Purification of Carbon Dioxide

Abstract

Refrigeration duty in a carbon dioxide purification unit (CPU) operating at elevated pressure and sub-ambient temperature can be provided in at least a first part by indirect heat exchange against at least latent heat of at least one liquid first refrigerant, preferably carbon dioxide liquid(s) produced in the CPU, thereby typically evaporating the liquid(s), and a second part by indirect heat exchange with sensible heat energy alone of a second refrigerant. The second refrigerant may be nitrogen gas imported from an integrated cryogenic air separation unit (ASU) or carbon dioxide liquid exported from the CPU, cooled and returned to the CPU. One advantage is that total power consumption of the CPU and an integrated ASU is reduced.

1 . A method of purifying crude carbon dioxide gas containing at least one non-condensible gas contaminant, under elevated pressure in a carbon dioxide purification unit (“CPU”), said method comprising:
 feeding crude carbon dioxide gas to the CPU; 
 cooling and condensing carbon dioxide gas from the crude carbon dioxide gas; and 
 separating condensed carbon dioxide gas from said non-condensible gas contaminant(s) to produce at least one carbon dioxide liquid and a tail gas comprising said non-condensible gas contaminant(s), 
 
       wherein the method requires refrigeration duty for cooling and condensing carbon dioxide gas, said refrigeration duty being provided in at least a first part by indirect heat exchange against at least one liquid first refrigerant thereby evaporating said first refrigerant(s), and a second part by indirect heat exchange against sensible heat energy alone of at least one second refrigerant. 
     
     
         2 . The method according to  claim 1 , wherein at least a portion of said first part of the refrigeration duty is provided by at least one of said carbon dioxide liquid(s) as said liquid first refrigerant(s). 
     
     
         3 . The method according to  claim 1 , wherein a further part of said refrigeration duty is provided by indirect heat exchange against said tail gas. 
     
     
         4 . The method according to  claim 3 , wherein said further part is no more than 10% of said refrigeration duty. 
     
     
         5 . The method according to  claim 3 , wherein said first and second parts provide the remainder of said refrigeration duty. 
     
     
         6 . The method according to  claim 1 , wherein the second refrigerant has a temperature that is sufficiently low to cool said crude carbon dioxide gas to below the CO 2  dew point temperature, and preferably close to the CO 2  triple point temperature. 
     
     
         7 . The method according to  claim 1 , wherein the second refrigerant has a temperature that is sufficiently low to cool said crude carbon dioxide gas to a temperature from about −56° C. to about 10° C. 
     
     
         8 . The method according to  claim 1 , wherein said refrigeration duty has a colder part that both cools and condenses said crude carbon dioxide gas and a warmer part that cools the crude carbon dioxide gas with no condensation, said second refrigerant providing at least a portion of said colder part. 
     
     
         9 . The method according to  claim 1 , wherein said second refrigerant is used in a quantity that is no more than that sufficient to optimize power consumption. 
     
     
         10 . The method according to  claim 1 , wherein said second refrigerant provides no more than 30%, preferably no more than 20%, of the refrigeration duty. 
     
     
         11 . The method according to  claim 1 , wherein said second refrigerant is independent of said crude carbon dioxide gas. 
     
     
         12 . The method according to  claim 1 , wherein the second refrigerant is derived from said crude carbon dioxide gas and exported from the CPU for cooling. 
     
     
         13 . The method according to  claim 1 , wherein said second refrigerant is imported into the CPU. 
     
     
         14 . The method according to  claim 1 , wherein said second refrigerant is a gas. 
     
     
         15 . The method according to  claim 1 , wherein said second refrigerant is nitrogen gas. 
     
     
         16 . The method according to  claim 1 , wherein the CPU is integrated with a cryogenic air separation unit (“ASU”) and the second refrigerant is nitrogen gas imported from the ASU. 
     
     
         17 . The method according to  claim 1 , comprising:
 importing a pressurized gas into the CPU; and   expanding said pressurized gas in said CPU after optionally cooling said gas, to produce said second refrigerant.   
     
     
         18 . The method according to  claim 1 , comprising:
 separating compressed air feed by cryogenic distillation in an ASU to produce nitrogen gas under pressure and gaseous oxygen;   importing at least a portion of said nitrogen gas into the CPU;   cooling said imported nitrogen gas by indirect heat exchange to form cooled nitrogen gas;   expanding said cooled nitrogen gas in the CPU to produce expanded nitrogen gas; and   using said expanded nitrogen gas as said second refrigerant to produce warmed nitrogen gas.   
     
     
         19 . The method according to  claim 18 , wherein said imported nitrogen gas is cooled by indirect heat exchange against said liquid first refrigerant(s) and/or said second refrigerant and/or said tail gas, to form said cooled nitrogen gas. 
     
     
         20 . The method according to  claim 18 , wherein the imported nitrogen gas is cooled to a temperature in the range from about −40° C. to about 10° C. 
     
     
         21 . The method according to  claim 18 , wherein the cooled nitrogen gas is expanded to a pressure from about 1 bar to about 4 bar. 
     
