Systems and methods for using multiple cryogenic hydraulic turbines

Abstract

There is provided a system and method for producing liquefied natural gas (LNG). An exemplary method includes flowing a high-pressure stream of LNG through a first series of liquid turbines. The exemplary method also includes generating electricity by reducing the pressure of the high-pressure stream of LNG to form a low-pressure stream of LNG. The exemplary method additionally includes bypassing any one the liquid turbines that has a failure while continuing to produce electricity from the first series.

What is claimed is: 
     
         1 . A method for generating electricity from liquid turbines, comprising:
 flowing a high-pressure liquid stream through a first plurality of liquid turbines coupled in a first series, wherein, after a first turbine in the series, an inlet of each liquid turbine is coupled to an outlet of a proceeding liquid turbine;   generating electricity from the first series by removing energy from the high-pressure liquid stream to form a low-pressure liquid stream; and   bypassing any one of the first plurality of liquid turbines that has a failure while continuing to produce electricity with the remaining turbines of the first series.   
     
     
         2 . The method of  claim 1 , further comprising:
 maintaining the total electrical output from the first series as a constant value when a liquid turbine is bypassed.   
     
     
         3 . The method of  claim 1 , further comprising:
 maintaining the pressure, temperature, and flow rate of the low-pressure liquid stream from the first series when a liquid turbine is bypassed.   
     
     
         4 . The method of  claim 1 , further comprising:
 removing a portion of the high-pressure liquid stream prior to the first series;   flowing the portion through a second plurality of liquid turbines coupled in a second series, wherein, after a first turbine in the series, an inlet of each liquid turbine is coupled to an outlet of a proceeding liquid turbine; and wherein the second series is in parallel with the first series; and   generating electricity from the second series by removing energy from the portion of the high-pressure liquid stream to form a low-pressure liquid stream.   
     
     
         5 . The method of  claim 1 , wherein the high-pressure liquid stream comprises a liquefied natural gas. 
     
     
         6 . The method of  claim 1 , further comprising:
 producing liquefied natural gas (LNG).   
     
     
         7 . The method of  claim 1 , further comprising:
 driving a variable frequency drive from the electric generator, and if the variable frequency drive fails:   adjusting a speed of a turbine coupled to the generator to synchronize a generator frequency with a grid frequency; and   directly coupling an output of the generator to the electrical grid.   
     
     
         8 . A method for producing liquefied natural gas (LNG), comprising:
 flowing a high-pressure stream of LNG through a first plurality of liquid turbines coupled in a first series;   generating electricity by reducing the pressure of the high-pressure stream of LNG to form a low-pressure stream of LNG; and   bypassing any one of the first plurality of liquid turbines that has a failure while continuing to produce electricity from the first series.   
     
     
         9 . The method of  claim 8 , further comprising:
 flowing a portion of the high-pressure stream of LNG through a second plurality of liquid turbines coupled in a second series, wherein the second series is in parallel with the first series; and   generating electricity in the second plurality of liquid turbines by removing energy from the portion of the high-pressure stream of LNG while reducing the pressure to form a low-pressure stream of LNG.   
     
     
         10 . A liquefied natural gas (LNG) plant, comprising:
 a first plurality of liquid turbine expanders, wherein:   the first plurality of liquid turbine expanders is in a first series in which, after a first liquid turbine expander, the inlet of each liquid turbine expander in the first series is coupled to a previous liquid turbine expander;   each one of the plurality of liquid turbine expanders comprises an electric generator configured to produce electricity with energy created by lowering a pressure of a liquid; and   each one of the plurality of liquid turbine expanders is configured to be bypassed while allowing the LNG plant to continue operating.   
     
     
         11 . The LNG plant of  claim 10 , further comprising:
 a second plurality of liquid turbine expanders, wherein:   the second plurality of liquid turbine expanders is in a second series in which, after a first liquid turbine expander, the inlet of each liquid turbine expander in the second series is coupled to a previous liquid turbine expander;   each one of the second plurality of liquid turbine expanders comprises an electric generator configured to produce electricity with energy removed from a liquid as the pressure is decreased;   the first series is in parallel with the second series; and   each one of the second plurality of liquid turbine expanders is configured to be bypassed while allowing the LNG plant to continue operating.   
     
     
         12 . The LNG plant of  claim 10 , wherein the liquid is LNG, a refrigerant, or both. 
     
     
         13 . The LNG plant of  claim 10 , further comprising an automated control system configured to bypass a liquid turbine expander based, at least in part, on a sensor reading from the liquid turbine expander. 
     
     
         14 . The LNG plant of  claim 13 , wherein the sensor reading comprises a high level on a vibration sensor. 
     
     
         15 . The LNG plant of  claim 13 , wherein the sensor reading comprises a failure detection on a variable frequency drive coupled to an electric generator. 
     
     
         16 . The LNG plant of  claim 10 , further comprising:
 a variable frequency drive coupled to each electric generator; and   an automated control system configured to bypass the variable frequency drive and directly couple the generator to an electrical grid.   
     
     
         17 . The LNG plant of  claim 10 , wherein at least one of the first plurality of turbines has a spare turbine coupled in parallel, wherein the spare turbine is configured to be brought on-line in place of the one of the first plurality of turbines. 
     
     
         18 . The LNG plant of  claim 10 , wherein the internal components of each one of the first plurality of turbines are of identical design. 
     
     
         19 . The LNG plant of  claim 11 , further comprising a coupling between the first series and the second series, wherein:
 the coupling is located after a first turbine in each series and before a last turbine in each series; and   the coupling is configured to allow flow of liquid between the first series and the second series.   
     
     
         20 . The LNG plant of  claim 10 , further comprising a single variable frequency drive coupled to all of the electric generators. 
     
     
         21 . The LNG plant of  claim 10 , further comprising:
 at least one electrical generator that is directly coupled to an electric grid; and   a variable frequency drive on a first turbine, a last turbine, or both.   
     
     
         22 . The LNG plant of  claim 10 , wherein the electric generators for all of the first plurality of turbines are directly connected to an electric grid.