Process and System for Removing Contaminants from a Natural Gas Stream

Abstract

A process and system for removing contaminants from a natural gas stream, the process comprising the steps of: (a) contacting part of the natural gas stream as a first gas stream at an elevated temperature with a first adsorbent bed in regeneration mode, to remove contaminants present on the first adsorbent bed, and to obtain a second gas stream that is enriched in contaminants compared to the first gas stream; (b) submitting the second gas stream to a gas/liquid separation step comprising cooling the second gas stream to a temperature such that at least some contaminants begin to condense into a first liquid phase that is rich in contaminants, and separating the first liquid phase from the second gas stream to create a third gas stream; wherein the gas/liquid separation step forms a first gas/liquid separation step, and wherein the process further comprises (c) submitting the third gas stream to a second gas/liquid separation step to obtain a second liquid phase that is rich in contaminants, and a lean gas stream.

1 . A process for removing contaminants from a natural gas stream, the process comprising the steps of: 
 (a) contacting part of the natural gas stream as a first gas stream at an elevated temperature with a first adsorbent bed in regeneration mode, to remove contaminants present on the first adsorbent bed, and to obtain a second gas stream that is enriched in contaminants compared to the first gas stream;    (b) submitting the second gas stream to a gas/liquid separation step comprising cooling the second gas stream to a temperature such that at least some contaminants begin to condense into a first liquid phase that is rich in contaminants, and separating the first liquid phase from the second gas stream to create a third gas stream;    wherein the gas/liquid separation step forms a first gas/liquid separation step, and wherein the process further comprises    (c) submitting the third gas stream to a second gas/liquid separation step to obtain a second liquid phase that is rich in contaminants, and a lean gas stream having a cricondentherm lower than that of the natural gas stream.    
     
     
         2 . The process according to  claim 1 , further comprising contacting another part of the natural gas stream with a second adsorbent bed in adsorption mode, to obtain a purified gas stream.  
     
     
         3 . The process according to  claim 2 , wherein the lean gas stream is contacted with the second adsorbent bed together with the other part of the natural gas stream.  
     
     
         4 . The process according to  claim 2 , wherein the lean gas stream is added to the purified gas stream.  
     
     
         5 . The process according to  claim 4 , wherein step (c) is performed in such a way that the lean gas stream has a cricondentherm at least 10° C. lower.  
     
     
         6 . The process according to  claim 5 , wherein step (c) is performed in such a way that the lean gas stream has a cricondentherm below 10° C.  
     
     
         7 . The process according to  claim 6 , wherein the lean gas stream is added to the purified gas stream in such a way that the resulting gas stream has a cricondentherm below 10° C.  
     
     
         8 . The process according to  claim 7 , wherein the cooling in step (b) is done against a temperature above water freezing temperature, in particular using a water cooler.  
     
     
         9 . The process according to  claim 8 , wherein the temperature of the second adsorbent bed is between 5 and 45° C.  
     
     
         10 . The process according to  claim 9 , wherein the temperature of the first adsorbent bed is between 200 and 350° C.  
     
     
         11 . The process according to  claim 10  wherein step (c) comprises cooling the third gas stream to a temperature that is below a temperature at which contaminants in the third gas stream will begin to condense into a second liquid phase, and separating the second liquid phase from the third gas stream.  
     
     
         12 . The process according to  claim 11 , wherein the third gas stream is cooled to a temperature below the cooling temperature in step (b).  
     
     
         13 . The process according to  claim 12 , wherein the second gas/liquid separation in step (c) is effected by means of an accelerated velocity inertia separator.  
     
     
         14 . The process according to  claim 13 , wherein the accelerated velocity inertia separator is a supersonic inertia separator and the fluid stream flows at supersonic velocity.  
     
     
         15 . The process according to  claim 14 , wherein a swirling motion is induced to the fluid stream flowing at supersonic velocity, thereby causing the contaminants, in particular water and hydrocarbons, to flow to a radially outer section of a collecting zone in the stream.  
     
     
         16 . The process according to  claim 11 , wherein the cooling of the third gas stream is effected by refrigeration  
     
     
         17 . The process according to  claim 16  wherein a hydrate inhibitor, is injected into the third gas stream prior to refrigeration.  
     
     
         18 . The process according to  claim 17 , wherein step (a) comprises 
 (a1) heating the first gas stream in a heating zone to obtain a heated first gas stream;    (a2) contacting the heated first gas stream with the first adsorbent bed in regeneration mode.    
     
     
         19 . The process according to  claim 18 , wherein the first gas stream is passed through a third adsorbent bed in cooling mode, prior to being contacted with the first adsorbent bed.  
     
     
         20 . A system for removing contaminants from a natural gas stream, the system comprising: 
 a first adsorption bed arranged to receive part of the natural gas stream as a first gas stream, and provided with a means for heating the first adsorbent bed, which first adsorption bed has an outlet for a second gas stream.    a cooler for cooling the second gas stream;    a first gas/liquid separator for separating the cooled second gas stream into a first liquid phase and a third gas stream; and    a second gas/liquid separator for separating the third gas stream into a second liquid phase and a lean gas stream.    
     
     
         21 . The system according to  claim 20 , further comprising a second adsorbent bed arranged to receive another part of the natural gas stream at a temperature at which contaminants are adsorbed, and having an outlet for a purified gas stream.  
     
     
         22 . The system according to  claim 21 , wherein the second adsorbent bed is arranged to receive the lean gas stream together with the other part of the natural gas stream.  
     
     
         23 . The system according to  claim 22 , wherein the first gas/liquid separator comprises a cooler arranged to condense liquid at a temperature above the freezing point of water, and wherein the second gas/liquid separator is arranged to separate contaminants that condense at a temperature lower than 0° C.  
     
     
         24 . The system according to  claim 23 , wherein the second gas/liquid separator an accelerated velocity inertia separator.  
     
     
         25 . The system according to  claim 24 , wherein the accelerated velocity inertia separator comprises means for inducing a swirling motion the fluid stream entering this separator, thereby causing the contaminants, in particular water and hydrocarbons, to flow to a radially outer section of a collecting zone in the stream.  
     
     
         26 . The system according to  claim 23 , wherein the second gas/liquid separator comprises a refrigerator.  
     
     
         27 . The system according to  claim 26 , wherein the means for heating the first adsorbent bed comprises a heater for the first gas stream.  
     
     
         28 . The system according to  claim 27 , further comprising a third adsorbent bed arranged to receive the first gas stream prior to the first adsorbent bed.