GB2571945A - Method for operating a natural gas processing plant - Google Patents

Method for operating a natural gas processing plant Download PDF

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Publication number
GB2571945A
GB2571945A GB1803974.3A GB201803974A GB2571945A GB 2571945 A GB2571945 A GB 2571945A GB 201803974 A GB201803974 A GB 201803974A GB 2571945 A GB2571945 A GB 2571945A
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GB
United Kingdom
Prior art keywords
processing
train
gas
feed gas
refrigerant
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB1803974.3A
Other versions
GB201803974D0 (en
Inventor
krebs Benjamin
Sabatier Francoise
Stützle Elke
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Linde GmbH
Original Assignee
Linde GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Linde GmbH filed Critical Linde GmbH
Priority to GB1803974.3A priority Critical patent/GB2571945A/en
Publication of GB201803974D0 publication Critical patent/GB201803974D0/en
Priority to PCT/EP2019/056155 priority patent/WO2019175167A1/en
Publication of GB2571945A publication Critical patent/GB2571945A/en
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0257—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0295—Start-up or control of the process; Details of the apparatus used, e.g. sieve plates, packings
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
    • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
    • C10L3/10—Working-up natural gas or synthetic natural gas
    • C10L3/101—Removal of contaminants
    • C10L3/102—Removal of contaminants of acid contaminants
    • C10L3/104—Carbon dioxide
    • 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
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
    • F25J3/0209—Natural gas or substitute 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
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0233—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 1 carbon atom or more
    • 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
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0238—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 2 carbon atoms or more
    • 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
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0266—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of carbon dioxide
    • 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
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/063—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream
    • F25J3/067—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream separation of carbon dioxide
    • 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
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/0695—Start-up or control of the process; Details of the apparatus used
    • 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/04—Processes or apparatus using separation by rectification in a dual pressure main column system
    • 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/40—Features relating to the provision of boil-up in the bottom of a column
    • 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/50—Processes or apparatus using separation by rectification using multiple (re-)boiler-condensers at different heights of the column
    • 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/70—Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
    • 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/72—Refluxing the column with at least a part of the totally condensed overhead 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/90—Details relating to column internals, e.g. structured packing, gas or liquid distribution
    • F25J2200/96—Dividing wall column
    • 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
    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
    • F25J2205/04—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum in the feed line, i.e. upstream of the fractionation step
    • 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
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/02—Multiple feed streams, e.g. originating from different sources
    • 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
    • F25J2220/66—Separating acid gases, e.g. CO2, SO2, H2S or RSH
    • 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
    • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
    • F25J2240/02—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed 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
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/02—Recycle of a stream in general, e.g. a by-pass 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
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/02—Bath type boiler-condenser using thermo-siphon effect, e.g. with natural or forced circulation or pool boiling, i.e. core-in-kettle heat exchanger
    • 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
    • F25J2260/00—Coupling of processes or apparatus to other units; Integrated schemes
    • F25J2260/20—Integration in an installation for liquefying or solidifying a fluid 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
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/02—Internal refrigeration with liquid vaporising loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/12—External refrigeration with liquid vaporising loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/88—Quasi-closed internal refrigeration or heat pump cycle, if not otherwise provided
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
    • F25J2270/902—Details about the refrigeration cycle used, e.g. composition of refrigerant, arrangement of compressors or cascade, make up sources, use of reflux exchangers etc.
    • 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
    • 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
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/50—Arrangement of multiple equipments fulfilling the same process step in parallel

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

Abstract

The invention relates to a method for operating a natural gas processing plant comprising at least two processing trains 400, 420 utilizing a cooling cycle, comprising: feeding a feed gas 1 to be processed comprising an initial CO2 content into a processing path of a first processing train 400 of the processing plant for processing of the raw natural gas, the processing comprising reducing the initial CO2 content of at least part of the feed gas to provide CO2 reduced feed gas, such as by a rectification column T2, and then feeding a first part 24, 25 of the CO2 reduced feed gas into the cooling cycle of the first processing train as a refrigerant and then utilizing a second part 23 of the CO2 reduced feed gas as provided by the first processing train as a start up refrigerant for a cooling cycle of a second processing train. Also disclosed is a processing plant arranged to perform such a method

Description

Method for operating a natural gas processing plant
The invention relates to a method for operating a natural gas processing plant and an associated processing plant. In particular, it relates to a method for operating a natural gas processing plant comprising at least two processing trains
Natural gas is a hydrocarbon gas mixture, which occurs naturally. This naturally occurring gas is referred to as raw natural gas. It mainly consists of methane, but also includes heavier hydrocarbons, such as ethane, propane or butane, and also amounts of acid gases such as carbon dioxide (CO2) and nitrogen.
