JP3394514B2 - Wet flue gas desulfurization method using spray type absorption tower - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting a spray droplet sprayed from a spray nozzle to an optimum droplet diameter in a wet flue gas desulfurization apparatus using a spray type absorption tower.

[0002]

2. Description of the Related Art In a wet flue gas desulfurization system using a spray type absorption tower, since the spray droplet diameter of the absorbing liquid sprayed from a spray nozzle affects the gas-liquid contact efficiency and the like, the gas-liquid contact is promoted. In order to improve the desulfurization performance, it is important to find the optimum diameter of the spray spray droplet diameter. Conventionally, in a flue gas desulfurization device using a spray type absorption tower, the optimum droplet diameter of the spray droplets sprayed from the spray nozzle is
The values obtained so far and the values obtained by phenomenological methods such as confirmation by experiments were used. Further, for example, in JP-A-8-19726, the average diameter of spray droplets from the spray nozzle injection port is 2.7 mm or more, and the spray port spacing of each nozzle is 0.25 to 1.1 m. It is described that collision interference between droplets is caused and the spray droplet diameter is set to 1.4 to 2.2 mm. Also,
In Japanese Unexamined Patent Publication No. 2000-176321, by optimizing the arrangement interval of the spray nozzles and causing the liquid droplets from the ejection ports to collide with each other, the particle diameter of the liquid droplets is made fine and the distribution of the liquid droplets is uniform. A spray type absorption tower adapted to be used is described.

[0003]

As described above, according to the prior art, in the flue gas desulfurization apparatus using the spray type absorption tower, the optimum droplet diameter is phenomenologically based on the actual value obtained so far or confirmation by experiments. Although the values obtained by various methods were used, these methods would lead to an increase in development cost and a longer development period, such as having to perform an experiment again when the device conditions and operating conditions changed. . In addition, the optimum droplet diameter obtained by this conventional method has a very high device dependency, and there is a drawback that it is impossible to predict what will happen under another operating condition of another device.

The present invention has been made in view of the above points, and an object of the present invention is to develop a wet flue gas desulfurization apparatus using a spray-type absorption tower, and to develop a phenomenological theory such as actual results and confirmation by experiments. The best spray droplet size for various spray type absorption towers such as the lime gypsum method was derived by deriving the optimum spray droplet size for a specific device shape and operating conditions by a theoretical method regardless of It is an object of the present invention to provide a wet flue gas desulfurization method capable of adjusting to an optimum diameter capable of obtaining absorption performance.

[0005]

In order to achieve the above object, a wet flue gas desulfurization method using a spray type absorption tower of the present invention is a method for producing a sulfur oxide-containing exhaust gas introduced into a spray type absorption tower, The absorption liquid pumped up from the bottom tank in the lower part of the absorption tower is sprayed from the spray nozzle in the form of spray droplets to absorb and remove the sulfur oxides in the exhaust gas, and the falling absorption liquid is stored again in the bottom tank for absorption performance. In the wet flue gas desulfurization method, in which a fixed flow rate of the absorbed liquid is extracted, the optimum spray droplet size in the spray type absorption tower is derived.
On the way out, the equation of motion acting on the spray droplets,
The absorption phenomenon of sulfur oxides in the exhaust gas into the spray droplets
Gas-liquid substances included in the described overall capacity coefficient K _G a definition formula
The transfer coefficient calculation formula, gas-liquid effective boundary area value, and conventional design value are given.
Based on the obtained reaction coefficient value, the specific equipment shape and operating conditions
The theoretical optimum spray droplet diameter for the above is derived, and the spray droplet diameter of the absorbing liquid sprayed from the spray nozzle is set to 20.
Range of 0-1200μm, desirably 300-600μm
It is configured to adjust to the range of.

[0006] As described above, description Upon deriving the optimal spray droplet size in the spray type absorption tower, the equation of motion describing the motion of the spray droplets, the absorption process of the sulfur oxide-containing exhaust gas into the spray droplets within The theoretical optimum spray droplet size for a particular device geometry and operating conditions can be derived from the gas-liquid mass transfer coefficient and reaction coefficient.

