AU2013203082B2 - Method and system for utilising waste heat generated from the processing of natural gas to produce liquefied natural gas - Google Patents

Method and system for utilising waste heat generated from the processing of natural gas to produce liquefied natural gas Download PDF

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AU2013203082B2
AU2013203082B2 AU2013203082A AU2013203082A AU2013203082B2 AU 2013203082 B2 AU2013203082 B2 AU 2013203082B2 AU 2013203082 A AU2013203082 A AU 2013203082A AU 2013203082 A AU2013203082 A AU 2013203082A AU 2013203082 B2 AU2013203082 B2 AU 2013203082B2
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stream
inlet air
refrigerant
coolant
waste heat
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AU2013203082A1 (en
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Geoffry Brian Byfield
Gurudutt Dattatreya Gulvadi
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Woodside Energy Technologies Pty Ltd
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Woodside Energy Technologies Pty Ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
    • F25J1/0281—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc. characterised by the type of prime driver, e.g. hot gas expander
    • F25J1/0283—Gas turbine as the prime mechanical driver
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0022—Hydrocarbons, e.g. natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
    • F25J1/007—Primary atmospheric gases, mixtures thereof
    • F25J1/0072—Nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
    • F25J1/008—Hydrocarbons
    • F25J1/0087—Propane; Propylene
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0211—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle
    • F25J1/0214—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a dual level refrigeration cascade with at least one MCR cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0211—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle
    • F25J1/0214—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a dual level refrigeration cascade with at least one MCR cycle
    • F25J1/0215—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a dual level refrigeration cascade with at least one MCR cycle with one SCR cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0211—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle
    • F25J1/0214—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a dual level refrigeration cascade with at least one MCR cycle
    • F25J1/0215—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a dual level refrigeration cascade with at least one MCR cycle with one SCR cycle
    • F25J1/0216—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a dual level refrigeration cascade with at least one MCR cycle with one SCR cycle using a C3 pre-cooling cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0228—Coupling of the liquefaction unit to other units or processes, so-called integrated processes
    • F25J1/0235—Heat exchange integration
    • F25J1/0242—Waste heat recovery, e.g. from heat of compression
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
    • F25J2270/906—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration by heat driven absorption chillers

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Abstract

- 26 A method for processing natural gas to produce liquefied natural gas is described. The method comprises the steps of (a) compressing a first refrigerant in a first compressor 5 driven by a first gas turbine, said first gas turbine having a first inlet air stream and a first exhaust stream; (b) recovering heat from the first exhaust stream in a waste heat recovery unit to produce a heated circulating fluid stream; (c) circulating at least a portion of the heated circulating fluid stream through a chilling circuit to produce a chilled coolant stream; and, (d) directing at least a portion of a chilled coolant stream to a first inlet air 10 cooling circuit to cool the first inlet air stream.

Description

- 1 METHOD AND SYSTEM FOR UTILISING WASTE HEAT GENERATED FROM THE PROCESSING OF NATURAL GAS TO PRODUCE LIQUEFIED NATURAL GAS 5 FIELD OF THE INVENTION The present invention relates to a process and system for liquefying natural gas and in one aspect relates to a process and system for liquefying natural gas wherein the inlet air to the gas turbines used in the system is cooled by utilising waste heat from within the system to thereby improve the operating efficiency of the turbines and hence, the overall efficiency 10 of the system. BACKGROUND TO THE INVENTION Most Liquefied Natural Gas ("LNG") plants constructed in the last 30 years or so have used industrial gas turbines to drive the refrigeration compressors required to liquefy the 15 natural gas. Typically, these gas turbines have inlet air filters but do not include any means for cooling the inlet air to the turbines. It is known that the amount of power available from a gas turbine is, in part, a function of the inlet air temperature. Since the temperature and density of the inlet air changes with the 20 ambient temperature, the amount of power available from a particular turbine varies from day to night and from summer to winter. This change in available power can be quite large; e.g. at times the power available during the hottest summer day can sometimes be less than about 80% of the power available during the coolest winter night. Also, the power from the turbine needed to provide the required refrigeration in an LNG process 25 increases as the ambient temperature increases. Due to these varying factors, the gas turbines used in a typical LNG plant usually include gas turbines large enough to supply the required horsepower when operating at the warmest ambient temperatures even though they may only operate at these temperatures for short periods of time. This means that most LNG plants have to be significantly over designed in order to ensure that the required 3 0 horsepower is always available regardless of the then current ambient temperature.
