JP2005283094A - Method and system for treating exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently remove moisture and a toxic gas component contained in an exhaust gas discharged from an LNG burning boiler or the like. <P>SOLUTION: In this method for treating the exhaust gas, nitrogen oxides contained in an exhaust gas are solidified to be separated from the exhaust gas, by passing the exhaust gas discharged from the LNG burning boiler, through a cooling medium stored in a dehydrating tower, to cooled to a temperature not solidifying carbon dioxide but solidifying the nitrogen oxides, and the carbon dioxide contained in the exhaust gas is solidified to be separated from the exhaust gas by cooling the exhaust gas to the second temperature at which the carbon dioxide is solidified. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas processing method and system, and more particularly, to a technique for efficiently removing harmful gas components contained in exhaust gas discharged from an LNG-fired boiler and the like and efficiently recovering carbon dioxide.

  Nitrogen oxides contained in exhaust gas discharged from an LNG-fired boiler or the like in a power plant or chemical plant are separated and removed using, for example, a denitration treatment apparatus using a denitration catalyst. Also, a so-called physical adsorption method using activated carbon is known as a more efficient method for separating and removing harmful gas components.

On the other hand, the amount of carbon dioxide in the atmosphere has increased recently, and the relationship with the rise in atmospheric temperature, called the greenhouse effect, has become a problem. The cause of the increase in the amount of carbon dioxide generation is mostly caused by the combustion of fossil fuels. For this reason, in a power plant, a chemical plant, etc., it is calculated | required not to discharge | emit the carbon dioxide contained in waste gas to air | atmosphere as much as possible from an environmental viewpoint.
JP 2000-317302 A

  As described above, regarding the treatment of exhaust gas discharged from an LNG-fired boiler, it is necessary to efficiently remove harmful gas components such as nitrogen oxides and also to efficiently collect carbon dioxide. And a mechanism to efficiently and continuously collect carbon dioxide as a series of processes are required.

  The present invention has been made in view of such a background, and is an exhaust gas treatment capable of efficiently removing harmful gas components and efficiently recovering carbon dioxide from exhaust gas discharged from an LNG-fired boiler or the like. It is an object to provide a method and system.

  The invention according to claim 1 of the present invention for achieving the above object is a method for treating exhaust gas, in which exhaust gas discharged from an LNG-fired boiler is circulated through a cooling medium so that carbon dioxide is not solidified but is oxidized by nitrogen. A first process of liquefying or solidifying nitrogen oxides contained as harmful gas components in the exhaust gas by cooling to a first temperature for liquefying or solidifying the product, and separating the exhaust gas from carbon dioxide; And a second process of solidifying carbon dioxide contained in the exhaust gas by cooling to the second temperature to be solidified and separating it from the exhaust gas.

  In the present invention, the exhaust gas discharged from the LNG-fired boiler is separated by liquefying or solidifying nitrogen oxides by cooling to a first temperature that does not solidify carbon dioxide but liquifies or solidifies nitrogen dioxide (first After that, the exhaust gas is further cooled to a second temperature at which carbon dioxide is solidified to solidify the carbon dioxide in the exhaust gas and separated from the exhaust gas. Here, in the first process, carbon dioxide contained in the exhaust gas is not separated, and carbon dioxide remains in the exhaust gas, and carbon dioxide can be reliably recovered in the subsequent second process. In addition, harmful gas components and carbon dioxide can be efficiently recovered from the exhaust gas containing harmful gas components such as nitrogen oxides.

The invention according to claim 2 of the present invention is the exhaust gas treatment method according to claim 1, wherein the nitrogen oxide solidified by the first process is guided to a solid-liquid separation device, whereby the nitrogen oxide is obtained. And a process of separating the cooling medium.
Thereby, the harmful gas component and the cooling medium mixed therewith can be separated.

The invention according to claim 3 of the present invention is the exhaust gas processing method according to claim 2, wherein the liquid separated by the solid-liquid separation device is vaporized by the cooling medium but not vaporized by the harmful gas component. And a process of separating the cooling medium by raising the temperature.
According to the present invention, the cooling medium can be efficiently recovered, and the cooling medium is effectively used.

The invention according to claim 4 of the present invention includes the process of circulating the cooling medium separated from the liquid as the cooling medium through which the exhaust gas is circulated in the exhaust gas processing method according to claim 3. To do.
By circulating the cooling medium in this way, the cooling medium is effectively used.

