JP2005305419A - Exhaust gas processing system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas processing system capable of efficiently removing a harmful gas component from exhaust gas and also efficiently recovering carbon dioxide. <P>SOLUTION: Nitrogen oxide and sulfur oxide contained in the exhaust gas as harmful gas components are liquefied or solidified by transporting through a cooling medium to cool the exhaust gas down to such a temperature that does not solidify carbon dioxide but liquefies or solidifies the nitrogen oxide and sulfur oxide, thereby separating them from the exhaust gas. The exhaust gas undergone the above separation is transported into a pressure resistant container 310 of a carbon dioxide separating unit 30 to cool and solidify the carbon dioxide, and the solidified carbon dioxide is heated and vaporized to liquefy the carbon dioxide by the pressure increase inside the pressure resistant container 310 due to the carbon dioxide being vaporized, and the liquefied carbon dioxide is discharged outside of the pressure resistant container 310. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas treatment system, and in particular, efficiently removes harmful gas components contained in exhaust gas discharged from coal-fired boilers, blast furnaces, coke ovens, converters, LNG-fired boilers in steelworks, and the like. The present invention relates to a technique for efficiently recovering carbon.

  Hazardous gas components such as sulfur oxides and nitrogen oxides contained in exhaust gas discharged from coal-fired boilers at power plants and chemical plants, blast furnaces, coke ovens, converters, LNG-fired boilers at steelworks, etc. They are separated and removed by using a wet desulfurization treatment device, a denitration treatment device using a denitration catalyst, or the like. 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

  In such circumstances, for example, regarding the treatment of exhaust gas discharged from coal-fired boilers, blast furnaces, coke ovens, converters, etc. in steelworks, while removing harmful gas components such as nitrogen oxides and sulfur oxides efficiently Further, it is necessary to efficiently collect carbon dioxide, and there is a need for an exhaust gas treatment system that can efficiently and continuously perform removal of harmful gas components and carbon dioxide recovery as a series of treatments.

  For example, 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 efficiently recover carbon dioxide. A mechanism for efficiently and continuously performing carbon recovery as a series of processes is required.

  The present invention has been made in view of such a background, and an object thereof is to provide an exhaust gas treatment system that can efficiently remove harmful gas components from exhaust gas and efficiently recover carbon dioxide. .

  The invention according to claim 1 of the present invention is an exhaust gas treatment system in which exhaust gas is circulated through a cooling medium and is cooled to a temperature at which nitrogen oxides and sulfur oxides are liquefied or solidified without solidifying carbon dioxide. The first apparatus for liquefying or solidifying nitrogen oxides and sulfur oxides contained as harmful gas components in the exhaust gas and separating them from the exhaust gas, and the exhaust gas after separating nitrogen oxides and sulfur oxides withstand pressure The carbon dioxide is cooled and solidified by circulating in a container, the pressure-resistant container is sealed, the solidified carbon dioxide is heated to vaporize, and the carbon dioxide is vaporized to increase the pressure inside the pressure-resistant container. A second device for liquefying carbon dioxide and discharging the liquefied carbon dioxide out of the pressure vessel.

  As described above, in the present invention, the nitrogen contained in the exhaust gas is cooled by cooling the exhaust gas containing the harmful gas component in the first apparatus to a temperature at which the carbon dioxide is not solidified but the nitrogen oxides and sulfur oxides are liquefied or solidified. Oxides and sulfur oxides are liquefied or solidified for separation. For this reason, carbon dioxide contained in the exhaust gas is not separated in the first device, and carbon dioxide remains in the exhaust gas, and carbon dioxide can be reliably recovered in the second device. Moreover, according to the 2nd apparatus, solidification and liquefaction of a carbon dioxide can be performed within the same pressure vessel. In addition, according to the exhaust gas treatment system of the present invention, carbon dioxide can be separated from exhaust gas with a simple device, and a mechanism for efficiently and reliably recovering carbon dioxide from exhaust gas at low cost can be realized. Further, carbon dioxide can be discharged as a convenient liquid for transportation and storage without using a special liquefaction device. Therefore, according to the exhaust gas treatment system of the present invention, carbon dioxide can be efficiently and reliably recovered from the exhaust gas containing harmful gas components such as nitrogen oxide and sulfur oxide while removing the harmful gas components.

The invention according to claim 2 of the present invention is the exhaust gas processing system according to claim 1, wherein the harmful gas component separated from the exhaust gas by the first device is included in the harmful gas component. The cooling medium includes a device that separates the harmful gas component and the cooling medium by raising the temperature to a temperature at which the cooling gas is vaporized but the harmful gas component is not vaporized.
As a result, the cooling medium can be reliably recovered from the harmful gas component, whereby the cooling medium can be effectively used.

