JPS61249527A - Wet type stack-gas desulfurization device - Google Patents

Abstract

PURPOSE:To simultaneously perform the oxidation of an absorption product and the concentration of an oxidized product together with the absorption and to simplify an apparatus by providing the feed means of an O2-contg. gas to an absorption tower and providing a partition chamber having a similar constitution with the exception of it. CONSTITUTION:An exhaust gas is introduced through an introduction port 32 and brought into contact with a circulating slurry fed through the nozzles 29 in a gas-liquid contact part 8 and SO2 is absorbed and removed. The slurry is reserved in a liquid reservoir part 9 and an absorbent slurry is fed through a feed pipe 13 and the replenishing water is sent through a water pipe 24 and one part of the slurry is sent with a circulation pump 10 and the other part thereof is reserved in the liquid reservoir part 21 of the partition chamber via an overflow inlet 31 provided to a partition wall 30 and circulated through a circulation line 36 and brought into contact with the exhaust gas in gas-liquid state. Air is fed to the concentrated slurry through the blow-in means 35 to oxidize and treat it and one part thereof is drawn out to a centrifugal separator 5 via a branched drawing-out pipe 25 and the by-product gypsum 18 is recovered.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a wet flue gas desulfurization device, and in particular to a wet flue gas desulfurization device that not only absorbs sulfur dioxide gas in flue gas, but also oxidizes the absorbed product and concentrates the oxidized product. The present invention relates to an absorption tower suitable for wet flue gas desulfurization.

As shown in Fig. 9, this type of conventional wet flue gas desulfurization equipment absorbs sulfur dioxide gas (hereinafter referred to as SO□) in the flue gas by using a calcium-based absorbent (for example, limestone Ca CO3, Ca
A cooling tower 1 and an absorption tower 2 are used to absorb and remove calcium sulfite (OsCa(OH)2, etc.) by contacting with the melted slurry, and calcium sulfite (CaSO
3.%H20) is oxidized to form gypsum (CaSO4.2H20).
), a Silafuna 4 for recovering gypsum, and a centrifugal separator 5. In an apparatus having such a configuration, exhaust gas sent from an exhaust gas source through a flue 6 is first introduced into a cooling tower 1, where it passes through a cooling tower circulation tank 7 and a cooling tower circulation pump 8, and then is circulated to be dispersed. It is brought into gas-liquid contact with the slurry to perform cooling and absorption and removal of some SO□ contained therein. The exhaust gas after the contact is then sent to the absorption tower 2, where it is brought into gas-liquid contact with the circulating slurry that is spread to the gas-liquid contacting section 8 via the lower liquid reservoir section 9 and the absorption tower circulation pump 10, and the remaining S02 After being absorbed and removed, it is discharged into the atmosphere through the flue 11 and chimney 12.

The absorbent (hereinafter represented by limestone CaCO3) is supplied to the lower liquid reservoir 9 of the absorption tower 2 through the slurry supply pipe 13, but a part of it is consumed in the absorption tower 2, and the rest is supplied to the communication pipe 14. It is present in the slurry sent through the cooling tower circulation tank 7 and is used in the cooling tower 1 to absorb SO□.

By the way, desulfurization performance is greatly influenced by the pH of the absorption liquid.
It is known that the higher the pH, that is, the higher the excess rate of caco3, the better the results.

This suggests that the improvement of desulfurization performance and the effective use of CaCO3 are in a trade-off relationship. For this reason, the pH of the absorption tower is generally set to about 5.8 to 6.0, and the pH of the cooling tower is set to about 5.0 to 5.5.
The amount of O3 supplied is the total SO□ absorbed and removed in the absorption process.
The amount is adjusted to be approximately 5 to 10% in excess of the equivalent amount.

In the absorption process, SO□ in the exhaust gas reacts with CaCO3, etc. to produce calcium sulfite, but a part of it is oxidized by 0□ in the exhaust gas and becomes gypsum. Therefore, in each circulating slurry of the cooling tower and absorption tower, these reaction products and unreacted CaCO3 are present in a certain proportion depending on the pH value, the 02 concentration in the gas, the residence time of the slurry in the absorption process, etc. It will exist.

