Controlled Freeze Zone Tower

Abstract

A cryogenic distillation tower is provided for the separation of a fluid stream containing at least methane and carbon dioxide. The cryogenic distillation tower has a lower stripping section, an upper rectification section, and an intermediate spray section. The intermediate spray section includes a plurality of spray nozzles that inject a liquid freeze zone stream. The nozzles are configured such that substantial liquid coverage is provided across the inner diameter of the intermediate spray section. The liquid freeze zone stream generally includes methane at a temperature and pressure whereby both solid carbon dioxide particles and a methane-enriched vapor stream are formed. The tower may further include one or more baffles below the nozzles to create frictional resistance to the gravitational flow of the liquid freeze zone stream. This aids in the breakout and recovery of methane gas. Additional internal components are provided to improve heat transfer and to facilitate the breakout of methane gas.

1 . A cryogenic distillation tower for the separation of a fluid stream containing at least methane and carbon dioxide, the cryogenic distillation tower defining an inner diameter that houses internal components, comprising:
 a lower stripping section comprising a melt tray and at least one mass transfer device below the melt tray, the lower stripping section being configured to operate at a temperature and pressure at which substantially no carbon dioxide solids are formed, and vaporized methane is released;   an intermediate spray section comprising a plurality of spray nozzles configured to inject a liquid freeze zone stream such that substantial liquid coverage of the intermediate spray section across the inner diameter is provided, the liquid freeze zone stream substantially comprising methane at a temperature and pressure whereby both solid carbon dioxide particles and a methane-enriched vapor stream are formed upon injection; and   an upper rectification section comprising a collector tray, and at least one mass transfer device above the collector tray, the upper rectification section being configured to receive the vaporized methane from the lower stripping section and the methane-enriched vapor stream from the intermediate spray section.   
   
   
       2 . The cryogenic distillation tower of  claim 1 , wherein the plurality of spray nozzles is disposed within at least one spray header. 
   
   
       3 . The cryogenic distillation tower of  claim 2 , wherein the plurality of spray nozzles is positioned in a first spray header having a first plurality of nozzles, and a second spray header below the first spray head also having a second plurality of nozzles. 
   
   
       4 . The cryogenic distillation tower of  claim 1 , wherein the plurality of nozzles are positioned at different levels within the upper rectification section. 
   
   
       5 . The cryogenic distillation tower of  claim 5 , wherein the plurality of spray nozzles in the first spray header forms a substantially linear arrangement, and the plurality of spray nozzles in the second spray header forms a substantially linear arrangement essentially transverse to and below the first spray header. 
   
   
       6 . The cryogenic distillation tower of  claim 5 , wherein the plurality of spray nozzles is positioned in:
 a first substantially linear spray header having a first plurality of nozzles,   a second substantially linear spray header below the first spray header also having a second plurality of nozzles, and   a third substantially linear spray header below the second spray header also having a third plurality of nozzles,   with the first spray header, second spray head and third spray header being offset relative to one another.   
   
   
       7 . The cryogenic distillation tower of  claim 1 , wherein the melt tray comprises:
 a base; and   a plurality of chimneys extending upward from the base.   
   
   
       8 . The cryogenic distillation tower of  claim 7 , wherein the melt tray further comprises a cap over each of the plurality of chimneys. 
   
   
       9 . The cryogenic distillation tower of  claim 7 , wherein:
 the base of the melt tray defines a generally radial base extending across the inner diameter of the cryogenic distillation tower, the base having a first side, and a second side opposite the first side, wherein the first side and second side are sloped inwardly towards an intermediate portion of the base; and   the base further comprises a sump disposed within the intermediate portion of the base to receive and direct liquids.   
   
   
       10 . The cryogenic distillation tower of  claim 9 , wherein the base further comprises a draw-off nozzle for receiving internal reflux fluids collected in the sump. 
   
   
       11 . The cryogenic distillation tower of  claim 7 , wherein the base of the melt tray has a generally sinusoidal profile. 
   
   
       12 . The cryogenic distillation tower of  claim 7 , wherein the base of the melt tray has a generally corrugated profile. 
   