The invention according to claim 3 of the present invention is the exhaust gas treatment system according to claim 1 or 2, wherein the harmful gas component separated from the exhaust gas by the first device is vaporized by sulfur oxide. However, the apparatus includes a device for separating sulfur oxides and nitrogen oxides contained in the harmful gas component by raising the temperature to a temperature at which nitrogen oxides are not vaporized.
Thereby, the nitrogen oxide contained in the harmful gas component can be separated from the exhaust gas, and the sulfur oxide and nitrogen oxide contained in the harmful gas component can be separated.

  The invention according to claim 4 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 as not to solidify carbon dioxide but to liquefy or solidify nitrogen oxides. A first apparatus for performing a process of liquefying or solidifying nitrogen oxides contained in the exhaust gas as harmful gas components by cooling them to separate them from the exhaust gas, and the exhaust gas after separating the nitrogen oxides in a pressure vessel The carbon dioxide is cooled and solidified, the pressure-resistant container is sealed, the solidified carbon dioxide is heated to vaporize, and the carbon dioxide is vaporized by the pressure increase inside the pressure-resistant container due to the vaporization of the carbon dioxide. A second device for liquefying carbon and discharging the liquefied carbon dioxide out of the pressure vessel.

  As described above, in the present invention, the exhaust gas discharged from the LNG-fired boiler in the first apparatus does not solidify carbon dioxide, but liquefies or solidifies nitrogen oxide by cooling to the first temperature at which nitrogen oxide is liquefied or solidified. I try to let them. For this reason, the carbon dioxide contained in the exhaust gas is not separated in the first apparatus, and carbon dioxide remains in the exhaust gas, so that the carbon dioxide can be efficiently and reliably recovered in the second apparatus. Further, according to the second apparatus, carbon dioxide can be solidified and liquefied in the same pressure vessel. Further, according to the exhaust gas treatment system of the present invention, carbon dioxide can be separated from the exhaust gas with a simple device, and a mechanism for recovering carbon dioxide from the exhaust gas efficiently at low cost can be realized. Further, carbon dioxide can be discharged as a convenient liquid for transportation and storage without using a special liquefaction device. Therefore, according to the exhaust gas treatment system of the present invention, carbon dioxide can be efficiently recovered while removing harmful gas components from exhaust gases containing harmful gas components such as nitrogen oxides.

The invention according to claim 5 of the present invention is the exhaust gas treatment system according to claim 4, wherein the nitrogen oxide solidified by the first device is led to a solid-liquid separation device, whereby the nitrogen oxide is obtained. And a device for separating the cooling medium.
Thereby, the harmful gas component and the cooling medium mixed therewith can be efficiently and reliably separated.

The invention according to claim 6 of the present invention is the exhaust gas treatment system according to claim 5, 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.
As a result, the cooling medium can be efficiently recovered, and the cooling medium is effectively used.

The invention according to claim 7 of the present invention is the exhaust gas treatment system according to any one of claims 1 to 6, wherein the cooling medium includes any one of dimethyl ether, methanol, ethanol, toluene, and ethylbenzene. .
In order to separate the liquefied or solidified harmful gas component from the cooling medium, it is required that the cooling medium itself does not solidify even at a temperature at which the toxic gas component is liquefied or solidified as the cooling medium. . 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 carbon dioxide contained in the exhaust gas, the cooling medium needs to have a property of hardly absorbing carbon dioxide. Dimethyl ether, methanol, ethanol, toluene, and ethylbenzene all satisfy these conditions.

The invention according to claim 8 of the present invention is the exhaust gas treatment system according to any one of claims 1 to 7, wherein the cooling and solidification of the carbon dioxide by the second device includes the carbon dioxide. It is assumed that the gas is brought into contact with the outer surface of a refrigerant circulation pipe provided in the pressure-resistant container and through which the refrigerant is circulated.
By doing in this way, dry ice will precipitate on the outer surface of a refrigerant | coolant flow pipe, and the continuous operation and automatic operation can be implemented easily, without the pipe line of a heat exchanger tube being obstruct | occluded.

The invention according to claim 9 of the present invention is the carbon dioxide separation method according to any one of claims 1 to 8, wherein the refrigerant flow pipe is provided in a meandering manner.
Thus, by providing the refrigerant flow pipe meandering, a sufficient contact area between the gas and the refrigerant flow pipe can be ensured, and carbon dioxide can be solidified efficiently.