Further, in the wet flue gas desulfurization method using the spray type absorption tower of the present invention, the sulfur oxide-containing exhaust gas introduced into the spray type absorption tower is absorbed by the calcium-based absorption pumped from the bottom tank in the lower part of the absorption tower. The liquid is sprayed from the spray nozzle in the form of spray droplets to absorb and remove the sulfur oxides in the exhaust gas, and the absorbed liquid that has fallen is stored again in the bottom tank, and the oxidizing gas is injected from the oxidizing gas blowing means installed in the bottom tank. In the wet flue gas desulfurization method that recovers the sulfur oxides absorbed by blowing in as gypsum, the calcium-based absorption liquid with the optimum spray droplet diameter derived by the above method is sprayed as spray droplets from a spray nozzle. I am trying.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and can be appropriately modified and implemented. . FIG. 1 shows a schematic configuration of an apparatus for carrying out a wet flue gas desulfurization method using a spray type absorption tower according to a first embodiment of the present invention. As shown in FIG. 1, SO ₂
The sulfur oxide-containing exhaust gas typified by is introduced into the spray type absorption tower 10, and the bottom tank 1 in the lower part of the absorption tower is
The calcium-based absorption liquid pumped up from No. 2 through the circulating liquid lines 14a, 14b, 14c is spray nozzle 16a,
Spray from 16b and 16c. As the calcium-based absorbing liquid, limestone slurry which is a mixture of limestone and water can be used. In the wet lime gypsum method, the limestone slurry as an absorbent and the sulfur oxide-containing exhaust gas come into contact with each other, the sulfur oxides in the exhaust gas are converted into sulfite ions and calcium sulfite, and fall into the bottom tank 12 in the lower part of the absorption tower. By blowing an oxidizing gas containing oxygen (as an example, air) from the oxidizing gas blowing means (as an example, an air blowing nozzle) 18 into the absorbing solution containing the sulfite ion and calcium sulfite, the sulfite ion and the calcium sulfite are removed. Immobilize as calcium sulfate, ie gypsum. As a result, the sulfur oxides in the exhaust gas are absorbed and removed, and the absorbed sulfur oxides can be recovered as gypsum.

The gypsum slurry extracted from the bottom tank 12 is separated from the absorption liquid by a gypsum separator 20 and the gypsum pit 22.
Sent to. The absorbing liquid separated by the gypsum separator 20 is stored in the filtrate tank 24. 26 is an absorption liquid circulation pump, 2
8 is a gypsum extraction pump, and 30 is an air blower. Also,
A supply port for the limestone slurry from the limestone slurry tank 32,
The supply port for the return liquid of the absorption liquid from the filtrate tank 24 is connected to the bottom tank 12. Reference numeral 34 is a limestone slurry pit (hopper), and 36 and 38 are supply pumps. In the present embodiment shown in FIG. 1, the limestone slurry to be supplied and the return liquid of the filtrate are put in the bottom tank, but it is also possible to put them in another system (for example, a circulating liquid line). In addition, in FIG. 1, as one example, the spray nozzles are installed in three stages in the absorption tower, but it is of course possible to provide two or less stages or four or more stages. Further, in FIG. 1, a partition member is provided in the absorption tower so that the gas flow direction is reversed near the top of the tower, but the structure of the absorption tower is not limited to this.

Next, a method for deriving the optimum spray droplet diameter in the wet flue gas desulfurization apparatus using the spray type absorption tower will be described. Equation of motion acting on spray droplets, calculation formula of gas-liquid mass transfer coefficient contained in definition equation of overall capacity K _G a describing absorption phenomenon of sulfur oxide in exhaust gas into spray droplets, gas-liquid Using the effective boundary area value and the reaction coefficient value given by the conventional design value, the optimum spray droplet diameter for a certain device shape and operating condition is calculated. The equation of motion for a single spray droplet particle is described by the following equation shown in Eq.

[0011]

[Equation 1]

The gas phase mass transfer coefficient k _G calculation formula is described by the following formula shown in the equation (2).