-2 In an attempt to mitigate the adverse effect of variations in ambient conditions, it is known for gas turbines used in a typical LNG plant to include helper motors to compensate for the reduced power (and efficiency) from turbines during hot seasons. 5 It is an object of the present invention to at least partially overcome the abovementioned problems associated with the prior art, or provide an alternative thereto. SUMMARY OF THE INVENTION According to a first aspect of the present invention there is provided a method for 10 processing natural gas to produce liquefied natural gas, said method comprising the step of: (a) compressing a first refrigerant in a first compressor driven by a first gas turbine, said first gas turbine having a first inlet air stream and a first exhaust stream; (b) recovering heat from the first exhaust stream in a waste heat recovery unit to 15 produce a heated circulating fluid stream; (c) circulating at least a portion of the heated circulating fluid stream through a chilling circuit to produce a chilled coolant stream; (d) directing at least a portion of a chilled coolant stream to a first inlet air cooling circuit to cool the first inlet air stream; and, 20 (e) liquefying said pre-cooled gas stream using one or both of the first refrigerant and a second refrigerant, wherein said second refrigerant is compressed in a second compressor driven by a second gas turbine, said second gas turbine having a second inlet air stream and a second exhaust stream. 25 In one form, the method further comprises the step of recovering heat from the second exhaust stream in a waste heat recovery unit to produce a heated circulating fluid stream, circulating at least a portion of the heated circulating fluid stream through a chilling circuit to produce a chilled coolant stream, and, directing at least a portion of a chilled coolant stream to one or both of: (i) a first inlet air cooling circuit to cool the first inlet air stream; 30 and, (ii) a second inlet air cooling circuit to cool the second inlet air stream.
-3 In one form, the chilling circuit includes a chiller, a coolant storage tank, and a circulation pump. In one form, the chiller is a vapour absorption chiller. In one form, the coolant storage tank is sized to store sufficient chilled coolant to be 5 circulated through one or both of the inlet air cooling circuits by the circulation pump for a predetermined amount of time in the event of tripping of the chiller. In one form, the chilled coolant stream produced by the chilling circuit has a temperature in the range of 5 degrees Celsius to 26 degrees Celsius. 10 In one form, one or both of the circulating fluid stream and the coolant is water. In one form, the coolant includes an anti-freeze agent. In one form, one or both of the first inlet air stream and the second inlet air stream is 15 cooled to a temperature in the range of 6 to 20'C; in the range of 10 to 20'C, or, in the range of 14 to 18'C. In one form, one or both of the first inlet air stream and the second inlet air stream is cooled to a temperature of about 16'C. In one form, the waste heat recovery unit is arranged to recover heat from the first exhaust 20 stream and a second waste heat recovery unit is arranged to recover heat from the second exhaust stream. In one form, the waste heat recovery unit is arranged to recover heat from the second exhaust stream and the control valve directs the chilled coolant stream to the first inlet air 25 cooling circuit. In one form, the waste heat recovery unit is arranged to recover heat from the first exhaust stream and the control valve directs the chilled coolant stream to the second inlet air cooling circuit. 30 In one form the method further comprises the step of cooling a circulating stream of cooling medium for the chiller through one or more air coolers, one or more fans, or a -4 cooling tower. In one form, the first refrigerant is: a mixed refrigerant; nitrogen; or, propane. In one form, the second refrigerant is a mixed refrigerant or nitrogen. 5 According to a second aspect of the present invention there is provided a system for processing natural gas to produce liquefied natural gas, the system comprising: (a) one or more pre-cooling heat exchangers arranged to cool a natural gas feed stream and produce a pre-cooled gas stream using a first refrigerant circuit in which a first 10 refrigerant is compressed in a first compressor driven by a first gas turbine, said first gas turbine having a first inlet air stream and a first exhaust stream; (c) a waste heat recovery unit arranged to receive a cooled circulating fluid return stream and produce a heated circulating fluid stream by recovery of heat from the first exhaust stream; 15 (d) a chilling circuit for recovering heat from the heated circulating fluid stream to produce a chilled coolant stream; (e) a control valve for directing at least a portion of a chilled coolant stream to a first inlet air cooling circuit for receiving at least a portion of the chilled coolant stream for cooling the first inlet air stream; and, 20 (f) one or more cryogenic heat exchangers arranged to receive said pre-cooled gas stream and produce a stream of liquefied natural gas using one or both the first refrigerant circuit and a second refrigerant circuit, wherein the second refrigerant is compressed in a second compressor driven by a second gas turbine, said second gas turbine having a second inlet air stream and a second exhaust stream. 25 In one form, the waste heat recovery unit is arranged to receive a cooled circulating fluid return stream and produce a heated circulating fluid stream by recovery of heat from one or both of the first exhaust stream and the second exhaust stream. 30 In one form, the control valve directs at least a portion of a chilled coolant stream to one or both of: (i) a first inlet air cooling circuit for receiving at least a portion of the chilled coolant stream for cooling the first inlet air stream; and, (ii) a second inlet air cooling -5 circuit to cool the second inlet air stream. In one form, the chilling circuit includes a chiller, a coolant storage tank, and a circulation pump. In one form, the chiller is a vapour absorption chiller. 5 In one form, the coolant storage tank is sized to store sufficient chilled coolant to be circulated through one or both of the inlet air cooling circuits by the circulation pump for a predetermined amount of time in the event of tripping of the chiller. In one form, the chilled coolant stream produced by the chilling circuit has a temperature 10 in the range of 5 degrees Celsius to 26 degrees Celsius, in the range of 6 to 20'C; in the range of 10 to 20'C, or, in the range of 14 to 18'C. In one form, one or both of the circulating fluid stream and the coolant is water. In one form, the coolant includes an anti-freeze agent. 15 In one form, the waste heat recovery unit is arranged to recover heat from the first exhaust stream and a second waste heat recovery unit is arranged to recover heat from the second exhaust stream. 20 In one form, the waste heat recovery unit is arranged to recover heat from the second exhaust stream and the control valve directs the chilled coolant stream to the first inlet air cooling circuit. In one form, the waste heat recovery unit is arranged to recover heat from the first exhaust 25 stream and the control valve directs the chilled coolant stream to the second inlet air cooling circuit. In one form, the system further comprises one or more air coolers, one or more fans, or a cooling tower for cooling a circulating stream of cooling medium for the chiller. 30 In one form, the first refrigerant is: a mixed refrigerant; nitrogen; or, propane. In one form, the second refrigerant is a mixed refrigerant or nitrogen.