  According to the present invention, harmful gas components can be efficiently removed from exhaust gas, and carbon dioxide can be efficiently recovered.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<< Example 1 >>
FIG. 1 shows a schematic configuration of an exhaust gas treatment system described as a first embodiment of the present invention. According to this exhaust gas treatment system, nitrogen oxides and sulfur oxides emitted from exhaust gas generation sources 10 such as coal-fired boilers / heavy oil fired boilers at power plants and chemical plants, blast furnaces, coke ovens, converters, etc. at steelworks. For exhaust gas containing harmful gas components such as substances, moisture and harmful gas components contained in the exhaust gas can be efficiently and reliably removed, and carbon dioxide (CO ₂ ) contained in the exhaust gas can be efficiently and reliably recovered. it can.

  In the exhaust gas treatment system of the present embodiment, as a pre-process, exhaust gas containing harmful gas components such as nitrogen oxides and sulfur oxides discharged from the exhaust gas generation source 10 is first converted into a heat exchanger 11 and a condenser (condenser). The product is cooled to about room temperature by introducing it into industrial water contained in 13. Next, as a first process, the exhaust gas cooled to about room temperature is cooled to a first temperature at which carbon dioxide is not solidified in the dehydration tower 17, so that moisture, nitrogen oxides, and sulfur oxides contained in the exhaust gas are removed. They are liquefied or solidified to separate them from the exhaust gas. Further, as a second process, the exhaust gas from which moisture, nitrogen oxides, and sulfur oxides are separated is introduced into the carbon dioxide separator 30 where the carbon dioxide contained in the exhaust gas is cooled and solidified for separation. At the same time, the separated carbon dioxide is liquefied and discharged.

  Although the cooling medium is mixed in the harmful gas component separated in the first process, in this system, the harmful gas component and the cooling gas are cooled by an evaporation method using a vaporization temperature difference between the cooling medium and the harmful gas component. The medium is separated and collected, and the collected cooling medium is circulated again as the cooling medium for effective use of the cooling medium. In addition, although heating energy is required in the evaporation method, heating energy can be reduced by adopting a cooling medium having a low boiling point.

  In order to efficiently recover the carbon dioxide contained in the exhaust gas in the second process, it is necessary to prevent the carbon dioxide from liquefying or solidifying when the moisture or harmful gas components are liquefied or solidified. It is. 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 liquefied or solidified harmful gas component from the cooling medium, the cooling medium needs to have a property that does not solidify even at a temperature at which the harmful gas component is liquefied or solidified. . Further, in order to efficiently liquefy or solidify the harmful gas component, the cooling medium needs to have a property of easily absorbing the harmful gas component. Furthermore, in order to efficiently recover carbon dioxide contained in the exhaust gas by the second process, it is necessary that the cooling medium has a property that carbon dioxide is hardly dissolved.

  Examples of substances that satisfy these requirements include dimethyl ether (hereinafter referred to as DME), inorganic salts (sodium chloride, potassium chloride, etc.), bromine compounds (lithium bromide, bromide bromide, etc.), ethers (dimethyl ether, methyl ether). Etc.), alcohols (methanol, ethanol, etc.), silicon oils, paraffinic hydrocarbons (propane, normal butane, etc.), olefinic hydrocarbons, toluene, ethylbenzene, and the like. 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 cooling medium and the harmful gas component is large. From such a viewpoint, ethers and alcohols are preferable as the refrigerant.

  FIG. 2 shows changes in the concentration of carbon dioxide in the simulated gas when a simulated gas having a carbon dioxide concentration of 10% is circulated through the DME. The concentration of carbon dioxide in the simulated gas temporarily decreases because the simulated gas dissolves in the DME at the start of distribution of the simulated gas to the DME, but after that, the concentration (10%) before gradually flowing into the DME with time. ) This is because when the carbon dioxide in the DME is saturated, the carbon dioxide is more difficult to dissolve in the DME. In addition, in order to confirm that DME easily absorbs harmful gas components such as nitrogen oxide and sulfur oxide, the present inventors have created a simulated gas containing nitrogen gas components (nitrogen dioxide: 60 ppm, sulfur dioxide: 80 ppm, (Ammonia: 10 ppm) was passed through DME. As a result, it was confirmed that all harmful gas components in the simulated gas were 1 ppm or less in about 1 hour after the start of distribution.

  Next, a specific treatment process of the exhaust gas treatment system will be described in order. First, in the previous process, exhaust gas containing harmful gas components such as nitrogen oxides and sulfur oxides discharged from the exhaust gas generation source 10 such as a coal fired boiler, a heavy oil fired boiler, a blast furnace, a coke oven, and a converter in an ironworks. And 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 and supplied 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 the seawater and the refrigerant by passing through the heat exchanger 11.

