Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
  • F28F13/06—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media
  • F28F13/12—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media by creating turbulence, e.g. by stirring, by increasing the force of circulation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/0053—Details of the reactor
  • B01J19/006—Baffles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/18—Stationary reactors having moving elements inside
  • B01J19/1812—Tubular reactors
  • B01J19/1825—Tubular reactors in parallel
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J2219/00049—Controlling or regulating processes
  • B01J2219/00051—Controlling the temperature
  • B01J2219/00157—Controlling the temperature by means of a burner

Definitions

• the invention relates to a process and apparatus for cracking hydrocarbon feedstocks. More specifically, the invention is directed to a process and furnace in which a hydrocarbon is cracked by heatmg it to a particular temperature and then self-quenching itself within the furnace.
• Thermal cracking of hydrocarbon feeds which is also known as hydrocarbon pyrolysis, to produce olefins, diolefins and aromatics is a common petrochemical process. This process is frequently referred to as steam cracking since the hydrocarbon feeds are usually mixed with steam when they are heated to an incipient cracking temperature and cracked.
• Hydrocarbon feedstocks typically include, but are not limited to, ethane, propane, naphtha, or gas oil.
• the cracking takes place in a cracking furnace that typically comprises a radiant section, a convection section, and heat recovery equipment.
• a mixture of the hydrocarbon feed and steam are heated to an incipient cracking temperature, normally in the range of 1100 °F to 1300 °F.
• the radiant, or cracking, section is where the cracking occurs.
• the heat recovery equipment recovers heat from the cracked hydrocarbons and the furnace flue gas.
• the steam cracking process described above has been in commercial use for over sixty years and most of the current cracking furnaces are similar, even though differences exist depending upon the furnace designer.
• the hydrocarbons being cracked in the radiant section of the furnace pass through high alloy tubes that receive heat from the burning of natural gas and/or the less desirable light gasses produced in the furnace tubes.
• the tubes typically range from one to three inches in diameter and are forty to eighty feet in length.
• Some furnaces have a plurality of smaller tubes at the inlet of the radiant section joined to a smaller number of larger tubes, up to eight inches in diameter, at the outlet of the radiant section of the furnace.
• the tubes in the radiant section of the furnace exit the radiant section and then pass into exchangers, which cool and quench the furnace effluent to stop the cracking reactions taking place within the tubes.
• the stream to be cracked is heated such that the bulk temperature of the stream is substantially higher than the incipient cracking temperature of the hydrocarbon being cracked. Cracking occurs in this bulk stream.
• the bulk stream to be cracked is heated to below the incipient cracking temperature but is passed through a very hot tube such that the boundary layer between the bulk fluid and the hot tube is heated to a sufficiently high temperature to cause cracking to take place only in the boundary layer. This results in the reaction being self quenching as the molecules pass back and forth between the hot boundary layer and the cool bulk fluid, which is at a temperature below incipient cracking temperature.
• Mixing is needed to enhance the transfer of the molecules between the bulk fluid and the boundary layer. Mixing is ideally performed by utilizing internals fins within the furnace tubes in which the cracking process occurs. Since cracking only occurs in the boundary layer the cracking residence time is substantially lower than with current technology and therefore the yields of the most desirable products are greatly enhanced.
• a new furnace has been developed to optimize the new hydrocarbon cracking process.
• the new furnace is designed to operate at the higher tube metal temperatures, with lower residence times, required for this process.
• the new furnace has at least two sections, but can have more.
• the first section, or convection section is for preheating the hydrocarbon feedstock fed to the furnace.
• the second section, or radiant section is where the cracking process occurs.
• Within the radiant section is a plurality of furnace, or radiant, tubes.
• the radiant tubes within the present furnace are much shorter and typically have smaller diameters than previous models.
• the radiant tubes also have internal fins internally mounted within to assist in the transferring of molecules between the bulk fluid layer and the boundary layer.
• FIGURE 1 is a simplified process flow diagram of the improved hydrocarbon cracking process in accordance to the present invention.
• FIGURE 2 is a partial cross-sectional view of a furnace for hydrocarbon cracking hydrocarbon feedstocks in accordance with the process in Figure 1;
• FIGURE 3 is a cross-sectional view of a furnace for hydrocarbon cracking hydrocarbon feedstocks in accordance with the process in Figure 1, taken along the line 3-3 of Figure 2;
• FIGURE 4 is a partial cross-sectional view of a radiant tube with internal fins in accordance with the apparatus of Figure 2.
• This invention is directed to a process and apparatus 10 for cracking a hydrocarbon feedstock 12 to recover olefins, diolefins, and aromatics from a feedstock 12.
• the apparatus 10 is typically called a furnace. It shall be noted that any type of furnace vessel 50 could be utilized, including, but not limited to, a heater, boiler, kiln, kettle, or cracker.
• the hydrocarbon cracking process begins by supplying a hydrocarbon feedstock 12 to the furnace 50.
• the furnace 50 has at least two sections.
• the first section 14 is typically called a convection section or a preheat section.
• steam 16 is added to the hydrocarbon feedstock 12 prior to entering the furnace 50 or prior to preheating the feedstock 12, either of which would be considered as adding steam 16 to the hydrocarbon feedstock 12 while it is being supplied to the furnace 50. All embodiments of the present invention are believed to work, whether or not steam 16 has been added to the hydrocarbon feedstock 12.
• the hydrocarbon feedstock 12 is preheated to a temperature in the range of about 500 °F to about 900 °F, or more preferably in the range of about 600 °F to about 800 °F.