A portion of the cooling tower circulation slurry is then extracted to a gypsum recovery step in proportion to the total amount of SO2 absorbed and removed in the absorption step. However, since this extracted slurry contains unreacted Ca CO3, firstly, sulfuric acid 16 is added in the oxidation tower supply tank 15 to remove unreacted Ca CO3.
The aCO3 is converted into gypsum and adjusted to a pH value (4.5-4.8) through the oxidation of calcium sulfite and then sent to the oxidation tower 3. The oxidation tower 3 is equipped with a device capable of generating fine bubbles, and by blowing high-pressure air 17 through this device, the oxidation of calcium sulfite is promoted. The thus produced slurry containing gypsum is sent to Shirafuna 4 and concentrated to about 2 Qwt%, and then dehydrated in centrifugal separator 5, thereby recovering powdered by-product gypsum 18.

However, in such conventional technology, it is necessary to satisfy the contradictory conditions of maintaining high desulfurization performance and reducing the excess rate of CaCO3, so two towers, a cooling tower and an absorption tower, are essential, and unreacted CaCO3 It is necessary to install sulfuric acid addition equipment to neutralize calcium sulfite, a special oxidation tower to oxidize calcium sulfite, Shirafuna to concentrate gypsum slurry, etc., depending on each function, and the component equipment The disadvantage is that there are many problems, which makes the system complicated.

(Problems to be Solved by the Invention) The object of the present invention is to eliminate the drawbacks of the prior art described above, and to absorb S02 in the exhaust gas, as well as oxidize the absorbed product and concentrate the oxidized product. An object of the present invention is to provide an absorption tower for wet flue gas tax sulfur, which can simplify the equipment.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a gas-liquid contact method that absorbs and removes sulfur dioxide gas by bringing exhaust gas into contact with a circulating calcium-based absorbent slurry. In a wet smoke flue gas blasting apparatus, the absorber is equipped with an absorption tower comprising a part and a liquid reservoir part for storing the slurry flowing down after the contact while being replenished with a calcium-based absorbent. A partition wall extending from the liquid contact part toward the bottom of the liquid reservoir, a partition chamber formed by the partition wall, an overflow inlet for the liquid reservoir slurry provided in the partition chamber, and a part of the exhaust gas intake. a gas-liquid contact part of the partition and a liquid reservoir part,
The exhaust gas that has passed through the gas-liquid contact part of the partition is transferred to the above (absorption tower).
A discharge port for discharging toward the gas-liquid contact area, a means for blowing oxygen-containing gas into the liquid reservoir in the partition, and an extraction of slurry from the liquid reservoir in the partition that branches off from the partition circulation slurry line and reaches the centrifugal separator. It is characterized by having a line.

The pH of the slurry in the above liquid reservoir (hereinafter referred to as absorption tower liquid reservoir) is 5.8 to 6.3, which is suitable for absorption of SO2, and the pH of the slurry in the partition chamber liquid reservoir is set to 5.8 to 6.3, which is suitable for absorbing SO2. It is preferable to maintain the temperature at 4°5 or less, which is suitable for oxidizing calcium sulfite).

Further, it is desirable to adjust the intake of a portion of the exhaust gas into the partition by providing an exhaust gas distribution damper at the entrance of the absorption tower and operating this damper.

According to the configuration of the present invention, S02 in the exhaust gas can be absorbed and removed in the absorption tower main body, which is composed of the gas-liquid contact section (hereinafter referred to as absorption tower gas-liquid contact section) and the absorption tower liquid reservoir section. , further absorption and removal of S02 (the CaC
(O3 is completely neutralized), gypsumization by oxidation of the calcium sulfite produced in the above absorption, and concentration of the slurry are simultaneously achieved, which eliminates the conventionally required oxidation tower supply tank, oxidation tower, shisofuna, etc. equipment can be omitted.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

FIG. 1(A) is a vertical cross-sectional system diagram of main parts of a wet flue gas desulfurization apparatus according to an embodiment of the present invention, and FIG. 1(B) is a cross-sectional view taken along the direction A-A in drawing (A). and this one is the 9th
The reference numerals shown in the figure and the parts to which their explanations are similarly referred to, the cooling tower circulation tank 7, and the oxidation tower supply tank 1, which are arranged from the cooling tower 1 in the same figure to the connecting pipe 14 and immediately before the centrifugal separator 5.
5, the oxidation tower 3 and the partition chamber 34 provided in place of the Shirafuna 4 and the like.

