WO2021148942A1 - Démarrage à grande vitesse de gaz d'un four de craquage d'éthylène - Google Patents

Démarrage à grande vitesse de gaz d'un four de craquage d'éthylène Download PDF

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Publication number
WO2021148942A1
WO2021148942A1 PCT/IB2021/050384 IB2021050384W WO2021148942A1 WO 2021148942 A1 WO2021148942 A1 WO 2021148942A1 IB 2021050384 W IB2021050384 W IB 2021050384W WO 2021148942 A1 WO2021148942 A1 WO 2021148942A1
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Prior art keywords
fluid
hydrocarbon
cracking
inlet
furnace
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PCT/IB2021/050384
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English (en)
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Michael KOSELEK
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Nova Chemicals (International) S.A.
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Priority to CA3166744A priority Critical patent/CA3166744A1/fr
Priority to EP21701181.6A priority patent/EP4093839A1/fr
Priority to US17/794,882 priority patent/US20230073862A1/en
Publication of WO2021148942A1 publication Critical patent/WO2021148942A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G9/00—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
    • C10G9/14—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils in pipes or coils with or without auxiliary means, e.g. digesters, soaking drums, expansion means
    • C10G9/16—Preventing or removing incrustation
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G9/00—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
    • C10G9/34—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils by direct contact with inert preheated fluids, e.g. with molten metals or salts
    • C10G9/36—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils by direct contact with inert preheated fluids, e.g. with molten metals or salts with heated gases or vapours
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G75/00—Inhibiting corrosion or fouling in apparatus for treatment or conversion of hydrocarbon oils, in general
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G9/00—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
    • C10G9/14—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils in pipes or coils with or without auxiliary means, e.g. digesters, soaking drums, expansion means
    • C10G9/18—Apparatus
    • C10G9/20—Tube furnaces
    • C10G9/206—Tube furnaces controlling or regulating the tube furnaces
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
    • C10G2300/10—Feedstock materials
    • C10G2300/1081—Alkanes
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
    • C10G2300/40—Characteristics of the process deviating from typical ways of processing
    • C10G2300/4006—Temperature
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
    • C10G2300/40—Characteristics of the process deviating from typical ways of processing
    • C10G2300/4012—Pressure
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
    • C10G2300/40—Characteristics of the process deviating from typical ways of processing
    • C10G2300/4018—Spatial velocity, e.g. LHSV, WHSV
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
    • C10G2300/40—Characteristics of the process deviating from typical ways of processing
    • C10G2300/4031—Start up or shut down operations
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
    • C10G2300/40—Characteristics of the process deviating from typical ways of processing
    • C10G2300/4075—Limiting deterioration of equipment

