WO2009098278A2 - Procédé et appareil de refroidissement d’un échangeur thermique cryogénique et procédé de liquéfaction d’un flux d’hydrocarbures - Google Patents

Procédé et appareil de refroidissement d’un échangeur thermique cryogénique et procédé de liquéfaction d’un flux d’hydrocarbures Download PDF

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Publication number
WO2009098278A2
WO2009098278A2 PCT/EP2009/051353 EP2009051353W WO2009098278A2 WO 2009098278 A2 WO2009098278 A2 WO 2009098278A2 EP 2009051353 W EP2009051353 W EP 2009051353W WO 2009098278 A2 WO2009098278 A2 WO 2009098278A2
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WIPO (PCT)
Prior art keywords
refrigerant
heat exchanger
cryogenic heat
module
valve
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PCT/EP2009/051353
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English (en)
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WO2009098278A3 (fr
Inventor
Clive Beeby
Maria Isabel Parra-Calvache
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Shell Internationale Research Maatschappij B.V.
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Application filed by Shell Internationale Research Maatschappij B.V. filed Critical Shell Internationale Research Maatschappij B.V.
Priority to US12/866,080 priority Critical patent/US20100326133A1/en
Priority to CN200980104368.XA priority patent/CN102405389B/zh
Priority to BRPI0907488A priority patent/BRPI0907488B8/pt
Priority to AU2009211380A priority patent/AU2009211380B2/en
Priority to RU2010137319/06A priority patent/RU2495343C2/ru
Publication of WO2009098278A2 publication Critical patent/WO2009098278A2/fr
Publication of WO2009098278A3 publication Critical patent/WO2009098278A3/fr

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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
    • F25J1/0211—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
    • F25J1/0002—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
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
    • F25J1/0052—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
    • 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
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
    • F25J1/0052—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
    • F25J1/0055—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream originating from an incorporated cascade
    • 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
    • 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
    • F25J1/0237—Heat exchange integration integrating refrigeration provided for liquefaction and purification/treatment of the gas to be liquefied, e.g. heavy hydrocarbon removal from natural gas
    • F25J1/0238—Purification or treatment step is integrated within one refrigeration cycle only, i.e. the same or single refrigeration cycle provides feed gas cooling (if present) and overhead gas cooling
    • 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
    • F25J1/0244—Operation; Control and regulation; Instrumentation
    • F25J1/0245—Different modes, i.e. 'runs', of operation; Process control
    • F25J1/0247—Different modes, i.e. 'runs', of operation; Process control start-up of the process
    • 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
    • F25J1/0244—Operation; Control and regulation; Instrumentation
    • F25J1/0245—Different modes, i.e. 'runs', of operation; Process control
    • F25J1/0249—Controlling refrigerant inventory, i.e. composition or quantity
    • 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
    • F25J1/02—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.
    • F25J1/0285—Combination of different types of drivers mechanically coupled to the same refrigerant compressor, possibly split on multiple compressor casings
    • F25J1/0287—Combination of different types of drivers mechanically coupled to the same refrigerant compressor, possibly split on multiple compressor casings including an electrical motor
    • 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.
    • F25J1/0292—Refrigerant compression by cold or cryogenic suction of the refrigerant 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
    • F25J1/02—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.
    • F25J1/0298—Safety aspects and control of the refrigerant compression system, e.g. anti-surge control
    • 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
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/64—Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
    • 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
    • F25J2280/00—Control of the process or apparatus
    • F25J2280/10—Control for or during start-up and cooling down of the installation

Definitions

  • the present invention relates to a method and apparatus for cooling down a cryogenic heat exchanger.
  • the cryogenic heat exchanger is adapted to liquefy a hydrocarbon stream, such as a natural gas stream.
  • the present invention relates to a method of liquefying such a hydrocarbon stream.
  • cryogenic heat exchangers may be used in methods of liquefying a natural gas stream to produce liquefied natural gas (LNG) .
  • LNG liquefied natural gas
  • the cryogenic heat exchanger is generally able to receive the hydrocarbon stream to be liquefied, to heat exchange the hydrocarbon stream against an at least partly evaporating refrigerant thereby at least partially liquefying the hydrocarbon stream, and to discharge the at least partially liquefied hydrocarbon stream.
  • a typical temperature at which for instance natural gas starts to liquefy may be at -135 0 C.
  • cryogenic heat exchanger needs to be cooled down, e.g. as part of a plant start-up routine.
  • cryogenic heat exchangers In order to prevent damage to the cryogenic heat exchanger, including for instance leaks that may result from thermal expansion and contraction distributions over the cryogenic heat exchanger, operators and manufacturers of such cryogenic heat exchangers typically recommend to avoid as much as possible to exceed a certain specified maximum temperature rate of change over time.
  • US Patent 4,809,154 describes an automated control system for the control of mixed refrigerant-type liquefied natural gas production facilities, wherein functional parameters are optimized. Optimization is accomplished by adjusting parameters including mixed refrigerant inventory, composition, compression ratio, and compressor turbine speeds to achieve the highest product output value for each unit of energy consumed by the facility.
  • '154 is implemented in a parallel processing computer system allowing parallel control processes to be executed on multiple processors having access to a common storage wherein values representative of the current state of every sensor and every controller associated with the production facility are stored.
  • a request queue and a return queue are maintained, as well as a priority table, which is used to resolve contention among parallel operating process loops .
  • the process controller system of US Pat. '154 may work satisfactorily to optimize or keep optimal quantity or quality of the liquefied gas being produced while the liquefaction process runs.
  • the process controller system of US Pat. '154 is not suitable for controlling the cryogenic heat exchanger during initial cooling down at start up, because that requires a sequence of steps to be carried out which cannot be handled using the system of priority tables and request and return queues.
  • the present invention provides an apparatus for cooling down a cryogenic heat exchanger adapted to liquefy a hydrocarbon stream, such as a natural gas stream, which cryogenic heat exchanger is arranged to receive the hydrocarbon stream to be liquefied and a refrigerant, to exchange heat between the hydrocarbon stream and the refrigerant, thereby at least partially liquefying the hydrocarbon stream, and to discharge the at least partially liquefied hydrocarbon stream and spent refrigerant that has passed through the cryogenic heat exchanger, the apparatus comprising
  • the refrigerant recirculation circuit comprising at least a compressor, a compressor recycle valve, a cooler, and a first JT valve;
  • a programmable controller arranged to (i) receive input signals representing sensor signals of one or more controlled variables;
  • the invention provides a method of cooling down a cryogenic heat exchanger adapted to liquefy a hydrocarbon stream, such as a natural gas stream, comprising the steps of - providing a cryogenic heat exchanger arranged to receive the hydrocarbon stream to be liquefied and a refrigerant, to exchange heat between the hydrocarbon stream and the refrigerant, thereby at least partially liquefying the hydrocarbon stream, and to discharge the at least partially liquefied hydrocarbon stream and spent refrigerant that has passed through the cryogenic heat exchanger,
  • the refrigerant recirculation circuit comprising at least a compressor, a compressor recycle valve, a cooler, and a first JT valve;
  • Fig. 1 schematically shows a cryogenic heat exchanger arrangement according to one embodiment
  • Fig. 2 schematically shows a cryogenic heat exchanger arrangement according to another embodiment
  • Fig. 3 schematically shows a block diagram of modules for automatically cooling down the cryogenic heat exchanger of Fig. 1 or Fig. 2
  • Fig. 4 schematically shows a main cryogenic heat exchanger arrangement according to another embodiment of the invention as used in a test
  • Fig. 5 schematically shows the line-up of Fig. 4 illustrating monitored temperatures and pressures
  • Fig. 6 shows a block diagram of the modules as used in the test in conjunction with the line-up of Fig. 4;
  • Fig. 7 schematically shows an alternative module structure that may be incorporated into the block diagram of Fig. 6.
  • the programmable controller can execute a computer program that comprises a network of at least three modules.