-6 According to a third aspect of the present invention there is provided a method of utilising waste heat generated from the processing of natural gas to produce liquefied natural gas to produce chilled coolant in chilling circuit, the method comprising the steps of: (a) compressing a first refrigerant in a first compressor driven by a first gas turbine, 5 said first gas turbine having a first inlet air stream and a first exhaust stream; (b) recovering heat from the first exhaust stream in a waste heat recovery unit to produce a heated circulating fluid stream; (c) circulating at least a portion of the heated circulating fluid stream through a chilling circuit to produce a chilled coolant stream; 10 (d) directing at least a portion of a chilled coolant stream to a first inlet air cooling circuit to cool the first inlet air stream; and, (e) liquefying said pre-cooled gas stream using one or both of the first refrigerant and a second refrigerant, wherein said second refrigerant is compressed in a second compressor driven by a second gas turbine, said second gas turbine having a second inlet 15 air stream and a second exhaust stream. In one form, the method further comprises the step of recovering heat from the second exhaust stream in a waste heat recovery unit to produce a heated circulating fluid stream, circulating at least a portion of the heated circulating fluid stream through a chilling circuit 20 to produce a chilled coolant stream, and, directing at least a portion of a chilled coolant stream to one or both of: (i) a first inlet air cooling circuit to cool the first inlet air stream; and, (ii) a second inlet air cooling circuit to cool the second inlet air stream. In one form, the chilling circuit includes a chiller, a coolant storage tank, and a circulation 25 pump. In one form, the chiller is a vapour absorption chiller. In one form, the coolant storage tank is sized to store sufficient chilled coolant to be circulated through one or both of the inlet air cooling circuits by the circulation pump for a predetermined amount of time in the event of tripping of the chiller. 30 In one form, the chilled coolant stream produced by the chilling circuit has a temperature in the range of 5 degrees Celsius to 26 degrees Celsius. In one form, wherein one or both -7 of the circulating fluid stream and the coolant is water. In one form, the coolant includes an anti-freeze agent. In one form, one or both of the first inlet air stream and the second inlet air stream is cooled to a temperature in the range of 6 to 20'C; in the range of 10 to 20'C, or, in the range of 14 to 18'C. In one form, one or both of the first inlet air stream 5 and the second inlet air stream is cooled to a temperature of about 16'C. In one form, the waste heat recovery unit is arranged to recover heat from the first exhaust stream and a second waste heat recovery unit is arranged to recover heat from the second exhaust stream. In one form, the waste heat recovery unit is arranged to recover heat from 10 the second exhaust stream and the control valve directs the chilled coolant stream to the first inlet air cooling circuit. In one form, the waste heat recovery unit is arranged to recover heat from the first exhaust stream and the control valve directs the chilled coolant stream to the second inlet air cooling circuit. 15 In one form, the method further comprises the step of cooling a circulating stream of cooling medium for the chiller through one or more air coolers, one or more fans, or a cooling tower. In one form, the first refrigerant is: a mixed refrigerant; nitrogen; or, propane. In one form, the second refrigerant is a mixed refrigerant or nitrogen. 20 BRIEF DESCRIPTION OF THE DRAWINGS In order to facilitate a more detailed understanding of the nature of the invention several embodiments of the process and system of the present invention will now be described in detail, by way of example only, with reference to the accompanying drawings, not necessarily to scale, in which like numerals identify like parts and in which: 25 FIG. 1 is a block flow diagram of an embodiment of a system for liquefaction of natural gas (LNG) using a single (first) refrigerant, including a vapour absorption chiller for recovering heat from the exhaust of a gas turbine to provide inlet air chilling; 30 FIG. 2 is a block flow diagram of an embodiment of a system for liquefaction of natural gas (LNG) using first and second refrigerants including a vapour absorption chiller for