Definitions

  • the present disclosure relates to the field of hydrocarbon cracking furnaces.
  • the present disclosure relates to start-up procedures for hydrocarbon cracking furnaces.
  • a feed is passed through several reactors or “furnaces”, each furnace including a radiant section with tubular metal coils, before exiting the furnace at an elevated temperature, typically above 750°C.
  • the steam and feed typically an alkane, usually a lower molecular weight alkane such as ethane, propane, butane and mixtures thereof, or heavier feed stock including naphtha, heavy aromatic concentrate (HAC) and heavy aromatic gas oil (HAGO) or any of the vacuum gas oils, undergoes a rearrangement yielding alkenes, including but not limited to ethylene, propylene, and butene, as well as hydrogen and other co-products.
  • Decokes can be costly as they represent time periods where costs are incurred without production of commercially valuable products. Reducing the time to perform a decoke can save money, but options for doing so are limited. Increasing the time between decokes by increasing the run length is another option for reducing the financial effect of the costly downtime.
  • a start-up method for a hydrocarbon cracking furnace that can extend run length.
  • the present disclosure seeks to provide a start-up procedure to extend a run length of a hydrocarbon cracking furnace, the hydrocarbon cracking furnace including at least one furnace tube, wherein the at least one furnace tube includes at least one inlet, at least one outlet, and a point of incipient cracking in between the inlet and outlet, the start-up procedure including: introducing a fluid including hydrocarbon and dilution steam to the at least one inlet; establishing and maintaining the fluid at the inlet to a temperature of between 25 °C and 225 °C; determining a number average molecular weight of the fluid proximate the inlet; determining a number average molecular weight of the fluid proximate the outlet; calculating an average of the number average molecular weights of the fluids at the inlet and the outlet; measuring a pressure drop of the fluid from the inlet to the outlet; calculating a fluid velocity at the point of incipient cracking; controlling the fluid velocity at the point of incipient cracking to a range between at least 90
  • the present disclosure also seeks to provide a start-up procedure to extend a run length of a hydrocarbon cracking furnace, the hydrocarbon cracking furnace including at least one furnace tube, wherein the at least one furnace tube includes at least one inlet, at least one outlet, and a point of incipient cracking in between the inlet and outlet, the start-up procedure including: introducing a fluid including hydrocarbon dilution steam to the at least one inlet; establishing and maintaining the fluid at the inlet to a temperature of between 25 °C and 225 °C; determining a number average molecular weight of the fluid proximate the inlet; determining a number average molecular weight of the fluid proximate the outlet; calculating an average of the number average molecular weights of the fluids at the inlet and the outlet; measuring a pressure drop of the fluid from the inlet to the outlet; calculating a fluid velocity at the point of incipient cracking; controlling the fluid velocity at the point of incipient cracking to a range between at least 90
  • Figure 1 illustrates a steam hydrocarbon cracking furnace 100 layout in a schematic process flow diagram in accordance with one embodiment.
  • Figure 2 illustrates a steam hydrocarbon cracking furnace 200 layout in a schematic process flow diagram in accordance with one embodiment.
  • Figure 3 illustrates a steam hydrocarbon cracking furnace 300 layout in a schematic process flow diagram in accordance with one embodiment.
  • Figure 4 illustrates a steam hydrocarbon cracking furnace 400 layout in a schematic process flow diagram in accordance with one embodiment.
  • Figure 5 illustrates a graph of the gas velocity in an industrial steam hydrocarbon cracking furnace over a 500 day period which includes 3 separate runs.
  • Aromatic hydrocarbon refers to a hydrocarbon with sigma bonds and delocalized pi electrons between carbon atoms forming a circle.
  • Cl - C4 alkane refers to one or more of methane, ethane, propane, and butane.
  • Deution steam refers to steam added to the hydrocarbon to be cracked in a hydrocarbon cracking furnace.
  • Fluid properties refers to properties of the fluid, including, but not limited to, density, viscosity, temperature, pressure, specific volume, specific weight, specific gravity, and number average molecular weight.
  • Fluid tube refers to a conduit, often described as a pass and where multiple passes are linked together in what is typically referred to as a coil, that can be used in a furnace, through which the fluid to be heated flows.
  • Heavy aromatic distillate refers to a combination of hydrocarbons obtained from distillation of aromatic streams. It consists predominantly of aromatic hydrocarbons having carbon numbers predominantly in the range of C9 through C16 and boiling in the range of approximately 165°C to 290°C. It can be a co-product from ethylene production (also known as HAD)
  • Hydrocarbon refers to an organic compound consisting entirely of hydrogen and carbon.
