Abstract:
The invention relates to an integrated power plant, which burns fuel using an oxygen-enriched stream in a combustion furnace and converts emissions of air pollutants and carbon dioxide into byproducts. The combustion flue gas stream, after leaving an economizer of a steam generation system, splits into stream A and stream B. Stream A recirculates back to the combustion furnace through the first flue gas recirculation fan for combustion temperature control. Stream B, after passing through a dust collector for fly ash removal, a series of condensers for byproduct recovery, and the second flue gas recirculation fan, mixes with an oxygen-enriched stream from an air separation unit and flows back to the combustion furnace. The plant does not need an exhaust stack and does not discharge combustion flue gases into the atmosphere.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     
       
         
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 U.S. Patent Documents 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 5,906,806 
                 May, 1999 
                 Clark 
                  60/649 
               
               
                   
                 5,937,652 
                 Aug., 1999 
                 Abdelmalek 
                  60/648 
               
               
                   
                 6,047,547 
                 Apr., 2000 
                 Heaf 
                  60/618 
               
               
                   
                 6,116,169 
                 Sep., 2000 
                 Miyoshi, et al 
                 110/216 
               
               
                   
                 6,196,000 
                 Mar., 2001 
                 Fassbender 
                  60/649 
               
               
                   
                 6,282,901 
                 Sep., 2001 
                 Marin, et al. 
                  60/649 
               
               
                   
                   
               
             
          
         
       
