JP5724600B2 - Carbon dioxide recovery method and recovery apparatus - Google Patents

Description

  The present invention relates to a carbon dioxide recovery method and a carbon dioxide recovery device for separating and recovering carbon dioxide from a gas containing carbon dioxide such as combustion gas and reducing clean gas to the atmosphere.

  Facilities such as thermal power plants, steelworks, and boilers use large amounts of fuel such as coal, heavy oil, and super heavy oil. Sulfur oxides, nitrogen oxides, and carbon dioxide emitted by the combustion of fuel are There is a need for quantitative and concentration restrictions on emissions from the perspective of air pollution prevention and global environmental protection. In recent years, carbon dioxide has been seen as a major cause of global warming, and movements to suppress emissions have become active worldwide. For this reason, in order to enable the recovery and storage of carbon dioxide from combustion exhaust gases and process exhaust gases without releasing them into the atmosphere, various researches have been vigorously advanced. As a carbon dioxide recovery method, for example, PSA ( Known are pressure swinging), membrane separation and concentration, and chemical absorption using reaction absorption by basic compounds.

  In the chemical absorption method, mainly alkanolamine-based basic compounds are used as the absorbent. In the treatment process, an aqueous liquid containing the absorbent is generally used as the absorbent, and carbon dioxide contained in the gas is absorbed into the absorbent. The absorbing solution is circulated so as to alternately repeat the absorbing step to be performed and the regeneration step of regenerating the absorbing solution by releasing the absorbed carbon dioxide from the absorbing solution (see, for example, Patent Document 1 below). In the regeneration process, heating for releasing carbon dioxide is necessary, and in order to reduce the operating cost of carbon dioxide recovery, it is important to reduce the energy required for heating / cooling for regeneration.

  Further, it is necessary to improve the recovery rate by improving the gas-liquid contact efficiency in the absorption tower and the regeneration tower, and also to improve the energy efficiency by optimizing the whole process. A part of the liquid is heated by the regeneration tower outlet gas, and in Patent Document 2 below, for the purpose of reducing the energy required for recovering carbon dioxide from the absorption liquid, the absorption liquid in the regeneration process is extracted and subjected to high temperature steam. The residual heat of the steam condensate generated from the regenerative heater for heat exchange is used for heating the absorbent. Patent Document 3 below describes introducing a stripping gas so as to accompany carbon dioxide in order to promote the release of absorbed carbon dioxide.

JP 2009-214089 A JP-A-2005-254212 Japanese Patent Laid-Open No. 2005-230808

  The energy required in the regeneration process includes sensible heat required to raise the temperature of the absorbing solution, reaction heat when releasing carbon dioxide from the absorbing solution, and latent heat to compensate for heat loss due to moisture evaporation of the absorbing solution. is there. The above-described prior art is a technique related to sensible heat or reaction heat.

  Since the latent heat of vaporization of moisture accounts for about 10 to 20% of the regenerative heat energy, the energy consumption of the latent heat is not negligible and this saving is useful. In particular, if the absorption efficiency of carbon dioxide by the absorption liquid is high, the heat energy required for the regeneration increases, and the importance in reducing the heat energy of latent heat increases.

  An object of the present invention is to provide a carbon dioxide recovery method and a recovery apparatus capable of reducing energy required for regenerating an absorbing solution and reducing operation costs.

  Further, an object of the present invention is to reduce the energy required to regenerate the absorbing liquid without burdening the apparatus and complicated work, and to reduce the energy cost with high carbon dioxide recovery efficiency. It is to provide a recovery method and a recovery device.

  In order to solve the above-mentioned problems, the present inventors have conducted extensive research and, as a result, reduced the supply of latent heat related to water evaporation of the absorption liquid by using the water vapor supply to the regeneration process, and effectively use this advantage. A possible form has been found and the present invention has been completed.

According to one aspect of the present invention, a carbon dioxide recovery device is configured to bring a gas containing carbon dioxide into contact with an absorption liquid, so that the absorption liquid absorbs carbon dioxide, and carbon dioxide is absorbed by the absorption tower. The absorption liquid that is absorbed is heated to release carbon dioxide from the absorption liquid to regenerate the absorption liquid, and the amount of water vapor contained in the recovered gas containing carbon dioxide that is discharged from the regeneration tower is measured. Using the measurement unit and the amount of water vapor of the recovered gas measured by the measurement unit as a reference amount, 0.4 to 1.0 times the amount of water vapor contained in the recovered gas is supplied to the regeneration tower. The main point is to have a water vapor supply system.

According to another aspect of the present invention, a method for recovering carbon dioxide includes an absorption step in which a gas containing carbon dioxide is brought into contact with an absorption liquid under pressure to cause the absorption liquid to absorb carbon dioxide, and the absorption Included in the regeneration step of regenerating the absorption liquid by heating the absorption liquid that has absorbed carbon dioxide in the process to release carbon dioxide from the absorption liquid, and the recovered gas containing carbon dioxide discharged from the regeneration process Based on the measurement step of measuring the amount of water vapor and the amount of water vapor of the recovered gas measured in the measurement step, the regenerated water vapor is 0.4 to 1.0 times the amount of water vapor contained in the recovered gas. And having a steam supply step for supplying to the tower.