recovering heat from the exhaust of a gas turbine to provide inlet air chilling; -8 5 10 THIS PAGE IS INTENTIONALLY BLANK 15 -9 FIG. 2 is a block flow diagram of an embodiment of a system for liquefaction of natural gas (LNG) using first and second refrigerants including a vapour absorption chiller for recovering heat from the exhaust of a gas turbine to provide inlet air chilling; 5 FIG. 3 is a block flow diagram of an embodiment of the system of the present invention in which the waste heat that is recovered from the exhaust stream of both of the first and second gas turbines is used as an energy source to produce chilled coolant that is circulated through the inlet air cooling circuit of both of the first gas turbine; 10 FIG. 4 is a block flow diagram of an embodiment of the system of the present invention in which the waste heat that is recovered from the exhaust stream of both of the first and second gas turbines is used as an energy source to produce chilled coolant that is circulated through the inlet air cooling circuit of the first gas turbine only; 15 FIG. 5 is a block flow diagram of an embodiment of the system of the present invention in which the waste heat recovered from the exhaust stream of the second gas turbine is used as an energy source to produce chilled coolant that is circulated through the inlet air cooling circuit of the first gas turbine. 20 FIG. 6 is a block flow diagram of an embodiment of the system of the present invention in which the waste heat recovered from the exhaust stream of the first gas turbine is used as an energy source to produce chilled coolant that is circulated through the inlet air cooling circuit of the second gas turbine. 25 While the present invention will be described in connection with its preferred embodiments, it will be understood that this invention is not limited thereto. On the contrary, the invention is intended to cover all alternatives, modifications, and equivalents which may be included within the spirit and scope of the invention, as defined by the appended claims. 30 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Throughout this specification various terms commonly used in the art are used. In the interests of clarity, such terms are now defined.
-10 The term 'LNG' refers to liquefied natural gas. The term 'vapour absorption chiller' refers to a device that provides cooling by way of evaporation of a liquid refrigerant to form a gaseous refrigerant whereby heat is extracted 5 from its surroundings. The gaseous refrigerant is thereafter absorbed or dissolved into another liquid to produce a refrigerant-laden liquid have a lower partial pressure. The refrigerant-laden liquid is then heated, causing the refrigerant to evaporate out. The refrigerant is condensed through a heat exchanger to replenish the supply of liquid refrigerant in the evaporator. 10 While the present invention is now described in connection with various embodiments, it will be understood that this invention is not limited thereto. On the contrary, the invention is intended to cover all alternatives, modifications, and equivalents which may be included within the spirit and scope of the invention, as defined by the appended claims. 15 FIG. 2 illustrates a system and process for liquefying natural gas (LNG) generally designated by reference numeral 10. In system 10, a natural gas feed stream 12 which has been pre-treated to remove freezable contaminants is directed to flow through one or more pre-cooling heat exchangers 14 where it is cooled by evaporating a first refrigerant to 20 produce a pre-cooled gas stream 16. The pre-cooled gas stream 16 is then directed to flow through one or more cryogenic heat exchangers 18 where it is liquefied by evaporating a second refrigerant to produce a liquefied natural gas (LNG) stream 20. By way of example, the first refrigerant may be propane while the second refrigerant may be a mixed refrigerant which is as a mixture of nitrogen, methane, ethane and propane. In a single 25 refrigerant system such as a nitrogen cycle, the first refrigerant has the same composition as the second refrigerant. In an analogous manner, in a multi-refrigerant system such as the liquefaction process known to a person skilled in the art as the 'Optimised Cascade' liquefaction process, the 'AP-X' process, the 'Mixed Fluid Cascade' process or a mixed refrigerant cascade liquefaction process, the first and second refrigerant may be mixed 3 0 with one or more further refrigerants.