     
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     KOH is the last name of the inventor, and this invention is called KOH flue gas recirculation power plant with waste heat and byproduct recovery. 
     The invention relates to a process for power generation, which is both environmentally sound and cost-effective. More specifically, the invention relates to a process of burning any combustible material for efficient power generation, elimination of air pollutants and carbon dioxide emissions, and recovery of liquid nitrogen dioxide, liquid sulfur dioxide, and liquid carbon dioxide. 
     2. Description of the Prior Art 
     A conventional power plant consisting of a combustion furnace, a steam boiler, steam turbines, and a dust collector has been implemented for power generation and steam production for several, decades. Conventional power plants, particularly for coal-fired plants, emit a huge amount of nitrogen oxides, sulfur dioxide, carbon monoxide, particulate matters, heavy metals, and incomplete combustion products. Since air pollution control requirements become more stringent from time to time, power plants must be equipped with more sophisticated and expensive pollution control systems to meet regulatory emission limits. For sulfur oxides emission control, a flue gas desulfurization system or a fluidized bed combustion furnace is widely used. For nitrogen oxides emission control, power plants have implemented a combustion flue gas recirculation for staged combustion with steam or water injection, low NOx burners, selective catalytic reduction systems, non-selective catalytic systems, or any combination thereof to meet the emission limits. 
     Since the 1980&#39;s, the integrated gasification combined cycle (IGCC) concept has been explored extensively. IGCC uses an oxygen stream for coal gasification and produces a gaseous stream consisting of methane, hydrogen sulfide, carbon monoxide, ammonia, etc. The gaseous stream passes through a sulfur removal system such as a Claus plant before burning in a gas turbine. In addition to requiring an expensive sulfur removal system, an IGCC plant must implement a nitrogen oxides removal system in order to meet regulatory requirements. 
     Since the Kyoto Accord for reduction of carbon dioxide, which is a greenhouse gas that causes global warming and associated climatic changes, coal-fired power plants have been extensively scrutinized. Although a coal-fired power plant is still the most cost-effective in power generation, its carbon dioxide emission is more than two times that of a natural gas fired plant. An MEA scrubbing system using monoethanolamine as absorbing agent has been implemented to recover carbon dioxide from combustion flue gases, but it is still not cost-effective. To enhance carbon dioxide recovery, oxygen is increasingly proposed as a replacement of air in fuel burning to reduce the volume of combustion flue gases and to increase the concentration of carbon dioxide in combustion flue gases. 
     U.S. Pat. No. 5,906,806 issued to Clark proposes to burn fuel using oxygen, water, and a recirculated combustion stream from a baghouse in two combustion furnaces. For additional air pollution control, Clark&#39;s proposal requires several expensive control systems, which include an electron beam reactor, an ozone oxidation chamber, and an electrostatic precipitator with catalytic reactor. In addition, the combustion product discharged to the atmosphere still contains some incomplete combustion products and nitrogen oxides and excess oxygen discharged with combustion flue gases reduces utilization of oxygen generated by an air separation unit. 
     U.S. Pat. 6,196,000 issued to Fassbender proposes to burn fuel using oxygen and liquid carbon dioxide recovered from combustion process. For enhancing thermodynamic efficiency and carbon dioxide recovery, Fassbender proposes to operate an elevated pressure power plant. All operating units including a reaction chamber, a combustion chamber, a catalyst chamber, a hydrocone, heat exchanges, and condensers are under extremely high pressure, ranging from 300 to 5000 psia. A pressurized vessel requires additional power to operate and become a safety concern. In addition, the pressurized power plant still vents to the atmosphere a combustion flue gas stream containing some air pollutants and oxygen. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is an integrated combustion process for efficient power generation, recovery of waste heat and byproduct, and elimination of air pollution. A combustion furnace, air separation units, a steam boiler with an economizer, a dust and acid gas removal system, several condensers, and absorption refrigeration units are integrated with two combustion flue gas recirculation loops to enhance steam production and to prevent combustion flue gases from being discharged into the atmosphere. 
     When oxygen is used instead of air for fuel combustion, the temperature of combustion products is extremely high. For combustion temperature control, the first combustion flue gas recirculation loop is implemented to recirculate part of the combustion gas stream from the economizer to the combustion furnace. How much of the combustion flue gas stream from the economizer to be recirculated back to the combustion furnace greatly depends on the chemical composition and heat content of fuel. 
     The combustion flue gas stream from the economizer, which is not recirculated back to the combustion furnace, passes through an oxygen-enriched stream heater for additional waste heat recovery, a fly ash and acid gas removal system, and several byproduct condensation units. After leaving the carbon dioxide condenser, it mixes with an oxygen-enriched stream from the air separation unit and flows back to the combustion furnace. The purpose of the second combustion flue gas recirculation loop is to eliminate any incomplete combustion products in the combustion furnace and reuse oxygen present in the combustion flue gas stream. Therefore, a combustion process designed according to the invention does not discharge combustion flue gases and air pollutants to the atmosphere. The nitrogen-enriched stream from the air separation unit is used in the condensers for byproduct recovery. 
