JP2014117675A - Method and apparatus for treating exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for treating an exhaust gas where mercury in the exhaust gas can be efficiently reduced by that dust containing much mercury separated from the cement firing exhaust gas is heated at a low temperature lower than the boiling point of mercury and mercury is effectively volatilized and separated from the dust.SOLUTION: In a method and the like for treating an exhaust gas, a separation step to separate dust from a mercury-containing exhaust gas exhausted from a cement kiln and a reduced pressure heating step to heat the separated dust to 160°C or more and 340°C or less under a pressure of 0.76 kPa or more and 74.4 kPa or less are implemented.

Description

  The present invention relates to an exhaust gas treatment method and an exhaust gas treatment apparatus for reducing mercury contained in exhaust gas discharged from a cement kiln.

A small amount of mercury is contained in the exhaust gas called cement firing exhaust gas discharged from the cement kiln. This mercury originates from natural materials such as limestone, which is a raw material for cement, and wastes.
Since the exhaust gas is discharged from the chimney to the atmosphere, it is necessary to reduce mercury contained in the exhaust gas.

  As a method for reducing mercury in the exhaust gas, for example, as described in Patent Document 1, dust containing a large amount of mercury is separated from exhaust gas discharged from a cement kiln, and the dust is heated. Therefore, a method of reducing mercury in exhaust gas by volatilizing mercury in dust and separating mercury from dust is employed. However, when mercury is volatilized from dust by such heating, it is necessary to heat to a temperature higher than the boiling point of mercury (356.73 ° C.).

  On the other hand, Patent Document 2 discloses a method of removing pollutants from soil by volatilizing volatile pollutants such as mercury from the contaminated soil by sealing contaminated soil containing mercury or the like in a decompressed space. Is described.

  However, since the mercury contained in the dust is a very small amount and adsorbed to unburned carbon in the dust, the mercury is sufficiently volatilized and removed from the dust only by reducing the pressure as described in Patent Document 2. It is difficult.

Japanese Patent Laid-Open No. 2002-355531 JP 2007-222873 A

  In view of the above problems, the present invention heats dust containing a large amount of mercury separated from cement-fired exhaust gas at a low temperature below the boiling point of mercury, and effectively volatilizes and separates mercury from the dust, so that It is an object of the present invention to provide an exhaust gas treatment method and an exhaust gas treatment device capable of efficiently reducing mercury.

  The method for treating exhaust gas according to the present invention includes a separation step of separating dust from exhaust gas discharged from a cement kiln and containing mercury, and the separated dust under a pressure of 0.76 kPa to 74.4 kPa at 160 ° C. or higher. A reduced pressure heating step of heating to 340 ° C. or lower is performed.

  According to the present invention, a separation step of separating dust from exhaust gas discharged from a cement kiln and containing mercury, and heating the dust to 160 ° C. or higher and 340 ° C. or lower under a pressure of 0.76 kPa to 74.4 kPa. By performing the reduced pressure heating step, mercury can be removed from the dust in the exhaust gas even by heating at a relatively low temperature.

  As one embodiment of the present invention, an activated carbon treatment step in which a gas containing mercury volatilized from the dust in the reduced pressure heating step is brought into contact with activated carbon may be performed.

  Mercury can be removed from the gas by bringing the gas containing mercury generated in the reduced pressure heating step into contact with activated carbon.

  Further, the present invention relating to an exhaust gas treatment apparatus includes a separation device that separates dust from exhaust gas that is discharged from a cement kiln and contains mercury, and a mercury removal device that removes mercury from the dust, the mercury removal device comprising: A main body for introducing the dust; a decompression device that depressurizes the main body to 0.76 kPa to 74.4 kPa; and a heating device that heats the main body to 160 ° C. to 340 ° C.

  As one aspect of the present invention relating to a dust mercury removing apparatus, the mercury removing apparatus includes a tank main body provided with an activated carbon layer therein, and a gas introduction path for introducing gas generated in the main body into the tank main body. You may further provide the activated carbon treatment apparatus provided with.

  As described above, according to the present invention, mercury in exhaust gas discharged from a cement kiln can be efficiently reduced.

The figure which showed the waste gas processing apparatus which concerns on one Embodiment of this invention. The schematic diagram which showed the testing apparatus used for the Example of this invention.

  Hereinafter, embodiments of an exhaust gas treatment method and an exhaust gas treatment apparatus according to the present invention will be described.

