Abstract:
A method for reducing energy requirements of a CO 2  capture system comprises: contacting a flue gas stream with a CO 2  lean absorbent stream in an absorber, thereby removing CO 2  from the flue gas and providing a CO 2  rich absorbent stream; heating a first portion of the CO 2  rich absorbent stream using heat from the CO 2  lean absorbent stream, and providing the heated first portion of the CO 2  rich absorbent stream to a regenerator; providing a second portion of the CO 2  rich absorbent stream to the regenerator, wherein the heated first portion is hotter than the second portion and the heated first portion is provided to the regenerator at a lower elevation in the regenerator relative to that of the second portion.

Description:
The present utility patent application claims priority to U.S. Provisional Application No. 61/382,205 filed on Sep. 13, 2010. 
    
    
     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 for reducing energy requirements of a CO 2  capture system. 
     BACKGROUND 
     In the combustion of a fuel, such as coal, oil, peat, waste, etc., in a combustion plant, such as a power plant, a hot process gas is generated, often referred to as a flue gas, containing, among other components, carbon dioxide, CO 2 . The negative environmental effects of releasing carbon dioxide into the atmosphere have been widely recognized, and have resulted in the development of systems and processes adapted for removing carbon dioxide from the hot process gas generated in the combustion of the above mentioned fuels. 
     In various systems/methods for CO 2  removal, an absorber vessel is provided in which an ionic solution is contacted in counter current flow with a flue gas stream containing CO 2 . One system and process previously disclosed is a single-stage chilled ammonia based system and method for removal of CO 2  from a post-combustion flue gas stream. Such a system and process has been proposed and taught in published US Patent Application Publication 2008/0072762 entitled Ultra Cleaning of Combustion Gas Including the Removal of CO 2 , which is incorporated by reference herein in its entirety. In the chilled ammonia system, the ionic solution is composed of, for example, water and ammonium ions, bicarbonate ions, carbonate ions, and/or carbamate ions. In other systems, it is contemplated that the ionic solution may be an amine. It is also contemplated that the ionic solution may be promoted by an enzyme (e.g., carbonic anhydrase) or amine (e.g., piperazine). 
     The absorber vessel is configured to receive a flue gas stream (FG) originating from, for example, the combustion chamber of a fossil fuel fired boiler. It is also configured to receive a CO 2  lean ionic solution supply from a regeneration system. The lean ionic solution is introduced into the vessel via a liquid distribution system while the flue gas stream FG is also received by the absorber vessel via a flue gas inlet. 
     The ionic solution is put into contact with the flue gas stream via a gas-liquid contacting device (hereinafter, mass transfer device, MTD) used for mass transfer and located in the absorber vessel and within the path that the flue gas stream travels from its entrance via an inlet at a bottom portion of the absorber vessel to its exit at a top portion of the absorber vessel. The MTD may be, for example, one or more commonly known structured or random packing materials, or a combination thereof. 
     The ionic solution is introduced at the top of the MTD and falls downward through the MTD coming into contact with the flue gas stream FG that is rising upward (opposite the direction of the ionic solution) and through the MTD. 
     Once contacted with the flue gas stream, the ionic solution acts to absorb CO 2  from the flue gas stream, thus making the ionic solution “rich” with CO 2  (rich solution). The rich ionic solution continues to flow downward through the mass transfer device and is then collected in the bottom of the absorber vessel. The rich ionic solution is then regenerated via a regenerator system to release the CO 2  absorbed by the ionic solution from the flue gas stream. The CO 2  released from the ionic solution may then be output to storage or other predetermined uses/purposes. Once the CO 2  is released from the ionic solution, the ionic solution is said to be “lean”. The lean ionic solution is then again ready to absorb CO 2  from a flue gas stream and may be directed back to the liquid distribution system whereby it is again introduced into the absorber vessel. 
     While CO 2  capture systems are effective in removing CO 2  resulting from power generation, in doing so they consume power that would otherwise be used elsewhere. In other words, CO 2  capture systems can place a “parasitic load” on the power generation plant. Thus, there is an ongoing need to reduce the parasitic load that CO 2  capture systems place on the power generation plant. 
