Abstract:
The present invention provides a method of regenerating a carbon dioxide absorbent which absorbs carbon dioxide emitted from various anthropogenic sources including fossil fuel combustion processes, industrial production processes, and natural gas processing. In the method, the absorbent is preheated using heat generated in a process of compressing the separated carbon dioxide in a compressor and the preheated absorbent is delivered to an absorbent flow control tank, before the used absorbent is delivered to a regeneration tower, thereby improving energy efficiency.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2008-0054098 filed Jun. 10, 2008, the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    (a) Technical Field 
         [0003]    The present invention relates to a method of regenerating a carbon dioxide absorbent. 
         [0004]    (b) Background Art 
         [0005]    Carbon dioxide (CO 2 ) is known to contribute to global warming and many approaches have been produced to reduce the amount of carbon dioxide emitted from various anthropogenic sources including fossil fuel combustion processes, industrial production processes, and natural gas processing. 
         [0006]    The methods of reducing the CO 2  emissions are broadly classified into reduction in energy consumption, capture and storage of CO 2 , and use of alternative energy. Among them, the CO 2  capture and storage method has been more intensively studied since it has less effect on industrial activity and the carbon dioxide captured by the methods can be reused. 
         [0007]    CO 2  can be captured by various ways including absorption process, adsorption process, or membrane separation process. The absorption process based capture method is considered superior to the other methods since it can treat high-volume exhaust gas with high removal efficiency even at low CO 2  concentration in the range of 8 to 15% contained in combustion exhaust gases emitted from various sources. 
         [0008]      FIG. 1  is a schematic diagram showing a conventional apparatus for regenerating a carbon dioxide absorbent by absorption process. 
         [0009]    As shown in  FIG. 1 , the exhaust gas containing carbon dioxide is brought into contact with an absorbent at a reaction tower, called an absorption tower  1 , in the temperature range of about 50° C. so that the carbon dioxide in the exhaust gas is absorbed in the absorbent. Next, the absorbent in which the carbon dioxide has been absorbed is heated in the temperature range of about 120° C. at a reaction tower, called a regeneration tower  2 , to separate the carbon dioxide from the absorbent. Then, the separated carbon dioxide is discharged to the top of the regeneration tower  2  and the absorbent is regenerated. Vaporized absorbent discharged along with the separated carbon dioxide is cooled in a cooler  3 , separated in a separation drum  4 , and refluxed to the regeneration tower  2 . Gaseous carbon dioxide is compressed by a compressor and stored in a storage tank  5  at a high pressure. 
         [0010]    This method, however, has a problem in that high energy consumption is required in the regeneration process of separating CO 2  from the absorbent to regenerate the absorbent. 
         [0011]    Accordingly, there is a need for a new method that can regenerate the absorbent more efficiently and with less energy. 
         [0012]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY OF THE DISCLOSURE 
       [0013]    In one aspect, the present invention provides a method of regenerating a carbon dioxide absorbent, comprising: contacting carbon dioxide with a carbon dioxide absorbent provided in an absorption tower such that the carbon dioxide absorbent absorbs the carbon dioxide; introducing to a multistage regeneration tower the carbon dioxide absorbent which has absorbed the carbon dioxide in the absorption tower; heating the introduced carbon dioxide absorbent in the regeneration tower to separate carbon dioxide from the carbon dioxide absorbent and discharging the separated carbon dioxide absorbent through a first predetermined stage of the regeneration tower and the separated carbon dioxide through a second predetermined stage of the regeneration tower, thereby regenerating the carbon dioxide absorbent; introducing the separated carbon dioxide to a cooler; and introducing the cooled carbon dioxide to a compressor for compressing the cooled carbon dioxide so as to be stored in a storage tank, wherein thermal energy generated when the cooled carbon dioxide is compressed in the compressor is used to preheat the carbon dioxide absorbent before the carbon dioxide absorbent is introduced to the regeneration tower. 
         [0014]    The above and other features of the invention are discussed infra. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments thereof illustrated the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present invention, and wherein: 
           [0016]      FIG. 1  is a schematic diagram showing a conventional apparatus for regenerating a carbon dioxide absorbent; and 
           [0017]      FIG. 2  is a schematic diagram showing an apparatus for regenerating a carbon dioxide absorbent in accordance with a preferred embodiment of the present invention. 
       