[0013]

[Equation 2]

The liquid phase mass transfer coefficient k _L calculation formula is described by the following formula shown in Eq.

[0015]

[Equation 3]

The gas-liquid effective boundary area a calculation formula is expressed by the following formula shown in equation (4).

[0017]

[Equation 4]

The general mass transfer coefficient K _G calculation formula is represented by the following formula shown in equation 5.

[0019]

[Equation 5]

V: Drop drop velocity, u: Exhaust gas flow velocity,
C _C : slip correction coefficient, C _D : resistance coefficient, D _P : spray droplet diameter, ρ _L : liquid density, ρ _G : gas density, μ _G : gas viscosity, t: spray droplet retention time, g: gravity Acceleration, S
h: Sherwood number, Re: Reynolds number, Sc: Schmidt number, R: Gas constant, T: Temperature, k _G : Gas phase mass transfer coefficient, D _Ag : Gas component A diffusion coefficient, k _L : Liquid phase mass transfer Coefficient, D _Al : diffusion coefficient of A component in liquid, L: liquid flow rate,
V: Absorption tower volume, K _G : Overall mass transfer coefficient, H: Henry's law constant, β: Reaction coefficient, a: Gas-liquid effective boundary area, A component:
Here, the SO ₂ component is shown.

The method of calculating the optimum droplet diameter for a specific device shape will be described below. (1) The spray droplet retention time t is calculated by fixing the reaction coefficient β and the spray droplet diameter D _P and repeating the droplet position / velocity calculation at every minute time based on the equation (a). (2) Using equations (b) to (e), the overall capacity coefficient K _G
Calculate a. (3) reaction coefficient beta, by varying the spray droplet diameter D _P repeating the calculation of (1) to (2), the relationship between the overall capacity coefficient K _G a spray droplet diameter D _P for each reaction coefficient beta Derive. (4) The spray droplet diameter D _{P at} which the overall volume coefficient K _G a takes the maximum value with respect to the actual machine reaction coefficient value β is concluded as the optimum spray droplet diameter of the target device, and adjusted to a spray droplet diameter within that range. The prepared product is sprayed from the spray nozzle in the wet flue gas desulfurization device.

Using the principle of the method for calculating the optimum droplet diameter described above, the result of calculating the correlation between the droplet diameter D _P and the overall volume coefficient K _G a for each reaction coefficient β is shown. Figure 2
Shown in. Note that in FIG. 2, for example, β = 1E3
[-] Means that the β value takes a value of 1 × 10 ³ [-]. In FIG. 2, the shape of the overall volume coefficient K _G a with respect to the droplet diameter D _P changes depending on the magnitude of the reaction coefficient value β. β
Shows a change in shape between 1 × 10 ^{4 and} 1 × 10 ⁵ ,
In the range where P is small, K _G a decreases with respect to the fine droplet size, and in the range where β is large, K _G a increases with respect to the fine droplet size. Since it has been confirmed that the reaction coefficient value in the actual apparatus in the wet lime gypsum method is 1 × 10 ⁴ or less, the droplet diameter D _P at which the overall volume coefficient K _G a has the maximum value is 200 from FIG. It can be inferred that it is about 1200 μm.

It should be noted that when the droplet diameter D _P is 1100 μm, the gravity and the drag force are just balanced and stay in the absorption tower, so that the droplet retention time t becomes infinitely large and the effective liquid-liquid field in equation (d) is used. The area a becomes infinitely large, but in the equation (c), the liquid-phase mass transfer coefficient k _L conversely approaches zero,
When evaluated by the overall capacity coefficient K _G a, the effect differs depending on whether the system is liquid side resistance control or gas side resistance control. Also,
When the droplet diameter D _P becomes smaller than 100 μm, the gas phase mass transfer coefficient k _G and the gas-liquid effective boundary area a become infinitely large from the equations (b) and (d), but the equation (c) In contrast, the liquid-phase mass transfer coefficient k _L, on the contrary, approaches zero, and the overall volume coefficient K _G a
In the same manner, the effect differs depending on whether the system is liquid-side resistance control or gas-side resistance control. The reaction coefficient value β of the flue gas desulfurization device in the wet lime gypsum method is usually 1 × 10
^Since it is in the range of ⁴ or less, the liquid side resistance is governed, and at this time, when the droplet diameter D _P approaches zero, or 1100
When approaching around μm, the overall capacity coefficient K _G a decreases.
When β is in the range of 1 × 10 ⁵ or more, the gas-side resistance control system is established, and when the droplet size D _P approaches zero or approaches 1100 μm, the overall capacity coefficient K _G a is infinite. Greatly increase. Therefore, in the wet flue gas desulfurization system, which is usually a system that controls the liquid side resistance,
The spray droplet size sprayed from the spray nozzle is 200
The best desulfurization performance is exhibited when sprayed with a particle size adjusted to ˜1200 μm.