  The cooled exhaust gas is then led to a condenser (condenser) 13. In the condenser 13, the exhaust gas 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 stored in the drainage tank 14 and then guided to the wastewater treatment device 50 by the drainage pump 15. The exhaust gas that has passed through the condenser 13 is guided to the dehydration tower 17 by the exhaust gas fan 16. The exhaust gas is cooled from about room temperature to, for example, 5 ° C. by heat exchange with industrial water in the condenser 13.

  In the dehydration tower 17, the exhaust gas is dehydrated (dehumidified) and harmful gas components are removed. In addition, by dehydrating the moisture in the exhaust gas, carbon dioxide can be efficiently recovered in a subsequent process for recovering carbon dioxide in the exhaust gas.

  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 to the DME filled in the dehydration tower 17 by a bubbling method. The exhaust gas is cooled by exchanging heat with DME. The cooling temperature at this time is a temperature at which toxic gas components such as moisture, nitrogen oxides and sulfur 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.

  The DME in the dehydration tower 17 is circulated from the DME cooling tower 18. A refrigerant (liquid nitrogen) cooled by the refrigerator 40 is circulated to the DME cooling tower 18 by a circulation pump 19. In the DME cooling tower 18, the DME is cooled by exchanging heat with the refrigerant.

  The DME in which the exhaust gas is circulated in the dehydration tower 17 is guided to the DME separation tower 20. This DME contains liquefied or solidified moisture and harmful gas components. The DME guided to the DME separation tower 20 is indirectly heat-exchanged with seawater here and heated (for example, −20 ° C.). At this temperature, the moisture and harmful gas components are liquid or solid, and DME becomes a gas. For this reason, DME floats above the DME separation tower 20 and is separated from other components. The floated DME is recovered from above the DME separation tower 20, led to the DME cooling tower 18, and further led to the dehydration tower 17. The DME is circulated and reused in this way, so that the cooling medium is efficiently utilized as a whole system.

  Next, moisture (liquid or solid) and harmful gas components remaining in the DME separation tower 20 are guided to the component separation tower 22 by the transport pump 21. Here, the moisture and harmful gas components are indirectly heat-exchanged with seawater to be heated (for example, 5 ° C.). At this temperature, moisture and nitrogen dioxide are liquids and sulfur dioxide is a gas. The sulfur dioxide that has been heated to become a gas is discharged from above the component separation tower 22 and then led to the heat exchanger 11 to cool the exhaust gas (for example, 55 ° C.) guided from the exhaust gas generation source 10. Used as a refrigerant. By using sulfur dioxide as a refrigerant in this way, the energy consumption of the entire system can be suppressed.

  The exhaust gas after being used as a refrigerant is heat-exchanged by the heat exchanger 11 and heated to, for example, 45 ° C., and then guided to the chimney 51 and discharged outside the system. Further, harmful gas components such as liquefied water and nitrogen dioxide other than sulfur dioxide remaining in the component separation tower 22 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 led from the dehydration tower 17 to the reversible heat exchanger 23 is cooled here, and then led to the carbon dioxide separator 30. The carbon dioxide separator 30 separates carbon dioxide contained in the exhaust gas and liquefies and discharges the separated carbon dioxide. The detailed configuration and function of the carbon dioxide separator 30 will be described later.

  The liquefied and discharged carbon dioxide is sent to the liquefied carbon dioxide storage tank 27 and stored. On the other hand, the exhaust gas after the carbon dioxide is separated in the carbon dioxide separator 30 is introduced into the reversible heat exchanger 23 and used as a refrigerant, and then guided to the heat exchanger 11. The exhaust gas is used again as a refrigerant in the heat exchanger 11 and then released from the chimney 51 to the outside of the system. Here, this atmospheric release is to release a part of the system out of the system in order to alleviate the accumulation of exhaust gas in the system. Therefore, the concentration of carbon dioxide contained in the discharged exhaust gas is very low.

  By the way, the refrigerator 40 mentioned above cools the nitrogen gas as a refrigerant | coolant. The refrigerator 40 cools the nitrogen gas by repeatedly compressing and expanding with energy such as electric energy. Liquid nitrogen produced by cooling is a liquid circulated in a separate system from the cooling of ethylene glycol circulated to the heat exchanger 11, the liquid nitrogen circulated to the DME cooling tower 18, the dry ice sublimator 24, and the like. Used for cooling refrigerants such as nitrogen. The refrigerator 40 is distributed as a turbine-type compressor 41 (nitrogen booster), a circulating nitrogen compressor 42, a refrigerating device 43 that expands a refrigerant to obtain a low temperature, liquid nitrogen that is a refrigerant, ethylene glycol, or another system. A heat exchanger 44 that exchanges heat with liquid nitrogen is provided.