    
    
       [0018]    Reference numerals set forth in the Drawings includes reference to the following elements as further discussed below: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 10: reservoir 
                 11: (carbon dioxide) compressor 
               
               
                   
                 12: high-pressure absorbent 
               
               
                   
                 flow control tank 
               
               
                   
                 13: first heat exchanger 
                 14: second heat exchanger 
               
               
                   
                 15: regeneration tower 
                 16: cooler 
               
               
                   
                 17: absorbent heater 
                 18: separation drum 
               
               
                   
                 20: storage tank 
               
               
                   
                   
               
             
          
         
       
     
         [0019]    It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
         [0020]    In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
       DETAILED DESCRIPTION 
       [0021]    Hereinafter reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
         [0022]    A method of regenerating a carbon dioxide absorbent in accordance with a preferred embodiment of the present invention can reduce the cost of regenerating carbon dioxide in such a manner that an absorbent used to absorb carbon dioxide is preheated using heat generated in a process of compressing the carbon dioxide to store the recovered carbon dioxide. Preferably, the absorbent may be further preheated using waste heat when the absorbent condensed in a separation drum of a regeneration tower is refluxed to the regeneration tower, thus improving thermal efficiency of the top of the regeneration tower. 
         [0023]    In detail, carbon dioxide is contacted with a carbon dioxide absorbent provided in an absorption tower. In the absorption tower, the carbon dioxide absorbent absorbs the carbon dioxide. The carbon dioxide absorbent which has absorbed the carbon dioxide in the absorption tower is then introduced to a multistage regeneration tower. In the regeneration tower, the introduced carbon dioxide absorbent is heated so as to separate carbon dioxide from the carbon dioxide absorbent. The separated carbon dioxide absorbent is discharged through a first predetermined stage of the regeneration tower and the separated carbon dioxide is discharged through a second predetermined stage of the regeneration tower, thereby regenerating the carbon dioxide absorbent. The separated carbon dioxide is introduced to a cooler where it is cooled. The cooled carbon dioxide is introduced to a compressor where it is compressed so as to be stored in a storage tank. Thermal energy generated when the cooled carbon dioxide is compressed in the compressor is used to preheat the carbon dioxide absorbent before the carbon dioxide absorbent is introduced to the regeneration tower. 
         [0024]    The carbon dioxide absorbent which has absorbed the carbon dioxide in the absorption tower is suitably stored in a reservoir before being introduced to the regeneration tower. The carbon dioxide absorbent stored in the reservoir is suitably delivered to the compressor provided with a heat exchanger therein by which the carbon dioxide absorbent is preheated before being introduced to the regeneration tower. The preheated carbon dioxide absorbent is suitably stored in an absorbent flow control tank before being introduced to the regeneration tower. The carbon dioxide absorbent stored in the reservoir is suitably delivered to a first heat exchanger where it is heat-exchanged with the carbon dioxide absorbent heated in and discharged from the regeneration tower, and then introduced into the regeneration tower. 
         [0025]    A portion of the carbon dioxide absorbent can be vaporized and discharged through the second predetermined stage of the regeneration tower with the separated carbon dioxide. The vaporized carbon dioxide absorbent and the separated carbon dioxide discharged through the second predetermined stage of the regeneration tower, after being cooled in the cooler, are suitably delivered to a separation drum in which the vaporized carbon dioxide absorbent is condensated. The condensated carbon dioxide absorbent is suitably delivered to a second heat exchanger where it is heat-exchanged with the carbon dioxide absorbent discharged from the first heat exchanger, and then introduced into a third predetermined stage of the regeneration tower. The carbon dioxide absorbent discharged from the first heat exchanger is suitably delivered to the absorption tower after being heat-exchanged with the condensated carbon absorbent in the second heat exchanger. 
