# US 2016/0258676 A1 · Method for fractionating a stream of cracked gas, using an intermediate recirculation current, and related plant > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2016/0258676 A1 - Document ID: US20160258676A1 - Status: Published application - Kind: A1 - Application number: 15/030,913 - Filed: 2014-10-23 - Published: 2016-09-08 - Earliest claimed: 2013-10-23 - Assignees: Technip France - Applicants: Technip France - Inventors: Bruno DESTOUR; Yvon SIMON; Aurélia DADOU; David CHAZALLET - Web page: https://patentgrep.com/patent/US20160258676A1 ## CPC - F25J 3/0219: {Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature} - C07C 5/327: Formation of non-aromatic carbon-to-carbon double bonds only - C07C 7/005: {Processes comprising at least two steps in series} - C07C 7/09: by fractional condensation - C10G 5/06: by cooling or compressing - C10G 9/002: {Cooling of cracked gases} - C10G 70/041: {by distillation} - C10G 70/043: {by fractional condensation} - C10L 3/00: Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas - F25J 3/0233: {separation of CnHm with 1 carbon atom or more} - F25J 3/0238: {separation of CnHm with 2 carbon atoms or more} - F25J 3/0252: {separation of hydrogen (production of hydrogen containing gas in general C01B3/00, e.g. separation of hydrogen or hydrogen containing gases form gaseous mixtures at low temperatures C01B3/506)} - F25J 3/0271: {separation of H2/CO mixtures, i.e. of synthesis gas (production of carbon monoxide containing gas in general C01B32/40, C10J, C10K, production of hydrogen containing gas C01B3/00)} - C10G 2400/20: C2-C4 olefins - C10G 2400/26: Fuel gas - C10L 2290/06: Heat exchange, direct or indirect - C10L 2290/10: Recycling of a stream within the process or apparatus to reuse elsewhere therein - C10L 2290/46: Compressors or pumps - C10L 2290/543: Distillation, fractionation or rectification for separating fractions, components or impurities during preparation or upgrading of a fuel - F25J 2200/70: Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified - F25J 2205/04: in the feed line, i.e. upstream of the fractionation step - F25J 2210/04: Mixing or blending of fluids with the feed stream - F25J 2210/06: Splitting of the feed stream, e.g. for treating or cooling in different ways - F25J 2210/12: Refinery or petrochemical off-gas - F25J 2215/62: Ethane or ethylene - F25J 2230/30: Compression of the feed stream - F25J 2245/02: Recycle of a stream in general, e.g. a by-pass stream - F25J 2270/02: Internal refrigeration with liquid vaporising loop - F25J 2270/06: with multiple gas expansion loops - F25J 2270/12: External refrigeration with liquid vaporising loop - F25J 2270/60: Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons - Y02P 30/40: Ethylene production - 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 (cryogenic pumps F04B37/08; gas storage vessels, gas holders F17; filing vessels with, or discharging from vessels, compressed, liquefied or solidified gases F17C; refrigeration machines, plants, or systems F25B)} - C07C: ACYCLIC OR CARBOCYCLIC COMPOUNDS - C10G: CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION (cracking to hydrogen or synthesis gas C01B; cracking or pyrolysis of hydrocarbon gases to individual hydrocarbons or mixtures thereof of definite or specified constitution C07C; cracking to cokes C10B); RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES - C10L: FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G OR C10K; LIQUIFIED PETROLEUM GAS; USE OF ADDITIVES TO FUELS OR FIRES; FIRE-LIGHTERS - Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS ## Abstract This method comprises: forming an expanded intermediate recirculation stream (170) from a liquid (112, 128) obtained during an upstream cooling and/or intermediate cooling step, upstream from the downstream cooling step; circulating the intermediate recirculation stream (170) at least in an upstream heat exchanger (42) to cool an upstream stream of cracked gas (102); reintroducing the reheated intermediate recirculation stream (170) in a raw cracked gas (20) upstream from at least one compressor (36, 38) of a cooling and compression stage (24). The upstream, intermediate and downstream cooling steps is carried out without a heat exchanger respectively of an upstream stream of cracked gas (102), an intermediate stream of cracked gas (114) and a downstream stream of cracked gas (140) with an external refrigeration cycle. ## Claims ### Claim 1 A method for fractionating a stream of cracked gas from a hydrocarbon pyrolysis plant to obtain an ethylene-rich cut and a C2+ hydrocarbon-lean fuel stream, the method comprising: compressing the stream of raw cracked gas in at least one compressor a cooling and compression stage to form a compressed cracked gas stream; upstream cooling and partial condensing, in at least one upstream heat