  According to the present invention, in the process of recovering carbon dioxide contained in the gas, it is possible to reduce the cost of operation by reducing the energy supply required for regeneration of the absorbing liquid, and it is also possible to reduce the burden on the apparatus, A carbon dioxide recovery device that can contribute to energy saving and environmental protection can be provided. In particular, the energy efficiency improvement is effective in the regeneration of the absorbing solution that has absorbed carbon dioxide at a high recovery rate, and is effective in preventing the deterioration of the absorbing solution and reducing the burden on the apparatus. The carbon dioxide recovery method does not require special equipment or expensive equipment, and can be easily performed using general equipment, which is economically advantageous.

1 is a schematic configuration diagram showing a carbon dioxide recovery apparatus according to a first embodiment of the present invention. The schematic block diagram which shows the collection | recovery apparatus of the carbon dioxide which concerns on the 2nd Embodiment of this invention.

  In general, as a method for releasing carbon dioxide from the absorbing liquid and regenerating it, the absorbing liquid is heated to supply reaction heat. For this purpose, sensible heat required for increasing the temperature of the absorbing liquid, and It is also necessary to supply latent heat to compensate for heat loss due to moisture evaporation of the absorbing liquid. In order to reduce the heat supply, it is possible to suppress the evaporation of moisture in the absorption liquid by increasing the boiling point of the absorption liquid by pressurization. In this method, the carbon dioxide is released from the absorption liquid. The heating temperature is also increased, and the required amount of sensible heat is increased, which is not preferable because the deterioration of the absorbing solution and the burden on the apparatus increase.

  Moisture evaporation from the absorption liquid is caused by the fact that the recovered gas discharged from the regeneration process contains not only carbon dioxide but also moisture. It is necessary to supply an amount of energy that is always vaporized from the absorption liquid in the process and lost as latent heat. If this energy supply can be reduced, even if the amount of carbon dioxide contained in the absorbent increases, supply of regenerative energy for sufficiently regenerating the absorbent does not have to be a burden. And the necessity for pressurizing the absorption liquid of a regeneration process decreases, and it becomes possible to reduce the heating temperature of an absorption liquid and to suppress the quality deterioration of an absorbent.

  In accordance with the above, the present invention suppresses vaporization of water from the absorbing liquid by supplying water vapor to the atmosphere above the absorbing liquid in the regeneration process and replenishing the moisture lost with the recovered gas discharged. To reduce latent heat loss. At this time, the water vapor to be supplied may be at a temperature equal to or higher than that of the absorbing liquid because it does not have to lower the temperature of the absorbing liquid to be regenerated. Thereby, since the latent heat loss is reduced and the supplied heat energy is efficiently used for regeneration, the regeneration of the absorbing liquid can be sufficiently and easily advanced. The effect of suppressing vaporization from the absorbing liquid increases with an increase in the amount of water vapor to be supplied, and works very effectively in the supply exceeding the amount that saturates the atmosphere.

  Hereinafter, the carbon dioxide recovery method and recovery apparatus of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a first embodiment of a carbon dioxide recovery method and a recovery apparatus for carrying out the same according to the present invention. The recovery device 1 brings the gas G containing carbon dioxide into contact with the absorption liquid, heats the absorption tower 10 that absorbs the carbon dioxide in the absorption liquid, and the absorption liquid that has absorbed the carbon dioxide, and removes the carbon dioxide from the absorption liquid. And a regeneration tower 20 for regenerating the absorbent by discharging. Furthermore, since the cooling tower 30 is provided so that the gas G supplied to the absorption tower 10 can be easily maintained at a low temperature suitable for absorption of carbon dioxide, various gases such as combustion exhaust gas and process exhaust gas can be handled. The gas G supplied to the recovery device is not particularly limited. The absorption tower 10, the regeneration tower 20, and the cooling tower 30 are each configured as a countercurrent gas-liquid contact device, and hold fillers 11, 21, 31 for increasing the contact area. The fillers 11, 21, 31 are generally made of ferrous metal materials such as stainless steel and carbon steel, but are not particularly limited, and are materials having durability and corrosion resistance at the processing temperature. It is preferable to select a shape that can provide the contact area. As the absorbing liquid, an aqueous liquid containing a compound having an affinity for carbon dioxide such as alkanolamines as an absorbent is used.

  The gas G supplied from the bottom of the cooling tower 30 passes through the filler 31 held in the tower, is cooled by the cooling water supplied from the upper part of the cooling tower 30, and is then supplied to the absorption tower 10. This prevents the temperature of the absorption tower 10 from rising due to the gas G. The cooling water whose temperature has been increased by cooling the gas G is sent to the water-cooled cooler 33 by the pump 32, cooled, and then returned to the cooling tower 30.

  The gas G containing carbon dioxide that has passed through the cooling tower 30 is supplied from the lower part of the absorption tower 10 through the check valve 18, the absorption liquid is supplied from the upper part of the absorption tower 10, and the gas G and the absorption liquid are filled with the filler. While passing through the gas 11, the carbon dioxide in the gas G comes into contact with the gas and liquid and is absorbed by the absorption liquid. The absorption liquid A1 that has absorbed carbon dioxide is stored at the bottom of the absorption tower 10 and is supplied to the regeneration tower 20 by a pump 12 through a supply path 16 that connects the bottom of the absorption tower 10 and the top of the regeneration tower 20.