     SUMMARY 
     According to aspects illustrated herein, there is provided a method for reducing energy requirements of a CO 2  capture system, the method comprising: contacting a flue gas stream with a CO 2  lean absorbent stream in an absorber, thereby removing CO 2  from the flue gas and providing a CO 2  rich absorbent stream; heating a first portion of the CO 2  rich absorbent stream using heat from the CO 2  lean absorbent stream, and providing the heated first portion of the CO 2  rich absorbent stream to a regenerator; providing a second portion of the CO 2  rich absorbent stream to the regenerator, wherein the heated first portion is hotter than the second portion and the heated first portion is provided to the regenerator at a lower elevation in the regenerator relative to that of the second portion. 
     In one embodiment, the method further comprises: separating a gaseous CO 2  from the heated first portion prior to providing the heated first portion to the regenerator; and compressing the gaseous CO 2  and providing the compressed gaseous CO 2  to the regenerator at a lower elevation in the regenerator relative to that of the liquid portion. In another aspect, after separating the gaseous CO 2  from the heated first portion and prior to providing the first portion to the regenerator, the first portion is further heated using heat from the CO 2  lean absorbent stream. In yet another aspect, the method further comprises: washing residual absorbent from the flue gas stream leaving the absorber; stripping CO 2  from the residual absorbent to provide overhead CO 2  vapors; and combining overhead CO 2  vapors with the gaseous CO 2  prior to compressing the gaseous CO 2 . 
     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 system used to reduce an amount of CO 2  in a flue gas stream. 
         FIG. 2  is an illustration of one embodiment of an absorbing system utilized in the system depicted in  FIG. 1 . 
         FIG. 3  is an illustration of one embodiment of a wash vessel utilized in the system depicted in  FIG. 1 . 
         FIG. 4  is an illustration of one embodiment of the system including a multiple-feed regenerator arrangement. 
         FIG. 5  is an illustration of one embodiment of the system of  FIG. 4  including a high-pressure, multiple feed regenerator arrangement. 
         FIG. 6  is an illustration of one embodiment of the system of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , a system  100  for reducing an amount of carbon dioxide (CO 2 ) present in a flue gas stream includes several devices and processes for removing a variety of contaminants from a flue gas stream  120  generated by combustion of a fuel in a furnace  122 . The system of  FIG. 1  may be as described in U.S. patent application Ser. No. 12/556,043, filed Sep. 9, 2009, entitled “Chilled Ammonia Based CO 2  Capture System with Water Wash System”, which is incorporated by reference in its entirety herein. As shown in  FIG. 1 , system  100  includes an absorbing system  130  to absorb CO 2  from the flue gas stream  120  and, in one embodiment, a cooled flue gas stream  140 . 
     Cooled flue gas stream  140  is generated by passing the flue gas stream  120  generated by the combustion of a fuel in a furnace  122  to a cooling system  142 . Before introduction to the cooling system  142 , flue gas stream  120  may undergo treatment to remove contaminants therefrom, such as, for example, a flue gas desulfurization process and particulate collector (not shown). 
     Cooling system  142  may be any system that can produce a cooled flue gas stream  140 , and may include, as shown in  FIG. 1 , a direct contact cooler  144 , one or more cooling towers  146  and one or more chillers  148 , that wash and/or scrub the flue gas stream  120 , capture contaminants, and/or lower the moisture content of the flue gas stream. However, it is contemplated that cooling system  142  may include less or more devices than are shown in  FIG. 1 . 
     In one embodiment, the cooled flue gas stream  140  has a temperature that is lower than the ambient temperature. In one example, cooled flue gas stream  140  may have a temperature between about zero degrees Celsius and about twenty degrees Celsius (0° C.-20° C.). In another embodiment, the cooled flue gas stream  140  may have a temperature between about zero degrees Celsius and about ten degrees Celsius (0° C.-10° C.). 
     As shown in  FIG. 1 , cooling system  142  is in communication with the absorbing system  130 . It is contemplated that the cooling system  142  may be in direct communication with the absorbing system  130 , i.e., there are no additional processes or devices between the cooling system and the absorbing system. Alternatively, the cooling system  142  may be in indirect communication with the absorbing system  130 , i.e., there may be additional processes or devices between the cooling system and the absorbing system, such as, but not limited to, particulate collectors, mist eliminators, and the like. 