         [0026]    In the above embodiments, the first, second and third stages of the regeneration tower can be designed to be identical or different. 
         [0027]    An apparatus and method for regenerating a carbon dioxide absorbent in accordance with a preferred embodiment of the present invention will be described referring to  FIG. 2 . 
         [0028]    An absorbent provided in an absorption tower under atmospheric pressure is brought into contact with exhaust gas, containing carbon dioxide so as to absorb the carbon dioxide. The absorbent that has absorbed the carbon dioxide is stored in a reservoir  10  (e.g., at a temperature of about 50° C.) and delivered to a carbon dioxide compressor  11 . 
         [0029]    The thus delivered absorbent absorbs (exchanges) thermal energy generated when the carbon dioxide is compressed in the carbon dioxide compressor  11 , using a heat exchanger mounted in the carbon dioxide compressor  11 . It is heated (e.g., to about 90° C.) and is then delivered to a high-pressure absorbent flow control tank  12 . 
         [0030]    The absorbent delivered to the absorbent flow control tank  12  is stored for a predetermined period of time to control the absorbent flow and flows in a first heat exchanger  13  to be heat-exchanged with the absorbent discharged from a bottom stage of a regeneration tower  15 . An absorbent heater  17  is provided in or near the bottom stage of the regeneration tower. The absorbent discharged from the bottom stage of the regeneration tower  15  is heated (e.g., to a temperature of about 100° C.) by the absorbent heater  17  before being introduced to the first heat exchanger  13 . Accordingly, the absorbent delivered to the absorbent flow control tank  12  is heated by this heat exchange (e.g., to a temperature of about 97° C.) before being introduced into a top stage of the regeneration tower  15 . 
         [0031]    The absorbent introduced into the top of the regeneration tower  15  is further heated as it passes through a filler in the regeneration tower  15 , and the carbon dioxide is separated and discharged from a top stage of the regeneration tower  15 . At this time, a portion of the absorbent is vaporized. The vaporized absorbent and carbon dioxide, which contain high concentration (e.g., 99% or higher) of carbon dioxide, are discharged from the top stage of the regeneration tower  15  and are transferred to a cooler  16  where they are cooled (e.g., to about 60° C.). The cooled vaporized absorbent and carbon dioxide are then transferred to a separation drum  18 . 
         [0032]    The absorbent is condensated in the separation drum  18 . The condensated absorbent is then transferred to a second heat exchanger  14  where it is heat-exchanged with the absorbent (e.g., at about 92° C.) delivered from the first heat exchanger  13 . The condensated absorbent is heated by this heat exchange (e.g., to about 82° C.) and is refluxed to a top stage of the regeneration tower  15 . On the other hand, the absorbent the absorbent delivered from the first heat exchanger  13  is delivered to the absorption tower. 
         [0033]    The carbon dioxide discharged from the separation drum is compressed at a high pressure by the carbon dioxide compressor  11 , and then stored in a storage tank  20 . Although the carbon dioxide compressor  11  is formed in four stages in  FIG. 2 , the number of kind of the compressor can be designed without limitation as long as it can recover the heat generated in the process of compressing carbon dioxide. 
         [0034]    As described above, the method of regenerating a carbon dioxide absorbent in accordance with the present invention uses the heat generated in the process of compressing the carbon dioxide separated from the used absorbent and in the process of regenerating the absorbent for preheating the absorbent, thus effectively reducing the cost of regenerating the absorbent. Furthermore, with the improvement of thermal efficiency, it is possible to reduce the capacity of the regeneration tower and boiler, thus reducing the facility investment cost. 
         [0035]    The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.