For certain applications, it is expedient to extract at least some of these componants from the raw natural gas, as these can either reduce the combustion quality of the gas, as is the case with nitrogen, or to be further processed as they are of commercial value, as is the case with heavier hydrocarbons.
Also, it is nessecary to remove or at least sufficiently reduce the CO2 content, if a cryogenic processing of the natural gas is to be affected. For example, for the removal of valuable heavier hydrocarbons or nitrogen, it is advantageous to use cryogenic processes including low temperature fractionation in industrial scale processing plants.
Raw natural gas is cleaned in these processing plants by separating impurities such as nitrogen and CCkas well as heavier hydrocarbons from the main gas stream of raw natural gas transported through the processing train.
Large processing plants typically comprise a number of processing trains. Each such processing train is essentially identical, and the capacity of the processing plant is increased by each additional train. Usually, these trains are constructed and started up one after the other with a certain time gap in between. In the context of the present invention, the term processing train is meant to refer to one of a larger number of processing trains (at least two) of a processing plant as a whole.
During the process of start-up of individual processing trains of such a plant configured and adapted for the processing of raw natural gas including removal of nitrogen, cryogenic trains (as parts of the respective processing trains) must be taken into operation. Such cryogenic units comprise cooling cycles, which require refrigerants.
During a start-up phase of a processing train, the temperature of the cryogenic unit for the removal of nitrogen must typically be brought down to around -150 to -160 °C using such a refrigerant in the cooling cycle. Typically, the cooling cycle works by compressing the refrigerant and afterwards expansion using the Joule-Thomson effect as driving force for the cool-down. As a refrigerant a gas mixture, mainly consisting of raw natural gas, nitrogen and heavier hydrocarbons if necessary is used. However, CO2, which is also present in the raw natural gas can easily freeze at relatively high temperatures of around -57 °C, under certain pressure conditions, leading to a clogging up of the cooling cycle during the start-up phase, when the gas is expanded to lower pressures and thus lower temperatures. It is known to remove CO2 from the raw natural gas by means of amine gas treatment, also known as acid gas removal, in order to produce an essentially CO2 reduced or free gas, which can then be used in or as the refrigerant. Additional investment costs arise for this form of acid gas removal.
On the other hand, without an acid gas removal unit, it takes considerable time during the start up phase to provide a sufficient amount of CO2 reduced gas as source for filling the cooling cycle. Using the raw natural gas with higher CO2 content in the refrigerant the pressure levels have to be adapted in order not to freeze the cycle during cool-down. Once the process is cold enough and prior to continuing the cooldown, CO2 has to be continuously purged out of the cycle until the CO2 content is reduced to the desired value. All in all, this leads to uneconomically long procedures for start-up of a processing train and thus the plant as a whole.
The object of the invention is to facilitate operation of a natural gas processing plant, especially during the start-up phase of individual trains.
This object is achieved by a method comprising the method steps of claim 1 and a processing plant comprising the features of claim 8.
1. According to a first aspect of the invention, there is provided a method for operating a natural gas processing plant comprising at least two processing trains utilising a cooling cycle, the method comprising the following steps:
- feeding a feed gas to be processed comprising an initial CO2 content into a processing path of a first processing train of the processing plant for processing of the raw natural gas, the processing comprising reducing the initial CO2 content of at least part of the feed gas to provide CO2 reduced feed gas, the CO2 content of which is reduced to a value below a presettable value,
- feeding a first part of the CO2 reduced feed gas into the cooling cycle of the first processing train as a refrigerant
- utilizing a second part of the CO2 reduced feed gas as provided by the first processing train as a start up refrigerant for a cooling cycle of a second processing train during a start up phase of the second processing train.