     Absorbing system  130  facilitates the absorption of CO 2  from the cooled flue gas stream  140  by contacting the cooled flue gas stream with an ammoniated solution or slurry (CO 2  lean stream)  150 . Ammoniated solution or slurry  150  may include dissolved ammonia and CO 2  species in a water solution and may also include precipitated solids of ammonium bicarbonate. 
     In one embodiment, absorbing system  130  includes a first absorber  132  and a second absorber  134 . However, it is contemplated that absorbing system  130  may include more or less absorbers as illustrated in  FIG. 1 . Additionally, it is contemplated that first absorber  132  and/or second absorber  134  may have one or more stages therein for absorbing CO 2  from the cooled flue gas stream  140 . 
     The ammoniated solution or slurry  150  introduced to the absorbing system  130  may be recycled and/or provided by a regeneration tower  160 . As shown in  FIG. 1 , ammoniated solution or slurry  150  may be introduced to the absorbing system  130  at a location within the first absorber  132 , however it is contemplated that the ammoniated solution or slurry may also be introduced at a location within the second absorber  134  or any of the absorbers present in the absorbing system  130 . Regeneration tower  160  is in direct or indirect communication with absorbing system  130 . 
     As shown in more detail in  FIG. 2 , ammoniated slurry or solution  150  is introduced to absorbing system  130 , e.g., in first absorber  132  or second absorber  134 , in a direction A that is countercurrent to a flow B of cooled flue gas stream  140 . As the ammoniated slurry or solution  150  contacts cooled flue gas stream  140 , CO 2  present in the cooled flue gas stream is absorbed and removed therefrom, thereby forming a CO 2  rich stream  152 . At least a portion of the resulting CO 2  rich stream  152  is transported from the absorbing system  130  to regeneration tower  160 . 
     It is contemplated that either a portion or all of CO 2  rich stream  152  may be transferred to regeneration tower  160 . As shown in  FIG. 1 , at least a portion of CO 2  rich stream  152  may pass through a buffer tank  162 , a high pressure pump  164  and a heat exchanger  166  prior to being introduced to regeneration tower  160 . In one embodiment, a separate portion of the CO 2  rich stream  152  may be passed from absorbing system  130  through a heat exchanger  168  where it is cooled prior to being returned to the absorbing system. Heat exchanger  168  is in communication with a cooling system  169 . As shown in  FIG. 1 , the cooling system  169  may have a direct contact chiller  169   a  as well as a cooling tower  169   b ; however, it is recognized the cooling system  169  may have more or less devices than what is illustrated herein. The CO 2  rich stream  152  is cooled prior to it being introduced into the absorbing system  130  with the ammoniated solution or slurry  150 . 
     Additionally, while not shown in  FIG. 1  or  2 , it is also contemplated that the portion of the CO 2  rich stream  152  may be transferred directly to the regeneration tower  160  without passing through the buffer tank  162 , the high pressure pump  164  and the heat exchanger  166 . 
     Regeneration tower  160  regenerates the CO 2  rich stream  152  to form the ammoniated slurry or solution  150  that is introduced to the absorbing system  130 . Regeneration tower  160  facilitates the regeneration of used ammoniated solution or slurry, i.e., the CO 2  rich stream  152 , which has been through the absorbing system  130  and removed CO 2 . Regeneration is performed by providing heat at the bottom of the regeneration tower  160 . Regeneration of the CO 2  rich stream  152  is also performed at high pressure. 
     The capacity of the ammoniated solution or slurry  150  to absorb CO 2  from the cooled flue gas stream  140  depends on, e.g., the ammonia concentration in the ammoniated solution or slurry, the NH3/CO 2  mole ratio, and the temperature and pressure of the absorbing system  130 . In one embodiment, the NH3/CO 2  mole ratio for absorption of CO 2  is between about 1.0 and about 4.0. In another embodiment, the NH3/CO 2  mole ratio for absorption of CO 2  is between about 1.0 and about 3.0. Additionally, 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 between about zero degrees Celsius and about twenty degrees Celsius (0° and 20° C.). In another embodiment, the absorbing system  130  operates at a temperature between about zero degrees Celsius and about ten degrees Celsius (0° and 10° C.). 