Next, as a concrete example of an apparatus for carrying out the method of the present invention and a comparative example thereof, data obtained by operating in a conventional manner using the wet flue gas desulfurization apparatus shown in FIG. Description will be made in comparison with the data when the system of the present invention is operated. Table 1 shows the operation data of the conventional method and the operation data of the method of the present invention. The spray droplet distributions in the method of the present invention and the conventional method are as shown in FIG. Further, in the wet flue gas desulfurization apparatus shown in FIG. 1, the spray droplet diameter was adjusted by changing at least one of the nozzle diameter of the spray nozzle and the initial spray velocity of the absorbing liquid.

[0025]

[Table 1]

As a result of performing the test under the test conditions shown in Table 1 on the spray droplet having the droplet size distribution shown in FIG.
The desulfurization rate of 7.0% was compared with that of the droplet size calculated by the above-described optimum droplet size calculation method (200 to 12).
It can be confirmed that the desulfurization rate is improved to 98.7% in the method of the present invention by using the (00 μm). This can be confirmed by the following theoretical consideration. A typical value of the reaction coefficient value β is about 100, and the average value of the overall volume coefficient K _G a is shown in FIG. 2 with respect to the conventional spray droplet distribution described in the spray droplet distribution chart of FIG. Is about 6160 [kmol / (m ³ · h · atm)]. On the other hand, when the average value of the overall capacity coefficient K _G a is calculated from FIG. 2 for the spray droplet distribution of the method of the present invention described in the spray droplet distribution chart of FIG. 3, it is about 7930 [kmol / (m ³・ H ・ atm)].
Thus, judging from the viewpoint of the overall capacity coefficient, it is derived that the droplet size of 200 to 1200 μm calculated by the above method is optimum for the sulfur oxide absorption reaction. Here, the general formula of the overall capacity coefficient K _G a and the defining formula of the desulfurization rate are shown below.

[0027]

[Equation 6]

Desulfurization rate = {1- (y ₂ / y ₁ )} × 100
[%] G _M : Gas flow rate per unit area, h: Tower height, y ₁ : Inlet SO ₂ concentration, y ₂ : Outlet SO ₂ concentration For example, if the result for the spray droplet distribution of the conventional method is a definite value, It becomes as follows.

[0029]

[Equation 7]

Further, when the result of the spray droplet distribution of the method of the present invention is an uncertain value, it is as follows.

[0031]

[Equation 8]

From the above two equations, the calculated value of the outlet SO ₂ concentration y ₂ when the spray droplet distribution of the method of the present invention is used is as follows. y ₂ = 7.6 [ppm] From this, the desulfurization rate becomes 98.9%, which is almost in agreement with the result of the method of the present invention in Table 1. Therefore, the liquid calculated by the above-described optimum droplet diameter calculation method Drop size (200-1200μ
The validity of m) was evaluated.