According to a fifth aspect of the present invention, in the exhaust gas treatment method according to any one of the first to fourth aspects, the cooling medium includes any of dimethyl ether, methanol, ethanol, toluene, and ethylbenzene. .
In the first process, in order to separate the liquefied or solidified harmful gas component from the cooling medium, the cooling medium itself is solidified even at a temperature at which the harmful gas component is liquefied or solidified. It is required to have no nature. Further, in order to efficiently liquefy or solidify the harmful gas component with the cooling medium, the cooling medium is required to have a property of easily absorbing the harmful gas component. Furthermore, in order to efficiently recover the carbon dioxide contained in the exhaust gas in the second process, the cooling medium is also required to have a property that hardly absorbs carbon dioxide. The dimethyl ether, methanol, ethanol, toluene, and ethylbenzene of the present invention all satisfy such conditions.

The invention according to claim 6 of the present invention is the exhaust gas treatment method according to any one of claims 1 to 5, wherein the first process includes a process of separating moisture contained in the exhaust gas from the exhaust gas. I will do it.
Thus, the water | moisture content contained in waste gas is isolate | separated in a 1st process, A carbon dioxide can be efficiently collect | recovered in a 2nd process.

The invention according to claim 7 of the present invention is the exhaust gas treatment method according to any one of claims 1 to 6, wherein the second process is a process of further liquefying the solidified carbon dioxide (dry ice). To include.
By liquefying carbon dioxide (dry ice) in this way, the storage and transportability of carbon dioxide can be improved, and the handleability of carbon dioxide can be improved.

The invention according to claim 8 of the present invention is the exhaust gas treatment method according to any one of claims 1 to 7, wherein the exhaust gas is cooled to room temperature and then heat exchanged with water before the first process. By doing so, a pre-process for removing moisture and harmful gas components contained in the exhaust gas is performed.
By performing such a pre-process, it becomes possible to reliably remove moisture and harmful gas components from the exhaust gas.

The invention according to claim 9 of the present invention is the exhaust gas treatment method according to any one of claims 1 to 8, wherein the first or second process is performed by heat of vaporization generated when LNG is used as gas fuel. The exhaust gas or the cooling medium in at least one of the processes is cooled.
In this way, the exhaust gas or the cooling medium in at least one of the first and second processes is cooled by using the heat of vaporization generated when LNG is used as the gas fuel, thereby cooling the exhaust gas or the cooling medium. Energy will be saved for.

  The invention according to claim 10 of the present invention is an exhaust gas treatment system in which exhaust gas discharged from an LNG-fired boiler is circulated through a cooling medium so that carbon dioxide is not solidified but nitrogen oxide is liquefied or solidified. A first apparatus for performing a process of liquefying or solidifying nitrogen oxides contained as harmful gas components in the exhaust gas by cooling to the temperature of the exhaust gas and separating the exhaust gas from the exhaust gas; and a second apparatus for solidifying the exhaust gas with carbon dioxide. And a second device that performs a process of solidifying carbon dioxide contained in the exhaust gas by cooling to a temperature and separating it from the exhaust gas.

  According to an eleventh aspect of the present invention, in the exhaust gas treatment system according to the tenth aspect, the nitrogen oxide solidified by the first device is guided to a solid-liquid separation device, thereby the nitrogen oxide. And a device for separating the cooling medium.

  The invention according to claim 12 of the present invention is the exhaust gas treatment system according to claim 11, wherein the liquid separated by the solid-liquid separator is vaporized by the cooling medium but not vaporized by the harmful gas component. And a device for separating the cooling medium by raising the temperature.

  The invention according to claim 13 of the present invention includes an apparatus for circulating the cooling medium separated from the liquid as the cooling medium for circulating the exhaust gas in the exhaust gas processing system according to claim 12. To do.

  According to a fourteenth aspect of the present invention, in the exhaust gas treatment system according to any one of the tenth to thirteenth aspects, the cooling medium includes any one of dimethyl ether, methanol, ethanol, toluene, and ethylbenzene. .

  The invention according to claim 15 of the present invention is the exhaust gas treatment system according to any one of claims 10 to 14, wherein the first device includes a device that separates moisture contained in the exhaust gas from the exhaust gas. I will do it.

  According to a sixteenth aspect of the present invention, in the exhaust gas treatment system according to any one of the tenth to fifteenth aspects, the second device is a device for further liquefying the solidified carbon dioxide (dry ice). To include.

