JP2880939B2 - Low temperature desulfurization method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention SOx from the exhaust gas or the like flue gases or chemical plants (sulfur dioxide SO _2, sulfur trioxide gas SO _3, etc.) relates to desulfurization of removing, in particular, 3
The present invention relates to a low-temperature desulfurization method effective for removing SOx contained in exhaust gas at a low temperature of 00 ° C. or lower.

[0002]

2. Description of the Related Art As a desulfurization method for removing SOx (sulfurous acid gas SO ₂ , anhydrous sulfuric acid gas SO _3, etc.) from various kinds of combustion exhaust gas and exhaust gas from a chemical plant, an alkaline solution is sprayed into the exhaust gas to remove SOx. There is a wet desulfurization method of absorbing and recovering water, and a dry desulfurization method of removing SOx by adsorption and absorption on a solid surface.

[0003] At present, wet desulfurization is widely used because of its high desulfurization efficiency. Among them, limestone (Ca
The method of using gypsum (CaSO ₄ ) as a by-product with CO ₃ ) as a desulfurizing agent has become very mainstream in large-scale treatment because of its extremely high desulfurization efficiency and stable operation.

[0004] However, the wet desulfurization method is expensive in terms of both equipment cost and operation cost. Therefore, it is economically advantageous to use the dry desulfurization method, which is relatively inexpensive. Since the desulfurization efficiency is not high as in the desulfurization method and a high reaction temperature is required, it is necessary to improve them by some method.

The present invention solves the above-mentioned problems of the prior art, and can reduce both equipment cost and operation cost, as well as high desulfurization without requiring a high reaction temperature. It is an object of the present invention to provide a low-temperature desulfurization method capable of obtaining efficiency.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention fluidizes an inert medium particle with an exhaust gas containing SOx to form a fluidized bed, and includes a desulfurizing agent in the fluidized bed. And a solution or slurry containing the solution is attached to the surface of the medium particles , and the temperature in the fluidized bed is exhausted.
The temperature is set to 10 to 50 ° C. higher than the dew point of the gas, the SOx in the exhaust gas is absorbed by the desulfurizing agent on the surface of the medium particles and the desulfurization reaction proceeds, and at the same time, the moisture in the desulfurizing agent is evaporated by the heat of the exhaust gas. The reaction product and the unreacted desulfurizing agent are dried and solidified on the surface of the medium particles, and the dried and solidified reaction product and the unreacted desulfurizing agent are exfoliated as fine powder from the surface of the medium particles. Means for exhausting the wastewater. The medium particles are made of silica sand, river sand, alumina, etc., which are hardly pulverized by fluidization, and have a particle size of 150 to 2000 μm.
m is adopted. Further, the exhaust gas employs means having a low temperature of 300 ° C. or less. Further, the desulfurizing agent employs a means which is a hydroxide of an alkali metal or a hydroxide of an alkaline earth metal which is highly active even at a low temperature of 300 ° C. or lower. The fluidized bed employs a means of a jet type fluidized bed without using a gas dispersion plate in a gas supply unit.

[0007]

According to the present invention, by employing the above-mentioned means, the inert medium particles are fluidized by the exhaust gas containing SOx to form a fluidized bed. Since the fluidized bed is in a state of being vigorously stirred by the exhaust gas, when a solution or slurry containing a desulfurizing agent is injected into the fluidized bed, they are uniformly attached to the surface of the medium particles by contact with the medium particles. . The desulfurizing agent attached to the surface of the medium particles absorbs SOx in the exhaust gas, and the desulfurization reaction proceeds. At the same time, the moisture in the desulfurizing agent evaporates due to the heat of the exhaust gas, and the reaction product and the unreacted desulfurizing agent are dried and solidified on the surface of the medium particles. The desulfurizing agent dried and solidified on the surface of the medium particles is separated from the surface of the medium particles by vigorous movement of the medium particles into a fine powder state, and the reaction product and the unreacted desulfurizing agent in the fine powder state are exhaust gas. Together with the fluidized bed.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventors of the present invention have previously filed patent applications relating to the dry desulfurization method (JP-A-6-79132 and JP-A-7-148417). These are methods in which inert media particles are fluidized by an exhaust gas containing SOx to form a fluidized bed and fine particles of a desulfurizing agent are injected into the fluidized bed. Although high desulfurization efficiency can be obtained due to stagnation, both have not yet reached desulfurization efficiency comparable to that of the wet desulfurization method.

