Abstract:
An apparatus and method to clean flue gases. As shown in FIG.  1 , a condenser  10  is provided having two packed beds ( 20/26 ) and two condensate loops. The condensate loops are configured such that anti-corrosive agent ( 40/41 ) may injected. Corrosives are removed from flue gases as condensate containing anti-corrosive agents passes over the flue gases.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 13/436,054, filed Mar. 30, 2012. 
    
    
     FIELD 
     The present disclosure relates to treatment of flue gases. More particularly, it relates to an apparatus and method to efficiently remove corrosives from flue gases. 
     BACKGROUND 
     Certain processes, such as combustion of carbon containing fuels, produce gaseous emissions of CO 2 . CO 2  has been identified as a “greenhouse” gas, which appears to contribute to global warming. Because of its status as a “greenhouse” gas, technologies have been developed to decrease CO 2  emissions, including: energy efficiency improvements; increased use of renewable energy sources such as solar and wind; promotion of CO 2  absorption/conversion in nature (reforestation); reduction in use of fossil fuels; etc. 
     Notwithstanding these efforts and technologies, fossil fuels continue to provide a substantial portion of the energy generated today. In addition to developing and exploring energy improvements and alternatives, technologies have also been developed to limit or prevent CO 2  release from combustion, including CO 2  capture and storage (CCS). Employing CCS technologies may substantially reduce the amount of CO 2  released to the atmosphere. 
     There are various methods or techniques utilized for CCS. Technologies generally fall into one of three areas: post combustion capture (PCC), where CO 2  is removed after combustion through absorption or other techniques; pre-combustion (PC), where the fuel is converted before combustion such that CO 2  is not a product of energy production; and oxy-firing combustion where the fuel is burned in enriched or pure oxygen instead of ambient air to concentrate the CO 2  combustion product. 
     Drawbacks of CCS technologies include increased capital costs and additional energy consumption associated with the technologies. For example, oxy-firing combustion creates a more concentrated stream of CO 2 , thereby reducing energy and capital costs of processing a flue stream to capture the CO 2  for later storage; however, oxy-firing typically requires an energy demanding air separation unit to generate pure or enriched oxygen. To address this drawback, chemical looping combustion (CLC) has been developed using oxygen carriers to deliver oxygen to a fuel reactor. The oxygen carrier is first oxidized in an air reactor and then oxidized carriers are transmitted to a fuel reactor where they are reduced in contact with the fuel. The carrier is then returned to the air reactor for re-oxidation. By using a carrier, combustion is accomplished in an oxygen rich atmosphere without cryogenically creating oxygen rich gas. 
     Although oxy-firing and CLC systems generally create a flue stream with a higher concentration of CO 2  and substantially reduced concentrations of non-reactive components of air (inerts), such as nitrogen, a flue stream will include H 2 O as a product of combustion. Moreover, even after initial heat recovery, a flue stream will still have elevated temperatures. CO 2  capture and processing is generally accomplished in a gas processing unit (GPU), which separates the CO 2  for removal, storage, or reuse, as appropriate. Before a flue stream may be processed in a GPU, H 2 O, which is gaseous as it exits a fuel reactor in a flue stream, is generally condensed out of the flue stream, leaving substantially concentrated CO 2 . The flue stream is also cooled before transmission to a GPU. Energy loss can occur both from a failure or inefficient recovery of heat present in a flue stream and from increased energy expenditures in deliberate cooling of a flue stream prior to transmission to a GPU. Moreover, corrosives, such as sulfur dioxide (SO 2 ), may be present in a flue stream and must be cleaned from the flue stream in order to minimize corrosion risks prior to transmission to the GPU. 