- 11 In the embodiment illustrated in FIG.2 and FIG.3, the first refrigerant is circulated through a first refrigerant circuit 22 in which the first refrigerant is compressed in one or more first compressors 24 which, in turn, are driven by a first gas turbine 26, said first gas turbine having a first inlet air stream 28 and first exhaust stream 30. The second refrigerant is 5 circulated through a second refrigerant circuit 32 in which the second refrigerant is compressed in one or more second compressors 34 which, in turn, are driven by a second gas turbine 36, the second gas turbine having a second inlet air stream 38 and a second exhaust stream 40. It is to be understood that the first and second compressors may be located on a common drive shaft. Alternatively or additionally, the first gas turbine may 10 be arranged to compress both of the first refrigerant and the second refrigerant in an arrangement referred to in the art as a 'SplitMR' liquefaction train. With reference to FIG.3, the present invention relies on utilization of waste heat recovered from one or both of the first and second exhaust streams 30 or 40, respectively, using a 15 waste heat recovery unit 42 arranged to receive a cooled circulating fluid return stream 44 and produce a heated circulating fluid stream 46. By way of example, when the circulating fluid is water, the heated circulating fluid stream is a steam of hot water at a temperature of about 220'C. The heated circulating fluid stream 46 is directed to flow through a chilling circuit 48 in which the waste heat recovered from the exhaust streams is used to produce a 20 chilled coolant stream 50. By way of example, the chilled coolant stream produced by the chilling circuit may have a temperature in the range of 5 degrees Celsius to 26 degrees Celsius. The chilled coolant stream 50 is directed to flow through one or both of (i) a first turbine inlet air cooling circuit 52 for chilling the inlet air of the first gas turbine 26 and, (ii) a second turbine inlet air cooling circuit 54 for chilling the inlet air of the second gas 25 turbine 36. In this way, the inlet air to one or both of the first and second gas turbines is chilled either intermittently or continuously to improve and control the operating efficiency of the turbines. The chilling circuit 48 includes a chiller 60, preferably a vapour absorption chiller, a 30 coolant storage tank 62, and a circulation pump 64. The chiller 60 can be any conventional cooling system which utilise waste heat as an energy source to produce chilled water using vapour absorption principles. A vapour absorption chiller is one - 12 suitable type of chiller that can be used in accordance with the system and method of the present invention. The absorption material in the vapour absorption chiller may, by way of example, be ammonia or lithium bromide. The coolant storage tank 62 is sized to store sufficient chilled coolant to be circulated through the inlet air cooling circuits 52 and 54 5 for a predetermined amount of time in the event of tripping (or unexpected shut down) of the chiller 60. In use, the chilled coolant stream 50 from the vapour absorption chiller 60 is stored in the coolant storage tank 62 so that it is available for use as required to be pumped to one or both of the inlet air cooling circuits 52 and 54 using the circulation pump 64. When the present invention is being used to provide a portion of the chilled 10 coolant stream 50 to both the inlet air cooling circuits 52 and 54, the chilling circuit includes a control valve 66 for controlling the relative flow rate of chilled coolant to each of the inlet air cooling circuits 52 and 54. One example of a suitable coolant is water. In some instances, it may be desirable to add an anti-freeze agent (e.g. ethylene glycol) with inhibitors to the coolant to mitigate the risk of ice forming and to control corrosion. 15 Each inlet air cooling circuit 52 and 54 includes one or more cooling coils positioned in front of the air intake of the first and second gas turbines 26 and 36, respective. As air flows into the inlets of the respective gas turbines, it passes over the cooling coils or the like of each inlet air cooling circuit whereby the inlet air is cooled before it enters its 20 respective turbine. Downstream of the first inlet air cooling circuit 52, a warmed coolant stream 68, is circulated back through the chiller 60. In an analogous manner, downstream of the second inlet air cooling circuit 54, a warmed coolant stream 70, is circulated back through the chiller 60. 25 By maintaining the inlet air for the turbines at a substantially constant low temperature, the amount of power generated by the gas turbines remains at a high level regardless of the ambient air temperature. Preferably, the inlet air will be cooled to a temperature of about 16'C. This allows the LNG plant to operate at a substantially constant production rate throughout the year. Furthermore, the present invention provides a natural gas liquefaction 30 (LNG) system and process wherein waste heat generated in a typical LNG system is used to cool the inlet air to the gas turbines in the system thereby improving the overall efficiency of the system.