Further, in the above-mentioned research, the inventors of the present invention used a fluidized bed using a desulfurizing agent solution or slurry to improve the quantitativeness of the desulfurizing agent injected into the fluidized bed and facilitate stable operation. And tried to inject it into the inside.

Recently, it has been discovered that the desulfurization efficiency can be significantly improved by injecting a desulfurizing agent solution or slurry instead of directly injecting the desulfurizing agent fine particles into the fluidized bed. Reached the present invention.

Hereinafter, embodiments of the present invention will be described. The temperature of various kinds of combustion exhaust gas and exhaust gas from a chemical factory is generally around 150 ° C. in many cases. Such an exhaust gas fluidizes inert medium particles that do not react with SOx to form a fluidized bed.

The fluidized bed is in a state of being vigorously stirred by the exhaust gas. When a solution or slurry containing a desulfurizing agent is injected therein, the desulfurizing agent comes into contact with the medium particles in a stirring state and uniformly adheres to the surface thereof. The desulfurizing agent attached to the surface of the medium particles absorbs SOx in the exhaust gas to cause a desulfurization reaction, and at the same time, heat in the exhaust gas evaporates water in the desulfurizing agent.

When the water in the desulfurizing agent is completely evaporated, the reaction product and the unreacted desulfurizing agent are dried and solidified on the surface of the medium particles. The dried and solidified reaction product and the unreacted desulfurizing agent are separated from the surface of the medium particles by vigorous motion of the medium particles to be in a fine powder state.

The reaction product in the form of fine powder and the unreacted desulfurizing agent are discharged from the fluidized bed together with the exhaust gas.
Collected by bag filter.

As described above, by using a desulfurizing agent as a solution or a slurry, the desulfurizing efficiency can be drastically improved. The reason is that sulfur dioxide gas has a very high solubility in water,
The presence of moisture significantly promotes the absorption of sulfurous acid gas. Since the desulfurizing agent adheres to the surface of the medium particles due to the moisture, the residence time of the desulfurizing agent in the fluidized bed can be significantly increased. Because.

As a result of further studies by the present inventors, it has been found that the temperature of the fluidized bed should be determined as follows.

The lower the temperature in the fluidized bed, the longer it takes to evaporate the water. But,
If the temperature in the fluidized bed is too low, the evaporation of water becomes insufficient, the reaction product and the unreacted desulfurizing agent become highly viscous on the surface of the medium particles, and the medium particles aggregate with each other to impair the flow state. Eventually, it becomes inoperable.

Therefore, the temperature in the fluidized bed must be at least higher than the dew point of the exhaust gas. It is also necessary to consider the physical properties of the desulfurizing agent and the product, fluctuations in various conditions of the exhaust gas, and the like. And as a result of considering these, it became clear that it is preferable to set the temperature in the fluidized bed to a temperature higher by 10 to 50 ° C. than the dew point of the exhaust gas.

As the desulfurizing agent used in this embodiment,
Those having high activity even at a low temperature of 300 ° C. or less are preferable. For example, hydroxides of alkali metals such as sodium hydroxide (NaOH) and potassium hydroxide (KOH) and slaked lime (C
a (OH) ₂ ), magnesium hydroxide (Mg (O
H) A hydroxide of an alkaline earth metal such as ₂ ) is preferred, but is not limited thereto, and may be any as long as a similar function can be obtained.

Since the amount of SOx is determined by the amount of exhaust gas and the concentration of SOx, it is sufficient to inject a corresponding amount of desulfurizing agent. Here, the stoichiometric ratio between the desulfurizing agent and the SOx amount is determined in consideration of the desulfurization efficiency. In the dry desulfurization method, the desulfurization efficiency is lower than in the wet desulfurization method. Need to be bigger.

The concentration of the desulfurizing agent contained in the solution or slurry, in other words, the amount of water injected together with the desulfurizing agent is
What is necessary is just to determine in consideration of the temperature in a fluidized bed. That is,
As described above, the temperature of the exhaust gas in the fluidized bed may be set so as to be 10 to 50 ° C. higher than the dew point.