  The invention according to claim 17 of the present invention is the exhaust gas treatment system according to any one of claims 10 to 16, wherein the exhaust gas is cooled to about room temperature before the process performed by the first device. An apparatus for performing a pre-process for removing moisture and harmful gas components contained in the exhaust gas by heat exchange with water is included.

  According to an eighteenth aspect of the present invention, in the exhaust gas treatment system according to any one of the tenth to seventeenth aspects, the first or second device is produced by heat of vaporization generated when LNG is used as a gaseous fuel. The exhaust gas or the cooling medium is cooled in at least one of the apparatuses.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to remove a harmful gas component efficiently from the waste gas containing the harmful gas component discharged | emitted from an LNG burning boiler etc., and to collect | recover the carbon dioxide contained in waste gas efficiently. .

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of an exhaust gas treatment system (hereinafter referred to as an exhaust gas treatment system) according to the present invention will be described in detail with reference to the accompanying drawings.

=== General Description ===
FIG. 1 shows a schematic configuration of an exhaust gas treatment system according to a second embodiment of the present invention. The exhaust gas treatment system according to the present embodiment is configured so that moisture contained in the exhaust gas is contained in exhaust gas containing harmful gas components such as nitrogen oxides discharged from the exhaust gas generation source 10 such as an LNG-fired boiler in a power plant or chemical plant. And a mechanism for efficiently recovering carbon dioxide contained in the exhaust gas.

  In this exhaust gas treatment system, first, as a pre-process, the exhaust gas containing harmful gas components such as nitrogen oxides discharged from the exhaust gas generation source 10 is stored in the heat exchanger 11 and the condenser (condenser) 13. Cool to room temperature by introducing it into water. Next, as a first process, the exhaust gas cooled to about room temperature is cooled to a first temperature at which the carbon dioxide is not solidified in the dehydration tower 17, thereby liquefying or solidifying moisture and nitrogen oxides contained in the exhaust gas. These are separated from the exhaust gas. Then, as a second process, the exhaust gas from which moisture and nitrogen oxides have been separated is cooled to a second temperature lower than the first temperature in the dry ice sublimator 24, thereby being contained in the exhaust gas. The carbon dioxide is solidified and separated from the exhaust gas.

  Here, in the harmful gas component separated in the first process, the separated harmful gas component and the cooling medium are mixed. In order to efficiently operate the exhaust gas treatment system, it is preferable to circulate this cooling medium and use it effectively. Therefore, in this embodiment, the harmful gas component and the cooling medium are separated and recovered by an evaporation method using the vaporization temperature difference between the cooling medium and the harmful gas component, and the recovered cooling medium is used again as the cooling medium. . In the evaporation method, energy for heating is required, but the energy can be reduced by employing a cooling medium having a low boiling point.

  In order to efficiently recover carbon dioxide contained in the exhaust gas in the second process, it is necessary to prevent the carbon dioxide from being liquefied or solidified when liquefying or solidifying moisture or harmful gas components. . Here, the carbon dioxide in the thermal power plant exhaust gas becomes dry ice at a predetermined temperature or lower. Therefore, in order to prevent the carbon dioxide from solidifying, the gas temperature at the outlet of the dehydration tower 17 is set higher than the predetermined temperature.

  In the first process, in order to separate the cooling medium from the liquefied or solidified harmful gas component, the cooling medium itself does not solidify even at a temperature at which the toxic gas component is liquefied or solidified. It is necessary to be. In order to efficiently liquefy or solidify the harmful gas component, the cooling medium is required to have a property of easily absorbing the harmful gas component. Furthermore, in order to efficiently recover carbon dioxide contained in the exhaust gas in the second process, the cooling medium is required to have a property that carbon dioxide is hardly dissolved.

  A specific cooling medium that satisfies these requirements is dimethyl ether (hereinafter referred to as DME) (freezing point: -141.5 ° C, boiling point: -24.9 ° C). Note that substances other than DME can be used as the cooling medium as long as the above-described requirements for the cooling medium are satisfied. For example, inorganic salts (such as sodium chloride and potassium chloride), bromine compounds (such as lithium bromide and bromide), ethers (such as dimethyl ether and methyl ether), alcohols (such as methanol and ethanol), silicone oils, paraffin Any material that satisfies the above requirements, such as a hydrocarbon based on propane or normal butane, or an olefinic hydrocarbon, can be used as the cooling medium. Specifically, methanol, ethanol, toluene, ethylbenzene or the like can be used as the cooling medium. In order to separate the liquefied or solidified harmful gas component from the cooling medium, it is advantageous that the difference in boiling point between the substance serving as the cooling medium and the harmful gas component is large. From such a viewpoint, ethers and alcohols are preferable as the refrigerant.

