JPS604726B2 - Flue gas desulfurization method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wet flue gas desulfurization method, and more particularly to a wet flue gas desulfurization method that enables integrated miniaturization of equipment and can produce high purity gypsum with high desulfurization efficiency.

Conventionally, flue gas desulfurization methods involve continuous gas-liquid contact using devices such as spray towers, perforated plate towers, or grid towers, but in these methods, the volume of gas-liquid contact is large. However, a satisfactory desulfurization effect could not be obtained.
Furthermore, scaling may occur, making it difficult to operate for a long time. The inventors previously disclosed that U.S. Pat.
He invented the flue gas desulfurization method described in the specification of No. 36630, and one European commercial plant is already in operation based on this invention, the largest of which has an exhaust gas volume of 100 NM3/
It's over a day.

This method cleans and removes sulfur dioxide gas from exhaust gas,
Sulfurous acid in the absorption liquid is oxidized with air in the presence of a ferric ion (Fe30) catalyst to form sulfuric acid, which is neutralized primarily with limestone to produce gypsum, and the gypsum is further separated from the liquid. This method fixes sulfur dioxide gas in exhaust gas as gypsum. In particular, the absorption step and the oxidation step are carried out separately under their own suitable conditions, and a portion of the sulfuric acid aqueous solution containing ferric ions flowing out from the oxidation step is directly used as the absorption liquid, while the sulfuric acid The concentration is controlled by adding limestone to a portion of the liquid extracted from the oxidation process to produce gypsum by using the circulating liquid from the crystallization process. The present inventors have completed the present invention as a result of repeated research into improving the above method, and the purpose of the present invention is to achieve desulfurization by eliminating the amount of externally circulated absorbed liquid by integrating the process and equipment and downsizing. An object of the present invention is to provide a highly efficient wet flue gas desulfurization method. The present invention has the following configuration to achieve the above object.

That is, the flue gas desulfurization method of the present invention is a flue gas desulfurization method in which sulfur dioxide gas is fixed as gypsum. A first zone, which is a continuous gas-liquid contact layer consisting of air bubbles and the sulfuric acid aqueous solution, is formed, and an oxygen-containing gas is introduced into the lower region of the sulfuric acid aqueous solution in which the gypsum is suspended. A second zone is formed directly below the oxygen-containing gas microbubbles and the sulfuric acid acidic aqueous solution, and is continuous with the first zone in the liquid phase and has a smaller amount of bubbles than the first zone. The compound is introduced in an amount sufficient to maintain the sulfuric acid concentration of the sulfuric acid acidic aqueous solution of the liquid-disconnection below 1% by weight, and the suspension containing gypsum from the second belt is brought to a slurry concentration of 3 to 4% by weight. It is characterized by taking out enough amount to maintain the condition. In addition, the flue gas desulfurization method of the present invention is a flue gas desulfurization method in which sulfur dioxide gas is fixed as gypsum, in which gypsum contained in a pot is suspended and the flue gas is dispersed and introduced into the upper part of a sulfuric acid acidic aqueous solution containing an oxidation catalyst. to form a first zone which is a gas-liquid contact layer of the liquid difference bowl consisting of fine bubbles of exhaust gas and the sulfuric acid acidic aqueous solution, and at the same time introducing an oxygen-containing gas into the lower region of the sulfuric acidic acidic aqueous solution in which the gypsum is suspended. Located directly under the first belt, it consists of microbubbles of oxygen-containing gas and the acidic aqueous solution of sulfuric acid, and is continuous with the first belt in the liquid phase.
and forming a second zone having a smaller amount of bubbles than the first zone, introducing a calcium compound in an amount sufficient to maintain the sulfuric acid concentration of the sulfuric acid acidic aqueous solution of the liquid-distance connection at 1% by weight or less, and Slurry concentration 3 of suspension containing gypsum from Obijo
It is characterized by taking out an amount sufficient to maintain the content at ~40% by weight. The method of the present invention explores a gas-liquid contact method using a liquid difference line, which is different from the conventional gas-liquid contact using a gas difference competition. Two belts can be brought into contact without any space, that is, with a liquid difference.