  • modules may manipulate one or more valves and has at least one clearly defined module target.
  • the modules may operate independently from each other, but there may be common variables monitored by several modules that can be affected by the action of more than one module.
  • This type of modular approach employing independently executable modules makes the invention suitable for automating the cooling down of any type of heat exchanger, including those of the so-called coil-wound type and of the plate-fin type.
  • One or more of the at least three modules receive a representation of one or more of the input signals and produce representations of one or more of the control signals.
  • the at least three modules are each arranged to
  • a communication signal is generated that marks the module has reached or achieved the predetermined module target.
  • the communication signal may be generated by the module itself, elsewhere in the programmable controller, or it may comprise for instance a sensor signal that indicates that a predetermined condition in or around the cryogenic heat exchanger has been reached.
  • the predetermined module target may be an intermediate result for the module in which case the module may continue to execute more computer readable instructions, e.g. to reach an additional module target.
  • the communication signal may be marking the completion of the execution of the module.
  • the modules in the network are interconnected such the trigger signal received by a second and a third module of the at least three modules corresponds to a communication signal that is generated when the first module of the at least three modules has reached the predetermined target for that module .
  • This way of interconnecting the modules allows for control of a sequential process wherein at least a specified task need to be completed before commencing one or more other tasks, and wherein at least two tasks need to be carried out one after another, while other tasks need to be carried out simultaneously.
  • each module waits until it receives a trigger signal before it may start to carry out its task, and it generates a communication signal upon completion of its task.
  • the completion of the task may be represented by the communication signal that marks the achieving of a predetermined target associated with the task for that module.
  • Any signal marking the completion of the predetermined module target may be passed on to and/or be received by one or more next module (s) that can then work on one or more next tasks in the sequential process.
  • the communication signal is received by two or more next modules, the two or more next modules are ready to start executing their computer readable instructions in parallel with each other.
  • the communication signal may be generated after reaching the target or it may be any signal from which can be inferred that the module has reached the predetermined target. It will be understood that second and/or third communication signals may be generated when the second and/or third modules have achieved their respective module targets, which second and third communications signals may act as trigger signal (s) for one or more subsequent modules or be used in another way in the procedure .
  • the task in a selected module may have to be carried out while being bound by some constraint on one or more of the controlled variables while these one or more controlled variables are not controlled by the selected module in question, but for instance by a simultaneously active other module.
  • the execution of the task of the selected module will automatically experience a delay if further executing of its task would lead to a violation of said constraint. This delay could end when the other module, that does influence the controlled variable, has advanced in executing its task such that the constraint is lifted or shifted giving space for the selected module in question to further advance in executing its task.
  • an effect of the proposed network structure of the modules involving independent modules operating in parallel with each other whereby a control action of one of the modules is constrained by a variable that is influenced by the manipulating one or more manipulated variables by another module, is that the module tasks are quasi-sequentially performed when needed and simultaneously if possible.
  • An additional option for the interconnection of at least two of the modules is that a content signal is generated in one module that is received by another module and causes a change in the operation of the other module other than the starting up of that module.
  • the content signal may trigger a parameter change in the other module when a certain condition is reached in the first module that causes the content signal to be generated.
  • the network of modules can be such that the trigger signal that marks the start of executing the predetermined instructions for a particular module, may be the nth trigger signal received by that module, whereby n can be any natural number.
  • a selected module may need to wait for, for instance, three other modules to achieve their targets upon which communication signal are generated, before it may start executing its sequence of computer readable instructions.
  • the programmable controller may be embedded in a distributed control system (DCS), wherein for instance the modules provide output via an interface server, such as an OLE (object-linking and embedding) for process control (OPC) that may communicate between the computer program and various interface blocks that may be present in the DCS.
  • DCS distributed control system
  • OLE object-linking and embedding
  • OPC process control
  • the DCS can take back control of the manipulated variables (such as selected valves) without waiting for the programmable controller to transfer control as may be desired during emergencies or the like.
  • the inventors associated with the present patent application have contemplated that the presently disclosed type of programmable controller is ideally suited for automation of cooling down of a cryogenic heat exchanger adapted to liquefy a hydrocarbon stream, such as a natural gas stream.
  • Automated cooling down of a cryogenic heat exchanger advantageously facilitates cooling down the cryogenic heat exchanger at the highest rate possible without exceeding the specified maximum rate of temperature change.
  • an operator typically has to maintain a wider margin between the rate of temperature change and the specified maximum.
  • the methods and apparatuses disclosed herein may also be used to avoid one or more spatial temperature gradients in or around the cryogenic heat exchanger to exceed a recommended maximum value (s) .
  • the advantages of the methods and apparatuses described herein are more pronounced for cooling down counter-current cryogenic heat exchangers, preferably using an external refrigerant, wherein the evaporating refrigerant flows counter-currently relative to the stream or streams that is/are to be cooled in the cryogenic heat exchanger against the evaporating refrigerant, than for cooling down co-current cryogenic heat exchangers.
  • 'manipulated variable' is used to refer to variables that are subject to control actions by the programmable controller
  • the term 'controlled variables' is used to refer to variables that have to be kept by the programmable controller at a predetermined value
  • set point or within a predetermined range
  • set range a predetermined range
  • the set point or set range does not have to be a fixed entity. In fact, it will often be subject to changes (either calculated during the cooling down, or as a predetermined sequence over time) .
  • a 'monitored variable' is measured and optionally logged, but in contrast to a controlled variable, it does not have to be kept by the programmable controller at a set point or within a set range.
  • monitored variables may serve as input for the programmable controller to enable it to take decisions based on these monitored variables, or to generate communications signals, or for instance give rise to the programmable controller to issue a warning signal or to pause and/or abort the automatic procedure .
  • the one or more controlled variables comprise a rate of change in temperature over time of one or more of: temperature of the refrigerant at the suction side of the first JT valve; temperature of the refrigerant at the discharge side of the first JT valve; temperature of the hydrocarbon stream at a point inside the cryogenic heat exchanger; and temperature of the hydrocarbon stream downstream of the cryogenic heat exchanger.
  • This provides a direct indication that further facilitates cooling down of the cryogenic heat exchanger without exceeding the specified maximum rate of temperature change.
  • the one or more controlled variables may comprise a selected spatial temperature gradient in or around the cryogenic heat exchanger. This facilitates cooling down of the cryogenic heat exchanger without exceeding a specified maximum spatial temperature gradient .
  • a suitable spatial temperature gradient to keep within a pre-determined maximum is the temperature gradient between a refrigerant tube and the shell wall.
  • the maximum temperature rate of change and/or maximum spatial temperature gradient is generally dependent on the type and/or specific design of the heat exchanger that is subject to the process of cooling down. Specific recommendations regarding such values may be provided by the manufacturer .
  • the selected spatial temperature gradient may reflect the temperature differential between a shell side of the cryogenic heat exchanger and a refrigerant-containing tube side.
  • a liquid/vapour separator is provided in the refrigerant recirculation circuit, to receive a partly condensed refrigerant and separate the partly-condensed refrigerant stream into a liquid heavy refrigerant fraction and a gaseous light refrigerant fraction and to discharge the liquid heavy refrigerant fraction via a liquid outlet and the gaseous light refrigerant fraction via a gas outlet, which fractions are passed to the cryogenic heat exchanger, wherein the first JT valve is arranged to control passage of one of these fractions, preferably the light refrigerant fraction.
  • the selected spatial temperature gradient may in such a line-up reflect one or more of: the temperature differential between the spent refrigerant and the refrigerant between the gas outlet and the gaseous refrigerant inlet of the cryogenic heat exchanger; and the temperature differential between spent refrigerant and the refrigerant between the liquid outlet and the liquid refrigerant inlet of the cryogenic heat exchanger.
  • a so-called surge deviation parameter may be determined based on sensor data to quantify the deviation between surge and actual operating condition of the compressor.
  • Typical sensor data that is taken into account for determining the surge deviation parameter includes the flow through the relevant compressor stage and inlet and discharge pressure of the relevant stage.