  As described above, in the exhaust gas treatment system of the present embodiment, coal-fired boilers, heavy oil-fired boilers, nitrogen oxides and sulfur oxides discharged from blast furnaces, coke ovens, converters, etc. in steelworks As for the exhaust gas containing noxious gas components, moisture and noxious gas components contained in the exhaust gas 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.

<Carbon dioxide separator 30>
The configuration and function of the carbon dioxide separator 30 will be described in detail. FIG. 3 is a schematic configuration of a carbon dioxide separator 30 described as an embodiment of the present invention. In this figure, a pressure vessel 310 is a substantially rectangular parallelepiped metal (for example, stainless steel) container having a vertical, horizontal, and height of about several meters each. A gas inlet 321 through which the exhaust gas guided from the reversible heat exchanger 23 flows is provided at a predetermined position on the upper surface of the pressure vessel 310. On the other hand, a gas discharge port 322 for discharging components other than carbon dioxide contained in the exhaust gas to the outside of the pressure vessel 310 is provided at a predetermined position on the lower surface of the pressure vessel 310. Further, at a predetermined position on the lower surface of the pressure vessel 310, a liquid discharge port 323 for discharging liquefied carbon dioxide accumulated at the bottom of the pressure vessel 310 is provided separately from the gas discharge port 322. Note that the gas discharge port 322 is provided at a position separated from the gas inlet 321 by a predetermined distance so that the exhaust gas flowing in from the gas inlet 321 stays in the pressure vessel 310 for a predetermined time or longer.

  A pipe (gas inflow pipe 331) connected to the gas inflow port 321 is provided with a control valve 341 for adjusting the inflow amount of the exhaust gas. A control valve 342 for adjusting the outflow amount of the exhaust gas is provided in the pipe (gas exhaust pipe 332) connected to the gas exhaust port 322. A pipe connected to the liquid discharge port 323 (liquid discharge pipe 333) is provided with a control valve 343 for adjusting the amount of liquid carbon dioxide to be discharged. By closing all of these control valves 341, 342, and 343, the inside of the pressure vessel 310 is completely sealed.

Inside the pressure vessel 310, a metal (for example, copper or stainless steel) refrigerant circulation pipe (cooler) 312 for circulating liquid nitrogen (LN ₂ ) as a refrigerant is provided. Note that liquid nitrogen serving as the refrigerant is supplied from the refrigerator 40. A control valve 344 that controls the flow rate of the refrigerant is provided upstream of the refrigerant flow pipe 312. The refrigerant flow pipe 312 is branched into two inside the pressure vessel 310 in order to ensure a sufficient contact area with the exhaust gas flowing inside the pressure vessel 310. The refrigerant flow pipe 312 is meandered inside the pressure-resistant vessel 1, and this also ensures a sufficient contact area with the gas.

  A heat transfer tube (heat transfer device) 313 is embedded in the wall surface of the pressure vessel 310. A control valve (not shown) for controlling the flow rate of the heat medium flowing through the heat transfer tube 313 is provided upstream of the heat transfer tube 313. The heat medium is, for example, dry air, and the heat medium is transported from the heat source 314 to the heat transfer tube 313. In addition, the effective utilization of the energy as the whole system is achieved by using the refrigerant | coolant circulated from the refrigerator 40 as said heat medium. The heat transfer tube 313 may be provided inside the pressure vessel 310 instead of being embedded in the wall surface of the pressure vessel 310. Instead of the heat transfer tube 313, an electrothermal heater (for example, a silicon rubber heater or a fluororesin heater) may be used.

  The pressure vessel 310 is provided with various sensors such as a sensor that measures the temperature of the gas in the pressure vessel 310 and a sensor that measures the temperature of the surface of the refrigerant flow pipe 312. The output value of each sensor is input to a measuring device or a computer (not shown) and monitored by an operator. In addition, a small window (not shown) is provided at a predetermined position of the pressure vessel 310 so that the inside of the pressure vessel 310 can be visually observed.

  Next, a process for separating carbon dioxide contained in exhaust gas, which is performed using the carbon dioxide separator 30, will be described with the process flow shown in FIG. 4. In the initial state, it is assumed that all the control valves 341, 342, and 343 are closed (S401).