  • Hydrocarbon cracking furnace refers to a furnace designed to break down or crack hydrocarbons, typically alkanes into alkenes.
  • Ideal Gas Law refers to the equation of state of a hypothetical ideal gas; it is a good approximation of the behavior of many gases under many conditions and may be used in place of measuring or calculating the actual properties of a gas.
  • Naphtha refers to a flammable liquid hydrocarbon mixture. Mixtures labelled naphtha have been produced from natural gas condensates, petroleum distillates, and the distillation of coal tar and peat. In different industries and regions naphtha may also be crude oil or refined products such as kerosene.
  • Numberer average molecular weight refers to the total weight of the sample divided by the number of molecules in the sample.
  • Point of incipient cracking refers to the location in the hydrocarbon cracking furnace where the hydrocarbon starts to crack, forming radicals. This location is often approximated, and is based on many factors, including the pressure in the hydrocarbon cracking furnace, feed composition, coke formation, desired products, etc.
  • the temperature at the point of incipient cracking can range as low as 370°C to as high as 850°C in industrial furnaces, typically 500-550°C. For this disclosure, the location where the temperature first reaches 525°C was chosen as it is typical temperature for a furnace cracking a predominately ethane feed.
  • the pressure at the point of incipient cracking was determined using SPYRO ® Suite 7 software from the Pyrotec Division of Technip Benelux B.V.
  • Pressure drop refers to the difference in total pressure between two points of a fluid carrying network.
  • Reference length refers to the length of time that a furnace tube is in hydrocarbon cracking operation.
  • Start-up procedure refers to the steps followed to start a hydrocarbon cracking furnace until it is producing the desired alkenes.
  • alkenes such as ethylene
  • steam cracking in which hydrocarbons are broken down into smaller, often unsaturated, hydrocarbons, by thermally cracking with the use of dilution steam in a bank of pyrolysis furnaces.
  • the starting hydrocarbons can be Cl - C4 alkanes, naphtha, or aromatic hydrocarbons such as heavy aromatic distillate (HAD).
  • each furnace there are typically several reactors or coils.
  • tubular metal coils or furnace tubes with one or more zones with one or more passes per furnace tube which proceed through a furnace where the fluid within exits the furnace tube at an elevated temperature typically above 750°C, usually in the range of 800°C to 900°C, the feed passing through the furnace tube in the radiant section of a cracker for a period of time from milliseconds to several seconds.
  • the one or more zones can be included of a convection section or pre-heat section and a radiant cracking section. After the fluid exits the radiant cracking section, it can be sent to a quench section to lower the fluid temperature.
  • the temperature of the fluid entering the pre-heat section is typically between 25 °C and 225 °C, whereas the temperature of the fluid entering the radiant section is typically between 600°C and 750°C.
  • the temperature at the point of incipient cracking can range as low as 370°C to as high as 850°C in industrial furnaces, typically 500-550°C at typical pressures and compositions, with 525°C being used in this disclosure in all calculations.
  • the dilution steam and hydrocarbon feed typically an alkane, typically a lower molecular weight alkane such as ethane, propane, butane and mixtures thereof, or heavier feed stock including naphtha, heavy aromatic distillate (HAD) and heavy aromatic gas oil (HAGO) or any of the vacuum gas oils, undergoes a rearrangement yielding alkenes, including but not limited to ethylene, propylene and butene as well as hydrogen and other coproducts.
  • alkane typically a lower molecular weight alkane such as ethane, propane, butane and mixtures thereof, or heavier feed stock including naphtha, heavy aromatic distillate (HAD) and heavy aromatic gas oil (HAGO) or any of the vacuum gas oils
  • Coke is an undesired but inevitable side product of the pyrolysis.
  • Surface catalyzed reactions lead to the formation of filamentous coke.
  • the coke formation is caused by nickel and iron on the alloy surface.
  • Amorphous coke is formed in the gas phase.
  • Increased pressure drop impaired heat transfer and higher fuel consumption due to the coke cause high production losses.
  • the external furnace tube skin temperature can also rise, which influences the process selectivity and leads to even more rapid coke formation.
  • the formed coke must be removed by controlled reaction with steam and air. It is a non productive downtime of the steam cracker furnace. Decoking cycles lead to shorter coil life of the steam cracker furnaces. During a decoking cycle, the furnace is taken off-line (i.e., hydrocarbon feed is no longer passing through the furnace tube) and the furnace tube is decoked, after which the furnace is returned to operation.
  • the present disclosure relates to field of hydrocarbon cracking furnaces.
  • the present disclosure relates to start-up procedures for hydrocarbon cracking furnaces.
  • the start-up procedures can be implemented for the first start-up of the hydrocarbon cracking furnace, after a decoking procedure, or any other time the hydrocarbon cracking furnace is starting up.