     Absorption refrigeration units are integrated with the process to recover and convert waste steam from steam turbines to cooling. Cooling generated by absorption refrigeration units is used for enhancing condensing processes as well as providing extra cooling for industrial, commercial, or residential uses. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The integrated nature of the present invention&#39;s steps is better understood by reviewing the detailed description of the invention in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a block flow diagram of the present invention showing relationship between each combustion flue gas stream, oxygen-enriched stream, and nitrogen-enriched stream; 
     FIG. 2 is a table listing coal chemical composition, combustion products, boiling and melting temperatures, and heat of vaporization; and 
     FIG. 3 is a schematic representation of an integrated power plant incorporating the present invention to achieve no discharge of combustion flue gas and air pollutants. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows the objects of the present invention that is a process consisting of two flue gas recirculation loops to prevent the discharge of combustion flue gas from a power plant. The first flue gas recirculation loop comprises combustion flue gas stream  01 A, combustion flue gas stream  02 A, and first recirculated combustion flue gas stream  03 A. The second flue gas recirculation loop comprises combustion flue gas stream  01 A, combustion flue gas stream  02 A, combustion flue gas stream  03 B, combustion flue gas stream  04 A, second recirculated combustion flue gas stream  05 A, oxygen-enriched stream  06 A, and oxygen-enriched stream  05 B. FIG. 3 graphically depicts the relationship among various unit operations and various streams. 
     The heat content with chemical composition of fuel determines theoretical oxygen requirement. One pound of coal with heat content and chemical composition shown in FIG. 2 needs about 2.4 pounds of oxygen compared to 4.0 pounds of oxygen needed for one pound of methane. During a startup mode, when fuel stream  62  burns with oxygen-enriched stream  44  in combustion furnace  11 , liquid carbon dioxide stream or water stream  63  is injected into combustion furnace  11 , through feed pump  11 C, for combustion temperature control until the process reaches a normal mode of operation. 
     To maintain the combustion temperature between 2000 and 2500.degree.F. inside a refractory-wall combustion furnace, one pound of coal, with heat content and chemical composition shown in FIG. 2, requires between 8 and 12 pounds of liquid carbon dioxide or between 4 and 5 pounds of water. For one pound of methane, it needs between 18 and 24 pounds of liquid carbon dioxide or between 7.5 and 9.5 pounds of water. For a water-wall combustion furnace, it needs a less amount of liquid carbon dioxide or water for combustion temperature control because water flowing through water-wall tubes reduces combustion temperature. Combustion furnace  11  is a combustion device commonly known by those of ordinary skill in the art. Bottom ash from combustion chamber  11  drops into bottom ash collection tank  12 , which is equipped with water seals to prevent air from entering combustion chamber  11 . Sludge steam  59  is drawn from bottom ash collection tank  12  to an ash management and disposal system 
     Combustion flue gas stream  27  with a temperature between 2000 and 2500.degree.F. from combustion furnace  11  enters steam boiler  13  to convert water/steam stream  54  from economizer  15  to superheated steam  50  used in steam turbine  14  for electricity generation. Combustion flue gas stream  28  with a temperature between 800 and 1000.degree.F from steam boiler  13  enters economizer  15  to preheat water/steam stream  53  from de-aerator  24 , through pump  24 A. Combustion flue gas stream  29 ,with a temperature between 600 and 800.degree.F from economizer  15  enters flue gas manifold  16 , where it splits into combustion flue gas stream  30  and combustion flue gas stream  31 . Steam boiler  13  and economizer  15  are indirect heat exchanges commonly known by those of ordinary skill in the art. 
     Combustion flue gas stream  30  is recirculated back to combustion furnace  11 , through flue gas recirculation pump  11 A, for combustion temperature control. Combustion flue gas stream  31  enters oxygen-enriched stream heater  17 . The ratio of combustion flue gas stream  30  to combustion flue gas stream  31  depends on fuel involved in combustion. When the process reaches its normal mode of operation, the ratio for coal discussed in FIG. 2 is between 4 and 7 compared to a ratio between 5 and 8.5 for methane. The ratio of combustion flue gas stream  30  to combustion flue gas stream  31  is significantly lower for a water-wall combustion furnace. 
     In a normal operation mode, the volume of combustion flue gas stream  31  is less than 30 percent of that generated by a conventional power plant using air stream for combustion. Oxygen-enriched stream heater  17  is an indirect heat exchanger, which is commonly known by those of ordinary skill in the art. Inside oxygen-enriched stream heater  17 , combustion flue gas stream  31  preheats oxygen-enriched stream  43  from water vapor condenser  18 . 