  First, the control valve 344 is opened, and the flow of the refrigerant (liquid nitrogen) to the refrigerant flow pipe 312 is started (S402). Here, carbon dioxide is solidified, but the temperature of the surface of the refrigerant flow pipe 312 is lowered to a temperature at which noxious gas components such as nitrogen oxides are not liquefied. FIG. 5 is a TP (temperature-pressure) diagram of carbon dioxide (carbon dioxide). As shown in the figure, the sublimation point of carbon dioxide is -78.5 ° C. at 1 atm. Therefore, assuming 1 atm, the surface temperature of the refrigerant flow pipe 312 is at least −78.5 ° C. or less.

  When the surface temperature of the refrigerant flow pipe 312 reaches the above temperature, the control valve 341 and the control valve 342 are opened next, and a gas for separating carbon dioxide is introduced from the control valve 341, and the gas flows to the pressure vessel 310. Is started (S403). Here, the gas flowing through the pressure vessel 310 is cooled by the refrigerant flow pipe 312, and carbon dioxide contained in the gas is deposited as dry ice 350 on the outer surface of the refrigerant flow pipe 312 (S404). On the other hand, the exhaust gas flowing into the pressure vessel 310 moves through the pressure vessel 310 and is discharged out of the pressure vessel 310 from the control valve 342 (S405).

  When the amount of dry ice 350 deposited on the surface of the refrigerant flow pipe 312 reaches a predetermined amount (S406: YES), the control valve 341 and the control valve 342 are closed to seal the pressure vessel 310 (S407). Further, the control valve 344 is closed to stop the flow of the refrigerant (liquid nitrogen) in the refrigerant flow pipe 312 (S408). Whether or not the amount of precipitation of the dry ice 350 has reached a predetermined amount is determined, for example, by visually observing the inside of the pressure vessel 310 from a small window or when a predetermined time has elapsed.

  Next, the control valve 345 is opened to allow the heat medium to flow through the heat transfer tube 313 (S409), and the temperature in the pressure vessel 310 is increased. As the temperature in the pressure vessel 310 rises, the dry ice 350 deposited on the surface of the refrigerant flow pipe 312 begins to vaporize (sublimate) (S410). On the other hand, when the dry ice 350 is vaporized, the pressure in the pressure vessel 310 is increased. Here, as shown in FIG. 9, the triple point of carbon dioxide is 5.11 atm / −56.6 ° C. For this reason, when the dry ice 350 is vaporized and the pressure container 310 is at a temperature and pressure higher than the temperature and pressure at the triple point, part of the carbon dioxide in the pressure container 310 begins to liquefy, and the liquid produced by liquefaction Carbon dioxide begins to accumulate at the bottom of the pressure vessel 310 (S411).

  Next, when the dry ice 350 deposited on the surface of the refrigerant flow pipe 312 is completely vaporized or liquefied (S411: YES), the control valve 343 is opened. As a result, carbon dioxide (liquid) accumulated at the bottom of the pressure vessel is discharged from the liquid discharge port 323 to the outside of the pressure vessel 310 by the pressure inside the pressure vessel 310 (S413). Note that whether or not the dry ice 350 has been completely vaporized or liquefied is determined, for example, by viewing the inside of the pressure vessel 310 from a small window or after a predetermined time has elapsed. Further, by setting the pressure and temperature at which the carbon dioxide is kept in a liquid state in the liquid discharge pipe 33 connected to the liquid discharge port 323, the carbon dioxide is discharged out of the pressure vessel 310 while being kept in a liquid state. can do.

  As explained above, according to the carbon dioxide separator 30 of the present embodiment, carbon dioxide contained in the gas can be efficiently separated. In addition, by closing the control valve 344 and the control valve 345 of the heat transfer tube 313 and repeating the process from S401 again, the carbon dioxide can be continuously separated from the exhaust gas sequentially introduced from the reversible heat exchanger 23. Yes (S414: NO).

  According to the carbon dioxide separator 30, carbon dioxide can be solidified and liquefied in the same pressure vessel 310. Moreover, since the carbon dioxide separator 30 has a simple device configuration as described above, it can be implemented at low cost. In the carbon dioxide separator 30, the dry ice 350 is deposited on the outer surface of the heat transfer pipe (refrigerant flow pipe 312), so that the pipe of the heat transfer pipe 313 is not blocked and continuous operation or automatic Easy to drive. Further, carbon dioxide can be discharged in a liquid state convenient for transportation and storage without using a special liquefying device.

  For example, each of the control valves 341 to 345 is an electromagnetic valve, and a control line for controlling each electromagnetic valve is connected to a computer, and the electromagnetic wave is controlled by computer hardware or control software that operates on the hardware. The valve may be remotely controlled. Further, all or part of the above-described process may be automatically executed based on the output values of the various sensors.