According to the invention, in a natural gas processing plant comprising at least two independently operable processing trains, refrigerant, the CO2 content of which has been reduced in the first processing train, is utilized as a start up refrigerant for a cooling cycle of a second processing train. This refrigerant from the first processing train, which is then utilized as start-up refrigerant for the second processing train, can especially be generated from feed gas of the first processing train, the CO2 content of which is reduced in the first processing train.
According to the invention, by providing a sufficiently clean gaseous refrigerant (with reduced CO2 content) during a start-up phase of a second processing train, this phase can be significantly shortened. Hereby, for example the costs for providing remotely located plants with an expedient refrigerant are substantially reduced.
Especially, a start up of the second and any further processing train can be performed essentially under normal operating pressures. During the start-up of the process, the pressures do not have to to be altered or tightly controlled in order to avoid reaching the freezing point of the CO2 which is mainly a function of pressure and temperature. It is also not necessary to perform any CO2 purges of the cooling cycles, as they are not subjected to any significant levels of CO2. Start up lines within a cryogenic unit can be significantly reduced and simplified. E.g. additional bypasses with valves around critical process equipment can be avoided.
According to the invention, the risk of erroneous operation leading to clogging of cooling cycles due to freezing out of CO2 during a start up phase is minimised.
Also, by providing such a refrigerant, the CO2 content of which is sufficiently low, as a backup during subsequent on spec operation of one processing train, a cryogenic unit of another processing train of a plant can be maintained in a cold mode even during phases where this processing train does not produce sufficient amounts of CO2 reduced gas. The cleaned refrigerant from one train can thus be delivered to any other train, where clean refrigerant is required, either for start-up or cold keeping.
According to a preferred embodiment of the invention, the processing further comprises generating a methane rich gas to be outputted from the processing plant. The method according to the invention is especially advantageous when utilized in such processing plant.
Expediently, the methane rich gas is transported to a place of usage remote from the processing plant by pipeline.
Advantageously, the feed gas, which is fed into the processing trains of the processing plant, is a raw natural gas. Such raw natural gas comprises a number of contaminants, which, according to the invention, can be removed in an advantageous and cost effective manner.
Typically, the initial CO2 content of a feed gas, especially a raw natural gas to be processed, ranges from 0.1 to 3, especially 0.2 to 2.5 mol-%. Especially, raw natural gas with such or even higher CO2 content (concentration) can easily freeze out during cryogenic processing. This problem is addressed in an effective and cost effective manner by the present invention.
Advantageously, the presettable value, i.e. the value to which the CO2 content of the feed gas, especially the raw natural gas is reduced, ranges from 0 to 0.05, especially from 0 to 0.005 mol-%.
According to a second aspect, there is provided a processing plant configured and adapted for processing a feed gas, comprising a at least two processing trains including a cooling cycle, a first and a second processing train each comprising:
- a feeding means for feeding a feed gas to be processed comprising an initial CO2 content, into a processing path of the processing train for processing of the feed gas, the processing comprising reducing the initial CO2 content of at least part of the feed gas to provide a CO2 reduced feed gas, the CO2 content of which is reduced to a value below a presettable value lower than the initial value,
- the first and the second processing train each being configured and adapted to
- feed at least part of the CO2 reduced feed gas into their respective cooling cycle as a refrigerant,
- wherein at least the second processing train is further configured and adapted to utilize CO2 reduced feed gas produced by the first processing train as a start up refrigerant for its cooling cycle during a start up phase of the second processing train.
According to a preferred embodiment of the invention, the first and/or the second processing train comprises a nitrogen removal unit and/or a LNG liquefaction unit.
LNG essentially consists of methane. Either unit requires cryogenic processing, utilizing a sufficiently CO2 reduced or CO2 free refrigerant.
Advantageously, the first and/or the second processing train comprises a partition wall fractioning column. Use of such a partition wall fractioning column provides an especially efficient way of generating CO2 reduced natural gas, which can be used as a refrigerant.
Figure 1 shows a schematic diagram of a prior art processing train for processing natural gas.
Figure 2 shows a schematic diagram of a processing train for processing a natural gas, wherein the invention can advantageously be implemented in cases of processing plants comprising such a processing train,
Figure 3 shows a schematic diagram of a further processing train for processing a natural gas, wherein the invention can advantageously be implemented in cases of processing plants comprising such a processing train, and
Figure 4 shows a preferred embodiment of a processing plant comprising two processing trains, with which the invention can advantageously be implemented.