  FIG. 2A shows the measurement result of the change in the concentration of carbon dioxide in the simulated gas when the simulated gas having a carbon dioxide concentration of 10% is circulated through the DME. As shown in this figure, the concentration of carbon dioxide in the simulated gas temporarily decreases because the simulated gas dissolves in the DME when the simulated gas starts to flow into the DME, but then gradually flows into the DME with time. It is approaching the concentration (10%) before being applied. This is because when the carbon dioxide in the DME is saturated, the carbon dioxide is more difficult to dissolve in the DME. In order to confirm that DME easily absorbs harmful gas components such as nitrogen oxides, a simulated gas (nitrogen dioxide: 60 ppm, sulfur dioxide: 80 ppm, ammonia: 10 ppm) containing harmful gas components is circulated in DME. I let you. As a result, it was confirmed that all harmful gas components in the simulated gas became 1 ppm or less in about 1 hour after the distribution of the simulated gas to the DME.

=== Detailed explanation ===
Next, a specific mechanism of the exhaust gas treatment system of the present embodiment will be described in detail. First, in the previous process, exhaust gas containing harmful gas components such as nitrogen oxides discharged from the exhaust gas generation source 10 such as an LNG-fired boiler is introduced into the heat exchanger 11. Seawater (for example, 25 ° C.) supplied by the seawater pump 12 and a refrigerant such as ethylene glycol circulated from the refrigerator 40 are guided to the heat exchanger 11. Exhaust gas (for example, 55 ° C.) guided from the exhaust gas generation source 10 is cooled to about room temperature by these seawater and refrigerant by passing through the heat exchanger 11.

  The exhaust gas cooled to about room temperature in the heat exchanger 11 is then led to a condenser (condenser) 13. The exhaust gas led to the condenser 13 is introduced into industrial water accommodated in the condenser 13. Thereby, moisture, harmful gas components, dust, etc. contained in the exhaust gas are removed. The liquefied water containing moisture, harmful gas components, dust, etc. removed from the exhaust gas is once stored in the drainage tank 14 and then guided to the wastewater treatment device 50 by the drainage pump 15. The exhaust gas after passing through the condenser 13 is then guided to the dehydration tower 17 by the exhaust gas fan 16. The exhaust gas is cooled to about room temperature by heat exchange with industrial water in the condenser 13 (for example, 5 ° C.).

  In the dehydration tower 17, the exhaust gas is further dehydrated (dehumidified) and harmful gas components are removed. In addition, the water | moisture content contained in waste gas can be dehydrated, and the carbon dioxide contained in waste gas can be efficiently recovered later.

  In the dehydration tower 17, exhaust gas is introduced from the lower side of the dehydration tower 17. Exhaust gas (for example, 5 ° C.) introduced into the dehydration tower 17 is circulated by a bubbling method to DME filled as a cooling medium for cooling the exhaust gas in the dehydration tower 17. The exhaust gas introduced into the dehydration tower 17 is cooled by exchanging heat with DME. The cooling temperature at this time is a temperature at which harmful gas components such as moisture and nitrogen oxides in the exhaust gas are liquefied or solidified but carbon dioxide is not solidified. By cooling the exhaust gas to such a temperature, harmful gas components are liquefied or solidified and separated from the exhaust gas, but carbon dioxide remains in the exhaust gas as a gas.

In order to confirm the function of removing harmful gas components from the exhaust gas in the dehydration tower 17, the amount of sulfur dioxide (SO ₂ ) and nitrogen monoxide (NO) dissolved in the cooling medium was measured. FIG. 2B shows the configuration of the apparatus used for this measurement. As shown in the figure, this apparatus 210 includes a mixer 211 for generating simulated exhaust gas, a cooling vessel 212 (for example, a test tube or a beaker) for cooling the simulated exhaust gas as viewed in the dehydration tower 17, and cooling the simulated exhaust gas. A gas introduction pipe 213 to be introduced into the container 212 and a gas discharge pipe 214 for discharging the gas accumulated above the cooling container 212 to the outside of the cooling container 212 are connected as shown in FIG.