The gas G ′ from which carbon dioxide has been removed is discharged from the top of the absorption tower 10. In this embodiment, the gas G ′ is configured to be discharged through the pressure control valve 19, so that the gas pressure in the absorption tower 10 can be adjusted by the pressure control valve 19 and set to a pressurized state as necessary. When the gas-liquid contact is performed, the transfer of carbon dioxide from the gas G to the absorbing liquid is promoted, and the absorption rate is improved as the gas pressure increases.

  Since the absorption liquid generates heat by absorbing carbon dioxide and the liquid temperature rises, a cooling condensing unit 13 for removing water vapor or the like that may be contained in the gas G ′ is provided at the top of the absorption tower 10 as necessary. Thus, the leakage of water vapor and the like to the outside of the tower can be suppressed to some extent. In order to further ensure this, a pump that circulates between the cooler 14 attached outside the absorption tower and a part of the condensed water (which may include the gas G ′ in the tower). 15, the condensed water or the like cooled by the cooler 14 and supplied to the top of the tower maintains the cooling condensing unit 13 at a low temperature and reliably cools the gas G ′ passing through the cooling condensing unit 13. Moreover, the composition fluctuation | variation of the absorption liquid in a tower is compensated by the condensed water which recirculate | refluxs to the filler 11. The temperature of the gas G ′ discharged to the outside of the tower is preferably about 60 ° C. or lower, more preferably 45 ° C. or lower. Although the cooler 14 of this embodiment is a water-cooling type, other cooling methods may be used, and the cooling accuracy may be increased by using a refrigerant refrigeration cycle.

  The absorption liquid A1 of the absorption tower 10 is supplied to the upper part of the regeneration tower 20, flows down on the filler 21, and is stored at the bottom. A reboiler is attached to the bottom of the regeneration tower 20. That is, a steam heater 22 provided outside the regeneration tower 20 for heating the absorption liquid and a circulation path 22 ′ for circulating the absorption liquid through the steam heater 22 are provided, and one of the absorption liquid A 2 at the bottom of the tower is provided. The part is branched to a steam heater 22 through a circulation path 22 ', heated by heat exchange with high-temperature steam, and then refluxed into the tower. By this heating, carbon dioxide is released from the absorption liquid at the bottom, and the filler 21 is also indirectly heated to promote the release of carbon dioxide by gas-liquid contact on the filler 21.

  The absorption liquid A2 regenerated by releasing carbon dioxide in the regeneration tower 20 is refluxed to the absorption tower 10 by the pump 23 through the reflux path 17, and is supplied from the absorption tower 10 to the regeneration tower 20 in the heat exchanger 24. It is cooled by exchanging heat with the absorbing liquid A1, and further cooled sufficiently to a temperature suitable for absorption of carbon dioxide by the cooler 25 using cooling water.

  The gas containing carbon dioxide released by heating in the regeneration tower 20 is discharged as a recovered gas C from the top through the condensing part 26 at the top of the regeneration tower 20. The condensing part 26 condenses the water vapor | steam contained in gas, suppresses excessive discharge | release, and also suppresses discharge | release of an absorber. The recovered gas C is sufficiently cooled by the cooler 27 using cooling water from the top of the regeneration tower 20 through the exhaust pipe 34 to condense the contained water vapor as much as possible, and then condensed by the gas-liquid separator 28. It is collected after removing. Carbon dioxide contained in the recovered gas C can be fixed and reorganized in the ground by, for example, injecting it into the ground or oil fields. The condensed water separated in the gas-liquid separator 28 is appropriately discharged and can be used as a supply source of water for adjusting the concentration of the absorbing liquid or water vapor as necessary.

  Since the recovered gas C discharged from the regeneration tower 20 contains at least condensed water vapor separated by the gas-liquid separator 28, at least the water vapor equivalent to the condensed water is vaporized from the absorption liquid in the regeneration tower 20. However, in the present invention, a pipe having a water vapor supply system 40 for supplying water vapor S into the regeneration tower 20 to supplement the water vapor released together with the recovered gas C and connected to the bottom of the regeneration tower 20. Steam 35 is supplied from 35. By supplying the water vapor S to the atmosphere on the absorption liquid A2 at the bottom of the regeneration tower 20, vaporization from the stored absorption liquid A2 and the absorption liquid in the vicinity thereof is suppressed, and latent heat required for vaporization is lost from the absorption liquid. Can be suppressed. Therefore, the regenerative heat energy supplied from the steam heater 22 can be reduced. The steam S supplied by the steam supply system 40 may be at a temperature that does not cool the absorption liquid in the regeneration tower 20, and therefore is at or above the temperature of the absorption liquid A 2, and relatively low-temperature steam can be used. The supply of water vapor S suppresses the latent heat loss of the absorption liquid and contributes to the supply of regeneration energy (reaction heat, sensible heat) of the absorption liquid. In this regard, the steam of the steam heater 22 that heats the absorbing liquid A2 as a reboiler requires a temperature difference for enabling heat exchange, and is practically at least about 20 ° C. higher than the absorbing liquid temperature. Since it is necessary to use high-temperature steam at around 200 ° C., the heat supply efficiency is lower than the supply by steam S. Therefore, it is preferable in terms of heat supply efficiency that a part of the supply energy from the steam heater 22 is replaced by the heat energy of the steam S directly supplied to the regeneration tower 20.