<< Example 2 >>
FIG. 6 shows a schematic configuration of an exhaust gas treatment system described as a second embodiment of the present invention. According to this exhaust gas treatment system, regarding 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, moisture contained in the exhaust gas or While removing harmful gas components efficiently, carbon dioxide (CO ₂ ) contained in the exhaust gas can be efficiently recovered.

  In the exhaust gas treatment system, as a pre-process, the exhaust gas containing harmful gas components such as nitrogen oxides discharged from the exhaust gas generation source 10 is converted into industrial water accommodated in the heat exchanger 11 and the condenser (condenser) 13. It cools to about room temperature by introducing. 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. Further, as a second process, the exhaust gas from which moisture and nitrogen oxides have been separated is introduced into the carbon dioxide separator 30 where the carbon dioxide contained in the exhaust gas is cooled and solidified for separation and separation. Carbon dioxide is liquefied and discharged.

Next, a specific treatment process of the exhaust gas treatment system will be described in order.
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 refrigerant such as ethylene glycol circulated from the refrigerator 40 are guided to the heat exchanger 11. The exhaust gas (for example, 55 ° C.) guided from the exhaust gas generation source 10 is cooled to about room temperature by the seawater and the refrigerant by passing through the heat exchanger 11.

  The cooled exhaust gas is then led to a condenser (condenser) 13. In the condenser 13, the exhaust gas 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 stored in the drainage tank 14 and then guided to the wastewater treatment device 50 by the drainage pump 15. The exhaust gas that has passed through the condenser 13 is guided to the dehydration tower 17 by the exhaust gas fan 16. The exhaust gas is cooled from about room temperature to, for example, 5 ° C. by heat exchange with industrial water in the condenser 13.

  In the dehydration tower 17, the exhaust gas is dehydrated (dehumidified) and harmful gas components are removed. In addition, by dehydrating the moisture in the exhaust gas, carbon dioxide can be efficiently recovered in a subsequent process for recovering carbon dioxide in the exhaust gas.

  In the dehydration tower 17, exhaust gas is introduced from the lower side of the dehydration tower 17. The exhaust gas (for example, 5 ° C.) introduced into the dehydration tower 17 is circulated to the DME (for example, −90 ° C.) filled in the dehydration tower 17 by a bubbling method. The exhaust gas is cooled by exchanging heat with DME. Here, at this temperature, moisture and harmful gas components in the exhaust gas are liquefied or solidified, but carbon dioxide is not solidified. For this reason, moisture and nitrogen dioxide are liquefied or solidified and separated from the exhaust gas, but carbon dioxide remains in the exhaust gas as a gas. The exhaust gas containing carbon dioxide floating above the dehydration tower 17 is guided to the reversible heat exchanger 23.

  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 in which the exhaust gas is circulated in the dehydration tower 17 is guided to the solid-liquid separator 28. At this stage, 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 above solidified product are separated. The DME separated by the solid-liquid separator 28 is led to the DME separation column 20 in order to reuse it. 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.). Here, at this temperature, the 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 and led to the DME cooling tower 18, and then cyclically led to the dehydration tower 17 again. In this way, DME is reused cyclically. As described above, the DME as the cooling medium is cyclically reused, so that 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.

  On the other hand, the exhaust gas led from the dehydration tower 17 to the reversible heat exchanger 23 is cooled here and then led to the carbon dioxide separator 30. The carbon dioxide separator 30 separates carbon dioxide contained in the exhaust gas and liquefies and discharges the separated carbon dioxide. The detailed configuration and function of the carbon dioxide separator 30 are the same as those described above.

  The liquefied and discharged carbon dioxide is sent to the liquefied carbon dioxide storage tank 27 and stored. On the other hand, the exhaust gas after the carbon dioxide is separated in the carbon dioxide separator 30 is introduced into the reversible heat exchanger 23 and used as a refrigerant, and then guided to the heat exchanger 11. The exhaust gas is used again as a refrigerant in the heat exchanger 11 and then released from the chimney 51 to the outside of the system. Here, this atmospheric release is to release a part of the system out of the system in order to alleviate the accumulation of exhaust gas in the system. Therefore, the concentration of carbon dioxide contained in the discharged exhaust gas is very low.

  By the way, in the refrigeration / heat exchanger 44 described above, by utilizing the heat of vaporization of LNG, 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. Cooling the refrigerant. For example, in a power plant using LNG as gas fuel, LNG is transported in a liquid state of, for example, −150 ° C. to −165 ° C. and stored in the LNG tank 60 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. In addition, carbon dioxide contained in the exhaust gas can be efficiently recovered.