The cooling container 212 contains toluene (0 to 5 ° C., liquid amount 100 cc) as a cooling medium. The opening of the gas introduction pipe is set so as to be located below the toluene liquid level. As the simulated gas carbon dioxide _(CO 2), sulfur dioxide _(SO 2), nitrogen monoxide (NO), was a mixture by a mixer nitrogen _{(N 2).} FIG. 2C shows the composition of the simulated exhaust gas. The measurement was performed by circulating the simulated exhaust gas through the cooling medium at a constant speed (1 l / h).

FIG. 2D shows the measurement results. In the drawing, the relationship between the temperature of the cooling medium (toluene) and the dissolved amount (ppm) of sulfur dioxide (SO ₂ ) and nitrogen monoxide (NO) is shown in a graph. The two curves shown in the graph are respectively the dissolved amount (ppm) of sulfur dioxide (SO ₂ ) and the dissolved amount (ppm) of nitric oxide (NO) as SRK (Soave-Redlich-Kwong). It is a theoretical value obtained by calculation by the method. In addition, the portion plotted with “◯” in the graph is an actual measurement value obtained by the above measurement, and the actual measurement value of the dissolved amount with respect to sulfur dioxide (SO ₂ ) is 48 (ppm), and nitric oxide (NO). The measured value of the dissolved amount of is 0.1 (ppm). Here, the theoretical value of the dissolved amount of sulfur dioxide (SO ₂ ) corresponding to the temperature of these plot portions is 36 (ppm), and the actually measured value of the dissolved amount of nitric oxide (NO) is 0.07 (ppm). It can be seen that all the measured values are almost in agreement with the theoretical values.

From the above measurement, it was confirmed that the amount of sulfur dioxide (SO ₂ ) and nitrogen monoxide (NO) dissolved according to the temperature of the cooling medium could be theoretically determined. In addition, it was verified that the dehydration tower 17 can efficiently separate harmful gas components from the exhaust gas.

  The DME in the dehydration tower 17 is circulated from the DME cooling tower 18. DME is cooled in the DME cooling tower 18. In the DME cooling tower 18, the refrigerant (liquid nitrogen) cooled in the refrigeration / heat exchanger 44 is circulated by a circulation pump 19, and the DME is cooled by heat exchange with the refrigerant.

  The DME that contains the liquefied or solidified moisture and harmful gas components due to the circulation of the exhaust gas in the dehydration tower 17 is then led to the solid-liquid separator 28. In this state, the solidified product of DME and moisture and harmful gas components is in a sherbet state (slurry). In the solid-liquid separator 28, DME and the solidified product contained in the DME are separated. The DME after being separated by the solid-liquid separator 28 is then led to the DME separation column 20 in order to reuse the DME. Note that some moisture and harmful gas components remain in the DME guided to the DME separation column 20.

  The DME guided from the dehydration tower 17 to the DME separation tower 20 is indirectly heat-exchanged with seawater and heated (for example, 5 ° C.). At this temperature, moisture and harmful gas components are liquid or solid, but DME is a gas. For this reason, DME becomes a gas and floats above the DME separation tower 20, whereby the DME is separated from other components. The DME that floats above the DME separation tower 20 is recovered from above the DME separation tower 20, led to the DME cooling tower 18, and cyclically led again to the dehydration tower 17. In this way, DME is reused cyclically. In addition, since the DME as the cooling medium is reused cyclically, the exhaust gas treatment system of the present embodiment is operated by efficiently using the cooling medium as the entire system. On the other hand, liquid or solid moisture and harmful gas components remaining in the DME separation tower 20 are guided to the waste water treatment apparatus 50.

  The exhaust gas containing carbon dioxide floating above the dehydration tower 17 is guided to the reversible heat exchanger 23. The exhaust gas guided to the reversible heat exchanger 23 is cooled by heat exchange with exhaust gas guided from a cyclone 25 described later in the reversible heat exchanger 23 and then guided to the dry ice sublimator 24. The exhaust gas led to the dry ice sublimator 24 is indirectly heat-exchanged with the refrigerant (liquid nitrogen) circulated through the refrigeration / heat exchanger 40 in the dry ice sublimator 24 and cooled.