The exhaust gas treatment apparatus 10 of the present embodiment is
A separation device for separating dust from exhaust gas discharged from a cement kiln and containing mercury;
A mercury removing device that removes mercury from the dust, the mercury removing device including a main body portion that introduces the dust, a decompression device that depressurizes the inside of the main body portion to 0.76 kPa to 74.4 kPa, and the main body And a heating device for heating the inside to 160 ° C. or higher and 340 ° C. or lower.

Specifically, for example, as shown in FIG. 1, the separation device of the exhaust gas treatment device 10 of the present embodiment is connected to a cement kiln 2 of a cement manufacturing facility 100, and exhaust gas from the cement kiln 2 is introduced. It is comprised so that.
For example, as shown in FIG. 1, the cement kiln 2 is connected to a heating device 3 including a preheater 3 a and a calcining furnace 3 b, and exhaust gas discharged from the most downstream side of the heating device 3. It is configured to be introduced into the separation device 5.

The separation device 5 includes a sedimentation chamber 5a, a stabilizer 5b, an electric dust collector 5c, and a bag filter 5d, in which dust is captured from the exhaust gas. The settling chamber 5a, the stabilizer 5b, the electrostatic precipitator 5c, and the bag filter 5d are each provided with a dust discharge path 7, and the dust discharge path 7 is connected to a dust reservoir 4a and separated by the separation device 5. The dust is stored in the dust storage part 4a.
The settling chamber 5a, the stabilizer 5b, the electrostatic precipitator 5c, and the bag filter 5d are each provided with a discharge path for discharging the gas after separating the dust in the exhaust gas. From the settling chamber 5a to the stabilizer 5b, the electric dust collector 5c and the bag filter 5d are introduced in this order, and discharged from the exhaust path 8 of the bag filter 5d to the outside of the exhaust gas treatment device 10.

The exhaust gas treatment apparatus 10 of the present embodiment includes a mercury removal apparatus 1 that removes mercury from the dust separated by the separation apparatus 5.
The main body 1a of the mercury removing device 1 is connected to the dust reservoir 4a, and is configured so that dust from the dust reservoir 4a can be accommodated therein.
As said main-body part 1a, metal containers, such as stainless steel, etc. are used suitably, for example.
The main body 1a may be provided with a filter such as a ceramic filter.

  The depressurization device may be any device as long as it depressurizes the inside of the main body 1a. For example, an exhaust pipe connected to an upper portion of the main body 1a and an exhaust pipe are attached. And an apparatus equipped with a vacuum pump.

  The heating device is preferably arranged around the main body 1a so as to heat the housing portion of the main body 1a. Examples of the heating device include an external heat jacket such as an electric heater and a hot air generator.

The mercury removing apparatus 1 of the present embodiment further includes an activated carbon treatment apparatus 1b including a tank main body provided with an activated carbon layer therein and a gas introduction path for introducing gas generated in the main body into the tank main body. Is provided.
The activated carbon treatment device 1b includes a tank main body provided with an activated carbon layer therein, and a gas introduction path 11a for introducing gas generated in the main body into the tank main body.
The tank body is further connected with a gas discharge path 11b for discharging the gas inside the tank body.

  The main body 1a of the mercury removing apparatus 1 is provided with a processing dust discharge path 9, and the processing dust discharge path 9 is connected to a raw material storage supply section 4 in which cement raw material is stored.

The raw material storage and supply unit 4 is provided with a supply path 4 b for introducing the cement raw material pulverized in the cement raw material pulverizer 6 and supplying the cement raw material to the cement manufacturing facility 100.
In addition, the said raw material storage supply part 4 and the said dust storage part 4a are connected so that dust can be introduce | transduced into the said raw material storage supply part 4 from the said dust storage part 4a.

  On the other hand, the gas discharge path 11b of the activated carbon treatment apparatus 1b is connected to the discharge path 8 for discharging the gas separated from the dust in the separation apparatus 5.

  Next, an exhaust gas treatment method performed using the exhaust gas treatment apparatus 10 will be described.

The method for treating cement fired exhaust gas of this embodiment is as follows:
A separation process for separating dust from exhaust gas discharged from a cement kiln and containing mercury;
And a reduced pressure heating step of heating the dust to 160 ° C. to 340 ° C. under a pressure of 0.76 kPa to 74.4 kPa.
Furthermore, in the exhaust gas treatment method of the present embodiment, an activated carbon treatment step is performed in which a gas containing mercury volatilized from the dust in the reduced pressure heating step is brought into contact with activated carbon.