The above-mentioned partition chamber includes a partition wall 30 that is located within the side wall surface of the absorption tower 2 and extends from the absorption tower gas-liquid contact section 8 toward the bottom of the liquid reservoir section 9, and an absorption tower liquid reservoir provided in this partition wall 30. A slurry overflow inlet 31 opens at the end of the flue 6, and the exhaust gas distribution damper 20 takes in a portion of the exhaust gas sent through the flue.
32) A partition chamber equipped with a spray header and nozzle 22 having the same configuration as the absorption tower gas-liquid contact section 8 and the absorption tower liquid reservoir section 9 except for the gas-liquid contact section 27 and limestone replenishment. The exhaust gas that has passed through the similarly configured partition chamber liquid reservoir 21 and partition chamber gas-liquid contact section 27 is transferred to the absorption tower gas-liquid contact section 8.
a means 35 for dispersing air, for example an oxygen-containing gas, sent via the supply line 23 into the compartment sump 21 and a partition; A slurry extraction line 25 is provided for the slurry in the partition chamber liquid reservoir, which branches off from the chamber circulation slurry line 36 and then reaches the centrifugal separator 5.

In an apparatus with such a configuration, most of the exhaust gas sent through the flue 6 is supplied to the gas-liquid contact section 8 of the absorption tower 2 under the adjustment of the exhaust gas distribution damper 20, and is supplied to the gas-liquid contact section 8 of the absorption tower 2 through the spray header and nozzle provided in multiple stages. The slurry is brought into contact with the circulating slurry from the absorption tower liquid reservoir section 9 which is sprayed through the slurry 29.

Through this contact treatment, So in the exhaust gas is absorbed and removed by the absorbent slurry, and the exhaust gas from which SO□ has been removed passes through the demister 19 and the flue 11 in the same manner as before, and then enters the atmosphere from the chimney 12. It is discharged.

On the other hand, the slurry flows down after the above contact and is stored in the absorption tower liquid storage section 9.

The slurry accumulated as described above is supplied with absorbent slurry via a supply pipe 13, and is also supplied with a water pipe 2 to prevent scaling.
The unevaporated portion of the make-up water and the wash water supplied to the demister 19 and the like, which are supplied to the inlet of the absorption tower through the demister 19, is replenished. With such replenishment, the water level of the slurry in the absorption tower liquid reservoir rises, but part of it is sent to the absorption tower circulation pump 10 for gas-liquid contact in the same manner as described above, and the other part is overflowed. It is stored in the partition liquid reservoir 21 through the inlet 31, then sprayed into the partition gas-liquid contact part 27 via the pump 28, spray header and nozzle 22 along the partition circulation line 36, and then supplied from the inlet 32. gas-liquid contact with part of the exhaust gas.

The exhaust gas from which a part of the SO served.

On the other hand, the concentrated slurry containing calcium sulfite, which is a new absorption product of S02, which came into contact with high-temperature exhaust gas at the gas-liquid contact part of the partition and was generated due to the consumption of excess calcium-based absorbent, flows down. The calcium sulfite contained therein is oxidized in the presence of air stored in the rear partition liquid storage section 21 and supplied here from the air blowing means 35.

The gypsum-containing concentrated slurry thus produced passes through the partition circulation line 36 and is subjected to gas-liquid contact in the same manner as described above, and this process is repeated thereafter, with a portion of it passing through the branch extraction line 25 and being sent to the centrifuge 5. By-product gypsum 1, which is extracted from and substantially free of calcium-based absorbent after dehydration
It is collected as 8.

Hereinafter, the effects of the embodiments of the present invention will be explained in more detail.

In order to suitably achieve the effects of the embodiments of the present invention, it is necessary to satisfy the following three points.