In the above description, the case where the harmful gas component to be removed from the exhaust gas is nitrogen dioxide has been described. For example, other nitrogen oxides (NO _X ) such as carbon monoxide and nitrogen monoxide, For other harmful gas components such as halogen compounds such as hydrogen fluoride, the same mechanism as in the present embodiment can be applied by appropriately selecting the above cooling medium.

  Further, for example, the control valves 341 to 344 are electromagnetic valves, respectively, and a control line for controlling each electromagnetic valve is connected to a computer, and the above-described electromagnetic waves are controlled by computer hardware or control software operating on the hardware. The valve may be remotely controlled. Further, all or part of the above-described process may be automatically executed based on the output values of the various sensors.

  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.

It is a figure showing a schematic structure of an exhaust gas treatment system by one embodiment of the present invention. It is a figure which shows the measurement result of the density | concentration change of the sulfur dioxide in the simulation gas at the time of distribute | circulating the simulation gas with 80 ppm of sulfur dioxide density | concentration in DME by one Embodiment of this invention. It is a figure which shows schematic structure of the carbon dioxide separator 30 by one Embodiment of this invention. It is a figure which shows the process flow explaining the process which isolate | separates the carbon dioxide contained in the waste gas performed using the carbon dioxide separator 30 by one Embodiment of this invention. It is a figure which shows the TP (temperature-pressure) diagram of a carbon dioxide. It is a figure showing a schematic structure of an exhaust gas treatment system by one embodiment of the present 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 22 Component separation tower 23 Reversible heat exchanger 27 Liquefied carbon dioxide storage tank 28 Solid-liquid separation apparatus 30 Carbon dioxide separation apparatus 40 Refrigerator 44 Refrigeration / heat exchanger 50 Waste water treatment apparatus 51 Chimney

Claims (9)

The exhaust gas is circulated through the cooling medium, and carbon dioxide is not solidified but cooled to a temperature at which nitrogen oxides and sulfur oxides are liquefied or solidified, thereby liquefying nitrogen oxides and sulfur oxides contained in the exhaust gas as harmful gas components. Or a first device for solidifying and separating from the exhaust gas;
The exhaust gas after separating nitrogen oxides and sulfur oxides is passed through a pressure vessel to cool and solidify the carbon dioxide, the pressure vessel is sealed, the solidified carbon dioxide is heated to vaporize, A second device for liquefying the carbon dioxide by an increase in pressure inside the pressure vessel due to vaporization of carbon dioxide, and discharging the liquefied carbon dioxide outside the pressure vessel;
An exhaust gas treatment system comprising: The exhaust gas treatment system according to claim 1,
The harmful gas component separated from the exhaust gas by the first device is vaporized with respect to the cooling medium contained in the harmful gas component, but is heated to a temperature at which the harmful gas component is not vaporized. Including a device for separating a gas component and the cooling medium;
An exhaust gas treatment system characterized by An exhaust gas treatment system according to claim 1 or 2,
The sulfur oxide and nitrogen contained in the harmful gas component are heated by raising the temperature of the harmful gas component separated from the exhaust gas by the first apparatus to a temperature at which sulfur oxide is vaporized but nitrogen oxide is not vaporized. Including a device for separating oxides;
An exhaust gas treatment system characterized by The exhaust gas discharged from the LNG-fired boiler is circulated through the cooling medium, and the nitrogen oxide contained in the exhaust gas as a harmful gas component is liquefied by cooling to a temperature that does not solidify carbon dioxide but liquefies or solidifies nitrogen oxide. Or a first device for solidifying and separating from the exhaust gas;
The exhaust gas after separation of nitrogen oxides is circulated through a pressure vessel to cool and solidify the carbon dioxide, the pressure vessel is sealed, the solidified carbon dioxide is heated to vaporize, and the carbon dioxide is vaporized. A second device for liquefying the carbon dioxide by increasing the pressure inside the pressure-resistant container, and discharging the liquefied carbon dioxide outside the pressure-resistant container;
An exhaust gas treatment system comprising: The exhaust gas treatment system according to claim 4,
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 5,
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 In the exhaust gas treatment system according to any one of claims 1 to 6,
The cooling medium includes any of dimethyl ether, methanol, ethanol, toluene, and ethylbenzene;
An exhaust gas treatment system characterized by An exhaust gas treatment system according to any one of claims 1 to 7,
The cooling and solidification of the carbon dioxide by the second device is performed by bringing the gas containing carbon dioxide into contact with the outer surface of a refrigerant circulation pipe that is provided in the pressure-resistant container and in which refrigerant is circulated. about,
An exhaust gas treatment system characterized by An exhaust gas treatment system according to any one of claims 1 to 8,
The refrigerant flow pipe is provided meandering;
An exhaust gas treatment system characterized by

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