Abstract:
A method of reducing mercury emissions using a combustion device including at least a combustion zone. The method includes receiving a flow of fuel including mercury at the combustion device assembly; injecting a first mercury oxidizer flow including MgCl 2  on the fuel upstream of the combustion device assembly; and oxidizing the mercury using a mercury oxidizer flows and the combustion device assembly.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to combustion devices and, more particularly, to emission control systems for combustion devices. 
         [0002]    During a typical combustion process within a furnace or boiler, for example, a flow of combustion gas is produced. The combustion gas contains combustion products including, without limitation, carbon dioxide, carbon monoxide, water, hydrogen, nitrogen and mercury generated as a direct result of combusting solid and/or liquid fuels. Before the combustion gas is emitted into the atmosphere, hazardous or toxic combustion products, such as mercury emissions and oxides of nitrogen (NO x ), are to be removed according to EPA or state governmental regulations, standards and procedures. 
         [0003]    At least some conventional methods of removing mercury from combustion gases include injecting activated carbon into the combustion gas as the combustion gases flow through duct work. However, with such methods, it may be difficult to obtain uniform distribution of the particulate matter within the duct work. As a result of poor mixing and/or carbon fallout, mercury may not be efficiently removed from the combustion gases. In an attempt to solve such problems, an injection rate of activated carbon is increased, which may further exacerbate the problems associated with the conventional methods. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    In one aspect, a method is provided for reducing mercury emissions using at least a solid fuel, furnace and flue gas system assembly. The method includes receiving a flow of fuel including mercury at the furnace assembly, injecting a flow of a solution including injecting a flow of mercury oxidizer MgCl 2 , and oxidizing the mercury using the mercury oxidizer MgCl 2  and furnace assembly. 
         [0005]    In another aspect, a furnace assembly is provided. The assembly includes a furnace combustion zone configured to facilitate at least an oxidation reaction of mercury. The assembly also includes a first injection port positioned at the furnace combustion zone. The injection port is configured to inject a flow of mercury oxidizer MgCl 2 . 
         [0006]    In a another aspect, a furnace combustion zone exhaust system includes a combustion chamber configured to combust materials including mercury such that mercury exits the combustion chamber in a flow of exhaust. The system also includes a furnace configured to facilitate at least an oxidation reaction of mercury and a second injection port positioned downstream of the furnace combustion zone. The second injection port is configured to inject a flow of mercury oxidizer MgCl 2 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic view of a exemplary power plant system in accordance with one aspect of the invention; 
           [0008]      FIG. 2  is a schematic view of a exemplary power plant system that may be used to facilitate removing mercury emissions from combustion gases generated with the power plant system shown in  FIG. 1 ; and 
           [0009]      FIG. 3  is a schematic view of an exemplary power plant system that may be used to facilitate removing mercury emissions from combustion gases generated with the power plant system shown in  FIG. 1  and  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0010]    An exemplary embodiment of the present invention provides a method and system for continuously removing and reducing hazardous and/or toxic compounds, such as mercury emissions from a flow of combustion gas produced during a combustion process within a furnace or boiler, for example. The flow of combustion gas having combustion products including, without limitation, carbon dioxide, carbon monoxide, water, hydrogen, nitrogen and mercury. This combustion gas is a direct result of combusting solid and/or liquid fuels. Before the flow of combustion gas is exhausted into the atmosphere, any toxic combustion products, such as mercury and oxides of nitrogen (NO x ), are removed according to governmental and environmental regulations and standards. 
         [0011]    The method is described below in reference to its application in connection with and operation of a system for continuously removing mercury from a supply of combustion gas generated during a combustion process. However, it will be obvious to those skilled in the art and guided by the teachings herein provided that the methods and systems described herein are likewise applicable to any combustion device including, without limitation, boilers and heaters, and may be applied to systems consuming fuels such as coal, oil or any solid, liquid or gaseous fuel. 
         [0012]    As used herein, references to “particulate matter” are to be understood to refer to particulate matter contained within the combustion gas. The particulate matter includes particles of matter including, without limitation, fly ash and carbon, contained within the combustion gas as a naturally occurring product of a combustion process, and may also include externally-introduced matter including, without limitation, at least one of active carbon particles and additional fly ash, recirculated or injected into the particulate matter contained within the combustion gas. 