Further, as the medium particles, silica sand, river sand, alumina or the like which is hardly pulverized by fluidization is used, and the particle diameter is preferably about 150 to 2000 μm. If the particle diameter is too small, the protrusion from the fluidized bed increases, and if the particle diameter is too large, the pressure loss of the exhaust gas increases.

It is preferable that the fluidized bed is at a low temperature as close as possible to the dew point of the exhaust gas and has a relatively vigorous fluidized state so that the medium particles do not agglomerate with each other. For this reason, the exhaust gas supply unit may be a jet-type fluidized bed in which the exhaust gas is introduced directly from below the cone-shaped fluidized bed without using a normal gas dispersion plate.

FIG. 1 shows an example of an apparatus for performing a low-temperature desulfurization method based on this embodiment. This apparatus is a test apparatus, and uses a sample gas obtained by adding a predetermined amount of SO ₂ to air as a supply gas.

The air supplied by the air supply device (compressor) 1 is supplied to an oil filter 2, a silica gel tower 3
Flow meter (orifice) after removing oil and water
, And the flow rate of SO ₂ gas from the cylinder 6 is measured by a flow meter (flow meter) 7. These gases are mixed to obtain a gas containing 500 to 1000 ppm of SO ₂ .

[0026] The gas containing the S0 _2, and heated to 70 to 300 ° C. in a gas heating furnace 8, the desulfurization reaction vessel 1 of particulate fluidized bed
0 to fluidize the media particles.

The heating furnace 9 is for adjusting the temperature of the fluidized bed. In the case of a large-sized fluidized bed, it is only necessary to keep the temperature sufficiently.

A solution or slurry of a desulfurizing agent is prepared in a slurry tank 11 and supplied to the desulfurization reactor 10 at a constant flow rate by a slurry metering pump 13 through a slurry circulation pump 12.

Reference numeral 17 denotes a cylindrical filter paper for collecting the reaction product and unreacted desulfurizing agent, 14 a thermocouple for measuring the reaction temperature, 15 a recorder thereof, and 18 a humidity for measuring the effluent gas. to dry - wet bulb thermometer, 20 SOx meter for measuring the inlet and S0 ₂ concentration in the outlet gas, 19 is a cooler for cooling the gases entering the SOx meter.

The results of tests performed using the above apparatus are shown below.

<Test Result 1> Desulfurization reactor ... Inner diameter 5 cm, height 100 cm Medium particles ... Silica sand (average particle diameter 600 μm) Stationary filling height ... ...... 30cm reactor inlet gas temperature ......... 100 ℃ fluidized bed temperature .................. 65 ℃ SO ₂ concentration ..................... 1000ppm superficial gas velocity .................. 80cm / s desulfurization agent ........................... slaked lime (Ca (OH) ₂₎ (average particle size 5 [mu] m) slurry concentration .................. 40% desulfurization agent supply amount .................. chemical against SO ₂ Stoichiometrically twice as much Desulfurization rate ………………… 90%

<Test result 2> Desulfurization reactor ... Inner diameter 5 cm, height 100 cm Medium particles ... Kawasuna (average particle diameter 700 μm) Stationary filling height ... … 20 cm reactor inlet gas temperature … 100 ° C. Fluidized bed temperature… 70 ° C. SO ₂ concentration… 1000 ppm Vapor gas velocity… 100 cm / s Desulfurizing agent Aqueous sodium hydroxide solution (NaOH) Desulfurizing agent concentration 20% Desulfurizing agent supply amount 1.5 times stoichiometrically with respect to SO ₂ Amount Desulfurization rate ………………… 95%

From the above test results, it can be clearly understood that the use of the low-temperature desulfurization method according to this embodiment can achieve high desulfurization efficiency with simple equipment without requiring a high reaction temperature.

