Configurations and methods for deep feed gas hydrocarbon dewpointing

Abstract

An natural gas processing plant allows for recovery of at least 98% of butane and heavier hydrocarbons, and about 60 to 80% of propane hydrocarbons from a rich feed gas stream with a single fractionator that operates at two different pressures, that receives a chilled gas from a turboexpander in the upper fractionator and a C5+ liquid in the lower section, while producing a C2− vapor stream in the lower section that is used as reflux to the upper section. Most typically, contemplated configurations and methods operate without the use of external refrigeration.

What is claimed is: 
     
         1 . A method of hydrocarbon dew point adjustment of a natural gas comprising C3 and C4 and heavier components, comprising:
 cooling the feed gas in a feed gas exchanger using a liquid phase of the cooled feed gas and an overhead product of an upper section of a fractionator;   separating the cooled feed gas in a phase separator into the liquid phase and a vapor phase;   feeding the liquid phase into a lower section of a fractionator and feeding the vapor phase into the upper section of the fractionator;   wherein the upper and lower sections of the fractionator are coupled to each other such that (a) an expansion device reduces pressure of and provides a vapor product of the lower section to the upper section as a two phase reflux stream, and (b) a pump increases pressure of and provides a liquid product of the upper section to the lower section;   cooling the vapor product in an overhead exchanger using the overhead product of the upper section of the fractionator; and   wherein the fractionator is operated such that recovery of the C3 from the feed gas is between 60% and 80%, and recovery of the C4 and heavier components from the feed gas is at least 95%.   
     
     
         2 . The method of  claim 1  wherein the fractionator is operated at a pressure of between 450 to 550 psig, and wherein the upper section is operated at a pressure that is at least 10 psig lower than a pressure of the lower section. 
     
     
         3 . The method of  claim 1  wherein the fractionator is operated at a pressure of between 450 to 550 psig, and wherein the upper section is operated at a pressure that is at least 30 psig lower than a pressure of the lower section. 
     
     
         4 . The method of  claim 1  wherein the upper section is operated at a temperature of −65° F. to −55° F. and wherein the lower section is operated at a temperature of 25° F. to 300° F. 
     
     
         5 . The method of  claim 1  further comprising a step of expanding the vapor phase in a turbo expander and reducing pressure of the liquid phase in a second expansion device before feeding the vapor phase and the liquid phase into the upper and lower sections of the fractionator, respectively. 
     
     
         6 . The method of  claim 1  wherein at least one of feed gas cooling and cooling of the vapor product of the lower section is performed without use of external refrigeration. 
     
     
         7 . The method of  claim 1  wherein feed gas cooling and cooling of the vapor product of the lower section to form the two phase reflux stream is performed without use of external refrigeration. 
     
     
         8 . A processing plant for hydrocarbon dew point of a natural gas feed gas delivered from a feed gas source, comprising:
 a feed gas exchanger fluidly coupled to the feed gas source and configured to cool the feed gas using a liquid phase of the cooled feed gas and an overhead product of an upper section of a fractionator;   a phase separator fluidly coupled to the feed gas exchanger and configured to separate the cooled feed gas into the liquid phase and a vapor phase;   wherein the fractionator further comprises a lower section that is configured to receive the liquid phase and the vapor phase in the upper section;   wherein the upper and lower sections of the fractionator are coupled to each other such that (a) an expansion device reduces pressure of and provides a vapor product of the lower section to the upper section, and (b) a pump increases pressure of and provides a liquid product of the upper section to the lower section; and   an overhead exchanger that is configured to cool the vapor product from the lower section to form a two phase reflux stream using the overhead product of the upper section of the fractionator.   
     
     
         9 . The processing plant of  claim 8  further comprising a second expansion device that is configured to receive and reduce pressure of the liquid phase, and further comprising a turbo expander that is configured to receive and reduce pressure of the vapor phase. 
     
     
         10 . The processing plant of  claim 8  wherein the pump increases the pressure of the liquid product in an amount of at least 10 psig. 
     
     
         11 . The processing plant of  claim 8  wherein the fractionator is configured to operate at a pressure of between 450 to 550 psig. 
     
     
         12 . The processing plant of  claim 8  wherein the upper section of the fractionator is configured to operate at a temperature of −65° F. to −55° F. and wherein the lower section of the fractionator is configured to operate at a temperature of 25° F. to 300° F. 
     
     
         13 . The processing plant of  claim 8  wherein the feed gas exchanger, the fractionator, and the expansion device are configured to allow for between 60% and 80% C3 recovery without use of external refrigeration. 
     
     
         14 . The processing plant of  claim 8  wherein the upper section and the lower section of the fractionator are configured to operate at a pressure differential of at least 10 psig. 
     
     
         15 . A method of hydrocarbon dew point adjustment of a natural gas comprising C3 and C4 and heavier components, comprising:
 separating the feed gas into a liquid phase and a vapor phase;   feeding the vapor phase into an upper section of a fractionator, and feeding the liquid phase into an lower section of the fractionator, wherein the upper section is operated at a lower pressure than the lower section;   cooling a vapor product of the lower section to form a two phase reflux stream and feeding the two phase reflux stream into the upper section;   increasing pressure in and feeding a liquid product of the upper section to the lower section; and   withdrawing an overhead product of the upper section of the fractionator as a dew point adjusted natural gas, and withdrawing a bottom product of the lower section comprising between 60% and 80% of C3 and at least 95% of the C4 and heavier components of the feed gas.   
     
     
         16 . The method of  claim 15  wherein the natural gas has a pressure of between 1000 psig and 1400 psig, and wherein the fractionator is operated at a pressure of between 450 to 550 psig. 
     
     
         17 . The method of  claim 15  wherein a pressure difference between the upper section and the lower section of the fractionator is at least 10 psig. 
     
     
         18 . The method of  claim 15  wherein the vapor product of the lower section is cooled using refrigeration content of the overhead product of the upper section of the fractionator. 
     
     
         19 . The method of  claim 18  wherein the feed gas is cooled using refrigeration content of the overhead product of the upper section of the fractionator. 
     
     
         20 . The method of  claim 18  wherein the feed gas is cooled using refrigeration content of the liquid phase after pressure reduction of the liquid phase.