(1) In order to increase the usage efficiency of calcium-based absorbent, the amount of absorbent remaining in the circulating slurry in the partition, that is, the excess rate of absorbent, should be reduced to zero. (2) Oxidation of calcium sulfite in the liquid reservoir in the partition (3) Concentrating the slurry in a partitioned room in a suitable manner First,
Regarding the first point, calcium-based absorbents (
The relationship between the excess rate of CaC03) and the slurry pH is shown in Figure 2. When the pH is set to 4.5 or less, C
It is known that the excess rate of aCO3 is zero, that is, the amount of unreacted CaCO3 is zero. Therefore, it is known that the amount of CaC0=supplied to the absorption tower may be equivalent to the amount of SO□ absorbed and removed in the entire absorption tower including the partition chamber. Therefore, the amount of SO□ to be absorbed in the partition needs to be equivalent to or more than the absolute amount of unreacted CaCO3 flowing from the absorption tower liquid reservoir 9 to the partition liquid reservoir 21, as determined from the following equation 0. be.

CaCO3+SO2+! 4H20→CaCO3・%H2
0+C02↑・・・・・・・・・■The absolute amount of unreacted CaCO3 mentioned above is the p of the absorption tower circulation slurry.
H, CaCO3 excess rate and SO absorbed in the entire absorption tower,
related to quantity. By the way, the pH of the slurry in the absorption tower
Figures 3 and 4 are obtained by determining the relationship between the liquid-gas ratio and the desulfurization rate, and the relationship between the liquid-gas ratio and the desulfurization rate.
It is known that it is advantageous to increase the However, as is clear from Figure 2, when the pH of the slurry is increased, CaC
The excess ratio of O3 increases, and for example, when the slurry pH is set to 6.0, the excess ratio of CaCO3 becomes about 10%. Therefore, the amount R1 of SO□ to be absorbed in the partition in this case is given by the following equation 0 by combining the above-mentioned relationships.

R-R1+R,......■ L=R......■ L-1, IXR,......■-'-Rt#0
．． 09xR・・・・・・・・・■ [In each formula, R is the absorbed S02 amount of the entire absorption tower (m.

It/h), R1 is the amount of SO to be absorbed in the partition (m
oJ/h), R2 is the amount of SO2 absorbed by the absorption tower (mot!/
h), L indicates the supply amount (non/h) of CaC0:z] In other words, the amount of SO□ to be absorbed in the partition is approximately 9% or more of the amount of SO□ absorbed in the entire absorption tower. It will be a good thing. This indicates that the amount of exhaust gas to be introduced into the partition can be kept at the same rate unless the slurry concentration aspect described later is taken into account.

Next, regarding the second point, the oxidation of calcium sulfite in the liquid reservoir of the partition, the relationship between the oxidation rate of calcium sulfite and the slurry pH is generally as shown in Figure 5.
Under H, particularly at a temperature of 4.5 or less where the amount of unreacted CaCO3 can be reduced to zero, oxidation can be achieved satisfactorily by supplying oxidizing air at a certain level or more, preferably at least twice the theoretical amount.

In this case, the following formula 0 holds true.

V-M/Z・・・・・・・・・
・■ [In the formula, ■ is the required capacity rpt of the liquid reservoir in the partition>,
M is the amount of calcium sulfite in the liquid reservoir of the partition (n.

17h”), Z is the oxidation rate (mo 1/II ・h)
``?'' As a method for blowing air into the liquid reservoir in the partition, known methods are widely applicable, and for example, a method of blowing air from multiple pipes may be used. Needless to say, it is possible to prevent slurry from being deposited on the surface.

The pressure of the blown air should be equal to or higher than the depth of the liquid inserted into the blowing means, generally about 0.5 kg/-.G, and therefore higher pressure such as 4 to 7 kg/-.G as in conventional oxidation towers. does not require.

Next, referring to the third point, slurry concentration in the partition, this is achieved by the heat balance between the amount of water to be evaporated in the partition and the amount of heat of the exhaust gas introduced into the partition. Generally, the concentration of absorption tower circulating slurry is about 1Qwt%,
To concentrate this in the partition chamber to the required 15 to 2 Qwt% on the centrifuge 5 side, approximately 40% of the water volume in the inflow slurry must be concentrated.
% to about 60 hours. The amount of exhaust gas introduced into the partition chamber is related to the temperature of the exhaust gas at the inlet and the amount of water flowing in from the absorption tower. In the case of 19 wt%, it is sufficient to use about 40 to 60% of the total amount of exhaust gas at the absorption tower inlet.