[0034]

According to the present invention, the inert medium particles are fluidized by the exhaust gas containing SOx to form a fluidized bed, and the temperature in the fluidized bed is reduced by the exhaust gas containing the SOx .
When a solution or slurry containing a desulfurizing agent is injected into the fluidized bed at a temperature higher than the dew point by 10 to 50 ° C. , the desulfurizing agent adheres to the surface of the medium particles, and the SOx in the exhaust gas is absorbed by the desulfurizing agent. Is done. At the same time, the moisture in the desulfurizing agent evaporates due to the heat of the exhaust gas, and the reaction product and the unreacted desulfurizing agent dry and solidify on the surface of the medium particles. The vigorous movement of the particles causes the surface of the medium particles to be separated into fine powder and peeled off. By discharging the separated fine powder from the fluidized bed together with the exhaust gas, SOx contained in the exhaust gas can be removed. In this case, since the desulfurizing agent is a solution or a slurry, the absorption of SOx gas can be remarkably promoted by the presence of water. In addition, since the desulfurizing agent will surely adhere to the surface of the medium particles due to moisture,
The desulfurizing agent stays in the fluidized bed for a long time, and the residence time of the desulfurizing agent in the fluidized bed can be significantly increased. Therefore, high reaction with simple equipment
High desulfurization efficiency can be obtained without the need for temperature
And

Further, since silica sand, river sand, alumina or the like which is hardly pulverized by fluidization is used as the medium particles, the medium particles, that is, the desulfurizing agent can be reliably retained in the fluidized bed for a long time. . Further, by setting the particle size of the medium particles to about 150 to 2000 μm, it is possible to reduce the protrusion of the medium particles from the fluidized bed and also to reduce the pressure loss of the gas.

Further, by using an alkali metal hydroxide or an alkaline earth metal hydroxide which is highly active even at a low temperature of 300 ° C. or less as a desulfurizing agent, a high reaction temperature is not required and a low reaction temperature can be obtained. SO contained in flue gas
x can be efficiently removed.

The fluidized bed is a spouted fluidized bed without using a gas dispersion plate in the gas supply section,
The medium particles do not agglomerate with each other and a relatively intense flow state is obtained, so that the desulfurization efficiency can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing an example of a test apparatus for carrying out an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Air supply device (compressor) 2 ... Oil filter 3 ... Silica gel tower 4 ... Pressure regulator 5 ... Flow meter (orifice) 6 ... Cylinder 7 ... Flow meter (flow meter) 8 ... Gas Heating furnace 9 Heating furnace 10 Desulfurization reactor 11 Slurry tank 12 Slurry circulation pump 13 Slurry metering pump 14 Thermocouple 15 Recorder 16 Three-way cock 17 Cylindrical filter paper 18 …… Dry-wet thermometer 19 …… Cooler 20 …… SOx meter

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B01D 53/50 B01D 53/81 B01J 8/24

Claims (5)

(57) [Claims] 1. Fluidizing inert media particles with exhaust gas containing SOx to form a fluidized bed, and injecting a solution or slurry containing a desulfurizing agent into the fluidized bed to adhere to the surface of the media particles. The temperature in the fluidized bed
The temperature is set to be 10 to 50 ° C. higher than the dew point , the SOx in the exhaust gas is absorbed by the desulfurizing agent on the surface of the medium particles , and the desulfurization reaction proceeds, and at the same time, the moisture in the desulfurizing agent is evaporated by the heat of the exhaust gas. The reaction product and the unreacted desulfurizing agent are dried and solidified on the surface of the medium particles, and the dried and solidified reaction product and the unreacted desulfurizing agent are peeled off as fine powder from the surface of the medium particles and discharged from the fluidized bed together with the exhaust gas. A low-temperature desulfurization method. 2. The low-temperature desulfurization method according to claim 1, wherein the medium particles are made of silica sand, river sand, alumina or the like which is hardly pulverized by fluidization, and have a particle size of about 150 to 2000 μm. 3. The low-temperature desulfurization method according to claim 1, wherein the exhaust gas has a low temperature of 300 ° C. or lower. 4. The low-temperature desulfurization method according to claim 1, wherein the desulfurizing agent is a hydroxide of an alkali metal or a hydroxide of an alkaline earth metal having a high activity even at a low temperature of 300 ° C. or lower. 5. The low-temperature desulfurization method according to claim 1, wherein the fluidized bed is a jet-type fluidized bed that does not use a gas dispersion plate in a gas supply unit.