  • the one or more manipulated variables may comprise one or both of: a first JT valve setting that represents a measure of amount of opening of the first JT valve; and a compressor recycle valve setting that represents a measure of amount of opening of the compressor recycle valve.
  • the amount of opening of the first JT valve quite directly affects the rate of cooling of the cryogenic heat exchanger because it is one of the factors that determine the Joule-Thomson effect that the JT valve has on the refrigerant stream as it passes through the JT valve, which determines the cooling power of the refrigerant .
  • the amount of opening of the compressor recycle valve also affects the rate of cooling of the cryogenic heat exchanger because it also influences the JT effect at the first JT valve because it is one way of controlling the pressure and flow rate of the refrigerant.
  • compressor speed may also be used as one of the manipulated variable (s) .
  • a valve is a very suitable item to manipulate in a control sequence that has relatively immediate effect on the pressure.
  • the methods and apparatuses disclosed herein may be used in a method of liquefying a hydrocarbon stream such as a natural gas stream.
  • a hydrocarbon stream such as a natural gas stream.
  • the cooling down of the cryogenic heat exchanger is followed by normal operation wherein the hydrocarbon stream is cooled in the cryogenic heat exchanger until it is liquefied, preferably followed by sub-cooling in the cryogenic heat exchanger or in a subsequent heat exchanger .
  • natural gas can be stored and transported over long distances more readily as a liquid than in gaseous form, because it occupies a smaller volume and does not need to be stored at a high pressure .
  • natural gas comprising predominantly methane
  • the purified gas is processed through a plurality of cooling stages using heat exchangers to progressively reduce its temperature until liquefaction is achieved.
  • the liquid natural gas is then optionally further cooled, and expanded through one or more expansion stages to final atmospheric pressure suitable for storage and transportation.
  • the flashed vapour from each expansion stage can be used as a source of plant fuel gas .
  • US 2006/0213223 Al discloses a liquefaction plant and method for producing liquefied natural gas .
  • Control of the plant may be fully or partially automated, such as by using an appropriate computer, a programmable logic circuit (PLC), using closed-loop and open-loop schemes, using proportional, integral, derivative (PID) control.
  • PLC programmable logic circuit
  • PID proportional, integral, derivative
  • 2006/0213223 does not teach a computer program or an algorithm as described in the present application.
  • a cryogenic heat exchanger 1 arranged to receive, via conduit 2 and hydrocarbon stream inlet 7, the hydrocarbon stream that is to be liquefied, in order to exchange heat between the hydrocarbon stream and an at least partly evaporating refrigerant 3.
  • the hydrocarbon stream may be at least partially liquefied.
  • the preferably at least partially liquefied hydrocarbon stream is discharged via hydrocarbon stream outlet 8 into conduit 4.
  • conduit 2 and conduit 4 connect via a tube side 29.
  • other types of heat exchangers are possible.
  • the cryogenic heat exchanger 1 comprises a refrigerant inlet 5 for an external refrigerant and a refrigerant outlet 6 for spent refrigerant that has passed through the cryogenic heat exchanger.
  • a refrigerant recirculation circuit 10 is provided to recirculate spent refrigerant back to the inlet 5.
  • the refrigerant recirculation circuit 10 comprises, at least, a compressor 11, a compressor recycle valve 12, a cooler 13, and a first Joule-Thompson (first JT) valve 14.
  • a JT valve may be used in combination with an expander.
  • the JT valve is preferably used for controlling the cooling.
  • the compressor may consist of a plurality of compression stages, for instance 15 compression stages or more.
  • a number of these stages, for instance 15 of these stages, may be provided in the form of an axial compressor or centrifugal compressor in one casing.
  • Each stage may comprise a dedicated recycle valve, and/or a single recycle valve may be shared by any number of subsequent stages.
  • Several compressors or compressor casings may be arranged in series one after another to form a compressor train.
  • Each casing (or compressor stage) may be followed by any number of optional coolers (or intercoolers ) , and optional knock-out drums to remove any liquid from the compressed vapour before passing the compressed vapour to the next compression stage.
  • the compressed refrigerant stream may be cooled.
  • a schematically simplified compressor line-up is depicted in Figs. 1 and 2, with only one compressor drawn in and one recycle valve.
  • spent (at least partly evaporated) refrigerant is drawn from the heat exchanger 1 via outlet 6, and at least a part of it is passed to a suction inlet of compressor 11 via conduit 25.
  • the gaseous part of the spent refrigerant stream in conduit 25 is compressed to yield a compressed refrigerant stream 16 that is subsequently cooled in one or more coolers, here depicted as cooler 13, thereby at least partially condensing the compressed refrigerant stream 16 to form an at least partially condensed refrigerant stream 17.
  • the at least partially condensed refrigerant stream 17 is expanded over first JT valve 14 and subsequently led into the heat exchanger 1 via inlet 5.
  • the refrigerant stream flows co- currently with the hydrocarbon stream (from left to right) through the heat exchanger 1.
  • the flow may be arranged counter-currently instead, such as is for example the case in Fig. 2.
  • FIG. 2 an alternative cryogenic heat exchanger arrangement is shown that comprises the same elements as the embodiment of Fig. 1, and in addition includes a refrigerant tube side 15 for auto-cooling the refrigerant. Both the hydrocarbon stream 2 and the refrigerant are heat exchanged against the evaporating refrigerant in the heat exchanger 1.
  • the compressed refrigerant stream 16 is subsequently cooled in one or more coolers, here depicted as cooler 13, followed by cooling in the heat exchanger 1, via tube side 15, thereby at least partially condensing the compressed refrigerant stream 16 to form the at least partially condensed refrigerant stream 17.
  • the auto-cooled, at least partially condensed refrigerant stream 17 is drawn from the heat exchanger at outlet 18 and led through first JT valve 14 before it is passed, via inlet 5, into the heat exchanger 1, where it is allowed to at least partially evaporate.
  • a refrigerant make-up system may be provided which is capable of changing the inventory of the refrigerant in particular in the case of a mixed refrigerant .
  • the first JT valve setting e.g. representing a measure of amount of opening of the first JT valve (X14) or of the flow through the first JT valve;
  • a compressor recycle valve setting e.g. representing a measure of amount of opening of the compressor recycle valve (X12) or of the flow through the recycle valve; are used as manipulated variable (s) .
  • the make-up valves of the refrigerant components may also be used as manipulated variables.
  • - compressor discharge pressure may be used as monitored variable.
  • FIG. 3 shows a schematic block diagram containing an example module structure of the computer program in the programmable controller for the automatic cool down method and apparatus.
  • a first module 201 defines initial conditions.
  • Module 201 may contain a graphic interface with a summary of warnings and information modes . It may contain information on critical and non-critical initial conditions.
  • the module ends the computer programme thereby stopping the procedure. The procedure may be resumed and/or restarted after the critical condition has been resolved, either manually by an operator or by running an automated control procedure to restore the initial condition.
  • the module 201 issues a warning. This module may further initiate the monitoring of critical variables. The module target is reached when all critical variables are within predetermined ranges. The end trigger can then be generated.
  • critical initial conditions are: - first JV valve 14 is not sufficiently closed (e.g. more than 0.1 % open or other suitable number);
  • - compressor 11 is not on-line and running, as can be determined by measuring compressor speed (e.g. compressor running at least 3400 rpm or other suitable speed) and verifying that the suction and discharge valves on the compressors are open;
  • compressor speed e.g. compressor running at least 3400 rpm or other suitable speed
  • - refrigerant pressure is too high (e.g. above 20 barg, or other suitable figure) ;
  • IGV - compressor inlet guide vane
  • thermoelectric valve 14 various actual temperatures, e.g. temperature of the refrigerant directly upstream of and directly downstream of the first JV valve 14, and/or temperature differentials ;
  • module 201 may be preceded by one or more other modules, e.g. modules related to cooling down to an intermediate temperature level or such, and it may start upon receipt of one or more trigger signals .