   
       13 . The cryogenic distillation tower of  claim 7 , wherein the at least one mass transfer device below the melt tray comprises:
 a base;   a plurality of openings in the base; and   a plurality of tabs, wherein each of the plurality of tabs extend over one of the plurality of openings in the base to substantially interfere with the gravitational flow of liquids downward through the one of the plurality of openings.   
   
   
       14 . The cryogenic distillation tower of  claim 7 , wherein the at least one mass transfer device below the melt tray comprises:
 a packing that creates a plurality of channels through which fluids gravitationally flow.   
   
   
       15 . The cryogenic distillation tower of  claim 1 , wherein the collector tray comprises:
 a base; and   a plurality of chimneys extending upward from the base.   
   
   
       16 . The cryogenic distillation tower of  claim 15 , wherein the collector tray further comprises a cap over each of the plurality of chimneys. 
   
   
       17 . The cryogenic distillation tower of  claim 1 , wherein the at least one mass transfer devices in the lower stripping section is fabricated from or coated with a fouling-resistant material. 
   
   
       18 . The cryogenic distillation tower of  claim 1 , wherein the at least one mass transfer device above the collector tray comprises:
 a base;   a plurality of openings in the base; and   a plurality of tabs, wherein each of the plurality of tabs extend over one of the plurality of openings in the base to substantially interfere with the gravitational flow of liquids downward through the one of the plurality of openings.   
   
   
       19 . The cryogenic distillation tower of  claim 1 , wherein the at least one mass transfer device above the collector tray comprises:
 a packing that creates a plurality of channels through which fluids gravitationally flow.   
   
   
       20 . The cryogenic distillation tower of  claim 1 , wherein the at least one mass transfer device in the lower stripping section or in the upper rectification section above the rectification tray is fabricated from or coated with a fouling-resistant material. 
   
   
       21 . The cryogenic distillation tower of  claim 4 , further comprising a baffle or grid packing below at least one of the plurality of spray headers for creating a frictional fluid path for liquids moving down the intermediate spray section. 
   
   
       22 . The cryogenic distillation tower of  claim 1 , wherein the at least one stripping tray comprises a plurality of stripping trays arranged to create a cascading liquid flow. 
   
   
       23 . The cryogenic distillation tower of  claim 1 , further comprising:
 an exit line which receives an exit fluid stream from the lower stripping section comprised primarily of carbon dioxide;   a reboiler wherein the exit fluids are warmed; and   a heater line for capturing gas vaporized by the reboiler, the vapor line carrying warmed vapor to the melt tray to heat the melt tray.   
   
   
       24 . The cryogenic distillation tower of  claim 1 , wherein the melt tray comprises a plurality of bubble caps to increase the surface area. 
   
   
       25 . The cryogenic distillation tower of  claim 2 , wherein the plurality of spray nozzles is arranged in:
 a first spray header to distribute a portion of the liquid freeze zone stream at a first temperature; and   a second spray header positioned at a different level in the intermediate spray section to distribute a portion of the liquid freeze zone stream at a second temperature that is higher than the first temperature.   
   
   
       26 . The cryogenic distillation tower of  claim 25 , wherein the first spray header is positioned above the second spray header. 
   
   
       27 . The cryogenic distillation tower of  claim 1 , further comprising an internal downcomer on the melt tray to provide reflux to the stripping section. 
   
   
       28 . The cryogenic distillation tower of  claim 1 , wherein the fluid stream is injected into the cryogenic distillation tower through at least one spray header having a plurality of nozzles. 
   
   
       29 . The cryogenic distillation tower of  claim 28 , wherein the at least one spray header comprises a first spray header, and a second spray header below the first spray header. 
   