  • the hydrocarbon cracking furnaces are typically taken off-line or may require being shut down on a periodic basis to remove coke accumulated on the internal surfaces of the furnace tubes.
  • the present disclosure is suitable for any cracking process where dilution steam with hydrocarbon molecules are converted to other hydrocarbon molecules at elevated temperatures where coke is a byproduct on the furnace tubes or reactors, such as a fluid catalyst cracker or a steam cracker, used to produce alkenes from corresponding alkanes at elevated temperatures.
  • the present disclosure seeks to provide a method for managing initial coke deposition on a hydrocarbon cracking furnace’s tube wall inner surface by maximizing boundary layer turbulence of the hydrocarbon and any diluent present.
  • the high gas velocity minimizes the thickness of the laminar flow of the boundary layer at the furnace tube wall providing a scouring effect upon the newly formed and typically deposited coke.
  • Figure 1 shows a schematic drawing of a hydrocarbon cracking furnace 100.
  • a dilution steam 102 is combined with a hydrocarbon feed 104 to be cracked.
  • the combined fluid enters a pre-heat section 106.
  • the fluid continues through the apparatus into a radiant section 108.
  • the fluid now contains dilution steam, some of the initial hydrocarbon feed and newly made cracked gas. Then the fluid enters a quench section 110.
  • FIG. 2 shows a schematic drawing of a hydrocarbon cracking furnace 200.
  • a dilution steam 202 is combined with a hydrocarbon feed 204 to be cracked.
  • the dilution steam 202 is preheated in a dilution steam pre-heat section 212.
  • the combined fluid enters a pre-heat section combined stream pre-heat section 214.
  • the dilution steam pre-heat section 212 and the combined stream pre-heat section 214 make up a pre-heat section 206.
  • the fluid continues through the apparatus into a radiant section 208.
  • the fluid now contains dilution steam, some of the initial hydrocarbon feed and newly made cracked gas. Then the fluid enters a quench section 210.
  • FIG. 3 shows a schematic drawing of a hydrocarbon cracking furnace 300.
  • dilution steam 302 is combined with hydrocarbon feed 304 to be cracked.
  • the dilution steam 302 is preheated in a dilution steam pre-heat section 312 and hydrocarbon feed 304 is preheated in a hydrocarbon feed pre-heat section 314.
  • the combined fluid enters a combined stream pre-heat section 316.
  • the dilution steam pre-heat section 312, the hydrocarbon feed pre-heat section 314 and the combined stream pre-heat section 316 make up a pre-heat section 306.
  • the fluid continues through the apparatus into a radiant section 308.
  • the fluid now contains dilution steam, some of the initial hydrocarbon feed and newly made cracked gas.
  • the fluid enters a quench section 310.
  • FIG. 4 shows a schematic drawing of a hydrocarbon cracking furnace 400.
  • dilution steam 402 is combined with hydrocarbon feed 404 to be cracked.
  • the dilution steam 402 is preheated in a dilution steam pre-heat section 412.
  • the hydrocarbon feed 404 is preheated in a hydrocarbon feed pre-heat section 414.
  • the hydrocarbon feed 404 to be cracked joins the dilution steam 402 on the outside of hydrocarbon cracking furnace 400.
  • the combined fluid re-enters the combined stream pre heat section 416.
  • the dilution steam pre-heat section 412, the hydrocarbon feed pre-heat section 414 and the combined stream pre-heat section 416 make up a pre-heat section 406.
  • the fluid continues through the apparatus into a radiant section 408.
  • the fluid now contains dilution steam, some of the initial hydrocarbon feed and newly made cracked gas.
  • the fluid enters a quench section 410. Decoking
  • the coke is physically scoured from the internal furnace tube walls.
  • a relatively high velocity stream of air, steam or a mixture thereof passes through the furnace tube resulting in small particulate materials being included in the effluent stream.
  • the coke on the internal wall is scoured or eroded from the wall.
  • One issue with this type of treatment is the erosion of the internal surface of the furnace tube, fittings and downstream equipment.
  • An additional concern with this type of treatment is downstream plugging with coke particulates scoured from the furnace tube walls.
  • An alternate treatment to decoke the furnace tube is to react or “burn” the carbon accumulation from the furnace tube wall.
  • air and steam are passed through the furnace tube at an elevated temperature to cause the coke to react or bum.
  • the progress of the decoking process may be measured in several different ways including measuring the carbon dioxide and carbon monoxide content in the effluent gasses leaving the furnace, measuring the furnace tube metal temperature, measuring changes in the furnace tube outlet pressure or changes in the furnace tube fouling factors.
  • a mixture of steam and air is passed through the coil while it is maintained at an elevated temperature from about 750°C to about 900°C, in some embodiments from 780°C to 850°C in some embodiments from 800°C to 830°C.