     As shown in  FIGS. 1 and 2 , and discussed above, after cooled flue gas stream  140  contacts ammoniated solution or slurry  150 , CO 2  rich stream  152  is formed, as well as an ammonia-containing flue gas stream  170 . Typically, the concentration of ammonia in the ammonia-containing flue gas stream  170  will vary depending on the system, the amount of ammoniated solution or slurry  150  introduced to the absorbing system  130 , and the amount of the CO 2  present in the cooled flue gas stream  140 , and therefore, the ammonia-containing flue gas stream may contain any concentration of ammonia. In one embodiment, the concentration of ammonia in the ammonia-containing flue gas stream  170  may be between about five hundred parts per million (500 ppm) and about thirty thousand parts per million (30,000 ppm). 
     It is contemplated that the concentration of ammonia present in the ammonia-containing flue gas stream  170  may be measured. For example, the ammonia concentration in the ammonia-containing flue gas stream  170  may be measured by, for example, a dragger tube or Fourier transform infrared spectroscopy (FTIR). While not shown, the amount or concentration of ammonia in the ammonia-containing flue gas stream  170  may be measured at any point prior to its introduction to a wash vessel  180 . Measurement of the amount or concentration of the ammonia in the ammonia-containing flue gas stream  170  may assist the operator of system  100  in removing or reducing the amount of ammonia in the ammonia-containing flue gas stream. 
     As shown in  FIG. 1 , ammonia-containing flue gas stream  170  is introduced to the wash vessel  180 . In one embodiment, wash vessel  180  reduces an amount of ammonia present in the ammonia-containing flue gas stream  170  and forms a reduced ammonia-containing flue gas stream  190 . However, it is contemplated that wash vessel  180  may be used in conjunction with other systems and methods that generate a flue gas stream containing ammonia, i.e., the wash vessel may be used in a system that does not contain absorbing system  130  and/or cooling system  142 . 
     The reduced ammonia-containing flue gas stream  190  may be released to the environment. The reduced ammonia-containing flue gas stream  190  may be directly released to the environment from wash vessel  180 . However, it is contemplated that the reduced ammonia-containing flue gas stream may be further processed prior to being emitted to the environment, for example, it may be washed in an acidic solution to further reduce contaminant content. Additionally, and while not shown in  FIG. 1 , it is contemplated that the amount of ammonia present in the reduced ammonia-containing flue gas stream  190  may be measured after the reduced ammonia-containing flue gas stream exits the wash vessel  180 . 
     In one embodiment, wash vessel  180  is configured to accept ammonia-containing flue gas stream  170 . As shown in  FIG. 3 , wash vessel  180  may have an opening  182  at a bottom of the wash vessel that allows the ammonia-containing flue gas stream  170  to flow into the wash vessel. While the opening  182  is shown at the bottom of the wash vessel  180 , it is contemplated that the opening may be at any point in the wash vessel and may vary from system to system depending on the application. 
     Wash vessel  180  may have one or more absorption stages, shown generally at  181 , to absorb ammonia from the ammonia-containing flue gas stream  170 . In one embodiment, as shown in  FIG. 3 , wash vessel  180  includes two absorption stages, a first absorption stage  181   a  and a second absorption stage  181   b . The wash vessel  180  is not limited in this regard as it is contemplated that the wash vessel may have more or less absorption stages. Each of the absorption stages  181 , e.g., first and second absorption stages  181   a  and  181   b , may include a mass transfer device  184 , a spray head system  186  and a liquid delivery path  188 . 
     The mass transfer device  184  may include packing, such as, for example, random packing, hydrophilic packing, and/or structural packing. Random packing is generally known in the art and refers to packing material introduced to the absorption stage in an un-organized fashion. Examples of random packing include, but are not limited to plastic, metal and/or ceramic packing material offered in different sizes, e.g., material having varying diameters, for example, diameters ranging between about 2.5 centimeters (2.5 cm) to about 7.6 centimeters (7.6 cm) (about 1 inch to about 3 inches). Random packing material is available from many suppliers, including, but not limited to Jaeger Products Inc. (Houston, Tex., United States). Random packing material may also include wood. Hydrophilic packing includes, but is not limited to polypropylene bags. 
     Structural packing is generally known in the art and refers to packing material that is arranged or organized in a specific fashion. Typically, structural packing is arranged in a manner to force fluids to take a complicated path, thereby creating a large surface area for contact between the liquid and gas. Structural packing includes, but is not limited to structures made of metal, plastic, wood, and the like. It is contemplated that different packing materials facilitate ammonia removal or reduction at different flow rates of a liquid into the wash vessel  180 . Additionally, it is contemplated that the different packing materials may provide more suitable pressure drops. 
