Liquefied natural gas plant with enhanced operating flexibility

Abstract

A method of increasing the production rate and operational flexibility of an LNG facility by overfiring one or more modular gas turbines employed to drive one or more refrigerant compressors in the LNG facility.

1 . A method of operating a first modular gas turbine employed in an LNG facility, said method comprising: overfiring said first modular gas turbine for at least about 6 hours per day for a period of at least 2 successive days, wherein said overfiring causes the power output of said first modular gas turbine to increase by at least about 5 percent over said first modular gas turbine's maximum power output prior to said overfiring. 
     
     
         2 . The method of  claim 1 , wherein said overfiring causes at least about a 5° F. increase in the firing temperature of said first modular gas turbine. 
     
     
         3 . The method of  claim 1 , further comprising shortening said first modular gas turbine's maintenance frequency by at least about 0.5 percent. 
     
     
         4 . The method of  claim 1 , wherein said first modular gas turbine is a multi-shaft turbine. 
     
     
         5 . The method of  claim 1 , wherein said overfiring is at least partly caused by increasing in the fuel-to-air ratio of said first modular gas turbine. 
     
     
         6 . The method of  claim 1 , wherein said overfiring causes the production rate of said LNG facility to increase by at least about 3 percent. 
     
     
         7 . The method of  claim 1 , wherein said first modular gas turbine has a thermal efficiency greater than about 37 percent at ISO standard conditions 
     
     
         8 . The method of  claim 1 , wherein said first modular gas turbine has a rated power of at least 35 megawatts at ISO standard conditions. 
     
     
         9 . The method of  claim 1 , wherein said first modular gas turbine is used to drive a compressor. 
     
     
         10 . The method of  claim 9 , wherein said compressor is used to compress a refrigerant in said LNG facility. 
     
     
         11 . The method of  claim 10 , wherein said refrigerant is a hydrocarbon-containing refrigerant 
     
     
         12 . The method of  claim 1 , wherein said LNG facility is positioned in a location where the average ambient temperature was less than 50° F. for at least two calendar months of at least one calendar year from 1995 to 2005. 
     
     
         13 . The method of  claim 1 , wherein said LNG facility utilizes cascade-type cooling to liquefy at least a portion of its natural gas feed. 
     
     
         14 . The method of  claim 1 , wherein said LNG facility includes a second modular gas turbine, wherein said first and second modular gas turbines power respective first and second refrigerant compressors, wherein said first and second refrigerant compressors operate in parallel. 
     
     
         15 . The method of  claim 14 , wherein said overfiring of said first modular gas turbine is carried out when said second modular gas turbine is shut down. 
     
     
         16 . The method of  claim 1 , wherein said LNG facility has a production rate of greater than about 3.8 million metric tons per annum. 
     
     
         17 . The method of  claim 1 , wherein said modular gas turbine is an aeroderivative gas turbine. 
     
     
         18 . A method of operating a modular gas turbine employed in an LNG facility, said method comprising:
 (a) determining the operating severity of said modular gas turbine;   (b) calculating an actual maintenance frequency of said modular gas turbine according to said operating severity;   (c) comparing said actual maintenance frequency of said modular gas turbine to a predicted maintenance frequency to determine a difference; and   (d) creating an updated maintenance frequency according to the results of step (c).   
     
     
         19 . The method of  claim 18 , wherein said predicted maintenance frequency is dependent on one or more manufacturer-specified turbine operating parameters. 
     
     
         20 . The method of  claim 19 , wherein said turbine-operating parameter is firing temperature. 
     
     
         21 . The method of  claim 18 , wherein said modular gas turbine is a multi-shaft modular gas turbine. 
     
     
         22 . The method of  claim 21 , wherein said multi-shaft modular gas turbine has a thermal efficiency of greater than about 37 percent at ISO standard conditions. 
     
     
         23 . The method of  claim 22 , wherein said modular gas turbine has a rated power output of greater than about 35 megawatts at ISO standard conditions. 
     
     
         24 . The method of  claim 18 , further comprising, prior to step (a), overfiring said modular gas turbine. 
     
     
         25 . The method of  claim 24 , wherein said overfiring causes the firing temperature of said modular gas turbine to increase by at least about 5° F.26. The method of  claim 18 , further comprising, prior to step (a), measuring the actual firing temperature of said modular gas turbine; comparing said actual firing temperature of said modular gas turbine to a recommended firing temperature for said modular gas turbine; comparing said actual firing temperature and said recommended firing temperature to determine a temperature difference; and using said temperature difference to determine said operating severity of said modular gas turbine. 
     
     
         27 . A process utilizing a computer to perform the method according to  claim 18 . 
     
     
         28 . The method of  claim 18 , wherein said LNG facility is positioned in a location where the average ambient temperature was less than 50° F. for at least two calendar months of at least one calendar year from 1995 to 2005. 
     
     
         29 . The method of  claim 18 , wherein said modular gas turbine is an aeroderivative gas turbine. 
     
     
         30 . In a process for producing liquefied natural gas at an LNG facility location where the average ambient temperature was less than 50° F. for at least two calendar months of at least one calendar year from 1995 to 2005, the improvement comprising: using an modular gas turbine to drive a refrigerant compressor of said LNG facility. 
     
     
         31 . The process of  claim 30 , wherein said modular gas turbine is a multi-shaft turbine. 
     
     
         32 . The process of  claim 30 , further comprising overfiring said modular gas turbine for a period of greater than about 48 hours. 
     
     
         33 . The process of  claim 30 , wherein said overfiring causes the power output of said modular gas turbine to increase by at least about 5 percent. 
     
     
         34 . The process of  claim 30 , further comprising decreasing the maintenance frequency of said modular gas turbine by at least about 0.5 percent. 
     
     
         35 . The process of  claim 30 , wherein said modular gas turbine has a thermal efficiency of greater than about 37 percent. 
     
     
         36 . The process of  claim 30 , wherein said refrigerant compressor is used to compress a hydrocarbon-containing refrigerant stream in said LNG facility. 
     
     
         37 . The process of  claim 36 , wherein said hydrocarbon-containing refrigerant is a mixed refrigerant. 
     
     
         38 . The process of  claim 36 , wherein said hydrocarbon-containing refrigerant is a pure-component refrigerant. 
     
     
         39 . The process of  claim 30 , wherein said LNG facility utilizes cascade-type cooling to liquefy at least a portion of its natural gas feed stream. 
     
     
         40 . The process of  claim 30 , wherein said modular gas turbine is an aeroderivative gas turbine. 
     
     
         41 . The process of  claim 30 , wherein said LNG facility has a production rate greater than about 2 million metric tons per annum. 
     
     
         42 . The process of  claim 30 , wherein the yearly variation in ambient temperature extremes of said LNG facility location was at least 50° F. for at least one calendar year from 1995 to 2005. 
     
     
         43 . The process of  claim 30 , wherein the yearly average ambient temperature of said LNG facility location was less than 50° F. for at least one calendar year from 1995 to 2005. 
     
     
         44 . The process of  claim 30 , wherein the yearly variation in ambient temperature extremes of said LNG facility location was in the range of from about 75° F. to about 150° F. for at least one calendar year from 1995 to 2005. 
     
     
         45 . The process of  claim 44 , wherein the yearly average ambient temperature of said LNG facility location was in the range of from about 0° to about 45° F. for at least one calendar year from 1995 to 2005.