Here, in order to confirm the recovery rate of carbon dioxide (CO ₂ ) in the dry ice sublimator 24, the recovery rate of carbon dioxide (CO ₂ ) with respect to the temperature of the simulated gas was measured. The structure of the dry ice sublimator 440 used in this measurement is shown in FIGS. 2E and 2F. 2E is a side view of the dry ice sublimator 440, while FIG. 2F is a side view of the dry ice sublimator 440 viewed from the direction indicated by the arrow A in FIG. 2E. As shown in these drawings, the dry ice sublimator 440 includes two first cylindrical tubes 441 (material is, for example, SUS304) arranged vertically, and horizontally below the first cylindrical tubes 441 ( That is, it is configured to include a second cylindrical tube 442 that is arranged perpendicularly to the first cylindrical tube 441 and communicates with the interior of each of the first cylindrical tubes 441. Inside the first cylindrical tube 441, there is a refrigerant flow tube 444 (material: copper, length 900 mm, 20 pieces, outer surface area 7.1 m ² ) through which a refrigerant (for example, liquid nitrogen) flows. Has been inserted. A screw-like fin (not shown) is formed on the outer surface of the refrigerant flow tube 444 to increase the contact area with carbon dioxide (CO ₂ ). Both ends of the first cylindrical tube 441 and the second cylindrical tube 442 are sealed with a sealing plug 446.

The simulation gas, carbon dioxide _(CO 2) 15%, nitrogen _(N 2) was used consisting of 85%. In the measurement, simulated gas is introduced at a flow rate of 670 (l / min) from an inlet 448 provided at a predetermined position of one of the first cylindrical tubes 241, and is introduced into a predetermined position of the other first cylindrical tube 441. It was made to distribute | circulate by discharging | emitting from the provided discharge port 449. The simulated gas introduced into the internal space 447 of the dry ice sublimator 440 comes into contact with the outer surface of the refrigerant flow pipe 444, so that carbon dioxide (CO ₂ ) is solidified, but nitrogen (N ₂ ) is not solidified. Until cooled. As a result, carbon dioxide in the simulated gas becomes dry ice and accumulates inside the second cylindrical tube 442 and the like. Further, the nitrogen component in the simulation gas is discharged from the discharge port 449.

FIG. 2G shows the measurement results. In the figure, the relationship between the temperature of the simulated gas discharged from the discharge port 449 and the carbon dioxide (CO ₂ ) recovery rate when a simulated gas having a carbon dioxide (CO ₂ ) concentration of 15% is used is shown in a graph. Show. As shown in this measurement result, it was confirmed that carbon dioxide (CO ₂ ) can be efficiently recovered by the dry ice sublimator 24.

  The dry ice generated in the dry ice sublimator 24 is then led to the cyclone 25. In the cyclone 25, dry ice and exhaust gas are separated. The exhaust gas separated here is guided to the reversible heat exchanger 23 as described above and functions as a refrigerant. Thus, by making the exhaust gas cooled by the dry ice sublimator 24 function as a refrigerant in the reversible heat exchanger 23, in the exhaust gas treatment system of the present embodiment, the energy consumption of the entire system required for cooling. Therefore, efficient processing is realized. The exhaust gas used as a refrigerant in the reversible heat exchanger 23 is guided to the heat exchanger 11. The exhaust gas is used again as a refrigerant in the heat exchanger 11 and then discharged from the chimney 51 to the outside of the system. In addition, about discharge | emission of waste gas to the atmosphere, in order to relieve | accumulate the accumulation | storage of waste gas in a system, a part is let out of the system. Therefore, the concentration of carbon dioxide in the exhaust gas released to the atmosphere is very low.

  The dry ice separated by the cyclone 25 is then guided to the dry ice melting machine 26. In the dry ice melting machine 26, the dry ice is liquefied by pressurization. The reason why the dry ice is liquefied is to improve the storage and transportability of carbon dioxide and make it easy to handle. In addition, in order to efficiently liquefy dry ice produced in a large amount, as the dry ice melting machine 26, for example, one using a screw type extrusion mechanism disclosed in JP 2000-317302 A or the like is used. The liquefied carbon dioxide is stored in the liquefied carbon dioxide storage tank 27 and used for various purposes as liquefied carbon dioxide.

  In addition, about the structure which consists of the dry ice sublimator 24 and the cyclone 25 which were shown in FIG. 1, the structure of the dry ice sublimator 440 which has the structure shown to FIG. 2E is also employable. In this case, the number of first cylindrical tubes 441 is not necessarily limited to two, and can be three or more.

