Patent Publication Number: US-2011068585-A1

Title: Method and system for capturing and utilizing energy generated in a flue gas stream processing system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 61/245,436, entitled “Method and System for Capturing and Utilizing Energy Generated in a Flue Gas Stream Processing System” filed on Sep. 24, 2009, the entirety of which is incorporated by reference herein. 
    
    
     FIELD 
     The disclosed subject matter relates to a system and method for removing carbon dioxide (CO 2 ) from a flue gas stream. More specifically, the disclosed subject matter relates to a system and method of capturing and utilizing energy generated during the removal of CO 2  from a flue gas stream. 
     BACKGROUND 
     Most of the energy used in the world is derived from the combustion of carbon and hydrogen-containing fuels such as coal, oil and natural gas. In addition to carbon and hydrogen, these fuels contain oxygen, moisture and contaminants such as ash, sulfur (often in the form of sulfur oxides, referred to as “SOx”), nitrogen compounds (often in the form of nitrogen oxides, referred to as “NOx”), chlorine, mercury, and other trace elements. Awareness regarding the damaging effects of the contaminants released during combustion triggers the enforcement of ever more stringent limits on emissions from power plants, refineries and other industrial processes. There is an increased pressure on operators of such plants to achieve near zero emission of contaminants. 
     Numerous processes and systems have been developed in response to the desire to achieve near zero emission of contaminants. Systems and processes include, but are not limited to desulfurization systems (known as wet flue gas desulfurization systems (“WFGD”) and dry flue gas desulfurization systems (“DFGD”)), particulate filters (including, for example, bag houses, particulate collectors, and the like), as well as the use of one or more sorbents that absorb contaminants from the flue gas. Examples of sorbents include, but are not limited to, activated carbon, ammonia, limestone, and the like. 
     It has been shown that ammonia, as well as amine solutions, efficiently removes CO 2 , as well as other contaminants, such as sulfur dioxide (SO 2 ) and hydrogen chloride (HCl), from a flue gas stream. In one particular application, absorption and removal of CO 2  from a flue gas stream with ammonia is conducted at a low temperature, for example, between zero (0) and twenty (20) degrees Celsius (0°-20° C.). 
     Removal of contaminants from a flue gas stream requires a significant amount of energy. Utilization of energy generated during the removal and processing of contaminants within a flue gas stream processing system may reduce expenses and resources required by the system. 
     SUMMARY 
     According to aspects illustrated herein, there is provided a process for utilizing energy generated within a flue gas processing system, the process comprising providing a carbon dioxide loaded solution to a regeneration system within a flue gas processing system; subjecting the carbon dioxide loaded solution to pressure in the regeneration system thereby removing carbon dioxide from the carbon dioxide loaded solution and generating a high pressure carbon dioxide stream and a reduced carbon dioxide containing solution; introducing at least a portion of the high pressure carbon dioxide stream to an expansion turbine to reduce the pressure of the high pressure carbon dioxide stream, thereby generating energy and a low pressure carbon dioxide stream; and utilizing the energy produced in the expansion turbine to generate power, thereby utilizing the energy generated within a flue gas processing system. 
     According to other aspects illustrated herein, there is provided a system for utilizing energy generated during processing of carbon dioxide removed from a flue gas stream, the system comprising: an absorbing system configured to receive a carbon dioxide containing flue gas stream, wherein the carbon dioxide containing flue gas stream contacts a carbon dioxide removing solution in the absorbing system to form a reduced carbon dioxide containing flue gas stream and a carbon dioxide loaded solution; a regeneration system configured to receive the carbon dioxide loaded solution, wherein the regeneration system generates a high pressure carbon dioxide stream and a reduced carbon dioxide containing solution; an expansion turbine configured to receive at least a portion of the high pressure carbon dioxide stream to reduce the pressure of the high pressure carbon dioxide stream to produce a low pressure carbon dioxide stream and energy; and a generator in communication with the expansion turbine, the generator utilizing the energy from the expansion turbine to generate electricity. 