(Separation process)
The exhaust gas discharged from the cement kiln 2 is introduced into the separation device 5 and separated into dust and gas in the exhaust gas.
Specifically, the exhaust gas is first introduced into the settling chamber 5a of the separation device 5 and separated into dust and gas. The gas discharged from the discharge path of the settling chamber 5a is then introduced into the stabilizer 5b and separated into dust and gas. Similarly, the gas is introduced in the order of the electrostatic precipitator 5c and the bag filter 5d, and the dust is separated in each device and introduced into the dust reservoir 4a from the dust discharge path 7 of each device.

  On the other hand, the exhaust gas discharged from the discharge path 8 of the bag filter 5d is discharged out of the exhaust gas treatment device 10.

(Reduced pressure heating process)
Next, a reduced pressure heating step is performed in which the dust is heated to 160 ° C. or higher and 340 ° C. or lower under a pressure of 0.76 kPa or higher and 74.4 kPa or lower.
Specifically, a part of the dust stored in the dust storage part 4 a is introduced into the housing part of the main body part 1 a of the mercury removing device 1.
And the said vacuum pump of the decompression device connected to the said main-body part is operated, and the accommodating part of the said main-body part is pressure-reduced.
At this time, the pressure is reduced by the pressure reducing device so that the pressure in the accommodating portion is 0.760 kPa to 74.4 kPa, preferably 2.30 kPa to 9.92 kPa.
Of the dust stored in the dust storage part 4a, the part not supplied to the mercury removing device 1 may be introduced directly into the raw material storage and supply part 4.

  After the decompression device is operated and the pressure in the housing part becomes the pressure, the inside of the housing part is heated to 160 ° C. or more and 340 ° C. or less, preferably 200 ° C. or more and 250 ° C. or less by the heating device.

  The reduced pressure heating step is carried out by maintaining the state of reaching the pressure and temperature for 10 minutes to 120 minutes, preferably 20 minutes to 60 minutes.

  The decompression device and the heating device may be operated simultaneously to start heating simultaneously with the decompression.

  In the reduced pressure heating step, mercury contained in the dust is volatilized and removed from the dust. Normally, it is difficult to volatilize mercury sufficiently from dust unless it is heated to a temperature higher than the boiling point of mercury, but the heating temperature is reduced by reducing the boiling point of mercury by reducing the pressure to the above pressure and heating the dust. Even if the temperature is lowered, mercury can be volatilized and removed from the dust.

In the present embodiment, since the exhaust gas is further passed through the preheater 3a and the calcining furnace 3b before the exhaust gas is introduced from the cement kiln 2 into the separation device 5, dust having a large particle size is generated in the preheater 3a. Classified and returned to cement kiln 2.
That is, the dust introduced into the mercury removing apparatus 1 is very fine dust.
When removing a very small amount of mercury contained in such fine dust from the dust, the dust mercury removing method of the present embodiment is suitable.

After carrying out the reduced pressure heating step, only dust is taken out from the main body 1a and introduced into the raw material storage and supply unit 4.
Since the mercury stored in the raw material storage and supply unit 4 is free of mercury, the exhaust gas discharged from the cement kiln is introduced into the raw material storage and supply unit 4 and returned to the cement kiln together with the cement raw material. There is no risk of increasing the mercury concentration in the inside.

(Activated carbon treatment process)
On the other hand, a gas containing mercury volatilized from dust in the reduced pressure heat treatment process is accumulated inside the main body 1a. Such gas is introduced from the main body into the activated carbon treatment apparatus 1b and brought into contact with the internal activated carbon layer. Mercury in the gas in contact with the activated carbon layer is adsorbed by the activated carbon, so that mercury is removed from the gas.
In addition, when the filter is provided in the inside of the said main-body part, when discharging | emitting gas from the main-body part 1a, the gas which isolate | separated dust can be discharged | emitted from a main-body part.
In the present embodiment, the gas discharged from the gas discharge path 11b of the activated carbon treatment device 1b is sent to the discharge path 8 of the separation device 5 and discharged to the outside together with the gas separated from the dust by the separation device 5.

  In the present embodiment, the separation device 5 includes a settling chamber 5a, a stabilizer 5b, an electric dust collector 5c, and a bag filter 5d. However, as the separation device, dust in exhaust gas is used. The device is not limited to this as long as it can be separated. For example, a separation device including only an electric dust collector may be used.