  • the amount of air fed to the tube or coil depends on the furnace and the coil design. In some instances, the air may be fed to the coil at a rate from about 10 kg/hr to about 1000 kg/hour. Steam is fed to the reactor to provide an initial weight ratio of steam to air from about 200:1 to about 170:3. The decoke is completed when the amount of gasified carbon (CO2 and CO) in the effluent stream from the tube or coil is below about 2,000 ppm of CO2. In some embodiments of the procedure, the rate of air feed to the coil may be increased up to about 1000 kg/hr/coil as a post bum and/or as a surface polishing step.
  • CO2 and CO gasified carbon
  • the temperature in the combustion side of the cracker (sometimes called the radiant box or zone) may range from about 760°C to about 1100°C.
  • the rate of decoking needs to be controlled to minimize or limit spalling of coke from the inner surface of the coil as this may interfere with downstream operation. Also during decoking, the external temperature of the tube should be maintained as uniform as possible to prevent damage to the tube.
  • the decoking may be finished with a steam scour at a steam feed rate of not less than 3500 kg/hr/reactor for a time from 0.5 to 10 hours, in some embodiments from about 6 to 9 hours under the same temperature conditions as the decoke bum-out process.
  • an anti-coking agent may also be included in the steam feed for the polish treatment or subsequent to the polish treatment.
  • Many anti-coking agents are known to those skilled in the art.
  • the anti-coking agent may be chosen from compounds of the formula RS n R' with n being the mean sulphur number ranging from 1 to 12 and R and R' chosen from H and a linear or branched C ⁇ -Ce alkyl, cycloalkyl or aryl radicals.
  • the anti-coking agent is added to the polish feed or a steam feed if the treatment is subsequent to the polish in an amount from 15 ppm to 2,500 ppm, for a period of time from 0.5 to 24, hours, preferably from about 1 to 6 hours at which time decreasing the dosing rate may begin.
  • the furnace tubes in hydrocarbon cracking furnaces are typically made of steel.
  • the present disclosure is applicable to steels typically including at least 12 wt% Cr, preferably at least 16 wt% of Cr.
  • the steel may be chosen from 304 stainless steel, 310 stainless steel,
  • the stainless steel preferably heat resistant stainless steel typically includes from 13 to 50, preferably 20 to 50, most preferably from 20 to 38 wt% of Cr.
  • the stainless steel may further include from 20 to 50, preferably from 25 to 50 most preferably from 25 to 48, desirably from about 30 to 45 wt% of Ni.
  • the balance of the stainless steel is substantially iron.
  • the present disclosure may also be used with nickel and/or cobalt based extreme austenitic high temperature alloys (HTAs).
  • HTAs include a major amount of nickel or cobalt.
  • the high temperature nickel-based alloys include from about 50 to 70, preferably from about 55 to 65 wt% of Ni; from about 20 to 10 wt% of Cr; from about 20 to 10 wt% of Co; and from about 5 to 9 wt% of Fe and the balance one or more of the trace elements noted below to bring the composition up to 100 wt%.
  • the high temperature cobalt based alloys include from 40 to 65 wt% of Co; from 15 to 20 wt% of Cr; from 20 to 13 wt% of Ni; less than 4 wt% of Fe and the balance one or more of the trace elements noted below to bring the composition up to 100 wt%.
  • the substrate may further include at least 0.2 wt%, up to 3 wt% typically 1.0 wt%, up to 2.5 wt% preferably not more than 2 wt% of manganese from 0.3 to 2, preferably 0.8 to 1.6 typically less than 1.9 wt% of Si; less than 3, typically less than 2 wt% of titanium, niobium (typically less than 2.0, preferably less than 1.5 wt% of niobium) and all other trace metals; and carbon in an amount of less than 2.0 wt%.
  • the present disclosure may also be used with 35 wt% nickel and 45 wt% chromium based alloys with an amount of aluminum of up to 4% with a propensity to form an aluminum oxide layer or an alumina layer on the inner surface of a reactor or pass.
  • the process of the present disclosure uses the practice of managing initial coke deposition in a cracking furnace’s radiant coil internal surface or tube wall inner surface by maximizing the boundary layer turbulence of the furnace tube with the characteristics of the fluid being cracked, i.e. hydrocarbon plus diluent.
  • the volumetric change in the gas results in a velocity increase of the gas as it travels to the outlet end of the furnace.
  • the high gas velocity minimizes the thickness of the laminar flow of the boundary at the furnace tube wall providing a scouring effect upon the newly formed and deposited coke.
  • desired gas velocity is determined by including the mass flow rate, molecular weight of the fluid, temperature of the fluid, the pressure, and area of the tube, as calculated thusly: wherein v is gas velocity (m/s), V is gas volume (m 3 /s), A is pipe area (m 2 ), rh is mass flow rate of a gas (g/hr), MW is a molecular weight (g/mol) of a gas, z is the compressibility factor of a gas, R is the ideal gas constant (8.314 J-moL ⁇ K -1 ), T is the temperature (K), P a bs is the absolute pressure (Pa), and r is the pipe radius (m), and the subscripts 1 and 2 refer to gas 1 and gas 2, respectively.
  • a feed gas chromatograph can provide the number average molecular weight of the hydrocarbon portion at the inlet of the furnace tube.
