Apparatus and process for separating CO2 from a flue gas

Abstract

An apparatus and a process for separating carbon dioxide from a flue gas of a coal burning power plant. The process includes compressing the flue gas to increase the pressure and temperature, and then passing the flue gas through a cryogenic heat exchanger that decreases the temperature even more prior to passing the cooled carbon dioxide through a turbine that decreases the temperature more and forms liquid and solid forms carbon dioxide. A carbon dioxide separator then separates the carbon dioxide from the flue gas, leaving both liquid and solids forms. A screw compressor compresses the solid carbon dioxide to produce only liquid carbon dioxide at a pressure suitable for sequestration. The liquid carbon dioxide is passed through the heat exchanger to cool the flue gas and to separate out any sulfur dioxide and water from the flue gas and to vaporize the liquid carbon dioxide prior to sequestration of the vapor carbon dioxide.

1 . An apparatus to separate carbon dioxide from a flue gas of a power plant comprising:
 a compressor to increase a pressure and a temperature of the flue gas;   an air cooler means located downstream from the compressor to cool the flue gas from the compressor;   a heat exchanger located downstream from the air cooler means to cool the flue gas exiting from the air cooler means and separate sulfur dioxide from the flue gas;   a turbine located downstream from the heat exchanger to form a liquid and a solid form of carbon dioxide from the flue gas;   a carbon dioxide separator means located downstream from the turbine to separate carbon dioxide from the flue gas from the turbine;   a screw compressor to liquefy the solid form of carbon dioxide from the carbon dioxide separator means and pass the liquid carbon dioxide through the heat exchanger to covert the liquid carbon dioxide into a vapor and cool the flue gas passing through the heat exchanger; and,   the flue gas from the carbon dioxide separator being passed through the heat exchanger to add heat to the liquid carbon dioxide from the screw compressor.   
     
     
         2 . The apparatus to separate carbon dioxide from a flue gas of  claim 1 , and further comprising:
 the air cooler means is an air cooler fan.   
     
     
         3 . The apparatus to separate carbon dioxide from a flue gas of  claim 1 , and further comprising:
 the air cooler means is a feed water heater with an air cooler fan located downstream from the feed water heater.   
     
     
         4 . The apparatus to separate carbon dioxide from a flue gas of  claim 1 , and further comprising:
 the air cooler means is a second heat exchanger that also heats up the flue gas from the first heat exchanger; and,   a second turbine to pass the flue gas from the first heat exchanger and drive an electric generator.   
     
     
         5 . The apparatus to separate carbon dioxide from a flue gas of  claim 1 , and further comprising:
 the carbon dioxide separator means includes a carbon dioxide separator located between the turbine and the heat exchanger.   
     
     
         6 . The apparatus to separate carbon dioxide from a flue gas of  claim 5 , and further comprising:
 the turbine located between the heat exchanger and the carbon dioxide separator means includes means to heat the turbine so that solid carbon dioxide does not form on the turbine.   
     
     
         7 . The apparatus to separate carbon dioxide from a flue gas of  claim 6 , and further comprising:
 the means to heat the turbine includes a passage formed within the turbine to pass a heated fluid.   
     
     
         8 . The apparatus to separate carbon dioxide from a flue gas of  claim 6 , and further comprising:
 the means to heat the turbine includes an electric heating element within the turbine.   
     
     
         9 . The apparatus to separate carbon dioxide from a flue gas of  claim 1 , and further comprising:
 the carbon dioxide separator means includes the heat exchanger with solid and liquid carbon dioxide from the heat exchanger passed into the screw compressor; and,   the liquid carbon dioxide from the screw compressor passed through the heat exchanger to convert the liquid carbon dioxide into a lapor.   
     
     
         10 . The apparatus to separate carbon dioxide from a flue gas of  claim 1 , and further comprising:
 the turbine located between the heat exchanger and the carbon dioxide separator drives an electric generator.   
     
     
         11 . The apparatus to separate carbon dioxide from a flue gas of  claim 1 , and further comprising:
 the heat exchanger is a cryogenic heat exchanger.   
     
     
         12 . A process for separating carbon dioxide from a flue gas of a power plant, the process comprising the steps of:
 increasing the pressure and the temperature of the flue gas;   cooling the flue gas without decreasing the pressure of the flue gas;   passing the flue gas through a heat exchanger to cool the flue gas and to separate water and sulfur dioxide from the flue gas;   passing the pressurized flue gas from the heat exchanger through a turbine to produce solid and liquid forms of carbon dioxide;   separating the solid and liquid forms of carbon dioxide from the flue gas;   increasing the pressure of the solid and liquid forms of carbon dioxide to eliminate the solid form of carbon dioxide and produce an all liquid form carbon dioxide and to a pressure suitable for sequestration of the carbon dioxide; and,   passing the pressurized and liquid form of carbon dioxide through the heat exchanger to cool the flue gas and convert the liquid carbon dioxide into a vapor.   
     
     
         13 . The process for separating carbon dioxide of  claim 12 , and further comprising the step of:
 heating the turbine to prevent carbon dioxide ice for forming within the turbine.   
     
     
         14 . The process for separating carbon dioxide of  claim 12 , and further comprising the step of:
 prior to passing the compressed flue gas through the first heat exchanger, passing the compressed flue gas through a second heat exchanger to heat the flue gas exiting from the first heat exchanger and drive a second turbine.   
     
     
         15 . The process for separating carbon dioxide of  claim 12 , and further comprising the step of:
 separating the solid and liquid forms of carbon dioxide from the flue gas exiting from the turbine and increasing the pressure of the solid and liquid forms of carbon dioxide to eliminate the solid carbon dioxide prior to passing the liquid carbon dioxide through the heat exchanger.   
     
     
         16 . The process for separating carbon dioxide of  claim 12 , and further comprising the steps of:
 separating the carbon dioxide from the flue gas in the heat exchanger to form a first flow of carbon dioxide and then in a second carbon dioxide separator after passing the flue gas through the turbine to form a second flow of carbon dioxide; and,   combining the two flows of carbon dioxide and pressurizing the carbon dioxide to form only liquid carbon dioxide to pass through the heat exchanger at a pressure suitable for sequestration.