Moreover, in this case, the volume of gas-liquid contact in the liquid-disconnection is small, and the gas-liquid contact area can be freely adjusted by changing the height of the liquid level. Furthermore, in the present invention, if a calcium compound is introduced, for example, into the contact surface between the first zone and the second zone, calcium will automatically be added to the sulfur dioxide gas in the first zone and the neutralization of the sulfuric acid produced. The compound is used effectively and has a remarkable effect on desulfurization, and furthermore, by integrating the process, it is possible to integrate and downsize the absorption tower, oxidation tower, neutralization tank, and crystallization tank, and reduce the amount of circulating absorption liquid to zero. I can do it. However, the introduction position of the calcium compound may be provided in the first zone or the second zone. Regarding the desulfurization rate, by bringing the first zone and the second zone into continuous liquid phase contact with no space and introducing a calcium compound, absorption, oxidation, and neutralization of sulfur dioxide gas proceed simultaneously. A high desulfurization rate can be achieved even though the sulfuric acid acidic aqueous solution has low solubility.
Furthermore, since the gas-liquid contact area can be freely changed by vertically changing the liquid level as described above, the desulfurization rate can also be easily adjusted. In the liquid phase continuous gas-liquid contact layer (first zone) in the present invention, mass transfer within the layer is caused by intense turbulent contact when high-speed gas collides with the liquid and breaks up the bubbles, and by intense turbulent contact when the high-speed gas collides with the liquid and breaks up the bubbles. A high desulfurization rate can be achieved because this process is carried out efficiently by the turbulent contact between microbubbles, that is, by extremely increasing the contact area.

One of the advantages of the present invention is that no pump is required to force the absorbent into the gas stream in a gas-disconnected configuration, so power costs for circulating the absorbent are greatly reduced. be. In other words, the gas-liquid contact in the first zone is not carried out on the surface of fine droplets, but on the surface of minute bubbles that are created when previously dispersed gas enters the liquid. . In other words, in the conventional method, gas-liquid contact is performed using liquid energy, whereas in the present invention, gas-liquid contact is performed using gas energy. Moreover, the pump that conveys the energy of the liquid,
Corrosion resistance and abrasion resistance are required because S02 must be handled and solids must be tolerated, but the gas blower of the present invention has the great advantage that it can be made of ordinary materials. The feature of the present invention that the gas-liquid contact is carried out at the liquid difference line is a great advantage in preventing the adhesion of particles. In other words, once solids adhere to pipe walls, it is difficult to remove them with a gas flow, but with the method of the present invention, solids are almost never blocked because they are always washed with liquid. . Next, in the present invention, since the second zone adjacent to the first zone containing exhaust gas bubbles also contains air bubbles and is a liquid connection, the first zone and the second zone are connected by means such as pumps and piping. There is no need to connect the first belt and the second belt with a special border at the top and bottom, and the advantage is that the device is compact and economically inexpensive. There is.

Furthermore, the first zone of the present invention contains exhaust gas bubbles, and the second zone is a liquid phase containing air bubbles, but the amount of air bubbles in the latter is 10% of the amount of exhaust gas bubbles contained in the former. As shown below, there is a difference in the amount of bubbles between the first belt castle and the second belt castle, and therefore there is a difference in the rising force of the liquid due to the bubbles.
As shown in the figure, it is also possible to mix the liquids without using a concentrate.

Of course, since there are particles of gypsum produced in the liquid, a mechanical flywheel may be used to ensure that they are suspended. In the method of the present invention, by locating the second band directly below the first band, the oxidation rate can be increased compared to the conventional method.