     In one embodiment, one of the absorption stages  181  of the wash vessel  180  includes random packing material as the mass transfer device  184  and another of the absorption stages  181  of the wash vessel  180  includes structural packing as the mass transfer device. For example, first absorption stage  181   a  may include random packing material as the mass transfer device  184  and second absorption stage  181   b  may include structural packing as the mass transfer device. It is contemplated that the ammonia-containing flue gas stream  170  enters the wash vessel  180  and passes through the second absorption stage  181   b  prior to passing through the first absorption stage  181   a.    
     As shown in  FIG. 3 , in each of the absorption stages  181 , the mass transfer device  184  is located beneath the spray head system  186 . Each of the spray head system  186  in wash vessel  180  sprays a liquid  187  into the absorption stages  181 . The liquid  187  is transported to the spray head system  186  via the liquid delivery path  188 . The liquid delivery path  188  is a conduit that transports the liquid  187  to the spray head system  186 . The liquid  187  may be any liquid suitable to facilitate the removal of ammonia from the ammonia-containing flue gas stream  170 . An example of liquid  187  is water, which is known to absorb, i.e., dissolve, ammonia through interactions between the ammonia and the water. 
     In one particular embodiment, liquid  187  introduced to the first absorption stage  181   a  is liquid  187   a , e.g., water provided by a stripping column  194 . The liquid  187  provided to the second absorption stage  181   b  is liquid  187   b , which is water-containing low concentration ammonia and CO 2  recycled from the bottom of the wash vessel  180  and passed through a heat exchanger  189 . 
     The liquid  187  is introduced at the top of each absorption stage  181 , e.g., liquid  181   a  is provided to the top of first absorption stage  181   a  and liquid  187   b  is provided to the top of second absorption stage  181   b , of the wash vessel  180 . The liquid  187  travels in a direction C down a length L of the wash vessel  180 , which is countercurrent to a direction D that the ammonia-containing flue gas stream  170  travels up the length L of the wash vessel  180 . As will be appreciated, the liquid  187  travels in direction C by virtue of gravity, while the ammonia-containing flue gas stream  170  travels in direction D by virtue of several factors, including pressure drops within the wash vessel  180 . 
     As the liquid  187  travels in the direction C, it passes through the mass transfer devices  184  in each of the absorption stages  181 . Likewise, as the ammonia-containing flue gas stream  170  travels in direction D, it passes through the mass transfer devices  184  in each of the absorption stages  181 . 
     As the liquid  187  travels in direction C down the length L of the wash vessel  180 , the ammonia concentration in the liquid increases, thereby forming an ammonia-rich liquid  192 . Conversely, as the ammonia-containing flue gas stream  170  travels in a direction D up a length, e.g., the length L, of the wash vessel  180 , the ammonia concentration in the ammonia-containing flue gas stream decreases thereby forming the reduced ammonia-containing flue gas stream  190 . 
     For example, liquid  187   a  is introduced at the top of wash vessel  180  through a spray head system  186  over the first absorption stage  181   a  and travels in a direction C down the length L of the wash vessel. The concentration of ammonia present in the liquid  187   a  exiting the first absorption stage  181   a  is higher than the ammonia concentration of the liquid  187   a  entering the first absorption stage  181   a  since the liquid has contacted the ammonia-containing flue gas stream  170  that travels in direction D up the length L of the wash vessel and absorbed ammonia therefrom. In this embodiment, a greater percentage of ammonia in the ammonia-containing flue gas stream  170  is absorbed by the liquid  187   a  that flows from the first absorption stage  181   a  to the second absorption stage  181   b  as well as the liquid  187   b  that provided to the second absorption stage since the ammonia-containing flue gas stream is entering the wash vessel  180  at the bottom is untreated and therefore has the highest concentration of ammonia. 