An example of a prior art gas processing train, is schematically shown in Figure 1 and generally designated 100. Processing train 100 is configured and adapted to process raw natural gas. Be it noted that, although not a preferred processing train for implementing the invention, a processing plant according to the invention may be implemented with two or more processing trains according to Figure 1, if one of the processing trains does not contain an acid gas removal unit 120.
Train 100 is adapted to process raw natural gas from a gas source 90. Raw natural gas is essentially methane rich, i.e. has a methane content of typically 75 % to 99 %. When extracted from source 90, it also typically comprises water and natural gas condensate, acid gases such as CO2, nitrogen and further (non-methane) heavier hydrocarbons.
The processing train comprises a water and condensate removal unit 110, an acid gas removal unit 120, a dehydration unit 121, an NGL (natural gas liquid) recovery unit 130 and a nitrogen rejection unit (NRU) 140. It is noted that units 130 and 140 may be provided in reverse order within the train. If expedient, a mercury removal unit (not shown) can also be provided upstream of unit 120 or downstream of unit 121. Further units typically included in such a train are not explicitly shown, but will, at least in part, be briefly referenced in the following.
First, the normal (on-spec) mode of operation of the train will be described, i.e. during times when input (i.e. raw natural gas) and outputs are on-spec, i.e. the train produces all desired outputs, especially methane gas, according to its specification. The path the raw natural gas to be processed takes through the train up to the point where it is output from the train as methane gas is refered to as processing path.
During this normal mode of operation, raw natural gas from source 90 is transported to water and condensate removal unit 110 for removal of free water and natural gas condensate. This waste water including hydrocarbons is usually disposed off as waste water.
The raw gas is subsequently transported to acid gas removal unit 120 for further processing. Here, acid gases such as hydrogen sulfide and CO2 are removed for example by amine treating. Other means of acid removal are also available. The produced off gas is usually burned in conjunction with a thermal oxidizer.
Gas exiting the acid gas removal unit 120 is transported to NGL recovery unit 130. Some state of the art natural gas processing trains are provided with NGL recovery units utilizing a further cryogenic low temperature fractionation process comprising expansion of the gas through a turbo expander and a subsequent distillation in a demethanising fractionating column. A thus recovered NGL stream (designated 134) can then be further processed through a fractionating train comprising a number of distillation towers (not shown).
Raw gas thus processed is then transported to NRU 140 for removal of nitrogen. NRU 140 is provided as a cryogenic unit using low temperature fractionation for the removal of nitrogen from the gas. This process can be adapted to also remove helium, if desired. NRU 140 is typically provided as a fractionating column comprising an internal or external cooling cycle, through which a methane containing gaseous refrigerant flows. During the normal mode of operation as presently described, it is advantageously possible to utilize raw gas, the CO2 content of which has been sufficiently reduced in acid gas removal unit 120, as gaseous refrigerant. This reduction of CO2 content is necessary to avoid a clogging up of the cooling cycle due to potential freezing out of CO2.
The residue from the NGL recovery unit is the final, sufficiently purified methane or output gas (designated 143), which is then typically pipelined to the end user markets.
The invention can advantageously be provided where an acid gas removal unit 120 is not provided, e.g. in order to save investment costs.
Such a train 200, which constitutes a first preferred embodiment of a processing train, with which the invention can be implemented, is schematically shown in Figure 2. Components or units also included in the prior art train according to Figure 1 are designated with the same reference numerals, and will not be explicitly introduced or explained again in the following. Units not provided in the prior art train of Figure 1, or which are modified over the units as provided in the prior art plant, are designated with adapted reference numerals. Train 200, corresponding to the prior art train, is fed with raw natural gas from source 90 and comprises units 110, 121, and 130 as described above.
Here, an NRU 240 is further configured and adapted to also remove CO2 from the raw gas, so that a specific acid gas removal unit 120 as provided in the prior art plant of Figure 1 may be omitted from the plant. This simultaneous removal of nitrogen and CO2 is achieved by providing the NRU 240 as a partition wall fractioning column, as will be further explained with reference to Figure 4.
During the start up phase of train 200, there is, initially, no sufficient amount of raw natural gas, the CO2 content of which has been sufficiently reduced, available, as an acid gas removal unit is not provided. If raw gas containing a too high amount of CO2 was used, there would be a realistic danger of a cooling cycle NRU 240 clogging up, which would lead to cumbersome and time consuming regeneration operations.