  The vaporization of the absorption liquid A2 in the regeneration tower 20 is preferably suppressed when the atmosphere on the absorption liquid A2 is saturated by the direct supply of the water vapor S. However, if excessive water vapor S is supplied, it is condensed in the regeneration tower 20. This will cause the concentration of the absorbent to decrease. Therefore, the steam supply system 40 adjusts the measurement unit 41 for determining the amount of water vapor contained in the recovered gas and the amount of water vapor supplied to the regeneration tower 20 so that the replenished water vapor S becomes an appropriate amount. Based on the amount of water vapor determined by the valve 42 and the measurement unit 41, the control unit 43 controls the control valve 42 so that the amount of water vapor supplied to the regeneration tower 20 is equal to the amount of water vapor contained in the recovered gas. . The measurement unit 41 includes a flow meter 44, a thermometer 45, and a pressure gauge 46 that detect the flow rate, temperature, and pressure of the gas passing through the exhaust pipe 34 at the top of the regeneration tower 20, and these are operations configured by a computer or the like. It is electrically connected to the processable control unit 43, and the detected flow rate, temperature and pressure data are constantly sent to the control unit 43. The pipe 35 is provided with a mass flow meter 47 for detecting the flow rate of the water vapor S. The mass flow meter 47 and the control valve 42 are electrically connected to the control unit 43 and detected by the mass flow meter 47. The flow rate data is constantly sent to the control unit 43. The control unit 43 determines the saturated water vapor pressure at that temperature from the gas temperature obtained from the measuring unit 41, and is discharged based on the gas pressure and saturated water vapor pressure of the recovered gas and the flow rate of the supplied water vapor S. The feed rate of the water vapor S is adjusted by controlling the opening of the control valve 42 so that the water vapor S in an appropriate ratio with respect to the saturated water vapor amount contained in the recovered gas is supplied. The amount of water vapor S to be supplied is controlled to be about 0.4 times or more, preferably about 0.5 to 1.0 times the saturated water vapor amount of the recovered gas. 1 is provided with a pressure regulating valve 29 in the exhaust pipe 34 of the regeneration tower 20 so that the pressure can be adjusted by pressurizing the inside of the regeneration tower 20 as necessary. If the atmospheric pressure is set, it may be omitted.

  A collection method implemented in the collection apparatus 1 of FIG. 1 will be described.

  In the absorption tower 10, when the gas G containing carbon dioxide such as combustion exhaust gas and process exhaust gas is supplied from the bottom and the absorption liquid is supplied from the top, the gas G and the absorption liquid come into gas-liquid contact on the filler 11, Carbon dioxide is absorbed by the absorbing solution. Since carbon dioxide is well absorbed at low temperatures, the liquid temperature of the absorbent or the temperature of the absorption tower 10 (particularly the filler 11) is adjusted so that it is generally about 50 ° C. or lower, preferably 40 ° C. or lower. Since the absorbing liquid generates heat due to absorption of carbon dioxide, it is desirable to take into consideration the increase in liquid temperature caused by this, so that the liquid temperature does not exceed 60 ° C. The gas G supplied to the absorption tower 10 is also adjusted to an appropriate temperature by the cooling tower 30 in consideration of the above. An aqueous liquid containing a compound having affinity for carbon dioxide as an absorbent is used as the absorbent. Although the gas pressure in the absorption tower 10 is set to normal pressure, when it is necessary to increase the carbon dioxide recovery rate of the absorption liquid, the pressure control valve 19 causes the pressure to be about 120 kPaG or less, preferably 10 to less than normal pressure. It may be adjusted to a pressure range of about 100 kPaG. Examples of the absorbent include alkanolamines and hindered amines having an alcoholic hydroxyl group, and specific examples of the alkanolamine include monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, diisopropanolamine, diisopropanolamine, and the like. Examples of the hindered amine having an alcoholic hydroxyl group include 2-amino-2-methyl-1-propanol (AMP), 2- (ethylamino) ethanol (EAE), and 2- (methylamino). ) Ethanol (MAE) and the like can be exemplified. Usually, the use of monoethanolamine (MEA) is preferred, and a plurality of these may be mixed. The absorbent concentration of the absorption liquid can be appropriately set according to the amount of carbon dioxide contained in the gas to be processed, the processing speed, etc. A concentration of about 10 to 50% by mass is applied. For example, an absorbent having a concentration of about 30% by mass is suitably used for the treatment of the gas G having a carbon dioxide content of about 20%. The supply rates of the gas G and the absorbing liquid are appropriately set so that the absorption proceeds sufficiently according to the amount of carbon dioxide contained in the gas, the gas-liquid contact efficiency, and the like.