• the manner in which the feedstock 12 is preheated will be apparent and is also known to one skilled in the art.
• the feedstock 12 is transferred to the second section 18 of the furnace 50.
• the second section 18 is typically called a radiant section, a cracking section, or a fired section of the furnace 50.
• the second section, or radiant section, 18 typically contains a plurality of radiant tubes 20 through which the preheated hydrocarbon feedstock 12 travels, as shown in Figures 2 and 3.
• the second section 18 also contains a plurality of burners 22 that supply the heat that is necessary for cracking the preheated hydrocarbon feedstock 12 contained within the radiant tubes 20. Natural gas or the lighter undesired cracked gasses are typically used as fuel gas, but any suitable alternate can be used.
• the radiant tubes 20 are typically constructed of a high alloy material to enable the tubes 20 to withstand the severe conditions within the furnace 50. However, any material suitable for this type of process is a suitable substitution, provided it has the requisite strength and durability to function within a furnace and is compatible with the chemicals in the method.
• the tubes 20 have a length in the range of about 4 feet to 12 feet or more preferably from about 5 feet to about 8 feet.
• the tube 20 diameters vary between about 0.5 inches to about 2.5 inches, or more preferably 0.75 inches to about 1.5 inches.
• a flow distributor 24 is installed at the inlet of each radiant tube 20, but external to the radiant section 18.
• the function of the flow distributor 24 is to evenly distribute the preheated hydrocarbon feedstock 12 flow to each of the radiant tubes 20.
• a venturi 25 is a suitable flow distributor 24 for this purpose.
• other devices or techniques that adequately perform the foregoing described function could, if desired, be used in the present method and apparatus, provided that they are constructed with materials that are compatible and the chemicals used in the present method and the severe conditions of the method.
• the preheated hydrocarbon feedstock 12 is transferred to the tubes 20 in the radiant section 18 at a mass velocity of about 1 lb/sec/ft 2 to about 5 lb/sec/fit 2 , or more preferably between about 2 lb/sec/ft 2 to about 4 lb/sec/ft 2 . If steam 16 has been added to the hydrocarbon feedstock 18, the mass velocity remains the same.
• the burners 22 within the radiant section 18 are those typically known in the art. The only requirement is that the burners 22 need to be able to supply enough heat to reach a tube metal temperature for the radiant tubes 20 in the range of about 2000 °F to about 2300 °F, or more preferably between about 2100 °F and 2200 °F.
• the feedstock 12 is heated until the radiant tubes 20 have a tube metal temperature in the range of about 2000 °F to about 2300 °F. The preferred range is between about 2100 °F and 2200 °F.
• a boundary layer 24 (not shown).
• At least some of the remaining uncracked, or partially or lesser cracked, preheated hydrocarbon feedstock 12 remains in what is called a bulk fluid layer 26 (not shown), which is also within the same tubes 20 as the boundary layer 24.
• the bulk fluid layer 26 contains uncracked molecules.
• the cracked molecules in the boundary layer 24 and the uncracked molecules in the bulk fluid layer 26 are mixed together.
• the use of internal fms 28 within the radiant tubes 20 is the preferred method of mixing the molecules in the two layers, as shown in Figure 4.
• Each tube 20 contains internal fins 28 that are about 0.05 inches to about 0.25 inches in height, or more preferably in the range of about 0.0625 to about 0.125 inches high.
• the fins 28 preferably have a spiral or circular configuration. However, it is believed that other fin configurations will work and should be included within the scope of this invention.
• the fins 28 are mounted internally within the tubes 20, as demonstrated in Figure 4.
• the mounting space between each fin 28 tip, or pitch, is in the range of about 2 inches to about 10 inches, or more preferably about 3 inches to about 6 inches.
• the first advantage is that the effective residence time for cracking, which is the time the hydrocarbon feedstock or partially cracked molecules spend above the incipient cracking temperature, will be between 0.002 and 0.005 seconds. Only the molecules in the boundary layer 24 will be above incipient cracking temperature.
• the lower residence time will result in enhanced yields of desirable products from the cracking furnace 50 when compared to conventional cracking furnaces.
• the lower residence time also decreases coke formation, as previously discussed.
• Another advantage of the current invention is that when the furnace effluent stream 30 exits the radiant section 18 with the bulk fluid below the hydrocarbon feedstock incipient cracking temperature, it is believed that mixing will cause an instantaneous quenching and cessation of cracking of the preheated hydrocarbon feedstock. Heat can then be recovered from the cracked effluent in much simpler and lower cost processes.
• additional heat exchangers are required to quench and stop the cracking process. This change is a considerable capital cost savings since no heat exchanger equipment is needed to quench the cracked hydrocarbons and stop the cracking process.
• lower pressure rated equipment can be used since the pressure of the hydrocarbons will be lower than in current processes, which also reduces capital costs.
• a further advantage of the new hydrocarbon cracking process is that the net energy required for this process is believed to be substantially lower than available alternate designs. Since the cracking is self-quenching, the lower net energy requirement is due to not having to cool the cracked hydrocarbon stream to stop the cracking process, which reduces the need for additional heat exchangers to quench the stream. Energy will be saved by removing the need for a heat exchanger to quench the reaction.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• General Chemical & Material Sciences (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)

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• 2002
  • 2002-08-02 US US10/211,226 patent/US20030209469A1/en not_active Abandoned
• 2003
  • 2003-05-07 EP EP03750088A patent/EP1509582A1/de not_active Withdrawn
  • 2003-05-07 AU AU2003243209A patent/AU2003243209A1/en not_active Abandoned
  • 2003-05-07 WO PCT/US2003/014346 patent/WO2003095590A1/en not_active Ceased
  • 2003-05-07 JP JP2004503584A patent/JP2005524757A/ja active Pending

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