     Combustion flue gas stream  32  with a temperature between 250 and 450.degree.F enters dust and acid gas removal unit  25  for fly ash and acid gas removal. Dust and acid gas removal unit  25  is a baghouse, a dry or wet cyclone, a dry or wet multiple-cyclone collector, a venturi scrubber, a packed bed absorber, an electrostatic precipitator, or any combination of thereof, which is commonly known by those of ordinary skill in the art. Dust and acid gas removal unit  25  is equipped with water seals to prevent air from entering combustion flue gas streams. For fuel containing chloride and other halogen, a multiple-cyclone collector with a packed bed absorber is preferably selected to remove fly ash, hydrogen chloride, sulfuric acid, and other hydrogen halides. If a baghouse is preferably implemented, carbon dioxide is used instead of air for bag cleaning to prevent air from entering combustion flue gas streams  32  and  33 . Fly ash and other acidic material collected by dust and acid gas removal unit  25  drop into fly ash collection tank  26  and sludge stream  60  is discharged to an ash management and disposal system. 
     Combustion flue gas stream  33  from dust and acid gas removal unit  25  enters water vapor condenser  18  for removal of water vapor, remaining fly ash, and any condensable material found in combustion flue gas stream  33 . Water vapor condenser  21  is an indirect heat exchanger, which is commonly known by those of ordinary skill in the art. Water collected from water vapor condenser  18  is preferably used for fly ash and bottom ash collection tanks. Inside water vapor condenser  18 , oxygen-enriched stream  42  from nitrogen dioxide condenser  19  serves as a main cooling stream. Nitrogen-enriched stream  48  from nitrogen dioxide condenser  19  as well as coolant stream  55  from absorption refrigeration unit  23  is arranged in the process to provide sufficient cooling for water vapor condenser  18 . 
     Combustion flue gas stream  34  with a temperature between 90 and 180.degree.F. from water collection tank  18 A, which is connected to water vapor condenser  18 , enters nitrogen dioxide condenser  19  for removal of nitrogen dioxide and any condensable material found in combustion flue gas stream  34 . Nitrogen dioxide condenser  21  is an indirect heat exchanger, which is commonly known by those of ordinary skill in the art. Inside nitrogen dioxide condenser  19 , oxygen-enriched stream  41  from sulfur dioxide condenser  20  serves as a main cooling stream. Nitrogen-enriched stream  47  from sulfur dioxide condenser  20  is arranged to provide sufficient cooling for nitrogen dioxide condenser  19 . Liquid nitrogen dioxide is a process byproduct, which could be used for production of nitric acid, nitrating or oxidizing agent, catalyst, rocket fuels, or polymerization inhibitor for acrylates. 
     Combustion flue gas stream  35  with a temperature between 20 and 60.degree.F. from liquid nitrogen dioxide collection tank  19 A, which is connected to nitrogen dioxide condenser  19 , enters sulfur dioxide condenser  20  for removal of sulfur dioxide and any condensable material found in combustion flue gas stream  35 . Sulfur dioxide condenser  20  is an indirect heat exchanger, which is commonly known by those of ordinary skill in the art. Inside sulfur dioxide condenser  20 , oxygen-enriched stream  40  from oxygen-enriched stream manifold  21 C serves as a main cooling stream. Nitrogen-enriched stream  46  from carbon dioxide condenser  21  is arranged to provide sufficient cooling for sulfur dioxide condenser  20 . Liquid sulfur dioxide is a process byproduct, which could be used for production of sulfuric acid, sulfite paper pulp, sulfonation of oil, antioxidant, reducing agent, and many other uses. 
     After leaving liquid sulfur dioxide collection tank  20 A, which is connected to sulfur dioxide condenser  20 , combustion flue gas stream  36  with a temperature between −60 and 10.degree.F. is pressurized by flue gas recirculation fan  21 B to a pressure above  77  psia and enters carbon dioxide condenser  21  for removal of carbon dioxide and any condensable material found in combustion flue gas stream  36 . Carbon dioxide condenser  21  is an indirect heat exchanger, which is commonly known by those of ordinary skill in the art. Inside carbon dioxide condenser  21 , both oxygen-enriched stream  38  and nitrogen-enriched stream  45  from air separation unit  22  serve as cooling streams. Liquid carbon dioxide is a major process byproduct, which could be used for refrigeration, carbonated beverages, aerosol propellant, fire extinguishing, fracturing and acidizing of oil wells, and many other uses. 
     After liquid carbon dioxide being removed, combustion flue gas stream  37  from liquid carbon dioxide collection tank  21 A, which is connected to carbon dioxide condenser  21 , is a small stream containing a small amount of carbon dioxide, carbon monoxide, nitric oxide, methane, ammonia, and oxygen. It enters oxygen-enriched stream manifold  21 C and combines with oxygen-enriched stream  39  from carbon dioxide condenser  21 . The purpose of this (second) combustion flue gas recirculation loop is to eliminate the discharge of combustion flue gases and air pollution into the atmosphere and fully utilize oxygen produced by air separation unit  22 . The combined stream, oxygen-enriched stream  40 , passes through sulfur dioxide condenser  20 , nitrogen dioxide condenser  19 , water vapor condenser  18 , and oxygen-enriched stream heater  17 . Then, it enters combustion furnace through forced draft fan  11 B to begin another combustion cycle. 
     Preferably, this invention incorporates absorption refrigeration unit  23 , which is commonly known by those of ordinary skill in the art, to recover waste steam stream  51  from steam turbine  14  for cooling, which is used for water vapor condenser  18 , air separation unit  22 , and other industrial, commercial, or residential use. For reducing energy consumption by air separation unit  22  in air separation process, coolant streams  57  and  58  are circulated between absorption refrigeration unit  23  and air separation unit  22 . To provide sufficient cooling for water vapor condenser  18 , coolant streams  55  and  56  are circulated between absorption refrigeration unit  23  and water vapor condenser  18 .