Note that the amount of introduced exhaust gas mentioned above is based on SO
The amount is higher than the amount required to absorb SO□, but even if the amount is increased in this way, if the pH of the slurry is below 4°5, SO□
It does not cause any particular problems as it absorbs very little.

Next, FIG. 6(A) is a longitudinal cross-sectional system diagram of the main parts of a wet flue gas desulfurization apparatus according to another embodiment of the present invention, and FIG. This shows a cross-sectional view along the absorption tower, and this one has the same configuration except that a partition wall 3OA along the side wall surface of the absorption tower is provided instead of the partition wall 30 provided in the absorption tower shown in FIG. .

With such a configuration, it is possible to further expand the effective slurry holding volume of the absorption tower liquid storage section 9 and improve the slurry stirring characteristics.

Next, FIG. 7 shows the SO2 concentration 37A1, the exhaust gas temperature 3°8A, the exhaust gas flow rate 39A1, and the slurry extraction flow rate 4 to the centrifugal separator from each measurement point 37 to 42 shown in FIG.
0A, the specific gravity of the slurry in the partition chamber liquid reservoir 41A and the slurry specific gravity in the absorption tower liquid reservoir 42A are determined, and based on these signals,
This figure shows an example of exhaust gas introduction control into a partition, which makes it possible to maintain the slurry concentration in the partition liquid reservoir at a desired value even under load fluctuations.

That is, the total exhaust gas flow rate 39A1 SO□ concentration 37A and exhaust gas temperature 38A at the equipment entrance are measured, and the slurry flow rate flowing into the partition is predicted by calculating the exhaust gas flow rate x 802 concentration, and this and the exhaust gas flow rate x exhaust gas temperature are calculated. Based on the calculated value of , advance control is performed that allows the opening degree of the exhaust gas distribution damper to be adjusted.

On the other hand, the slurry specific gravity 42A, 41A in the absorption tower liquid storage section and the partition chamber liquid storage section and the slurry flow rate 40A extracted from the partition chamber are measured, and the actual gas amount for slurry concentration calculated from these signals is calculated. perform feedback control on
This makes it possible to follow load changes.

This will be further explained below with reference to operational examples.

(Example) Using the apparatus shown in Figure 6, desulfurization operation was performed under the conditions (1) and (2) below.
%, the amount of exhaust gas required to be fed into the partition chamber was 41% of the total amount of exhaust gas, and when concentrating to 20 wt%, it was 63%.

(1) Basic operating conditions for the m-sulfur unit a) Amount of treated exhaust gas (wet gas) 600, 000 No? /h (786,000kg/h) Processed exhaust gas amount (dry gas) 549.600 Nn? /h (745,500kg/h) c) Moisture in exhaust gas 8.4Vo1% b) Equipment inlet SO□ concentration 500 ppm e) Desulfurization rate
(2) Amount of slurry flowing into the partition from the absorption tower liquid reservoir a) Amount of solids unreacted CaCO3-100 kg/h CaS03-! 4820-780 #CaSO42
H20-900 -90# 1.870kg/h mouth) H2O-16,830kg/h c) Slurry amount -18,700kg/h (10w
t% slurry) (3) Amount of gas required to concentrate 10wt% to 15-2Qwt% a) Amount of dry gas required for concentrating to 15wt% -18,700X16.5 -308.550 kg/h (processed gas (approximately 41% of the amount) (mouth) Required dry gas amount when concentrating to 20 wt% -18,700x25.0 -467.500 kg/h (approximately 63% of the processed gas amount) (Effects of the invention) According to the present invention By providing a partition with the same configuration as the absorption tower except for providing means for supplying oxygen-containing gas, a portion of the excess calcium-based absorbent in the slurry sent from the liquid reservoir of the absorption tower is removed from the exhaust gas in the partition In addition, the slurry in the liquid reservoir of the partition can be kept at a pH of 4.5 or below, which is suitable for oxidizing calcium sulfite, which is an absorption product, and through the gas-liquid contact, It can be concentrated to a concentration suitable for dehydration using a centrifuge.

As a result, the conventionally required equipment such as sulfuric acid addition equipment, calcium sulfite oxidation tower, and gypsum slurry concentration silafuna can be omitted, as well as eliminating the need for sulfuric acid addition and improving the utilization efficiency of CaCO3. Operating costs can be reduced.

