System and method for natural gas and nitrogen liquefaction with direct drive machines for turbines and boosters

Abstract

Liquefier arrangements configured for co-production of both liquid natural gas (LNG) and liquid nitrogen (LIN) configured to operate using direct drive motor/generator arrangement for the warm and/or cold booster compressors and turbines. Alternatively, the use of a conventional generator with a bull gear in lieu of the direct drive motor/generator arrangement on the warm turbine and warm booster compressor coupling is also disclosed.

What is claimed is: 
     
         1 . A method of liquefaction to co-produce liquid nitrogen and liquid natural gas, the method comprising the steps of:
 (i) receiving a gaseous nitrogen feed stream;   (ii) compressing the gaseous nitrogen feed stream and one or more gaseous nitrogen recycle streams in a recycle compressor to produce a gaseous nitrogen effluent stream;   (iii) further compressing a first portion of the effluent stream in a cold booster compressor to form a part of a primary nitrogen liquefaction stream and further compressing a second portion of the effluent stream in a warm booster compressor to form a warm nitrogen recycle stream, wherein the warm booster compressor is coupled to a direct drive motor/generator arrangement;   (iv) cooling the primary nitrogen liquefaction stream in a first heat exchange passage in a multi-pass brazed aluminum heat exchanger;   (v) expanding a first portion of the cooled primary nitrogen liquefaction stream extracted at a primary intermediate location of the first heat exchange passage in a cold booster loaded turbine to produce a cold turbine exhaust;   (vi) warming the cold turbine exhaust in a second heat exchange passage in the multi-pass brazed aluminum heat exchanger to form a gaseous nitrogen recycle stream;   (vii) cooling the warm nitrogen recycle stream in a third heat exchange passage in the multi-pass brazed aluminum heat exchanger;   (viii) expanding the cooled stream exiting the third heat exchange passage in a warm booster loaded turbine to produce a warm turbine exhaust wherein the warm booster loaded turbine is also operatively coupled to the direct drive motor/generator arrangement;   (ix) warming the warm turbine exhaust in the second heat exchange passage to form part of the gaseous nitrogen recycle stream;   (x) subcooling a second portion of the primary nitrogen liquefaction stream to produce a subcooled liquid nitrogen stream;   (xi) liquefying a natural gas feed stream in a fifth heat exchange passage of the multi-pass brazed aluminum heat exchanger against a first portion of the subcooled liquid nitrogen stream in a fourth heat exchange passage of the multi-pass brazed aluminum heat exchanger and the gaseous nitrogen recycle stream to produce the liquid natural gas; and   (xii) taking a second portion of the subcooled liquid nitrogen stream as the liquid nitrogen.   
     
     
         2 . The method of  claim 1  further comprising the step of compressing the natural gas feed stream prior to the step of liquefying the natural gas feed stream in the fifth heat exchange passage of the multi-pass brazed aluminum heat exchanger. 
     
     
         3 . The method of  claim 1  further comprising the step of expanding the second portion of the primary nitrogen liquefaction stream in a liquid turbine disposed downstream of the multi-pass brazed aluminum heat exchanger or a throttle valve disposed downstream of the multi-pass brazed aluminum heat exchanger. 
     
     
         4 . The method of  claim 1  wherein the cold booster compressor and the cold booster loaded turbine are operatively coupled to a second direct drive motor/generator arrangement. 
     
     
         5 . A liquefaction system configured to co-produce liquid nitrogen and liquid natural gas, the liquefaction system comprising:
 a natural gas feed stream;   a gaseous nitrogen feed stream;   a multi-pass brazed aluminum heat exchanger;   a recycle compressor configured to compress the gaseous nitrogen feed stream and a gaseous nitrogen recycle stream to produce an effluent stream;   a cold recycle circuit having a cold booster compressor and a booster loaded cold turbine and configured to further compress a first portion of the effluent stream to form a primary nitrogen liquefaction stream; cool the primary nitrogen liquefaction stream in a first heat exchange passage of the multi-pass brazed aluminum heat exchanger; expand a first portion of the cooled primary nitrogen liquefaction stream extracted at a cold intermediate location of the first heat exchange passage in the booster loaded cold turbine to produce a cold turbine exhaust; warm the cold turbine exhaust in a second heat exchange passage of the multi-pass brazed aluminum heat exchanger; and recycle the warmed stream exiting the second heat exchange passage as the gaseous nitrogen recycle stream;   a warm recycle circuit having a warm booster compressor and a booster loaded warm turbine operatively coupled to a direct drive motor/generator arrangement and configured to compress a second portion of the effluent stream in the warm booster compressor to form warm nitrogen recycle stream, cool the further compressed warm nitrogen recycle stream in a third heat exchange passage in the multi-pass brazed aluminum heat exchanger; expand the cooled, warm nitrogen recycle stream in the booster loaded warm turbine to produce a warm turbine exhaust; warm the warm turbine exhaust in the second heat exchange passage to form part of the gaseous nitrogen recycle stream;   a subcooler configured to subcool a second portion of the primary nitrogen liquefaction stream to produce a subcooled liquid nitrogen stream;   the multi-pass brazed aluminum heat exchanger further having a fourth heat exchange passage and a fifth heat exchange passage and configured to liquefy the natural gas feed stream in the fifth heat exchange passage against a first portion of the subcooled liquid nitrogen stream in the fourth heat exchange passage and the gaseous nitrogen recycle stream;   wherein the liquid nitrogen product stream is a second portion of the subcooled liquid nitrogen stream and the liquid natural gas stream is the liquefied natural gas exiting a cold end of the fifth heat exchange passage.   
     
     
         6 . The liquefaction system of  claim 5  further comprising a natural gas compressor configured to compress the natural gas feed stream prior to liquefaction of the natural gas feed stream in the fifth heat exchange passage of the multi-pass brazed aluminum heat exchanger. 
     
     
         7 . The liquefaction system of  claim 5  further comprising a liquid turbine disposed downstream of the multi-pass brazed aluminum heat exchanger and configured to expand the second portion of the primary nitrogen liquefaction stream. 
     
     
         8 . The liquefaction system of  claim 5  further comprising a second direct drive motor/generator arrangement operatively coupled to the cold booster compressor and the cold booster loaded turbine.