  • the communication signal may be emitted and received by the module 202, which has a module target first opening of the first JT valve 14. This may involve an algorithm that takes into account any non-linear behaviour of the JT valve. Once a cooling trend is detected, the valve will be closed partially to avoid a too high cooling rate.
  • the communication signal of module 202 (or a corresponding signal) triggers module 203, which then starts by simply waiting some time.
  • the purpose is to wait for the apparatus to stabilize after the first critical action of module 202.
  • the waiting time may depend on the final condition of the module 202.
  • a signal corresponding to the communication signal of module 203 is received by two modules (204, 205), which are consequently triggered simultaneously.
  • Module 204 further opens the first JT valve 14.
  • strong cooling may cause condensation of the refrigerant.
  • the valve movements are preferably slowed down, and the moment that condensation is detected the valve may be closed partially to avoid too high a cooling rate that would otherwise be caused by a sudden increase in flow rate due to condensation (an increase of 100 tpd in 10 sees is not uncommon) .
  • the valve opening may be normalized and continued until the JT effect of the valve opening in diminished. This is the module target.
  • the JT effect may be monitored during the further opening of the JT valve, for instance based on a temperature difference between the temperature of the refrigerant upstream of the JT valve and the temperature of the refrigerant downstream of the JT valve. An assumption may be made that the JT effect is present if the temperature difference exceeds 8 0 C.
  • Condensation may be detected by deferment from one or both of a temperature and flow measurement at the JT valve.
  • the temperature of the refrigerant downstream of the JT valve 14 may be used and/or the flow through the JT valve, which in turn may be estimated by determining a pressure differential over the JT valve 14.
  • the module cannot close the JT valve 14 further than a minimum opening corresponding to the opening at the start of this module.
  • the changes in JT effect upon further opening of the JT valve may be small.
  • the refrigerant pressure is increased as module 205 is module 205 is executing its instructions at the same time as module 204.
  • Module 205 manipulates the recycle valve 12 to meet a target surge deviation of the compressor (or number of compression stages) . This module monitors the surge deviation of the compressor 11, and closes the recycle valve 12 if the surge deviation exceeds a pre- determined maximum deviation.
  • a suitable predetermined maximum deviation is 0.3.
  • each recycle valve may be manipulated individually (but simultaneously) taking into account a dedicated surge deviation parameter for the corresponding stage through which each particular recycle valve controls the recirculation. Since the closing of recycle valve 12 affects the compressor suction pressure, this pressure is preferably monitored by the module 205 to not go below a recommended limit, such as e.g. 1.8 barg. Closing the recycle valve decreases the suction pressure as well. Therefore, the closing of the recycle valve is made conditional to avoid causing the suction pressure to go below predetermine target value. The objective is to maintain a ramp (increase) on the discharge pressure by closing the recycle valves steadily while monitoring surge deviation. When the surge deviation is below the considered minimum level (e.g. 0.1) then the module activity is stopped. However surge deviation is monitored throughout the whole final cool down procedure, and the recycle valves closed when allowed by the surge deviation and the suction pressure is within a predetermined range.
  • a recommended limit such as e.g. 1.8 barg.
  • a communication signal is generated in modules 204 and 205, which is received by module 206.
  • an operating temperature could be -160 0 C.
  • a corresponding single trigger signal that marks said condition and is passed on to the module in question is considered to be a signal corresponding to the communication signals of both the modules the module in question.
  • Module 206 fully closes the recycle valve 12 as much as possible, provided that the surge deviation does not stop this from occurring. If the surge deviation prevents further closing of the recycle valve, in case the surge value is too low (typically below 0.1), a warning message may be generated and outputted to alert the operator that an IGV adjustment may be necessary.
  • An IGV movement has a similar effect as the closing of the recycle valve 12. However, any IGV movement may be constrained by the molecular weight of the passing refrigerant that must exceed a pre-determined minimum value. A typical MR minimum molecular weight is 24 g/mol . Obviously, this warning signal may not be a useful option if no IGV is present on the compressor in use.
  • module 206 may be superfluous and therefore omitted, thereby relying fully on module 205.
  • Module 207 may be an end module which may be programmed to hand over control to an operator and/or present a status output or generate an operator alerting signal to inform the operator that normal operation of the cryogenic heat exchanger may proceed, or the like .
  • module 207 may also be a start module for a subsequent control procedure, e.g. normal operating control such as advanced process control as described in e.g. US Pat. 7,266,975 and/or US Pat. 6,272,882, or any other type of module .
  • Typical examples of such overriding boundaries are: - a pre-determined maximum temperature rate of change on any selected temperature, suitably one or more of a temperature of the hydrocarbon product at a location in tube side 29 and/or in conduit 4; the spent refrigerant temperature; the refrigerant temperature at the discharge side of the first JT valve 14 or the suction side thereof (particularly after auto-cooling) ; any shell side temperature in the heat exchanger 1;
  • the refrigerant recirculation circuit may circulate a single component refrigerant, such as methane, ethane, propane, or nitrogen; or a multi-component mixed refrigerant, sometimes referred to simply as mixed refrigerant (MR), based on two or more components. These components may preferably be selected from the group comprising nitrogen, methane, ethane, ethylene, propane, propylene, butane and pentane .
  • MR mixed refrigerant
  • the refrigerant circuit may involve any number of separate lines or streams of refrigerant to cool different hydrocarbon streams, and any number of common elements or features, including compressors, coolers, expanders, etc. Some refrigerant streams may be common and some may be separate.
  • the described method of cooling down a cryogenic heat exchanger is part of a method of liquefying a hydrocarbon stream such as natural gas from a feed stream.
  • the apparatus as described herein may be used in such a method of liquefying a hydrocarbon stream.
  • the hydrocarbon stream may be any suitable hydrocarbon-containing, preferably methane-containing, stream to be liquefied, but is usually drawn from a natural gas stream obtained from natural gas or petroleum reservoirs.
  • the natural gas stream may also be obtained from another source, also including a synthetic source such as a Fischer-Tropsch process.
  • natural gas is comprised substantially of methane.
  • the feed stream comprises at least 60 mol% methane, more preferably at least 80 mol% methane .
  • a hydrocarbon feed stream may be liquefied by passing it through a number of cooling stages. Any number of cooling stages can be used, and each cooling stage can involve one or more heat exchangers, as well as optionally one or more steps, levels or sections. Each cooling stage may involve two or more heat exchangers either in series, or in parallel, or a combination of same .
  • heat exchangers able to cool and liquefy a hydrocarbon feed stream are known in the art and the present invention may be applied to any one of them.
  • heat exchanger types are heat exchangers available from Air Products & Chemicals Inc. and Linde AG, typically comprising one, or two, or three, or more bundles.
  • Suitable heat exchangers able to cool and liquefy a feed stream such as a hydrocarbon stream such as natural gas are known in the art, including single mixed refrigerant (SMR) arrangements, dual mixed refrigerant (DMR) arrangements, propane-mixed refrigerant arrangements (C3-MR), arrangements based on three or more cycles, such as e.g. a so-called APX arrangement launched by Air Products & Chemicals Inc. based on C3-MR-N2 cycles, and cascade arrangements including those with a sub-cooling cycle.
  • SMR single mixed refrigerant
  • DMR dual mixed refrigerant
  • C3-MR propane-mixed refrigerant arrangements
  • APX arrangement launched by Air Products & Chemicals Inc. based on C3-MR-N2 cycles
  • cascade arrangements including those with a sub-cooling cycle.
  • the present invention may be applied to any heat exchanger in any of such arrangements, and other suitable arrangements, with some minor modifications that are within the reach of the person
  • the cooling and liquefying of the hydrocarbon feed stream involves two (or more) cooling stages comprising a pre-cooling stage and a main cooling stage.
  • the pre-cooling stage cools the hydrocarbon stream to below 0 0 C, typically between -80 and -30 0 C
  • the second stage which may be referred to as a main cryogenic stage, cools to below -100 0 C to liquefy the hydrocarbon stream.