   
       30 . A method for producing hydrocarbon gases, comprising:
 receiving an initial fluid stream containing at least methane and carbon dioxide;   chilling the initial fluid stream to a substantially liquefied phase;   introducing the liquefied fluid stream into a cryogenic distillation tower to separate the carbon dioxide from the methane, the distillation tower defining an inner diameter which houses internal components comprising:
 a lower stripping section comprising a melt tray and at least one mass transfer device below the melt tray, the lower stripping section being configured to operate at a temperature and pressure at which substantially no carbon dioxide solids are formed and vaporized methane is released; 
 an intermediate spray section comprising a plurality of spray nozzles configured to inject a spray stream such that substantial liquid coverage of the intermediate spray section across the inner diameter is provided, the spray stream substantially comprising methane at a temperature and pressure whereby both solid carbon dioxide particles and a methane-enriched vapor stream are formed upon injection; and 
 an upper rectification section comprising a collector tray, the upper rectification section being configured to receive vaporized methane from the lower stripping section and the methane-enriched vapor stream from the intermediate spray section; and 
   recovering vaporized methane from the upper rectification section.   
   
   
       31 . The method of  claim 30 , wherein the plurality of spray nozzles is disposed within at least one spray header. 
   
   
       32 . The method of  claim 31 , wherein the cryogenic distillation tower further comprises a baffle below at least one of the spray headers for creating a fluid path for liquids moving down the intermediate spray section. 
   
   
       33 . The method of  claim 30 , wherein the plurality of spray nozzles is positioned in a first spray head having a first plurality of nozzles, and a second spray header below the first spray header also having a second plurality of nozzles. 
   
   
       34 . The method of  claim 33 , wherein the plurality of spray nozzles in the first spray header forms a substantially linear arrangement, and the plurality of spray nozzles in the second spray header forms a substantially linear arrangement essentially transverse to and below the first spray header. 
   
   
       35 . The method of  claim 33 , wherein the plurality of spray nozzles is positioned in:
 a first substantially linear spray header having a first plurality of nozzles,   a second substantially linear spray header below the first spray header also having a second plurality of nozzles, and   a third substantially linear spray header below the second spray header also having a third plurality of nozzles,   with the first spray header, second spray header and third spray header being offset relative to one another.   
   
   
       36 . The method of  claim 30 , wherein the spray nozzles are each capable of providing about a 70° to 140° spray distribution. 
   
   
       37 . The method of  claim 30 , wherein the spray header defines at least two intersecting fluid lines supporting nozzles. 
   
   
       38 . The method of  claim 30 , wherein the melt tray comprises:
 a base; and   a plurality of chimneys extending upward from the base.   
   
   
       39 . The method of  claim 38  wherein the melt tray further comprises a cap over each chimney. 
   
   
       40 . The method of  claim 30 , wherein the at least one mass transfer device below the melt tray comprises:
 a base;   a plurality of openings in the base; and   tabs extending over the respective openings in the base to substantially interfere with the gravitational flow of liquids downward through the openings.   
   
   
       41 . The method of  claim 40 , wherein the melt tray is fabricated from or coated with a fouling-resistant material. 
   
   
       42 . The method of  claim 30 , wherein the at least one mass transfer device below the melt tray comprises a plurality of stripping trays arranged to create a cascading liquid flow. 
   
   
       43 . The method of  claim 30 , wherein the cryogenic distillation tower further comprises:
 an exit line which receives exit fluids from the stripping section comprised primarily of carbon dioxide; and   a reboiler wherein exit fluids are warmed.   
   
   
       44 . The method of  claim 43 , wherein the cryogenic distillation tower further comprises
 a heater line for capturing gas vaporized by the reboiler, the vapor line carrying warmed vapor to the melt tray to heat the melt tray.   
   
   
       45 . The method of  claim 43 , further comprising:
 collecting the carbon dioxide for use as a miscible agent in an enhanced oil recovery operation.   
   
   
       46 . The method  claim 30 , wherein the melt tray comprises a plurality of bubble caps to increase the surface area. 
   
   
       47 . The method of  claim 30 , wherein the spray nozzles are arranged in:
 a first spray header to distribute a portion of the liquid stream at a first temperature; and   a second spray header positioned at a different level in the intermediate spray section to distribute a portion of the liquid stream at a second temperature that is higher than the first temperature.   
   
   
       48 . The method of  claim 47 , wherein the first spray header is positioned above the second spray header.