         [0013]      FIG. 1  is a schematic view of an exemplary power plant system  100  according to one embodiment of the present invention. In the exemplary embodiment, system  100  includes a fuel storage device  12  such as but not limited to a bin, bunker, pile or silo in which a fuel supply is stored and collected prior to transport for combustion. The fuel storage device  12  is coupled in flow communication with a fuel transport device  14  which includes but is not limited to a feeder and piping arrangement used to transport fuel for combustion. A first injection port  16  extends into fuel transport device  14  and provides flow communication to fuel transport device  14 . In an alternative embodiment, first injection port  16  is positioned upstream of fuel storage device  12 . In the exemplary embodiment, system  100  includes a furnace combustion device  18  that combusts a plurality of fuels, such as but not limited to coal, oil, or any solid, liquid or gaseous fuels in which a supply of combustion gases is produced. Combustion device  18  includes a combustion zone  20  wherein a fuel-air mixture is combusted causing a stream of high temperature combustion gas  24  to be generated. 
         [0014]    Fuel transport device  14  is coupled to combustion device  18  and is in flow communication therewith. Contained within combustion device  18  is a fuel combustion zone  20 . In the exemplary embodiment, an air injection port  22  extends into combustion device  18  and channels and is in flow communication with combustion zone  20 . In an alternative embodiment, a second injection port extends into combustion device  18  and is in flow communication with combustion zone  20 . In an alternative embodiment, a third injection port extends into combustion device  18  downstream of combustion zone  20  and is in flow communication with a high temperature combustion gas  24 . Combustion device  18  is coupled to a gas outlet duct  26  that is configured to direct a combustion exhaust gas  28  from combustion device  18 . In the exemplary embodiment, a first injection port  16  extends into fuel transport device  14  and is configured to inject a flow of mercury oxidizer to the combustible materials directed through fuel transport device  14 . First injection port  16  is formed as an injection tree, injection ring header or any other injection device configured to inject a flow of mercury oxidizer. 
         [0015]    In an alternative embodiment, the first injection port is positioned upstream of fuel storage device  12  to provide mercury oxidizer flow to the combustible materials directed to fuel storage device  12 . In the exemplary embodiment, the first mercury oxidizer is injected on the combustible materials in the fuel transport device. Fuel transport device  14  provides a flow of combustible materials including the first mercury oxidizer to combustion device  18 . 
         [0016]    In the exemplary embodiment, combustion device  18  is configured to combust a plurality of fuels, such as but not limited to coal, oil, or any solid, liquid or gaseous fuels in which a supply of combustion gases are produced. Combustion device  18  is configured with a combustion zone  20  wherein a fuel-air mixture is combusted causing a stream of high temperature combustion gas  24  to be generated. In an alternative embodiment, combustion device  18  is configured with but not limited to, additional combustion gas emission reducing equipment such as over fire air injection ports and gas reburn systems that have a temperature in excess of 2500 degrees Fahrenheit. In the exemplary embodiment, air injection port  22  extends into combustion device  18  to provide combustion air flow to combustion zone  20 . In an alternative embodiment, a second injection port is configured with combustion device  18  to provide a mercury oxidizer flow to combustion zone  20 . In an alternative embodiment, a third injection port is configured with combustion device  18  downstream of combustion zone  20  to provide mercury oxidizer flow to high temperature combustion gas  24   
         [0017]    More specifically, combustion exhaust gases  28  are contained in gas outlet duct  26 , or other suitable connection, which directs combustion exhaust gas  28  through system  100 . Gas outlet duct  26  generally provides flow communication between components of system  100  through a passage in which combustion exhaust gas  28  is channeled. It is apparent to those skilled in the art and guided by the teachings herein provided that gas outlet duct  26  may have any suitable size, shape and/or diameter to accommodate any supply of combustion gas produced during the described combustion process. 
         [0018]    In the exemplary embodiment, gas outlet duct  26  is coupled to a pollution control device  32  and is in flow communication therewith. Pollution control device  32  is coupled to exit duct  34  and is in flow communication therewith. Exit duct  34  is coupled to chimney  36  and is in flow communication to chimney  36 . Exit gases are released into the atmosphere through chimney  36 . 