In other words, it is known that the rate of absorption of oxygen in the air is approximately proportional to the partial pressure of 02, but the air blown into the second belt under the conditions of a liquid difference bowl is of course Even in the first belt, it exists as independent bubbles and always has the same partial pressure as air, about 0.2 tm, and is absorbed into the liquid at a rate according to that partial pressure and performs an oxidizing action. However, with the conventional method of blowing 02 directly into the exhaust gas, the air is not in the form of bubbles and is mixed with the exhaust gas, so the partial pressure increases by less than one-tenth of the above value, or only 0.02 tm at most, resulting in oxidation. The speed will also be slower. According to the present invention, the chemical reactions required for flue gas desulfurization are not performed in stages, but are completed all at once and in the same device by the reaction of the following formula.

S. 20 CaC03 20 Group 201 CaS.

4- is 20HC.

2↑ This means that the present invention is fundamentally different from the conventional lime slurry method using calcium sulfite and the flue gas desulfurization method using sulfuric acid described in U.S. Patent No. 383,663, which the inventors previously filed. This is the reason for the difference in performance, and as a result, scaling troubles can be prevented and economical efficiency can be improved.

The method of the present invention will be explained in more detail with reference to the drawings.

FIG. 1 shows the mechanism and flow sheet of an apparatus showing one embodiment of the present invention, in which sulfur dioxide gas is introduced from a conduit 1 through a gas disperser 3 below the surface of a gypsum-suspended sulfuric acid acidic aqueous solution in a tank 2. , an oxygen-containing gas inlet 6 which absorbs sulfur dioxide gas in the first zone forming a gas-liquid contact layer with a continuous liquid phase and is provided at a lower liquid level than the exhaust gas inlet in the gypsum-suspended sulfuric acid acidic aqueous solution. Oxygen from the second zone into which air is introduced absorbs sulfur dioxide gas and simultaneously oxidizes it to sulfuric acid.
At this time, due to the calcium compound introduced from the conduit 21 into the contact surface between the first zone and the second zone in an amount sufficient to maintain the sulfuric acid concentration at 1% by weight or less, a neutralization reaction simultaneously proceeds to produce gypsum. . The gas from which the sulfur dioxide gas has been removed undergoes gas-liquid separation in the space above the liquid surface of the slag 2 and is discharged from the conduit 4. The generated gypsum is extracted from a conduit 5 into a centrifugal separator 8 by a pump 7 so that the gypsum concentration in the tank is maintained at a concentration of 3 to 4% by weight, which is suitable for crystal growth, and coarse gypsum crystals are grown. . Next, the dehydrated gypsum 9 is separated and taken out by a centrifugal separator 8, and the mother liquor is passed from a conduit 10 through a mother liquor tank 11 and is used by a pump 12 to cool exhaust gas together with make-up water 14 from a conduit 13 using a spray 15. 1 of the liquid discharged from the sludge 2
part is introduced from the conduit 16 into a tank 19 equipped with a loss filter 17,
Calcium compound 18 is slurried, and this is pump 2
The water is supplied from the river to the tank 2 through a conduit 121. The concentration of the sulfuric acid acidic aqueous solution suitable for implementing the method of the present invention is 1% by weight or less, preferably 0.01 to 1% by weight, and 0.01% to 1% by weight.
If the sulfuric acid concentration is less than 0.01% by weight, unreacted calcium compounds may remain when using calcium compounds with normal particle sizes, resulting in a decrease in the utilization rate of the calcium compounds and the quality of the produced gypsum, as well as scaling. 0.0
When reducing the amount to 1% by weight or less, add 20% of the calcium compound.
0 mesh 90% pass, if the sulfuric acid concentration is 0.001% by weight or less, it is finely pulverized than the 325 mesh 95% pass to accelerate the reaction rate and remove unreacted calcium compounds to an acceptable value for gypsum quality. It is possible to reduce it to According to the present invention, when the concentration is high in this concentration range, for example 1% by weight, an oxidation catalyst such as a trivalent oxidation catalyst is added to the absorption liquid, that is, a sulfuric acid acidic aqueous solution in which gypsum is suspended, in order to maintain a high desulfurization rate. The addition of iron compounds was found to be effective. Furthermore, the sulfuric acid acidic aqueous solution may contain the following substances depending on the exhaust gas source and the accompanying pretreatment. For example, ammonium sulfate, ramie, carbon, FeS04, Fe2(S04)3,
CaC12, HN03, (NH4)2S04, Mountain 2 (S
04)3, MgS04, NaCI, etc. Furthermore, when carrying out the method of the present invention, the gypsum concentration in the tank should be adjusted to 3 to 4% by weight.
This is necessary to obtain coarse gypsum crystals, and when the gypsum concentration becomes 3% by weight or less, the grain size of the gypsum crystals becomes small and gypsum scale tends to occur.

