Method and apparatus for compressing rich natural gas

Abstract

A method and apparatus for compressing rich natural gas is described. The apparatus has a compression stage that has a gas inlet for receiving rich natural gas. The compression stage includes one or more compressors and one or more cooling elements. A pressure vessel is also included for receiving the compressed gas from the compression stage and a liquid outlet is connected between the compression stage and a vessel having a pressure that is less than the pressure in the compression stage. The vessel has a gas outlet connected to the gas inlet. The method includes the steps of subjecting a stream of rich natural gas to a compression cycle to form a compressed gas and a condensate, separating the condensate from the compressed gas, flashing at least a portion of the condensate to a gas and recycling the flashed condensate into the compression cycle.

1 . A method of compressing rich natural gas, comprising the steps of:
 subjecting a stream of rich natural gas to a compression cycle to form a compressed gas and a condensate;   separating the condensate from the compressed gas;   flashing at least a portion of the condensate to a gas; and   recycling the flashed condensate into the compression cycle.   
     
     
         2 . The method of  claim 1 , wherein the compression cycle comprises more than one compression stage and more than one cooling stage. 
     
     
         3 . The method of  claim 2 , wherein the cooling stage uses ambient air to cool the compressed gas. 
     
     
         4 . The method of  claim 2 , wherein the cooling stage uses a refrigeration unit to cool the compressed gas below ambient temperatures. 
     
     
         5 . The method of  claim 2 , wherein the rich natural gas is compressed and cooled to a pressure and temperature that is outside the phase envelope of the compressed gas. 
     
     
         6 . The method of  claim 1 , wherein at least a portion of the condensate is flashed to a gas by reducing the pressure. 
     
     
         7 . The method of  claim 1 , further comprising the step of loading the compressed gas into a pressure vessel. 
     
     
         8 . The method of  claim 7 , wherein the pressure vessel is at substantially the same pressure and substantially the same temperature as the compressed gas. 
     
     
         9 . The method of  claim 7 , wherein the pressure vessel is at a pressure that is less than the pressure of the compressed gas. 
     
     
         10 . The method of  claim 9 , wherein the compressed gas forms a condensate when loaded into the pressure vessel, and further comprising the step of removing the condensate from the pressure vessel through a liquid outlet. 
     
     
         11 . The method of  claim 10 , wherein at least a portion of the condensate from the pressure vessel is flashed to a gas and recycled into the compression cycle. 
     
     
         12 . A method of compressing rich natural gas, the phase of the rich natural gas being defined by a phase diagram having a phase envelope, comprising the steps of:
 defining a path on the phase diagram from an uncompressed state to a compressed state, at least a portion of the path being within the phase envelope of the phase diagram;   manipulating the rich natural gas along the path to form a compressed gas and a condensate;   removing the condensate from the rich natural gas and flashing at least a portion of the condensate to a gas;   reintroducing the flashed condensate into the path.   
     
     
         13 . The method of  claim 12 , wherein manipulating the rich natural gas along the path comprises using a compression cycle having more than one compression stage and more than one cooling stage. 
     
     
         14 . The method of  claim 13 , wherein the cooling stage uses ambient air to cool the compressed gas. 
     
     
         15 . The method of  claim 13 , wherein the cooling stage uses a refrigeration unit to cool the compressed gas below ambient temperatures. 
     
     
         16 . The method of  claim 13 , wherein the compressed state is a pressure and temperature that is outside the phase envelope of the compressed gas. 
     
     
         17 . The method of  claim 12 , wherein at least a portion of the condensate is flashed to a gas by reducing the pressure. 
     
     
         18 . The method of  claim 12 , further comprising the step of loading the compressed gas into a pressure vessel. 
     
     
         19 . The method of  claim 18 , wherein the pressure vessel is at substantially the same pressure and substantially the same temperature as the compressed gas. 
     
     
         20 . The method of  claim 18 , wherein the pressure vessel is at a pressure that is less than the pressure of the compressed gas. 
     
     
         21 . The method of  claim 20 , wherein the compressed gas forms a condensate when loaded into the pressure vessel, and further comprising the step of removing the condensate from the pressure vessel through a liquid outlet. 
     
     
         22 . The method of  claim 21 , wherein at least a portion of the condensate from the pressure vessel is flashed to a gas and recycled into the compression cycle. 
     
     
         23 . An apparatus for compressing rich natural gas, comprising:
 a compression stage having a gas inlet for receiving rich natural gas, the compression stage comprising one or more compressors and one or more cooling elements;   a first vessel for receiving the compressed gas from the compression stage; and   a liquid outlet connected between the compression stage and a second vessel having a pressure that is less than the pressure in the compression stage, the vessel having a gas outlet connected to the gas inlet of the compression stage.   
     
     
         24 . The apparatus of  claim 23 , wherein the rich natural gas is compressed and cooled to a pressure and temperature that is outside the phase envelope of the compressed gas. 
     
     
         25 . The apparatus of  claim 23 , wherein the first vessel is at substantially the same pressure and substantially the same temperature as the compressed gas. 
     
     
         26 . The apparatus of  claim 23 , wherein the first vessel is at a pressure that is less than the pressure of the compressed gas. 
     
     
         27 . The apparatus of  claim 23 , wherein the first vessel comprises a liquid outlet for removing condensate from the pressure vessel.