On the other hand, waiting for a sufficient amount of CO2 reduced raw gas to become available, i.e. to be produced in NRU 240, before reaching normal operation and onspec production in NRU 240 would lead to any raw natural gas being processed in the plant during this time typically having to be burned off, as its nitrogen content would be too high for further use.
According to the present invention, it is suggested to provide a sufficiently clean gaseous refrigerant by utilizing refrigerant produced in another processing train, as will be explained with reference to Figure 4 below.
A further preferred embodiment of a natural gas processing train, with which the invention can advantageously be implemented, is shown in Figure 3, and generally designated 300. Again, components or units already described above are designated using the same reference numerals, and will not be introduced or explained again.
Here, the order of the processing steps in the pretreatment (up to unit 240) is the same as the embodiment of Figure 2. Also, a specific acid gas removal unit is not necessary in this embodiment.
The processing train 300 again comprises a condensate and water removal unit 110, a dehydration unit 121, an NGL recovery unit 130 and a nitrogen rejection unit (NRU) 240, which is, as in the first embodiment of the invention as shown in Figure 2, provided as a partition wall fractioning column for removal of CO2 from the raw gas. Additionally, the produced methane rich gas, provided as output from NRU 240, is liquefied in the liquefaction unit 250.
As in the previous embodiment shown in Figure 2, raw natural gas from source 90 is processed in the train, and water, condensate, heavier hydrocarbons and nitrogen are removed in units 110, 121, 130 and 240.
As in the first preferred embodiment as shown in Figure 2, after removal of free liquid water and natural gas condensate in unit 110 as well as dehydration in unit 121, the raw gas is transported to NGL recovery unit 130, which can also be configured and adapted to utilize a cryogenic low temperature fractionation process. A thus recovered NGL stream 134 can again, as in the previous embodiment of the invention shown in Figure 2, be further processed through a fractionating train comprising a number of distillation towers (not shown).
Gas exiting NGL recovery unit 130 is then transported to NRU 240. NRU 240 is again provided as a cryogenic unit using low temperature fractionation for the removal of nitrogen from the gas. This process can be adapted to also remove helium, if desired.
According to this embodiment, NRU 240 is configured and adapted to also remove CO2 from the gas, as mentioned above. This simultaneous removal of nitrogen and CO2 is achieved by providing the NRU 240 as a partition wall fractioning column.
The gas entering NRU 240 is processed to reduce its CO2 content to a sufficiently low level to be able to use it in the cooling cycle of NRU 240, as described above in connection with the train shown in Figure 2.
Additionally, the produced methane rich gas 143 exiting NRU 240 is further processed in a methane liquefaction unit 250. Here the gas is liquefied and as a product LNG is produced (designated 253). In order to deliver the cooling for the process here an external cooling cycle including compression and expansion of gas is used. The refrigerant is a gas mixture, mainly consistent of the raw natural gas, nitrogen and heavier hydrocarbons if neccessary.
As in the first embodiment of the invention as shown in Figure 2, during a start up phase of train 300, the cooling cycle of NRU 240 is fed with a gaseous refrigerant generated in a further processing train, as will be explained below with reference to Figure 4.
Be it noted that in this embodiment the external cooling cycle of the methane liquefaction unit 250, may also be fed with such a start up phase gaseous refrigerant during the start up phase.
A preferred embodiment of a plant including two processing trains 400,420, each comprising a cryogenic train, especially a NRU comprising a partition wall fractioning column, with which the invention can be advantageously implemented, is shown in Figure 4. Be it noted that in the embodiment as shown in Figure 4, both processing trains 400,420 are provided in an essentially identical manner. Obviously, the invention shall also cover plants with two non-identical processing trains, for which the concept of the invention is, however, also applicable. For example, a first and/or second processing train could be provided in the form of the processing trains as described above with reference to Figures 1 to 3.
It is noted that a more detailed description of the various processes as performed in each train of such a plant, albeit without implementation of the present invention, is disclosed in DE 102015001858, the content of which is herewith incorporated by reference. Also, not all processing steps as performed in the plant according to Figure 4 will be explained in detail in the following description. Only the steps relevant in connection with explaining the present invention will be further expanded on.