     It should be appreciated that the amount of ammonia removed from the ammonia-containing flue gas stream  170  varies from system to system and application to application. It is contemplated that the system is designed in a manner that the ammonia concentration in the reduced ammonia containing flue gas stream  170  is low and close to an equilibrium concentration of ammonia in the gas relative to the vapor pressure of the ammonia in the liquid. The equilibrium concentration of ammonia in the flue gas stream  170  may be as low as below ten parts per million (10 ppm) and typically in the range of between about zero parts per million (0 ppm) to about two hundred parts per million (200 ppm). In one embodiment, the reduced ammonia containing flue gas stream  190  contains at least about seventy percent (70%) less ammonia as compared to a level of ammonia in the ammonia-containing flue gas stream  170 . In another embodiment, the reduced ammonia containing flue gas stream  190  contains at least about seventy five percent (75%) less ammonia as compared to a level of ammonia in the ammonia-containing flue gas stream  170 . In yet a further embodiment, the reduced ammonia containing flue gas stream  190  contains at least about eighty percent (80%) less ammonia as compared to a level of ammonia in the ammonia-containing flue gas stream  170 . In another embodiment, the reduced ammonia containing flue gas stream  190  contains at least about eighty five (85%) less ammonia as compared to a level of ammonia in the ammonia-containing flue gas stream  170 . It is contemplated that the level of ammonia in the reduced ammonia containing flue gas stream  190  may be about ninety percent (90%), ninety five percent (95%), ninety nine percent (99%) or ninety nine and a half percent (99.5%) less than the level of ammonia in the ammonia-containing flue gas stream  170 . 
     A flow rate of liquid  187  suitable to reduce the amount of ammonia in the flue gas varies from system to system. In one embodiment, the flow rate is suitable to reduce an amount of ammonia in the flue gas to an amount close to the equilibrium concentration and typically to below two hundred parts per million (200 ppm) in the flue gas stream. In another embodiment, the flow rate is suitable to reduce an amount of ammonia in the flue gas from about two thousand parts per million (2000 ppm) to between about seventy parts per million and about one hundred parts per million (70-100 ppm). In another embodiment, the flow rate of the liquid  187  is between about 1.8 liters per minute (1.8 lpm, or about 0.5 gallons per minute) to about 7.5 liters per minute (7.5 lpm or about 2 gallons per minute) per one thousand cubic feet per minute (1000 cfm) of flue gas. 
     Still referring to  FIG. 3 , the liquid  187  falls to the bottom of the wash vessel  180  and is removed therefrom as ammonia-rich liquid  192 . As shown in  FIG. 3 , in one embodiment, a portion of the ammonia-rich liquid  192  is recycled to the wash vessel  180  as liquid  187  and a portion of the ammonia-rich liquid is sent to the stripping column  194  (shown in  FIG. 1 ). For example, a portion of the ammonia-rich liquid  192  is cooled in a heat exchanger  189  and recycled to second absorption stage  181   b  as liquid  187   b . While not illustrated, it is contemplated that a portion of the ammonia-rich liquid  192  may be recycled from the bottom of the wash vessel  180  to first absorption stage  181   a  as liquid  187   a . Additionally, while not shown, it is contemplated that the entire amount of the ammonia-rich liquid  192  may be sent to the stripping column  194  and then returned to the wash vessel  180  as liquid  187   a.    
     Still referring to  FIG. 3 , the portion of ammonia-rich liquid  192  sent to stripping column  194  is regenerated to form liquid  187   a , which is introduced via spray head system  186  in first absorption stage  181   a . In the stripping column  194 , the ammonia, as well as other contaminants, such as CO 2 , is removed from the ammonia-rich liquid  192  to form the liquid  187   a , which may be water, or water having, for example, trace contaminants of ammonia. When introduced in this manner, the liquid  187   a  that is introduced to the first absorption stage  181   a  is referred to as “once through liquid” since it is “clean liquid” that has not been recycled from the bottom of the wash vessel  180 . 
     In one embodiment, stripping column  194  utilizes steam to remove ammonia, as well as other contaminants, from the ammonia-rich liquid  192  to form the liquid  187  that will be introduced to the wash vessel  180 . However, it is contemplated that stripping column  194  may utilize other technology or techniques in order to remove the ammonia and other contaminants from the ammonia-rich liquid  192 . In one embodiment, the stripping column  194  may be operated at vacuum conditions to reduce the temperature of the steam utilized in the stripping column. 
     While not shown in  FIG. 1 , it is contemplated that the ammonia removed from ammonia-rich liquid  192  may be re-utilized within system  100 . For example, the ammonia may be introduced in the absorbing system  130  as ammoniated solution or slurry  150 . However, it is contemplated that the ammonia may be utilized at other points inside and outside of system  100 . 