- 13 It is to be understood that the present invention can be performed in a system that includes only a single (first) refrigerant as illustrated in FIG. 1 for which like reference numerals refer to like parts. In this embodiment, a first refrigerant is compressed in a first compressor driven by a first gas turbine, said first gas turbine having a first inlet air stream 5 and a first exhaust stream. Heat from the first exhaust stream is recovered in a waste heat recovery unit to produce a heated circulating fluid stream. At least a portion of the heated circulating fluid stream is circulated through a chilling circuit to produce a chilled coolant stream. At least a portion of the chilled coolant stream is direcgted to a first inlet air cooling circuit to cool the first inlet air stream. In FIG. 1, a natural gas feed stream 12 10 which has been pre-treated to remove freezable contaminants is cooled by evaporating a first refrigerant to produce a liquefied natural gas (LNG) stream 20. By way of example, the first refrigerant may be a mixed refrigerant or nitrogen. The first refrigerant is circulated through a first refrigerant circuit 22 in which the first refrigerant is compressed in one or more first compressors 24 (two first compressors arranged on a common drive 15 shaft are illustrated in FIG.1) which, in turn, are driven by a first gas turbine 26, said first gas turbine having a first inlet air stream 28 and first exhaust stream 30. Waste heat is recovered from the first exhaust streams 30 using a waste heat recovery unit 42 arranged to receive a cooled circulating fluid return stream 44 and produce a heated circulating fluid stream 46. The heated circulating fluid stream 46 is directed to flow through the chilling 20 circuit 48 (described above in relation to FIG. 2) in which the waste heat recovered from the exhaust streams is used to produce a chilled coolant stream 50. The chilled coolant stream 50 is directed to flow through a first turbine inlet air cooling circuit 52 for chilling the inlet air of the first gas turbine 26. In this way, the inlet air to one or both of the first gas turbine is chilled either intermittently or continuously to improve and control the 25 operating efficiency of the first gas turbine. In the embodiment illustrated in FIG. 3, a first waste heat recovery unit 42' is arranged to receive the first exhaust stream 30 and a second waste heat recovery unit 42" is arranged to receive the second exhaust stream 40. Each of the waste heat recovery units is arranged to 30 receive a portion of the cooled circulating fluid return stream 44 and produce a portion of the heated circulating fluid stream 46. It is to be understood, that a common waste heat recovery unit may be arranged to receive both of the first exhaust stream 30 and the second -14 exhaust stream 40. Preferably, the first and second waste heat recovery units 42' and 42" are operated in parallel. In the embodiment illustrated in FIG.3, both of the first and second turbine cooling circuits 52 and 54, respectively, are arranged to receive a portion of the chilled coolant stream 50. In an alternative embodiment illustrated in FIG.4, the first 5 turbine cooling circuit 52 is arranged to receive the chilled coolant stream 50 without any of the chilled coolant stream being directed to the second turbine cooling circuit 54. The capital and operating costs associated with the turbines that furnish the power requirements of LNG liquefaction is a significant factor in the capital and operating costs 10 of the system. The onset of global warming, the ambient temperature is likely to increase year after year making the operation of gas turbines less and less efficient. Incorporating the inlet air cooling on turbines will help mitigate the negative impacts from global warming and improve efficiency. This allows the LNG plant to be designed for more capacity and allows the plant to operate at a substantially constant production rate 15 throughout the year. Further, since the present invention utilizes waste heat recovery, no additional heating source is required to carry out the invention. In the embodiment illustrated in FIG. 5, a waste heat recovery unit 42 is arranged to receive the second exhaust stream 40 and the waste heat recovered from the second 20 exhaust stream 40 is being used as an energy source to produce chilled coolant that is being circulated through the first turbine inlet air cooling circuits 52 of the first gas turbine 26. In the embodiment illustrated in FIG. 6, a waste heat recovery unit 42 is arranged to receive the first exhaust stream 30 and the waste heat recovered from the first exhaust stream 30 is being used as an energy source to produce chilled coolant that is being 25 circulated through the second turbine inlet air cooling circuit 54 of the second gas turbine 36. In the embodiments illustrated in FIGS 3, 5 and 6, one or more air coolers 82, one or more fans, or a cooling tower are used to provide the cooling to a stream of circulating cooling 30 medium 80. The stream of circulating cooling medium is used to cool and thus condense the refrigerant circulating through the vapour absorption chiller 60.
- 15 Now that several embodiments of the invention have been described in detail, it will be apparent to persons skilled in the chemical engineering arts that numerous variations and modifications can be made without departing from the basic inventive concepts. All such modifications and variations are considered to be within the scope of the present invention, 5 the nature of which is to be determined from the foregoing description and the appended claims. Furthermore, the preceding examples are provided to illustrate specific embodiments of the invention and are not intended to limit the scope of the process of the invention.

Claims (47)

1. A method for processing natural gas to produce liquefied natural gas, said method comprising the step of: 5 (a) compressing a first refrigerant in a first compressor driven by a first gas turbine, said first gas turbine having a first inlet air stream and a first exhaust stream; (b) recovering heat from the first exhaust stream in a waste heat recovery unit to produce a heated circulating fluid stream; (c) circulating at least a portion of the heated circulating fluid stream through a 10 chilling circuit to produce a chilled coolant stream; (d) directing at least a portion of a chilled coolant stream to a first inlet air cooling circuit to cool the first inlet air stream; and, (e) liquefying said pre-cooled gas stream using one or both of the first refrigerant and a second refrigerant, wherein said second refrigerant is compressed in a second 15 compressor driven by a second gas turbine, said second gas turbine having a second inlet air stream and a second exhaust stream.