  • the natural gas may contain varying amounts of hydrocarbons heavier than methane such as ethane, propane, butanes and pentanes as well as some aromatic hydrocarbons.
  • the natural gas stream may also contain non-hydrocarbons such as H2O, N2, CO2, H2S and other sulphur compounds, and the like.
  • the hydrocarbon streams may be pre-treated before using them in the present invention.
  • This pre-treatment may comprise removal of any undesired components present such as CO2 and H2S, or other steps such as pre-cooling, pre-pressurizing or the like. As these steps are well known to the person skilled in the art, they are not further discussed here.
  • the liquefied natural gas may be further processed, if desired.
  • the obtained LNG may be depressurized by means of a Joule-Thomson valve or by means of a cryogenic turbo-expander .
  • the present invention may involve one or more other or further refrigerant circuits, for example in a pre- cooling stage. Any other or further refrigerant circuits could optionally be connected with and/or concurrent with the refrigerant circuit for cooling the hydrocarbon stream.
  • Figure 4 shows a larger type of cryogenic heat exchanger 100, embedded in a system of various pre- cooling heat exchangers, serviced by such a further refrigerant circuit, and other equipment, as may be found in a hydrocarbon liquefaction plant.
  • the further refrigerant circuit may hereinafter be referred to as the "pre-cooling refrigerant circuit” or “pre-cooling refrigerant cycle”.
  • items such as compressors and the refrigerant may also be referred to as "pre- cooling refrigerant compressor” or "pre-cooling refrigerant”.
  • the cryogenic heat exchanger 100 of this embodiment will hereinafter be referred to as the main cryogenic heat exchanger 100, to distinguish it from any other heat exchangers present in the embodiment.
  • the main cryogenic heat exchanger 100 comprises a warm end 33, a cold end 50 and a mid-point 27.
  • the wall of the main cryogenic heat exchanger 100 defines a shell side 110. In the shell side 110 are located:
  • first tube side 29 extending from the warm end 33 to the cold end 50, preferably extending between a hydrocarbon stream inlet 7 and a hydrocarbon stream outlet 8;
  • a third tube side 15 extending from the warm end 33, preferably from a liquid refrigerant inlet 49b at the warm end 33, to the cold end 50.
  • a refrigerant compressor train as shown here symbolically comprising first and second compressors 30 and 31, is provided to compress the refrigerant.
  • Each of these compressors is provided with a number of recycle valves, which are here schematically represented by recycle valves 130 and 131 in a recycle line that connects the compressor discharge, downstream of the respective coolers, to the low pressure suction inlet.
  • the first refrigerant compressor 30 is driven by a suitable motor, for example a gas turbine 35, which is provided with a helper motor 36 for start-up, and the second refrigerant compressor 31 is driven by a suitable motor, for example a gas turbine 37 provided with a helper motor (not shown) .
  • a suitable motor for example a gas turbine 35 provided with a helper motor (not shown)
  • the compressors 30 and 31 may be driven on a single shaft on a shared motor .
  • a gaseous, preferably methane-rich hydrocarbon feed stream is supplied at elevated pressure through supply conduit 20 to the first tube side 29 of the main cryogenic heat exchanger 100 at its warm end 33.
  • the hydrocarbon feed stream passes through the first tube side 29 where it is cooled, liquefied and optionally sub-cooled, against a mixed refrigerant (MR) evaporating in the shell side 110 forming spent refrigerant.
  • MR mixed refrigerant
  • the resulting liquefied hydrocarbon stream is removed from the main cryogenic heat exchanger 100 at its cold end 50 through conduit 40.
  • the flow of the hydrocarbon stream through the system may be controlled, e.g. using rundown valve 44 provided in conduit 40.
  • Stream 40 may optionally be passed through a suitable end flash system, wherein the pressure is brought down to storage and/or transportation pressure. Finally, liquefied hydrocarbon stream is passed as the product stream to storage where it is stored as liquefied product, or optionally directly to transportation.
  • valve 66 During normal operation, and during cooling down of the main cryogenic heat exchanger, spent refrigerant is removed from the shell side 110 of the main cryogenic heat exchanger 100 at its warm end 33 through conduit 25 and passed to knock-out drum 56.
  • a refrigerant make-up adjustment conduit 65 also feeds into knock-out drum 56 to optionally add refrigerant inventory to the spent refrigerant stream.
  • the adding of the various refrigerant components is controlled by one or more valves, typically one valve per component. Here, these valves are schematically represented as valve 66.
  • refrigerant compressors 30 and 31 Other refrigerant compressor arrangements are possible.
  • ambient cooler 23 which may comprise an air cooler and/or a water cooler and/or any other type of ambient cooler.
  • an intercooler (not shown) may be provided between two successive compressor stages of a compressor.
  • the compressed refrigerant stream in conduit 32 is cooled in air cooler 42 and partly condensed in one or more pre-cool heat exchangers (shown are 43 and 41) against a pre-cool refrigerant cycle that will be described in more detail later hereinbelow.
  • the pre-cool heat exchangers 41,31 may be operating at mutually different pressures and/or be using different refrigerant compositions .
  • the partly condensed refrigerant stream 39 is then passed to and let into a liquid/vapour separator via an inlet device, here depicted as separator vessel 45 and inlet device 46.
  • separator vessel 45 the partly- condensed refrigerant stream is separated into a, at this point liquid, heavy refrigerant fraction (HMR) and a, at this point gaseous, light refrigerant fraction (LMR) .
  • HMR heavy refrigerant fraction
  • LMR gaseous, light refrigerant fraction
  • These streams may each be individually controlled by means of a JT valve or the like, the first JT valve 58 for controlling the vapour (light) refrigerant stream and a second JT valve 51 for controlling the liquid (heavy) refrigerant stream.
  • the liquid heavy refrigerant fraction is removed from the separator vessel 45 through conduit 47, and the gaseous light refrigerant fraction is removed through conduit 48.
  • the heavy refrigerant fraction is sub-cooled in the second tube side 28 of the main cryogenic heat exchanger 100 to get a sub-cooled heavy refrigerant stream 54.
  • the sub-cooled heavy refrigerant stream is removed from the main cryogenic heat exchanger 100 through conduit 54, and allowed to expand over an expansion device comprising second JT valve 51.
  • the expansion device may further comprise a dynamic expander (not shown) in series with the second JT valve 51, which does not have to be operated during any cool down procedure of the main cryogenic heat exchanger.
  • the sub-cooled heavy refrigerant stream is, at reduced pressure, introduced through conduit 52 and nozzle 53 into the shell side 110 of the main cryogenic heat exchanger 100 at its mid-point 27.
  • the heavy refrigerant stream is allowed to evaporate in the shell side 110 at reduced pressure, thereby cooling the fluids in the tube sides 29, 28 and 15.
  • the gaseous light refrigerant fraction removed from separator vessel 45 through conduit 48 is passed to the third tube side 15 in the main cryogenic heat exchanger 100 where it is cooled, liquefied and sub-cooled to get a sub-cooled light refrigerant stream 57.
  • the sub-cooled light refrigerant stream is removed from the main cryogenic heat exchanger 100 through conduit 57, and allowed to expand over an expansion device comprising first JT valve 58. At reduced pressure it is introduced through conduit 59 and nozzle 60 into the shell side 110 of the main cryogenic heat exchanger 100 at its cold end 50.
  • the light refrigerant stream is allowed to evaporate in the shell side 110 at reduced pressure, thereby cooling the fluids in the tube sides 29, 28 and 15.
  • an optional side stream may be drawn from the gaseous light refrigerant stream 48, which may be cooled, liquefied and sub-cooled against one or more other cold streams in one or more other heat exchangers other then the main cryogenic heat exchanger 100. For instance, it may be cooled, liquefied and sub- cooled against cold flash vapour generated from stream 40 in an optional end flash system.