     According to other aspects illustrated herein, there is provided a process for recycling energy generated during removal of carbon dioxide from a flue gas stream, the process comprising: providing a carbon dioxide containing flue gas stream to an absorbing system; contacting the carbon dioxide containing flue gas stream with a carbon dioxide removing solution, thereby removing carbon dioxide from the flue gas stream and forming a reduced carbon dioxide containing flue gas stream and a carbon dioxide loaded solution; subjecting the carbon dioxide loaded solution to a pressure in a range between 1723.7 kpascal and 3447.4 kpascal, thereby forming a high pressure carbon dioxide stream and a reduced carbon dioxide containing solution, wherein the high pressure carbon dioxide stream has a pressure in a range between 1723.7 kpascal and 3447.4 kpascal; reducing pressure of the high pressure carbon dioxide stream to form a low pressure carbon dioxide stream and energy, the low pressure carbon dioxide stream having a pressure in a range between 68.9 kpascal and 689.5 kpascal; and utilizing the energy to provide electricity to the absorbing system, thereby recycling energy generated during removal of carbon dioxide from a flue gas stream. 
     The above described and other features are exemplified by the following figures and detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike: 
         FIG. 1  is a schematic representation of a flue gas stream processing system utilized to remove contaminants from the flue gas stream. 
         FIG. 2  is an illustration of one embodiment of an absorbing system utilized in the system depicted in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     One embodiment, as shown in  FIG. 1 , includes a system  100  for removing contaminants from a flue gas stream  120 . Flue gas stream  120  is generated by combustion of a fuel in a furnace  122 . Flue gas stream  120  may include numerous contaminants, including, but not limited to, sulfur oxides (SOx), nitrogen oxides (NOx), as well as mercury (Hg), hydrochloride (HCl), particulate matter, CO 2 , and the like. While not shown in  FIG. 1 , flue gas stream  120  may undergo treatment to remove contaminants therefrom, such as, for example, treatment by a flue gas desulfurization process and particulate collector, which may remove SOx and particulates from the flue gas. 
     Still referring to  FIG. 1 , flue gas stream  120  may also undergo treatment to remove CO 2  therefrom by passing the flue gas stream  120  through an absorbing system  130 . While not shown in  FIG. 1 , it is contemplated that flue gas stream  120  may proceed through a cooling system prior to entering the absorbing system  130 . The cooling system may cool the flue gas stream  120  to a temperature below ambient temperature. 
     As shown in  FIG. 2 , the absorbing system  130  is configured to receive the CO 2  containing flue gas stream  120  (via an inlet or opening) to facilitate the absorption of CO 2  from the flue gas stream. Absorption of CO 2  from the flue gas stream  120  occurs by contacting the flue gas stream with a CO 2  removing solution  140  that is supplied to the absorbing system  130 . In one embodiment, CO 2  removing solution  140  is an ammoniated solution or slurry  140  that includes dissolved ammonia and CO 2  species in a water solution and may also include precipitated solids of ammonium bicarbonate. In another embodiment, CO 2  removing solution  140  is an amine solution. 
     In one embodiment, the absorbing system  130  includes a first absorber  132  and a second absorber  134 . Absorbing system  130  is not limited in this regard and, in other embodiments, may include more or less absorbers than illustrated in  FIG. 2 . 
     As shown in more detail in  FIG. 2 , CO 2  removing solution  140  is introduced to absorbing system  130 . In one embodiment, the CO 2  removing solution  140  is introduced to the absorbing system in first absorber  132  in a direction A that is countercurrent to a flow of flue gas stream  120  in direction B in the absorbing system  130 . As the CO 2  removing solution  140  contacts flue gas stream  120 , CO 2  present in the flue gas stream is absorbed and removed therefrom, thereby forming a carbon dioxide loaded solution  142  and a reduced carbon dioxide containing flue gas stream  150  exiting the absorbing system  130 . At least a portion of the resulting carbon dioxide loaded solution  142  is transported from the absorbing system  130  to a regeneration system  136  ( FIG. 1 ) downstream of the absorbing system. In the regeneration system  136 , the carbon dioxide loaded solution  142  may be regenerated to form the CO 2  removing solution  140  that is introduced to the absorbing system  130 . 
     While the CO 2  removing solution  140  is shown in the illustrated embodiment as being introduced into the first absorber  132 , the system  100  is not limited in this regard as the CO 2  removing solution may instead be introduced into the second absorber  134  or be introduced to both the first absorber and the second absorber. 
     In one embodiment, the absorbing system  130  operates at a low temperature, particularly at a temperature less than about twenty degrees Celsius (20° C.). In one embodiment, the absorbing system  130  operates at a temperature range of between about zero degrees Celsius to about twenty degrees Celsius (0° to 20° C.). In another embodiment, the absorbing system  130  operates at a temperature range between about zero degrees Celsius to about ten degrees Celsius (0° to 10° C.). However, the system is not limited in this regard, since it is contemplated that the absorbing system may be operated at any temperature. 