     The amount of ammonia released to the environment is reduced or substantially eliminated by passing an ammonia-containing flue gas stream through wash vessel  180 . The amount of liquid  187  introduced to the various absorption stages  181 , e.g., liquid  187   a  introduced to the first absorption stage  181   a  and liquid  187   b  introduced to the second absorption stage  181   b , may be controlled either continually or at predetermined time periods, to some extent by an operator, depending on, for example, the amount or flow of flue gas introduced to the wash vessel, a level of contaminants measured within emission from the system  100 , and the like. The ability to control an amount of water used in the system may facilitate the savings of resources and reduce operating expenses. 
       FIG. 4  depicts a system  200  for reducing an amount of CO 2  present in a flue gas stream. System  200  may include the features of system  100 , shown in  FIG. 1 , and like elements are numbered alike in the two figures. In system  200 , the ionic solution may comprise, for example, water and ammonium ions, bicarbonate ions, carbonate ions, and/or carbamate ions, and the system  200  may be a chilled ammonia system. It is also contemplated that the ionic solution may be an amine. In either case, it is further contemplated that the ionic solution may be promoted by an enzyme (e.g., carbonic anhydrase) or amine (e.g., piperazine). 
     In system  200 , a first portion of the CO 2  rich stream  152  from the absorber  132  (and or  134 ), indicated at  204 , is provided to the regenerator vessel  160  after being heated in heat exchanger  166 , while a second portion of the CO 2  rich stream  152 , indicated at  202 , is provided directly to the regenerator  16 , bypassing heat exchanger  166 . Because a portion  202  is bypassed around the heat exchanger  166 , the amount of CO 2  rich stream  152  passing through heat exchanger  166  is reduced compared to the arrangement in  FIG. 1 . A reduction in the amount of CO 2  rich stream  152  that flows through heat exchanger  166  results in an increased temperature of the stream  204  compared to that of stream  202 . The greater temperature may increase the amount of CO 2  that will be released (flashed) from the CO 2  rich stream  152  prior to reaching regenerator  160 . Stream  202 , which is cooler than stream  204 , is introduced near the top of the regenerator  160 , where CO 2  is released to compressor  208 , while the relatively hotter stream  204  is introduced closer to the bottom of the regenerator  160 . This arrangement promotes increased temperatures near the bottom of the regenerator, where the reboiler  206  provides heat to regenerate the CO 2  rich stream, and thus reduces the reboiler heat load. 
       FIG. 5  depicts a system  300  for reducing an amount of CO 2  present in a flue gas stream, which is substantially similar to system  200  of  FIG. 4 , with like elements numbered alike. System  300  includes a flash drum (gas/liquid separator)  301  to separate the CO 2  gas that has flashed from the liquid portion of CO 2  rich stream  204 . The CO 2  gas stream, indicated at  302 , is provided to a compressor  304 , which compresses the CO 2  gas stream  302  to above the pressure within the regenerator  160  (e.g., from about 10 bar to about 21 bar). The CO 2  gas stream  302 , which increases in temperature due to compressor  304 , is introduced near the bottom of the regenerator, where it serves to heat the CO 2  rich absorbent collected at the bottom of the regenerator  160 . 
     The liquid portion of stream  204  leaves the flash drum  301  as stream  306 , and is introduced to a heat exchanger  308 , where stream  204  is heated by the CO 2  lean stream  150  before being introduced to the regenerator  160 . It will be appreciated that stream  302  is relatively hotter than streams  306  and  200 , and that stream  306  is relatively hotter than stream  200 . As a result, this arrangement further promotes increased temperatures near the bottom of the regenerator  160 , where the reboiler  206  provides heat to regenerate the CO 2  rich stream, and thus reduces the reboiler heat load. The use of heat from the heat exchangers  166  and  308 , as well as the heat imparted by compressor  304 , is believed to reduce up to 7-8% points on parasitic load of the system  300 . 
       FIG. 6  depicts a system  400  for reducing an amount of CO 2  present in a flue gas stream, which is substantially similar to system  300  of  FIG. 5 , with like elements numbered alike. System  400  provides overhead CO 2  vapors removed from stripper  194  ( FIG. 1 ) to compressor  304 , in addition to the stream  302 , to further increase the temperature of the compressed stream provided to the bottom of the regenerator  160 . 
     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.