         [0019]    In operation, a stream of high temperature combustion gas  24  is generated and directed to flow through gas outlet duct  26 . Combustion gas  24  is discharged as combustion exhaust gas  28 . Combustion exhaust gas  28  is directed to pollution control device  32 . It is apparent to those skilled in the art and guided by the teachings herein provided that pollution control device  32  may have any suitable size, shape and/or diameter to accommodate any supply of combustion exhaust gas  28  produced during the described combustion process. Pollution control device  32  includes for example, but is not limited to a selective catalyst reduction device, an electrostatic precipitator, a baghouse, an activated carbon injection device, a flue gas desulfurization device, and/or any other mercury emission, nitrogen oxide emission and particulate emission control system technologies. Pollution control device  32  discharges into and provides a flow stream to exit duct  34  which directs a flow stream to chimney  36 . Exit gases are released into the atmosphere through chimney  36 . 
         [0020]    In operation, system  100  facilitates continuously removing and reducing hazardous and/or toxic compounds, such as mercury emissions from the high temperature combustion gas stream produced during combustion within combustion device  18 . 
         [0021]    In one exemplary embodiment, a method of injecting a mercury oxidizer upstream of combustion device  18  is presented. As used herein, a mercury oxidizer relates to an ion in solution or compound that combines with a mercury atom. In the exemplary embodiment, the mercury oxidizer includes MgCl 2 , which is stable up to 2600 degrees Fahrenheit. Specifically, in one embodiment, the mercury oxidizer includes at least one of a powder including MgCl 2  and an aqueous solution including MgCl 2 . MgCl 2  has a solubility in water of 54 g/100 ml and, therefore, an aqueous solution may contain up to 54% MgCl 2 . In another embodiment, the mercury oxidizer includes MgCl 2  along with air. The efficiency of mercury removal can be improved by adding MgCl 2  to the materials to be combusted. In an alternative embodiment, the efficiency of mercury removal can be improved by injecting MgCl 2  into the flue gas. In the exemplary embodiment, the solution is added in a ratio of approximately 0.5 pounds to approximately 3 pounds of MgCl 2  per approximately one ton of coal. Thermal decomposition of MgCl 2  produces Cl-containing species (HCl, Cl 2 , and Cl) which results in improved mercury oxidation and improves the efficiency of mercury removal. In an alternative embodiment, a method is provided of improving the efficiency of mercury removal by, for example, activated carbon injection, wet scrubbers and other mercury control technologies. 
         [0022]      FIG. 2  is a schematic view of an exemplary power plant system  200  according to one embodiment of the present invention. System  200  components  12 ,  14 ,  18 ,  20 ,  24 ,  26 ,  28 ,  32 ,  34  and  36  are also illustrated in  FIG. 1 . 
         [0023]    In the exemplary embodiment, system  200  includes a fuel storage device  12  such as but not limited to a bin, bunker, pile or silo in which a fuel supply is stored and collected prior to transport for combustion. Fuel storage device  12  is coupled in flow communication with a fuel transport device  14  which includes but is not limited to a feeder and piping arrangement used to transport fuel for combustion. In an alternative embodiment, an injection port extends into fuel transport device  14  and provides flow communication to fuel transport device  14 . Fuel transport device  14  is coupled to combustion device  18  and provides flow communication to combustion device  18 . Contained within combustion device  18  is fuel combustion zone  20 . In the exemplary embodiment, a second injection port  23  extends into combustion device  18  and channels and is in flow communication with combustion zone  20 . In an alternative embodiment, a third injection port extends into combustion device  18  downstream of combustion zone  20  and channels and is in flow communication with high temperature combustion gas  24 . 
         [0024]    In the exemplary embodiment, system  200  includes a furnace combustion device  18  that combusts a plurality of fuels, such as but not limited to coal, oil, or any solid, liquid or gaseous fuels in which a supply of combustion gases are produced. Combustion device  18  includes a combustion zone  20  wherein a fuel-air mixture is combusted causing a stream of high temperature combustion gas  24  to be generated. Combustion device  18  is coupled to gas outlet duct  26  that is configured to channel combustion exhaust gas  28  from combustion device  18 . 