  • the optional sub-cooled side stream may be recombined with the light refrigerant stream in conduit 57 or 59 in which case it needs an auxiliary expander means such as an auxiliary first JT valve.
  • Pre-cool heat exchangers 41,43 are operated using a pre-cooling refrigerant, which may be a mixed component refrigerant or a single component refrigerant.
  • a pre-cooling refrigerant which may be a mixed component refrigerant or a single component refrigerant.
  • propane has been used.
  • Evaporated propane is compressed in pre-cool compressor 127 driven by a suitable motor, such as a gas turbine 128.
  • a pre-cooling refrigerant compressor recycling valve 129 is provided as well, here symbolically shown in a line connecting the first stage compressor low pressure suction inlet with the intermediate pressure level.
  • a recycling line may optionally be provided across all of or a selection of compression stages.
  • Compressed propane is then condensed in air cooler 130, and the condensed compressed propane, at elevated pressure, is then passed through conduits 135 and 136 to heat exchangers 43 and 41 which are arranged in series with each other.
  • the condensed propane is allowed to expand to an intermediate pressure over expansion valve 138, before entering into heat exchanger 43.
  • the propane partly evaporates against the heat from the multi-component refrigerant in conduit 32, and the resulting evaporated gaseous fraction is passed through conduit 141 to an intermediate pressure inlet of the propane compressor 127.
  • the liquid fraction is passed through conduit 145 to the heat exchanger 41.
  • the propane Before entering into the heat exchanger 41, the propane is allowed to expand to a low pressure over expansion valve 148.
  • the evaporated propane is passed through conduit 150 to a suction inlet of the propane compressor 127.
  • knock-out drums or the like may be provided in any conduit connecting to a compressor suction to avoid feeding a non gaseous phase to the compressor.
  • An economizer may also be provided.
  • two pre-cooling heat exchangers have been shown operating at two pressure levels. However, any number of heat pre-cooling heat exchangers and corresponding pressure levels may be employed.
  • the pre-cooling refrigerant cycle may also be used to obtain hydrocarbon stream 20, for instance as follows.
  • a hydrocarbon feed in the present example a natural gas feed, is passed at elevated pressure through supply conduit 90.
  • the natural gas feed which typically is a multi-component mixture of methane and heavier constituents, is partially condensed in at least one heat exchanger 93.
  • this heat exchanger operates at approximately the same pressure level as pre-cooling heat exchanger 43, using a side stream 137 of the pre- cooling refrigerant drawn from conduit 135.
  • conduit 137 connects to conduit 137a.
  • the pre- cooling refrigerant Prior to entering into the heat exchanger 93, the pre- cooling refrigerant is allowed to expand over valve 139 to approximately intermediate pressure.
  • the resulting evaporated gaseous fraction is passed through conduits 140a and 140 to conduit 141 where it is recombined with the gaseous fraction drawn from pre-cooling heat exchanger 43.
  • the liquid fraction of the pre-cooling refrigerant is drawn from the heat exchanger 93 in conduit 151 and fed into heat exchanger 91 after expansion over valve 152 to approximately the low pressure.
  • the evaporated pre-cooling refrigerant is then led to conduit 150 via conduits 153a and 153.
  • heat exchangers 43 and 93 and/or heat exchangers 41 and 91 may be provided in the form of combined heat exchangers comprising separate sides for the natural gas and for the refrigerant in conduit 32.
  • the partly condensed feed 92 is introduced, e.g. via an inlet device 94, into a gas/liquid separator 95 which may be provided e.g. in the form of a scrub column or similar.
  • a gas/liquid separator 95 which may be provided e.g. in the form of a scrub column or similar.
  • the partly condensed feed is separated to get a methane-enriched gaseous overhead stream 97 and a liquid, methane-depleted bottom stream 115.
  • the gaseous overhead stream 97 is passed through conduit 97 via heat exchanger 91 to an overhead separator 102.
  • the gaseous overhead stream is partly condensed against the pre-cooling refrigerant in conduit 151, and the partly condensed overhead stream is introduced into the overhead separator 102 via inlet device 103.
  • the partly condensed overhead stream is separated into a gaseous, stream 20 (which is substantially depleted from C5+ components and/or relatively rich in methane when compared to the feed stream) and a liquid bottom stream 105.
  • the gaseous stream 20 forms the hydrocarbon feed at elevated pressure in conduit 20.
  • At least part of the liquid bottom stream 105 may be introduced through conduit 105 and nozzle 106 into the scrub column 95 as reflux.
  • the conduit 105 is provided with a flow control valve (not shown) and/or pump 108.
  • conduit 20 If there is less reflux required than there is liquid in the partly condensed gaseous overhead stream 105, the surplus may be passed on to conduit 20 over a bypass conduit (not shown) and a flow control valve (not shown) .
  • an external reflux medium suitably butane, may be added from an external source (not shown), suitably into conduit 105.
  • the liquid, C3+-enriched bottom stream is removed from the scrub column 95 via conduit 115.
  • it may be withdrawn from the process, sent to a fractionation train and/or storage/transport and/or a reboiler in any fashion known to the person skilled in the art.
  • the main cryogenic heat exchanger Prior to its normal operation as described above, the main cryogenic heat exchanger has to be cooled down to operating temperature.
  • the presently disclosed methods and apparatuses achieve an automated cooling down of the main cryogenic heat exchanger. This has been demonstrated in accordance with the following.
  • FIG. 5 shows the points in and around the main cryogenic heat exchanger 100 where in a test the temperature sensors (TR20; TR25; TR33; TR40; TR47; TR48; TR52; TR54; TR57; TR59) and differential temperature sensors (TDR2547; TDR2548; TDR2715; TDR5254; TDR5759) were provided in addition to other temperature and temperature differential sensors that will not be further discussed here as they were considered of less relevance for the described automation.
  • the temperature sensors TR20; TR25; TR33; TR40; TR47; TR48; TR52; TR54; TR57; TR59
  • differential temperature sensors TDR2547; TDR2548; TDR2715; TDR5254; TDR5759
  • Fig. 5 corresponds to the line-up of Fig. 4, but the reference numbers have been omitted in the interest of highlighting the reference numbers corresponding to the various sensors that are shown.
  • Temperature sensors are marked by "TR" followed by a number that corresponds to the reference number assigned to the component, stream or line (conduit) where the sensor is provided.
  • the code TDR is used followed by two two-digit numbers corresponding to the reference numbers assigned to the components, streams or lines (conduits) between which the differential sensor is provided.
  • the temperature sensors and differential temperature sensors generate sensor signals that may be received by and monitored by the programmable controller which may use one or more of these as controlled variables.
  • temperatures in conduits 57 and 59, upstream and downstream of the first JT valve 58 were monitored using temperature sensors TR57 and TR59. The difference between these temperatures was also monitored, which may be used to determine the actual JT effect over the first JT valve .
  • the difference between the shell temperature at midpoint 27 was measured and the temperature in tube side 15 at mid-point 27 was determined (TDR2715) .
  • the shell temperature near the warm end 33 was measured using TR33, as well as the temperature of the spent refrigerant drawn from the heat exchanger in conduit 25 (TR25) .
  • the inlet temperature of the heavy liquid refrigerant fraction may be measured using TR47
  • inlet temperature of the hydrocarbon stream immediately upstream of the main cryogenic heat exchanger 100 may be measured using TR20
  • the temperature of the hydrocarbon rundown stream immediately downstream of the main cryogenic heat exchanger 100 may be measured using TR40. All temperature measurements stabilize and are reliable when there is forward flow. Thus, the measurements can be unreliable at times, for instance when stagnant gas goes back to the temperature sensor at the beginning of cool down.
  • the monitoring depends on the initial conditions, pressure conditions for example.
  • the temperature that indicates the end of the cool down is the hydrocarbon product rundown line temperature TR40.
