Configurations and methods of integrated NGL recovery and LNG liquefaction

Abstract

Contemplated plants include a NGL recovery portion and a LNG liquefaction portion, wherein the NGL recovery portion provides a low-temperature and high-pressure overhead product directly to the LNG liquefaction portion. Feed gas cooling and condensation are most preferably performed using refrigeration cycles that employ refrigerants other than the demethanizer/absorber overhead product. Thus, cold demethanizer/absorber overhead product is compressed with the turbo-expansion and delivered to a liquefaction portion at significantly lower temperature and higher pressure without net compression energy expenditure.

1 . A gas processing plant, comprising: 
 a separator that is configured to receive a partially expanded vapor portion of a natural gas feed stream, and that is further configured to produce a cold overhead product stream;    an expander operationally coupled to drive a compressor, wherein the expander is configured to produce the partially expanded vapor portion and wherein the compressor is configured to produce a compressed cold overhead product stream from the cold overhead product stream; and    wherein the separator and the compressor are fluidly coupled to each other such that the compressed cold overhead product stream has a pressure of at least 700 psig at a temperature of no warmer than −50° F.    
   
   
       2 . The plant of  claim 1  wherein the separator is configured to receive another expanded vapor portion of the natural gas feed stream at a separate location.  
   
   
       3 . The plant of  claim 1  wherein the separator is configured to operate as a demethanizer.  
   
   
       4 . The plant of  claim 3  further comprising a deethanizer that is configured to produce a C3+ product and a C2 product.  
   
   
       5 . The plant of  claim 4  further comprising a conduit that provides at least part of the C2 product to the cold overhead product stream.  
   
   
       6 . The plant of  claim 1  wherein the separator is configured to operate as a refluxed absorber.  
   
   
       7 . The plant of  claim 6  wherein the demethanizer is configured to provide a reflux stream to the absorber.  
   
   
       8 . The plant of  claim 6  wherein the demethanizer is configured to operate at a lower pressure than the absorber.  
   
   
       9 . The plant of  claim 6  further comprising at least one of a conduit that provides a cooled absorber bottom product the absorber for C2 recovery and a conduit that provides a heated absorber bottom product the absorber for C2 rejection.  
   
   
       10 . A method of producing a liquefied natural gas, comprising: 
 producing a cold overhead product stream in a separator and compressing the product stream in a compressor without prior substantial heating of the cold product stream;    wherein the compressor is driven by an expander that expands a vapor portion of a natural gas feed, and wherein the expanded vapor portion is fed into the separator; and    liquefying the cold compressed product stream in a liquefaction unit.    
   
   
       11 . The method of  claim 10  wherein the separator is operated as a demethanizer that further receives another portion of a natural gas feed.  
   
   
       12 . The method of  claim 10  further comprising a deethanizer that receives a bottom product of the separator and that optionally provides a C2 product to the cold overhead product stream.  
   
   
       13 . The method of  claim 10  wherein the separator is operated as a refluxed absorber.  
   
   
       14 . The method of  claim 11  wherein a demethanizer provides a reflux stream to the absorber, wherein the absorber provides a bottom product to the demethanizer, and wherein the demethanizer is operated at a lower pressure than the absorber.  
   
   
       15 . The method of  claim 14  wherein the absorber bottom product is heated for C2 rejection prior to entering the demethanizer or cooled for C2 recovery prior to entering the demethanizer.  
   
   
       16 . The method of  claim 14  wherein a deethanizer receives a bottom product of the demethanizer for C2 and C3+ recovery.  
   
   
       17 . The method of  claim 10  wherein the cold compressed product stream has a pressure of at least 700 psig and a temperature of no warmer than −50° F.  
   
   
       18 . A method of producing LNG comprising: 
 separating in a separator a cold overhead product from a natural gas containing feed gas;    compressing the cold overhead product using expansion energy from the feed gas to form a cold compressed overhead product at a pressure and temperature suitable for liquefaction in a liquefaction unit;    wherein the cold compressed overhead product is formed at neutral or negative net compression energy requirement.    
   
   
       19 . The method of  claim 17  wherein the step of separating is performed in an absorber or a demethanizer.  
   
   
       20 . The method of  claim 17  wherein the cold compressed overhead product has a pressure of at least 700 psig and a temperature of no warmer than −50° F.