In the following, the first processing train 400 will be described in detail. As can be seen from Figure 4, second processing train is provided in an essentially identical manner, the only difference being that a refrigerant generated in the first processing train 400 can be fed to the second processing train 420, as will be described in the following.
Referring to the first processing train 400, a raw natural gas stream 1 is led through heat exchangers E1 and E2 and partially condensed in these by means of further processing streams. Natural gas stream 2 exiting heat exchanger E2 is separated in separator D1 into a liquid phase 3 and a gaseous phase 4. The former is fed to to separation column T1 via expansion valve V1. Gaseous phase 4 is expanded in expander X1 and also fed to Column T1 , i.e. into its head section. A partial stream 5 of gaseous phase is refluxed to column T1 after condensation in heat exchanger E2 via expansion valve V4.
A high boiler depleted gas fraction 10 is extracted from the head of column T1 and at least partially condensed in heat exchanger E4 and fed to a second column T2 via expansion valve V6.
In column T2 a rectification separation into a methane rich liquid fraction 11, which is extracted from the sump of column T2, and a low boiler rich gaseous fraction 12, which is extracted from the head of column T2, is executed.
The further processing of these fractions 11,12, leading to product streams 11', 12' as shown in Figure 1, will not be further expanded on in the present context.
The second column T2 is provided with a separation wall T, which is provided at least partly in the region within the column at which the high boiler depleted fraction 10 is fed to the column and at which a hydrocarbon rich fraction 26, which will be further described in the following, is extracted. Seperation wall T has the effect that these two fractions do not come into material contact with one another.
The reflux for the second column T2 is generated by an open cooling cycle. The refrigerant of this cooling cycle has a methane content of around 80-85 mol-%. It is known from DE 102015 001 858 A1 to use the hydrocarbon depleted fraction 26 as mentioned above.This is extracted from column T2 via regulating valve V13, vapourized in side condenser E8, heated in heat exchangers E5' and ET, fed to a first stage of refrigerant compressor C1, and, together with refrigerant stream 23 from the head of column T2, compressed to an intermediate pressure.
After cooling in intermediate cooler E9, the compressed refrigerant is further compressed to the desired cycle pressure in a second stage of compressor C1. After cooling in further cooler E10 the compressed refrigerant 20, after separation into two partial streams, is cooled in heat exchangers ET and E6, and after mixing, fully condensed against partial stream 13 in heat exchanger E5. The fully condensed refrigerant 21 is then fed to buffer container D4. From this, the two refrigerant streams 24,25 are extracted. Stream 24 is subcooled in heat exchanger E5', and then expanded into column T2 via valve V12, while stream 25 after subcooling in heat exchanger E6 is fed to head condenser E7 of column T2. From this head condenser the partial refrigerant stream is extracted via line 23, heated in heat exchanger E6 and then fed to the first stage of condenser C1.
In head condenser E7 and side condenser E8 the refrigerant streams 25 and 24 are vapourized against reflux streams 14 and 15.
Due to the rectification in column T2 as well as the separation wall T, the CO2 concentration or content in the refrigerant fraction in line 26 can be reduced to under 0.05 mol-% or even 0.005 mol-% ( especially to under 50vppm or 5 vppm).
In other words, column T2 receives raw natural gas including CO2, nitrogen (plus possible inert gases) and methane. By means of providing a partition wall T within the column T2, it is possible to withdraw gas, the CO2 content of which is significantly reduced compared to the gas fraction 10 entering the column. Hereby, the majority of CO2 and methane fraction are pushed down into the sump, without contaminating the gas fraction 26. This gas fraction 26 can be fed into the cooling cycles as soon as column T2 has produced a sufficient amount of gas with reduced CO2 content.
However, during start-up of such a processing train, no reflux for column T2 is available and the column cannot produce a CO2 reduced fraction. As described before, using this gas phase for the start-up of the cooling cycle has several disadvantages, especially as it must be ensured that CO2 within the refrigerant does not freeze out, which can lead to clogging up of cooling cycles. As a consequence, if there is no sufficient amount of CO2 reduced fraction available as refrigerant, start up of first processing train 400 can only be executed at a slow speed, maintaining a strict temperature and pressure regime.