  • this measurement may not be reliable at the beginning of cool down when the hydrocarbon flow is extremely low. Therefore, at the beginning of cool down another temperature, suitably the LMR temperature TR59 downstream of the first JT valve 58, may be monitored instead. However at the end of cool down the reference temperature will be TR40.
  • pressures and pressure differentials in various points in the line-up, may be monitored by the programmable controller during the cool down process.
  • the most relevant pressure sensors PR32; PR54; PR55; PR57; PR150
  • PR32; PR54; PR55; PR57; PR150 are indicated in Figure 5, using PR followed by a number that corresponds to the reference number assigned to the component or line (conduit) where the sensor is provided.
  • the most important pressures to be monitored include the pre-cool compressor suction pressure PR150 in conduit 150, the mixed refrigerant compressor 30 suction pressure (PR55) in conduit 55; and the mixed refrigerant compressor discharge pressure PR32 in conduit 32.
  • These pressure sensors generate sensor signals that may be received by and monitored by the programmable controller which may use one or more of these as controlled variables.
  • PR57 and PR54 LMR and HMR tube pressure upstream of the first (58) and second (51) JT valves, respectively
  • Any valve manipulation may have faster dynamics if these pressures are too high, so as initial condition the system should have a pressure level that is lower than a predetermined initial maximum pressure value (in the test we used 20 barg) .
  • Flow rates may be calculated for the LMR and HMR streams, in order to be used as a controlled variable or at least a variable to be monitored. Such calculations may be based on the differential in pressure and the nominal valve opening of the first (58) or second (51) JT valve, respectively. For this, measurements of the pressures before the first and second JT valves on both LMR and HMR circuits (PR57 and PR54, respectively) and the suction pressure (PR55) of the refrigerant circuit before going to the compressors may be used.
  • ⁇ HMR K HMR -X 51 - y l ⁇ PR54 - PR55
  • F LM R (-F 7 HMR) represents the flow rate in the LMR conduit 48 (HMR conduit 47);
  • X 5Q (X51) represents the amount of opening of the first (second) JT valve 58, resp. 51;
  • i?LMR (- ⁇ HMR) represents the least squares linear model constant corresponding to the slope.
  • a linear least squares model has been found to satisfy the desired accuracy.
  • other types of functions may be employed instead.
  • a quadratic function could be estimated for the HMR, while for the LMR flow a characteristic shape resembling a square root function has been found.
  • the main cryogenic heat exchanger 100 was first pre-cooled, under manual control, to a temperature between about -25 0 C and about -35 0 C.
  • Other tasks that have been completed at this stage, for the time being manually but these could also be automated and incorporated in the module structure as presently disclosed, include:
  • any in-line NGL natural gas liquid, typically consisting of molecules having mass comparable to propane and higher
  • extraction column e.g. scrub column
  • FIG. 6 schematically shows the module structure as was used in the test.
  • Module 301 defines initial conditions much in the same way as described above for module 201. Examples of critical initial conditions are:
  • refrigerant compressors 30, 31, and pre- cool refrigerant compressor 127 is not on-line and running (as e.g. monitored by compressor speed);
  • - pre-cooling refrigerant compressor 127 suction pressure outside of a predetermined pressure window (suitably a window around approximately 0.5 barg);
  • one or more of refrigerant compressor recycle valves are not sufficiently open (the test used less than 99 % open) ;
  • a signal corresponding to the communication signal of module 301 triggers 308.
  • Module 302 is also triggered by the same signal that corresponds to the communication signal of module 301.
  • Module 302 marks the first module in a sub-network of modules, here being modules 303, 304, 305, and 309 to 312. Hence, the entire sub-network of modules described below will operate in parallel with and concurrently to module 308.
  • Module 302 in itself first opens the first JT valve 58 much in the same way as that module 202 first opens JT valve 14.
  • Module 303 is triggered by module 302, and it waits some time, much in the same way as described above for module 203.
  • Modules 305, 305, 309, and 310 trigger on a signal that corresponds to the communication signal of module 303.
  • Module 304 further opens the first JT valve 58 much in the way as described for JT valve 14 in module 204.
  • Module 305 adjusts the compressor recycle valve (or valves) 131 much in the same way as described above for module 205 which adjusts recycle valve 12.
  • module 309 operating at the same level in the network as module 305, which closes the compressor recycle valve 130, preferably in response to when a pre-determined temperature indicative of the main cryogenic heat exchanger temperature has reached a predetermined value.
  • the closing of the compressor recycle valve 130 is constrained by the surge deviation, which is in part influenced by modules 304 and 310 to 312.
  • module 309 maximizes the refrigerant pressure as far as possible while maintaining an allowable surge deviation .
  • the pre-determined temperature is the temperature TR57 and the pre-determined value is such that it is certain that the auto-cooled LMR and HMR fractions flowing in conduits 57 and 52 are fully condensed such that the closing of the recycle valve (s) does not cause unexpected effects on the cooling rate.
  • the predetermined temperature value may be -135 0 C but it depends on the constituents of the multiple component refrigerant used. Of course, a too low surge deviation forms a constraint on closing of the recycle valve (s) . A message may be generated for the operator that an IGV move may be necessary instead.
  • module 309 may contain computer executable instruction to close the recycle valve 130 before the temperature has reached the pre-determined value but triggered by other urgent conditions.
  • Such another urgent condition may, for instance, occur if the surge deviation of the compressor 30 has a value above a pre-determined maximum value (typically 0.3) . Excessive surge deviation may be the cause of physical vibration of the compressor and therefore the recycle valve (s) 130 are closed even if the pre-determined temperature has not yet been reached.
  • Module 310 controls the first opening of the second JT valve 51. It is opened enough so that a cooling trend is established that is faster than with only the first JT valve (58) movements.
  • the first opening of the second JT valve 51 involves an algorithm that takes into account non-linear behaviour of the valve by first opening. The module attempts to keep the initial cooling rate below the maximum limit, in this cooling less fast than
  • the module 310 opens the second JT valve at pre-determined time intervals, e.g. every minute, until a cooling temperature change is detected (in the test, until a cooling rate faster than 0.1 °C/h was detected) . It then closes the valve 51 by a small amount. Then there is a further check in the cooling to make sure that the second JT valve 51 is not closed again or that the cooling is not too fast. If it is too fast, further closing of the second JT valve will take place. If the cooling trend stopped then open the valve until a cooling trend is established again.
  • the communication signal is generated upon reaching a stable cooling trend within a pre-determined range .
  • the communication signal from module 310 is received by module 311 and it also triggers module 312.
  • Module 311 further moves the second JT valve 51.
  • Three cases are taken into account : i) above condensation range, control is done on the second JT valve position; ii) just before condensation occurs in the heavy refrigerant in conduit 54, any JT valve movements are slowed slow down; iii) when condensation is detected the second JT valve 51 is closed a little bit, too avoid a high cooling rate caused by condensed flow.
  • the flow of the heavy refrigerant will be controlled on a remote set point setting using a flow controller.
  • the temperature rate of change TR54 and the temperature on TR25 will determine the step on the flow controller set point.
  • the final temperature target for both TR54 and TR 25 will stop the valve actions.
  • Module 311 is finished when top temperature, e.g. at TR57 or at TR40, has reached its target value. Any contribution from the heavy refrigerant to the cooling duty will from then on reduce, unless the refrigerant make-up is adjusted.
  • the make up adjustment is controlled by module 312, which as stated above, is triggered to start simultaneously with module 311 based on the communication signal generated in module 310.
  • the module manipulates the make-up to:
  • a target composition which may be an end target for normal operation of the main cryogenic heat exchanger 100 or an intermediate target.
  • the refrigerant target composition may change during the cool down procedure. It may change gradually or step wise upon a controlled variable reaching a predetermined value. For instance, it may change once the temperature
  • TR57 goes below a predetermined value of -135°C or
  • Nitrogen make up is preferably done only when there is an opportunity, for instance then when the MR compressor 30 suction pressure is low (e.g. below 2.0 barg) . This is because the nitrogen supply pressure during the text was only about 2 barg.