  By the way, in the above-described refrigeration / heat exchanger 44, using the vaporization heat of the LNG 60, ethylene glycol circulated to the heat exchanger 11, liquid nitrogen circulated to the DME cooling tower 18, the dry ice sublimator 24, and the like. Cool the refrigerant. For example, in a power plant using LNG as gas fuel, LNG is transported in a liquid state (for example, −150 ° C. to −165 ° C.) and stored in an LNG tank or the like. Here, when LNG is used as a gas fuel, the heat of vaporization is obtained from the atmosphere or seawater and the temperature is raised to vaporize. The refrigeration / heat exchanger 44 uses the heat of vaporization at this time to generate ethylene glycol or Cooling refrigerant such as liquid nitrogen. That is, the exhaust gas or the cooling medium is cooled by using the heat of vaporization generated when LNG is used as the gas fuel. A technique for solidifying and separating carbon dioxide contained in the exhaust gas by using the heat of vaporization of LNG is described in, for example, Japanese Patent Application Laid-Open No. 8-12314.

  As described above, in the exhaust gas treatment system of the present embodiment, the exhaust gas containing harmful gas components such as nitrogen oxides discharged from an LNG fired boiler, etc. The gas component can be efficiently removed. Moreover, carbon dioxide contained in the exhaust gas can be efficiently recovered while efficiently removing moisture and harmful gas components.

In the above description, examples of harmful gases to be removed from exhaust gas include other nitrogen oxides (NO _X ) such as carbon monoxide and nitrogen monoxide, and other sulfur oxides such as sulfur monoxide. (SO _x ), halogen compounds such as hydrogen fluoride, etc., by appropriately setting the solidification temperature of carbon dioxide and the liquefaction or solidification temperature of harmful gas components, and selecting an appropriate cooling medium as described above, These harmful gas components can be efficiently removed. That is, the exhaust gas containing other types of harmful gases is circulated through the cooling medium and cooled to the first temperature to liquefy or solidify the harmful gas components contained in the exhaust gas, and separate the exhaust gas from the exhaust gas. By cooling to a second temperature lower than the temperature 1, the carbon dioxide contained in the exhaust gas is solidified and separated from the exhaust gas, thereby realizing an exhaust gas treatment system.

  The above description is intended to facilitate understanding of the present invention and is not intended to limit the present invention. It goes without saying that the present invention can be changed and improved without departing from the gist thereof, and the present invention includes equivalents thereof.

1 is a diagram showing a schematic configuration of an exhaust gas treatment system according to an embodiment of the present invention. It is a figure which shows the measurement result of the density | concentration change of the sulfur dioxide in simulation gas when the simulation gas with a sulfur dioxide concentration of 80 ppm by one Example of this invention is distribute | circulated in DME. It is a figure which shows the structure of the apparatus used for the measurement of the melt | dissolution amount to the cooling medium about sulfur dioxide and nitric oxide by one Embodiment of this invention. It is a figure which shows the composition of the simulation exhaust gas by one Embodiment of this invention. It is a figure which shows the measurement result of the melt | dissolution amount to the cooling medium about sulfur dioxide and nitric oxide by one Embodiment of this invention. It is a figure which shows the structure of the dry ice sublimator 24 used for the measurement of the recovery rate of the carbon dioxide with respect to the temperature of the simulation gas by one Embodiment of this invention. It is a side view of dry ice sublimator 24 seen from the direction shown by arrow A in Drawing 2E by one embodiment of the present invention. It is a figure which shows the measurement result of the recovery rate of the carbon dioxide with respect to the temperature of the simulation gas by one Embodiment of this invention.

Explanation of symbols

10 Exhaust gas source 11 Heat exchanger 13 Condenser
DESCRIPTION OF SYMBOLS 14 Drain tank 17 Dehydration tower 18 DME cooling tower 20 DME separation tower 23 Reversible heat exchanger 24 Dry ice sublimator 25 Cyclone 26 Dry ice melting machine 27 Liquefied carbonic acid storage tank 28 Solid-liquid separation apparatus 44 Refrigeration / heat exchanger 50 Waste water treatment apparatus 51 Chimney

Claims (18)