         [0025]    More specifically, combustion exhaust gases  28  are contained in gas outlet duct  26 , or other suitable connection, which directs combustion exhaust gas  28  through system  200 . Gas outlet duct  26  generally provides flow communication between components of system  200  through a passage in which combustion exhaust gas  28  is channeled. It is apparent to those skilled in the art and guided by the teachings herein provided that gas outlet duct  26  may have any suitable size, shape and/or diameter to accommodate any supply of combustion gas produced during the described combustion process. 
         [0026]    In the exemplary embodiment, gas outlet duct  26  is coupled to a pollution control device  32  and is in flow communication therewith. Pollution control device  32  is coupled to exit duct  34  and is in flow communication therewith. Exit duct  34  is coupled to chimney  36  and is in flow communication with chimney  36 . Exit gases are released into the atmosphere through chimney  36 . 
         [0027]    In operation, system  200  facilitates continuously removing and reducing hazardous and/or toxic compounds, such as mercury emissions from the stream of high temperature combustion gas  24  produced during combustion within combustion device  18 . 
         [0028]    Fuel storage device  12  provides the combustible materials in flow communication with fuel transport device  14  which includes but is not limited to a feeder and piping arrangement used to transport fuel for combustion. In an alternative embodiment, a first injection port extends into fuel transport device  14  and is configured to inject a flow of mercury oxidizer to the combustible materials directed through fuel transport device  14 . In another embodiment, a first injection port is positioned upstream of fuel storage device  12  and provides mercury oxidizer to the combustible materials directed to fuel storage device  12 . Fuel transport device  14  provides a flow of combustible materials including the mercury oxidizer to combustion device  18 . 
         [0029]    In the exemplary embodiment, combustion device  18  is configured to combust a plurality of fuels, such as but not limited to coal, oil, or any solid, liquid or gaseous fuels in which a supply of combustion gases are produced. Combustion device  18  is configured with a combustion zone  20  wherein a fuel-air mixture is combusted causing a stream of high temperature combustion gas  24  to be generated. In an alternative embodiment, combustion device  18  is configured with but not limited to, additional combustion gas emission reducing equipment such as over fire air injection ports and gas reburn systems. 
         [0030]    In an alternative embodiment, an air injection port  22  (shown in  FIG. 1 ) is coupled with combustion device  18  to provide combustion air flow to combustion zone  20 . In the exemplary embodiment, a second injection port  23  is coupled with combustion device  18  to provide a mercury oxidizer flow to combustion zone  20 . Second injection port  23  is formed as an injection tree, injection ring header or any other injection device configured to inject a flow of mercury oxidizer. In an alternative embodiment, a third injection port is coupled with combustion device  18  downstream of combustion zone  20  to provide mercury oxidizer flow to high temperature combustion gas  24 . 
         [0031]    In one exemplary embodiment, a method is provided of injecting a mercury oxidizer on the materials to be combusted in combustion zone  20  of combustion device  18 . The mercury oxidizer, in one embodiment, is at least one of an ion in solution and a compound that combines with a mercury atom. In the exemplary embodiment, the mercury oxidizer includes MgCl 2 , which is stable up to 2600 degrees Fahrenheit. Specifically, in one embodiment, the mercury oxidizer includes at least one of a powder including MgCl 2  and an aqueous solution including MgCl 2 . MgCl 2  has a solubility in water of 54 g/100 ml and, therefore, an aqueous solution may contain up to 54% MgCl 2 . In another embodiment, the mercury oxidizer includes MgCl 2  along with air. The efficiency of mercury removal can be improved by injecting MgCl 2  to the materials to be combusted in combustion zone  20 . In an alternative embodiment, the efficiency of mercury removal can be improved by injecting MgCl 2  into the flue gas downstream of combustion zone  20 . In another alternative embodiment, the efficiency of mercury removal can be improved by injecting MgCl 2  into the materials to be combusted upstream of combustion device  18 . In the exemplary embodiment, the solution is added in a ratio of approximately 0.5 pounds to approximately 3 pounds of MgCl 2  per approximately one ton of coal. Thermal decomposition of MgCl 2  produces Cl-containing species (HCl, Cl 2 , and Cl) which results in improved mercury oxidation and improves the efficiency of mercury removal. In an alternative embodiment, a method is provided of improving the efficiency of mercury removal by using activated carbon injection, wet scrubbers and other mercury control technologies. 
