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 method of producing a liquefied natural gas (LNG) from a natural gas feed stream, comprising:
 providing the natural gas stream at a pressure of between 800 and 1600 psig, and cooling the natural gas stream using a feed gas pre-cooling circuit to form a vapor portion and a liquid portion of the cooled natural gas stream;   expanding the vapor portion of the natural gas stream in an expander to form an expanded natural gas vapor, and feeding the expanded natural gas vapor to a separator;   producing a cold overhead product stream in the separator, wherein the separator receives a reflux stream that is cooled in a reflux refrigeration circuit;   compressing the cold overhead product stream in a compressor without prior substantial heating of the cold product stream, wherein the compressor is driven by the expander, and wherein the compressed cold product stream has a pressure of at least 700 psig and a temperature of less than −50° F.;   liquefying the cold compressed product stream in a liquefaction unit using refrigeration content from a liquefaction refrigeration circuit; and   wherein the feed gas pre-cooling circuit, the reflux refrigeration circuit, and the liquefaction refrigeration circuit are distinct circuits.   
     
     
         2 . The method of  claim 1  further comprising a step of feeding the liquid portion of the cooled natural gas stream to the separator and operating the separator as a demethanizer. 
     
     
         3 . The method of  claim 1  further comprising a step of feeding a bottom product of the separator to a deethanizer, wherein the deethanizer optionally provides a C2 product to the cold overhead product stream of the separator. 
     
     
         4 . The method of  claim 1  wherein the separator is operated as a refluxed absorber. 
     
     
         5 . The method of  claim 1  further comprising a step of providing a reflux stream from a demethanizer to the absorber, and providing a bottom product of the absorber to the demethanizer, and operating the demethanizer at a lower pressure than the absorber. 
     
     
         6 . The method of  claim 5  further comprising a step of heating the absorber bottom product for C2 rejection prior to entering the demethanizer. 
     
     
         7 . The method of  claim 5  further comprising a step of cooling the absorber bottom product for C2 recovery prior to entering the demethanizer. 
     
     
         8 . The method of  claim 5  further comprising a step of feeding a bottom product of the demethanizer to a deethanizer for C2 and C3+ recovery. 
     
     
         9 . The method of  claim 1  wherein the feed gas pre-cooling circuit is operated at a temperature range of 10° F. to −35° F., wherein the reflux refrigeration circuit is operated at a temperature range of −60° F. to −160° F., and wherein the liquefaction refrigeration circuit is operated at a temperature range of −180° F. to −270° F. 
     
     
         10 . 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 of at least 700 psig and a temperature of less than −50° F.;   feeding the cold compressed overhead product to a liquefaction unit; and   wherein the cold compressed overhead product is formed at neutral or negative net compression energy requirement.   
     
     
         11 . The method of  claim 10  wherein the step of separating is performed in an absorber or a demethanizer. 
     
     
         12 . The method of  claim 10  wherein the feed gas has a pressure of between 800 and 1600 psig. 
     
     
         13 . The method of  claim 10  wherein the separator is a refluxed demethanizer or refluxed absorber. 
     
     
         14 . The method of  claim 10  wherein the feed gas is cooled in a feed gas pre-cooling circuit, wherein the reflux for the refluxed demethanizer or refluxed absorber is cooled in a reflux refrigeration circuit, wherein the liquefaction unit uses refrigeration content from a liquefaction refrigeration circuit, and wherein the feed gas pre-cooling circuit, the reflux refrigeration circuit, and the liquefaction refrigeration circuit are distinct circuits.