  When the absorption liquid A1 that has absorbed carbon dioxide is supplied to the regeneration tower 20, it is heated to a high temperature near the boiling point, but before being supplied to the regeneration tower 20, the heat exchanger 24 recirculates from the regeneration tower 20. Therefore, the absorption liquid A1 is heated to a temperature close to the heating temperature in the regeneration tower 20 and charged into the regeneration tower 20 in a state where carbon dioxide is easily released. In this embodiment, the regeneration tower 20 is charged at about 90 to 115 ° C. Furthermore, the release of carbon dioxide is promoted by gas-liquid contact on the filler 21, and the temperature rise and the release of carbon dioxide further progress by heating at the bottom of the regeneration tower 20. The absorbent A2 stored in the bottom is heated to the vicinity of the boiling point by partial circulation heating, and the boiling point of the absorbent depends on the composition (absorbent concentration) and the pressure in the regeneration tower 20. At this time, it is necessary to supply the latent heat of vaporization of water lost from the absorbing solution and the sensible heat of the absorbing solution. However, when pressurization is performed to suppress vaporization, the sensible heat increases due to the rise in boiling point. In consideration of the above, it is necessary to pressurize the inside of the regeneration tower 20 and heat the absorbent to 120 to 130 ° C. In particular, when the inside of the absorption tower 10 is pressurized to increase the carbon dioxide absorption rate of the absorption liquid, sufficient heating for regeneration of the absorption liquid is necessary, but the vaporization of the absorption liquid is suppressed by the supply of the water vapor S. Then, since the necessity of the pressurization temperature raising as mentioned above is reduced, in the present invention, the gas pressure in the regeneration tower 20 can be suitably set in the range of about atmospheric pressure to 100 kPaG, and the absorbing liquid The heating temperature can be set in the range of 100 ° C. to less than 120 ° C. When steam S that is 0.4 times or more the saturated steam amount of the recovered gas is supplied to the regeneration tower 20 at atmospheric pressure, an energy reduction effect equivalent to that obtained when the regeneration tower is pressurized to 100 kPaG without supplying steam is obtained. . From the viewpoint of carbon dioxide recovery efficiency, a pressurized state of about 20 to 85 kPaG is suitable and efficient. At a pressure in this range, the water vapor S is about 0.2 times or more the saturated water vapor amount of the recovered gas. By supplying the same amount as when pressurized to 100 kPaG, when 0.5 times or more, preferably 0.8 times or more of the steam S is supplied, the energy reduction amount is reduced by the steam supply at 100 kPaG. It becomes equal to or more than the amount. The energy reduction effect due to the water vapor supply becomes more prominent as the pressure is lower. The amount of water vapor at which the energy reduction amount due to the water vapor supply at atmospheric pressure is equal to or greater than the energy reduction amount under pressure is 1. It will be about 5 times. Considering these, it is not necessary to set the supply amount of the water vapor S to 1.5 times or more of the saturated water vapor amount of the recovered gas, and from the point of avoiding dilution of the absorption liquid with condensed water, It is preferable to supply about 0.4 to 1.0 times. By supplying the water vapor S, an energy saving effect can be obtained because the heating temperature of the absorbing liquid itself can be set lower, and the heat deterioration of the absorbent contained in the absorbing liquid is also reduced. When dilution or concentration of the absorbing solution occurs, the concentration may be adjusted by extracting the absorbing solution and adding a high concentration absorbing solution or water as necessary. It is also possible to adjust by changing the supply amount of the water vapor S.

  The temperature of the water vapor S supplied to the regeneration tower 20 may be equal to or higher than the temperature of the absorption liquid, and is preferably higher. However, in the present invention, low-grade exhaust heat can be used. The temperature is preferably about 0 to 150 ° C., and therefore about 100 to 250 ° C. is preferable. The water vapor S supplied to the bottom of the regeneration tower 20 increases the humidity of the atmosphere above the liquid surface of the absorbing liquid A2 stored in the bottom, and the heat loss and temperature decrease due to vaporization of water on the liquid surface of the absorbing liquid A2 are suppressed. Therefore, as described above, the energy of the steam heater 22 required for heating the absorption liquid A2 of the regeneration tower 20 can be reduced.

The control unit 43 uses the physical properties of the recovered gas detected by the flow meter 44, the thermometer 45, and the pressure gauge 46, that is, the gas flow rate V [Nm ³ / hour] of the exhaust pipe 34, the gas temperature T [K], and the gas Based on the pressure P [kPa] and the flow rate Vg [Nm ³ / hour] of the water vapor S detected by the mass flow meter 45 of the pipe 35, the flow rate Pg of the water vapor S supplied to the regeneration tower 20 is the recovered gas. The opening degree of the control valve 42 is controlled so as to be substantially equal to the amount of water vapor contained in. As a specific procedure in the control, the saturated water vapor pressure Pw of the recovered gas is determined from the temperature T of the recovered gas according to the following Tetens equation, and the ratio of the recovered gas gas pressure P to the saturated water vapor pressure Pw is determined as the recovered gas. When the flow rate Vg (= V × Pw / P) of the water vapor S that is equal to the ratio between the flow rate of the water vapor S and the flow rate Vg of the supplied water vapor S is calculated, the flow rate Vg becomes equal to the saturated water vapor amount of the recovered gas. Therefore, using this as the reference amount, the product value of the magnification set in accordance with the above and the reference amount is determined as the supply amount, and the control valve 42 is controlled to the opening at which this amount of water vapor S is supplied.