     Still referring to  FIG. 2 , the reduced carbon dioxide containing flue gas stream  150  may be subjected to further contaminant removal processes and systems prior to emission to the environment. The carbon dioxide loaded solution  142  is provided to the regeneration system  136 . 
     Referring back to  FIG. 1 , regeneration system  136  may be any regeneration system configured to receive carbon dioxide loaded solution  142  and facilitate the removal of CO 2  from the carbon dioxide loaded solution to form a reduced carbon dioxide containing solution  137  and a high pressure carbon dioxide stream  138 . 
     As shown in  FIG. 1 , regeneration system  136  includes an inlet  139  that introduces carbon dioxide loaded solution  142  into the regeneration system. While  FIG. 1  illustrates inlet  139  located at a specific position on the regeneration system  136 , it is contemplated that inlet  139  may be located at any position on the regeneration system. 
     In one embodiment, regeneration system  136  employs steam (not shown) to facilitate the removal of CO 2  from the carbon dioxide loaded solution  142 . In another embodiment, the regeneration system is operated at a pressure in the range between about 1723.7 kpascal (about 250 pounds per square inch [gauge] (psig)) and about 3447.4 kpascal (about 500 pounds per square inch [gauge] (psig)) to remove CO 2  from the carbon dioxide loaded solution  142 . In another embodiment, the regeneration system  136  may utilize a combination of steam and pressure to remove CO 2  from the carbon dioxide loaded solution  142 . 
     As shown in  FIG. 1 , the reduced carbon dioxide containing solution  137  generated in regeneration system  136  may be provided to the absorbing system  130  for use with the CO 2  removing solution  140 . While not shown in the illustrated embodiment, the reduced carbon dioxide containing solution  137  may combine with fresh CO 2  removing solution  140  or CO 2  removing solution that is recycled from the absorbing system  130 . Alternatively, and while not shown in the illustrated embodiment, the reduced carbon dioxide containing solution  137  may be directly provided to the absorbing system  130  without combining with fresh CO 2  removing solution  140  or CO 2  removing solution recycled from the absorbing system. 
     In one embodiment, the carbon dioxide loaded solution  142  is subjected to pressure in the regeneration system  136 . Operation of regeneration system  136  at a pressure in the range between about 1723.7 kpascal (about 250 pounds per square inch [gauge] (psig)) to about 3447.4 kpascal (about 500 pounds per square inch [gauge] (psig)) generates a high pressure carbon dioxide stream  138 . 
     The high pressure carbon dioxide stream  138  has a pressure in the range of between about 1723.7 kpascal (about 250 pounds per square inch [gauge] (psig)) and about 3447.4 kpascal (about 500 pounds per square inch [gauge] (psig)). In one embodiment, the pressure of the high pressure carbon dioxide stream  138  is in a range between about 2068.4 kpascal (about 300 psig) and about 3447.4 kpascal (about 500 psig). In another embodiment, the pressure of the high pressure carbon dioxide stream  138  is in a range between about 2068.4 kpascal (about 300 psig) and about 3102.6 kpascal (about 450 psig). In a further embodiment, the pressure of the high pressure carbon dioxide stream  138  is about 2068.4 kpascal (about 300 psig). 
     As shown in  FIG. 1  high pressure carbon dioxide stream  138  is provided to a heat exchanger  138   a  and subsequently provided to an expansion turbine  160 . In one embodiment, after proceeding through heat exchanger  138   a,  at least a portion of high pressure carbon dioxide stream  138  may be provided to a dehydration unit  170 , while a separate portion of the high pressure carbon dioxide stream  138  is provided to the expansion turbine  160 . 
     Dehydration unit  170  removes excess moisture from the high pressure carbon dioxide stream  138  before recirculating that portion of the high pressure carbon dioxide stream back to the regeneration system  136 . The moisture content of the high pressure carbon dioxide stream  138  recirculated to regeneration system  136  will be in the range between about 100 parts per million by volume (ppmv) and 600 ppmv, depending on the system and application. 
     While not shown, it is contemplated that all of the high pressure carbon dioxide stream  138  may be provided from the regeneration system  136  to the expansion turbine  160 . 