However, for any further processing train, which is started up after the first processing train is on spec, the invention can advantageously be implemented in that the CO2 reduced fraction from the first processing train 400, which is typically already working on-spec, can be used as a start-up phase refrigerant for the second processing train 420.
For example, as shown in Figure 4, the CO2 reduced fraction from the first processing train 400 can be used as refrigerant and for example, introduced into stream 23 of the second processing train 420 upstream of compressor C1. In Figure 4, the CO2 reduced fraction is introduced via line 60. The process within the second processing train can then be started-up with the normal process pressures and cooled down until column T2 of the second processing train produces CO2 reduced refrigerant in a corresponding manner to the first processing train. Once this CO2 reduced refrigerant generated in the second processing train is available, the introduction of CO2 reduced refrigerant from the first processing train can be reduced and finally be terminated, especially by closing off line 60 by means of valves V20 and/or V41. This also works the other way around. If the second processing train 420 is producing CO2 reduced refrigerant, this can be introduced via line 60 into the first processing train 400 by opening valves V21 and V40. Once on-spec refrigerant is also available in train 400, the valves can be closed again.
When the second processing train is in its on-spec operational state, it is possible to provide any further processing train (not shown) of the processing plant with CO2 reduced refrigerant for a start up phase from either the first or the second processing train. Also, in case for example of an intermediate shut-down of the first processing plant, for example in connection with a malfunction or a safety overhaul, it is possible to provide the first processing train with CO2 reduced refrigerant as generated ny the second, or if provided, any further processing train of the plant. All in all, by providing and/or maintaining at least one processing train of a processing plant in an on-spec mode of operation, it can be ensured that any feasible number of further processing trains can be started up in an optimised manner.

Claims (11)

Claims
1. Method for operating a natural gas processing plant comprising at least two processing trains utilising a cooling cycle, the method comprising the following steps:
- feeding a feed gas to be processed comprising an initial CO2 content into a processing path of a first processing train of the processing plant for processing of the raw natural gas, the processing comprising reducing the initial CO2 content of at least part of the feed gas to provide CO2 reduced feed gas, the CO2 content of which is reduced to a value below a presettable value,
- feeding a first part of the CO2 reduced feed gas into the cooling cycle of the first processing train as a refrigerant
- utilizing a second part of the CO2 reduced feed gas as provided by the first processing train as a start up refrigerant for a cooling cycle of a second processing train during a start up phase of the second processing train.
2. Method according to claim 1, wherein the processing further comprises generating a methane rich gas to be outputted from the processing plant.
3. Method according to claim 2, wherein the methane rich gas is transported to a place of usage remote from the processing plant by pipeline.
4. Method according to any one of the preceding claims, wherein the feed gas is a raw natural gas.
5. Method according to any one of the preceding claims, wherein the initial CO2 ranges from 0.1 to 3, especially 0.2 to 2.5 mol-%.
6. Method according to any one of the preceding claims, wherein the presettable value ranges from 0 to 0.05. especially from 0 to 0.005 mol-%.
7. Method according to any one of the preceding claims, wherein the first and/or the second processing train comprises a nitrogen removal unit and/or a LNG liquefaction unit.
8. Processing plant configured and adapted for processing a feed gas, comprising a at least two processing trains (400,420) including a cooling cycle, a first and a second processing train each comprising:
- a feeding means (1) for feeding a feed gas to be processed comprising an initial CO2 content, into a processing path of the processing train for processing of the feed gas, the processing comprising reducing the initial CO2 content of at least part of the feed gas to provide a CO2 reduced feed gas, the CO2 content of which is reduced to a value below a presettable value lower than the initial value,
- the first and the second processing train (400,420) each being configured and adapted to
- feed at least part of the CO2 reduced feed gas into their respective cooling cycle as a refrigerant,
- wherein at least the second processing train (420) is further configured and adapted to utilize CO2 reduced feed gas produced by the first processing train (400) as a start up refrigerant for its cooling cycle during a start up phase of the second processing train.
9. Processing plant according to claim 8, wherein at least one processing train (400,420) comprises a nitrogen removal train.
10. Processing plant according to claim 8 or 9, wherein at least one processing train (400,420) comprises a LNG liquefaction train.
11. Processing plant according to any one of claims 8 to 10, wherein at least one processing train (400,420) comprises a partition wall fractioning column (T2).
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