     
         22 . The method according to  claim 18 , wherein a portion of the carbon dioxide liquid(s) is removed from the CPU as a liquid product and optionally pumped and warmed to ambient temperature. 
     
     
         23 . The method according to  claim 18 , wherein said cooled nitrogen gas is expanded in a first expander, warmed and then further expanded in a second expander. 
     
     
         24 . The method according to  claim 1 , comprising importing said second refrigerant into the CPU and using said second refrigerant directly to provide said second part of the refrigeration duty. 
     
     
         25 . The method according to  claim 1 , comprising:
 separating compressed air feed by cryogenic distillation in an ASU to produce nitrogen gas under pressure and gaseous oxygen;   expanding at least a portion of said nitrogen gas in the ASU to produce expanded nitrogen gas;   importing said expanded nitrogen gas into the CPU; and   using said expanded nitrogen gas as said second refrigerant to produce warmed nitrogen gas.   
     
     
         26 . The method according to  claim 25 , comprising:
 removing water and carbon dioxide from compressed air in a purification unit having at least one sorbent bed to produce said compressed air feed for the ASU; and   regenerating said sorbent bed(s) using at least a portion of said warmed nitrogen gas.   
     
     
         27 . The method according to  claim 1  wherein the second refrigerant is a liquid. 
     
     
         28 . The method according to  claim 1 , wherein the second refrigerant is carbon dioxide liquid. 
     
     
         29 . The method according to  claim 1 , wherein the second refrigerant is at least a portion of said carbon dioxide liquid(s). 
     
     
         30 . The method according to  claim 1 , wherein said CPU comprises two phase separators, said method comprising:
 cooling and condensing carbon dioxide gas in the crude carbon dioxide gas;   separating the condensed carbon dioxide gas from said non-condensible gas contaminant(s) in a first phase separator to produce a first carbon dioxide liquid and a first overhead vapour comprising said non-condensible gas contaminant(s);   dividing said first carbon dioxide liquid into three portions;   pumping a first portion of said first carbon dioxide liquid to produce a pumped first portion;   reducing the pressure of a second portion of said first carbon dioxide liquid to produce a reduced pressure second portion;   pumping a third portion of said first carbon dioxide liquid to produce a pumped third portion, and cooling the pumped third portion to produce a cooled third portion;   cooling and condensing carbon dioxide gas in said first overhead vapour;   separating the condensed carbon dioxide gas from said non-condensible gas contaminant(s) in a second phase separator to produce a second carbon dioxide liquid and said tail gas comprising said non-condensible gas contaminant(s);   warming said tail gas by indirect heat exchange to produce warmed tail gas; and   reducing the pressure of said second carbon dioxide liquid after optionally warming said liquid, to produce reduced pressure second carbon dioxide liquid, wherein the liquid first refrigerant(s) providing the first part of the refrigeration duty are the pumped first portion of first carbon dioxide liquid, the reduced pressure second portion of first carbon dioxide liquid and the reduced pressure second carbon dioxide liquid, and wherein the second refrigerant is the cooled third portion of the first carbon dioxide liquid.   
     
     
         31 . The method according to  claim 30 , wherein the pumped third portion of the first carbon dioxide liquid is cooled by indirect heat exchange against expanded nitrogen gas in an integrated ASU. 
     
     
         32 . The method according to  claim 1 , wherein the CPU is integrated with an oxyfuel combustion unit producing a net flue gas that is compressed and dried to produce said crude carbon dioxide gas. 
     
     
         33 . The method according to  claim 30 , wherein oxygen for the oxyfuel combustion unit is supplied from an ASU integrated with the CPU. 
     
     
         34 . The method according to  claim 1 , wherein at least a portion of the carbon dioxide liquid(s) is removed from the CPU and stored as a liquid. 
     
     
         35 . The method according to  claim 1 , wherein at least a portion of the carbon dioxide liquid(s) is removed from the CPU, pumped and optionally heated to ambient temperature. 
     
     
         36 . A method for generating power, said method comprising:
 combusting a fuel selected from the group consisting of carbonaceous fuels, hydrocarbonaceous fuels and biomass, in an oxygen-rich atmosphere within an oxyfuel combustion unit to produce heat and flue gas;   recovering at least a portion of said heat to generate said power;   dividing said flue gas after optionally desulfurizing said flue gas, into recycle flue gas and net flue gas;   recycling said recycle flue gas to the oxyfuel combustion unit;   compressing and drying said net flue gas to produce dry flue gas under elevated pressure containing at least one non-condensible contaminant;   feeding said dry flue gas to a CPU wherein carbon dioxide gas from said dry flue gas is cooled and condensed, and separated from said non-condensible gas contaminant(s) to produce at least one carbon dioxide liquid and a tail gas comprising said non-condensible gas contaminants;   separating compressed air by cryogenic distillation in an ASU to produce nitrogen gas under elevated pressure and gaseous oxygen;   feeding at least a portion of said gaseous oxygen to said oxyfuel combustion unit;   feeding at least a portion of said nitrogen gas to the CPU wherein the nitrogen gas is cooled by indirect heat exchange to produce cooled nitrogen gas which is then expanded to produce expanded nitrogen gas;   
       wherein the method in the CPU requires refrigeration duty, said refrigeration duty being provided in at least a first part by indirect heat exchange against at least a portion of said carbon dioxide liquid(s) thereby evaporating said liquid(s), and a second part by indirect heat exchange against sensible heat energy alone of said expanded nitrogen gas. 
     