exchanger, of an upstream stream of cracked gas, obtained from the compressed cracked gas stream, and separation of an upstream liquid in at least one upstream balloon to form an intermediate stream of cracked gas pre-cooled at first temperature; intermediate cooling and partial condensing of the intermediate stream of cracked gas in an intermediate heat exchanger and separation of an intermediate liquid in an intermediate separating balloon to form a downstream stream of cracked gas cooled to a second temperature lower than the first temperature; downstream cooling and partial condensing of the downstream stream of cracked gas in at least one downstream heat exchanger to a third temperature lower than the second temperature; introducing of the downstream stream of partially condensed cracked gas from the downstream heat exchanger in a downstream separator; recovering, at the head of the downstream separator a gas stream of high-pressure fuel, lean in C2+ hydrocarbons, and recovering, at the bottom of the downstream separator, a downstream liquid, rich in C2+ hydrocarbons; passing of the stream of high-pressure fuel through the downstream exchanger and the intermediate exchanger to form a heated high-pressure fuel stream; expanding of the heated high-pressure fuel stream in at least one first dynamic expansion device to obtain a stream of partially expanded fuel; heating of the stream of partially expanded fuel through the downstream exchanger and the intermediate exchanger; treating of at least one liquid stream obtained during the upstream cooling, intermediate cooling and downstream cooling to form the ethylene-rich cut; forming an expanded intermediate recirculation stream (170) from a liquid obtained during the upstream cooling and/or intermediate cooling steps, upstream from the downstream cooling step; circulating the intermediate recirculation stream at east in the upstream heat exchanger to cool the upstream stream of cracked gas; reintroducing the reheated intermediate recirculation stream in the raw cracked gas upstream from at least one compressor of the cooling and compression stage, the upstream, intermediate and downstream steps being carried out without heat exchange respectively of the upstream stream of cracked gas, the intermediate stream of cracked gas and the downstream stream of cracked gas with an external refrigeration cycle. ### Claim 2 (depends on 1) The method according to claim 1, wherein the pressure of the expanded intermediate recirculation stream is greater than 15%. ### Claim 3 (depends on 1) The method according to claim 1, wherein the pressure of the expanded intermediate recirculation stream is greater than 5 bars. ### Claim 4 (depends on 1) The method according to claim 1, wherein the molar flow rate of the expanded intermediate recirculation stream is greater than 25%. ### Claim 5 (depends on 1) The method according to claim 1, wherein the molar ethylene content in the expanded intermediate recirculation stream is greater than 50%. ### Claim 6 (depends on 5) The method according to claim 5, wherein the molar content level of ethane in the intermediate recirculation stream is comprised between 15% and 30%, the molar content level of methane in the intermediate recirculation stream being comprised between 10% and 20%. ### Claim 7 (depends on 1) The method according to claim 1, wherein the ratio of the molar ethylene content to the molar hydrogen content in the compressed raw cracked gas stream, after reintroduction of the expanded intermediate recirculation stream, is greater than 1.3 times the ratio of the molar ethylene content to the molar hydrogen content in the raw cracked gas stream, before the reintroduction of the expanded intermediate recirculation stream in the raw cracked gas stream. ### Claim 8 (depends on 1) The method according to claim 1, wherein the temperature of the intermediate recirculation stream is comprised between −75° C. and −95° C., after expansion, and before introduction in a heat exchanger. ### Claim 9 (depends on 1) The method according to claim 1, comprising forming an expanded recirculation stream from at least one fraction of an intermediate liquid and/or at least one fraction of the downstream liquid, and introducing the expanded recirculation stream into the downstream heat exchanger, and/or into the intermediate heat exchanger, before mixing the expanded recirculation stream with the raw cracked gas stream before the passage of the raw cracked gas stream in at least one compressor of the cooling and compression stage, the pressure of the expanded recirculation stream being lower than the pressure of the expanded intermediate recirculation stream. ### Claim 10 (depends on 9) The method according to claim 9, comprising injection of at least one fraction taken from the high-pressure fuel gas stream into the expanded recirculation