[0033]

Since the present invention is configured as described above, it has the following effects. (1) Conventionally, in a flue gas desulfurization apparatus using a spray type absorption tower, the spray spray droplet diameter was found to be the optimum diameter by experiments, etc., but particularly large-scale experiments are conducted by using the method of the present invention. It is possible to derive the optimum droplet size for a specific device shape and operating conditions without changing the spray droplet size in various spray type absorption towers such as the wet lime gypsum method, etc. It becomes possible to adjust. (2) In deriving the optimum droplet diameter in the spray-type absorption tower, the overall capacity coefficient K _G a describing the equation of motion acting on the spray droplets and the absorption phenomenon of sulfur oxide in the exhaust gas into the spray droplets Calculate the optimum droplet diameter for a specific device shape and operating conditions using the formula for calculating the gas-liquid mass transfer coefficient, the effective liquid-liquid interface value, and the reaction coefficient value given by the conventional design value included in the definition formula. be able to. (3) In a wet flue gas desulfurization apparatus using a spray type absorption tower, the desulfurization performance can be improved by adjusting the spray droplet diameter of the absorbing liquid sprayed from the spray nozzle within the range of 200 to 1200 μm.

[Brief description of drawings]

FIG. 1 is a systematic schematic configuration explanatory view showing an apparatus for carrying out a wet flue gas desulfurization method using a spray type absorption tower according to a first embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the droplet size and the overall volume coefficient for each reaction coefficient in the wet flue gas desulfurization apparatus.

FIG. 3 is a graph showing spray droplet particle size distributions of the method of the present invention and the conventional method during operation of the wet flue gas desulfurization apparatus shown in FIG.

[Explanation of symbols]

10 Spray type absorption tower 12 Bottom tank 14a, 14b, 14c Circulating liquid line 16a, 16b, 16c Spray nozzle 18 Oxidizing gas blowing means 20 gypsum separator 22 plaster pit 24 Filtrate tank 26 Absorption liquid circulation pump 28 Gypsum withdrawal pump 30 air blower 32 Limestone slurry tank 34 Limestone slurry pit (hopper) 36, 38 supply pump

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kuniomi Minoshima 3-1-1 Higashikawasaki-cho, Chuo-ku, Kobe Kawasaki Heavy Industries, Ltd. Inside the Kobe factory (72) Inventor Kazuto Marui 3-chome, Higashikawasaki-cho, Chuo-ku, Kobe No. 1 Kawasaki Heavy Industries, Ltd. Kobe factory (72) Inventor Daisuke Shindo 3-1-1 Higashikawasaki-cho, Chuo-ku, Kobe-shi Kawasaki Heavy Industries Ltd. Kobe factory (56) Reference JP-A-8-206448 (JP, A) JP-A-5-154337 (JP, A) JP-A-56-21628 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01D 53/34

Claims (2)

(57) [Claims] 1. Sulfur oxidation in the exhaust gas by spraying the absorbing liquid pumped from a bottom tank in the lower part of the absorption tower in the form of spray droplets onto the exhaust gas containing sulfur oxide introduced into the spray type absorption tower. In the wet flue gas desulfurization method in which substances are absorbed and removed, the falling absorbing liquid is stored in the bottom tank again, and the absorbing liquid with reduced absorption performance is withdrawn at a constant flow rate, the optimum spray droplet diameter in the spray absorption tower
The motion method that acts on the spray droplets when deriving
Equation, absorption of sulfur oxides in exhaust gas into spray droplets
Gas-liquid included in the defining equation for the overall capacity coefficient K _G a that describes an elephant
Mass transfer coefficient calculation formula, gas-liquid effective boundary area value, conventional design value
From the reaction coefficient value given by
Derivation of the theoretical optimum spray droplet size for the conditions,
A wet flue gas desulfurization method using a spray type absorption tower, characterized in that a spray droplet diameter of an absorbing liquid sprayed from a spray nozzle is adjusted to a range of 200 to 1200 μm . 2. A sulfur-oxide-containing exhaust gas introduced into a spray type absorption tower is sprayed with a calcium-based absorption liquid pumped from a bottom tank in the lower part of the absorption tower in the form of spray droplets from a spray nozzle. Wet flue gas that absorbs and removes sulfur oxides, stores the fallen absorbing liquid again in the bottom tank, and recovers the absorbed sulfur oxides as gypsum by blowing the oxidizing gas from the oxidizing gas blowing means installed in the bottom tank. In the desulfurization method, a calcium-based absorbent having an optimum spray droplet diameter derived by the method according to claim 1 is sprayed as spray droplets from a spray nozzle. .