         [0032]    In the exemplary embodiment, system  200  generates a stream of high temperature combustion gas  24  that is in flow communication with gas outlet duct  26  and is discharged as combustion exhaust gas  28 . Combustion exhaust gas  28  is in flow communication with pollution control device  32 . It is apparent to those skilled in the art and guided by the teachings herein provided that pollution control device  32  may have any suitable size, shape and/or diameter to accommodate any supply of combustion exhaust gas  28  produced during the described combustion process. Pollution control device  28  includes, for example, but is not limited to, a selective catalyst reduction device, an electrostatic precipitator, a baghouse, an activated carbon injection device, a flue gas desulfurization device, and/or any other mercury emission, nitrogen oxide emission and particulate emission control system technologies. Pollution control device  32  discharges flow to exit duct  34  which directs flow to chimney  36 . Exit gases are released into the atmosphere through chimney  36 . 
         [0033]      FIG. 3  is a schematic view of an exemplary power plant system  300  according to one embodiment of the present invention. System  300  components  12 ,  14 ,  18 ,  20 ,  24 ,  26 ,  28 ,  32 ,  34  and  36  are also shown in  FIGS. 1 and 2 . In the exemplary embodiment, system  300  includes a fuel storage device  12  such as but not limited to a bin, bunker, pile or silo in which a fuel supply is stored and collected prior to transport for combustion. Fuel storage device  12  is coupled in flow communication with a fuel transport device  14  which includes but is not limited to a feeder and piping arrangement used to transport fuel for combustion. In an alternative embodiment, the first injection port extends into fuel transport device  14  and is in flow communication therewith. Fuel transport device  14  is coupled to combustion device  18  and is in flow communication therewith. Contained within combustion device  18  is fuel combustion zone  20 . In an alternative embodiment, the second mercury oxidizer injection port extends into combustion device  18  and is in flow communication with combustion zone  20 . The third mercury oxidizer injection port  25  extends into combustion device  18  downstream of combustion zone  20  and is in flow communication with high temperature combustion gas  24 . 
         [0034]    In the exemplary embodiment, system  300  includes a furnace combustion device  18  that combusts a plurality of fuels, such as but not limited to coal, oil, or any solid, liquid or gaseous fuels in which a supply of combustion gases is produced. Combustion device  18  includes a combustion zone  20  wherein a fuel-air mixture is combusted causing a stream of high temperature combustion gas  24  to be generated. Combustion device  18  is coupled to gas outlet duct  26  that is configured to channel combustion exhaust gas  28  from combustion device  18 . 
         [0035]    More specifically, combustion exhaust gases  28  are contained in gas outlet duct  26 , or other suitable connection, which directs combustion exhaust gas  28  through system  300 . Gas outlet duct  26  generally provides flow communication between components of system  300  through a passage in which combustion exhaust gas  28  is channeled. It is apparent to those skilled in the art and guided by the teachings herein provided that gas outlet duct  26  may have any suitable size, shape and/or diameter to accommodate any supply of combustion gas produced during the described combustion process. 
         [0036]    In the exemplary embodiment, gas outlet duct  26  is coupled to a pollution control device  32  and is in flow communication therewith. Pollution control device  32  is coupled to exit duct  34  and is in flow communication therewith. Exit duct  34  is coupled to chimney  36  and provides flow communication to chimney  36 . Exit gases are released into the atmosphere through chimney  36 . 
         [0037]    In operation, system  300  facilitates continuously removing and reducing hazardous and/or toxic compounds, such as mercury emissions from the stream of high temperature combustion gas  24  produced during combustion within combustion device  18 . Fuel storage device  12  provides the combustible materials in flow communication with fuel transport device  14  which includes but is not limited to a feeder and piping arrangement used to transport fuel for combustion. In an alternative embodiment, a first injection port extends into fuel transport device  14  and is configured to inject a flow of mercury oxidizer into the combustible materials directed through fuel transport device  14 . In another alternative embodiment, a first injection port is positioned upstream of fuel storage device  12  to provide mercury oxidizer flow to the combustible materials directed to fuel storage device  12 . Fuel transport device  14  provides a flow of combustible materials including the first mercury oxidizer to combustion device  18 . 
