‧‧ Absorption liquid extraction tube

14‧‧‧Second partition

15‧‧‧ Third Room

16‧‧‧Exhaust riser

17‧‧‧wash liquid supply pipe

18‧‧‧washing liquid discharge port

A‧‧‧Gas-liquid mixed layer (foam layer)

B‧‧‧Solid-liquid separation space

L‧‧‧ Absorbent

Claims (3)

An impurity removing method includes the steps of forming a foam layer in the aforementioned tank by blowing a gas containing impurities into the absorption liquid contained in the tank through a gas dispersion tube, wherein The proportion of gas is gas retention, then (i) set the gas retention of the foam layer to 0.4 to 0.9, (ii) set the height of the foam layer to 0.2 to 1.8 m, and (iii) set the The gas-liquid contact area per unit volume is set to 1500 to 2500 m ² / m ³ . The method for removing impurities according to item 1 of the scope of patent application, wherein the impurities include dust in the gas. The impurity removing method according to item 1 or item 2 of the scope of patent application, wherein the gas contains impurities having a particle diameter of 0.1 to 10 μm.