     Expansion turbine  160  is configured to receive at least a portion of high pressure carbon dioxide stream  138  (by an inlet or opening) to reduce the pressure of the high pressure carbon dioxide stream and produce a low pressure carbon dioxide stream  162  and energy  164 . 
     In one embodiment, the pressure of high pressure carbon dioxide stream  138  is reduced at least fifty percent (50%) to form the low pressure carbon dioxide stream  162 . In another embodiment, the pressure of high pressure carbon dioxide stream  138  is reduced at least seventy five percent (75%) to form the low pressure carbon dioxide stream  162 . 
     Specifically, in one embodiment, the pressure of low pressure carbon dioxide stream  162  is in a range between about 68.9 kpascal (about 10 psig) and about 1066.6 kpascal (about 140 psig). In another embodiment, the pressure of low pressure carbon dioxide stream  162  is in a range between about 68.9 kpascal (about 10 psig) and about 689.5 kpascal (about 100 psig). In another embodiment, the pressure of low pressure carbon dioxide stream  162  is in a range between about 68.9 kpascal (about 10 psig) and about 620.5 kpascal (about 90 psig). In a further embodiment, the pressure of low pressure carbon dioxide stream  162  is in a range between about 137.9 kpascal (about 20 psig) and about 206.8 kpascal (30 psig). In yet a further embodiment, the pressure of low pressure carbon dioxide stream  162  is about 137.9 kpascal (about 20 psig). 
     As shown in  FIG. 1 , low pressure carbon dioxide stream  162  is sent to a cooler  165  prior to providing a low pressure carbon dioxide stream  162   a  to a storage vessel  166 . Low pressure carbon dioxide stream  162  may be liquefied and cooled to a temperature between about 10 degrees and 80 degrees Celsius in the cooler  165 . The temperature reduction of the low pressure carbon dioxide stream  162  resulting from the pressure expansion in the expansion turbine  160  reduces the energy required by cooler  165  to lower the temperature of the low pressure carbon dioxide stream to the liquidification point. 
     In one embodiment, the low pressure carbon dioxide stream  162   a  is stored in the storage vessel  166  only temporarily before it is transported to another location for use or further processing. 
     Reducing the pressure of high pressure carbon dioxide stream  138  to generate low pressure carbon dioxide stream  162  in expansion turbine  160  also generates energy  164 . In one embodiment, energy  164  is in the form of work that rotates a shaft of the expansion turbine  160 , which in turn, is used to drive a piece of equipment, such as a generator  167 . As can be appreciated, the high pressure carbon dioxide stream  138  undergoes an isentropic expansion in expansion turbine  160  and exits as low pressure carbon dioxide stream  162  having a low temperature. 
     As shown in  FIG. 1 , the energy  164  is utilized by the generator  167  to generate power  168 . Generator  167  may be any type of generator that facilitates the transformation of energy  164  provided by the expansion turbine  160  to generate power  168 . In one embodiment, generator  167  is an electric generator for generating electricity as the power  168 . 
     In another embodiment, expansion turbine  160  may be coupled to a separate piece of equipment (not shown), such as a pump, a compressor, a refrigeration compressor, a fan, a blower, or the like. Energy  164  may be used to provide power to the equipment coupled to the expansion turbine  160 , i.e., the energy may be the prime mover of the equipment coupled to the expansion turbine. 
     Power  168  produced by the generator  167  may be utilized within system  100 . For example, the power  168  may be provided to and used by the power plant  122 . In another example, the power  168  may be provided to and used by various devices within system  100 , including, but not limited to pumps within absorbing system  130 , pumps in communication with the regeneration system  136 , coolers and condensers used within system  100 , fans used within system  100 , recycle pumps and ball mills used in connection with wet flue gas desulfurization systems used in system  100 . Alternatively, or in addition to providing power  168  to devices within system  100 , power  168 , in the form of electricity, may be provided to a consumer electric grid  180  or another device or system outside of the system  100 . 
     Utilization of power  168  within the system  100  alleviates, reduces or eliminates the need to obtain power from a source outside of the system. By alleviating, reducing or eliminating the need to obtain power from an outside source the system  100  may be more efficient and/or cost effective than a system that obtains power from an outside source. Efficiency and cost reduction may also be experienced by systems and devices, such as consumer electric grid  180 , when power  168  is sent outside of system  100 . 
     The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. 
     While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.