Pw = 0.611 × 10 ^{7.5 T / (T + 237.3)} (Tetens formula)

  In this way, by adjusting the supply amount of water vapor by controlling the control valve 42 based on the saturated water vapor pressure of the recovered gas, the water vapor S is supplemented according to the amount of water vapor discharged from the regeneration tower 20, and the regeneration tower The water vapor evaporated from the absorption liquid in 20 decreases. The water condensed by the cooler 27 is separated by the gas-liquid separator 35 and is appropriately discharged.

  In this way, the absorption liquid circulates between the absorption tower 10 and the regeneration tower 20, and the absorption process and the regeneration process are alternately repeated. Since the regeneration energy of the absorbent is reduced by suppressing the latent heat loss by supplying the steam S to the regeneration tower 20 and the heating temperature is lowered, the regeneration efficiency of the absorbent is improved, and the consumption of the absorbent and the burden on the apparatus are reduced. It becomes the recovery device of the collected dioxide. Moreover, since the regeneration efficiency of the absorbing liquid is good, the absorbing liquid can be efficiently regenerated even when the carbon dioxide recovery rate is increased by pressurization in the absorption tower 10.

  FIG. 2 shows a second embodiment of the carbon dioxide recovery method of the present invention and a recovery apparatus for carrying out the method. Unlike the first embodiment, the recovery device 2 is different from the first embodiment in that the flow rate of the water vapor S supplied to the regeneration tower 20 is adjusted based on the water level of the condensed water stored in the gas-liquid separator 28. The amount of condensed water stored is determined from the change in the water level of the vessel 28, and this amount is used as the flow rate of water vapor discharged together with the recovered gas.

  Specifically, the steam supply system 40 ′ in this embodiment detects the water level of the condensed water in the gas-liquid separator 28 as a measurement unit that measures a physical property value for determining the amount of water vapor contained in the recovered gas. A water level gauge 48 is attached to the gas-liquid separator 28, and the control unit 43 ′ calculates the flow rate of water vapor contained in the recovered gas based on the water level measured by the water level gauge 48, and in accordance with this flow rate the water vapor at the aforementioned magnification. The flow rate of the water vapor S is adjusted by controlling the opening of the control valve 42 so that S is supplied to the regeneration tower 20. The water level meter 48 is electrically connected to the control unit 43 ′, and the water level data measured by the water level meter 48 is constantly sent to the control unit 43 ′, and the amount of increase in condensed water per unit time is calculated from the water level increase. The The increased amount is regarded as the amount of water contained in the recovered gas as water vapor, that is, the saturated water vapor amount of the recovered gas, and the supply rate is determined by integrating the above-mentioned magnifications, and this amount of water vapor S is supplied to the regeneration tower 20. Supply.

  In this case, since the recovered gas passing through the gas-liquid separator 28 contains some moisture, the amount of increase in condensed water determined by the water level gauge 48 is slightly smaller than the amount of water vapor discharged from the regeneration tower 20 together with the recovered gas. Can be less. In such a case, in order to compensate for this, using the saturated water vapor pressure Pw ′ at the temperature of the cooler 27 and the discharge flow rate V of the recovered gas, the deficient water vapor flow rate Vg ′ ( = V × Pw ′ / P), and this amount can be preset by the control unit 43 so as to be added to the water vapor flow rate Vg based on the water level data. The condensed water in the gas-liquid separator 28 is appropriately discharged so that the change in the water level can be measured in a timely manner. The recovery device 2 of FIG. 2 has an advantage that the device configuration is simple.

  Since the second embodiment is configured in the same manner as the first embodiment except for the above points, the description thereof is omitted.

In order to evaluate the relationship between the steam supply amount and the regenerative energy in the implementation of the present invention, in the recovery apparatus 1 of the first embodiment, a 30% by mass monoethanolamine aqueous solution is used as an absorbing liquid, and carbon dioxide recovery processing is performed. When performing, the pressure in the regeneration tower 20 is changed to examine the recovery rate and the regeneration energy (processing A1 to A4), and further, the steam S is supplied to the regeneration tower 20 so that the steam supply amount of the recovery rate and the regeneration energy. Table 1 shows the variation due to the above (processing B1 to B4, C1 to C4, D1 to D4). In this recovery process, the gas G supply rate is 7 Nm ³ / Hr, the absorption liquid circulation rate is 42 L / Hr, the temperature of the absorption tower 10 is 40 to 60 ° C., and the absorption liquid of the regeneration tower 20 by the steam heater 22 is used. The heating temperature was the boiling point, and the temperature of the steam S supplied to the regeneration tower 20 was the same as the boiling point. “Energy reduction amount” in Table 1 is the percentage of the amount of regenerative energy reduced from the regenerative energy of treatment A4 (absorption tower pressure: 0 kPaG, regenerative tower pressure: 100 kPaG, water vapor: none) as a reference (100%). Indicates.