  • a hydrocarbon cracking furnace might have a front-end “sweetening” system, wherein about 65% of the total hydrocarbon feed to the hydrocarbon cracking furnace has gone through an amine contactor and has become saturated with water. This hydrocarbon can be blended with dry, recycled hydrocarbon so the water content’ s influence on the molecular weight of the hydrocarbon is not considered.
  • the molecular weight of the dilution steam can be estimated as 18.015.
  • the number average molecular weight of the fluid entering the furnace can then calculated thusly: where rhhc is the total mass flow of hydrocarbon, and rhsteam is the total mass flow of the dilution stream.
  • An analogous method can be used to calculate the number average molecular weight of the gas at the outlet of the furnace tube.
  • the number average molecular weights can be varied by changing the composition of the fluid, such as by varying the steam to hydrocarbon ratio, or changing the types of hydrocarbons in the feed.
  • the start-up procedure after commissioning a furnace tube, or after a decoking has taken place, or for any other reason that the hydrocarbon cracking furnace is starting up can include a number of steps that are well known in the art.
  • the fluid velocity at the point of incipient cracking is not typically measured or controlled. If not measured, the fluid velocity at the point of incipient cracking can be estimated by measuring or calculating the number average molecular weight of the fluid at the inlet of the furnace tube, measuring or calculating the number average molecular weight of the fluid at the outlet of the furnace tube, calculating an average of the number average molecular weights of the fluids at the inlet and the outlet to estimate the number average molecular weight at the point of incipient cracking, measuring or calculating the fluid velocities and the fluid pressures at the inlet and outlet and a pressure drop of the fluid from the inlet to the outlet. Using the Ideal Gas Law as above, the fluid velocity at the point of incipient cracking can be calculated.
  • the fluid velocity at the point of incipient cracking is surprisingly a key variable in the operation of an industrial stream hydrocarbon cracking furnace, including the run length of the furnace before it needs to be shut down to perform a decoke.
  • a hydrocarbon cracking furnace start-up in which the fluid velocity at the point of incipient cracking is maintained at a sufficient velocity from the start-up shall reduce the coke buildup on the inner walls of the furnace tube.
  • the fluid velocity at the point of incipient cracking should be at least about 80 m/s to about 120 m/s, preferably at least about 85 m/s to about 115 m/s, preferably at least about 90 m/s to about 115 m/s, preferably at least about 90 m/s to about 110 m/s, preferably at least about 85 m/s to about 105 m/s, preferably at least about 90 m/s to about 105 m/s, preferably at least about 95 m/s to about 105 m/s.
  • the fluid velocity at the point of incipient cracking chosen to be 525°C, in this disclosure, should be maintained for at least five (5) 24-hour days, preferably 10 days, preferably 20 days.
  • the fluid velocity entering the radiant section can be greater than 295 ft/sec or 90 m/s, preferably greater than 311 ft/sec or 95 m/s, preferably greater than 340 ft/sec or 103.6 m/s. This velocity can be attained within five hours of introducing feed into the furnace tube, preferably with three hours, most preferably within less than 60 minutes.
  • Figure 5 shows the change in gas velocity (fluid velocity) over a 500 hundred day period, during which three consecutive runs of an industrial steam hydrocarbon cracking furnace were conducted.
  • the three bars on the figure are plotted versus the x-axis showing 82 days (run 1), 39 days (run 2), and 343 days (run 3) for each of the three runs.
  • the days indicates the number of cracking days, which is the number of days online, from hydrocarbon feed-in to hydrocarbon feed-out. The furnace was decoked after each run.
  • the left y-axis on Figure 5 indicates the calculated value of the fluid velocity at the point of incipient cracking, the values calculated using the procedure described above.
  • the gas velocity at the point of incipient cracking was only allowed to exceed 90 m/s for three days, resulting in a run length of 82 days before the hydrocarbon cracking furnace required decoking.
  • the gas velocity at the point of incipient cracking was only allowed to exceed 90 m/s for less than 1.5 days, resulting in a run length of 39 days before the hydrocarbon cracking furnace required decoking.
  • the gas velocity at the point of incipient cracking was allowed to exceed 90 m/s for greater than 20 days, resulting a run length of 343 days before the hydrocarbon cracking furnace required decoking.
  • run length of a hydrocarbon cracking furnace can be improved by controlling the fluid velocity at the point of incipient cracking, including maintaining a fluid velocity at the point of incipient cracking of at least 90 m/s, for at least the first 5 days after start-up.
  • the disclosure is related to operation of hydrocarbon cracking furnaces. Specifically, a start-up procedure is disclosed which allows longer run times before decoking is required.

