System for combined cycle mechanical drive in cryogenic liquefaction processes

Abstract

A system for producing liquefied and sub-cooled natural gas by means of a refrigeration assembly using a single phase gaseous refrigerant comprises at least two expanders; a compressor assembly; a heat exchanger assembly for heat absorption from natural gas; and a heat rejection assembly, in which the expanders are arranged in expander loops and the refrigerant to the respective expander is served in a compressed flow by means of the compressor assembly having compressors or compressor stages enabling adapted inlet and outlet pressures for the respective expander. According to the present the expanders and compressors assembly are assembled in two mechanically connected compressor and expander packages of which one is driven by a gas turbine and the other is driven by a steam turbine, the steam primarily being generated by exhaust gases from the gas turbine in a waste heat recovery unit, and in that the expanders and compressors assemblies are distributed between the two compressor and expander packages to optimize the steam utilization and to balance the power generated by the gas turbine and the steam turbine.

1 . A system for producing liquefied and sub-cooled natural gas by means of a refrigeration assembly using a single phase gaseous refrigerant comprising:
 at least two expanders;   a compressor assembly;   a heat exchanger assembly for heat absorption from natural gas; and   a heat rejection assembly, in which the expanders are arranged in expander loops and the refrigerant to the respective expander is served in a compressed flow by the compressor assembly having compressors or compressor stages enabling adapted inlet and outlet pressures for the respective expander, wherein the expanders and compressors or their stages are assembled in two mechanically connected compressor and expander packages, of which one is driven by a gas turbine and the other is driven by a steam turbine, the steam primarily being generated by exhaust gases from the gas turbine in a waste heat recovery unit, and wherein the expanders and compressors or their stages are distributed between the two compressor and expander packages to optimize the steam utilization and to balance the power generated by the gas turbine and the steam turbine.   
     
     
         2 . A system according to  claim 1 , wherein a duct burner arranged in the waste heat recovery unit or another heat source compensates for smaller deficits in steam demand as to optimize the process. 
     
     
         3 . A system according to  claim 1 , wherein each of the gas and steam turbines are mechanically coupled to an integrated gear box comprising different combinations of compressor and expander units. 
     
     
         4 . A system according to  claim 1 , wherein each expander loop is part of fluidly separated refrigerant cycles, wherein all compressors and expanders are associated with at least one of the refrigerant cycles being arranged on the gearbox directly driven by the gas turbine so that cooling duty can be established and controlled independent of the status of the steam system. 
     
     
         5 . A system according to  claim 1 , wherein each of the gas and steam turbines are mechanically coupled to individual compressor sections, the expanders being arranged on separate stand-alone expander-booster-compressor skids.