     
         37 . The method according to  claim 36 , wherein the imported nitrogen gas is cooled to a temperature in the range from about −40° C. to about 10° C. 
     
     
         38 . The method according to  claim 36 , wherein the cooled nitrogen gas is expanded to a pressure in the range from about 1 bar to about 4 bar. 
     
     
         39 . The method according to  claim 36 , wherein a portion of the carbon dioxide liquid(s) is removed from the CPU as a liquid product and optionally pumped and warmed to ambient temperature. 
     
     
         40 . The method according to  claim 36 , wherein said cooled nitrogen gas is expanded in a first expander, warmed and then further expanded in a second expander to produce said expanded nitrogen gas. 
     
     
         41 . A method for generating power, said method comprising:
 combusting a fuel selected from the group consisting of carbonaceous fuels, hydrocarbonaceous fuels and biomass, in an oxygen-rich atmosphere within an oxyfuel combustion unit to produce heat and flue gas;   recovering at least a portion of said heat to generate said power;   dividing said flue gas after optionally desulfurizing said flue gas, into recycle flue gas and net flue gas;   recycling said recycle flue gas to the oxyfuel combustion unit;   compressing and drying said net flue gas to produce dry flue gas under elevated pressure containing at least one non-condensible contaminant;   feeding said dry flue gas to a CPU wherein carbon dioxide gas from said dry flue gas is cooled and condensed, and separated from said non-condensible gas contaminant(s) to produce at least one carbon dioxide liquid and a tail gas comprising said non-condensible gas contaminants;   separating compressed air by cryogenic distillation in an ASU to produce nitrogen gas under elevated pressure and gaseous oxygen;   feeding at least a portion of said gaseous oxygen to said oxyfuel combustion unit;   expanding in the ASU at least a portion of said nitrogen gas to produce expanded nitrogen gas; and   feeding said expanded nitrogen gas to said CPU;   
       wherein the method in the CPU requires refrigeration duty, said refrigeration duty being provided in at least a first part by indirect heat exchange against at least a portion of said carbon dioxide liquid(s) thereby evaporating said liquid(s), and a second part by indirect heat exchange against sensible heat energy alone of said expanded nitrogen gas. 
     
     
         42 . A method for generating power, said method comprising:
 combusting a fuel selected from the group consisting of carbonaceous fuels, hydrocarbonaceous fuels and biomass, in an oxygen-rich atmosphere within an oxyfuel combustion unit to produce heat and flue gas;   recovering at least a portion of said heat to generate said power;   dividing said flue gas after optionally desulfurizing said flue gas, into recycle flue gas and net flue gas;   recycling said recycle flue gas to the oxyfuel combustion unit;   compressing and drying said net flue gas to produce dry flue gas under elevated pressure containing at least one non-condensible contaminant;   feeding said dry flue gas to a CPU for purification, said purification comprising:
 cooling and condensing carbon dioxide gas in the dry flue gas; 
 separating the condensed carbon dioxide gas from said non-condensible gas contaminant(s) in a first phase separator to produce a first carbon dioxide liquid and a first overhead vapour comprising said non-condensible gas contaminant(s); 
 dividing said first carbon dioxide liquid into three portions; 
 pumping a first portion of said first carbon dioxide liquid to produce a pumped first portion; 
 reducing the pressure of a second portion of said first carbon dioxide liquid to produce a reduced pressure second portion; 
 pumping a third portion of said first carbon dioxide liquid to produce a pumped third portion, and cooling the pumped third portion to produce a cooled third portion; 
 cooling and condensing carbon dioxide gas in said first overhead vapour; 
 separating the condensed carbon dioxide gas from said non-condensible gas contaminant(s) in a second phase separator to produce a second carbon dioxide liquid and said tail gas comprising said non-condensible gas contaminant(s); 
 warming said tail gas by indirect heat exchange to produce warmed tail gas; and 
 reducing the pressure of said second carbon dioxide liquid after optionally warming said liquid, to produce reduced pressure second carbon dioxide liquid, separating compressed air by cryogenic distillation in an ASU to produce nitrogen gas under elevated pressure and gaseous oxygen; 
   feeding at least a portion of said gaseous oxygen to said oxyfuel combustion unit; and   expanding at least a portion of said nitrogen gas to produce expanded nitrogen gas;   
       wherein the method in the CPU requires refrigeration duty, said refrigeration duty being provided in at least a first part by indirect heat exchange with the pumped first portion of first carbon dioxide liquid, the reduced pressure second portion of first carbon dioxide liquid and the reduced pressure second carbon dioxide liquid, and a second part by indirect heat exchange with sensible heat energy alone of the cooled third portion of the first carbon dioxide liquid. 
     
     
         43 . The method according to  claim 42 , wherein the pumped third portion of the first carbon dioxide liquid is cooled by indirect heat exchange against said expanded nitrogen gas.