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  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)

Abstract

La présente invention concerne des réacteurs soumis à une cokéfaction dans des procédés chimiques de craquage d'hydrocarbure. Pendant le procédé de décokage, une cémentation du substrat métallique peut se produire, ayant un impact négatif sur la durée de vie du réacteur. Les décokages sont également coûteux en raison du temps d'indisponibilité où les coûts sont encourus sans production de produits commerciaux. La réduction de la fréquence des décokages fournit une opportunité de réduire les impacts financiers des temps d'arrêt. L'invention concerne une procédure de démarrage qui limite le dépôt de coke initial, conduisant à une tendance réduite à la cémentation du substrat métallique, améliorant la durée de vie du réacteur, et plus important encore, prolongeant la durée de fonctionnement du réacteur.
PCT/IB2021/050384 2020-01-22 2021-01-19 Démarrage à grande vitesse de gaz d'un four de craquage d'éthylène WO2021148942A1 (fr)

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US17/794,882 US20230073862A1 (en) 2020-01-22 2021-01-19 High gas velocity start-up of an ethylene cracking furnace

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2023107815A1 (fr) * 2021-12-06 2023-06-15 Exxonmobil Chemical Patents Inc. Procédés et systèmes de vapocraquage de charges d'hydrocarbures

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WO2015181638A1 (fr) * 2014-05-28 2015-12-03 Sabic Global Technologies B.V. Processus et système relatifs à un four d'éthylène
WO2019133215A1 (fr) * 2017-12-29 2019-07-04 Exxonmobil Chemical Patents Inc. Atténuation du coke dans la pyrolyse d'hydrocarbures

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Publication number Priority date Publication date Assignee Title
WO2015181638A1 (fr) * 2014-05-28 2015-12-03 Sabic Global Technologies B.V. Processus et système relatifs à un four d'éthylène
WO2019133215A1 (fr) * 2017-12-29 2019-07-04 Exxonmobil Chemical Patents Inc. Atténuation du coke dans la pyrolyse d'hydrocarbures

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LOUGH: "COMPUTER MODEL FOR REACTOR DESIGN OF AN ETHANE CRACKING UNIT", 31 December 1971 (1971-12-31), pages 1 - 51, XP055640115, Retrieved from the Internet <URL:http://archives.njit.edu/vol01/etd/1970s/1971/njit-etd1971-002/njit-etd1971-002.pdf> [retrieved on 20191107] *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2023107815A1 (fr) * 2021-12-06 2023-06-15 Exxonmobil Chemical Patents Inc. Procédés et systèmes de vapocraquage de charges d'hydrocarbures

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