stream. ### Claim 11 (depends on 1) The method according to claim 1, comprising withdrawing a bypass stream from the intermediate cracked gas stream upstream from the intermediate heat exchanger injecting the bypass stream, after expansion, in the expanded intermediate recirculation stream. ### Claim 12 (depends on 1) The method according to claim 1, comprising forming at least one intermediate recirculation stream from the upstream liquid coming from the upstream separator balloon and forming at least one intermediate recirculation stream from the intermediate liquid from the intermediate separator balloon. ### Claim 13 (depends on 1) The method according to claim 1, comprising providing a heat exchange relationship between at least one fraction of the compressed cracked gas stream and a refrigerant circulating in an outside refrigeration cycle, introducing said at least one fraction into an upstream separator balloon to form the upstream stream of cracked gas. ### Claim 14 A fractionating plant for a first stream of cracked gas coming from a hydrocarbon pyrolysis plant to obtain an ethylene-rich cut and a C2+ hydrocarbon-lean fuel stream, the fractionating plant comprising: a cooling and compression stage for the stream of raw cracked gas comprising at least one compressor, to form a stream of compressed cracked gas; an upstream cooling and partial condensation stage for an upstream stream of cracked gas, obtained from the stream of compressed cracked gas, the upstream stage comprising at least one upstream heat exchanger, and at least one upstream separator balloon for an upstream liquid to form an intermediate stream of cracked gas pre-cooled to a first temperature; an intermediate cooling and partial condensation stage for the intermediate stream of cracked gas, the intermediate stage comprising an intermediate heat exchanger and an intermediate separating balloon for an intermediate liquid to form a downstream stream of cracked gas cooled to a second temperature below the first temperature; a downstream cooling and partial condensation stage for the downstream stream of cracked gas to cool the downstream stream of cracked gas to a third temperature below the second temperature, the downstream stage comprising at least one downstream heat exchanger; a downstream separator and an introducer for introducing the downstream stream of partially condensed cracked gas coming from the downstream heat exchanger into the downstream separator; a recovery stage, at the head of the downstream separator, for recovering a gaseous stream of high-pressure fuel, lean in C2+ hydrocarbons, and recovering, at the bottom of the downstream separator, a downstream liquid, rich in C2+ hydrocarbons; a passage assembly for the stream of high-pressure fuel through the downstream exchanger and the intermediate exchanger to form a stream of reheated high-pressure fuel; at least first one dynamic expansion device for the stream of reheated high-pressure fuel to obtain a partially expanded fuel stream; a passage for the stream of partially expanded fuel through the downstream exchanger and the intermediate exchanger to reheat the stream of partially expanded fuel; a treatment stage for at least one liquid stream obtained in at least one of the upstream cooling, intermediate cooling, and downstream cooling stages to form the ethylene-rich cut; a former for forming an expanded intermediate recirculation stream from a liquid obtained in at least one of the upstream cooling and/or intermediate cooling stages, upstream from the downstream cooling stage; a circulator for circulating the intermediate recirculation stream at least in the upstream heat exchanger to cool the upstream stream of cracked gas; a reintroducer for reintroducing the heated intermediate recirculation stream into the raw cracked gas upstream from at least one compressor of the cooling and compression stage, the upstream, intermediate and downstream stages assemblies being configured to respectively cool the upstream stream of cracked gas, the intermediate stream of cracked gas and the downstream stream of cracked gas without heat exchange with an outside refrigeration cycle. ### Claim 15 (depends on 2) The method according to claim 2, wherein the pressure of the expanded intermediate recirculation stream is comprised between 20% and 50% of the pressure of the compressed cracked gas stream. ### Claim 16 (depends on 3) The method according to claim 3, wherein the pressure of the expanded intermediate recirculation flow is comprised between 5 bars and 20 bars. ### Claim 17 (depends on 4) The method according to claim 4, wherein said molar flow rate is comprised between 30% and 60% of the molar flow rate of the stream of raw cracked gas ### Claim 18 (depends on 5) The method according to claim 5, wherein said molar ethylene content is comprised between 55% and 65%.