  According to the results in Table 1, it is clear that the renewable energy can be reduced by supplying water vapor, but the tendency of reducing the renewable energy differs depending on the supply amount. Specifically, in the state where steam is not supplied, if the pressure in the regeneration tower is low, the regeneration energy increases. However, if steam exceeding the saturation amount of the recovered gas is supplied, conversely, the pressure in the regeneration tower is higher. The regenerative energy is large, and the energy reduction effect at atmospheric pressure is more remarkable than the pressurized state (processing D1 to D4). When the supply amount of water vapor is equal to the saturation amount of the recovered gas, energy can be reduced to the same extent regardless of the pressure in the regeneration tower (processing C1 to C4).

  If the relationship between the amount of steam supplied in Table 1 and the amount of reduction in regeneration energy is graphed, when the pressure in the regeneration tower is set to atmospheric pressure, steam that is about 0.4 times or more the saturated steam amount of the recovered gas It can be seen that, if supplied, a regenerative energy reduction effect equivalent to or higher than the effect of pressurization of 100 kPaG can be obtained. Moreover, when the supply amount of water vapor is about 1.2 ± 0.2 times the saturated water vapor amount of the recovered gas, the amount of reduction in the reduction amount of the regeneration energy due to the pressure of the regeneration tower is small, and the control of the energy supply is simple. From the viewpoint of making it, it is better to set it to about 1.2 ± 0.2 times. However, considering the influence of water vapor condensation, the upper limit is preferably about 1.2 times, and preferably about 0.4 to 1.0 times. Practically, it may be set as appropriate within a range of about 0.4 to 1.2 times in consideration of errors and the like.

In Table 2 below, the influence of the temperature of the supplied steam is evaluated, and a process C5 in which the steam temperature in the process C1 of Table 1 is set to 200 ° C. is described. According to this, it is understood that the carbon dioxide recovery rate does not substantially change depending on the temperature of the water vapor, but if the temperature of the water vapor is increased, the energy supply efficiency is improved by the direct supply of thermal energy, thereby contributing to energy reduction. The

If not supplied steam, carbon dioxide regeneration heat in the processing conditions to be 4.0GJ / t-CO ₂ mm, equivalent to the latent heat of vaporization of about 1.2GJ / t-CO ₂ of which is lost from the absorption liquid A2 However, in the state where water vapor is supplied, the latent heat of vaporization lost is reduced to about 0.6 GJ / t-CO ₂ or less, and the regeneration heat of carbon dioxide can be reduced to about 3.4 GJ / t-CO ₂ or less.

  If the pressure in the regeneration tower 20 is low, the carbon dioxide recovery rate in the absorption tower is decreased, which is considered to be due to a decrease in the regeneration ratio of the absorption liquid. Even if the pressure of 20 decreases, the regenerative energy does not increase, and the carbon dioxide recovery rate does not change much when water vapor is not supplied. In other words, the steam itself does not have an action of releasing carbon dioxide, but it is considered that the supply of steam suppresses the loss of regeneration energy and releases carbon dioxide efficiently. Therefore, by replenishing the regeneration tower 20 with water vapor, it is possible to reduce the heating temperature and energy required for the regeneration of the absorbing liquid, improve the efficiency of use of energy in the regeneration, and promote the regeneration efficiently. As a result, a decrease in the absorption rate in the absorption tower 10 is prevented.

  Depending on the content of the exhaust gas to be treated, there may be situations where a high carbon dioxide recovery rate is not required. In that case, it is preferable that it is easy to change the setting of the processing conditions so as to reduce the operation cost and the equipment burden. The carbon dioxide recovery rate of the absorption liquid changes depending on the circulation speed of the absorption liquid and the contact time with the exhaust gas. However, according to the above, it also changes depending on the pressure in the regeneration tower 20, in other words, the pressure in the regeneration tower. It can also be handled by control. In this case, in order to continue the proper supply of regenerative energy, it is preferable that the correction with a change in pressure is less, and the supply amount of water vapor is set to about 1.0 times the saturated water vapor amount of the recovered gas. This is preferable in adopting an energy supply means such as a reboiler because the correction of the regenerative energy to be supplied can be prevented from becoming complicated.

  INDUSTRIAL APPLICABILITY The present invention is useful for reducing the amount of carbon dioxide released and its influence on the environment, for example, in the treatment of carbon dioxide-containing gas discharged from facilities such as thermal power plants, ironworks, and boilers. The cost required for the carbon dioxide recovery process can be reduced, and a carbon dioxide recovery device that can contribute to energy saving and environmental protection can be provided.

1, 2: Recovery device, 10: Absorption tower, 20: Regeneration tower, 30: Cooling tower,
40, 40 ′: water vapor supply system, 11, 21, 31: filler,
12, 15, 23, 32: pump, 13: cooling condensing part,
14, 25, 27, 33: cooler, 16: supply path,
17: reflux path, 18: check valve, 19, 29: pressure regulating valve,
22: Steam heater, 22 ': Circuit, 24: Heat exchanger,
26: Condensing unit, 28: Gas-liquid separator, 41: Measuring unit, 42: Control valve,
43, 43 ′: control unit, 44: flow meter, 45: thermometer,
46: Pressure gauge, 47: Mass flow meter, 48: Water level gauge,
G, G ′: gas, A1, A2: absorbing liquid, C: recovered gas.