  • the module 312 was provided with some robustness in the case of failure in obtaining a reliable measurement on the methane inventory in the MR stream (e.g. due to communication failure between instrument and DCS, or due to sensor failure), which has been found to be quite common.
  • the methane composition was estimated from the compositions of C2 (ethane), C3 (propane) and N2 by assuming that the balance was methane.
  • the entire sub-network as described above (containing modules 303, 304, 305, and 309 to 312) as a whole is executed in parallel to the module 308 which adjusts one or more of the pre-cool refrigerant compressor recycle valve (s), here in the form of the first stage recycle valve 129 that controls recycle stream through the first compression stage of compressor 127.
  • the module objective is to maintain a suction pressure on the pre-cool refrigerant suction pressure (in conduit 150 of Fig. 4) within a pre-determined range, e.g. 0.25 - 0.50 barg, but without reducing the surge deviation too close to the control line.
  • the low pressure will assure that the temperature of the hydrocarbon feed gas going into the main cryogenic heat exchanger 100
  • conduit 20 has a reasonable value. Therefore, the temperature in conduit 20 itself does not need to be monitored or used as condition for control in this module . Additionally, the pre-cooling refrigerant compressor
  • overriding boundaries for one or more of the monitored variables. Crossing of one of these boundaries (i.e. exceeding a pre-determined maximum and/or minimum value) by one or more of the monitored variables may result in issuance of a warning signal to alert an operator, or pausing the cooling down, or abortion of the cooling down, or a combination of these .
  • Typical examples of such overriding boundaries are: - a pre-determined maximum temperature rate of change (e.g. 28 °C/hour as specified for an Air Products cryogenic heat exchanger) on any selected temperature, suitably one or more of a temperature of the hydrocarbon product at a location in tube side 29 and/or in the discharge conduit 40; the spent refrigerant temperature (e.g. in bottom warm end of the shell side 33 or in conduit 25); the refrigerant temperature at the discharge side of the first JT valve 58 or the second JT valve 51, or at the suction side thereof; any shell side temperature in the heat exchanger 1;
  • a pre-determined maximum temperature rate of change e.g. 28 °C/hour as specified for an Air Products cryogenic heat exchanger
  • a pre-determined maximum spatial temperature gradient reflecting a specified maximum temperature difference between two spatially separated points in or around the heat exchanger (e.g. a maximum temperature difference of 28 0 C), suitably the temperature difference TDR2547 between the light refrigerant upstream of main cryogenic heat exchanger 100 and the spent refrigerant (also possible: TDR3347, not shown); the temperature difference TDR2548 between the heavy refrigerant upstream of main cryogenic heat exchanger 100 and the spent refrigerant (also possible: TDR3348, not shown); TDR2715; and TDR5759; - a predetermined maximum content (0.08 mol%) of heavy components in the hydrocarbon feed stream that would freeze in the main cryogenic heat exchanger 100;
  • overriding boundaries may be used, e.g. in case of other types of cryogenic heat exchangers being used.
  • Table I shows all the variables used in the test as manipulated variable
  • Table II shows all the variables used in the test as controlled variables or monitored variables for decision making.
  • the automated procedure for final cool down of the main cryogenic heat exchanger as described above gradually reduced the main cryogenic heat exchanger overall temperature by manipulating the mixed refrigerant flow, composition and first and second JT valves which in part determine the compression ratio flashing across these JT valves.
  • Fig. 6 Although not implemented in the test, it has been contemplated to further embed the module structure of Fig. 6 (or a similar one for another line-up or heat exchanger) in a larger module network comprising other, preceding modules, or subsequent modules, or both.
  • An example of embedding in subsequent modules is shown in Fig. 7.
  • Fig. 7 shows a module structure with some post cool- down tasks. These may, for instance, be intermediate tasks that need to be completed before an automatic process control system for normal operation can take over the control.
  • module 401 manipulates the run down valve 44, with the goal to ramp up the flow through conduit 20 and 40 and the hydrocarbon tube side 29.
  • manipulated variables relevant at this stage include all the manipulated variables of the cool-down stage as described above plus possibly the IGV and any pre-cooling refrigerant compressor recycle valves that were not included as manipulated variable in the cool- down automation.
  • the LMR and HMR manipulation is done based on flow control rather than valve opening.
  • any reflux stream on an in-line NGL extraction could be included as manipulated variable.
  • normal level control can take over after the hydrocarbon feed rate has reached its normal operating range.
  • module 402 has been depicted, but also included could be a module for ramping up any fractionation section that may be provided downstream of any NLG extraction column to receive and further fractionate the extracted NLG liquids.
  • the person of skill in the art would be able to work out which manipulated and controlled variables could be used, depending on the type of line-up and equipment used.
  • the apparatuses and methods described herein may be applied to cryogenic heat exchangers whenever a cryogenic heat exchanger needs to be cooled down before operation. This could for instance be initial cooling down, or cooling down after a maintenance operation or after a trip: the reason why the heat exchanger was warmer than operation temperature is not material to the application of the subject matter described herein.
  • the person skilled in the art will understand that the present invention can be carried out in many various ways without departing from the scope of the appended claims.
  • the invention has been described with particularity, including providing target values for certain controlled variables. However, it will be apparent to the person skilled in the art that these values were chosen in connection to the specific line up and equipment used for the test. Such details may need to be optimized when the invention is to be carried out on another line-up using other equipment, and therefore should not be considered as limiting the scope of the present invention.

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Abstract

Procédé et appareil de refroidissement d’un échangeur thermique cryogénique, utilisant un régulateur programmable qui reçoit des signaux d’entrée, qui représentent des signaux de capteurs d’une ou de plusieurs variables contrôlées dans le cadre d’un procédé choisi, et qui produit des signaux de commande afin de contrôler une ou plusieurs variables manipulées dans le cadre du procédé choisi. Le régulateur programmable peut exécuter un programme informatique qui comprend un réseau d’au moins trois modules. Les modules du réseau sont interconnectés afin qu’un signal de déclenchement reçu par un second et un troisième module desdits trois modules corresponde à un signal de communication qui est généré lorsque le premier module desdits trois modules ou plus a atteint une cible prédéterminée pour ce module.
PCT/EP2009/051353 2008-02-08 2009-02-06 Procédé et appareil de refroidissement d’un échangeur thermique cryogénique et procédé de liquéfaction d’un flux d’hydrocarbures WO2009098278A2 (fr)

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US12/866,080 US20100326133A1 (en) 2008-02-08 2009-02-06 Method and apparatus for cooling down a cryogenic heat exchanger and method of liquefying a hydrocarbon stream
CN200980104368.XA CN102405389B (zh) 2008-02-08 2009-02-06 用于冷却低温换热器的方法和设备以及使烃流液化的方法
BRPI0907488A BRPI0907488B8 (pt) 2008-02-08 2009-02-06 aparelho para resfriar um trocador de calor criogênico, método para resfriar um trocador de calor criogênico, e, métodos de liquefação de uma corrente de hidrocarboneto
AU2009211380A AU2009211380B2 (en) 2008-02-08 2009-02-06 Method and apparatus for cooling down a cryogenic heat exchanger and method of liquefying a hydrocarbon stream
RU2010137319/06A RU2495343C2 (ru) 2008-02-08 2009-02-06 Способ и устройство для охлаждения криогенного теплообменника и способ сжижения углеводородного потока

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MY155810A (en) 2015-11-30
BRPI0907488A2 (pt) 2015-07-14
KR20100120184A (ko) 2010-11-12
CN102405389A (zh) 2012-04-04
RU2495343C2 (ru) 2013-10-10
AU2009211380B2 (en) 2012-05-03
US20100326133A1 (en) 2010-12-30
BRPI0907488B8 (pt) 2020-08-18
CN102405389B (zh) 2014-12-03
AU2009211380A1 (en) 2009-08-13
BRPI0907488B1 (pt) 2020-08-04
RU2010137319A (ru) 2012-03-20

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