  Moreover, although this embodiment demonstrated the case where the said mercury removal apparatus 1 was equipped with one unit in the exhaust gas treatment apparatus, the exhaust gas treatment apparatus may be equipped with two or more said mercury removal apparatuses. In this case, switching operation is possible, and even when one mercury removing device is in a state where cleaning or maintenance is required, continuous processing can be performed by operating another mercury removing device.

  Further, in the present embodiment, the mercury removal apparatus 1 is provided with an activated carbon treatment apparatus, and the case where exhaust gas containing mercury volatilized in the main body is treated in the activated carbon treatment process has been described. It is not limited to providing and implementing an activated carbon treatment process.

  The exhaust gas treatment method and exhaust gas treatment apparatus according to the present embodiment are as described above, but the embodiment disclosed this time should be considered as illustrative in all points and not restrictive. . The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  Examples An exhaust gas treatment method and an exhaust gas treatment apparatus and method according to the present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples.

In this example, the test apparatus shown in FIG. 2 was used.
The test apparatus comprises a stainless steel main body (volume: 200 ml), an electric heater as a heating device arranged around the main body, and a vacuum as a decompression device connected to the main body via an exhaust pipe. With a pump.
Further, the test apparatus is provided with an air horn through an air supply pipe for sending air into the main body.
A manual valve is attached to each of the exhaust pipe and the air supply pipe, and a flow meter is attached to the air supply pipe.

30 g of EP dust (mercury concentration: 11 mg / kg as Hg concentration) collected by an electric dust collector of a cement manufacturing facility was accommodated in the main body of the test apparatus.
The valve of the exhaust pipe was opened, and the inside of the main body was reduced to each pressure shown in Table 1 with a vacuum pump, and at the same time, the inside of the main body was heated to each temperature shown in Table 1 with an electric heater.
After holding each temperature and each pressure state shown in Table 1 for the time shown in Table 1, the electric heater was stopped to stop heating, and 0.5 liters were discharged from the air cylinder while evacuating with a vacuum pump. The air inside the main body was discharged by flowing air at a flow rate of 10 minutes per minute.

Thereafter, the dust was taken out, and the mercury removal rate was determined by the following formula from the result of measuring the mercury concentration of the dust.

Mercury removal rate (%) = (Mercury concentration before heat treatment under reduced pressure−Mercury concentration after heat treatment under reduced pressure) ÷ Mercury concentration before heat treatment under reduced pressure × 100

The mercury removal rate and the boiling point of mercury at each pressure are listed in Table 1.

From the results in Table 1, the following can be understood.
In Comparative Examples 1 to 3 where heat treatment was performed under atmospheric pressure (101 kPa), the mercury removal rate is low unless heated to a high temperature of 350 ° C. or higher.
On the other hand, in Examples 1 to 5 in which the pressure was reduced to 0.76 to 74.4 kPa, which is lower than the atmospheric pressure, mercury removal exceeded 85% even at a temperature of 340 ° C. or lower.
Even in a reduced pressure state, the mercury removal rate was low in Comparative Example 5 that was not heated and Comparative Example 4 that was heated to a relatively low temperature of 120 ° C.

  DESCRIPTION OF SYMBOLS 1 ... Mercury removal apparatus, 2 ... Cement kiln, 5 ... Separation apparatus, 10 ... Exhaust gas treatment apparatus.

Claims (4)

A separation process for separating dust from exhaust gas discharged from a cement kiln and containing mercury;
A method for treating exhaust gas, comprising: performing a reduced pressure heating step of heating the separated dust to 160 ° C. to 340 ° C. under a pressure of 0.76 kPa to 74.4 kPa.   The exhaust gas treatment method according to claim 1, wherein an activated carbon treatment step in which a gas containing mercury volatilized from the dust in the reduced pressure heating step is brought into contact with activated carbon. A separation device for separating dust from exhaust gas discharged from a cement kiln and containing mercury;
A mercury removing device for removing mercury from the dust,
The mercury removing device is
A main body for introducing the dust;
A decompression device for decompressing the inside of the main body to 0.76 kPa or more and 74.4 kPa or less;
An exhaust gas treatment apparatus comprising a heating device for heating the inside of the main body to 160 ° C. or higher and 340 ° C. or lower. The mercury removing device is
A tank body with an activated carbon layer inside,
The exhaust gas treatment apparatus according to claim 3, further comprising an activated carbon treatment apparatus provided with a gas introduction path for introducing a gas generated in the main body into the tank body.

Images