     A condenser may be used to condense water from a flue stream and cool the flue stream. A condenser may be of various types, including a direct contact condenser, which may be a column condenser having a packed bed element. In a condenser having a packed bed element, external heat exchangers may be incorporated for recovery of heat from the flue gases and to assist in cooling of flue gases; however, there is a requirement that difference between temperatures of the flue gas and temperatures of return condensate should be minimized, typically, not more than 4° C. Generally, higher liquid loads are preferred for maximizing cooling of flue gases. The lower the liquid load employed the more area of packing bed needed to cool the flue gases. Increasing the liquid load, however, will cause the temperature difference between flue gases and return condensate to exceed the temperature difference requirement. In order to minimize the difference in temperatures, the liquid load through the packed bed element is reduced, which lowers efficiency of heat transfer from flue stream to condensate flow and reduces cooling of the flue stream. Because of the requirement to minimize the temperature difference, requiring a low liquid load through a packed bed element, a high tower is required to sufficiently condense H 2 O, which sacrifices cooling of the flue gas. Accordingly, there is a need for an improved condenser and method of cooling a flue stream to more efficiently recover heat from flue gases, cool flue gases for transmission to a GPU and remove sulfur dioxide from the flue gases to avoid corrosion risks. 
     SUMMARY 
     According to the aspects illustrated herein, there is provided a condenser having a column member with a lower end, an upper end and a wall connecting the lower end and upper end forming a central cavity. A first packed bed is located within the cavity above the lower end. At least a second packed bed is located within the cavity above the first packed bed. A first heat exchanger is configured to receive condensate flow from the first packed bed. A second heat exchanger is configured to receive condensate flow at least in part from the second packed bed. At least a first valve is connected to a condensate flow of a packed bed. The lower end of the column member is configured to receive flue gases via a gas inlet. The upper end is configured to permit flue gases to exit the column member via a gas outlet. The packed beds are configured to provide a flow of condensate in an opposite direction of a flue gas flow. Anti-corrosive reagents are injected into condensate flows via at least the first valve. 
     According to other aspects illustrated herein, there is provided a condenser having a column member with a lower end, an upper end and a wall connecting the lower end and upper end forming a central cavity. A first packed bed is located within the cavity above the lower end. At least a second packed bed is located within the cavity above the first packed bed. The lower end of the column member is configured to receive flue gases via a gas inlet. The upper end allows gases to exit the column member via a gas outlet. The condenser is configured to receive anti-corrosive reagents in a condensate flow of the condenser. 
     According to other aspects illustrated herein, there is provided a method to clean flue gases by transmitting the flue gases to a condenser having a lower end, an upper end, and a side wall connecting the lower end and upper end to form a column with a central cavity; injecting the flue gases into the lower end of the condenser; transmitting the flue gases upwards through the condenser; transmitting the flue gases out of the condenser at the upper end of the column; forming condensate from the flue gases as the flue gases pass upwards through the condenser; and cleaning the flue gases by adding anti-corrosive reagents to the condensate. The compressor contains a least two packed beds and at least two condensate loops. Each condensate loop is connected to heat exchanger. 
     The above described and other features are exemplified by the following figures and detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now the figures, which are exemplary embodiments, and wherein the like elements are numbered alike: 
         FIG. 1  is a cross-sectional drawing of an exemplary embodiment of the present disclosure. 
         FIG. 2  is a cross-sectional drawing of another exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     According to an exemplary embodiment of the present disclosure, a condenser is provided having a column member, which may be generally cylindrical, connected to an upper end and a lower end, forming a central cavity. A first packed bed is located within the central cavity above the lower and at least a second packed bed is located within the central cavity below the upper end and above the first packed bed. Packing materials may include any materials generally used for packing purposes. A first heat exchanger is configured to receive condensate from the first packed bed and a second heat exchanger is configured to receive condensate at least in part from the second packed bed. The second heat exchanger may also receive a portion of condensate from the first packed bed after said condensate first passes through the first heat exchanger. The lower end of the column member is configured to receive flue gases via a gas inlet and the upper end of the column member is configured to permit flue gases to exit the column member via a gas outlet. The packed beds provide a flow of condensate in an opposite direction of a flue gas flow. The first packed bed and condensate flow may be configured to maximize heat recovery from the flue gases. The second packed bed and condensate may be configured to maximize cooling of the flue gases. The first heat exchanger may be configured to provide heat recovery from condensate flow of the first packed bed. The second heat exchanger may be configured to receive cooling liquid to increase cooling of condensate. The present disclosure may incorporate the addition of reagents, which may be sodium hydroxide. Addition of reagents may be controlled through pH measurements. Reagents may be utilized to remove corrosives such as sulfur dioxide. 