In addition, if the gypsum concentration exceeds 4% by weight, it becomes difficult to operate because it tends to cause stagnation in tanks and piping, and there is almost no effect on the particle size of gypsum crystals, so operation at concentrations above 4% by weight must be avoided. . According to the method of the present invention, the purity of the gypsum produced is good, and the COD (chemical oxygen demand) of wastewater can also be suppressed to 3 or less.

Conventionally, absorption in wet flue gas desulfurization using an alkaline absorption liquid depends on the pH.
5 to 7, some of the sulfite is extracted from the absorption band, sulfuric acid is added to eliminate the reactant, the pH is lowered, and oxidized to sulfate with air, but sulfuric acid is added in excess. In addition, because it is difficult to perform complete oxidation, there have been problems such as a decrease in the purity of the produced gypsum and difficulty in achieving COD wastewater standard values, but the present invention solves these problems at once. can. That is, since the absorption liquid used in the method of the present invention is an acidic sulfuric acid aqueous solution, there is naturally no unreacted limestone in the system, and the utilization rate of limestone is 100%, making it unnecessary to add sulfuric acid. Also, because the pH is low and absorption and oxidation of sulfur dioxide gas progresses at the same time, 3 is added as needed.
The valent iron compounds exert a significant effect on oxidation and the sulfites are completely oxidized, resulting in a low COD of the wastewater. As described above, the present invention achieves miniaturization through equipment integration, realization of high desulfurization rate, production of high purity gypsum, and wastewater carbonization.
This is a flue gas desulfurization method that has advantages such as lower OD.

Next, in order to explain the effects of the present invention, the results of a comparative experiment between an experimental example using an apparatus using a spray tower, which is a type of conventional method, and an experimental example using the method of the present invention will be described.

The experimental apparatus using a spray tower will be explained with reference to FIG.

Boiler exhaust gas of 98 M3/day with a sulfur dioxide gas concentration of 109 Qpm was introduced into the spray tower 2' with a total length of 15 mm, through conduit 1', and the absorption liquid was extracted through conduit 6'.
The 10 M3' was circulated by pump 7', sprayed from spray 5', and the desulfurized gas was discharged from conduit 3'.

On the other hand, a slurry of limestone powder with a 95% pass of 325 mesh was introduced through conduit 4, and a portion of the circulating liquid was discharged through conduit 8'. As a result, when the pH of the absorption liquid was adjusted to 5.5 to 6.0, a desulfurization rate of about 90% was obtained, but scaling progressed and long-term operation was not possible. The analysis results of the solid composition in the absorption liquid at this time were as follows. CaC.

3 19 mol%C
aS0301/2nd 20
70〃CaS04・2nd 20
11. Next, we tried desulfurization using an acidic sulfuric acid aqueous solution to prevent scaling, and as seen in the results of B (spray tower) and C (perforated plate tower) in the graph of Figure 3, the sulfuric acid concentration was 0. At .01% by weight or more, desulfurization could hardly be achieved.

