System and method to produce liquefied natural gas using two distinct refrigeration cycles with an integral gear machine

Abstract

A system and method for liquefaction of natural gas using two distinct refrigeration circuits having compositionally different working fluids and operating at different temperature levels is provided. The turbomachinery associated with the liquefaction system are driven by a single three-pinion or four-pinion integral gear machine with customized pairing arrangements. The system and method of natural gas liquefaction further includes the conditioning of a lower pressure natural gas containing feed stream to produce a purified, compressed natural gas stream at a pressure equal to or above the critical pressure of natural gas and substantially free of heavy hydrocarbons to be liquefied.

What is claimed is: 
     
         1 . An integral gear machine for natural gas liquefaction system, comprising:
 wherein the natural gas liquefaction system comprises a refrigeration circuit comprising: (i) at least two compositionally different working fluids operating at different temperature levels thereby forming a first refrigeration circuit and a second refrigeration circuit; (ii) at least one heat exchanger configured to liquefy and subcool a purified, compressed natural gas containing feed stream via indirect heat exchange with a first refrigerant stream traversing the first refrigeration circuit and a second refrigerant stream traversing the second refrigeration circuit; (iii) two or more turbines/expanders configured to expand the at least two compositionally different working fluids to provide refrigeration; and (iv) one or more refrigerant compression stages configured to recycle the expanded and warmed working fluids; and   wherein the integral gear machine comprises a bull gear, a driver assembly, and at least three pinions arranged to drive the plurality of refrigerant compression stages and at least one natural gas compression stage as well as for receiving work produced by two or more turbines, wherein each pinion of the at least three pinions is a net absorber of power from the drive assembly.   
     
     
         2 . The integral gear machine for natural gas liquefaction system of  claim 1 , wherein the two or more turbines/expanders further comprise one natural gas expander, and wherein the natural gas expander and at least one natural gas compression stage are operatively coupled to the integral gear machine by a third pinion of the at least three pinions and the at least one natural gas compression stage is configured to further compressed a natural gas stream to a pressure above the critical pressure of natural gas. 
     
     
         3 . The integral gear machine for natural gas liquefaction system of  claim 2 , wherein the natural gas compression stage is configured to further compress the natural gas stream to a pressure between about 50 bar(a) and 80 bar(a). 
     
     
         4 . The integral gear machine for natural gas liquefaction system of  claim 2 , wherein the one or more refrigerant compression stages include a plurality of primary refrigerant recycle compression stages that are operatively coupled to the integral gear machine by the first pinion and the second pinion of the at least three pinions. 
     
     
         5 . The integral gear machine for natural gas liquefaction system of  claim 4 , wherein the adsorbed power on the third pinion is between about 0.05 kw*hr per kilogram of liquified natural gas produced to 0.20 kw*hr per kilogram of liquified natural gas produced. 
     
     
         6 . The integral gear machine for natural gas liquefaction system of  claim 4 , wherein the two or more turbines/expanders further comprise a warm turbine configured to expand a warm portion of a primary refrigerant stream and produce a warm exhaust that is recycled to the one or more refrigerant compression stages and a cold turbine configured to expand a warm portion of a primary refrigerant stream and produce a warm exhaust that is recycled to the one or more refrigerant compression stages. 
     
     
         7 . The integral gear machine for natural gas liquefaction system of  claim 6 , wherein the warm turbine and one of primary refrigerant recycle compression stages are operatively coupled to the integral gear machine by the first pinion of the at least three pinions and the cold turbine and another one of primary refrigerant recycle compression stages are operatively coupled to the integral gear machine by the second pinion of the at least three pinions. 
     
     
         8 . The integral gear machine for natural gas liquefaction system of  claim 7 , wherein the adsorbed power on the pinion coupling the warm turbine and one of the plurality of primary refrigerant recycle compression stages is between about 0.10 kw*hr per kilogram of liquified natural gas produced to 0.20 kw*hr per kilogram of liquified natural gas produced. 
     
     
         9 . The integral gear machine for natural gas liquefaction system of  claim 7 , wherein the adsorbed power on the pinion coupling the cold turbine and one of the plurality of primary refrigerant recycle compression stages is between about  0 . 10  kw*hr per kilogram of liquified natural gas produced to 0.20 kw*hr per kilogram of liquified natural gas produced. 
     
     
         10 . The integral gear machine for natural gas liquefaction system of  claim 1 , wherein the driver assembly is an electric motor, a steam turbine, or a gas turbine.