2. The method of claim 1 further comprising the step of recovering heat from the second exhaust stream in a waste heat recovery unit to produce a heated circulating fluid 20 stream, circulating at least a portion of the heated circulating fluid stream through a chilling circuit to produce a chilled coolant stream, and, directing at least a portion of a chilled coolant stream to one or both of: (i) a first inlet air cooling circuit to cool the first inlet air stream; and, (ii) a second inlet air cooling circuit to cool the second inlet air stream. 25
3. The method of any one of claims 1 or 2 wherein the chilling circuit includes a chiller, a coolant storage tank, and a circulation pump. 30
4. The method of claim 3 wherein the chiller is a vapour absorption chiller.
5. The method of claim 3 or 4 wherein the coolant storage tank is sized to store sufficient chilled coolant to be circulated through one or both of the inlet air cooling - 17 circuits by the circulation pump for a predetermined amount of time in the event of tripping of the chiller.
6. The method of any one of the preceding claims wherein the chilled coolant stream 5 produced by the chilling circuit has a temperature in the range of 5 degrees Celsius to 26 degrees Celsius.
7. The method of any one of the preceding claims wherein one or both of the circulating fluid stream and the coolant is water. 10
8. The method of any one of the preceding claims wherein the coolant includes an anti-freeze agent.
9. The method of any one of the preceding claims wherein one or both of the first 15 inlet air stream and the second inlet air stream is cooled to a temperature in the range of 6 to 20'C; in the range of 10 to 20'C, or, in the range of 14 to 18'C.
10. The method of any one of the preceding claims wherein one or both of the first inlet air stream and the second inlet air stream is cooled to a temperature of about 16 0 C. 20
11. The method of any one of the preceding claims wherein the waste heat recovery unit is arranged to recover heat from the first exhaust stream and a second waste heat recovery unit is arranged to recover heat from the second exhaust stream. 25
12. The method of any one of the preceding claims wherein the waste heat recovery unit is arranged to recover heat from the second exhaust stream and the control valve directs the chilled coolant stream to the first inlet air cooling circuit.
13. The method of any one of the preceding claims wherein the waste heat recovery 30 unit is arranged to recover heat from the first exhaust stream and the control valve directs the chilled coolant stream to the second inlet air cooling circuit. - 18
14. The method of any one of the preceding claims further comprising the step of cooling a circulating stream of cooling medium for the chiller through one or more air coolers, one or more fans, or a cooling tower. 5
15. The method of any one of the preceding claims wherein the first refrigerant is: a mixed refrigerant; nitrogen; or, propane.
16. The method of any one of the preceding claims wherein the second refrigerant is a 10 mixed refrigerant or nitrogen.
17. A system for processing natural gas to produce liquefied natural gas, the system comprising: (a) one or more pre-cooling heat exchangers arranged to cool a natural gas feed 15 stream and produce a pre-cooled gas stream using a first refrigerant circuit in which a first refrigerant is compressed in a first compressor driven by a first gas turbine, said first gas turbine having a first inlet air stream and a first exhaust stream; (c) a waste heat recovery unit arranged to receive a cooled circulating fluid return stream and produce a heated circulating fluid stream by recovery of heat from the first 20 exhaust stream; (d) a chilling circuit for recovering heat from the heated circulating fluid stream to produce a chilled coolant stream; (e) a control valve for directing at least a portion of a chilled coolant stream to a first inlet air cooling circuit for receiving at least a portion of the chilled coolant stream for 25 cooling the first inlet air stream; and, (f) one or more cryogenic heat exchangers arranged to receive said pre-cooled gas stream and produce a stream of liquefied natural gas using one or both the first refrigerant circuit and a second refrigerant circuit, wherein a second refrigerant is compressed in a second compressor driven by a second gas turbine, said second gas turbine having a 30 second inlet air stream and a second exhaust stream. - 19
18. The system of claim 17 wherein the waste heat recovery unit is arranged to receive a cooled circulating fluid return stream and produce a heated circulating fluid stream by recovery of heat from one or both of the first exhaust stream and the second exhaust stream. 5
19. The system of claim 18 wherein the control valve directs at least a portion of a chilled coolant stream to one or both of: (i) a first inlet air cooling circuit for receiving at least a portion of the chilled coolant stream for cooling the first inlet air stream; and, (ii) a second inlet air cooling circuit to cool the second inlet air stream. 10
20. The system of any one of claims 17 to 19 wherein the chilling circuit includes a chiller, a coolant storage tank, and a circulation pump.
21. The system of claim 20 wherein the chiller is a vapour absorption chiller. 15
22. The system of claim 20 or 21 wherein the coolant storage tank is sized to store sufficient chilled coolant to be circulated through one or both of the inlet air cooling circuits by the circulation pump for a predetermined amount of time in the event of tripping of the chiller. 20
23. The system of any one of claims 17 to 22 wherein the chilled coolant stream produced by the chilling circuit has a temperature in the range of 5 degrees Celsius to 26 degrees Celsius, in the range of 6 to 20'C; in the range of 10 to 20'C, or, in the range of 14 to 18 0 C. 25
24. The system of any one of claims 17 to 23 wherein one or both of the circulating fluid stream and the coolant is water.