Therefore, when experiments using the method of the present invention were carried out using the apparatus shown in Fig. 1, as shown by A in the graph of Fig. 3, a high desulfurization rate was obtained even at a sulfuric acid concentration of 0.01% by weight or more. No reaction occurred at all, and there was no amount of reactive limestone or unoxidized calcium sulfite, and the utilization rate of limestone was 100%. (See Example 1 below) It is clear from the above experiments that the method using gas-liquid contact using liquid difference competition according to the present invention is superior to the conventional method using gas-liquid contact using continuous gas phase. Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way.

* Homare Example 1 Using a device of the type shown in Figure 1, simulated exhaust gas M8/day with a sulfur dioxide concentration of 112, an oxygen concentration of 3%, and a temperature of approximately 200°C from a boiler fueled by heavy oil, The tower 6000 side was cooled to about 60 oo with spray 15 and filled with absorption liquid,
It was introduced into a 60-barrel ◇ vessel.

At this time, the depth of the first zone was 100 mounds, and the depth of the second zone was 350 mounds. Oxidizing air IONM3/H conduit 6
325 mesh 95% pass limestone powder (4
．． 7k9/H) was introduced so as to maintain the sulfuric acid concentration at 0.02 to 0.3% by weight. The desulfurization rate at this time was as shown in Figure 3. The amount of absorption liquid sent to the centrifuge 8 by the pump 7 was 100 days/day, and the gypsum concentration in the tank 2 was maintained at 8% by weight. This mother liquor and about 70 g/day of make-up water were introduced into the spray 15 to cool the exhaust gas. The analysis results of the generated gypsum are as follows. CaS04・2nd 20 98.
9 heavy weight PH 6C
aC03 0″ Average particle size 6
0〃CaS03 0″ Condensation time First train
8 minutes 30 seconds adhering moisture 9 〃 Ending 22 minutes 40 seconds Tensile strength 10.7&
/Umamata: The utilization rate of limestone was 100%, and there was no sign of scaling after one month of continuous operation.

Example 2 Using the apparatus of Example 1, 950 NM' of exhaust gas from a boiler fueled by heavy oil with a sulfur dioxide concentration of 105 μm, an oxygen concentration of 4%, and a temperature of about 20,000 NH30.2
A gas to which NM3/N (added to lower the fog point of S03) was introduced from conduit 1 into vessel 2 holding an absorption liquid in which 500 Ppm of trivalent iron sulfate was dissolved.

Oxidizing air IONW/day is introduced from conduit 6, and 325
Limestone powder (3.8k9/H) with a 95% mesh pass was supplied so that the sulfuric acid concentration was maintained at 0.03 to 0.0% by weight. The desulfurization rate at this time was 94 to 97%. Also, the N area of the exhaust gas at the exit was zero. After 5 days of operation, analysis of the absorption liquid revealed that the ammonium sulfate concentration was 9% by weight (produced amount: 70 kg), confirming that the added NH3 was absorbed and then oxidized by the blown air. .

After 1968, the concentration of ammonium sulfate was increased by
The mother wave after centrifugation was discharged at the same rate for 150 days.

The amount of gypsum centrifuged was 8k9/day, and analysis showed that CaC03 and CaS03 in the gypsum were zero. Example 3 Using the apparatus of Example 1, 550 NM3/H' of exhaust gas from a boiler fueled by heavy oil with a sulfur dioxide concentration of 107cm, an oxygen concentration of 3%, and a temperature of about 200 qo was collected in a cylinder at 5NM3. /H was added to make the sulfur dioxide gas concentration about 1000 μm, and the mixture was introduced into the tank 2 holding the absorption liquid.

Oxidizing air of 50 NM3/day was introduced from conduit 6, and
5 mesh 95% pass limestone powder (23k9'H),
The sulfuric acid concentration was maintained at 0.03 to 0.0% by weight. The desulfurization rate at this time was 90 to 93%. Example
4 Using the apparatus of Example 1, exhaust gas of 1250N per day from a boiler fueled by heavy oil with a sulfur dioxide concentration of 390%, oxygen concentration of 3%, and a temperature of approximately 200°C, and trivalent iron of 200% The solution was introduced into tank 2 which holds the dissolved absorption liquid.