         [0038]    In the exemplary embodiment, combustion device  18  is configured to combust a plurality of fuels, such as but not limited to coal, oil, or any solid, liquid or gaseous fuels in which a supply of combustion gases is produced. Combustion device  18  is coupled with a combustion zone  20  wherein a fuel-air mixture is combusted causing a stream of high temperature combustion gas  24  to be generated. In an alternative embodiment, combustion device  18  is configured with but not limited to, additional combustion gas emission reducing equipment such as over fire air injection ports and gas reburn systems. 
         [0039]    In an alternative embodiment, an air injection port is coupled with combustion device  18  to provide combustion air flow to combustion zone  20 . In another alternative embodiment, a second injection port is coupled with combustion device  18  to provide a mercury oxidizer flow to combustion zone  20 . In the exemplary embodiment, a third injection port  25  is coupled with combustion device  18  downstream of combustion zone  20  to provide mercury oxidizer flow to high temperature combustion gas  24 . The third injection port  25  is formed as an injection tree, injection ring header or any other injection device configured to inject a flow of mercury oxidizer. The mercury oxidizer includes, in one embodiment, at least one of an ion in solution and compound that combines with a mercury atom. In the exemplary embodiment, the mercury oxidizer includes MgCl 2 , which is stable up to 2600 degrees Fahrenheit. Specifically, in one embodiment, the mercury oxidizer includes at least one of a powder including MgCl 2  and an aqueous solution including MgCl 2 . MgCl 2  has a solubility in water of 54 g/100 ml and, therefore, an aqueous solution may contain up to 54% MgCl 2 . In another embodiment, the mercury oxidizer includes MgCl 2  along with air. The efficiency of mercury removal can be improved by injecting MgCl 2  into the flue gas downstream of the combustion zone  20 . In an alternative embodiment, the efficiency of mercury removal can be improved by injecting MgCl 2  to the materials to be combusted in combustion zone  20 . In another alternative embodiment, the efficiency of mercury removal can be improved by injecting MgCl 2  into the materials to be combusted upstream of combustion device  18 . In the exemplary embodiment, the solution is added in a ratio of approximately 0.5 pounds to approximately 3 pounds of MgCl 2  per approximately one ton of coal. Thermal decomposition of MgCl 2  produces Cl-containing species (HCl, Cl 2 , and Cl) which results in improved mercury oxidation and improves the efficiency of mercury removal. In an alternative embodiment, a method is provided of improving the efficiency of mercury removal by utilizing activated carbon injection, wet scrubbers and other mercury control technologies. 
         [0040]    In the exemplary embodiment, system  300  includes a stream of high temperature combustion gas  24  that is generated and is in flow communication with gas outlet duct  26  and is discharged as combustion exhaust gas  28 . Combustion exhaust gas  28  is in flow communication with pollution control device  32 . It is apparent to those skilled in the art and guided by the teachings herein provided that pollution control device  32  may have any suitable size, shape and/or diameter to accommodate any supply of combustion exhaust gas  28  produced during the described combustion process. Pollution control device  28  includes, for example, at least one of a selective catalyst reduction device, an electrostatic precipitator, a baghouse, an activated carbon injection device, a flue gas desulfurization device, and/or any other mercury emission, nitrogen oxide emission and particulate emission control system technologies. Pollution control device  32  discharges flow to exit duct  34 . Exit duct  34  is in flow communication with chimney  36 . Exit gases are released into the atmosphere through chimney  36 . 
         [0041]    Exemplary embodiments of a method and system for continuously removing mercury from a supply of combustion gas are described above in detail. The method and system are not limited to the specific embodiments described herein, but rather, steps of the method and/or components of the system may be utilized independently and separately from other steps and/or components described herein. Further, the described method steps and/or system components can also be defined in, or used in combination with, other methods and/or systems, and are not limited to practice with only the method and system as described herein. 
         [0042]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.