25. The system of any one of claims 17 to 24 wherein the coolant includes an anti 30 freeze agent. - 20
26. The system of any one of claims 17 to 25 wherein the waste heat recovery unit is arranged to recover heat from the first exhaust stream and a second waste heat recovery unit is arranged to recover heat from the second exhaust stream. 5
27. The system of any one of claims 17 to 26 wherein the waste heat recovery unit is arranged to recover heat from the second exhaust stream and the control valve directs the chilled coolant stream to the first inlet air cooling circuit.
28. The system of any one of claims 17 to 27 wherein the waste heat recovery unit is 10 arranged to recover heat from the first exhaust stream and the control valve directs the chilled coolant stream to the second inlet air cooling circuit.
29. The system of any one of claim 17 to 28 further comprising one or more air coolers, one or more fans, or a cooling tower for cooling a circulating stream of cooling 15 medium for the chiller.
30. The system of any one of claim 17 to 29 wherein the first refrigerant is: a mixed refrigerant; nitrogen; or, propane. 20
31. The method of any one of claims 17 to 30 wherein the second refrigerant is a mixed refrigerant or nitrogen.
32. A method of utilising waste heat generated from the processing of natural gas to produce liquefied natural gas to produce chilled coolant in chilling circuit, the method 25 comprising the steps of: (a) compressing a first refrigerant in a first compressor driven by a first gas turbine, said first gas turbine having a first inlet air stream and a first exhaust stream; (b) recovering heat from the first exhaust stream in a waste heat recovery unit to produce a heated circulating fluid stream; 30 (c) circulating at least a portion of the heated circulating fluid stream through a chilling circuit to produce a chilled coolant stream; (d) directing at least a portion of a chilled coolant stream to a first inlet air cooling - 21 circuit to cool the first inlet air stream; and, (e) liquefying said pre-cooled gas stream using one or both of the first refrigerant and a second refrigerant, wherein said second refrigerant is compressed in a second compressor driven by a second gas turbine, said second gas turbine having a second inlet 5 air stream and a second exhaust stream.
33. The method of claim 32 further comprising the step of recovering heat from the second exhaust stream in a waste heat recovery unit to produce a heated circulating fluid stream, circulating at least a portion of the heated circulating fluid stream through a 10 chilling circuit to produce a chilled coolant stream, and, directing at least a portion of a chilled coolant stream to one or both of: (i) a first inlet air cooling circuit to cool the first inlet air stream; and, (ii) a second inlet air cooling circuit to cool the second inlet air stream. 15
34. The method of claim 32 or 33 wherein the chilling circuit includes a chiller, a coolant storage tank, and a circulation pump.
35. The method of claim 34 wherein the chiller is a vapour absorption chiller. 20
36. The method of claim 34 or 35 wherein the coolant storage tank is sized to store sufficient chilled coolant to be circulated through one or both of the inlet air cooling circuits by the circulation pump for a predetermined amount of time in the event of tripping of the chiller. 25
37. The method of any one of claims 32 to 36 wherein the chilled coolant stream produced by the chilling circuit has a temperature in the range of 5 degrees Celsius to 26 degrees Celsius. 30
38. The method of any one of claims 32 to 37 wherein one or both of the circulating fluid stream and the coolant is water. - 22
39. The method of any one of claims 32 to 38 wherein the coolant includes an anti freeze agent.
40. The method of any one of claims 32 to 39 wherein one or both of the first inlet air 5 stream and the second inlet air stream is cooled to a temperature in the range of 6 to 20'C; in the range of 10 to 20'C, or, in the range of 14 to 18'C.
41. The method of any one of claims 32 to 40 wherein one or both of the first inlet air stream and the second inlet air stream is cooled to a temperature of about 16'C. 10
42. The method of any one of claims 32 to 41 wherein the waste heat recovery unit is arranged to recover heat from the first exhaust stream and a second waste heat recovery unit is arranged to recover heat from the second exhaust stream. 15
43. The method of any one of claims 32 to 42 wherein the waste heat recovery unit is arranged to recover heat from the second exhaust stream and the control valve directs the chilled coolant stream to the first inlet air cooling circuit.
44. The method of any one of any one of claims 32 to 43 wherein the waste heat 20 recovery unit is arranged to recover heat from the first exhaust stream and the control valve directs the chilled coolant stream to the second inlet air cooling circuit.
45. The method of any one of claims 32 to 44 further comprising the step of cooling a circulating stream of cooling medium for the chiller through one or more air coolers, one 25 or more fans, or a cooling tower.
46. The method of any one of claims 32 to 45 wherein the first refrigerant is: a mixed refrigerant; nitrogen; or, propane. 30
47. The method of any one of claims 32 to 46 wherein the second refrigerant is a mixed refrigerant or nitrogen.
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