Oxidizing air ION sail/day is introduced from conduit 6, and 325
Limestone powder (2k9/H) with a 95% mesh pass was supplied so that the sulfuric acid concentration was maintained at 0.02 to 0.04% by weight.
The desulfurization rate at this time was 97 to 99%.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing a specific example of the apparatus used in carrying out the method of the present invention, Fig. 2 is a system diagram of an apparatus using a secondary spray tower system, and Fig. 3 is a system diagram showing a specific example of the apparatus used in carrying out the method of the present invention. and a graph showing the relationship between sulfuric acid concentration and desulfurization rate when using each perforated plate column system. 1...Sulfur dioxide gas conduit, 2...Reaction tank, 3...Gas disperser, 4...Gas exhaust pipe, 5... Gypsum discharge pipe, 6...Oxygen-containing gas introduction pipe, 7...Pump, 8...
Centrifuge, 9...Gypsum, 10...Mother liquor conduit, 11...Mother liquor tank, 12...Pump, 13...Mother liquor Transport conduit, 14...
・Supplementary water, 15...Spray, 16...
・Ishikari slurry conduit, 17... rope azusa machine, 18.
... Calcium compound, 19 ... Calcium compound slurry tank, 20 ... Pump, 21
...Calcium compound slurry conduit, 1'...
...Boiler exhaust gas pipe, 2'...Spray tower, 3'...Gas discharge pipe, 4'...
・Limestone powder slurry conduit, 5'...spray,
6' Absorption liquid extraction conduit, 7'...Pump, 8
′...Gypsum discharge conduit. Kyoryo Zuyō 2 Zuyō 3

Claims (1)

[Claims] 1. In the flue gas desulfurization method in which sulfur dioxide gas is fixed as gypsum, the flue gas is dispersed and introduced into the upper region of a sulfuric acid acid aqueous solution in which gypsum is suspended in a tank, and the fine bubbles of the flue gas and the A gas-liquid contact layer having a continuous liquid phase is formed in the first zone consisting of the sulfuric acid acid aqueous solution, and an oxygen-containing gas is introduced into the lower region of the sulfuric acid acid aqueous solution in which the gypsum is suspended, so as to be located directly below the first zone. A second zone is formed, which is composed of microbubbles of oxygen-containing gas and the sulfuric acid acid aqueous solution, is continuous with the first zone in the liquid phase, and has a smaller amount of bubbles than the first zone. The sulfuric acid concentration of the sulfuric acid acidic aqueous solution is 1% by weight.
A method for flue gas desulfurization, characterized in that a sufficient amount is introduced to maintain a slurry concentration of 3 to 40% by weight, and a sufficient amount is withdrawn from a second zone to maintain a slurry concentration of 3 to 40% by weight. 2. The method according to claim 1, wherein the calcium compound is introduced at the interface between the first zone and the second zone. 3
In the flue gas desulfurization method, which fixes sulfur dioxide gas as gypsum, gypsum stored in a tank is suspended, and the flue gas is dispersed and introduced into the upper region of a sulfuric acid acidic aqueous solution containing an oxidation catalyst. A first zone, which is a gas-liquid contact layer with a continuous liquid phase consisting of an acidic aqueous solution, is formed, and an oxygen-containing gas is introduced into the lower region of the sulfuric acid acidic aqueous solution in which the gypsum is suspended, and the gas is located immediately below the first zone. A second zone is formed of fine bubbles of oxygen-containing gas and the sulfuric acid acidic aqueous solution, and is continuous with the first zone in the liquid phase and has a smaller amount of bubbles than the first zone. The sulfuric acid concentration of the acidic aqueous solution is introduced in an amount sufficient to maintain the sulfuric acid concentration at 1% by weight or less, and the gypsum-containing suspension is removed from the second zone in an amount sufficient to maintain the slurry concentration at 3 to 40% by weight. flue gas desulfurization method.