Nitrogen oxidation contained in the exhaust gas as a harmful gas component by circulating the exhaust gas discharged from the LNG-fired boiler through a cooling medium and cooling to a first temperature that does not solidify carbon dioxide but liquefies or solidifies nitrogen oxides A first process for liquefying or solidifying an object and separating it from the exhaust gas;
A second process for solidifying and separating carbon dioxide contained in the exhaust gas from the exhaust gas by cooling the exhaust gas to a second temperature for solidifying carbon dioxide;
Including,
An exhaust gas treatment method characterized by the above. The exhaust gas treatment method according to claim 1,
A method for treating exhaust gas, comprising a step of separating the nitrogen oxide and the cooling medium by introducing the nitrogen oxide solidified by the first process to a solid-liquid separator. The method for treating exhaust gas according to claim 2,
Including a process of separating the cooling medium by raising the temperature of the liquid separated by the solid-liquid separator to a temperature at which the cooling medium is vaporized but the harmful gas components are not vaporized.
An exhaust gas treatment method characterized by the above. In the processing method of the exhaust gas according to claim 3,
Including a process of circulating the cooling medium separated from the liquid as the cooling medium through which the exhaust gas flows.
An exhaust gas treatment method characterized by the above. In the processing method of the exhaust gas in any one of Claims 1-4,
The cooling medium includes any of dimethyl ether, methanol, ethanol, toluene, and ethylbenzene;
An exhaust gas treatment method characterized by the above. In the processing method of the exhaust gas in any one of Claims 1-5,
The first process includes a process of separating moisture contained in the exhaust gas from the exhaust gas;
An exhaust gas treatment method characterized by the above. In the processing method of the exhaust gas in any one of Claims 1-6,
The exhaust gas treatment method, wherein the second process includes a process of further liquefying the solidified carbon dioxide (dry ice). In the processing method of the exhaust gas in any one of Claims 1-7,
Before the first process, performing a pre-process for removing moisture and harmful gas components contained in the exhaust gas by heat exchange with water after cooling the exhaust gas to about room temperature,
An exhaust gas treatment method characterized by the above. In the processing method of the exhaust gas in any one of Claims 1-8,
Exhaust gas treatment characterized by cooling the exhaust gas or the cooling medium in at least one of the first and second processes by vaporization heat generated when LNG is used as gas fuel. Method. Nitrogen oxides contained as harmful gas components in the exhaust gas by cooling the exhaust gas discharged from the LNG-fired boiler to the cooling medium to cool to a first temperature that does not solidify carbon dioxide but liquefy or solidify nitrogen oxides A first device for performing a process of liquefying or solidifying and separating from the exhaust gas;
A second apparatus for performing a process of solidifying carbon dioxide contained in the exhaust gas and separating it from the exhaust gas by cooling the exhaust gas to a second temperature for solidifying carbon dioxide;
Including,
An exhaust gas treatment system characterized by The exhaust gas treatment system according to claim 10,
Including a device for separating the nitrogen oxide and the cooling medium by introducing the nitrogen oxide solidified by the first device to a solid-liquid separation device;
An exhaust gas treatment system characterized by The exhaust gas treatment system according to claim 11,
Including a device for separating the cooling medium by raising the temperature of the liquid separated by the solid-liquid separation device to a temperature at which the cooling medium is vaporized but the harmful gas components are not vaporized,
An exhaust gas treatment system characterized by The exhaust gas treatment system according to claim 12,
Including a device for circulating the cooling medium separated from the liquid as the cooling medium for circulating the exhaust gas;
An exhaust gas treatment system characterized by In the exhaust gas treatment system according to any one of claims 10 to 13,
The exhaust gas treatment system, wherein the cooling medium includes any one of dimethyl ether, methanol, ethanol, toluene, and ethylbenzene. In the exhaust gas processing system according to any one of claims 10 to 14,
The first apparatus includes an apparatus for separating water contained in the exhaust gas from the exhaust gas. The exhaust gas treatment system according to any one of claims 10 to 15,
The second apparatus includes an apparatus for further liquefying solidified carbon dioxide (dry ice). The exhaust gas treatment system according to any one of claims 10 to 16,
Including a device for performing a pre-process for removing moisture and harmful gas components contained in the exhaust gas by performing heat exchange with water after the exhaust gas is cooled to about room temperature before the process performed by the first device. ,
An exhaust gas treatment system characterized by The exhaust gas treatment system according to any one of claims 10 to 17,
Cooling the exhaust gas or the cooling medium in at least one of the first and second devices by vaporization heat generated when LNG is used as a gas fuel;
An exhaust gas treatment system characterized by

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