Claims (12)

An absorption tower in which a gas containing carbon dioxide is brought into contact with an absorption liquid, and the absorption liquid absorbs carbon dioxide;
A regeneration tower for heating the absorption liquid that has absorbed carbon dioxide in the absorption tower to release carbon dioxide from the absorption liquid to regenerate the absorption liquid;
A measuring unit for measuring the amount of water vapor contained in the recovered gas containing carbon dioxide discharged from the regeneration tower;
A water vapor supply system for supplying the regeneration tower with water vapor in an amount 0.4 to 1.0 times the flow rate of water vapor contained in the recovered gas, using the amount of water vapor of the recovered gas measured by the measuring unit as a reference amount; A carbon dioxide recovery device.   The carbon dioxide recovery device according to claim 1, wherein the temperature of the water vapor supplied by the water vapor supply system is equal to or higher than the temperature of the absorbing liquid heated in the regeneration tower. The measurement unit detects a physical property value for determining a flow rate of water vapor contained in the recovered gas,
The water vapor supply system includes:
In order to adjust the flow rate of the water vapor supplied to the regeneration tower to the ratio, the control valve capable of adjusting the flow rate of the water vapor supplied to the regeneration tower based on the physical property value measured by the measurement unit The carbon dioxide recovery device according to claim 1, further comprising: a control unit that controls the control valve. Furthermore, it has a pressure control valve capable of adjusting the inside of the regeneration tower to a pressurized state,
The measurement unit has a thermometer and a pressure gauge for measuring the temperature and pressure of the recovered gas as the physical property values,
Wherein, based on the temperature and pressure of the collected gas to be measured by the measuring unit, and calculates the saturated vapor pressure of the collected gas steam supplied before Symbol regenerator using the saturated vapor pressure The carbon dioxide recovery apparatus according to claim 3 , wherein the flow rate is determined. The measuring unit further includes a flow meter for measuring the flow rate of the recovered gas, and the control unit is configured such that a ratio between the flow rate of the recovered gas and the flow rate of water vapor supplied to the regeneration tower is equal to that of the recovered gas. 5. The carbon dioxide according to claim 4 , wherein the control valve is controlled so as to supply water vapor at the ratio with the flow rate of the water vapor being equal to a ratio of a pressure and a saturated water vapor pressure of the recovered gas as the reference amount. Recovery equipment. The measurement unit has a water level meter that measures the water level of the condensed water separated from the recovered gas as the physical property value,
The control unit calculates a flow rate of water vapor contained in the recovered gas based on a change in the water level of the condensed water measured by the measurement unit, and supplies the calculated flow rate of water vapor as a reference amount to the regeneration tower. The carbon dioxide recovery device according to claim 3 , wherein the flow rate of the water vapor to be determined is determined. An absorption step in which a gas containing carbon dioxide is brought into contact with an absorbing solution under pressure, and the absorbing solution absorbs carbon dioxide;
A regeneration step of regenerating the absorbing liquid by heating the absorbing liquid that has absorbed carbon dioxide in the absorbing step to release carbon dioxide from the absorbing liquid;
A measurement step of measuring the amount of water vapor contained in the recovered gas containing carbon dioxide discharged from the regeneration step;
A steam supply step of supplying the regeneration tower with water vapor in an amount 0.4 to 1.0 times the flow rate of water vapor contained in the recovered gas, based on the water vapor amount of the recovered gas measured in the measuring step. A method for recovering carbon dioxide. The method for recovering carbon dioxide according to claim 7 , wherein the temperature of the water vapor supplied in the water vapor supply step is equal to or higher than the temperature of the absorption liquid heated in the regeneration step. In the measurement step, a physical property value for determining the flow rate of water vapor contained in the recovered gas is detected,
The steam supply step includes
An adjustment step for adjusting a flow rate of water vapor supplied to the regeneration step, and a control step for controlling the adjustment in the adjustment step based on the physical property value measured in the measurement step so that the flow rate becomes the ratio. The method for recovering carbon dioxide according to 7 or 8 . The pressure in the regeneration tower step can be adjusted to a pressurized state,
In the measurement step, the temperature and pressure of the recovered gas are measured as the physical property values,
In the control step, on the basis of the temperature and pressure of the collected gas to be measured in the measuring step, the steam supply before Symbol regeneration step using the saturated water vapor pressure and calculates the saturated vapor pressure of the collected gas The method for recovering carbon dioxide according to claim 9 , wherein the flow rate is determined. In the measurement step, the flow rate of the recovered gas is further measured, and in the control step, the ratio between the flow rate of the recovered gas and the flow rate of water vapor supplied to the regeneration step is the pressure of the recovered gas and the recovered gas. The flow rate of the carbon dioxide according to claim 10 , wherein the adjustment of the flow rate in the adjustment step is controlled so as to supply water vapor in the ratio, with the flow rate of the water vapor being equal to the ratio of the saturated water vapor pressure to the reference amount. Collection method. In the measurement step, the water level of the condensed water separated from the recovered gas is measured as the physical property value,
In the control step, the flow rate of water vapor contained in the recovered gas is calculated based on the change in the water level of the condensed water measured in the measurement step, and the flow rate of the calculated water vapor is used as the reference amount for the regeneration step. The method for recovering carbon dioxide according to claim 9 , wherein a flow rate of water vapor to be supplied is determined.

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