[Brief explanation of the drawing]

FIG. 1(A) is a longitudinal cross-sectional system diagram of the main parts of a wet flue gas desulfurization device according to an embodiment of the present invention, and FIG. 1(B) is a diagram of FIG.
), FIG. 2 is a relationship between the pH of the slurry and CaCO3 excess rate, FIG. 3 is a relationship between the pH of the absorption tower slurry and the desulfurization rate, and FIG. is a diagram showing the relationship between the absorption tower liquid-gas ratio and the desulfurization rate, FIG. 5 is a diagram showing the relationship between the slurry pH and the oxidation rate of calcium sulfite, and FIG. A vertical cross-sectional system diagram of the main parts of the flue gas desulfurization equipment, FIG. 6 (B) is a cross-sectional view taken along the direction B-B of FIG. 6 (A), and FIG. The introduction control system diagram, Figure 8, shows the system diagram of the system shown in Figure 6.
FIG. 9 is a system diagram showing measurement points designated for sending primitive signals to the control system shown in the figure. FIG. 9 is a system diagram of a conventional wet flue gas desulfurization apparatus. 2... Absorption tower, 4... Shirafuna, 5... Centrifugal separator, 8... Absorption tower gas-liquid contact section, 9... Absorption tower liquid reservoir section, 13... Limestone slurry supply pipe , 18... By-product gypsum, 20... Exhaust gas distribution damper, 21... Partition chamber liquid reservoir, 22... Spray header and nozzle, 23...
... Air supply line, 24 ... Water pipe, 25 ... Branch extraction line, 26 ... Mist eliminator, 27
...Partition room gas-liquid contact part, 30.30A...Partition wall,
31... Overflow inlet, 32... Partition room exhaust gas inlet,
33... Partition room exhaust gas outlet, 34... Partition room, 3
5--Air blowing means, 36--Divided chamber circulation line, 37--SO, concentration measurement point, 38--Exhaust gas temperature measurement point, 39--Exhaust gas flow rate measurement point, 40--Centrifugal Slurry extraction flow rate measurement point to the separator, 41... Partition room liquid reservoir slurry specific gravity needle measurement point, 42... Absorption tower liquid reservoir slurry specific gravity measurement point. lj: Air transfer line Jb: (Makiri 111
Rental line Figure 1 (B) Slurry PH (-) Figure 3 Figure 4 One tile blade su, tower wave bus trap ()/m3N) Figure 5 Slurry pH (-) Figure 7

Claims (3)

[Claims] (1) A gas-liquid contact section that absorbs and removes the sulfur dioxide gas by bringing the exhaust gas into contact with the calcium-based absorbent slurry that is circulated, and the slurry that flows down after the contact is stored while being replenished with the calcium-based absorbent. In a wet flue gas desulfurization apparatus equipped with an absorption tower comprising a liquid reservoir, the absorption tower has a partition wall that is located within the side wall surface of the absorption tower and extends from the gas-liquid contact part toward the bottom of the liquid reservoir, and the partition wall A partition formed by
A liquid reservoir provided in the partition has an overflow inlet for slurry, an inlet for taking in part of the exhaust gas, a gas-liquid contact part and a liquid reservoir in the partition, and exhaust gas that has passed through the gas-liquid contact part of the partition. an outlet for discharging the gas toward the gas-liquid contact section of the above-mentioned (absorption tower), a means for blowing oxygen-containing gas into the liquid reservoir in the partition, and a partition that branches off from the circulation slurry line in the partition and reaches the centrifuge. A wet flue gas desulfurization device characterized by having a chamber liquid reservoir and a slurry extraction line. (2) Claim 1 is characterized in that the pH of the absorption tower liquid reservoir slurry and the partition chamber liquid reservoir slurry is maintained at about 5.8 to about 6.3 and about 4.5 or less, respectively. Wet flue gas desulfurization equipment. (3) The wet smoke flue gas according to claim 1, characterized in that the intake of a portion of the exhaust gas into the partition chamber can be adjusted by operating an exhaust gas distribution damper provided at the entrance of the absorption tower. Desulfurization equipment.