     According to an exemplary embodiment of the present disclosure, a first liquid distributor may be configured to distribute condensate across a top portion of the first packed bed. A first liquid collector, which may be a separate collector or the lower end of the column member, is configured to collect condensate below the first packed bed. A second liquid distributor may be configured to distribute condensate across a top portion of the second packed bed. A second liquid collector may be configured to collect condensate below the second packed bed. In an alternative embodiment, the second liquid collector may be configured to permit a portion of condensate collected from the second packed bed to be distributed across a top portion of the first packed bed. This alternative may include a perforated second liquid collector allowing some condensate to pass through the second liquid collector and fall upon a top portion of the first packed bed. 
     According to an exemplary embodiment of the present disclosure, at least two separate condensate loops may be included such that the a first condensate loop is configured to receive condensate from the first liquid collector. The first condensate loop may be further configured to distribute condensate to a top portion of the first packed bed. The first condensate loop may be configured such that the condensate flows through the first heat exchanger for heat recovery from the condensate. A second condensate loop may be configured to receive condensate from the second liquid collector. Alternatively, the second condensate loop may be configured to receive condensate from the first heat exchanger or the second liquid collector, or both. The second condensate loop may be configured to distribute condensate to a top portion of the second packed bed. The second condensate loop may include the second heat exchanger which may further receive a cooling liquid. The condensate loops may be configured to permit addition of reagents to control pH. An example reagent may be NaOH. Addition of reagents to control pH allows the present disclosure to clean the flue gases, removing potential corrosives, such as sulfur dioxide. 
     Accordingly to an exemplary embodiment of the present disclosure, a method is provided to recover heat from and cool flue gases by transmitting the flue gases to a condenser having a lower end, and upper end, and a side wall connecting the lower end and the upper end to form a column with a central cavity. The flue gases may be injected into the lower end of the condenser, transmitted upward through the condenser, and released from the condenser at the upper end. Condensate is formed from the flue gases as the flue gases pass upwards through the condenser, which condenser may have two or more packed beds. A first packed bed may be configured to provide efficient heat transfer to condensate distributed to a top portion of the first packed bed such that heat may be recovered via a first heat exchanger. A second packed bed may be configured to provide efficient cooling of flue gases. Heat recovered in the first heat exchanger may be integrated into a steam cycle. Condensate distributed to the second packed bed may be cooled via a second heat exchanger which may be supplied a cooling liquid. 
     Referring to the exemplary embodiment shown in  FIG. 1 , a condenser  10  is provided having a column member  18 , which may be generally cylindrical, a lower end  14 , and an upper end  16 , forming a central cavity. Flue gases enter  12  the condenser  10  via a gas inlet at the lower end  14  and exit  34  the condenser  10  via a gas outlet at the upper end  16 . Within the central cavity, a first packed bed  20  rests upon a first support grid  22 . Condensate passing through first packed bed  20  may be collected by first liquid collector  24 . Alternatively, condensate passing through the first packed bed  20  may be collected by the lower end  14  of condenser  10 . Condensate from the first packed bed  20  may be transmitted via a first pump member  36  to a first heat exchanger  44 . Reagents  40 , such as NaOH, may be added to condensate prior to transmission to first heat exchanger  44 . A first valve  42  may be incorporated to control influx of reagent  40 . First heat exchanger  44  may be utilized to recover heat for integration into a steam cycle. Condensate  66  may be further transmitted to a first liquid distributor  31 . A portion  68  of condensate  66  may be discharged. A first pH meter  62  may be incorporated to measure pH of condensate being returned to the first packed bed  20 . Measured pH value may be used to control influx of reagent  40  via first valve  42 . First liquid distributor  31  distributes condensate to a top portion of the first packed bed. 
     Still referring to the exemplary embodiment shown in  FIG. 1 , within the central cavity, a second packed bed  26  rests upon a second support grid  28 . Condensate passing through second packed bed  26  may be collected by second liquid collector  74 . The second liquid collector  74  may have openings configured to permit gas to pass from the first bed  20  to the second bed  26 . Condensate from the second packed bed  26  may be transmitted via a second pump member  48  to a second heat exchanger  52 . Reagents  41 , such as NaOH, may be added to condensate prior to transmission to second heat exchanger  52 . A second valve  76  may be incorporate to control influx of reagent  41 . Second heat exchanger  52  may be configured to receive a cooling liquid. Condensate  54  may be further transmitted to a second liquid distributor  30 . Third valve  50  may be incorporated to control a flow of condensate exiting second heat exchanger  52 . A portion  60  of condensate  54  may be discharged. A second pH meter  56  may be incorporated to measure pH of condensate being returned to the second packed bed  26 . Measured pH value may be used to control influx of reagent  41  via second valve  76 . A first temperature gauge  58  may be incorporated to measure temperatures of condensate being returned to the second packed bed  26 . Measured temperature may used to control flow of condensate  64 . Second liquid distributor  30  distributes condensate to a top portion of the second packed bed  26 . 
     Referring to the exemplary embodiment shown in  FIG. 2 , a condenser is provided condenser  11  having column member  18 , which may be generally cylindrical, lower end  14 , and upper end  16 , forming a central cavity. Flue gases enter  12  the condenser  10  via a gas inlet at the lower end  14  and exit  34  the condenser  10  via a gas outlet at the upper end  16 . Within the central cavity, first packed bed  20  rests upon first support grid  22 . Condensate passing through first packed bed  20  may be collected by first liquid collector  24 . Alternatively, condensate passing through the first packed bed  20  may be collected by the lower end  14  of condenser  11 . Condensate from first packed bed  20  may be transmitted via first pump member  36  to first heat exchanger  44 . Reagents  40 , such as NaOH, may be added to condensate prior to transmission to first heat exchanger  44 . First valve  42  may be incorporated to control influx of reagent  40  using a pH value measured by the second pH meter  62 . First heat exchanger  44  may be utilized for steam generation. Condensate  46  may be further transmitted second heat exchanger  52 . Condensate from second packed bed  26  may be added to condensate  46  via second pump  48  prior transmission to second heat exchanger  52 . Second valve  50  may be incorporated to control the flow of condensate from the second packed bed  26  to second heat exchanger  52  using a temperature measured by the first temperature gauge  58 . In this embodiment a second liquid collector  23  is located below the second packed element  26 . Second liquid collector  23  may be configured to permit a portion of condensate from the second packed bed to flow  21  past the second liquid collector and upon a top portion of the first packed element in an opposite direction  25  of flue gases. Reagents  40  may be added via first valve  42  which influx may be controlled by pH measurements of second pH meter  56 . 
     Embodiments of the present disclosure maximize both heat recovery from flue gases and cooling of flue gases prior to transmission of the flue gases to a GPU. Temperature differences of condensate  38  from the first packed bed  20  and flue gas  12  entering condenser ( 11  or  12 ) may be maintained below 4° C., potentially below 2° C. Temperature differences of exiting gas stream  34  and condensate stream  54  generally can be below 2° C., potentially less than 1° C. Moreover, if reagents  40 / 41  are utilized in the present disclosure, efficiently cleaning of flue gases may be accomplished, removing corrosives. SO 2  concentration in exit stream  34  may generally be reduced to less than 1 ppmv, potentially below 0.1 ppmv. Thus present disclosure overcomes limitations of prior condensers by utilizing at least two separate packed beds in a condenser column with separate or partially integrated condensate loops which may be separately configured to permit maximum heat recovery in one loop and maximum cooling in another loop. 
     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 teaching 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.